1.
Green algae
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The green algae are a large, informal grouping of algae consisting of the Chlorophyte and Charophyte algae, which are now placed in separate divisions. The land plants, or Embryophytes, are thought to have emerged from the Charophytes, therefore, cladistically, Embryophytes belong to green algae as well. However, as the Embryophytes are traditionally classified as neither algae nor green algae, the clade that includes both green algae and embryophytes is monophyletic and is referred to as the clade Viridiplantae and as the kingdom Plantae. The green algae include unicellular and colonial flagellates, most with two flagella per cell, as well as various colonial, coccoid and filamentous forms, and macroscopic, in the Charales, the closest relatives of higher plants, full cellular differentiation of tissues occurs. There are about 8,000 species of green algae, many species live most of their lives as single cells, while other species form coenobia, long filaments, or highly differentiated macroscopic seaweeds. A few other organisms rely on green algae to conduct photosynthesis for them, the chloroplasts in euglenids and chlorarachniophytes were acquired from ingested green algae, and in the latter retain a nucleomorph. Green algae are also found symbiotically in the ciliate Paramecium, and in Hydra viridissima, some species of green algae, particularly of genera Trebouxia of the class Trebouxiophyceae and Trentepohlia, can be found in symbiotic associations with fungi to form lichens. In general the species that partner in lichens cannot live on their own. Trentepohlia is a green alga that can live independently on humid soil. Green algae have chloroplasts that contain chlorophyll a and b, giving them a green color, as well as the accessory pigments beta carotene and xanthophylls. The cell walls of green algae usually contain cellulose, and they store carbohydrate in the form of starch, all green algae have mitochondria with flat cristae. When present, paired flagella are used to move the cell and they are anchored by a cross-shaped system of microtubules and fibrous strands. Flagella are only present in the male gametes of charophytes and are absent from the gametes of Pinophyta. Members of the class Chlorophyceae undergo closed mitosis in the most common form of division among the green algae. By contrast, charophyte green algae and land plants undergo open mitosis without centrioles, instead, a raft of microtubules, the phragmoplast, is formed from the mitotic spindle and cell division involves the use of this phragmoplast in the production of a cell plate. This primary endosymbiosis event gave rise to three autotrophic clades with primary plastids, the plants, the red algae and the glaucophytes. Green algae are classified with their embryophyte descendants in the green plant clade Viridiplantae. Viridiplantae, together with red algae and glaucophyte algae, form the supergroup Primoplantae, the Viridiplantae diverged into two clades
2.
Chara (alga)
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Chara is a genus of charophyte green algae in the family Characeae. They are multicellular and superficially resemble land plants because of stem-like and leaf-like structures and they are found in fresh water, particularly in limestone areas throughout the northern temperate zone, where they grow submerged, attached to the muddy bottom. They prefer less oxygenated and hard water and are not found in waters where mosquito larvae are present and they are covered with calcium carbonate deposits and are commonly known as stoneworts. Cyanobacteria have been growing as epiphytes on the surfaces of Chara, where they may be involved in fixing nitrogen. The branching system of Chara species is complex with branches derived from cells which cut off segments at the base to form nodal and internodal cells alternately. The main axes bear whorls of branches in a resemblance to Equisetum. They are typically anchored to the substrate by means of branching underground rhizoids. Chara plants are rough to the touch because of deposited calcium salts on the cell wall, the metabolic processes associated with this deposition often give Chara plants a distinctive and unpleasant smell of hydrogen sulfide. The plant body is a gametophyte and it consists of a main axis, dimorphic branches, rhizoids and stipulodes. Vegetative reproduction takes place by tubers, amylum stars and secondary protonema, the fructifications for sexual reproduction are globule or antheridium and nucule or archegonium. The sex organs are multicellular and jacketed, the antheridia and archegonia may occur on separate plants, together on the same plant or separately on the same plant. After fertilization, the zygote develops into an oospore, Chara has a cosmopolitan distribution, from 69 degrees north in northern Norway to about 49 degrees south in Kerguelen Islands. About 27 species are found in India, there are about 40 species of Chara in Europe, where they are commonly found in the specific habitat-type designated as H3140 in the Natura 2000 plans of the European Union. Although this habitat is all across Europe, it is threatened. The Netherlands are home to 20 species of Chara, growing in lakes, the H3140 habitats in the Netherlands, are considered important in the overall preservation efforts and therefore also for the Chara species in general. Here, many former Chara habitats have been polluted by either toxins or excessive amounts of nutrients, Chara is found growing in the very clean hard water lakes of Thy National Park like Nors Sø for example. Tissø lake is also a H3140 habitat and contains Chara species, Chara rudis Leonhardii and Nitella flexilis C. Agardh
3.
Antheridium
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An antheridium is a haploid structure or organ producing and containing male gametes. The plural form is antheridia, and a structure containing one or more antheridia is called an androecium, androecium is also used as the collective term for the stamens of flowering plants. Antheridia are present in the phase of cryptogams like bryophytes. Many algae and some fungi, for example ascomycetes and water moulds, in gymnosperms and angiosperms, the male gametophytes have been reduced to pollen grains and in most of these the antheridia have been reduced to a single generative cell within the pollen grain. During pollination, this cell divides and gives rise to sperm cells. The female counterpart to the antheridium in cryptogams is the archegonium, an antheridium typically consists of sterile cells and spermatogenous tissue. The sterile cells may form a support structure or surround the spermatogenous tissue as a protective jacket. The spermatogenous cells give rise to spermatids via mitotic cell division, in some bryophytes, the antheridium is borne on an antheridiophore, a stalk-like structure that carries the antheridium at its apex. Hornworts have antheridia, in some cases arranged within androecia, microsporangia produce spores that give rise to male gametophytes. National council for Science and the Environment
4.
Archegonium
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An archegonium, from the ancient Greek ἀρχή and γόνος, is a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female gamete. The corresponding male organ is called the antheridium, the archegonium has a long neck canal or venter and a swollen base. Archegonia are typically located on the surface of the plant thallus, in the moss Physcomitrella patens, archegonia are not embedded but are located on top of the leafy gametophore. The Polycomb protein FIE is expressed in the egg cell as the blue colour after GUS staining reveals. Soon after fertilisation the FIE gene is inactivated in the young embryo and they are much-reduced and embedded in the megagametophytes of gymnosperms. The term is not used for angiosperms or the gnetophytes Gnetum and Welwitschia because the megagametophyte is reduced to just a few cells, the function of surrounding the gamete is assumed in large part by diploid cells of the megasporangium inside the ovule. Gymnosperms have their archegonium formed after pollination inside female conifer cones
5.
Reproductive system
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The reproductive system or genital system is a system of sex organs within an organism which work together for the purpose of sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are also important accessories to the reproductive system, unlike most organ systems, the sexes of differentiated species often have significant differences. These differences allow for a combination of material between two individuals, which allows for the possibility of greater genetic fitness of the offspring. In mammals, the organs of the reproductive system include the external genitalia as well as a number of internal organs including the gamete producing gonads. Diseases of the reproductive system are very common and widespread. Most other vertebrate animals have generally similar reproductive systems consisting of gonads, ducts, however, there is a great diversity of physical adaptations as well as reproductive strategies in every group of vertebrates. Vertebrate animals all share key elements of their reproductive systems and they all have gamete-producing organs or gonads. In females, these gonads are then connected by oviducts to an opening to the outside of the body, typically the cloaca, the human reproductive system usually involves internal fertilization by sexual intercourse. During this process, the male inserts his penis into the females vagina and ejaculates semen. The sperm then travels through the vagina and cervix into the uterus or fallopian tubes for fertilization of the ovum, upon successful fertilization and implantation, gestation of the fetus then occurs within the females uterus for approximately nine months, this process is known as pregnancy in humans. Gestation ends with birth, the process of birth is known as labor, labor consists of the muscles of the uterus contracting, the cervix dilating, and the baby passing out the vagina. Humans babies and children are nearly helpless and require high levels of care for many years. One important type of care is the use of the mammary glands in the female breasts to nurse the baby. The female reproductive system has two functions, The first is to produce egg cells, and the second is to protect, the male reproductive system has one function, and it is to produce and deposit sperm. Humans have a level of sexual differentiation. In addition to differences in nearly every organ, numerous differences typically occur in secondary sexual characteristics. The male reproductive system is a series of organs located outside of the body, the primary direct function of the male reproductive system is to provide the male sperm for fertilization of the ovum. The major reproductive organs of the male can be grouped into three categories, the first category is sperm production and storage
6.
Testis
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The testicle or testis is the male gonad in animals. Like the ovaries to which they are homologous, the testicles are components of both the system and the endocrine system. The primary functions of the testes are to produce sperm and to produce androgens, both functions of the testicle are influenced by gonadotropic hormones produced by the anterior pituitary. Luteinizing hormone results in testosterone release, the presence of both testosterone and follicle-stimulating hormone is needed to support spermatogenesis. Almost all healthy male vertebrates have two testicles and they are typically of similar size, although in sharks, that on the right side is usually larger, and in many bird and mammal species, the left may be the larger. The primitive jawless fish have only a single testis, located in the midline of the body, the testicles of a dromedary camel are 7–10 cm long,4.5 cm deep and 5 cm in width. The right testicle is often smaller than the left, the testicles of a male red fox attain their greatest weight in December–February. Spermatogenesis in male golden jackals occurs 10–12 days before the females enter estrus and, during this time, in mammals, the testes are often contained within an extension of the abdomen called the scrotum. In mammals with external testes it is most common for one testicle to hang lower than the other. While the size of the varies, it is estimated that 21. 9% of men have their higher testicle being their left. This is due to differences in the anatomical structure on the right. In healthy European adult humans, average volume is 18 cm³ per testis. The average testicle size after puberty measures up to around 2 inches long,0.8 inches in breadth, measurement in the living adult is done in two basic ways, comparing the testicle with ellipsoids of known sizes. Measuring the length, depth and width with a ruler, a pair of calipers or ultrasound imaging, the volume is then calculated using the formula for the volume of an ellipsoid, 4/3 π × × ×. Human testicles are smaller than chimpanzee testicles but larger than gorilla testicles, under a tough membranous shell, the tunica albuginea, the testis of amniotes and some teleost fish, contains very fine coiled tubes called seminiferous tubules. The tubules are lined with a layer of cells that from puberty into old age, the sperm move into the vas deferens, and are eventually expelled through the urethra and out of the urethral orifice through muscular contractions. Amphibians and most fish do not possess seminiferous tubules, instead, the sperm are produced in spherical structures called sperm ampullae. These are seasonal structures, releasing their contents during the breeding season, before the next breeding season, new sperm ampullae begin to form and ripen
7.
Moss
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Mosses are small flowerless plants that typically grow in dense green clumps or mats, often in damp or shady locations. Although some species have conducting tissues, these are poorly developed. Mosses do not have seeds and after fertilisation develop sporophytes with unbranched stalks topped with single capsules containing spores and they are typically 0. 2–10 cm tall, though some species are much larger. Dawsonia, the tallest moss in the world, can grow to 50 cm in height, mosses are commonly confused with lichens, hornworts, and liverworts. Lichens may superficially look like mosses, and have names that include the word moss. This contrasts with the pattern in all plants, where the diploid sporophyte generation is dominant. Mosses are now classified on their own as the division Bryophyta, the main commercial significance of mosses is as the main constituent of peat, although they are also used for decorative purposes, such as in gardens and in the florist trade. Traditional uses of mosses included as insulation and for the ability to absorb liquids up to 20 times their weight, botanically, mosses are non-vascular plants in the land plant division Bryophyta. They are small plants that absorb water and nutrients mainly through their leaves and harvest carbon dioxide. They differ from plants in lacking water-bearing xylem tracheids or vessels. As in liverworts and hornworts, the gametophyte generation is the dominant phase of the life cycle. This contrasts with the pattern in all plants, where the diploid sporophyte generation is dominant. Mosses reproduce using spores, not seeds, and have no flowers, Moss gametophytes have stems which may be simple or branched and upright or prostrate. Their leaves are simple, usually only a layer of cells with no internal air spaces. They do not have roots, but have threadlike rhizoids that anchor them to their substrate. Mosses do not absorb water or nutrients from their substrate through their rhizoids and they can be distinguished from liverworts by their multi-cellular rhizoids. Spore-bearing capsules or sporangia of mosses are borne singly on long, unbranched stems, thereby distinguishing them from the polysporangiophytes, the spore-bearing sporophytes are short-lived and dependent on the gametophyte for water supply and nutrition. Also, in most mosses, the capsule enlarges and matures after its stalk elongates
8.
Gametophyte
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A gametophyte is a stage in the life cycle of plants and algae that undergo alternation of generations. It is a multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the phase in the life cycle of plants. It develops sex organs that produce gametes, haploid sex cells that participate in fertilization to form a diploid zygote in which each cell has two sets of chromosomes. Cell division of the results in a new diploid multicellular organism, the second stage in the life cycle known as the sporophyte. In some multicellular green algae, red algae and brown algae sporophytes and gametophytes may be externally indistinguishable, in Ulva the gametes are isogamous, all of one size, shape and general morphology. In land plants, anisogamy is universal, as in animals, female and male gametes are called, respectively, eggs and sperm. Either the sporophyte or the gametophyte may be reduced, in bryophytes, the gametophyte is the most visible stage of the life cycle. The bryophyte gametophyte is longer lived, nutritionally independent, and the sporophytes are typically attached to the gametophytes, when a moss spore germinates it grows to produce a filament of cells. The mature gametophyte of mosses develops into leafy shoots that produce sex organs that produce gametes, eggs develop in archegonia and sperm in antheridia. In some bryophyte groups such as many liverworts of the order Marchantiales, in most ferns, gametophyte is a photosynthetic free living organism called a prothallus. However, in groups, notably the clade that includes Ophioglossaceae and Psilotaceae. Extant lycophytes produce several different types of gametophytes, in the families Lycopodiaceae and Huperziaceae, gametophytes are subterranean and mycotrophic, deriving nutrients from symbiosis with fungi. The gametophytes of Isoetes appear to be similar in respect to those of the extinct Carboniferous giant arborescent clubmosses, Lepidodendron. By contrast, in seed plants, gametophytes develop into multicellular organisms while still enclosed within the sporangium, vascular plants that produce only one type of spore are said to be homosporous. They have exosporic gametophytes—that is, the gametophyte is free-living and develops outside of the spore wall, exosporic gametophytes are normally bisexual, capable of producing both sperm and eggs. In heterosporous vascular plants, the gametophyte develops endosporically, within the spore wall and these gametophytes are unisexual, producing either sperm or eggs but not both. All vascular plants are dominant, and a trend toward smaller
9.
Flower
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A flower, sometimes known as a bloom or blossom, is the reproductive structure found in plants that are floral. The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs, Flowers may facilitate outcrossing or allow selfing. Some flowers produce diaspores without fertilization, Flowers contain sporangia and are the site where gametophytes develop. Many flowers have evolved to be attractive to animals, so as to them to be vectors for the transfer of pollen. After fertilization, the ovary of the flower develops into fruit containing seeds, the essential parts of a flower can be considered in two parts, the vegetative part, consisting of petals and associated structures in the perianth, and the reproductive or sexual parts. A stereotypical flower consists of four kinds of structures attached to the tip of a short stalk, each of these kinds of parts is arranged in a whorl on the receptacle. The four main whorls are as follows, Collectively the calyx, corolla, the next whorl toward the apex, composed of units called petals, which are typically thin, soft and colored to attract animals that help the process of pollination. Androecium, the whorl, consisting of units called stamens. Stamens consist of two parts, a called a filament, topped by an anther where pollen is produced by meiosis. Gynoecium, the innermost whorl of a flower, consisting of one or more units called carpels, the carpel or multiple fused carpels form a hollow structure called an ovary, which produces ovules internally. Ovules are megasporangia and they in turn produce megaspores by meiosis which develop into female gametophytes and these give rise to egg cells. The gynoecium of a flower is described using an alternative terminology wherein the structure one sees in the innermost whorl is called a pistil. A pistil may consist of a carpel or a number of carpels fused together. 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. The relationship to the gynoecium on the receptacle is described as hypogynous, perigynous, although the arrangement described above is considered typical, plant species show a wide variation in floral structure. These modifications have significance in the evolution of flowering plants and are used extensively by botanists to establish relationships among plant species, the four main parts of a flower are generally defined by their positions on the receptacle and not by their function. Many flowers lack some parts or parts may be modified into other functions and/or look like what is typically another part, in some families, like Ranunculaceae, the petals are greatly reduced and in many species the sepals are colorful and petal-like. Other flowers have modified stamens that are petal-like, the flowers of Peonies and Roses are mostly petaloid stamens
10.
Flowering plant
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The flowering plants, also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants, with 416 families, approx. 13,164 known genera and a total of c.295,383 known species, etymologically, angiosperm means a plant that produces seeds within an enclosure, in other words, a fruiting plant. The term angiosperm comes from the Greek composite word meaning enclosed seeds, the ancestors of flowering plants diverged from gymnosperms in the Triassic Period, during the range 245 to 202 million years ago, and the first flowering plants are known from 160 mya. They diversified extensively during the Lower Cretaceous, became widespread by 120 mya, angiosperms differ from other seed plants in several ways, described in the table. These distinguishing characteristics taken together have made the angiosperms the most diverse and numerous land plants, the amount and complexity of tissue-formation in flowering plants exceeds that of gymnosperms. The vascular bundles of the stem are arranged such that the xylem and phloem form concentric rings, in the dicotyledons, the bundles in the very young stem are arranged in an open ring, separating a central pith from an outer cortex. In each bundle, separating the xylem and phloem, is a layer of meristem or active formative tissue known as cambium, the soft phloem becomes crushed, but the hard wood persists and forms the bulk of the stem and branches of the woody perennial. Among the monocotyledons, the bundles are more numerous in the stem and are scattered through the ground tissue. They contain no cambium and once formed the stem increases in diameter only in exceptional cases, the characteristic feature of angiosperms is the flower. Flowers show remarkable variation in form and elaboration, and provide the most trustworthy external characteristics for establishing relationships among angiosperm species, the function of the flower is to ensure fertilization of the ovule and development of fruit containing seeds. The floral apparatus may arise terminally on a shoot or from the axil of a leaf, occasionally, as in violets, a flower arises singly in the axil of an ordinary foliage-leaf. There are two kinds of cells produced by flowers. Microspores, which divide to become pollen grains, are the male cells and are borne in the stamens. The female cells called megaspores, which divide to become the egg cell, are contained in the ovule. The flower may consist only of parts, as in willow. Usually, other structures are present and serve to protect the sporophylls, the individual members of these surrounding structures are known as sepals and petals. The outer series is usually green and leaf-like, and functions to protect the rest of the flower, the inner series is, in general, white or brightly colored, and is more delicate in structure. It functions to attract insect or bird pollinators, attraction is effected by color, scent, and nectar, which may be secreted in some part of the flower
11.
Pollen
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Pollen is a fine to coarse powdery substance comprising pollen grains which are male microgametophytes of seed plants, which produce male gametes. If pollen lands on a compatible pistil or female cone, it germinates, individual pollen grains are small enough to require magnification to see detail. The study of pollen is called palynology and is useful in paleoecology, paleontology, archaeology. Pollen in plants is used for transferring haploid male genetic material from the anther of a flower to the stigma of another in cross-pollination. In a case of self-pollination, this takes place from the anther of a flower to the stigma of the same flower. Pollen itself is not the male gamete, each pollen grain contains vegetative cells and a generative cell. In flowering plants the vegetative tube cell produces the pollen tube, pollen is produced in the microsporangia in the male cone of a conifer or other gymnosperm or in the anthers of an angiosperm flower. Pollen grains come in a variety of shapes, sizes. Pollen grains of pines, firs, and spruces are winged, the smallest pollen grain, that of the forget-me-not, is around 6 µm in diameter. Wind-borne pollen grains can be as large as about 90–100 µm, in angiosperms, during flower development the anther is composed of a mass of cells that appear undifferentiated, except for a partially differentiated dermis. As the flower develops, four groups of cells form within the anther. The fertile sporogenous cells are surrounded by layers of cells that grow into the wall of the pollen sac. Some of the cells grow into nutritive cells that supply nutrition for the microspores that form by meiotic division from the sporogenous cells, in a process called microsporogenesis, four haploid microspores are produced from each diploid sporogenous cell, after meiotic division. After the formation of the four microspores, which are contained by callose walls, the exine is what is preserved in the fossil record. Two basic types of microsporogenesis are recognised, simultaneous and successive, in simultaneous microsporogenesis meiotic steps I and II are completed prior to cytokinesis, whereas in successive microsporogenesis cytokinesis follows. While there may be a continuum with intermediate forms, the type of microsporogenesis has systematic significance, the predominant form amongst the monocots is successive, but there are important exceptions. During microgametogenesis, the unicellular microspores undergo mitosis and develop into mature microgametophytes containing the gametes, in some flowering plants, germination of the pollen grain may begin even before it leaves the microsporangium, with the generative cell forming the two sperm cells. Except in the case of submerged aquatic plants, the mature pollen grain has a double wall
12.
Egg cell
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The egg cell, or ovum, is the female reproductive cell in oogamous organisms. The egg cell is not capable of active movement. When egg and sperm fuse, a cell is formed. Karl Ernst von Baer discovered the mammalian ovum in 1827, the fusion of spermatozoa with ova was observed by Oskar Hertwig in 1876. In animals, egg cells are known as ova. The term ovule is used for the young ovum of an animal, in vertebrates, ova are produced by female gonads called ovaries a number of ova are present at birth in mammals and mature via oogenesis. White et al. disproved the longstanding dogma that all of the ova are produced before birth, the team from the Vincent Center for Reproductive Biology, Massachusetts, Boston could prove that oocyte fromation takes place in ovaries of reproductive-age women. This report challenged a fundamental belief, held since the 1950s, in all mammals the ovum is fertilized inside the female body. The human ova grow from primitive germ cells that are embedded in the substance of the ovaries, each of them divides repeatedly to give secretions of the uterine glands, ultimately forming a blastocyst. The ovum is one of the largest cells in the human body, the human ovum measures approximately 0.12 mm in diameter. Ooplasm is the yolk of the ovum, a substance at its center, which contains its nucleus, named the germinal vesicle. Mammalian ova contain only an amount of the nutritive yolk. In contrast, bird eggs contain enough to supply the chick with nutriment throughout the period of incubation. In the oviparous animals the ova develop protective layers and pass through the oviduct to the outside of the body and they are fertilized by male sperm either inside the female body, or outside. After fertilization, an embryo develops, nourished by nutrients contained in the egg and it then hatches from the egg, outside the mothers body. See egg for a discussion of eggs of oviparous animals, the egg cells cytoplasm and mitochondria are the sole means the egg is able to reproduce by mitosis and eventually form a blastocyst after fertilization. Some fish, reptiles and many use this technique. Nearly all land plants have alternating diploid and haploid generations, gametes are produced by the gametophyte, which is the haploid generation
13.
Ovule
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In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts, The integument forming its outer layer, the nucellus, and female gametophyte in its center, the female gametophyte—specifically termed a megagametophyte—is also called the embryo sac in angiosperms. The megagametophyte produces an egg cell for the purpose of fertilization, after fertilization, the ovule develops into a seed. In flowering plants, the ovule is located inside the portion of the called the gynoecium. The ovary of the gynoecium produces one or more ovules and ultimately becomes the fruit wall, ovules are attached to the placenta in the ovary through a stalk-like structure known as a funiculus. Different patterns of attachment, or placentation, can be found among plant species. Axile placentation, The ovary is divided into segments, with placentas in separate locules. Ventral sutures of carpels meet at the centre of the ovary, Placentae are along fused margins of carpels. Basal placentation, The placenta is at the base of the ovary on a protrusion of the thalamus, simple or compound carpel, unilocular ovary. Free-central placentation, Derived from axile as partitions are absorbed, leaving ovules at the central axis, there is only one elongated placenta on one side of the ovary, as ovules are attached at the fusion line of the carpels margins. Parietal placentation, Placentae on inner wall within a non-sectioned ovary. Two or more carpels, unilocular ovary, in gymnosperms such as conifers, ovules are borne on the surface of an ovuliferous scale, usually within an ovulate cone. In some extinct plants, megasporangia and perhaps ovules were borne on the surface of leaves, in other extinct taxa, a cupule surrounds the ovule. The ovule appears to be a megasporangium with integuments surrounding it, ovules are initially composed of diploid maternal tissue, which includes a megasporocyte. Megaspores remain inside the ovule and divide by mitosis to produce the female gametophyte or megagametophyte. The remnants of the megasporangium tissue surround the megagametophyte, megagametophytes produce archegonia, which produce egg cells. After fertilization, the contains a diploid zygote and then, after cell division begins. In flowering plants, a sperm nucleus fuses with other nuclei in the megagametophyte forming a typically polyploid endosperm tissue
14.
Conifer
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The Pinophyta, also known as Coniferophyta or Coniferae, or commonly as conifers, are a division of vascular land plants containing a single class, Pinopsida. They are gymnosperms, cone-bearing seed plants, all extant conifers are perennial woody plants with secondary growth. The great majority are trees, though a few are shrubs, examples include cedars, Douglas firs, cypresses, firs, junipers, kauri, larches, pines, hemlocks, redwoods, spruces, and yews. As of 1998, the division Pinophyta was estimated to contain eight families,68 genera, although the total number of species is relatively small, conifers are ecologically important. They are the dominant plants over large areas of land, most notably the taiga of the Northern Hemisphere, boreal conifers have many wintertime adaptations. The narrow conical shape of northern conifers, and their downward-drooping limbs, many of them seasonally alter their biochemistry to make them more resistant to freezing. While tropical rainforests have more biodiversity and turnover, the conifer forests of the world represent the largest terrestrial carbon sink. Conifers are of economic value for softwood lumber and paper production. The earliest conifers in the record date to the late Carboniferous period, possibly arising from Cordaites. Pinophytes, Cycadophytes, and Ginkgophytes all developed at this time, an important adaptation of these gymnosperms was allowing plants to live without being so dependent on water. Other adaptations are pollen and the seed, which allows the embryo to be transported and developed elsewhere, Conifers appear to be one of the taxa that benefited from the Permian–Triassic extinction event, and were the dominant land plants of the Mesozoic. They were overtaken by the plants, which first appeared in the Cretaceous. They were the food of herbivorous dinosaurs, and their resins and poisons would have given protection against herbivores. Reproductive features of modern conifers had evolved by the end of the Mesozoic era, Conifer is a Latin word, a compound of conus and ferre, meaning the one that bears cone. A descriptive name in use for the conifers is Coniferae. Alternatively, descriptive botanical names may also be used at any rank above family and this means that if conifers are considered a division, they may be called Pinophyta or Coniferae. As a class they may be called Pinopsida or Coniferae, as an order they may be called Pinales or Coniferae or Coniferales. Conifers are the largest and economically most important component group of the gymnosperms, the division Pinophyta consists of just one class, Pinopsida, which includes both living and fossil taxa
15.
Conifer cone
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A cone is an organ on plants in the division Pinophyta that contains the reproductive structures The familiar woody cone is the female cone, which produces seeds. The male cones, which produce pollen, are usually herbaceous, the name cone derives from the fact that the shape in some species resembles a geometric cone. The individual plates of a cone are known as scales, the male cone is structurally similar across all conifers, differing only in small ways from species to species. Extending out from an axis are microsporophylls. Under each microsporophyll is one or several microsporangia, the female cone contains ovules which, when fertilized by pollen, become seeds. The female cone structure varies more markedly between the different conifer families, and is crucial for the identification of many species of conifers. The members of the family have cones that are imbricate. The scales are arranged in fibonacci number ratios. The female cone has two types of scale, the scales, derived from a modified leaf, and the seed scales, one subtended by each bract scale. On the upper-side base of each seed scale are two ovules that develop into seeds after fertilization by pollen grains. The bract scales develop first, and are conspicuous at the time of pollination, the scales open temporarily to receive gametophytes, then close during fertilization and maturation, and then re-open again at maturity to allow the seed to escape. Maturation takes 6–8 months from pollination in most Pinaceae genera, but 12 months in cedars, the cones open either by the seed scales flexing back when they dry out, or by the cones disintegrating with the seed scales falling off. The cones are conic, cylindrical or ovoid, and small to large, from 2–60 cm long. After ripening, the opening of non-serotinous pine cones is associated with their moisture content—cones are open when dry and this assures that the small, wind disseminated seeds will be dispersed during relatively dry weather, and thus, the distance traveled from the parent tree will be enhanced. A pine cone will go through cycles of opening and closing during its life span. This process occurs with older cones while attached to branches and even after the cones have fallen to the forest floor. The condition of fallen pine cones is an indication of the forest floors moisture content. Closed cones indicate damp conditions while open cones indicate the forest floor is dry, members of the Araucariaceae have the bract and seed scales fully fused, and have only one ovule on each scale
16.
Latin
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Latin is a classical language belonging to the Italic branch of the Indo-European languages. The Latin alphabet is derived from the Etruscan and Greek alphabets, Latin was originally spoken in Latium, in the Italian Peninsula. Through the power of the Roman Republic, it became the dominant language, Vulgar Latin developed into the Romance languages, such as Italian, Portuguese, Spanish, French, and Romanian. Latin, Italian and French have contributed many words to the English language, Latin and Ancient Greek roots are used in theology, biology, and medicine. By the late Roman Republic, Old Latin had been standardised into Classical Latin, Vulgar Latin was the colloquial form spoken during the same time and attested in inscriptions and the works of comic playwrights like Plautus and Terence. Late Latin is the language from the 3rd century. Later, Early Modern Latin and Modern Latin evolved, Latin was used as the language of international communication, scholarship, and science until well into the 18th century, when it began to be supplanted by vernaculars. Ecclesiastical Latin remains the language of the Holy See and the Roman Rite of the Catholic Church. Today, many students, scholars and members of the Catholic clergy speak Latin fluently and it is taught in primary, secondary and postsecondary educational institutions around the world. The language has been passed down through various forms, some inscriptions have been published in an internationally agreed, monumental, multivolume series, the Corpus Inscriptionum Latinarum. Authors and publishers vary, but the format is about the same, volumes detailing inscriptions with a critical apparatus stating the provenance, the reading and interpretation of these inscriptions is the subject matter of the field of epigraphy. The works of several hundred ancient authors who wrote in Latin have survived in whole or in part and they are in part the subject matter of the field of classics. The Cat in the Hat, and a book of fairy tales, additional resources include phrasebooks and resources for rendering everyday phrases and concepts into Latin, such as Meissners Latin Phrasebook. The Latin influence in English has been significant at all stages of its insular development. From the 16th to the 18th centuries, English writers cobbled together huge numbers of new words from Latin and Greek words, dubbed inkhorn terms, as if they had spilled from a pot of ink. Many of these words were used once by the author and then forgotten, many of the most common polysyllabic English words are of Latin origin through the medium of Old French. Romance words make respectively 59%, 20% and 14% of English, German and those figures can rise dramatically when only non-compound and non-derived words are included. Accordingly, Romance words make roughly 35% of the vocabulary of Dutch, Roman engineering had the same effect on scientific terminology as a whole
17.
DNA
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Deoxyribonucleic acid is a molecule that carries the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms and many viruses. DNA and RNA are nucleic acids, alongside proteins, lipids and complex carbohydrates, most DNA molecules consist of two biopolymer strands coiled around each other to form a double helix. The two DNA strands are termed polynucleotides since they are composed of simpler units called nucleotides. Each nucleotide is composed of one of four nitrogen-containing nucleobases—cytosine, guanine, adenine, or thymine —a sugar called deoxyribose, and a phosphate group. The nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. The nitrogenous bases of the two polynucleotide strands are bound together, according to base pairing rules, with hydrogen bonds to make double-stranded DNA. The total amount of related DNA base pairs on Earth is estimated at 5.0 x 1037, in comparison the total mass of the biosphere has been estimated to be as much as 4 trillion tons of carbon. The DNA backbone is resistant to cleavage, and both strands of the double-stranded structure store the same biological information and this information is replicated as and when the two strands separate. A large part of DNA is non-coding, meaning that these sections do not serve as patterns for protein sequences, the two strands of DNA run in opposite directions to each other and are thus antiparallel. Attached to each sugar is one of four types of nucleobases and it is the sequence of these four nucleobases along the backbone that encodes biological information. RNA strands are created using DNA strands as a template in a process called transcription, under the genetic code, these RNA strands are translated to specify the sequence of amino acids within proteins in a process called translation. Within eukaryotic cells DNA is organized into structures called chromosomes. During cell division these chromosomes are duplicated in the process of DNA replication, eukaryotic organisms store most of their DNA inside the cell nucleus and some of their DNA in organelles, such as mitochondria or chloroplasts. In contrast prokaryotes store their DNA only in the cytoplasm, within the eukaryotic chromosomes, chromatin proteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed, DNA was first isolated by Friedrich Miescher in 1869. DNA is used by researchers as a tool to explore physical laws and theories, such as the ergodic theorem. The unique material properties of DNA have made it an attractive molecule for material scientists and engineers interested in micro-, among notable advances in this field are DNA origami and DNA-based hybrid materials. DNA is a polymer made from repeating units called nucleotides
18.
Copulation
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Sexual intercourse, or coitus or copulation, is principally the insertion and thrusting of the penis, usually when erect, into the vagina for sexual pleasure, reproduction, or both. This is also known as vaginal intercourse or vaginal sex, other forms of penetrative sexual intercourse include anal sex, oral sex, fingering, and penetration by use of a dildo. These activities involve physical intimacy between two or more individuals and are used among humans solely for physical or emotional pleasure. A variety of views concern what constitutes sexual intercourse or other sexual activity and it is usually defined by sexual penetration, while non-penetrative sex acts, such as non-penetrative forms of cunnilingus or mutual masturbation, have been termed outercourse. Non-penetrative sex acts, however, may additionally be considered sexual intercourse, the term sex, often a shorthand for sexual intercourse, can mean any form of sexual activity. Religious beliefs also play a role in decisions about sexual intercourse or other sexual activity, such as decisions about virginity, or legal. Religious views on sexuality vary significantly between different religions and sects of the religion, though there are common themes, such as prohibition of adultery. For most non-human mammals, mating and copulation occur at the point of estrus, however, bonobos, dolphins and chimpanzees are known to engage in sexual intercourse regardless of whether or not the female is in estrus, and to engage in sex acts with same-sex partners. Sexual intercourse may be defined by different words, including coitus, copulation, coition and this is often termed vaginal intercourse or vaginal sex. The term vaginal sex, and less often vaginal intercourse, may refer to any vaginal sexual activity, particularly if penetrative. The World Health Organization states that non-English languages and cultures use different terms for sexual activity, various vulgar or slang words and euphemisms are also used to describe sexual intercourse or other sexual activity, such as the term fuck, shag, and the phrase sleep together. Penetration of the vagina by the penis is additionally known as intromission. Vaginal, anal and oral sex are recognized as sexual intercourse more often than other sexual behaviors, lesbians may define oral sex or fingering as sexual intercourse and subsequently an act of virginity loss, or tribadism as a primary form of sexual activity. Researchers commonly define sexual intercourse as penile–vaginal intercourse while using terms, such as anal sex or oral sex. Scholars Richard M. Lerner and Laurence Steinberg state that researchers also rarely disclose how they define sex or even whether they resolved potential discrepancies in definitions of sex. This focus can also relegate other forms of sexual activity to foreplay or contribute to them not being regarded as real sex. Studies regarding the definition of sexual intercourse sometimes conflict, a 1999 study by the Kinsey Institute examined the definition of sex based on a 1991 random sample of 599 college students from 29 U. S. The specificity of questions concerning sexual activity can additionally affect definitions of sexual intercourse or other sexual behaviors, another study by the Kinsey Institute sampled 484 people, ranging in ages 18–96
19.
Gonopore
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A gonopore, sometimes called a gonadopore, is a genital pore in many invertebrates. Hexapods, including insects have a single common gonopore, except mayflies, more specifically, in the unmodified female it is the opening of the common oviduct, and in the male, it is the opening of the ejaculatory duct. The position of the gonopore varies considerably between groups, but is generally constant within groups, allowing its position to be used as a segmental marker. In Malacostraca, it is on the sixth segment, in Symphyla it is on the fourth trunk segment, in arachnids. In insects and centipedes, the gonopores are close to the tail, while in millipedes they are on third body segment behind the head. The positions of the male and female gonopores, either on the base of the leg or on the sternum, is important in the systematics of crabs
20.
Spermatophore
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Spermatophores may additionally contain nourishment for the female, in which case it is called a nuptial gift, as in the instance of bush crickets. In the case of the toxic moth Utetheisa ornatrix, the spermatophore includes sperm, nutrients, however, in some species such as the Ediths Checkerspot butterfly, the gift provides little nutrient value. The spermatophore transferred at mating has little effect on female reproductive output, the alternative hypothesis of its usefulness is that the process of eating the spermatophore prevents the female from subsequent copulation, thereby giving the males sperm more time to fertilize. Spermatophores are the norm in arachnids and several soil arthropods, in various insects, such as bush crickets, the spermatophore is often surrounded by a proteinaceous spermatophylax. The function of the spermatophylax is to cause the female to relinquish some of her control over the process allowing full sperm transfer from the spermatophore. Some species of butterflies and moths also deposit a spermatophore into the female during copulation, examples include the speckled wood butterfly or the ornate moth, where males invest up to 10% of their body mass in creating a single spermatophore. Some vertebrates also reproduce via spermatophores, males of most salamander and newt species create spermatophores, which the females may choose to take up or not, depending on the success of the males mating display
21.
Mammalian reproduction
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Most mammals are viviparous, giving birth to live young. However, the five species of monotreme, the platypuses and the echidnas, the monotremes have a sex determination system different from that of most other mammals. In particular, the sex chromosomes of a platypus are more like those of a chicken than those of a therian mammal, the mammary glands of mammals are specialized to produce milk, a liquid used by newborns as their primary source of nutrition. The monotremes branched early from other mammals and do not have the nipples seen in most mammals, the young lick the milk from a mammary patch on the mothers belly. Viviparous mammals are in the subclass Theria, those living today are in the Marsupialia and Placentalia infraclasses. Some placentals, e. g. guinea pig, give birth to fully developed young, usually after long periods, while some others, e. g. mouse. The mammalian male reproductive system contains two divisions, the penis and the testicles, the latter of which is where sperm are produced. In humans, both of these organs are outside the cavity, but they can be primarily housed within the abdomen in other animals. For instance, a penis is covered by a penile sheath except when mating. Having the testicles outside the abdomen best facilitates temperature regulation of the sperm, the external location may also cause a reduction in the heat-induced contribution to the spontaneous mutation rate in male germinal tissue. Sperm are the smaller of the two gametes and are generally very short-lived, requiring males to produce them continuously from the time of maturity until death. The produced sperm are stored in the epididymis until ejaculation, the sperm cells are motile and they swim using tail-like flagella to propel themselves towards the ovum. The sperm follows temperature gradients and chemical gradients to locate the ovum, the mammalian female reproductive system likewise contains two main divisions, the vagina and uterus, which act as the receptacle for the sperm, and the ovaries, which produce the females ova. All of these parts are always internal, the vagina is attached to the uterus through the cervix, while the uterus is attached to the ovaries via the Fallopian tubes. At certain intervals, the release an ovum, which passes through the fallopian tube into the uterus. If, in transit, it meets with sperm, the egg selects sperm with which to merge. The fertilization usually occurs in the oviducts, but can happen in the uterus itself, the zygote then implants itself in the wall of the uterus, where it begins the processes of embryogenesis and morphogenesis. When developed enough to survive outside the womb, the cervix dilates and contractions of the uterus propel the fetus through the birth canal, which is the vagina
22.
Labia
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The labia are part of the female genitalia, they are the major externally visible portions of the vulva. In humans, there are two pairs of labia, the labia majora are larger and fattier, while the labia minora are folds of skin between the outer labia, the labia surround and protect the clitoris and the openings of the vagina and the urethra. Labium is a Latin-derived term meaning lip, labium and its derivatives are used to describe any lip-like structure, but in the English language, labium often specifically refers to parts of the vulva. The labia majora often have an appearance, and are thicker towards the anterior. The anterior junction of the labia majora is called the anterior commissure, to the posterior, the labia majora join at the posterior commissure, which is above the perineum and below the frenulum of the labia minora. The labia minora, also called inner labia or inner lips, are two soft folds of fat-free, hairless skin between the labia majora and they enclose and protect the vulvar vestibule, urethra and vagina. The upper portion of each labium minora splits to join both the clitoral glans, and the clitoral hood. The labia minora meet posterially at the frenulum of the labia minora, the fourchette is more prominent in younger women, and often recedes after sexual activity and childbirth. The outer surface of the labia majora is pigmented skin, the inner surface of the labia majora is smooth, hairless skin, which resembles a mucous membrane, and is only visible when the labia majora and labia minora are drawn apart. Both the inner and outer surfaces of the labia majora contain sebaceous glands, apocrine sweat glands, the labia majora have fewer superficial nerve endings than the rest of the vulva, but the skin is highly vascularized. The internal surface of the labia minora is a thin moist skin and they contain many sebaceous glands, and occasionally have eccrine sweat glands. The labia minora have many nerve endings, and have a core of erectile tissue. The color, size, length and shape of the labia can vary extensively from woman to woman. In some women the labia minora are almost non-existent, and in others they can be fleshy and they can range in color from a light pink to brownish black, and texturally can vary between smooth and very rugose. The biological sex of an individual is determined at conception, which is the moment a sperm fertilizes an ovum, the chromosome type contained in the sperm determines the sex of the zygote. A Y chromosome results in a male, and an X chromosome results in a female, a male zygote will later grow into an embryo and form testes, which produce androgens, usually causing male genitals to be formed. Female genitals will usually be formed in the absence of significant androgen exposure, the genitals begin to develop after approximately 4 to 6 weeks of gestation. Initially, the external genitals develop the way regardless of the sex of the embryo
23.
Indecent exposure
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Social and community attitudes to the exposing of various body parts and laws covering what is referred to as indecent exposure vary significantly in different countries. It ranges from outright prohibition to prohibition of exposure of certain parts, such as the genital area. Decency is generally judged by the standards of the local community, such standards may be based on religion, morality or tradition, or justified on the basis of necessary to public order. Non-sexual exhibitionism or public nudity is considered indecent exposure. If sexual acts are performed, with or without an element of nudity, this can be considered gross indecency, in some countries, exposure of the body in breach of community standards of modesty is also considered to be public indecency. The legal and community standards of what states of undress constitute indecent exposure vary considerably and these standards have also varied over time, making the definition of indecent exposure itself a complex topic. It is generally accepted, at least in countries, that a naked human body is not in itself indecent. That principle is reflected, for example, in depiction of the form in art of various forms. Nevertheless, as a rule, it is also commonly expected that people when they appear in a public place will be appropriately attired. Inappropriateness is viewed in context, so that, for example, what may be appropriate on a beach may be inappropriate in a street, school or workplace. Depending on the context, some degree of inappropriateness may be tolerated, and perhaps described as eccentric, what is an inappropriate state of dress in a particular context depends on the standards of decency of the community where an exposure takes place. There is generally no implication that the state of dress objected to is of a nature, and if such an allegation were to be made. The standards of decency have varied over time, during the Victorian era, for example, exposure of a womans legs and some extent the arms, was considered indecent in much of the Western world. Hair was sometimes required to be covered in formal occasions as in a form a hat or bonnet. As late as the 1930s and to some extent, the 1950s, an adult woman exposing her navel was also considered indecent in the West into the 1960s and 1970s, and even as late as the 1980s. Moral values changed drastically during the 1990s and 2000s, which in turn changed the criteria for indecent exposure, Public exposure of the navel has been accepted during the 1990s, such as in beaches, while in the 2000s, the buttocks can be exposed while wearing a thong. Today, however, it is common for women to go topless at public beaches throughout Europe and South America. The effects may be enhanced by intended or unintended publication of a photograph or film of the act, breastfeeding in public does not constitute indecent exposure under the laws of the United States, Canada, Australia, or Scotland
24.
Mammal
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Mammals are any vertebrates within the class Mammalia, a clade of endothermic amniotes distinguished from reptiles by the possession of a neocortex, hair, three middle ear bones and mammary glands. All female mammals nurse their young with milk, secreted from the mammary glands, Mammals include the largest animals on the planet, the great whales. The basic body type is a quadruped, but some mammals are adapted for life at sea, in the air, in trees. The largest group of mammals, the placentals, have a placenta, Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale. With the exception of the five species of monotreme, all modern mammals give birth to live young, most mammals, including the six most species-rich orders, belong to the placental group. The largest orders are the rodents, bats and Soricomorpha, the next three biggest orders, depending on the biological classification scheme used, are the Primates, the Cetartiodactyla, and the Carnivora. Living mammals are divided into the Yinotheria and Theriiformes There are around 5450 species of mammal, in some classifications, extant mammals are divided into two subclasses, the Prototheria, that is, the order Monotremata, and the Theria, or the infraclasses Metatheria and Eutheria. The marsupials constitute the group of the Metatheria, and include all living metatherians as well as many extinct ones. Much of the changes reflect the advances of cladistic analysis and molecular genetics, findings from molecular genetics, for example, have prompted adopting new groups, such as the Afrotheria, and abandoning traditional groups, such as the Insectivora. The mammals represent the only living Synapsida, which together with the Sauropsida form the Amniota clade, the early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period, this group diverged from the line that led to todays reptiles. Some mammals are intelligent, with some possessing large brains, self-awareness, Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals, singing, and echolocation. Mammals can organize themselves into fission-fusion societies, harems, and hierarchies, most mammals are polygynous, but some can be monogamous or polyandrous. They provided, and continue to provide, power for transport and agriculture, as well as commodities such as meat, dairy products, wool. Mammals are hunted or raced for sport, and are used as model organisms in science, Mammals have been depicted in art since Palaeolithic times, and appear in literature, film, mythology, and religion. Defaunation of mammals is primarily driven by anthropogenic factors, such as poaching and habitat destruction, Mammal classification has been through several iterations since Carl Linnaeus initially defined the class. No classification system is accepted, McKenna & Bell and Wilson & Reader provide useful recent compendiums. Though field work gradually made Simpsons classification outdated, it remains the closest thing to a classification of mammals
25.
Male
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A male organism is the physiological sex that produces sperm. Each spermatozoon can fuse with a female gamete, or ovum. A male cannot reproduce sexually without access to at least one ovum from a female, most male mammals, including male humans, have a Y chromosome, which codes for the production of larger amounts of testosterone to develop male reproductive organs. Not all species share a common sex-determination system, in most animals, including humans, sex is determined genetically, but in some species it can be determined due to social, environmental, or other factors. For example, Cymothoa exigua changes sex depending on the number of females present in the vicinity, the existence of two sexes seems to have been selected independently across different evolutionary lineages. There is an argument that this pattern was driven by the physical constraints on the mechanisms by which two gametes get together as required for sexual reproduction. Accordingly, sex is defined operationally across species by the type of gametes produced, male/female dimorphism between organisms or reproductive organs of different sexes is not limited to animals, male gametes are produced by chytrids, diatoms and land plants, among others. In land plants, female and male designate not only the female and male gamete-producing organisms and structures, as of the year 2012, the United Arab Emirates has the highest ratio of human males in the world, followed by Qatar. A common symbol used to represent the male sex is the Mars symbol, the symbol is identical to the planetary symbol of Mars. It was first used to sex by Carl Linnaeus in 1751. The symbol is called a stylized representation of the Roman god Mars shield. According to Stearn, however, all the historical evidence favours that it is derived from θρ, the sex of a particular organism may be determined by a number of factors. These may be genetic or environmental, or may change during the course of an organisms life. Although most species with male and female sexes have individuals that are male or female, hermaphroditic animals. Most mammals, including humans, are determined as such by the XY sex-determination system where males have an XY sex chromosome. During reproduction, a male can give either an X sperm or a Y sperm, a Y sperm and an X egg produce a male, while an X sperm and an X egg produce a female. The part of the Y-chromosome which is responsible for maleness is the region of the Y-chromosome. The ZW sex-determination system, where males have a ZZ sex chromosome may be found in birds and some insects and other organisms
26.
Female
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Female is the sex of an organism, or a part of an organism, that produces non-mobile ova. Most female mammals, including humans, have two X chromosomes. The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, a female individual cannot reproduce sexually without access to the gametes of a male. Some organisms can reproduce sexually and asexually. There is no single genetic mechanism behind sex differences in different species, oogamy is a form of anisogamy. There is an argument that this pattern was driven by the constraints on the mechanisms by which two gametes get together as required for sexual reproduction. Other than the difference in the type of gamete produced. The concept is not limited to animals, egg cells are produced by chytrids, diatoms, water moulds and land plants, among others. In land plants, female and male designate not only the egg- and sperm-producing organisms and structures, the word female comes from the Latin femella, the diminutive form of femina, meaning woman. It is not etymologically related to the male, but in the late 14th century the spelling was altered in English to parallel the spelling of male. A distinguishing characteristic of the class Mammalia is the presence of mammary glands, the mammary glands are modified sweat glands that produce milk, which is used to feed the young for some time after birth. Mammary glands are most obvious in humans, as the human body stores large amounts of fatty tissue near the nipples. Mammary glands are present in all mammals, although they are vestigial in the male of the species, most mammalian females have two copies of the X chromosome as opposed to the male which carries only one X and one smaller Y chromosome. To compensate for the difference in size, one of the females X chromosomes is inactivated in each cell of placental mammals while the paternally derived X is inactivated in marsupials. In birds and some reptiles, by contrast, it is the female which is heterozygous and carries a Z and a W chromosome whilst the male carries two Z chromosomes. Intersex conditions can give rise to other combinations, such as XO or XXX in mammals. However, these conditions result in sterility. A common symbol used to represent the female sex is ♀, according to Schott, the most established view is that the male and female symbols are derived from contractions in Greek script of the Greek names of these planets, namely Thouros and Phosphoros
