Vascular plants known as tracheophytes, form a large group of plants that are defined as those land plants that have lignified tissues for conducting water and minerals throughout the plant. They have a specialized non-lignified tissue to conduct products of photosynthesis. Vascular plants include the clubmosses, ferns and angiosperms. Scientific names for the group include Tracheophyta and Equisetopsida sensu lato; the term higher plants should be avoided as a synonym for vascular plants as it is a remnant of the abandoned concept of the great chain of being. Vascular plants are defined by three primary characteristics: Vascular plants have vascular tissues which distribute resources through the plant; this feature allows vascular plants to evolve to a larger size than non-vascular plants, which lack these specialized conducting tissues and are thereby restricted to small sizes. In vascular plants, the principal generation phase is the sporophyte, which produce spores and is diploid. By contrast, the principal generation phase in non-vascular plants is the gametophyte, which produces gametes and is haploid.
They have true roots and stems if one or more of these traits are secondarily lost in some groups. The formal definition of the division Tracheophyta encompasses both these characteristics in the Latin phrase "facies diploida xylem et phloem instructa". One possible mechanism for the presumed switch from emphasis on the haploid generation to emphasis on the diploid generation is the greater efficiency in spore dispersal with more complex diploid structures. In other words, elaboration of the spore stalk enabled the production of more spores, enabled the development of the ability to release them higher and to broadcast them farther; such developments may include more photosynthetic area for the spore-bearing structure, the ability to grow independent roots, woody structure for support, more branching. A proposed phylogeny of the vascular plants after Kenrick and Crane is as follows, with modification to the gymnosperms from Christenhusz et al. Pteridophyta from Smith et al. and lycophytes and ferns by Christenhusz et al.
This phylogeny is supported by several molecular studies. Other researchers state that taking fossils into account leads to different conclusions, for example that the ferns are not monophyletic. Water and nutrients in the form of inorganic solutes are drawn up from the soil by the roots and transported throughout the plant by the xylem. Organic compounds such as sucrose produced by photosynthesis in leaves are distributed by the phloem sieve tube elements; the xylem consists of vessels in flowering plants and tracheids in other vascular plants, which are dead hard-walled hollow cells arranged to form files of tubes that function in water transport. A tracheid cell wall contains the polymer lignin; the phloem however consists of living cells called sieve-tube members. Between the sieve-tube members are sieve plates, which have pores to allow molecules to pass through. Sieve-tube members lack such organs as nuclei or ribosomes, but cells next to them, the companion cells, function to keep the sieve-tube members alive.
The most abundant compound in all plants, as in all cellular organisms, is water which serves an important structural role and a vital role in plant metabolism. Transpiration is the main process of water movement within plant tissues. Water is transpired from the plant through its stomata to the atmosphere and replaced by soil water taken up by the roots; the movement of water out of the leaf stomata creates a transpiration pull or tension in the water column in the xylem vessels or tracheids. The pull is the result of water surface tension within the cell walls of the mesophyll cells, from the surfaces of which evaporation takes place when the stomata are open. Hydrogen bonds exist between water molecules; the draw of water upwards may be passive and can be assisted by the movement of water into the roots via osmosis. Transpiration requires little energy to be used by the plant. Transpiration assists the plant in absorbing nutrients from the soil as soluble salts. Living root cells passively absorb water in the absence of transpiration pull via osmosis creating root pressure.
It is possible for there to be no evapotranspiration and therefore no pull of water towards the shoots and leaves. This is due to high temperatures, high humidity, darkness or drought. Xylem and phloem tissues are involved in the conduction processes within plants. Sugars are conducted throughout the plant in the phloem and other nutrients through the xylem. Conduction occurs from a source to a sink for each separate nutrient. Sugars are produced in the leaves by photosynthesis and transported to the growing shoots and roots for use in growth, cellular respiration or storage. Minerals are transported to the shoots to allow cell division and growth. Fern allies Non-vascular plant “Higher plants” or “vascular plants”
Insects or Insecta are hexapod invertebrates and the largest group within the arthropod phylum. Definitions and circumscriptions vary; as used here, the term Insecta is synonymous with Ectognatha. Insects have a chitinous exoskeleton, a three-part body, three pairs of jointed legs, compound eyes and one pair of antennae. Insects are the most diverse group of animals; the total number of extant species is estimated at between ten million. Insects may be found in nearly all environments, although only a small number of species reside in the oceans, which are dominated by another arthropod group, crustaceans. Nearly all insects hatch from eggs. Insect growth is constrained by the inelastic exoskeleton and development involves a series of molts; the immature stages differ from the adults in structure and habitat, can include a passive pupal stage in those groups that undergo four-stage metamorphosis. Insects that undergo three-stage metamorphosis lack a pupal stage and adults develop through a series of nymphal stages.
The higher level relationship of the insects is unclear. Fossilized insects of enormous size have been found from the Paleozoic Era, including giant dragonflies with wingspans of 55 to 70 cm; the most diverse insect groups appear to have coevolved with flowering plants. Adult insects move about by walking, flying, or sometimes swimming; as it allows for rapid yet stable movement, many insects adopt a tripedal gait in which they walk with their legs touching the ground in alternating triangles, composed of the front & rear on one side with the middle on the other side. Insects are the only invertebrates to have evolved flight, all flying insects derive from one common ancestor. Many insects spend at least part of their lives under water, with larval adaptations that include gills, some adult insects are aquatic and have adaptations for swimming; some species, such as water striders, are capable of walking on the surface of water. Insects are solitary, but some, such as certain bees and termites, are social and live in large, well-organized colonies.
Some insects, such as earwigs, show maternal care, guarding their eggs and young. Insects can communicate with each other in a variety of ways. Male moths can sense the pheromones of female moths over great distances. Other species communicate with sounds: crickets stridulate, or rub their wings together, to attract a mate and repel other males. Lampyrid beetles communicate with light. Humans regard certain insects as pests, attempt to control them using insecticides, a host of other techniques; some insects damage crops by feeding on sap, fruits, or wood. Some species are parasitic, may vector diseases; some insects perform complex ecological roles. Insect pollinators are essential to the life cycle of many flowering plant species on which most organisms, including humans, are at least dependent. Many insects are considered ecologically beneficial as predators and a few provide direct economic benefit. Silkworms produce silk and honey bees produce honey and both have been domesticated by humans.
Insects are consumed as food in 80% of the world's nations, by people in 3000 ethnic groups. Human activities have effects on insect biodiversity; the word "insect" comes from the Latin word insectum, meaning "with a notched or divided body", or "cut into", from the neuter singular perfect passive participle of insectare, "to cut into, to cut up", from in- "into" and secare "to cut". A calque of Greek ἔντομον, "cut into sections", Pliny the Elder introduced the Latin designation as a loan-translation of the Greek word ἔντομος or "insect", Aristotle's term for this class of life in reference to their "notched" bodies. "Insect" first appears documented in English in 1601 in Holland's translation of Pliny. Translations of Aristotle's term form the usual word for "insect" in Welsh, Serbo-Croatian, etc; the precise definition of the taxon Insecta and the equivalent English name "insect" varies. In the broadest circumscription, Insecta sensu lato consists of all hexapods. Traditionally, insects defined in this way were divided into "Apterygota" —the wingless insects—and Pterygota—the winged insects.
However, modern phylogenetic studies have shown that "Apterygota" is not monophyletic, so does not form a good taxon. A narrower circumscription restricts insects to those hexapods with external mouthparts, comprises only the last three groups in the table. In this sense, Insecta sensu stricto is equivalent to Ectognatha. In the narrowest circumscription, insects are restricted to hexapods that are either winged or descended from winged ancestors. Insecta sensu strictissimo is equivalent to Pterygota. For the purposes of this article, the middle definition is used; the evolutionary relationship of insects to other animal groups remains unclear. Although traditionally grouped with millipedes and centiped
Cerci are paired appendages on the rear-most segments of many arthropods, including insects and symphylans. Many forms of cerci serve as sensory organs, but some serve as pinching weapons or as organs of copulation. In many insects, they may be functionless vestigial structures. In basal arthropods, such as silverfish, the cerci originate from the eleventh abdominal segment; as segment eleven is reduced or absent in the majority of arthropods, in such cases, the cerci emerge from the tenth abdominal segment. It is not clear. In the Symphyla they are associated with spinnerets. Most cerci are segmented and jointed, or filiform, but some take different forms; some Diplura, in particular Japyx species, have large, stout forcipate cerci that they use in capturing their prey. The Dermaptera, or earwigs, are well known for the forcipate cerci that most of them bear, though species in the suborders Arixeniina and Hemimerina do not, it is not clear how many of the Dermaptera use their cerci for anything but defense, but some feed on prey caught with the cerci, much as the Japygidae do.
Crickets have long cerci while other insects have cerci that are too small to be noticeable. However, it is not always obvious; some insects such as mayflies and bristletails have an accompanying third central tail filament which extends from the tip of the abdomen. This is not regarded as a cercus. Aphids have tube-like cornicles or siphunculi that are sometimes mistaken for cerci but are not morphologically related to cerci. Like many insect body parts, including mandibles and stylets, cerci are thought to have evolved from what were legs on the primal insect form. University of Sydney Biology Dept Media related to Cerci at Wikimedia Commons
The Devonian is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian, 419.2 million years ago, to the beginning of the Carboniferous, 358.9 Mya. It is named after Devon, where rocks from this period were first studied; the first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods became well-established. Fish reached substantial diversity during this time, leading the Devonian to be dubbed the "Age of Fishes." The first ray-finned and lobe-finned bony fish appeared, while the placoderms began dominating every known aquatic environment. The ancestors of all four-limbed vertebrates began adapting to walking on land, as their strong pectoral and pelvic fins evolved into legs.
In the oceans, primitive sharks became more numerous than in the Late Ordovician. The first ammonites, species of molluscs, appeared. Trilobites, the mollusc-like brachiopods and the great coral reefs, were still common; the Late Devonian extinction which started about 375 million years ago affected marine life, killing off all placodermi, all trilobites, save for a few species of the order Proetida. The palaeogeography was dominated by the supercontinent of Gondwana to the south, the continent of Siberia to the north, the early formation of the small continent of Euramerica in between; the period is named after Devon, a county in southwestern England, where a controversial argument in the 1830s over the age and structure of the rocks found distributed throughout the county was resolved by the definition of the Devonian period in the geological timescale. The Great Devonian Controversy was a long period of vigorous argument and counter-argument between the main protagonists of Roderick Murchison with Adam Sedgwick against Henry De la Beche supported by George Bellas Greenough.
Murchison and Sedgwick named the period they proposed as the Devonian System. While the rock beds that define the start and end of the Devonian period are well identified, the exact dates are uncertain. According to the International Commission on Stratigraphy, the Devonian extends from the end of the Silurian 419.2 Mya, to the beginning of the Carboniferous 358.9 Mya. In nineteenth-century texts the Devonian has been called the "Old Red Age", after the red and brown terrestrial deposits known in the United Kingdom as the Old Red Sandstone in which early fossil discoveries were found. Another common term is "Age of the Fishes", referring to the evolution of several major groups of fish that took place during the period. Older literature on the Anglo-Welsh basin divides it into the Downtonian, Dittonian and Farlovian stages, the latter three of which are placed in the Devonian; the Devonian has erroneously been characterised as a "greenhouse age", due to sampling bias: most of the early Devonian-age discoveries came from the strata of western Europe and eastern North America, which at the time straddled the Equator as part of the supercontinent of Euramerica where fossil signatures of widespread reefs indicate tropical climates that were warm and moderately humid but in fact the climate in the Devonian differed during its epochs and between geographic regions.
For example, during the Early Devonian, arid conditions were prevalent through much of the world including Siberia, North America, China, but Africa and South America had a warm temperate climate. In the Late Devonian, by contrast, arid conditions were less prevalent across the world and temperate climates were more common; the Devonian Period is formally broken into Early and Late subdivisions. The rocks corresponding to those epochs are referred to as belonging to the Lower and Upper parts of the Devonian System. Early DevonianThe Early Devonian lasted from 419.2 ± 2.8 to 393.3 ± 2.5 and began with the Lochkovian stage, which lasted until the Pragian. It spanned from 410.8 ± 2.8 to 407.6 ± 2.5, was followed by the Emsian, which lasted until the Middle Devonian began, 393.3± 2.7 million years ago. During this time, the first ammonoids appeared. Ammonoids during this time period differed little from their nautiloid counterparts; these ammonoids belong to the order Agoniatitida, which in epochs evolved to new ammonoid orders, for example Goniatitida and Clymeniida.
This class of cephalopod molluscs would dominate the marine fauna until the beginning of the Mesozoic era. Middle DevonianThe Middle Devonian comprised two subdivisions: first the Eifelian, which gave way to the Givetian 387.7± 2.7 million years ago. During this time the jawless agnathan fishes began to decline in diversity in freshwater and marine environments due to drastic environmental changes and due to the increasing competition and diversity of jawed fishes; the shallow, oxygen-depleted waters of Devonian inland lakes, surrounded by primitive plants, provided the environment necessary for certain early fish to develop such essential characteristics as well developed lungs, the ability to crawl out of the water and onto the land for short periods of time. Late DevonianFinally, the Late Devonian started with the Frasnian, 382.7 ± 2.8 to 372.2 ± 2.5, during which the first forests took shape on land. The first tetrapods appeared in the fossil record in the ensuing Famennian subdivisi
Anostraca is one of the four orders of crustaceans in the class Branchiopoda. They are 6–25 mm long. Most species have 20 body segments, bearing 11 pairs of leaf-like phyllopodia, the body lacks a carapace, they live in vernal pools and hypersaline lakes across the world, including pools in deserts, in ice-covered mountain lakes and in Antarctica. They swim "upside-down" and feed by filtering organic particles from the water or by scraping algae from surfaces, they are an important food for many birds and fish, are cultured and harvested for use as fish food. There are 300 species spread across 8 families; the body of a fairy shrimp is divided into segments. The whole animal is 6–25 millimetres long, but one species, Branchinecta gigas does not reach sexual maturity until it reaches 50 mm long, can grow to 170 mm long; the exoskeleton is thin and flexible, lacks any sign of a carapace. The body can be divided into three distinct parts – head and abdomen; the head is morphologically distinct from the thorax.
It bears two compound eyes on prominent stalks, two pairs of antennae. The first pair of antennae are small unsegmented, uniramous; the second pair are long and cylindrical in females, but in males they are enlarged and specialised for holding the female during mating. In some groups, males have an additional frontal appendage; the thorax of most anostracans has 13 segments. All but the last two are similar, with a pair of biramous phyllopods; the last two segments are fused together, their appendages are specialised for reproduction. Most anostracans have separate sexes; the abdomen comprises 6 segments without appendages, a telson, which bears two flattened caudal rami or "cercopods". The head contains the small lobate stomach that they empty into; this is connected to a long intestine, which terminates in a short rectum, with the anus located on the telson. The haemocoel of anostracans is pumped by a long, tubular heart, which runs through most of the animal's length. A series of slits allow haemocoel into the heart, pumped out of the anterior opening by peristalsis.
The nervous system consists of two nerve cords which run the length of the body, with two ganglia and two transverse commissures in most of the body segments. Gas exchange is thought to take place through the entire body surface, but that of the phyllopodia and their associated gills, which may be responsible for osmotic regulation. Two coiled glands at the bases of the maxillae are used to excrete nitrogenous waste in the form of urea. Most of the animal's nitrogenous waste is, however, in the form of ammonia, which diffuses into the environment through the phyllopodia and gills. Anostracans inhabit inland waters ranging from hypersaline lakes to lakes that are devoid of dissolved substances; the large size of fairy shrimp, together with their slow means of locomotion, makes them an easy target for predatory fish and waterfowl. This has led to their distribution being restricted to environments with fewer predators, such as vernal pools, salt lakes and lakes at high altitudes or latitudes; the southernmost recorded fairy shrimp is Branchinecta gaini from the Antarctic Peninsula, while the altitude record is held by B. brushi, which lives at 5,930 metres in the Chilean Andes.
Other genera, such as Streptocephalus, occur in deserts throughout the world. Anostracans swim gracefully by movements of their phyllopodia in a metachronal rhythm; when swimming, the animal's ventral side is uppermost. They filter food indiscriminately from the water as they swim, but scrape algae and other organic materials from solid surfaces, for which they turn to have their ventral side against the food surface. Another important aspect of the fairy shrimp’s life cycle is their universal ability to enter diapause, a state of biological dormancy where growth and metabolism are arrested, as an egg; this trait assists in overcoming adverse environmental conditions. Once dormant, these cysts can withstand conditions as harsh and diverse as droughts, hypersalinity, complete desiccation, exposure to UV radiation and the vacuum of space, it is the only way for the fairy shrimps to colonize new habitats—facilitated by a variety of conditions including wind, currents—as the soft-bodied adults are unable to leave the freshwater system.
Once in diapause, these cysts can remain viable for centuries, the mixing of system sediment results in the hatching of different aged cysts in each generation. This inbreeding slows the rate of selection by resisting gene flow and minimizing phenotypic variation, in turn promoting the stability of the existing, successful phenotype. Anostracans are an important food source for many birds and fish. For example, they provide much of the food for female pintails and mallards in the Prairie Pothole Region of the Great Plains in North America in years when temporary wetlands are abundant. Artemia forms an important part of the diet of flamingos wherever it can be found. Brine shrimp are used as other organisms in aquaria and aquaculture, their drought-resistant eggs are stored and transported dry. They hatch when submerged in salt water; this is a multimillion-dollar