A eukaryote is any organism whose cells contain a nucleus and other organelles enclosed within membranes. Eukaryotes belong to the taxon Eukarya or Eukaryota, the presence of a nucleus gives eukaryotes their name, which comes from the Greek εὖ and κάρυον. Eukaryotic cells contain other membrane-bound organelles such as mitochondria and the Golgi apparatus, in addition and algae contain chloroplasts. Eukaryotic organisms may be unicellular or multicellular, only eukaryotes form multicellular organisms consisting of many kinds of tissue made up of different cell types. Eukaryotes can reproduce asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two identical cells. In meiosis, DNA replication is followed by two rounds of division to produce four daughter cells each with half the number of chromosomes as the original parent cell. These act as sex cells resulting from genetic recombination during meiosis, the domain Eukaryota appears to be monophyletic, and so makes up one of the three domains of life.
The two other domains and Archaea, are prokaryotes and have none of the above features, eukaryotes represent a tiny minority of all living things. However, due to their larger size, eukaryotes collective worldwide biomass is estimated at about equal to that of prokaryotes. Eukaryotes first developed approximately 1. 6–2.1 billion years ago, in 1905 and 1910, the Russian biologist Konstantin Mereschkowsky argued three things about the origin of nucleated cells. Firstly, plastids were reduced cyanobacteria in a symbiosis with a non-photosynthetic host, the host had earlier in evolution formed by symbiosis between an amoeba-like host and a bacteria-like cell that formed the nucleus. Thirdly, plants inherited photosynthesis from cyanobacteria, the split between the prokaryotes and eukaryotes was introduced in the 1960s. The concept of the eukaryote has been attributed to the French biologist Edouard Chatton, the terms prokaryote and eukaryote were more definitively reintroduced by the Canadian microbiologist Roger Stanier and the Dutch-American microbiologist C. B.
van Niel in 1962. In his 1938 work Titres et Travaux Scientifiques, Chatton had proposed the two terms, calling the bacteria prokaryotes and organisms with nuclei in their cells eukaryotes. However he mentioned this in one paragraph, and the idea was effectively ignored until Chattons statement was rediscovered by Stanier. In 1967, Lynn Margulis provided microbiological evidence for endosymbiosis as the origin of chloroplasts and mitochondria in cells in her paper. In the 1970s, Carl Woese explored microbial phylogenetics, studying variations in 16S ribosomal RNA and this helped to uncover the origin of the eukaryotes and the symbiogenesis of two important eukaryote organelles and chloroplasts
China, officially the Peoples Republic of China, is a unitary sovereign state in East Asia and the worlds most populous country, with a population of over 1.381 billion. The state is governed by the Communist Party of China and its capital is Beijing, the countrys major urban areas include Shanghai, Beijing, Shenzhen and Hong Kong. China is a power and a major regional power within Asia. Chinas landscape is vast and diverse, ranging from forest steppes, the Himalaya, Karakoram and Tian Shan mountain ranges separate China from much of South and Central Asia. The Yangtze and Yellow Rivers, the third and sixth longest in the world, Chinas coastline along the Pacific Ocean is 14,500 kilometers long and is bounded by the Bohai, East China and South China seas. China emerged as one of the worlds earliest civilizations in the basin of the Yellow River in the North China Plain. For millennia, Chinas political system was based on hereditary monarchies known as dynasties, in 1912, the Republic of China replaced the last dynasty and ruled the Chinese mainland until 1949, when it was defeated by the communist Peoples Liberation Army in the Chinese Civil War.
The Communist Party established the Peoples Republic of China in Beijing on 1 October 1949, both the ROC and PRC continue to claim to be the legitimate government of all China, though the latter has more recognition in the world and controls more territory. China had the largest economy in the world for much of the last two years, during which it has seen cycles of prosperity and decline. Since the introduction of reforms in 1978, China has become one of the worlds fastest-growing major economies. As of 2016, it is the worlds second-largest economy by nominal GDP, China is the worlds largest exporter and second-largest importer of goods. China is a nuclear weapons state and has the worlds largest standing army. The PRC is a member of the United Nations, as it replaced the ROC as a permanent member of the U. N. Security Council in 1971. China is a member of numerous formal and informal multilateral organizations, including the WTO, APEC, BRICS, the Shanghai Cooperation Organization, the BCIM, the English name China is first attested in Richard Edens 1555 translation of the 1516 journal of the Portuguese explorer Duarte Barbosa.
The demonym, that is, the name for the people, Portuguese China is thought to derive from Persian Chīn, and perhaps ultimately from Sanskrit Cīna. Cīna was first used in early Hindu scripture, including the Mahābhārata, there are, other suggestions for the derivation of China. The official name of the state is the Peoples Republic of China. The shorter form is China Zhōngguó, from zhōng and guó and it was applied to the area around Luoyi during the Eastern Zhou and to Chinas Central Plain before being used as an occasional synonym for the state under the Qing
South China (continent)
South China had been part of many past supercontinents, including Rodinia, Gondwana, Pangaea and Eurasia. About a billion years ago, the supercontinent, Rodinia formed, South China was part of the supercontinent. South China was bordered by Mirovia Ocean to the north, Siberia to the east, Australia to the west,750 million years ago, Rodinia rifted and South China became an isolated continent. A hundred million years later, these pieces of continent assembled back together to create the supercontinent of Pannotia. South China collided with North China and Eastern Gondwana, when Pannotia disintegrated 550 million years ago, South China became part of and remained with Eastern Gondwana for millions of years. Late in the Silurian, South China, rifted away from Gondwana and moved across the ancient, a new ocean was forming in its southern end, Paleo-Tethys Ocean. By the Late Carboniferous, while North China collided with Siberia and Kazakhstania, completely closing the Proto-Tethys, for much of the Permian Period, South China remained in the tropical latitudes.
And also, while most of the giant lycopods of the Carboniferous disappeared, giant lycopods remained in South China, Cimmeria, a microcontinent that consisted of todays Tibet, Iran and parts of Southeast Asia rifted away from Gondwana, and was heading towards Laurasia. Paleo-Tethys Ocean started to shrink, while the new Tethys Ocean expanded, in the Middle Triassic, the eastern portion of Cimmeria collided with South China, and together drew northwards, towards Laurasia. In the Late Triassic Epoch, South China collided with North China, North China and South China had been together since their collision in the Jurassic. Much of South China became a mountain range because of Indias collision with Cimmerias southern coastline
The Ediacaran biota consisted of enigmatic tubular and frond-shaped, mostly sessile organisms that lived during the Ediacaran Period. Trace fossils of organisms have been found worldwide, and represent the earliest known complex multicellular organisms. The Ediacaran biota radiated in an event called the Avalon explosion,575 million years ago, the biota largely disappeared with the rapid increase in biodiversity known as the Cambrian explosion. Most of the existing body plans of animals first appeared in the fossil record of the Cambrian rather than the Ediacaran. For macroorganisms, the Cambrian biota appears to have replaced the organisms that dominated the Ediacaran fossil record. Multiple hypotheses exist to explain the disappearance of this biota, including bias, a changing environment. The morphology and habit of some taxa suggest relationships to Porifera or Cnidaria, Kimberella may show a similarity to molluscs, and other organisms have been thought to possess bilateral symmetry, although this is controversial.
Most macroscopic fossils are morphologically distinct from life-forms, they resemble discs, one palaeontologist proposed a separate kingdom level category Vendozoa in the Linnaean hierarchy for the Ediacaran biota. The concept of Ediacaran Biota is, of course, somewhat artificial as it can not be defined geographically, stratigraphically, the first Ediacaran fossils discovered were the disc-shaped Aspidella terranovica in 1868. Their discoverer, Scottish geologist Alexander Murray, found them useful aids for correlating the age of rocks around Newfoundland, they were interpreted as gas escape structures or inorganic concretions. No similar structures elsewhere in the world were known and the one-sided debate soon fell into obscurity. It was not until the British discovery of the iconic Charnia in 1957 that the pre-Cambrian was seriously considered as containing life. This frond-shaped fossil was found in Englands Charnwood Forest, and due to the geological mapping of the British Geological Survey there was no doubt these fossils sat in Precambrian rocks.
All specimens discovered until 1967 were in coarse-grained sandstone that prevented preservation of fine details, poor communication, combined with the difficulty in correlating globally distinct formations, led to a plethora of different names for the biota. Ediacaran and Ediacarian were subsequently applied to the epoch or period of geological time, in March 2004, the International Union of Geological Sciences ended the inconsistency by formally naming the terminal period of the Neoproterozoic after the Australian locality. The term Ediacaran biota and similar has, at times, been used in a geographic, taphonomic, or biological sense. Microbial mats are areas of sediment stabilised by the presence of colonies of microbes that secrete sticky fluids or otherwise bind the sediment particles. They appear to migrate upwards when covered by a layer of sediment but this is an illusion caused by the colonys growth, individuals do not, themselves
The molluscs compose the large phylum Mollusca of invertebrate animals. Around 85,000 extant species of molluscs are recognized, molluscs are the largest marine phylum, comprising about 23% of all the named marine organisms. Numerous molluscs live in freshwater and terrestrial habitats and they are highly diverse, not just in size and in anatomical structure, but in behaviour and in habitat. The phylum is divided into 9 or 10 taxonomic classes. The gastropods are by far the most numerous molluscs in terms of classified species, the three most universal features defining modern molluscs are a mantle with a significant cavity used for breathing and excretion, the presence of a radula, and the structure of the nervous system. Other than these things, molluscs express great morphological diversity, so many textbooks base their descriptions on an ancestral mollusc. This has a single, limpet-like shell on top, which is made of proteins and chitin reinforced with calcium carbonate, the underside of the animal consists of a single muscular foot.
Although molluscs are coelomates, the coelom tends to be small, the main body cavity is a hemocoel through which blood circulates, their circulatory systems are mainly open. The generalized mollusc has two paired nerve cords, or three in bivalves, the brain, in species that have one, encircles the esophagus. Most molluscs have eyes, and all have sensors to detect chemicals, the simplest type of molluscan reproductive system relies on external fertilization, but more complex variations occur. All produce eggs, from which may emerge trochophore larvae, more complex veliger larvae, good evidence exists for the appearance of gastropods and bivalves in the Cambrian period 541 to 485.4 million years ago. Molluscs have, for centuries, been the source of important luxury goods, notably pearls, mother of pearl, Tyrian purple dye and their shells have been used as money in some preindustrial societies. Mollusc species can represent hazards or pests for human activities, the bite of the blue-ringed octopus is often fatal, and that of Octopus apollyon causes inflammation that can last for over a month.
Stings from a few species of large tropical cone shells can kill, schistosomiasis is transmitted to humans via water snail hosts, and affects about 200 million people. Snails and slugs can be serious pests, and accidental or deliberate introduction of some snail species into new environments has seriously damaged some ecosystems. The words mollusc and mollusk are both derived from the French mollusque, which originated from the Latin molluscus, from mollis, molluscus was itself an adaptation of Aristotles τα μαλακά, the soft things, which he applied to cuttlefish. The scientific study of molluscs is accordingly called malacology, as it is now known these groups have no relation to molluscs, and very little to one another, the name Molluscoida has been abandoned. The most universal features of the structure of molluscs are a mantle with a significant cavity used for breathing and excretion
Lasting for about the next 20–25 million years, it resulted in the divergence of most modern metazoan phyla. Additionally, the event was accompanied by major diversification of other organisms, prior to the Cambrian explosion, most organisms were simple, composed of individual cells occasionally organized into colonies. Over the following 70 to 80 million years, the rate of diversification accelerated by an order of magnitude, almost all present animal phyla appeared during this period. There is strong evidence for species of Cnidaria and Porifera existing in the Ediacaran, bryozoans dont appear in the fossil record until after the Cambrium, in the Lower Ordovician. The Cambrian explosion has generated extensive scientific debate, interpretation is difficult due to a limited supply of evidence, based mainly on an incomplete fossil record and chemical signatures remaining in Cambrian rocks. The first discovered Cambrian fossils were trilobites, described by Edward Lhuyd, nineteenth-century geologists such as Adam Sedgwick and Roderick Murchison used the fossils for dating rock strata, specifically for establishing the Cambrian and Silurian periods.
He reasoned that earlier seas had swarmed with living creatures, earlier fossil evidence has since been found. Fossils of more complex cells, from which all animals, plants. Rocks dating from 580 to 543 million years ago contain fossils of the Ediacara biota, organisms so large that they are likely multicelled, the most common organism, was clearly an arthropod, but not a member of any known arthropod class. Stephen Jay Goulds popular 1989 account of work, Wonderful Life, brought the matter into the public eye. While differing significantly in details, both Whittington and Gould proposed that all animal phyla had appeared almost simultaneously in a rather short span of geological period. Other analyses, some recent and some dating back to the 1970s. Radiometric dates for much of the Cambrian, obtained by analysis of elements contained within rocks, have only recently become available. Therefore, dates or descriptions of sequences of events should be regarded with some caution until better data become available, fossils of organisms bodies are usually the most informative type of evidence.
Fossilization is an event, and most fossils are destroyed by erosion or metamorphism before they can be observed. Hence, the record is very incomplete, increasingly so as earlier times are considered. Despite this, they are adequate to illustrate the broader patterns of lifes history. Also, biases exist in the record, different environments are more favourable to the preservation of different types of organism or parts of organisms
A primate is a mammal of the order Primates. In taxonomy, primates include two distinct lineages and haplorhines, Primates arose from ancestors that lived in the trees of tropical forests, many primate characteristics represent adaptations to life in this challenging three-dimensional environment. Most primate species remain at least partly arboreal, with the exception of humans, who inhabit every continent except for Antarctica, most primates live in tropical or subtropical regions of the Americas and Asia. Based on fossil evidence, the earliest known true primates, represented by the genus Teilhardina, an early close primate relative known from abundant remains is the Late Paleocene Plesiadapis, c. Molecular clock studies suggest that the branch may be even older. The order Primates was traditionally divided into two groupings and anthropoids. Prosimians have characteristics more like those of the earliest primates, and include the lemurs of Madagascar, simians include monkeys and hominins.
Simians are divided into two groups, catarrhine monkeys and apes of Africa and Southeast Asia and platyrrhine or New World monkeys of South, catarrhines consist of Old World monkeys and great apes, New World monkeys include the capuchin and squirrel monkeys. Humans are the only extant catarrhines to have spread successfully outside of Africa, South Asia, New primate species are still being discovered. More than 25 species were described in the decade of the 2000s. Considered generalist mammals, primates exhibit a range of characteristics. Some primates are primarily terrestrial rather than arboreal, but all species possess adaptations for climbing trees, locomotion techniques used include leaping from tree to tree, walking on two or four limbs, knuckle-walking, and swinging between branches of trees. Primates are characterized by large brains relative to other mammals, as well as a reliance on stereoscopic vision at the expense of smell. These features are developed in monkeys and apes and noticeably less so in lorises.
Three-color vision has developed in some primates, most have opposable thumbs and some have prehensile tails. Many species are dimorphic, differences include body mass, canine tooth size. Primates have slower rates of development than other similarly sized mammals and reach maturity later, depending on the species, adults may live in solitude, in mated pairs, or in groups of up to hundreds of members. The relationships among the different groups of primates were not clearly understood until relatively recently, for example, ape has been used either as an alternative for monkey or for any tailless, relatively human-like primate
The simians are the monkeys, cladistically including the apes, the New World monkeys or platyrrhines, and the catarrhine clade consisting of the Old World monkeys and apes. The simian line and the line diverged about 60 million years ago. Forty million years ago, simians from Africa colonized South America, the remaining simians split 25 million years ago into apes and Old World monkeys. Under modern classification, the tarsiers and simians are grouped under the suborder Haplorhini while the strepsirrhines are placed in suborder Strepsirrhini, in anthropoidea, evidences indicate that the Old and the New World primates went through parallel evolution. Primatology, paleoanthropology, and other related fields are split on their usage of the synonymous infraorder names and Anthropoidea. According to Robert Hoffstetter, the term Simiiformes has priority over Anthropoidea because of the taxonomic term Simii by van der Hoeven, from which it is constructed, dates to 1833. In contrast, Anthropoidea by Mivart dates to 1864, while Simiiformes by Haeckel dates to 1866, Hoffstetter argued that Simiiformes is constructed like a proper infraorder name, whereas Anthropoidea ends in -oidea, which is reserved for superfamilies.
He noted that Anthropoidea is too easily confused with anthropoïdes, the simians are split into three distinct groups. The New World monkeys in parvorder Platyrrhini split from the rest of the line about 40 mya. This group split about 25 mya between the Old World monkeys and the apes
In paleogeography, Gondwanaland, is the name given to an ancient supercontinent. It is believed to have sutured about 600 to 530 million years ago, Gondwana formed prior to Pangaea, and became part of it. Around 335 to 250 million years ago Gondwana and Laurasia joined together to form the supercontinent Pangaea, Gondwana separated from Laurasia in the breakup of Pangaea, drifting farther south after the split. Gondwana itself also broke apart, the continent of Gondwana was named by Austrian scientist Eduard Suess, after the Gondwana region of central northern India which is derived from Sanskrit for forest of the Gonds. The name had previously used in a geological context, first by H. B. From which the Gondwana sedimentary sequences are described, for example, the plant family Proteaceae, known only from southern South America, South Africa and New Zealand, is considered to have a Gondwanan distribution. This pattern is considered to indicate an archaic, or relict. The assembly of Gondwana was a protracted process, several orogenies led to its final amalgamation 550 to 500 million years ago at the end of the Ediacaran, and into the Cambrian.
These include the Brasiliano Orogeny, the East African Orogeny, the Malagasy Orogeny, the final stages of Gondwanan assembly overlapped with the opening of the Iapetus Ocean between Laurentia and western Gondwana. During this interval, the Cambrian explosion occurred and this is the Famatinian block and it formerly continued the line of the Appalachians southwards. One of the sites of Gondwanan amalgamation was the East African Orogeny. The East African Orogeny at about 650–630 Mya affected a part of Arabia, north-eastern Africa, East Africa. Collins and Windley propose that in this orogeny, Azania collided with the Congo–Tanzania–Bangweulu Block, the Malagasy orogeny at about 550–515 Mya affected Madagascar, eastern East Africa and southern India. In it, Neoproterozoic India collided with the already combined Azania and Congo–Tanzania–Bangweulu Block, at the same time, in the Kunga Orogeny Neoproterozoic India collided with the Australia/Mawson continent. Other large continental masses, including the core cratons of North America, when Pangaea broke up, two large masses and Laurasia, were formed.
During the late Paleozoic, Gondwana extended from a point at or near the South Pole to near the Equator, across much of Gondwana, the climate was mild. During the Mesozoic, the world was on average warmer than it is today. Gondwana was host to a variety of flora and fauna for many millions of years
Geologically, the Indian subcontinent is related to the land mass that rifted from Gondwana and merged with the Eurasian plate nearly 55 million years ago. Geographically, it is the region in south-central Asia delineated by the Himalayas in the north, the Hindu Kush in the west. Politically, the Indian subcontinent usually includes Bangladesh, India, Nepal, sometimes, the term South Asia is used interchangeably with Indian subcontinent. There is no consensus about which countries should be included in each and it is first attested in 1845 to refer to the North and South Americas, before they were regarded as separate continents. Its use to refer to the Indian subcontinent is seen from the twentieth century. It was especially convenient for referring to the region comprising both the British India and the states under British Paramountcy. The term Indian subcontinent has a geological significance and it was, like the various continents, a part of the supercontinent of Gondwana. A series of tectonic splits caused formation of basins, each drifting in various directions.
The geological region called the Greater India once included the Madagascar, Antartica, as a geological term, Indian subcontinent has meant that region formed from the collision of the Indian basin with Eurasia nearly 55 million years ago, towards the end of Paleocene. The Indian subcontinent has been a particularly common in the British Empire. The region, state Mittal and Thursby, has labelled as India, Greater India. The BBC and some sources refer to the region as the Asian Subcontinent. Some academics refer to it as South Asian Subcontinent, the terms Indian subcontinent and South Asia are sometimes used interchangeably. There is no accepted definition on which countries are a part of South Asia or Indian subcontinent. In dictionary entries, the term subcontinent signifies a large, distinguishable subdivision of a continent, the region experienced high volcanic activity and plate subdivisions, creating Madagascar, Antartica and the Indian subcontinent basin. The Indian subcontinent drifted northeastwards, colliding with the Eurasian plate nearly 55 million years ago and this geological region largely includes Bangladesh, India, Nepal and Sri Lanka.
The zone where the Eurasian and Indian subcontinent plates meet remains one of the active areas. The English term mainly continues to refer to the Indian subcontinent, physiographically, it is a peninsular region in south-central Asia delineated by the Himalayas in the north, the Hindu Kush in the west, and the Arakanese in the east
Dinosaurs are a diverse group of reptiles of the clade Dinosauria that first appeared during the Triassic. Although the exact origin and timing of the evolution of dinosaurs is the subject of active research and they became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201 million years ago. Their dominance continued through the Jurassic and Cretaceous periods and ended when the Cretaceous–Paleogene extinction event led to the extinction of most dinosaur groups 66 million years ago, until the late 20th century, all groups of dinosaurs were believed to be extinct. As such, birds were the dinosaur lineage to survive the mass extinction event. This article deals primarily with non-avian dinosaurs, Dinosaurs are a varied group of animals from taxonomic and ecological standpoints. Birds, at over 10,000 living species, are the most diverse group of vertebrates besides perciform fish, using fossil evidence, paleontologists have identified over 500 distinct genera and more than 1,000 different species of non-avian dinosaurs.
Dinosaurs are represented on every continent by both extant species and fossil remains, while dinosaurs were ancestrally bipedal, many extinct groups included quadrupedal species, and some were able to shift between these stances. Elaborate display structures such as horns or crests are common to all dinosaur groups, evidence suggests that egg laying and nest building are additional traits shared by all dinosaurs.7 meters and heights of 18 meters and were the largest land animals of all time. Still, the idea that dinosaurs were uniformly gigantic is a misconception based in part on preservation bias, as large. Many dinosaurs were small, for example, was only about 50 cm long. Through the first half of the 20th century, before birds were recognized to be dinosaurs, most of the community believed dinosaurs to have been sluggish. Most research conducted since the 1970s, has indicated that all dinosaurs were active animals with elevated metabolisms and numerous adaptations for social interaction.
The large sizes of some groups, as well as their seemingly monstrous and fantastic nature, have ensured dinosaurs regular appearance in best-selling books and films. Persistent public enthusiasm for the animals has resulted in significant funding for dinosaur science, the term is derived from the Greek words δεινός and σαῦρος. Though the taxonomic name has often interpreted as a reference to dinosaurs teeth, claws. Instead, like many forms of reptile sub-groups, did not exhibit characteristics which were traditionally regarded as reptilian. Under phylogenetic nomenclature, dinosaurs are usually defined as the group consisting of Triceratops, their most recent common ancestor, Birds are now recognized as being the sole surviving lineage of theropod dinosaurs. In traditional taxonomy, birds were considered a class that had evolved from dinosaurs
The flowering plants, 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, 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 and nectar, which may be secreted in some part of the flower