More Important Topics of Botanic Cylinder

A fertilized seed contains the embryo from which a new plant will grow under proper conditions. It also contains a supply of stored food and is wrapped in the seed coat or testa. The stored food begins as a tissue called endosperm derived from the parent plant. Endosperm becomes rich in

oil or starch, and protein. In some species, the embryo is imbedded in the endosperm, which the seedling will use upon germination.

In others, the endosperm is absorbed by the embryo as the latter grows within the developing seed, and the cotyledons of the embryo become filled with this stored food. At maturity, seeds of these species have no endosperm. Some common plant seeds that lack an endosperm are bean, pea, oak, walnut, squash, sunflower, and radish. Plant seeds with an endosperm include all conifers and most monocotyledons (e.g., grasses and palms), and also e.g., brazil nut, castor bean.

The seed coat develops from tissues (called integument) originally surrounding the ovule. The seed coat in the mature seed can be a paper-thin layer (as for example, in the peanut) or something more substantial (as for example, thick and hard in honey locust and coconut). The seed coat helps protect the embryo from mechanical injury and from drying out. In order for the seed coat to split, the embryo must imbibe (soak up water), which causes it to swell, splitting the seed coat.

However, the nature of the seed coat determines how rapidly water can penetrate and subsequently initiate germination. For seeds with a very thick coat, scarification of the seed coat may be necessary before water can reach the embryo. Examples of scarification include: gnawing by animals, freezing and thawing, battering on rocks in a stream bed, or passing through an animal's digestive tract.

In the latter case, the seed coat protects the seed from digestion, while perhaps weakening the seed coat such that the embryo is ready to sprout when it gets deposited (along with a bit of fertilizer) far from the parent plant.

In species with thin seed coats, light may be able to penetrate into the dormant embryo. The presence of light or the absence of light may trigger the germination process, inhibiting germination in some seeds buried too deeply or in others not buried in the soil. Abscisic acid is usually the growth inhibitor in seeds.

The seeds of angiosperms are contained in a hard or fleshy (or with layers of both) structure called a fruit. Gymnosperm seeds begin their development "naked" on the bracts of cones, although the seeds do become covered by the cone scales as they develop. An example of a hard fruit layer surrounding the actual seed is that of the so-called stone fruits (such as the peach).

Unlike animals, plants are limited in their ability to seek out favorable conditions for life and growth. As a consequence, plants have evolved many ways to disperse and spread the population through their seeds (see also vegetative reproduction). A seed must somehow "arrive" at a location and be there at a time favorable for germination and growth.

Those properties or attributes that promote the movement of the next generation away from the parent plant may involve the fruit more so than the seeds themselves. The function of a seed is one of serving as a delaying mechanism: a way for the new generation to suspend its growth and allow time for dispersal to occur or to survive harsh, unfavorable conditions of cold or dryness, or both.

In many, if not most cases, each plant species achieves success in finding ideal locations for placement of its seeds through the basic approach of producing numerous seeds. This is certainly the approach used by plants, such as ferns, which disperse by spores. However, seeds involve a considerably greater investment in energy and resources than do spores, and the payoff must come in achieving similar or greater success with fewer dispersal units.

The seed of a higher plant is a small package produced in a flower or cone containing an embryo and stored food reserves. Under favorable conditions, the seed begins to

germinate, and the embryonic tissues resume growth, developing towards a seedling.

The part of the plant that emerges from the seed first is termed a radicle. In some definitions, the appearance of the radicle marks the end of germination and the beginning of "establishment", a period that ends when the seedling has exhausted the food reserves stored in the seed.

These are critical phases in the life of a plant. The mortality between dispersal of seeds and completion of establishment can be so high, that many species survive only by producing huge numbers of seeds.

Some seeds require particular conditions to germinate, such as the heat of a fire (e.g., many Australian native plants), or soaking in a body of water for a long period of time.

A flower (<Old French flo(u)r<Latin florem<flos), also known as a bloom or blossom, is the reproductive structure and it is the most sexy flower of em all found in flowering plants (plants of the division Magnoliophyta, also called angiosperms).

The flower structure contains the plant's reproductive organs, and its function is to produce seeds through sexual reproduction. For the higher plants, seeds are the next generation, and serve as the primary means by which individuals of a species are dispersed across the landscape. After fertilization, portions of the flower develop into a fruit containing the seeds.

Flowering plants are heterosporangiate (producing two types of reproductive spores) and the pollen (male spores) and ovules (female spores) are produced in different organs, but these are together in a bisporangiate strobilus that is the typical flower.

A flower is regarded as a modified stem (Eames, 1961) with shortened internodes and bearing, at its nodes, structures that may be highly modified leaves. In essence, a flower structure forms on a modified shoot or axis with an apical meristem that does not grow continuously (growth is determinate).

The stem is called a pedicel, the end of which is the torus or receptacle. The parts of a flower are arranged in whorls on the torus. The four main parts or whorls (starting from

the base of the flower or lowest node and working upwards) are as follows: calyx – the outer whorl of sepals; typically these are green, but are petal-like in some species.

corolla – the whorl of petals, which are usually thin, soft and colored to attract insects that help the process of pollination.

androecium (from Greek andros oikia: man's house) – one or two whorls of stamens, each a filament topped by an anther where pollen is produced. Pollen contains the male gametes.

Gynoecium (from Greek gynaikos oikia: woman's house) – one or more pistils. The female reproductive organ is the carpel: this contains an ovary with ovules (female gametes). A pistil may consist of a number of carpels merged together, in which case there is only one pistil to each flower, or of a single individual carpel (the flower is then called apocarpous).

The sticky tip of the pistil, the stigma, is the receptor of pollen. The supportive stalk, the style becomes the pathway for pollen tubes to grow from pollen grains adhering to the stigma, to the ovules, carrying the reproductive material.

Although the floral structure described above is considered the "typical" structural plan, plant species show a wide variety of modifications from this plan. These modifications have significance in the evolution of flowering plants and are used extensively by botanists to establish relationships among plant species.

For example, the two subclasses of flowering plants may be distinguished by the number of floral organs in each whorl: dicotyledons typically having 4 or 5 organs (or a multiple of 4 or 5) in each whorl and monocotyledons having three or some multiple of three. The number of carpels in a compound pistil may be only two, or otherwise not related to the above generalization for monocots and dicots.

In the majority of species, individual flowers have both pistils and stamens as described above. These flowers are described by botanists as being perfect, bisexual, or hermaphrodite.

However, in some species of plants the flowers are imperfect or unisexual: having only either male (stamens) or female (pistil) parts. In the latter case, if an individual plant is either male or female the species is regarded as dioecious. However, where unisexual male and female flowers appear on the same plant, the species is considered monoecious.

Some flowers with both stamens and a pistil are capable of self-fertilization, which does increase the chance of producing seeds but limits genetic variation. The extreme case of self-fertilization occurs in flowers that always self-fertilize, such as the common dandelion.

Conversely, many species of plants have ways of preventing self-fertilization. Unisexual male and female flowers on the same plant may not appear at the same time, or pollen from the same plant may be incapable of fertilizing its ovules. The latter flower types, which have chemical barriers to their own pollen, are referred to as self-sterile or self-incompatible (see also: Plant sexuality).

Additional discussions on floral modifications from the basic plan are presented in the articles on each of the basic parts of the flower. In those species that have more than one flower on an axis, the collection of flowers is termed an inflorescence. In this sense, care must be exercised in considering what is a flower. In botanical terminology, a single daisy or sunflower for example, is not a flower but a flower head—an inflorescence comprised of numerous small flowers (sometimes called florets). Each small flower may be anatomically as described above.

The function of a flower is to mediate the union of male and female gametes. The process is termed pollination. Many flowers are dependent upon the wind to move pollen between flowers of the same species. Others rely on animals (especially insects) to accomplish this feat. The period of time during which this process can take place (the flower is fully expanded and functional) is called anthesis.

Many flowers in nature have evolved to attract animals to pollinate the flower, the movements of the pollinating agent contributing to the opportunity for genetic recombinations within a dispersed plant population. Flowers that are insect pollinated are called entomophilous (literally "insect loving"). Flowers commonly have glands called nectaries on their various parts that attract these animals. Birds and bees are common pollinators: both having color vision, thus opting for "colorful" flowers.

Some flowers have patterns, called nectar guides, that are evident in the ultraviolet range, visible to bees but not to humans. Flowers also attract pollinators by scent. In any case, pollinators are attracted to the plant, perhaps in search of nectar, which they eat. The arrangement of the stamens ensures that pollen grains are transferred to the bodies of the pollinator. In gathering nectar from many flowers of the same species, the pollinators transfer pollen between all of the flowers it visits.

Flower scent is not always pleasant to our sense of smell. Some plants, such as Rafflesia, the titan arum, and the North American pawpaw (Asimina triloba) are pollinated by flies, so produce a scent imitating rotting meat.

Other flowers are pollinated by the wind, and the flowers of these species (for example, grasses) have no need to attract pollinators and therefore tend not to be "showy". Wind pollinated flowers are referred to as anemophilous.

Whereas the pollen of entomophilous flowers tends to be large grained, sticky, and contain significant protein (another "reward" for pollinators), Anemophilous flower pollen is usually small grained, very light, and of little nutritional value to insects, though it may still be gathered, in times of dearth. Honeybees and bumblebees actively gather anemophilous corn (maize) pollen, though it is of little value to them.

There is much confusion about the role of flowers in allergies. For example the showy and entomophilous goldenrod (Solidago) is frequently blamed for respiratory allergies, of which it is innocent, since its pollen cannot be airborne. Instead the allergen is usually the pollen of the contemporary bloom of anemophilous ragweed (Ambrosia) which can drift for many kilometers.

There exists considerable variation in form of petals among the flowering plants. The petals can be united towards the base, forming a floral tube. In some flowers, the entire perianth forms a cup (called a calyx tube) surrounding the gynoecium, with the sepals, petals, and stamens attached to the rim of the cup.

The flowers of some species lack or have very much reduced petals. These are often referred to as apetalous. Examples of flowers with much reduced perianths are found among the grasses.

The petals are usually the most conspicuous parts of a flower, and the petal whorl or corolla may be either radially or bilaterally symmetrical. If all of the petals are essentially identical in size and shape, the flower is said to be regular or actinomorphic (meaning 'ray-formed').

Many flowers are symmetrical in only one plane (i.e., symmetry is bilateral) and are termed irregular or zygomorphic (meaning yoke- or pair-formed). In irregular flowers, other floral parts may be modified from the regular form, but the petals show the greatest deviation from radial symmetry. Examples of zygomorphic flowers may be seen in orchids and members of the pea family.

A form of budding called suckering is the reproduction or regeneration of an plant by shoots that arise from an existing root system. Species that characteristically produce suckers include Elm (Ulmus), Dandelion (Taraxacum), and members of the Rose Family (Rosa).

Another types of vegetative reproduction is the production of bulbs. Plants like onion (Allium cepa), hyacinth (Hyacinth), narcissus (Narcissus) and tulips (Tulipa) reproduce by forming bulbs. Other plants like potatoes (Solanum tuberosum) and dahlia (Dahlia) reproduce by a similar method of producing tubers. Gladiolas and crocuses (Crocus) reproduce by forming a bulb-like structure called a corm.

Another type of asexual reproduction is known as apomixis. Apomixis is a type of reproduction involving unfertilized seeds to form new offspring. Hawkweeds (Hieracium), dandelions (Taxaxacum), and Kentucky blue grass (Poa pratensis) all use this form of asexual reproduction.

La reproducción sexual o gámica

Sexual reproduction is a type of reproduction that results in increasing genetic diversity of the offspring. It is characterized by two processes. The first, meiosis, involves the halving of the number of chromosomes. The second process, fertilization, leads the fusion of two gametes and the restoration of the original number of chromosomes. During meiosis, the chromosomes of each pair usually cross over to achieve genetic recombination.

The evolution of sex is a major puzzle in modern evolutionary biology. The first fossilized evidence of sexually reproducing organisms is from eukaryotes of the Stenian period, about 1.2 to 1 billion years before the present time. Sexual reproduction is the primary method of reproduction for the vast majority of visible organisms, including almost all animals and plants.

Bacterial conjugation, the transfer of DNA between two bacteria, is often mistakenly confused with sexual reproduction, because the mechanics are similar.

In flowering plants, a stamen produces gametes called pollen grains, which attach to a pistil, in which the female gametes (ovules) are located. Here, the female gamete is fertilized and develops into a seed. The ovary, which produced the gamete then grows into a fruit, which surrounds the seed(s). Plants may either self-pollinate or cross-pollinate.

Vegetative reproduction is asexual reproduction, but other terms that apply are vegetative propagation and vegetative multiplication. In essence it is any process by which new plant "individuals" arise or are obtained without production of seeds or spores. It is both a natural process in many plant species (including organisms that may or may not be considered "plants", such as bacteria and fungi) and one utilized or encouraged by horticulturists to obtain quantities of economically valuable plants.

Natural vegetative reproduction is mostly a process found in herbaceous and woody perennials, and typically involves structural modifications of the stem, although any

horizontal, underground part of a plant (whether stem or a root) can contribute to vegetative reproduction of a plant.

And, in a few species (such as Kalanchoë shown at right), leaves are involved in vegetative reproduction. Most plant species that survive and significantly expand by vegetative reproduction would be perennial almost by definition, since specialized organs of vegetative reproduction, like seeds of annuals, serve to survive seasonally harsh conditions. A plant that persists in a location through vegetative reproduction of individuals over a long period of time constitutes a clonal colony.

In a sense, this process is not one of "reproduction" but one of survival and expansion of biomass of the individual. When an individual organism increases in size via cell multiplication and remains intact, the process is called "vegetative growth". However, in vegetative reproduction, the new plants that result are new individuals in almost every respect except genetic. And of considerable interest is how this process appears to reset the aging clock.

Sometimes the petals and the sepals have the same color, then we call them tepals.

Sepal: Each of the pieces that form the chalice of a flower.

The stamen is the male organ of a flower. Each stamen generally has a stalk called the filament, and, on top of the

filament, an anther.

The anther is usually composed of four pollen sacs, which are called microsporangia. The development of the microsporangia and the contained haploid spores (called pollen-grains) is closely comparable with that of the microsporangia in gymnosperms or heterosporous ferns.

The pollen is set free by the opening (dehiscence) of the anther, generally by means of longitudinal slits, but sometimes by pores, as in the heath family (Ericaceae), or by valves, as in the barberry family (Berberidaceae). It is then dropped, or carried by some external agent — wind, water or some member of the animal kingdom — onto the receptive surface of the carpel of the same or another flower, which is thus pollinated.

Typical flowers have six stamens inside a perianth (the petals and sepals together), arranged in a whorl around the carpel (pistil). But in some species there are many more than six present in a flower (see, for example, the spider tree flower, below).

Collectively, the stamens are called an androecium (from Greek andros oikia: man's house). They are positioned just below the gynoecium. The anthers are bilocular, i.e. they have two locules. Each locule contains a microsporangium. The tissue between the locules and the cells is called the connective.

In an immature, unopened flower bud, the filaments are still short. Their function is then to transport nutrients to the developing pollen. They start to lengthen once the bud opens. The anther can be attached to the filament in two ways:

basifixed : attached at its base to the filament; this gives rise to a longitudinal dehiscence (opening along its length to release pollen)

versatile : attached at its center to the filament; pollen is then released through pores (poricidal dehiscence).

Stamens can be connate (fused or joined in the same whorl):

monadelphous : fused into a single, compound structure

diadelphous : joined partially into two androecial structures

synantherous : only the anthers are connate (such as in the Asteraceae)

Stamens can also be adnate (fused or joined from more than one whorl):

epipetalous : adnate to the corolla

didynamous : occurring in two pairs of different length

tetradynamos : occurring as a set of six filaments with two shorter ones

exserted : extending beyond the corolla

included : not extending from the corolla.

Plant sexuality

Main article: Plant sexuality

In the typical flower (that is, the majority of flowering plant species) each flower has both a pistil and stamens. Bisexual plants are called hermaphrodites or perfect flowers.

In some species, however, the flowers are unisexual with only either male or female parts (monoecious = on the same plant; dioecious = on different plants). A flower with only male reproductive parts is called androecious. A flower with only female reproductive parts is called gynoecious.

A flower having only functional stamens is called a staminate flower.

An abortive or rudimentary stamen is called a staminodium, such as in Scrophularia nodosa.

The pistil and the stamens of orchids are fused into a column. The top part of the column is formed by the anther. This is covered by an anther cap.

Simple

Composed

Flower cigomorfa of columbaria (Cymbalaria muralis) Según the general symmetry

Cigomorfa (Zigomorfa): With bilateral symmetry.

Actinomorfa: With radial symmetry concerning an axis.

Asymmetric: without axis of symmetry

According to the separation of the sepals

Dialisépala: With separated sepals.

Gamosépala: With close sepals.

According to the separation petals

Dialipétala: With separated petals.

Gamosépala: With close petals.

According to the length of the styles with regard to the stamen

longistilas

brevistilas

According to the position of the ovary with regard to the corolla

Superovariada or Súpera: Ovary on the point of insertion of the petals. This is the normal condition.

Inferovariada or Ínfera: Ovary under the point of insertion of the petals.

The ovary remains shut up inside the pedicelo that supports the flower.

Classification of the flowers for his sex:

hermaphrodite or bisexual, when it has androceo and gineceo

* unisexual, if only it presents androceo (estaminada) or gineceo (pistilada)

* monoica, plant with masculine and feminine flowers

In vascular plants, the root is that organ of a plant body that typically lies below the surface of the soil (compare with stem). However, this is not always the case, since a root can also be aerial (that is, growing above the ground) or aerating (that is, growing up above the ground or especially above water).

On the other hand, a stem normally occurring below ground is not exceptional either (see rhizome). So, it is better to define root as a part of a plant body that bears no leaves, and therefore also lacks nodes.

There are also important internal structural differences between stems and roots. The two major functions of roots are 1) absorption of water and inorganic nutrients and 2) anchoring the plant body to the ground.

At the tip of every growing root is a conical covering of tissue called the root cap. It usually is not visible to the naked eye.

It consists of undifferentiated soft tissue (parenchyma) with unthickened walls covering the apical meristem. The root cap provides mechanical protection to the meristem

cells as the root advances through the soil, its cells worn away but quickly replaced by new cells generated by cell division within the meristem. The root cap is also involved in the production of mucigel, a sticky mucilage that coats the new formed cells. These cells contain statoliths, starch grains that move in response to gravity and thus control root orientation.

The outside surface of a root is the epidermis. Recently produced epidermal cells absorb water from the surrounding environment and produce outgrowths called root hairs that greatly increase the cell's absorptive surface. Root-hairs are very delicate and generally short-lived, remaining functional for only a few days.

However, as the root grows, new epidermal cells emerge and these form new root hairs, replacing those that die. The process by which water is absorbed into the epidermal cells from the soil is known as osmosis. For this reason, water that is saline is more difficult for most plant species to absorb.

Beneath the epidermis is the cortex, which comprises the bulk of the root. Its main function is storage of starch. Intercellular spaces in the cortex aerate cells for respiration. An endodermis is a thin layer of small cells forming the innermost part of the cortex and surrounding the vascular tissues deeper in the root.

The tightly packed cells of the endodermis contain a substance known as suberin and create an impermeable barrier of sorts. Water can only flow in one direction through the endodermis: in towards the center of the root, rather than outward from the stele to the cortex.

The vascular cylinder, or stele, consists of the cells inside the endodermis. The outer part, known as the pericycle, surrounds the actual vascular tissue. In monocotyledonous plants, the xylem and phloem cells are arranged in a circle around a pith or center, whereas in dicotyledons, the xylem cells form a central "hub" with lobes, and phloem cells fill in the spaces between the lobes.

Early root growth is a function of the apical meristem located near the tip of the root. The meristem cells more or less continuously divide, producing more meristem, root cap cells (these sacrificed to protect the meristem), and undifferentiated root cells.

The latter will become the primary tissues of the root, first undergoing elongation, a process that pushes the root tip forward in the growing medium. Gradually these cells differentiate and mature into specialized cells of the root tissues.

Roots will generally grow in any direction where the correct environment of air, nutrients and water exists to meet the plant's needs. Roots will not grow in dry soil. Over time, given the right conditions, roots can crack foundations, snap water lines, and lift sidewalks. At germination, roots grow downward due to gravitropism, the growth mechanism of plants that also causes the shoot to grow upward. In some plants (such as ivy), the "root" actually clings to walls and structures; this is known as thigmotropism, or response to touch.

Most plants experience growth only along the apical meristems; this is known as primary growth, which encompasses all vertical growth. On the other hand, secondary growth encompasses all lateral growth, a major component of woody plant tissues.

Secondary growth occurs at the lateral meristems, namely the vascular cambium and cork cambium. The former forms secondary xylem and secondary phloem, while the latter forms the periderm, found only in woody plants.

In woody plants, the vascular cambium, originating between the xylem and the phloem, forms a cylinder of tissue along the stem and root. The cambium layer forms new cells on both the inside and outside of the cambium cylinder, with those on the inside forming secondary xylem cells, and those on the outside forming secondary phloem cells.

As secondary xylem accumulates, the "girth" (lateral dimensions) of the stem and root increases. As a result, tissues beyond the secondary phloem (including the epidermis and cortex, in many cases) tend to be pushed outward and are eventually "sloughed off" (shed).

At this point, the cork cambium (noting that this process only occurs in woody plants) begins to form the periderm, consisting of protective cork cells containing suberin. In roots, the cork cambium originates in the pericycle, a component of the vascular cylinder.

The vascular cambium produces new layers of secondary xylem annually. This dead tissue is responsible for most water transport through the vascular tissue (systems and roots).

Types of roots

A true root system consists of a primary root and secondary roots (or lateral roots).

The primary root originates in the radicle of the seedling. During its growth it rebranches to form the lateral roots. Generally, two categories are recognized:

the taproot: the primary root is prominent and has a single, dominant axis; there are fibrous secondary roots running outward. Usually allows for deeper roots capable of reaching low water tables. Most common in dicots

the primary root is not dominant: the whole root system is fibrous and branches in all directions. Most common in monocots.

Adventitous roots arise from the stem and not from another root. They usually occur in monocots and pteridophytes, but also in a few dicots, such as strawberry (Fragaria vesca) and white clover (Trifolium repens).

Specialized roots

The roots, or parts of roots, of many plant species have become specialized to serve adaptive purposes besides the two primary functions described in the introduction.

Aerating roots (or pneumatophores): roots rising above the ground, especially above water such as in some mangrove genera (Avicennia, Sonneratia)

Aerial roots: roots entirely above the ground, such as in ivy (Hedera helix) or in epiphytic orchids. They function as prop roots or anchor roots.

Contractile roots: they pull bulbs or corms of monocots deeper in the soil through expanding radially and contracting longitudinally. They show a wrinkled surface.

Haustorial roots: roots of parasitic plants that can absorb water and nutrients from another plant, such as in mistletoe (Viscum album) and Rafflesia.

Proteoid roots or cluster roots: dense clusters of rootlets of limited growth that develop under low phosphate or low iron conditions in plants from the following families Betulaceae, Casuarinaceae, Eleagnaceae, Moraceae, Fabaceae and Myricaceae.

Stilt roots: these are adventitious support roots, common among mangroves. They grow down from lateral branches, branching in the soil.

Storage roots: these roots are modified for storage of nutrients, such as carrots and beets

Tubiferous roots: A portion of a root forms into a roundish knob called a (tuber) for food.

Rooting depths

The distribution of vascular plant roots within the soil depends on plant life form, and the spatial and temporal availability of water and nutrients in the soil. The deepest roots are generally found in deserts and temperate coniferous forests; the shallowest in tundra, boreal forest and temperate grasslands.

The deepest observed living root, at least 60 m below the ground surface, was observed during the excavation of an open-pit mine in Arizona, USA.

It is the result of the fertilization of the ovary, especially for the engrosamiento of the walls of this one, although some fruits have another origin since they can they come from the engrosamiento of the floral container or from another place of the flower.

In the plants angiospermas, the fruit comes from the ovary of the flower after being fertilized. The wall of the ovary transforms in wall of the fruit and is named a pericarp. The function of the pericarp is to protect to the seed. In the

gimnospermas plants and plants without flowers there are no real fruits, although to reproductive structures as the cones of the pines, commonly one takes them as fruits.

Functions of the fruit:

Anyone that is his origin and aspect, the fruit fulfills two important functions:

To contain and to protect to the seed

To contribute dispersion of the seed.

To attract animals that disperse the seeds.

The animals that eat fruits and disperse the seeds have contributed to the selective reproduction of the plants that produce the best fruits.

Many fruits take economic importance as a source of food and prime matters. To the eatable fruits there are called they commonly a Fruit .

The fruit is the part of the vegetables that is in charge of protecting the seeds and assuring his dispersion. It is the result of the fertilization of the ovary, especially for the thickness of

the walls of this one, although some fruits have another origin since they can come from the engrosamiento of the floral container or from another place of the flower.

Classes of fruits

Beefy fruits: Berry - Cinorrodon - Eterio - Hesperidio - Drupe - Pepónide - Polydrupe - Knob

Dry fruits indehiscentes: Aquenio - Cariópside - Núcula - Nut - Sámara

Dry fruits dehiscentes: Capsule - Follicle - Vegetable - Pixidio - Silicua

Parts of the fruit

The pericarpo is the wall of the ovary; it can include also the textiles extracarpelares associate. It is all that that makes a detour to the seed.

It consists of three parts:

- The exocarpo or epicarpo that is the most external part of the fruto.sería what we know as skin

The surface can have very different aspects:

1. smooth (pepper, cherry. apple)

2. pruinosa (with waxes) (grape, plum)

affiliation of the fruits in two basic groups:

1) Dry, with pericarpo of structure similar to the episperma. They can be indehiscentes or dehiscentes, unispermos or with several seeds. In case of the fruits indehiscentes the teguments of the ovum in most cases disappear or melt with the pericarpo.

3. hairy (peach).

4. with hooked hair or hooked thorns (Desmodium, Melilotus).

5. thorns (Datura ferox, chamico).

- the mesocarpo is the thickest part of the majority of the fruits. In a peach (peach), for example, it would be " the meat " that we eat up.

- the endocarpo is the normally hard part that covers the seed. In a plum, for example, it would be " the bone ".

The consistency of the wall of the fruit determines

2) Beefy, in them the pericarpo intervenes and sometimes woven extracarpelares and also afterbirths. They are filogenéticamente newer.

They can have rind (histologically differentiated) as the orange, or not to take it as the tomato.

The fruit

The fruits are a set of vegetable food that come from the fruit of certain plants, be already grasses as the melonera or trees as the apricot tree. The fruits possess a typical flavor and an aroma and present a few nourishing properties and a chemical composition that distinguishes them from other food

Every fruit takes diverse varieties an as as for example the apple that can be of many types (Golden, Starking, Pippin, Green Maiden), as well as the pears (Limonera, of water, Ercolina), the oranges (Navel, Navel Late, Navelina, Salustiana and Blood) or the tangerines (Satsuma and Clementinas).

Classification of the fruit:

According to since it is the seed that contains the fruit, the fruits qualify in:

Fruits of bone or carozo: They are those that have a big seed and of hard rind,

as the apricot or the peach.

Fruits of pip: They are the fruits that have several small seeds and of less hard rind as the pear and the apple.

Fruit of grain: It is those fruits that take infinity of minuscule seeds as the fig and the strawberry.

According to since it is the time from his compilation, the fruit qualifies in:

Fresh fruit, if the consumption is realized immediately or a few days after his crop, of direct form, without any type preparation or cooked.

Dried fruit or fruit happens: It is the fruit that after a process of drying it is possible to consume a months, and even some years after his compilation. The dried fruit is not synonymous of dry fruit.

Other groups of fruit understand:

Citrus fruits as the orange, the grapefruit and the lemon

Exotic as the pineapple, the lychee, the kiwi, the handle, the guanabana, the durian, the papaya, the mangostan, the fruit of bread, the fruit of pony,

banana tree, the guava, the cannon, the maracuyá, the passionflower, the grenade, the rambutan, the anon and the chirimoya.

According to since there takes place the process of maturation of the fruit, they qualify in climateric and not climateric fruits.

In the maturation of the fruits there takes place an intensive process of respiration dependent on oxygen. This intensive respiration is named a climateric increase and serves to classify to the fruits in two big groups:

Climateric fruits: They are those who suffer sudden the climateric increase. Between the climateric fruits we have: apple, pear, banana, peach, apricot and chirimoya. These fruits suffer a sudden maturation and big changes of color, texture and composition.

Normally they are gathered in preclimateric state, and are stored in controlled conditions so that the maturation does not take place up to the moment to extract them to the market.

Not climateric fruits: They are those who present a climateric increase slowly and of attenuated form. Between not climateric ones we have: orange, lemon, tangerine, pineapple, grape, melon and strawberry. These fruits mature of slow form and do not have sudden changes in his aspect and composition. They present major content of starch. The compilation does after the maturation because if it does when they are green then they do not mature, only they become soft.

According to the development of the fruits:

Single fruits: They develop from only one pistil, monkey or pluricarpelares as for example the grapes, oranges or the melon. In turn the simple fruits can cause five principal forms:

Berry: The entire pericarpo, that is to say three layers exo, meso and endocarpo, is slightly differentiated. The walls of the ovary engrosan and they become juicy. Part of the exocarpo forms a skin like for ejmplo the bananas, dates, kiwis, bilberries. They possess one or several seeds.

Hesperidio: It is a special type of berry with rough skin. The interior of the fruit is divided for septos or dividing walls causing so many segments as carpelos, for example all the citrus fruits. They possess several seeds, even without seeds, for partenocarpia.

Peponides: It is another variant of the fruit in berry with hard skin. The interior of this fruit is not divided for septos, as for example the watermelons and the melons. The seeds can be dispersed for the pericarpo or grouped in filaments. The endocarpo does not differ.

Drupe: They possess few seeds (one or in very short number) surrounded with a fibrous and hard endocarpo, generally leaving a hollow between he and the beefy mesocarpo. The exocarpo causes a soft skin as for example the peaches, plums, cherries and handles.

The almond, against what its believed, is not the covering of the seed but the endocarpo. Also they are called "bony" fruits.

Poma: It is a beefy fruit. The seeds or pips are surrounded by an endocarpo coriaceo similar to the role. The beefy part comes from the floral pipe as for example the apple and the pear.

Added fruits: They develop from several independent pistils that give birth to several small little fruits that are inserted in a common container as the strawberries and the raspberries.

Multiple fruits:

They develop from a conglomerate of flowers or inflorescence that possess multiple ovaries, each of them proceeding from a different flower, which they fuse in a fruit, generally beefy, on having reached the ripeness as the figs and the tropical pineapple.

Composition of the fruit: The chemical composition of the fruits depends especially on the type of fruit and on his grade of maturation.

It waters down: More than 80 % and up to 90 % of the composition of the fruit it is a water. Due to this high percentage of water and the aromas of his composition, the fruit is very refreshing.

Glucids: Between 5 % and 18 % of the fruit are formed by carbohydrates. The content can change from 20 % in the banana up to 5 % in the melon, watermelon and strawberries. Other fruits have an average value of 10 %. The content in glúcidos can change according to the species and also according to the epoch of compilation.

The carbohydrates are generally single sugars as fructosa, saccharose and glucose, sugars of easy digestion and rapid absorption. In the slightly mature they turn in single sugars.

Fiber: Approximately 2 % of the fruit is a dietetic fiber. The components of the vegetable fiber that we can be in the fruits are principally pectins and hemicelulosa.

The skin of the fruit is the one that possesses major concentration of fiber, but also it are where we can meet some pollutants as rests of insecticides, which are difficult to eliminate if it is not with peeled of the fruit.

The soluble fiber or gelificante like the pectins form with the water viscous miscellanies. The grade of stickiness depends on the fruit from which it comes and from the grade of maturation. The pectins redeem therefore a very important role in the consistency of the fruit.

Vitamins: As the carotenos, vitamin C, vitamins of the group B. According to the content in vitamins we can do two big groups of fruits:

Rich in vitamin C: they contain 50 mg/100. Between these fruits the citrus fruits are, also the melon, the strawberries and the kiwi.

Rich in vitamin A: They are rich in carotenos, as the apricots, peach and plums.

Mineral: As the vegetables, the fruits are rich in potassium, magnesium, iron and calcium. You them go out minerals they are always important but especially during the growth for the ossification. The most important mineral is the potassium. Those who are richer in potassium are the fruits of bone as the apricot, cherry, plum, peach, etc.

Caloric value: The caloric value will come determined by his concentration in sugars, ranging between 30-80 Kcal/100g. As exception we take greasy fruits as the avocado that there possess 16 % of lípidos and the coconut that it goes so far as to have up to 60 %.

The avocado contains acid oleico that is a greasy acid monoinsaturado, but the coconut is rich in fats saturated as the acid palmítico. On having had a high value lipídico, they have a high energy value of up to 200 Kilocalorías/100gramos. But the majority of the fruits are hypocaloric with regard to his weight.

Proteins and fats: The nitrogenous compounds as the proteins and the fat are scarce in the eatable part of the fruits, although they are important in the seeds of some of them. This way the content of fat can range between 0,1 and 0,5 %, whereas the proteins it can be between 0,1 and 1,5 %.

Fragrance and pigments: The fruit contains acids and other aromatic substances that along with the big content of water of the fruit it does than this one is refreshing. The flavor of every fruit will come determined by his content in acids, azúcares and other aromatic substances.

The acid malic prevails in the apple, the citric acid in oranges, lemons and tangerines and the tartaric acid in the grapes. Therefore the colourings, the aromas and the components phenolic astringent although they are in very low concentrations, they influence in a crucial way the organoleptic acceptance of the fruits.

In botany, a leaf is an above-ground plant organ specialized for photosynthesis. For this purpose, a leaf is typically flat (laminar) and thin, to expose the cells containing chloroplast (chlorenchyma tissue, a type of parenchyma) to light over a broad area, and to allow light to penetrate fully into the tissues.

Leaves are also the sites in most plants where respiration, transpiration, and guttation take place. Leaves can store food and water, and are modified in some plants for other purposes. The comparable structures of ferns are correctly referred to as fronds. Furthermore, leaves are prominent in the human diet as leaf vegetables.

Leaf anatomy

A structurally complete leaf of an angiosperm consists of a petiole (leaf stem), a lamina (leaf blade), and stipules (small processes located to either side of the base of the petiole). The petiole attaches to the stem at a point that is called the "leaf axil". Not every species produces leaves

with all of these structural components. In some species, paired stipules are not obvious or are absent altogether. A petiole may be absent, or the blade may not be laminar (flattened). The tremendous variety shown in leaf structure (anatomy) from species to species is presented in detail below under Leaf morphology. After a period of time (i.e. seasonally, during the autumn), deciduous trees shed their leaves. These leaves decompose into the soil.

A leaf is considered to be a plant organ, typically consisting of the following tissues:

An epidermis that covers the upper and lower surfaces

An interior chlorenchyma called the mesophyll

An arrangement of veins (the vascular tissue).

Epidermis

The epidermis is the outer multi-layered group of cells covering the leaf. It forms the boundary separating the plant's inner cells from the external world. The epidermis serves several functions: protection against water loss, regulation of gas exchange, secretion of metabolic compounds, and (in some species) absorption of water.

Most leaves show dorsoventral anatomy: the upper (adaxial) and lower (abaxial) surfaces have somewhat different construction and may serve different functions.

The epidermis is usually transparent (epidermal cells lack chloroplasts) and coated on the outer side with a waxy cuticle that prevents water loss. The cuticle is in some cases thinner on the lower epidermis than on the upper epidermis, and is thicker on leaves from dry climates as compared with those from wet climates.

The epidermis tissue includes several differentiated cell types: epidermal cells, guard cells, subsidiary cells, and epidermal hairs (trichomes). The epidermal cells are the most numerous, largest, and least specialized. These are typically more elongated in the leaves of monocots than in those of dicots.

The epidermis is covered with pores called stomata, part of a stoma complex consisting of a pore surrounded on each side by chloroplast-containing guard cells, and two to four subsidiary cells that lack chloroplasts.

The stoma complex regulates the exchange of gases and water vapor between the outside air and the interior of the leaf. Typically, the stomata are more numerous over the abaxial (lower) epidermis than the adaxial (upper) epidermis.

Mesophyll

Most of the interior of the leaf between the upper and lower layers of epidermis is a parenchyma (ground tissue) or chlorenchyma tissue called the mesophyll (Greek for "middle leaf"). This assimilation tissue is the primary location of photosynthesis in the plant. The products of photosynthesis are called "assimilates".

In ferns and most flowering plants the mesophyll is divided into two layers:

An upper palisade layer of tightly packed, vertically elongated cells, one to two cells thick, directly beneath the adaxial epidermis. Its cells contain many more chloroplasts than the spongy layer. These long cylindrical cells are regularly arranged in one to five rows. Cylindrical cells, with the chloroplasts close to the walls of the cell, can take optimal advantage of light.

The slight separation of the cells provides maximum absorption of carbon dioxide. This separation must be minimal to afford capillary action for water distribution. In order to adapt to their different environment (such as sun or shade), plants had to adapt this structure to obtain optimal result. Sun leaves have a multi-layered palisade layer, while shade leaves or older leaves closer to the soil, are single-layered.

Beneath the palisade layer is the spongy layer. The cells of the spongy layer are more rounded and not so tightly packed. There are large intercellular air spaces. These cells contain fewer chloroplasts than those of the palisade layer.

The pores or stomata of the epidermis open into substomatal chambers, connecting to air spaces between the spongy layer cells.

These two different layers of the mesophyll are absent in many aquatic and marsh plants. Even an epidermis and a mesophyll may be lacking. Instead for their gaseous exchanges they use a homogeneous aerenchyma (thin-walled cells separated by large gas-filled spaces). Their stomata are situated at the upper surface.

Leaves are normally green in color, which comes from chlorophyll found in plastids in the chlorenchyma cells. Plants that lack chlorophyll cannot photosynthesize.

Leaves in temperate, boreal, and seasonally dry zones may be seasonally deciduous (falling off or dying for the inclement season). This mechanism to shed leaves is called abscission. After the leaf is shed, a leaf scar develops on the twig.

In cold autumns they sometimes change color, and turn yellow, bright orange or red as various accessory pigments (carotenoids and anthocyanins) are revealed when the tree responds to cold and reduced sunlight by curtailing chlorophyll production.

Veins

The veins are the vascular tissue of the leaf and are located in the spongy layer of the mesophyll. They are typical examples of pattern formation through ramification. The pattern of the veins is called venation.

The veins are made up of:

xylem, which brings water from the roots into the leaf.

phloem, which usually moves sap out, the latter containing the glucose produced by photosynthesis in the leaf.

The xylem typically lies over the phloem. Both are embedded in a dense parenchyma tissue, called "pith", with usually some structural collenchyma tissue present.

Leaf morphology

External leaf characteristics (such as shape, margin, hairs, etc.) are important for identifying plant species, and botanists have developed a rich terminology for describing leaf characteristics.

These structures are a part of what makes leaves determinant, they grow and achieve a specific pattern and shape, then stop. Other plant parts like stems or roots are non-determinant, and will usually continue to grow as long as they have the resources to do so.

Classification of leaves can occur through many different designative schema, and the type of leaf is usually characteristic of a species, although some species produce more than one type of leaf. The longest type of leaf is a leaf from palm trees, measuring at nine feet long.

Conifer leaves are typically needle-, awl-, or scale-shaped

Angiosperm (flowering plant) leaves: the standard form includes stipules, a petiole, and a lamina.

Lycophytes have microphyll leaves.

Sheath leaves (type found in most grasses).

Other specialized leaves (such as those of Nepenthes)

Arrangement on the stem

Different terms are usually used to describe leaf placement (phyllotaxis):

Alternate — leaf attachments are singular at nodes, and leaves alternate direction, to a greater or lesser degree, along the stem.

Opposite — leaf attachments are paired at each node; decussate if, as typical, each successive pair is rotated 90° progressing along the stem; or distichous if not rotated, but two-ranked (in the same geometric flat-plane).

Whorled — three or more leaves attach at each point or node on the stem. As with opposite leaves, successive whorls may or may not be decussate, rotated by half the angle between the leaves in the whorl (i.e., successive whorls of three rotated 60°, whorls of four rotated 45°, etc). Opposite leaves may appear whorled near the tip of the stem.

Rosulate — leaves form a rosette

As a stem grows, leaves tend to appear arranged around the stem in a way that optimizes yield of light. In essence, leaves form a helix pattern centred around the stem, either clockwise or counterclockwise, with (depending upon the species) the same angle of divergence.

There is a regularity in these angles and they follow the numbers in a Fibonacci sequence: 1/2, 2/3, 3/5, 5/8, 8/13, 13/21, 21/34, 34/55, 55/89. This series tends to a limit of 360° x 34/89 = 137.52 or 137° 30', an angle known mathematically as the golden angle.

In the series, the numerator indicates the number of complete turns or "gyres" until a leaf arrives at the initial position. The denominator indicates the number of leaves in the arrangement. This can be demonstrated by the following:

alternate leaves have an angle of 180° (or 1/2)

120° (or 1/3) : three leaves in one circle

144° (or 2/5) : five leaves in two gyres

135° (or 3/8) : eight leaves in three gyres.

The fact that an arrangement of anything in nature can be described by a mathematical formula is not in itself mysterious. Mathematics are the science of discovering numerical relationships and applying formulae to these relationships.

The formulae themselves can provide clues to the underlying physiological processes that, in this case, determine where the next leaf bud will form in the elongating stem.

the blade separated along a main or secondary vein. Because each leaflet can appear to be a simple leaf, it is important to recognize where the petiole occurs to identify a compound leaf.

Compound leaves are a characteristic of some families of higher plants, such as the Fabaceae. The middle vein of a compound leaf or a frond, when it is present, is called a rachis.

Palmately compound leaves have the leaflets radiating from the end of the petiole, like fingers off the palm of a hand, e.g. Cannabis (hemp) and Aesculus (buckeyes).

Pinnately compound leaves have the leaflets arranged along the main or mid-vein.

odd pinnate: with a terminal leaflet, e.g. Fraxinus (ash).

even pinnate: lacking a terminal leaflet, e.g. Swietenia (mahogany).

Bipinnately compound leaves are twice divided: the leaflets are arranged along a secondary vein that is one of several branching off the rachis. Each leaflet is called a "pinnule". The pinnules on one secondary vein are called "pinna"; e.g. Albizia (silk tree).

trifoliate: a pinnate leaf with just three leaflets, e.g. Trifolium (clover), Laburnum (laburnum).

pinnatifid: pinnately dissected to the midrib, but with the leaflets not entirely separate, e.g. Polypodium, some Sorbus (whitebeams).

Characteristics of the petiole

Petiolated leaves have a petiole. Sessile leaves do not: the blade attaches directly to the stem. In clasping or decurrent leaves, the blade partially or wholly surrounds the stem, often giving the impression that the shoot grows through the leaf.

When this is actually the case, the leaves are called "perfoliate", such as in Claytonia perfoliata. In peltate leaves, the petiole attaches to the blade inside from the blade margin.

In some Acacia species, such as the Koa Tree (Acacia koa), the petioles are expanded or broadened and function like leaf blades; these are called phyllodes. There may or may not be normal pinnate leaves at the tip of the phyllode.

A stipule, present on the leaves of many dicotyledons, is an appendage on each side at the base of the petiole resembling a small leaf.

Stipules may be lasting and not be shed (a stipulate leaf, such as in roses and beans), or be shed as the leaf expands, leaving a stipule scar on the twig (an exstipulate leaf).

The situation, arrangement, and structure of the stipules is called the "stipulation".

free

adnate : fused to the petiole base

ochreate : provided with ochrea, or sheath-formed stipules, e.g. rhubarb,

encircling the petiole base

interpetiolar : between the petioles of two opposite leaves.

intrapetiolar : between the petiole and the subtending stem

Venation (arrangement of the veins)

There are two subtypes of venation, namely, craspedodromous, where the major veins stretch up to the margin of the leaf, and camptodromous, when major veins extend close to the margin, but bend before they intersect with the margin.

Feather-veined, reticulate — the veins arise pinnately from a single mid-vein and subdivide into veinlets. These, in turn, form a complicated network. This type of venation is typical for dicotyledons.

Pinnate-netted, penniribbed, penninerved, penniveined; the leaf has usually one main vein (called the mid-vein), with veinlets, smaller veins branching off laterally, usually somewhat parallel to each other; eg Malus (apples).

Three main veins originate from the base of the lamina, as in Ceanothus.

Palmate-netted, palmate-veined, fan-veined; several main veins diverge from near the leaf base where the petiole attaches, and radiate toward the edge of the leaf; e.g. most Acer (maples).

Parallel-veined, parallel-ribbed, parallel-nerved, penniparallel — veins run parallel most the length of the leaf, from the base to the apex. Commissural veins (small veins) connect the major parallel veins. Typical for most monocotyledons, such as grasses.

Dichotomous — There are no dominant bundles, with the veins forking regularly by pairs; found in Ginkgo and some pteridophytes.

[edit] Leaf morphology changes within a single plant

Homoblasty - Characteristic in which a plant has small changes in leaf size, shape, and growth habit between juvenile and adult stages.

Heteroblasty - Charactistic in which a plant has marked changes in leaf size, shape, and growth habit between juvenile and adult stages.

[edit] Margins (edge)

The leaf margin is characteristic for a genus and aids in determining the species.

entire: even; with a smooth margin; without toothing

ciliate: fringed with hairs

crenate: wavy-toothed; dentate with rounded teeth, such as Fagus (beech)

dentate: toothed, such as Castanea (chestnut)

coarse-toothed: with large teeth

glandular toothed: with teeth that bear glands.

denticulate: finely toothed

doubly toothed: each tooth bearing smaller teeth, such as Ulmus (elm)

lobate: indented, with the indentations not reaching to the center, such as many Quercus (oaks)

palmately lobed: indented with the indentations reaching to the center, such as Humulus (hop).

serrate: saw-toothed with asymmetrical teeth pointing forward, such as Urtica (nettle)

serrulate: finely serrate

sinuate: with deep, wave-like indentations; coarsely crenate, such as many Rumex (docks)

spiny: with stiff, sharp points, such as some Ilex (hollies) and Cirsium (thistles).

acute: ending in a sharp, but not prolonged point

cuspidate: with a sharp, elongated, rigid tip; tipped with a cusp.

emarginate: indented, with a shallow notch at the tip.

mucronate: abruptly tipped with a small short point, as a continuation of the midrib; tipped with a mucro.

mucronulate: mucronate, but with a smaller spine.

obcordate: inversely heart-shaped, deeply notched at the top.

obtuse: rounded or blunt

truncate: ending abruptly with a flat end, that looks cut off.

Base of the leaf

acuminate: coming to a sharp, narrow, prolonged point.

acute: coming to a sharp, but not prolonged point.

auriculate: ear-shaped

cordate: heart-shaped with the norch away from the stem.

cuneate: wedge-shaped.

hastate: shaped like an halberd and with the basal lobes pointing outward.

oblique: slanting.

reniform: kidney-shaped but rounder and broader than long.

rounded: curving shape.

sagittate: shaped like an arrowhead and with the acute basal lobes pointing downward.

truncate: ending abruptly with a flat end, that looks cut off.

Surface of the leaf

The surface of a leaf can be described by several botanical terms:

farinose: bearing farina; mealy, covered with a waxy, whitish powder.

glabrous: smooth, not hairy.

glaucous: with a whitish bloom; covered with a very fine, bluish-white powder.

glutinous: sticky, viscid.

papillate, papillose: bearing papillae (minute, nipple-shaped protuberances).

pubescent: covered with erect hairs (especially soft and short ones)

punctate: marked with dots; dotted with depressions or with translucent glands or colored dots.

rugose: deeply wrinkled; with veins clearly visible.

scurfy: covered with tiny, broad scalelike particles.

tuberculate: covered with tubercles; covered with warty prominences.

verrucose: warted, with warty outgrowths.

viscid, viscous: covered with thick, sticky secretions.

The leaf surface is also host to a large variety of microorganisms; in this context it is referred to as the phyllosphere.

Hairiness (trichomes)

"Hairs" on plants are properly called trichomes. Leaves can show several degrees of hairiness. The meaning of several of the following terms can overlap.

glabrous: no hairs of any kind present.

arachnoid, arachnose: with many fine, entangled hairs giving a cobwebby appearance.

barbellate: with finely barbed hairs (barbellae).

bearded: with long, stiff hairs.

bristly: with stiff hair-like prickles.

canescent: hoary with dense grayish-white pubescence.

ciliate: marginally fringed with short hairs (cilia).

ciliolate: minutely ciliate.

floccose: with flocks of soft, woolly hairs, which tend to rub off.

glandular: with a gland at the tip of the hair.

hirsute: with rather rough or stiff hairs.

hispid: with rigid, bristly hairs.

hispidulous: minutely hispid.

hoary: with a fine, close grayish-white pubescence.

lanate, lanose: with woolly hairs.

pilose: with soft, clearly separated hairs.

puberulent, puberulous: with fine, minute hairs.

pubescent: with soft, short and erect hairs.

scabrous, scabrid: rough to the touch

sericeous: silky appearance through fine, straight and appressed (lying close and flat) hairs.

silky: with adpressed, soft and straight pubescence.

stellate, stelliform: with star-shaped hairs.

strigose: with appressed, sharp, straight and stiff hairs.

tomentose: densely pubescent with matted, soft white woolly hairs.

cano-tomentose: between canescent and tomentose

felted-tomentose: woolly and matted with curly hairs.

villous: with long and soft hairs, usually curved.

woolly: with long, soft and tortuous or matted hairs.

Adaptations

In the course of evolution, leaves adapted to different environments in the following ways:

A certain surface structure avoids moistening by rain and contaminations (Lotus effect).

Sliced leaves reduce wind resistance.

Hairs on the leaf surface trap humidity in dry climates and creates a large boundary layer and reduces water loss.

Waxy leaf surfaces reduce water loss.

Shiny leaves deflect the sun's rays.

Reductions of leaf sizes accompanied by a transfer of the photosynthetic functions to the stems reduces water loss.

In more or less opaque or buried in the soil leaves translucent windows filter the light before the photosynthetis takes place at the inner leaf surfaces (e.g. Fenestraria).

Thicker leaves store water (leaf succulents).

Aromatic oils, poisons or pheromones produced by leaf borne glands deter herbivores (e.g. eucalypts).

Inclusions of crystalline minerals deters herbivores.

A transformation into petals attracts pollinators.

A transformation into spines protects the plants (e.g. cactus).

A transformation into insect traps helps feeding the plants (carnivorous plants).

A transformation into bulbs helps storing food and water (e.g. onion).

A transformation into tendrils allow the plant to climb (e.g. pea).

A transformation into bracts and pseudanthia (false flowers) replaces normal flower structures if the true flowers are extremely reduced (e.g. Spurges).

precursor tissues), and terminal or apical meristem above the ground.

The surface cells differentiate and mature into a protective epidermal layer. A few cells interior differentiate as chollenchyma, providing support to the young stem. Clusters of elongated cells appear — these are the provascular strands. The remainder of the stem consists of parenchyma cells:

those lying between the epidermis and the provascular strands forming a cortex and those interior to the provascular strands forming a pith. Parenchyma radiating from the pith between the precursors of the vascular bundles are called pith rays.

These tissues are the early precursors of the mature stem tissues, and define the basic functions of the stem:

Structural support;

Growth through increase in diameter (girth) and

elongation;

Transport of fluids between the roots and the leaves.

Modified stems for other functions include:

Tubers

The common potato.

Stolons

Commonly seen on the strawberry plant.

Bulbs

Bulbs store energy in fleshy leaves for the initial spring growth spurt of a plant, for example tulips.

Corms

Store energy to allow the plant to have multiple flowering seasons, and can grow new corms out of itself. Taro is an example.

Thorns

Thorns are modified stems, and function to prevent the plant from being grazed upon. They grow from the axils of leaves. Spines and prickles however, are not modified stems, but modified leaves.

Monocot stems

Vascular bundles are present throughout the moncot stem, although concentrated towards the outside. This differs from the monocot root that has a ring of vascular bundles and often none in the center.

The shoot apex in monocot stems is more elongated. Leaf sheathes grow up around it, protecting it. Monocot leaves have continuous vascular tissue going down from a shoot or stem.

This is most clearly evidenced when pulling apart the leaves of corn or grass; the leaf fibers continue down wrapped around the stem to its base. This is true to some extent of almost all monocots, and is one of their traits that is more evolved than the older type, dicots.

Monocots rarely produce secondary growth and are therefore seldom woody. The cotyledons are not pushed above ground in monocots as they are in dicots.

Dicot Stems

Dicot stems have a pith in the center with vascular tissues in a distinct ring visible in a cross section. They have secondary growth originating from their lateral or secondary meristems: the vascular cambium and the cork cambium.

The vascular cambium grows cells that differentiate into secondary xylem and secondary phloem. Secondary xylem is commercially important as wood. The seasonal variation in growth from the vascular cambium is what creates yearly tree rings in most climates.

A tree can be defined as a large, perennial, woody plant. Though there is no set definition regarding minimum size, the term generally applies to plants at least 6 m (20 ft) high at maturity and, more importantly, having secondary branches supported on a single main stem or trunk (see shrub for comparison).

Compared with most other plant forms, trees are long-lived. A few species of trees grow to 100 m tall, and some can live for several thousand years.

Trees are important components of the natural landscape and significant elements in landscaping and agriculture,

supplying orchard crops (such as apples). Trees also play an important role in many of the world's mythologies (see Trees in mythology).

A tree is a plant form and trees occur in many different orders and families of plants. Trees thus show a wide variety of growth form, leaf type and shape, bark characteristics, reproductive structures, etc. The earliest trees were tree ferns and horsetails, which grew in vast forests in the Carboniferous Period; tree ferns still survive, but the only surviving horsetails are not of tree form.

Later, in the Triassic Period, conifers, ginkgos, cycads and other gymnosperms appeared, and subsequently flowering plants in the Cretaceous Period. Most species of trees today are flowering plants and conifers. The listing below gives examples of many well-known trees and how they are typically classified.

A small group of trees growing together is called a grove or copse, and a landscape covered by a dense growth of trees is called a forest. Several biotopes are defined largely by the trees that inhabit them; examples are rainforest and taiga (see ecozones). A landscape of trees scattered or spaced across grassland (usually grazed or burned over periodically) is called a savanna.

Morphology

The basic parts of a tree are the roots, trunk(s), branches, twigs and leaves. Tree stems consist mainly of support and transport tissues (xylem and phloem). Wood consists of xylem cells, and bark is made of phloem and other tissues external to the vascular cambium.

Trees may be broadly grouped into exogenous and endogenous trees according to the way in which their stem diameter increases. Exogenous trees, which comprise the great majority of modern trees (all conifers, and all broadleaf trees), grow by the addition of new wood outwards, immediately under the bark. Endogenous trees, mainly in the monocotyledons (e.g. palms), grow by addition of new material inwards.

As an exogenous tree grows, it creates growth rings. In temperate climates, these are commonly visible due to changes in the rate of growth with temperature variation over an annual cycle. These rings can be counted to determine the age of the tree, and used to date cores or even wood taken from trees in the past; this practice is known as the science of dendrochronology.

In some tropical regions with constant year-round climate, growth is continuous and distinct rings are not formed, so age determination is impossible. Age determination is also impossible in endogenous trees.

The roots of a tree are generally embedded in earth, providing anchorage for the above-ground biomass and absorbing water and nutrients from the soil. Above ground, the trunk gives height to the leaf-bearing branches, aiding in competition with other plant species for sunlight. In many trees, the arrangement of the branches optimizes exposure of the leaves to sunlight.

Not all trees have all the plant organs or parts mentioned above. For example, most palm trees are not branched, the saguaro cactus of North America has no functional leaves, tree ferns do not produce bark, etc. Based on their general shape and size, all of these are nonetheless generally regarded as trees. Indeed, sometimes size is the more important consideration.

A plant form that is similar to a tree, but generally having smaller, multiple trunks and/or branches that arise near the ground, is called a shrub. However, no sharp differentiation between shrubs and trees is possible. Given their small size, bonsai plants would not technically be 'trees', but one should not confuse reference to the form of a species with the size or shape of individual specimens.

A spruce seedling does not fit the definition of a tree, but all spruces are trees. Bamboos by contrast, do show most of the characteristics of trees, yet are rarely called trees.

Non-vascular plants (bryophytes)

Marchantiophyta - liverworts

Anthocerotophyta - hornworts

Bryophyta - mosses

Vascular plants (tracheophytes)

Lycopodiophyta - clubmosses

Equisetophyta - horsetails

Pteridophyta - "true" ferns

Psilotophyta - whisk ferns

Ophioglossophyta - adderstongues

Seed plants (spermatophytes)

†Pteridospermatophyta - seed ferns

Pinophyta - conifers

Cycadophyta - cycads

Ginkgophyta - ginkgo

Gnetophyta - gnetae

Magnoliophyta - flowering plants

Aquatic plants — also called hydrophytic plants or hydrophytes — are plants that have adapted to living in or on aquatic environments.

Because living on or under the water surface requires numerous special adaptations, aquatic plants can only grow in water or permanently saturated soil.

Aquatic vascular plants can be ferns or angiosperms (from

both monocot and dicot families). Seaweeds are not vascular plants but multicellular marine algae, and therefore not typically included in the category, "aquatic plants."

Many fish keepers and aquarium hobbyists keep aquatic plants in their tanks to oxygenate the water for their fish.

Many species of aquatic plant are invasive species in different parts of the world. Aquatic plants make particularly good weeds because they reproduce vegetatively from fragments.

Examples:

Utricularia (from Latin, utriculus, a little bag or bottle) is a genus of slender aquatic plants, the leaves of which are furnished with floating bladders. They are called bladderworts.

A spine is a rigid, pointed surface protuberance or needle-like structure on an animal, shell, or plant, presumably serving as a defense against attack by predators.

For examples: the quills of a porcupine, the needles of a cactus, or the prickles of a shrub like the rose are all spines. Although spines generally serve as a passive defense

mechanism, in some species they can be hollow and contain poisonous substances that cause lasting pain or even paralysis.

Plant spines and thorns

Botanists use several terms somewhat loosely when referring to spine- or needle-like structures on plants; however, the following differences are typically distinguished:

prickle – a sharp outgrowth from the epidermis, also called an emergence and usually involving some subdermal tissue as well; see also hair.

spine – a modified stipule or sharp branchlet found in a leaf axil or on the margin of a leaf.

thorn – Sharp outgrowth from a stem other than at a node; a modified stem.

Thorns and prickles, most notably those on roses, are common literary symbols for the hidden dangers or woes of something beautiful or pleasant, as in "Every rose has its thorn." Roses lack true thorns since their prickles emerge from the epidermis rather that the pericycle.

Growth from the pericycle would make it a modifided stem and therefore a thorn. Some roses have been bred not to have prickles. Other examples of plants with these characteristics include: the thistle, some berry plants, and a number of plants in the weed family.

A carnivorous plant is a plant that derives some or most of its nutrients (but not energy) by trapping and consuming animals, especially insects and other arthropods.

Carnivorous plants usually grow in places where the soil is thin or poor in nutrients, especially nitrogen, such as acidic bogs and rock outcroppings. Charles Darwin wrote the first well-known treatise on carnivorous plants in 1875. There are five basic trapping mechanisms that have evolved in

carnivorous plants. These are:

Pitfall traps (pitcher plants), which trap prey in a rolled leaf that contains a pool of digestive enzymes and/or bacteria;

Flypaper traps, which trap prey using a sticky mucilage;

Snap traps, which trap prey with rapid leaf movements;

Bladder traps, which suck in prey with a bladder that generates an internal vacuum; Lobster-pot traps, which use inward pointing hairs to force prey to move towards a digestive organ.

These traps may also be classified as active or passive. For example, there are both passive flypapers, such as Triphyophyllum, which secrete mucilage, but whose leaves do not grow or move in response to prey capture; and there are also active flypapers, such as sundews, whose leaves undergo rapid growth, aiding in the retention and digestion of prey.

Finding healing powers in plants is an ancient idea. People in all continents have long used hundreds, if not thousands, of indigenous plants, for treatment of various ailments dating back to prehistory. There is evidence that Neanderthals living 60,000 years ago in present-day Iraq

used plants for medicinal purposes.[citation needed] These plants are still widely used in ethnomedicine around the world.

Plants have an almost limitless ability to synthesize aromatic substances, most of which are phenols or their oxygen-substituted derivatives such as tannins. Most are secondary metabolites, of which at least 12,000 have been isolated, a number estimated to be less than 10% of the total.

In many cases, these substances serve as plant defense mechanisms against predation by microorganisms, insects, and herbivores. Many of the herbs and spices used by humans to season food yield useful medicinal compounds.

The use and search for drugs and dietary supplements derived from plants have accelerated in recent years. Pharmacologists, microbiologists, botanists, and natural-products chemists are combing the Earth for phytochemicals and leads that could be developed for treatment of various diseases.--Dr M Tariq Salman 19:06, 30 January 2006 (UTC).

network (called the mycelium) of filaments or hyphae. In a much broader sense, mushroom is applied to any visible fungus, or especially the fruiting body of any fungus, with the mycelium usually being hidden under bark, ground, rotted wood, leaves, etc.

The technical term for the spore-producing structure of "true" mushrooms is the basidiocarp. The term "toadstool" is used typically to designate a basidiocarp that is poisonous to eat.

The main types of mushrooms are agarics (including the button mushroom, the most common mushroom eaten in the U.S.), boletes, chanterelles, tooth fungi, polypores, puffballs, jelly fungi, coral fungi, bracket fungi, stinkhorns, and cup fungi. Mushrooms and other fungi are studied by mycologists.

The "true" mushrooms are classified as Basidiomycota (also known as "club fungi"). A few mushrooms are classified by mycologists as Ascomycota (the "cup fungi"), the morel and truffle being good examples. Thus, the term mushroom is more one of common application to macroscopic fungal fruiting bodies than one having precise taxonomic meaning.

Edible mushrooms are used extensively in cooking,in many cuisines. Though commonly thought to contain little nutritional value, many varieties of mushrooms are high in fiber and protein, and provide vitamins such as thiamine, riboflavin, niacin, biotin, B12 and ascorbic acid, and minerals including iron, selenium, potassium and phosphorus. However, a number of species of mushrooms are poisonous, and these may resemble edible varieties, although eating them could be fatal.

Picking mushrooms in the wild is risky — riskier than gathering edible plants — and a practice not to be undertaken by amateurs. The problem is due to the fact that separating edible from poisonous species is dependent upon the application of only a few easily recognizable traits. People who collect mushrooms for consumption are known as mushroom hunters, and the act of collecting them as such is called mushroom hunting.

Identifying mushrooms requires a basic understanding of their macroscopic structure. A "typical" mushroom consists of a cap or pileus supported on a stem or stipe. Both can have a variety of shapes and be ornamented in various ways.

The underside of the cap (in agarics) is fitted with gills or lamellae where the actual spores are produced. How the gills are attached is another important characteristic used in identification. In the boletes, the gills are replaced by small openings called pores. Bracket fungi essentially lack a stipe, and the cap is attached like a bracket to the substratum, usually a log or tree trunk. Some bracket fungi have gills, others have pores.

In general, identification to genus can be accomplished in the field using a local mushroom guide. Identification to species, however, requires more effort; one must remember that a mushroom develops from a young bud into a mature structure and only the latter can provide certain identification of the species. Examination of mature spores, or at least knowing their color, is often essential. To this end, a common method used to assist in identification is the spore print.

Apical Germ Pore

Apical Germ Pore is a term applied to mushroom spores which have a pore at one end. Some spores have a hole in the cell wall where the first strand of germinating mycelium emerges. If the cell wall is divided from one end to the other, this is called a germ slit. Commonly the germ pore is at one end of the mushroom spore and is called an apical pore.

Mushroom genuses with apical germ pores include Agrocybe, Panaeolus, Psilocybe, and Pholiota.

A fungus (plural fungi) is a eukaryotic organism that digests its food externally and absorbs the nutrient molecules into its cells. Fungi are very important economically: yeasts are responsible for fermentation of beer and bread, and mushroom farming is a large industry in many countries. Fungi are the primary decomposers of dead plant and animal matter in many ecosystems, and are commonly seen on old bread as mold. However, the complex biology of fungi extends beyond this common knowledge and experience of them.

Originally classified as plants, fungi are not true plants, because they are heterotrophs (they do not fix their own carbon through photosynthesis but use the carbon fixed by other organisms.) Fungi are more closely related to animals than to plants, but, unlike animals, they absorb their food rather than ingest it, and their cells have cell walls surrounding them. For these reasons, these organisms are now placed in their own kingdom, Fungi.

The Fungi are a monophyletic group, meaning all varieties of fungi come from a common ancestor. Mycologists (scientists who study fungi) believe they are monophyletic because they have chitin in their cell walls and are absorbtive heterotrophs, along with other shared characteristics.

Although often inconspicuous, fungi occur in every environment on earth and play very important roles in most ecosystems. Some fungi are major decomposers of dead plant and animal matter in forests and many other environments. Some types of fungi are parasites on plants and animals, including humans.

They are responsible for numerous diseases, such as athlete’s foot and ringworm in humans and Dutch elm disease in plants. Other fungi are partners in symbiotic relationships with other organisms. For example, lichens are formed by a symbiotic relationship between algae or cyanobacteria and fungi. Most vascular plants benefit from a symbiosis between their roots and fungi.

Fungi have a long history of use by humans. Many types of mushrooms and other fungi are eaten, including button mushrooms, shiitake mushrooms, and oyster mushrooms. Of course, many species of mushrooms are poisonous and are responsible for numerous cases of sickness and death every year.

A type of fungus called yeast is used in baking bread and fermenting alcoholic beverages. Fungi are also used to produce industrial chemicals like lactic acid, and even to make stonewashed jeans. Some types of fungi are ingested for their psychedelic properties, both recreationally and religiously (as entheogens) (see main article, Psychedelic mushroom).

Fungi may be single-celled or multicellular. Multicellular fungi are composed networks of long hollow tubes called hyphae. The hyphae often aggregate in a dense network known as mycelium. The mycelium grows through the substrate on which the fungus feeds. Because fungi are imbedded in the medium in which they grow, they are often not visible to the naked eye.

Although fungi lack true organs, the mycelia of ascomycetes and basidiomycetes may become organized into more complex reproductive structures called fruiting bodies, or sporocarps, when conditions are right. "Mushroom" is the common name given to the above-ground fruiting bodies of many fungal species.

Although these above-ground structures are the most conspicuous to humans, they make up only a small portion of the entire fungal body. Some fungi form rhizoids, which are underground root-like structures that provide support and transport nutrients from the soil to the rest of the mycelium.

The largest organism in the world is purported to be a single Armillaria ostoyae individual growing in a forest in eastern Oregon, USA. The underground mycelial network may cover as much as 890 ha (2200 acres

Fungi may reproduce sexually or asexually. In asexual reproduction, the offspring are genetically identical to the “parent” organism (they are clones). During sexual reproduction, a mixing of genetic material occurs so that the offspring exhibit traits of both parents. Many species can use both strategies at different times, while others are apparently strictly sexual or strictly asexual.

Sexual reproduction has not been observed in some fungi of the Glomeromycota and Ascomycota. These are commonly referred to as Fungi imperfecti or Deuteromycota.

Yeasts and other unicellular fungi can reproduce simply by budding, or “pinching off” a new cell. Many multicellular species produce a variety of different asexual spores that are easily dispersed and resistant to harsh environmental conditions. When the conditions are right, these spores will germinate and colonize new habitats.

Sexual reproduction in fungi is somewhat different from that of animals or plants, and each fungal division reproduces using different strategies. Fungi that are known to reproduce sexually all have a haploid stage and a diploid stage in their life cycles. Ascomycetes and basidiomycetes also go through a dikaryotic stage, in which the nuclei inherited by the two parents do not fuse right away, but remain separate in the hyphal cells (see heterokaryosis).

In zygomycetes, the haploid hyphae of two compatible individuals fuse, forming a zygote, which becomes a resistant zygospore. When this zygospore germinates, it quickly undergoes meiosis, generating new haploid hyphae and asexual sporangiospores.

These sporangiospores may then be distributed and germinate into new genetically-identical individuals, each producing their own haploid hyphae. When the hyphae of two compatible individuals come into contact with one another, they will fuse and generate new zygospores, thus completing the cycle.

In ascomycetes, when compatible haploid hyphae fuse with one another, their nuclei do not immediately fuse. The dikaryotic hyphae form structures called asci (sing. ascus), in which karyogamy (nuclear fusion) occurs. These asci are embedded in an ascocarp, or fruiting body, of the fungus. Karyogamy in the asci is followed immediately by meiosis and the production of ascospores.

The ascospores are disseminated and germinate to form new haploid mycelium. Asexual conidia may be produced by the haploid mycelium. Many ascomycetes appear to have lost the ability to reproduce sexually and reproduce only via conidia.

Sexual reproduction in basidiomycetes is similar to that of ascomycetes. Sexually compatible haploid hyphae fuse to produce a dikaryotic mycelium. This leads to the production of a basidiocarp. The most commonly-known basidiocarps are mushrooms, but they may also take many other forms. Club-like structures known as basidia generate haploid basidiospores following karyogamy and meiosis. These basidiospores then germinate to produce new haploid myceliumata.

Edible and poisonous fungi

Some of the most well-known types of fungi are the edible and poisonous mushrooms. Many species are commercially raised, but others must be harvested from the wild. Button mushrooms (Agaricus bisporus) are the most commonly eaten species, used in salads, soups, and many other dishes.

Portobello mushrooms are also members of this species, but grow to a much larger size. Other commercially-grown mushrooms that have gained in popularity in the West and are often available fresh in grocery stores include oyster mushrooms, shiitakes, and enoki mushrooms.

There are many more mushroom species that are harvested from the wild for personal consumption or commercial sale. Morels, chanterelles, truffles, black trumpets, and porcini mushrooms (also known as king boletes) all command a high price on the market. They are often used in gourmet dishes.

Hundreds of mushroom species are toxic to humans, causing anything from upset stomachs to hallucinations to death. Some of the most deadly belong to the genus Amanita, including A. virosa (the "Destroying Angel") and A. phalloides (the "Death Cap"). Stomach cramps, vomiting, and diarrhea usually occur within 6-24 hours after ingestion of these mushrooms, followed by a brief period of remission (usually 1-2 days).

Patients often fail to present themselves for treatment at this time, assuming that they have recovered. However, within 2-4 weeks liver and kidney failure leads to death if untreated. There is no antidote for the toxins in these mushrooms, but kidney dialysis and administration of corticosteroids may help. In severe cases, a liver transplant may be necessary (Kaminstein 2002).

Fly agaric mushrooms (A. muscaria) are also responsible for a large number of poisonings, but these cases rarely result in death. The most common symptoms are nausea and vomiting, drowsiness, and hallucinations. In fact, this species is used ritually and recreationally for its hallucinogenic properties. However, if it is taken in over a long period of time (regularly over more than six months), this species might cause a temporary loss of sight, which can last from several minutes to an hour.

Photosynthesis is an important biochemical process in which plants, algae, protistans, and some bacteria harness the energy of sunlight to chemical energy and store it in the bonds of sugar, glucose.

Ultimately, nearly all living things depend on energy produced from photosynthesis for their nourishment, making it vital to life on Earth. It is also responsible for producing the oxygen that makes up a large portion of the Earth's atmosphere.

Organisms that produce energy through photosynthesis are called photoautotrophs. Plants are the most visible representatives of photoautotrophs, but it should be emphasized that bacteria and algae as well contribute to the conversion of free energy into usable energy.

Most plants are photoautotrophs (exceptions include the infamous venus fly trap), which means they are able to synthesize food directly from inorganic compounds using light energy, instead of eating other organisms or relying on material derived from them. This is distinct from chemoautotrophs that do not depend on light energy, but use energy from inorganic compounds.

The energy for photosynthesis ultimately comes from absorbed photons and involves a reducing agent, which is water in the case of plants, releasing oxygen as a waste product.

The light energy is converted to chemical energy, in the form of ATP and NADPH, using the light-dependent reactions and is then available for carbon fixation. Most notably plants use the chemical energy to fix carbon dioxide into carbohydrates and other organic compounds through light-independent reactions. The overall equation for photosynthesis in green plants is:

n CO2 + 2n H2O + light energy ? (CH2O)n + n O2 + n H2O

Where n is defined according to the structure of the resulting carbohydrate. However, hexose sugars and starch are the primary products, so the following generalised equation is often used to represent photosynthesis:

6 CO2 + 12 H2O + light energy ? C6H12O6 + 6 O2 + 6 H2O

More specifically, photosynthetic reactions usually produces an intermediate product, which is then converted to the final hexose carbohydrate products. These carbohydrate products are then variously used to form other organic compounds, such as the building material cellulose, as precursors for lipid and amino acid biosynthesis or as a fuel in cellular respiration.

The latter not only occurs in plants, but also in animals when the energy from plants get passed through a food chain. In general outline, cellular respiration is the opposite of photosynthesis: glucose and other compounds are oxidised to produce carbon dioxide, water, and chemical energy. However, both processes actually take place through a different sequence of reactions and in different cellular compartments.

Plants capture light primarily using the pigment chlorophyll, which is the reason that most plants have a green color. The function of chlorophyll is often supported by other accessory pigments such as carotenoids and xanthophylls. Both chlorophyll and accessory pigments are contained in organelles (compartments within the cell) called chloroplasts. Although all cells in the green parts of a plant have chloroplasts, most of the energy is captured in the leaves.

The cells in the interior tissues of a leaf, called the mesophyll, contain about half a million chloroplasts for every square millimeter of leaf. The surface of the leaf is uniformly coated with a water-resistant, waxy cuticle, that protects the leaf from excessive evaporation of water as well as decreasing the absorption of ultraviolet or blue light to reduce heating. The transparent, colourless epidermis layer allows light to pass through to the palisade mesophyll cells where most of the photosynthesis takes place.

Algae range from multicellular forms like kelp to microscopic, single-celled organisms. Although they are not as complex as land plants, photosynthesis takes place biochemically the same way. Like plants, algae have chloroplasts and chlorophyll, but various accessory pigments are present in some algae such as phycoerythrin in red algae (rhodophytes) , resulting in a wide variety of colours. All algae produce oxygen, and many are autotrophic. However, some are heterotrophic, relying on materials produced by other organisms.

Photosynthetic bacteria do not have chloroplasts (or any membrane-bound organelles), instead, photosynthesis takes place directly within the cell. Cyanobacteria contain thylakoid membranes very similar to those in chloroplasts and are the only prokaryotes that perform oxygen-generating photosynthesis, in fact chloroplasts are now considered to have evolved from an endosymbiotic bacterium, which was also an ancestor of and later gave rise to cyanobacterium.

The other photosynthetic bacteria have a variety of different pigments, called bacteriochlorophylls, and do not produce oxygen. Some bacteria such as Chromatium, oxidize hydrogen sulfide instead of water for photosynthesis, producing sulfur as waste.

The light energy is converted to chemical energy using the light-dependent reactions. The products of the light dependent reactions are ATP from photophosphorylation and NADPH from photoreduction. Both are then utilized as an energy source for the light-independent reactions.

Z scheme

In plants, the light-dependent reactions occur in the thylakoid membranes of the chloroplasts and use light energy to synthesize ATP and NADPH. The photons are captured in the antenna complexes of photosystem I and II by chlorophyll and accessory pigments (see diagram at right). When a chorophyll a molecule at a photosystem's reaction center absorbs energy, an electron is excited and transferred to an electron-acceptor molecule through a process called Photoinduced charge separation.

These electrons are shuttled through an electron transport chain that initially functions to generate a chemiosmotic potential across the membrane, the so called Z-scheme shown in the diagram. An ATP synthase enzyme uses the chemiosmotic potential to make ATP during photophosphorylation while NADPH is a product of the terminal redox reaction in the Z-scheme.

Water photolysis

The NADPH is the main reducing agent in chloroplasts, providing a source of energetic electrons to other reactions. Its production leaves chlorophyll with a deficit of electrons (oxidized), which must be obtained from some other reducing agent. The excited electrons lost from chlorophyll in photosystem I are replaced from the electron transport chain by plastocyanin. However, since photosystem II includes the first steps of the Z-scheme, an external source of electrons is required to reduce its oxidized chlorophyll a molecules.

This role is played by water during a reaction known as photolysis and results in water being split to give electrons, oxygen and hydrogen ions. Photosystem II is the only known biological enzyme that carries out this oxidation of water. Initially, the hydrogen ions from photolysis contribute to the chemiosmotic potential but eventually they combine with the hydrogen carrier molecule NADP+ to form NADPH. Oxygen is a waste product of light-independent reactions, but the majority of organisms on Earth use oxygen for cellular respiration, including photosynthetic organisms.

Oxygen and photosynthesis

With respect to oxygen and photosynthesis, there are two important concepts.

Plant and algal cells also use oxygen for cellular respiration, although they have a net output of oxygen since much more is produced during photosynthesis.

Oxygen is a product of the photolysis reaction not the fixation of carbon dioxide during the light-independent reactions. Consequently, the source of oxygen during photosynthesis is water, NOT carbon dioxide.

Bacterial variations

The concept that oxygen production is not directly associated with the fixation of carbon dioxide was first proposed by Cornelis Bernadus van Neil in the 1930s, who studied photosynthetic bacteria. Aside from the cyanobacteria, bacteria only have one photosystem and use reducing agents other than water. They get electrons from a variety of different inorganic chemicals including sulfide or hydrogen, so for most of these bacteria oxygen is not produced.

Others, such as the halophiles (an Archeae) produced so called purple membranes where the bacteriorhodopsin could harvest light and produce energy. The purple membranes was one of the first to be used to demonstrate the chemiosmotic theory: light hit the membranes and the pH of the solution that contained the purple membranes dropped as protons were pumping out of the membrane.

Carbon fixation

Main article: Carbon fixation

The fixation of carbon dioxide is a light-independent process in which carbon dioxide combines with a five-carbon sugar, ribulose bisphosphate (RuBP), to give two molecules of a three-carbon compound, glycerate 3-phosphate (GP). This compound is also sometimes known as 3-phosphoglycerate (PGA). GP, in the presence of ATP and NADPH from the light-dependent stages, is reduced to glyceraldehyde 3-phosphate (G3P).

This product is also referred to as 3-phosphoglyceraldehyde (PGAL) or even as triose phosphate (a three-carbon sugar). This is the point at which carbohydrates are produced during photosynthesis. Some of the triose phosphates condense to form hexose phosphates, sucrose, starch and cellulose or are converted to acetylcoenzyme A to make amino acids and lipids. Others go on to regenerate RuBP so the process can continue (see Calvin cycle).

Cell division begins with interphase, when the cell replicates all of its genomic and cytoplasmic material and

prepares for division. After preparation is complete, the cell enters the 4-phased mitosis. In mitosis, the cell sequentially goes through prophase, metaphase, anaphase, and telophase. Immediately after the completion of telophase, cytokenesis is initiated to end cell division by literally separating the cell in two.

Interphase

Before a cell can enter cell division, it needs to prepare itself by replicating its

genetic information and all of the organelles. All of the preparations are done during the interphase. Interphase proceeds in three stages, G1, S, and G2. Cell division operates in a cycle. Therefore, interphase is preceded by the previous cycle of mitosis and cytokenesis.

G1 Phase

After mitosis is complete the new daughter cell begins to accelerate its biochemical processes which were slowed down by mitosis. The length of the G1 phase creates the difference between fast dividing cells and slowly dividing cells.

The G1 phase can be slowed by reducing the nutrients available in a system - thus the cell will take longer to build up the resources necessary for cell division. If there is a severe depletion in nutrients the cells can virtually stop growing. It is

interesting to note that cells that aren't growing are always stopped in the G1 phase, being mitotically arrested. This suggests that once the cell enters the S phase, it is committed to cell division, regardless of the external cell conditions.

S Phase

The S phase begins with the replication of the cellular DNA. This is described in further detail in DNA replication. When the cellular DNA has been duplicated, leaving the cell with twice as many chromosomes (each chromosome is made up of two identical chromatids), the cell moves onto the G2 phase.

G2 Phase

During this phase proteins, such as kinase (which catalyzes protein phosphorylation), which are necessary for cell division are synthesized at this time. The chromosome begins to condense and the proteins necessary for construction of the mitotic spindle also are synthesized. When the chromosomes become visible the cell enters the first stage of mitosis, prophase.

Prophase

During prophase the chromosomes are identical chromatids connected at the center by a centromere, forming a X-shaped object. The distinguishing feature of prophase is the setup of the mitotic spindle, which is used to maneuver the chromosomes about the cell. The spindle is formed by excess parts from the dismantled cytoskeleton. The spindle is initially setup outside the nucleus.

The cell's centioles are duplicated to form two pairs of centrioles. Each pair becomes the part of the mitotic center which forms the focus for an array of microtubules, called the aster. The two asters lie side by side close the the nuclear envelope. Near the end of prophase the asters pull apart and the spindle is formed.

Metaphase

Prometaphase

The prometaphase provides a transition from prophase to metaphase. In prometaphase the nuclear envelope, which surrounds the nucleus, breaks up. The spindle now can move into the center of the cell. Kinetochores develop, which are attached to kinetochore fibers, which are linked to the chromosomes.

The kinetochores then control the movements of the chromosomes. During this period the kinetochores are wildly oscillating as they try to attach themselves to one of the polar fibers. When they manage to do so the chromosome settles down

In Metaphase the kinetochores that are responsible for moving the chromosomes jump begin to orientate the chromosomes. The chromosomes are orientated so that 1. each kinetochore faces the pole and 2. it moves each chromosome into a plane at the center of the spindle so that each chromosome tail is facing each other.

Anaphase

In anaphase two events occur. First the kinetochores begin to move towards the poles. Then the polar fibers elongate, spreading the poles farther apart from each other.

Telophase

By telophase there are two separate groups of chromosomes at each pole. A nuclear envelope begins to form around each set of chromosomes to form two nuclei, that are temporarily in one cell. After the envelope reassembles RNA synthesis begins to break down the chromosomes, causing the nucleolus to reappear.

Cytokynesis

Now there are two separate nuclei, but they are in the same cell. The cell now needs to be split in half. Cytokenesis begins in anaphase and continues on through telophase. The first visible sign of cytokenesis is when the cell begins to pucker in, a process called furrowing.

Furrowing tends to take place at right angles to the axis of the spindle (so that each nucleus is placed in a different cell of course!). The cytoskeleton is reused to build the next spindle for mitosis. Now the two cells will continue the cell cycle and begin their interphase again!

In plant photosynthesis, incoming light is absorbed by chlorophyll and other accessory pigments in the antenna complexes of photosystem I and photosystem II.

The antenna pigments are predominantly chlorophyll a, chlorophyll b and carotenoids; their absorption spectrums are non-overlapping, to broaden the range of light that can be absorbed for photosynthesis. The carotenoids have another role as an antioxidant, to prevent photo-oxidative damage to the chlorophyll molecules.

Each antenna complex has between 250 and 400 pigment molecules, and the energy they absorb is shuttled by resonance energy transfer to a specialized chlorophyll a at the reaction center of each photosystem. When either of the two chorophyll a molecules at the reaction center absorb energy, an electron is excited and transferred to an electron-acceptor molecule, leaving an electron hole in the donor chlorophyll.

In a poorly-understood reaction, electrons from water are oxidized, the hole is filled, and diatomic oxygen is produced. The resulting chemical energy is then captured in the form of ATP and NADPH, and is ultimately used to convert carbon dioxide (CO2) to carbohydrates. This CO2 fixation process results in the conversion of 3% to 6% of total solar radiation, with a theoretical maximum efficiency of 11%.

The photosystem reaction centers consist of a pair of chlorophyll a molecules that are characterised by their specific absorption maximum. The chorophyll a of photosystem I is designated P700, and the one from photosystem II is designated P680. The P is short for pigment, and the number is the specific absorption peak in nanometers for the chlorophyll molecules in each reaction center.

Chlorophyll a is common to all eukaryotic photosynthetic organisms, and, due to its central role in the reaction center, is essential for photosynthesis. The accessory pigments such as chlorophyll b and carotenoids are not essential.

Some algae, such as brown algae and diatoms, use chlorophyll c as a substitute for chlorophyll b. Historically, red algae have been assumed to have chlorophyll d, although it could not be isolated from all species.

This puzzle has recently been resolved, since the chlorophyll d is actually from an epiphytic cyanobacterium (Acaryochloris marina) that lives on the red algae. These cyanobacteria have a ratio of chlorophyll d: chlorophyll a of approximately 30:1, and represent a rare example of a photosystem with chlorophyll d at the reaction center of the photosystem. All other known eukaryotes and cyanobacteria use chlorophyll a.

Other chemical variations of chlorophyll are found in photosynthetic bacteria, other than cyanobacteria. Purple bacteria use bacteriochlorophyll, which absorbs infrared light between 800nm - 900nm, and the green sulphur bacteria chlorobium chlorophyll.

Chloroplasts are one of the forms a plastid may take, and are generally considered to have originated as endosymbiotic cyanobacteria. In this respect they are

similar to mitochondria, but are found only in plants and protista.

Both organelles are surrounded by a double celled composite membrane with an intermembrane space; both have their own DNA and are involved in energy metabolism; and both have reticulations, or many infoldings, filling their inner spaces. In green plants chloroplasts are surrounded by two lipid-bilayer membranes. The inner membrane is now thought to correspond to the outer membrane of the ancestral cyanobacterium.

The chloroplast genome is considerably reduced compared to that of free-living cyanobacteria, but the parts that are still present show clear similarities. Many of the missing genes are encoded in the nuclear genome of the plant, algae or

protist. It is interesting to note that in some algae (such as the heterokonts and other protists such as Euglenozoa and Cercozoa), chloroplasts seem to have arisen through a secondary event of endosymbiosis, in which a eukaryotic cell engulfed a second eukaryotic cell containing chloroplasts, forming chloroplasts with three or four membrane layers. In some cases, such secondary endosymbionts have themselves been engulfed by still other eukaryotes, forming tertiary endosymbionts.

The chloroplast has a two membrane envelope termed the Inner & Outer membrane respectively. Between these two layers is the Intermembrane space.

The fluid within the chloroplast is called the stroma, corresponding to the cytoplasm of the bacterium, and contains tiny circular DNA and ribosomes, though most of their proteins are encoded by genes contained in the cell nucleus, with the protein products trafficked to the chloroplast.

Within the stroma are stacks of thylakoids, the sub-organelles where photosynthesis actually takes place. A stack of thylakoids is called a granum. A thylakoid looks like a flattened disk, and inside is an empty area called the thylakoid space or lumen. The photosynthesis reaction takes place on the membrane of the thylakoid, and, as is also the case with mitochondria, involves the coupling of cross-membrane fluxes with biosynthesis.

The photosynthetic proteins in the membrane bind chlorophyll, which is present with various accessory pigments. These give chloroplasts their green color. During autumn, the removal of chlorophyll from plant leaves exposes red and yellow pigments (such as xanthophyll) which were previously masked. Algal chloroplasts may be golden, brown, or red and show variation in the number of membranes and the presence of thylakoids.

Pigments undergo electronic excitations driven by the absorption of sunlight — red and blue for chlorophyll. The green we see is the color not absorbed. The energy released by the electronically-excited pigments as they return to their ground state is the basis for the energy captured by photosynthesis to produce ATP and NADPH and the ultimate formation of sugars.

Energy of the absorbed photons not used to produce chemical energy is eventually given off to the surroundings. Thus, chloroplasts are small heat engines operating between the hot light from the sun and the lower ambient molecular temperature. (Photovoltaic cells do likewise.)

All of these components are reservoirs of carbon. The cycle is usually thought of as four main reservoirs of carbon

interconnected by pathways of exchange. The reservoirs are the atmosphere, terrestrial biosphere (usually includes freshwater systems), oceans, and sediments (includes fossil fuels). The annual movements of carbon, the carbon exchanges between reservoirs, occur because of various

chemical, physical, geological, and biological processes. The ocean contains the largest pool of carbon near the surface of the Earth, but most of that pool is not involved with rapid exchange with the atmosphere.

The global carbon budget is the balance of the exchanges (incomes and losses) of carbon between the carbon reservoirs or between one specific loop (e.g., atmosphere - biosphere) of the carbon cycle. An examination of the carbon budget of a pool or reservoir can provide information about whether the pool or reservoir is functioning as a source or sink for carbon dioxide.

Carbon exists in Earth's atmosphere primarily as the gas carbon dioxide (CO2). Although it is a very small part of the atmosphere overall (approximately 0.04%, though rising), it plays an important role in supporting life.

Other gases containing carbon in the atmosphere are methane and chlorofluorocarbons (the latter are entirely artificial). These are all greenhouse gases whose concentration in the atmosphere has been increasing in recent decades, contributing to global warming.

Carbon is taken from the atmosphere in two ways:

When the sun is shining, plants perform photosynthesis to convert carbon dioxide into carbohydrates, releasing oxygen in the process. This process is most prolific in relatively new forests where tree growth is still rapid.

At the surface of the oceans near the poles, where the water becomes cooler and able to dissolve more carbon dioxide (see the entries on the solubility and biological pumps).

Carbon can be released back into the atmosphere in many different ways.

Through the respiration performed by plants and animals. This is an exothermic reaction and it involves the breaking down of glucose (or other organic molecules) into carbon dioxide and water.

Through the decay of animal and plant matter. Fungi and bacteria break down the carbon compounds in dead animals and plants and convert the carbon to carbon dioxide if oxygen is present, or methane if not.

Through combustion of organic material which oxidizes the carbon it contains, producing carbon dioxide (as well as other things, like smoke). Burning fossil fuels such as coal, petroleum products, and natural gas releases carbon that has been stored in the geosphere for millions of years. This is a major reason for rising atmospheric carbon dioxide levels.

Through reactions of limestone. Limestone, marble and chalk are composed mainly of calcium carbonate. As deposits of these rocks are eroded by water, the calcium carbonate is broken down to eventually form, among other things, carbon dioxide and carbonic acid. Production of cement and lime is done by heating limestone, which produces a substantial amount of carbon dioxide.

At the surface of the oceans where the water becomes warmer, dissolved carbon dioxide is released back into the atmosphere

Volcanic eruptions release gases into the atmosphere. These gases include water vapor, carbon dioxide and sulfur dioxide.

Carbon is an essential part of life on the Earth. It plays an important role in the structure, biochemistry, and nutrition of all living cells. And life plays an important role in the carbon cycle:

Autotrophs are organisms that produce their own organic compounds using carbon dioxide from the air or water in which they live. To do this they require an external source of energy. Almost all autotrophs use solar radiation to provide this, and they production process is called photosynthesis.

A small number of autotrophs exploit chemical energy sources, chemosynthesis. The most important autotrophs for the carbon cycle are trees in forests on land and phytoplankton in the Earth's oceans.

Carbon is transferred within the biosphere as heterotrophs feed on other organisms or their parts (e.g., fruits). This includes the uptake of dead organic material (detritus) by fungi and bacteria for fermentation or decay.

Most carbon leaves the biosphere through respiration. When oxygen is present, aerobic respiration occurs, which releases carbon dioxide into the surrounding air or water. Otherwise, anaerobic respiration occurs and releases methane into the surrounding environment, which eventually makes its way into the atmosphere or hydrosphere (e.g., as marsh gas or flatulence).

Carbon may also leave the biosphere when dead organic matter (such as peat) becomes incorporated in the geosphere. Animal shells of calcium carbonate, in particular, may eventually become limestone through the process of sedimentation.

Much remains to be learned about the cycling of carbon in the deep ocean. For example, a recent discovery is that larvacean mucus houses (commonly known as "sinkers") are created in such large numbers that they can deliver as much carbon to the deep ocean as has been previously detected by sediment traps.

Because of their size and composition, these houses are rarely collected in such traps, so most biogeochemical analyses have erroneously ignored them.

Models of the carbon cycle can be incorporated into global climate models, so that the interactive response of the oceans and biosphere on future CO2 levels can be modelled. There are considerable uncertainties in this, both in the physical and biogeochemical submodels (especially the latter).

Such models typically show that there is a positive feedback between temperature and CO2. For example, Zeng et al. (GRL, 2004) find that in their model, including a coupled carbon cycle increases atmospheric CO2 by about 90 ppmv at 2100 (over that predicted in models with non-interactive carbon cycles), leading to an extra 0.6°C of warming (which, in turn, may lead to even greater atmospheric CO2).

The cell is the structural and functional unit of all living organisms, and is sometimes called the "building block of life." Some organisms, such as bacteria, are unicellular, consisting of a single cell. Other organisms, such as humans, are multicellular, (humans have an estimated 100,000 billion or 1014 cells).

The cell theory, first developed in 1839 by Schleiden and Schwann, states that all organisms are composed of one or more cells; all cells come from preexisting cells; all vital functions of an organism occur within cells, and cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next

generation of cells.

The word cell comes from the Latin cella, a small room. The name was chosen by Robert Hooke when he compared the cork cells he saw to small rooms monks lived in.

Some (Lynn Margulis and Dorian Sagan, 1995) have argued that the cell is the smallest unit of life.

Each cell is at least somewhat self-contained and self-maintaining: it can take in nutrients, convert these nutrients into energy, carry out specialized

functions, and reproduce as necessary. Each cell stores its own set of instructions for carrying out each of these activities.

All cells share several abilities:

Reproduction by cell division.

Metabolism, including taking in raw materials, building cell components, converting energy, molecules and releasing by-products. The functioning of a cell depends upon its ability to extract and use chemical energy stored in organic molecules. This energy is derived from metabolic pathways.

Synthesis of proteins, the functional workhorses of cells, such as enzymes.

A typical mammalian cell contains up to 10,000 different proteins.

Response to external and internal stimuli such as changes in temperature, pH or nutrient levels.

Traffic of vesicles.

All cells, whether prokaryotic or eukaryotic, have a membrane, which envelopes the cell, separates its interior from its environment, controls what moves in and out, and maintains the electric potential of the cell. Inside the membrane, a salty cytoplasm takes up most of the cell volume. All cells possess DNA, the hereditary material of genes, and RNA, containing the information necessary to build various proteins such as enzymes, the cell's primary machinery. There are also other kinds of biomolecules in cells. This article will list these primary components of the cell, then briefly describe their function.

Cell membrane - a cell's protective coat

Main article: Cell membrane

The cytoplasm of a eukaryotic cell is surrounded by a plasma membrane. A form of plasma membrane is also found in prokaryotes, but is usually referred to as the cell membrane. This membrane serves to separate and protect a cell from its surrounding environment and is made mostly from a double layer of lipids (fat-like molecules) and proteins. Embedded within this membrane is a variety of other molecules that act as channels and pumps, moving different molecules into and out of the cell.

Cytoskeleton - a cell's scaffold

Main article: Cytoskeleton

The cytoskeleton is an important, complex, and dynamic cell component made up of microfilaments. It acts to organize and maintain the cell's shape; anchors organelles in place; helps during endocytosis, the uptake of external materials by a cell; and moves parts of the cell in processes of growth and motility. There is a great number of proteins associated with the cytoskeleton, each controlling a cell's structure by directing, bundling, and aligning filaments.

Genetic material

Two different kinds of genetic material exist: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Most organisms use DNA for their long-term information storage, but some viruses (retroviruses) have RNA as their genetic material. The biological information contained in an organism is encoded in its DNA or RNA sequence. RNA is also used for information transport (e.g., mRNA) and enzymatic functions (e.g., ribosomal RNA) in organisms that use RNA for the genetic code itself.

Prokaryotic genetic material is organized in a simple circular DNA molecule (the bacterial chromosome) in the nucleoid region of the cytoplasm. Eukaryotic genetic material is divided into different, linear molecules called chromosomes inside a discrete nucleus, usually with additional genetic material in some organelles like mitochondria and chloroplasts (see endosymbiotic theory).

A human cell has genetic material in the nucleus (the nuclear genome) and in the mitochondria (the mitochondrial genome). The nuclear genome is divided into 46 linear DNA molecules called chromosomes. The mitochondrial genome is a circular DNA molecule separate from the nuclear DNA. Although the mitochondrial genome is very small, it codes for some important proteins.

Foreign genetic material (most commonly DNA) can also be artificially introduced into the cell by a process called transfection. This can be transient, if the DNA is not inserted into the cell's genome, or stable, if it is.

Organelles

Main article: Organelle

The human body contains many different organs, such as the heart, lung, and kidney, with each organ performing a different function. Cells also have a set of "little organs," called organelles, that are adapted and/or specialized for carrying out one or more vital functions. Membrane-bound organelles are found only in eukaryotes.

Cell nucleus - a cell's information center: The cell nucleus is the most conspicuous organelle found in a eukaryotic cell. It houses the cell's chromosomes, and is the place where almost all DNA replication and RNA synthesis occur. The nucleus is spheroid in shape and separated from the cytoplasm by a double membrane called the nuclear envelope.

The nuclear envelope isolates and protects a cell's DNA from various molecules that could accidentally damage its structure or interfere with its processing. During processing, DNA is transcribed, or copied into a special RNA, called mRNA. This mRNA is then transported out of the nucleus, where it is translated into a specific protein molecule. In prokaryotes, DNA processing takes place in the cytoplasm.

Ribosomes - the protein production machine: Ribosomes are found in both prokaryotes and eukaryotes. The ribosome is a large complex composed of many molecules, including RNAs and proteins, and is responsible for processing the genetic instructions carried by an mRNA.

The process of converting an mRNA's genetic code into the exact sequence of amino acids that make up a protein is called translation. Protein synthesis is extremely important to all cells, and therefore a large number of ribosomes — sometimes hundreds or even thousands — can be found throughout a cell.

Mitochondria and chloroplasts - the power generators: Mitochondria are self-replicating organelles that occur in various numbers, shapes, and sizes in the cytoplasm of all eukaryotic cells. As mitochondria contain their own genome that is separate and distinct from the nuclear genome of a cell, they play a critical role in generating energy in the eukaryotic cell, a process involving a number of complex metabolic pathways.

Chloroplasts are larger than mitochondria, and convert solar energy into a chemical energy ("food") via photosynthesis. Like mitochondria, chloroplasts have their own genome. Chloroplasts are found only in photosynthetic eukaryotes, like plants and algae. There is a number of plant organelles that are modified chloroplasts; they are broadly called plastids, and are often involved in storage.

Endoplasmic reticulum and Golgi apparatus - macromolecule managers:: The endoplasmic reticulum (ER) is the transport network for molecules targeted for certain modifications and specific destinations, as compared to molecules that will float freely in the cytoplasm. The ER has two forms: the rough ER, which has ribosomes on its surface, and the smooth ER, which lacks them.

Translation of the mRNA for those proteins that will either stay in the ER or be exported from the cell occurs at the ribosomes attached to the rough ER. The smooth ER is important in lipid synthesis, detoxification and as a calcium reservoir. The Golgi apparatus, sometimes called a Golgi body or Golgi complex is the central delivery system for the cell and is a site for protein processing, packaging, and transport. Both organelles consist largely of heavily-folded membranes.

Lysosomes and peroxisomes - the cellular digestive system: Lysosomes and peroxisomes are often referred to as the garbage disposal system of a cell. Both organelles are somewhat spherical, bound by a single membrane, and rich in digestive enzymes, naturally-occurring proteins that speed up biochemical processes.

For example, lysosomes can contain more than three dozen enzymes for degrading proteins, nucleic acids, and certain sugars called polysaccharides. Here we can see the importance behind compartmentalization of the eukaryotic cell. The cell could not house such destructive enzymes if they were not contained in a membrane-bound system.

Centrioles help in the formation of mitotic appratus. Two centrioles are present in the animal cells. They are also found in some fungi and algae cells.

Vacuoles store food and waste. Some vacuoles store extra water. They are often described as liquid filled space and are surrounded by a membrane.

Anatomy of cells

Prokaryotic cells

Prokaryotes are distinguished from eukaryotes on the basis of nuclear organization, specifically their lack of a nuclear membrane. Prokaryotes also lack most of the intracellular organelles and structures that are characteristic of eukaryotic cells (an important exception is the ribosomes, which are present in both prokaryotic and eukaryotic cells).

Most of the functions of organelles, such as mitochondria, chloroplasts, and the Golgi apparatus, are taken over by the prokaryotic plasma membrane. Prokaryotic cells have three architectural regions: appendages called flagella and pili — proteins attached to the cell surface; a cell envelope consisting of a capsule, a cell wall, and a plasma membrane; and a cytoplasmic region that contains the cell genome (DNA) and ribosomes and various sorts of inclusions. Other differences include:

The plasma membrane (a phospholipid bilayer) separates the interior of the cell from its environment and serves as a filter and communications beacon.

Most prokaryotes have a cell wall (some exceptions are Mycoplasma (a bacterium) and Thermoplasma (an archaeon)). It consists of peptidoglycan in bacteria, and acts as an additional barrier against exterior forces. It also prevents the cell from "exploding" from osmotic pressure against a hypotonic environment. A cell wall is also present in some eukaryotes like fungi, but has a different chemical composition.

A prokaryotic chromosome is usually a circular molecule (an exception is that of the bacterium Borrelia burgdorferi, which causes Lyme disease). Even without a real nucleus, the DNA is condensed in a nucleoid. Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are usually circular. Plasmids can carry additional functions, such as antibiotic resistance.

Eukaryotic cells

There are two types of cells, eukaryotic and prokaryotic. Eukaryotic cells are usally found in multi-cellular organisms, while prokaryotic cells are usually on their own. Eukaryotic cells are about 10 times the size of a typical prokaryote and can be as much as 1000 times greater in volume.

The major difference between prokaryotes and eukaryotes is that eukaryotic cells contain membrane-bound compartments in which specific metabolic activities take place. Most important among these is the presence of a cell nucleus, a membrane-delineated compartment that houses the eukaryotic cell's DNA. It is this nucleus that gives the eukaryote its name, which means "true nucleus." Other differences include:

The plasma membrane resembles that of prokaryotes in function, with minor differences in the setup. Cell walls may or may not be present.

The eukaryotic DNA is organized in one or more linear molecules, called chromosomes, which are highly condensed (i.e. folded around histones). All chromosomal DNA is stored in the cell nucleus, separated from the cytoplasm by a membrane. Some eukaryotic organelles can contain some DNA.

Eukaryotes can move using cilia or flagella. The flagella are more complex than those of prokaryotes.

Between successive cell divisions, cells grow through the functioning of cellular metabolism. Cell metabolism is the process by which individual cells process nutrient molecules. Metabolism has two distinct divisions: catabolism, in which the cell breaks down complex molecules to produce energy and reducing power, and anabolism, wherein the cell uses energy and reducing power to construct complex molecules and perform other biological functions.

Complex sugars consumed by the organism can be broken down into a less chemically-complex sugar molecule called glucose. Once inside the cell, glucose is broken down to make adenosine triphosphate (ATP), a form of energy, via two different pathways.

The first pathway, glycolysis, requires no oxygen and is referred to as anaerobic metabolism. Each reaction is designed to produce some hydrogen ions that can then be used to make energy packets (ATP). In prokaryotes, glycolysis is the only method used for converting energy. The second pathway, called the Krebs cycle, or citric acid cycle, occurs inside the mitochondria and is capable of generating enough ATP to run all the cell functions.

Cell division involves a single cell (called a mother cell) dividing into two daughter cells. This leads to growth in multicellular organisms (the growth of tissue) and to procreation (vegetative reproduction) in unicellular organisms. Prokaryotic cells divide by binary fission. Eukaryotic cells usually undergo a process of nuclear division, called mitosis, followed by division of the cell, called cytokinesis.

A diploid cell may also undergo meiosis to produce haploid cells, usually four. Haploid cells serve as gametes in multicellular organisms, fusing to form new diploid cells. DNA replication, or the process of duplicating a cell's genome, is required every time a cell divides. Replication, like all cellular activities, requires specialized proteins for carrying out the job.

Protein synthesis

Protein synthesis is the process in which the cell builds proteins. DNA transcription refers to the synthesis of a messenger RNA (mRNA) molecule from a DNA template. This process is very similar to DNA replication. Once the mRNA has been generated, a new protein molecule is synthesized via the process of translation.

The cellular machinery responsible for synthesizing proteins is the ribosome. The ribosome consists of structural RNA and about 80 different proteins. When the ribosome encounters an mRNA, the process of translating an mRNA to a protein begins.

The ribosome accepts a new transfer RNA, or tRNA—the adaptor molecule that acts as a translator between mRNA and protein—bearing an amino acid, the building block of the protein. Another site binds the tRNA that becomes attached to the growing chain of amino acids, forming the a polypeptide chain that will eventually be processed to become a protein.

Origins of cells

The origin of cells has to do with the origin of life, and was one of the most important steps in evolution of life as we know it. The birth of the cell marked the passage from prebiotic chemistry to biological life.

Origin of first cell

If life is viewed from the point of view of replicators, that is DNA molecules in the organism, cells satisfy two fundamental conditions: protection from the outside environment and confinement of biochemical activity. The former condition is needed to maintain the fragile DNA chains stable in a varying and sometimes aggressive environment, and may have been the main reason for which cells evolved. The latter is fundamental for the evolution of biological complexity.

If freely-floating DNA molecules that code for enzymes are not enclosed into cells, the enzymes that benefit a given DNA molecule (for example, by producing nucleotides) will automatically benefit the neighbouring DNA molecules. This might be viewed as "parasitism by default."

Therefore the selection pressure on DNA molecules will be much lower, since there is not a definitive advantage for the "lucky" DNA molecule that produces the better enzyme over the others: All molecules in a given neighbourhood are almost equally advantaged.

If all the DNA molecule is enclosed in a cell, then the enzymes coded from the molecule will be kept close to the DNA molecule itself. The DNA molecule will directly enjoy the benefits of the enzymes it codes, and not of others.

This means other DNA molecules won't benefit from a positive mutation in a neighbouring molecule: this in turn means that positive mutations give immediate and selective advantage to the replicator bearing it, and not on others.

This is thought to have been the one of the main driving force of evolution of life as we know it. (Note. This is more a metaphor given for simplicity than complete accuracy, since the earliest molecules of life, probably up to the stage of cellular life, were most likely RNA molecules, acting both as replicators and enzymes: see RNA world hypothesis . But the core of the reasoning is the same.)

Biochemically, cell-like spheroids formed by proteinoids are observed by heating amino acids with phosphoric acid as a catalyst. They bear much of the basic features provided by cell membranes. Proteinoid-based protocells enclosing RNA molecules could (but not necessarily should) have been the first cellular life forms on Earth.

Another theory holds that the turbulent shores of the ancient coastal waters may have served as a mammoth laboratory, aiding in the countless experiments necessary to bring about the first cell. Waves breaking on the shore create a delicate foam composed of bubbles. Winds sweeping across the ocean have a tendency to drive things to shore, much like driftwood collecting on the beach. It is possible that organic molecules were concentrated on the shorelines in much the same way.

Shallow coastal waters also tend to be warmer, further concentrating the molecules through evaporation. While bubbles comprised of mostly water tend to burst quickly, oily bubbles happen to be much more stable, lending more time to the particular bubble to perform these crucial experiments. The Phospholipid is a good example of a common oily compound prevalent in the prebiotic seas. Phospholipids can be constructed in ones mind as a hydrophilic head on one end, and a hydrophobic tail on the other.

Phospholipids also possess an important characteristic, that is being able to link together to form a bilayer membrane. A lipid monolayer bubble can only contain oil, and is therefore not conducive to harbouring water-soluble organic molecules. On the other hand, a lipid bilayer bubble can contain water, and was a likely precursor to the modern cell membrane.

If a protein came along that increased the integrity of its parent bubble, then that bubble had an advantage, and was placed at the top of the natural selection waiting list. Primitive reproduction can be envisioned when the bubbles burst, releasing the results of the experiment into the surrounding medium.

Once enough of the 'right stuff' was released into the medium, the development of the first prokaryotes, eukaryotes, and multi-celluar organisms could be achieved. This theory is expanded upon in the book, "The Cell: Evolution of the First Organism" by Joseph Panno Ph.D.

Origin of eukaryotic cells

The eukaryotic cell seems to have evolved from a symbiotic community of prokaryotic cells. It is almost certain that DNA-bearing organelles like the mitochondria and the chloroplasts are what remains of ancient symbiotic oxygen-breathing bacteria and cyanobacteria, respectively, where the rest of the cell seems to be derived from an ancestral archaean prokaryote cell – a theory termed the endosymbiotic theory.

There is still considerable debate on if organelles like the hydrogenosome predated the origin of mitochondria, or viceversa : see the hydrogen hypothesis for the origin of eukaryotic cells.

Generally of showy color in the plants entomogamas.

The corolla composes of petals. The corolla is gamopetal: Corolla of only one piece.

The petals are welded between yes; the number of petals that form her it is warned counting the teeth or lobes of the limbo.

simpetal: With the petals welded by his margins, at least in the base.

The chalice and the corolla are known also as the perianto of the flower. When there do not exist clear differences between the external verticilo (chalice) and the intern (corolla), the floral pieces are named tépalos and the set is named perigonio. They constitute, also, the incidental verticilos that can be absent completely in a flower.

In a "typical" flower the petals are showy and colored and surround the reproductive parts. The number of petals in a flower (see merosity) is indicative of the plant's classification: dicots having typically four or five petals and monocots having three, or some multiple of three, petals.

There exists considerable variation in form of petals among the flowering plants. The petals can be united towards the base, forming a floral tube. In some flowers, the entire perianth forms a cup (called a calyx tube) surrounding the gynoecium, with the sepals, petals, and stamens attached to the rim of the cup.

The flowers of some species lack or have very much reduced petals. These are often referred to as apetalous. Examples of flowers with much reduced perianths are found among the grasses.

The petals are usually the most conspicuous parts of a flower, and the petal whorl or corolla may be either radially or bilaterally symmetrical. If all of the petals are essentially identical in size and shape, the flower is said to be regular or actinomorphic (meaning 'ray-formed').

Many flowers are symmetrical in only one plane (i.e., symmetry is bilateral) and are termed irregular or zygomorphic (meaning yoke- or pair-formed). In irregular flowers, other floral parts may be modified from the regular form, but the petals show the greatest deviation from radial symmetry. Examples of zygomorphic flowers may be seen in orchids and members of the pea family.

American bellflower (Campanulastrum americanum) is a tall, annual bellflower that grows mainly in the Great Plains and eastern coast of the United States. Its flowers are light blue to violet and usually form in elongated clusters. It is an unusual bellflower in that its flowers are usually flat and not bell-shaped.

Campanula is one of several genera of in the family Campanulaceae with the common name bellflower. It takes its name from their bell-shaped flowers, and campanula is Latin for "little bell".

The genus includes about 300 species and several subspecies, distributed across the temperate regions of the Northern Hemisphere, with the highest diversity in the Mediterranean region east to the Caucasus.

The species include annual, biennial and perennial plants, and vary in habit from dwarf arctic and alpine species under 5 cm high, to large temperate grassland and woodland species growing to 2 m tall.

The leaves are alternate, sessile, and often vary in shape on a single plant, with larger, broader leaves at the base of the stem and smaller, narrower leaves higher up; the leaf margin may be either entire or serrated (sometimes both on the same plant). Many species contain white latex in the leaves and stems.

The flowers are produced in panicles (sometimes solitary), and have a bell-shaped, five-lobed corolla, typically large (2-5 cm or more long), mostly blue to purple, sometimes white or pink. The fruit is a capsule containing numerous small seeds.

Well-known species include the northern European Campanula rotundifolia, commonly known as Harebell in England and Bluebell in Scotland, and the southern European Campanula medium, commonly known as Canterbury Bells, which is a cultivated garden plant in the United Kingdom. As well as several species occurring naturally in the wild in northern Europe, there are many cultivated garden species.

The species Campanula rapunculus, commonly known as Rampion Bellflower, Rampion, or Rover Bellflower, is an annual vegetable and a popular garden plant, though sometimes considered too invasive. There are blue, purple and white varieties. The Brothers Grimm's tale Rapunzel gave its name to this plant.

Campanula species are used as food plants by the larvae of some Lepidoptera species including Common Pug (recorded on Harebell), Dot Moth, Ingrailed Clay (recorded on Harebell), Lime-speck Pug and Mouse Moth.

Impatiens is a genus of about 800-1000 species of flowering plants in the family Balsaminaceae. The genus has a wide distribution throughout the northern hemisphere and tropics, although they are not found in South America.

Some species are annual plants and produce flowers from early summer until the first frost, while perennial species, found in milder climates, can flower all year.

They can exist both in, and out, of direct sunlight. Some Impatiens hybrids have commercial importance as garden plants. Major common names for one or more species include balsam, jewelweed and busy lizzie.

The plant derives its scientific name Impatiens ("impatient") and the common name "touch-me-not" from the plant's seed pods. When the seed's pods mature, they

"explode" when touched, sending seeds several metres away. This mechanism is also known as "explosive dehiscence". See also Rapid plant movement. Impatiens species are used as food plants by the larvae of some Lepidoptera species including Dot Moth.

Datura stramonium is, on average, 30 to 150 cm tall with erect, forking and purple stems. The leaves are large, 7 to 20 cm long and have irregular teeth à la oaks. The flowers are one of the most distinctive characteristics of Datura stramonium: they are trumpet-shaped, white to purple, and 5-12.5 cm long. The flowers open and close at irregular intervals during the evening, earning the plant the nickname Moonflower. The fruit are grape-sized, egg-

shaped, and covered in prickles, they split into four chambers, each with a few kidney shaped seeds . All parts of the plant emit a foul odor when crushed or bruised .

To grow well, sunflowers need full sun. They grow best in fertile, moist, well-drained soil with a lot of mulch. Seeds should be 45 cm (1.5') apart and planted 2.5 cm (1") deep.

Sunflower "whole seeds" (fruit) are sold as snacks, especially in China, the United States and Europe, and as food for birds. Those seeds are also used directly in cooking and salad. Sunflower oil, extracted from the seeds, is used for cooking (but is less cardiohealthy than olive oil), as a carrier oil and is used to produce biodiesel, for which it is less expensive than the olive product.

The cake remaining after the seeds have been processed for oil is used as a livestock feed. Some recently developed cultivars have drooping heads.

These cultivars are less attractive to gardeners growing the flowers as ornamental plants, but appeal to farmers, because they reduce bird damage and losses from some plant diseases. There are also new breeds of sunflowers which are transgenic, so that they are resistant to some diseases. Sunflowers also produce latex and are the subject of experiments to improve their suitability as an alternative crop for producing hypoallergenic rubber.

The sunflower is the state flower of the U.S. state of Kansas, and one of the city flowers of Kitakyushu, Japan. The Jerusalem artichoke (Helianthus tuberosa) is related to the sunflower. The Mexican sunflower is Tithonia rotundifolia. False sunflower refers to plants of the genus Heliopsis.

Scientific literature reports, from 1567, that a 12 m (40'), traditional, single-head, sunflower plant was grown in Padua. The same seed lot grew almost 8 m (24') at other times and places (e.g. Madrid). Much more recent feats (past score years) of over 8 m (25') have been achieved in both Netherlands and Canada (Ontario).

The term "sunflower" is also used to refer to all plants of the genus Helianthus, many of which are perennial plants.

What is called the flower is actually a head (formerly composite flower) of numerous flowers crowded together. The outer flowers are the ray florets and can be yellow, maroon, orange, or other colors. These flowers are sterile. The flowers that fill the circular head inside the ray flowers are called disc florets.

The arrangement of florets within this cluster is typically such that each is separated from the next by approximately the golden angle, producing a pattern of spirals where the number of left spirals and the number of right spirals are successive Fibonacci numbers, typically 34 in one direction and 55 in the other; on a very large sunflower you may see 89 in one direction and 144 in the other.

The disc florets mature into "seeds". However, what we commonly call the seeds are actually the fruit (an achene) of the plant, with the true seeds encased in an inedible husk.

Heliotropism

Most flowerheads on a field of blooming sunflowers are turned towards the east, where the sun rises each morning. Immature sunflowers in the bud stage exhibit heliotropism; on sunny days the bud tracks the sun on its journey along the sky from east to west, while at night or at dawn it returns to its eastward orientation.

The motion is performed by motor cells in the pulvinus, a flexible segment of the stem just below the bud. The stem stiffens at the end of the bud stage, and when the blooming stage is reached the stem freezes in its eastward direction. Thus, blooming sunflowers are not heliotropic anymore, even though most flowerheads are facing the direction where the sun rises.

The inflorescence of the wild sunflower seen on roadsides does not turn toward the sun. In this sunflower, the flowering heads face many directions when mature. But the leaves exhibit some heliotropism.

Belongs to the family of the Pontederiaceas, receives the name of water hyacinth because of its showy inflorescence of violet flowers that seem a little like the flowers of hyacinth.

Its an aquatic perennial plant. The leaves, of a bright green color, Se trata de una planta acuática perenne Las hojas, de color verde brillante, measure between 5 y 15 cm. They meet forming a roseta. The sheets nearest to the root, placed in the base of the roseta, are shorter, and they possess one petiole increased to favor the flotation.

The biggest sheets can reach approximately 15 cm long.

The flowering is summer and quite short, since it usually does not go beyond 2 or 3 days, but the beauty of the flowers is unquestionable. The floral stem increased in his base, grows from the center of the rose window.

The inflorescence in the shape of ear can contain between 5 and 30 flowers from 1 to 3 cm long. In whole the set measures approximately 15 cm.

The system radicular, developed good, is formed by a thick jumble that they hang under the rose window of sheets. An unmistakable characteristic of the roots of the aquatic hyacinth it is his color, They are black or brown with tones roses or blue in the side roots.

Normally they measure between 15 and 40 cm, overcoming loosely the length of the biggest sheets, but they can go so far as to overcome the meter of long.

As other floating plants, it is very demanding in what to lighting refers. He needs at least 11 daily hours of intense light of solar type.

A few species of cyanobacteria may also be counted as seaweeds. Seaweeds are named after terrestrial "weeds",

and are not to be confused with things like seagrasses which are vascular plants and not algae.

Seaweeds may have an appearance that resembles non-arboreal terrestrial plants.

thallus: the algal body

blade: a flattened structure that is somewhat leaf-like

sorus: spore cluster on Fucus - - Air bladders: float-assist organ (on blade)

on kelp -- floats: float-assist organ (in between blade and stipe)

stipe: a stem-like structure, may be absent

holdfast: specialized basal structure providing attachment to the bottom

The stipe and blade are collectively known as frond.

Uses

Seaweeds are extensively used as food by coastal peoples, particularly in Japan and Korea, but also in China, Vietnam, Indonesia, Peru, the Canadian Maritimes, Scandinavia, Ireland, Wales, Philippines, and Scotland, among other places.

For example, Porphyra is a red alga used in Wales to make laverbread, and in Japan dried, formed into sheets called nori which is widely used in soups, and for wrapping sushi, boiled rice stuffed with bits of raw fish, sea urchin roe, or other ingredients. Chondrus crispus (commonly known as Irish moss) is another red alga used in producing various food additives.

Seaweed is also used for the production of Alginate, a versatile product that is used for many applications, including the production of Agar, which is used in microbiology as a substrate for culturing organisms. Alginates are also used in the production of foodstuffs to improve texture. Typical products which use alginates include ice-cream and a range of proprietary desserts (see Carrageenan).

Other seaweeds may be used as seaweed fertiliser.