1.
Centaurea maculosa
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Centaurea maculosa is a species of flowering plant in the family Asteraceae. Centaurea maculosa, the spotted knapweed, is a species of Centaurea native to eastern Europe and this short-lived perennial usually has a stout taproot, pubescent stems with wooly or cobwebby hairs when young. The erect or ascending plant stems grow 20 to 150 cm tall and it grows on stream banks, pond shorelines, sand prairies, old fields and pastures, roadsides, and along railroads, and many open, disturbed areas. Apparently, is should be treated with two varieties as (Centaurea stoebe var. stoebe and var. micranthos Hayek and it has been introduced to North America, where it is considered an invasive plant species in much of the western United States and Canada. In 2000, C. maculosa occupied more than 7 million acres in the US, Knapweed is a pioneer species found in recently disturbed sites or openings. Once it has been established at a site, it continues to spread into the surrounding habitat. It is also suspected to be allelopathic, releasing a toxin from its roots that stunts the growth of plants of other species. Its seed is an achene about a quarter of an inch long, the leaves are a pale grayish-green. They are covered in short hairs. First year plants produce a basal rosette, alternate, up to 6 inches long and it produces a stem in its second year of growth. Stem leaves are progressively less lobed, getting smaller toward the top, the stem is erect or ascending, slender, hairy and branching, and can grow up to three feet tall. Because cattle prefer the native bunchgrass over knapweed, overgrazing occurs, increasing the density, human disturbance is also a major cause of infestations. But in general, biocontrol has not been shown to be effective against C. maculosa, in some instances, root-herbivory on C. maculosa stimulates additional release of catechin, the main allelopathic chemical which the species emits. In addition, moderate levels of herbivory by biocontrol agents can cause compensatory growth, prescribed grazing may be an effective means of controlling infestations. All growth forms are nutritious to sheep, high-density infestations can be controlled by fencing in the control area with sheep until the desired level of removal is achieved. The roots of C. maculosa exude -catechin and this acts as an herbicide to inhibit competition by a wide range of other plant species. This phytotoxic compound inhibits seed germination and growth in making more available in certain soils. It leads to death of competing plants by acidification of the cytoplasm
2.
Species
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In biology, a species is the basic unit of biological classification and a taxonomic rank. A species is defined as the largest group of organisms in which two individuals can produce fertile offspring, typically by sexual reproduction. While this definition is often adequate, looked at more closely it is problematic, for example, with hybridisation, in a species complex of hundreds of similar microspecies, or in a ring species, the boundaries between closely related species become unclear. Other ways of defining species include similarity of DNA, morphology, all species are given a two-part name, a binomial. The first part of a binomial is the genus to which the species belongs, the second part is called the specific name or the specific epithet. For example, Boa constrictor is one of four species of the Boa genus, Species were seen from the time of Aristotle until the 18th century as fixed kinds that could be arranged in a hierarchy, the great chain of being. In the 19th century, biologists grasped that species could evolve given sufficient time, Charles Darwins 1859 book The Origin of Species explained how species could arise by natural selection. Genes can sometimes be exchanged between species by horizontal transfer, and species may become extinct for a variety of reasons. In his biology, Aristotle used the term γένος to mean a kind, such as a bird or fish, a kind was distinguished by its attributes, for instance, a bird has feathers, a beak, wings, a hard-shelled egg, and warm blood. A form was distinguished by being shared by all its members, Aristotle believed all kinds and forms to be distinct and unchanging. His approach remained influential until the Renaissance, when observers in the Early Modern period began to develop systems of organization for living things, they placed each kind of animal or plant into a context. Many of these early delineation schemes would now be considered whimsical, animals likewise that differ specifically preserve their distinct species permanently, one species never springs from the seed of another nor vice versa. In the 18th century, the Swedish scientist Carl Linnaeus classified organisms according to shared physical characteristics and he established the idea of a taxonomic hierarchy of classification based upon observable characteristics and intended to reflect natural relationships. At the time, however, it was widely believed that there was no organic connection between species, no matter how similar they appeared. However, whether or not it was supposed to be fixed, by the 19th century, naturalists understood that species could change form over time, and that the history of the planet provided enough time for major changes. Jean-Baptiste Lamarck, in his 1809 Zoological Philosophy, described the transmutation of species, proposing that a species could change over time, in 1859, Charles Darwin and Alfred Russel Wallace provided a compelling account of evolution and the formation of new species. Darwin argued that it was populations that evolved, not individuals and this required a new definition of species. Darwin concluded that species are what appear to be, ideas
3.
Lichen
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A lichen is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi in a symbiotic relationship. The combined lichen has properties different from those of its component organisms, Lichens come in many colours, sizes, and forms. The properties are sometimes plant-like, but lichens are not plants, Lichens may have tiny, leafless branches, flat leaf-like structures, flakes that lie on the surface like peeling paint, or other growth forms. A macrolichen is a lichen that is either bush-like or leafy, here, macro and micro do not refer to size, but to the growth form. Common names for lichens may contain the word moss, and lichens may superficially look like and grow with mosses, Lichens do not have roots that absorb water and nutrients as plants do, but like plants, they produce their own food by photosynthesis. When they grow on plants, they do not live as parasites, Lichens occur from sea level to high alpine elevations, in many environmental conditions, and can grow on almost any surface. Lichens are abundant growing on bark, leaves, mosses, on other lichens and they grow on rock, walls, gravestones, roofs, exposed soil surfaces, and in the soil as part of a biological soil crust. Different kinds of lichens have adapted to survive in some of the most extreme environments on Earth, arctic tundra, hot dry deserts, rocky coasts and they can even live inside solid rock, growing between the grains. It is estimated that 6% of Earths land surface is covered by lichen, there are about 20,000 known species of lichens. Some lichens have lost the ability to reproduce sexually, yet continue to speciate, Lichens may be long-lived, with some considered to be among the oldest living things. They are among the first living things to grow on fresh rock exposed after an event such as a landslide, the long life-span and slow and regular growth rate of some lichens can be used to date events. In American English, lichen is pronounced the same as the verb liken, in British English, both this pronunciation and one rhyming with kitchen /ˈlɪtʃən/) are used. Lichens grow in a range of shapes and forms. The shape of a lichen is determined by the organization of the fungal filaments. The nonreproductive tissues, or vegetative body parts, is called the thallus, Lichens are grouped by thallus type, since the thallus is usually the most visually prominent part of the lichen. Thallus growth forms typically correspond to a few basic internal structure types, Common names for lichens often come from a growth form or color that is typical of a lichen genus. When a crustose lichen gets old, the center may start to crack up like old-dried paint, old-broken asphalt paving and this is called being rimose or areolate, and the island pieces separated by the cracks are called areolas. The areolas appear separated, but are connected by an underlying prothallus or hypothallus, when a crustose lichen grows from a center and appears to radiate out, it is called crustose placodioid
4.
Transpiration
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Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. Water is necessary for plants but only an amount of water taken up by the roots is used for growth. The remaining 97–99. 5% is lost by transpiration and guttation, leaf surfaces are dotted with pores called stomata, and in most plants they are more numerous on the undersides of the foliage. The stomata are bordered by guard cells and their stomatal accessory cells that open, transpiration also cools plants, changes osmotic pressure of cells, and enables mass flow of mineral nutrients and water from roots to shoots. Two major factors influence the rate of flow from the soil to the roots, the hydraulic conductivity of the soil. Both of these factors influence the rate of flow of water moving from the roots to the stomatal pores in the leaves via the xylem. Mass flow of water from the roots to the leaves is driven in part by capillary action. This movement lowers the potential in the leaf airspace and causes evaporation of liquid water from the mesophyll cell walls. This evaporation increases the tension on the water menisci in the cell walls, water is absorbed at the roots by osmosis, and any dissolved mineral nutrients travel with it through the xylem. The Cohesion-tension theory explains how leaves pull water through the xylem, water molecules stick together, or exhibit cohesion. As a water molecule evaporates from the surface of the leaf, it pulls on the adjacent water molecule, plants regulate the rate of transpiration by controlling the size of the stomatal apertures. The rate of transpiration is also influenced by the demand of the atmosphere surrounding the leaf such as boundary layer conductance, humidity, temperature, wind. Soil water supply and soil temperature can influence stomatal opening, the amount of water lost by a plant also depends on its size and the amount of water absorbed at the roots. Transpiration accounts for most of the loss by a plant by the leaves. Transpiration serves to evaporatively cool plants, as the water carries away heat energy due to its large latent heat of vaporization of 2260 kJ per litre. During a growing season, a leaf will transpire many times more water than its own weight, an acre of corn gives off about 3, 000–4,000 gallons of water each day, and a large oak tree can transpire 40,000 gallons per year. The transpiration ratio is the ratio of the mass of water transpired to the mass of dry matter produced, transpiration rates of plants can be measured by a number of techniques, including potometers, lysimeters, porometers, photosynthesis systems and thermometric sap flow sensors. Isotope measurements indicate transpiration is the component of evapotranspiration
5.
Photosynthesis
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Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organisms activities. In most cases, oxygen is released as a waste product. Most plants, most algae, and cyanobacteria perform photosynthesis, such organisms are called photoautotrophs, in plants, these proteins are held inside organelles called chloroplasts, which are most abundant in leaf cells, while in bacteria they are embedded in the plasma membrane. In these light-dependent reactions, some energy is used to strip electrons from suitable substances, such as water, in the Calvin cycle, atmospheric carbon dioxide is incorporated into already existing organic carbon compounds, such as ribulose bisphosphate. Using the ATP and NADPH produced by the light-dependent reactions, the compounds are then reduced and removed to form further carbohydrates. Cyanobacteria appeared later, the oxygen they produced contributed directly to the oxygenation of the Earth. Today, the rate of energy capture by photosynthesis globally is approximately 130 terawatts. Photosynthetic organisms also convert around 100–115 thousand million tonnes of carbon into biomass per year. Photosynthetic organisms are photoautotrophs, which means that they are able to synthesize food directly from carbon dioxide, however, not all organisms that use light as a source of energy carry out photosynthesis, photoheterotrophs use organic compounds, rather than carbon dioxide, as a source of carbon. In plants, algae, and cyanobacteria, photosynthesis releases oxygen and this is called oxygenic photosynthesis and is by far the most common type of photosynthesis used by living organisms. Although there are differences between oxygenic photosynthesis in plants, algae, and cyanobacteria, the overall process is quite similar in these organisms. There are also varieties of anoxygenic photosynthesis, used mostly by certain types of bacteria. Carbon dioxide is converted into sugars in a process called carbon fixation, photosynthesis provides the energy in the form of free electrons that are used to split carbon from carbon dioxide that is then used to fix that carbon once again as carbohydrate. Carbon fixation is a redox reaction, so photosynthesis supplies the energy that drives both process. In the first stage, light-dependent reactions or light reactions capture the energy of light and use it to make the energy-storage molecules ATP, during the second stage, the light-independent reactions use these products to capture and reduce carbon dioxide. Most organisms that utilize oxygenic photosynthesis use visible light for the light-dependent reactions, some organisms employ even more radical variants of photosynthesis. Some archea use a method that employs a pigment similar to those used for vision in animals. The bacteriorhodopsin changes its configuration in response to sunlight, acting as a proton pump and this produces a proton gradient more directly, which is then converted to chemical energy
6.
Anemophily
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Anemophily or wind pollination is a form of pollination whereby pollen is distributed by wind. Almost all gymnosperms are anemophilous, as are plants in the order Poales. Other common anemophilous plants are oaks, sweet chestnuts, alders and members of the family Juglandaceae, features of the wind-pollination syndrome include a lack of scent production, a lack of showy floral parts, reduced production of nectar, and the production of enormous numbers of pollen grains. This distinguishes them from entomophilous and zoophilous species, anemophilous pollen grains are light and non-sticky, so that they can be transported by air currents. They are typically 20–60 micrometres in diameter, although the pollen grains of Pinus species can be much larger, anemophilous plants possess well-exposed stamens so that the pollens are exposed to wind currents and also have large and feathery stigma to easily trap airborne pollen grains. Pollen from anemophilous plants tends to be smaller and lighter than pollen from entomophilous ones, however, insects sometimes gather pollen from staminate anemophilous flowers at times when higher-protein pollens from entomophilous flowers are scarce. Anemophilous pollens may also be captured by bees electrostatic field. This may explain why, though bees are not observed to visit ragweed flowers, anemophily is an adaptation that helps to separate the male and female reproductive systems of a single plant, reducing the effects of inbreeding. It often accompanies dioecy – the presence of male and female structures on separate plants. Almost all pollens that are allergens are from anemophilous species, grasses are the most important producers of aeroallergens in most temperate regions, with lowland or meadow species producing more pollen than upland or moorland species. Media related to Wind pollination at Wikimedia Commons
7.
Pollination
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Pollination is the process by which pollen is transferred to the female reproductive organs of a plant, thereby enabling fertilization to take place. Like all living organisms, seed plants have a major goal. The reproductive unit is the seed, and pollination is a step in the production of seeds in all spermatophytes. The process is different in angiosperms from what it is in gymnosperms. In angiosperms, after the grain has landed on the stigma. Sperm cells from the pollen grain then move along the tube, enter the egg cell through the micropyle and fertilise it. A successful angiosperm pollen grain containing the gametes is transported to the stigma. Its two gametes travel down the tube to where the containing the female gametes are held within the carpel. One nucleus fuses with the bodies to produce the endosperm tissues. In gymnosperms, the ovule is not contained in a carpel, details of the process vary according to the division of gymnosperms in question. Two main modes of fertilization are found in gymnosperms, the study of pollination brings together many disciplines, such as botany, horticulture, entomology, and ecology. The pollination process as an interaction between flower and pollen vector was first addressed in the 18th century by Christian Konrad Sprengel and it is important in horticulture and agriculture, because fruiting is dependent on fertilization, the result of pollination. The study of pollination by insects is known as anthecology, pollen germination has three stages, hydration, activation and pollen tube emergence. The pollen grain is severely dehydrated so that its mass is reduced enabling it to be easily transported from flower to flower. Germination only takes place after rehydration, ensuring that premature germination does not take place in the anther, hydration allows the plasma membrane of the pollen grain to reform into its normal bilayer organization providing an effective osmotic membrane. Activation involves the development of actin filaments throughout the cytoplasm of the cell, hydration and activation continue as the pollen tube begins to grow. In conifers, the structures are borne on cones. The cones are either pollen cones or ovulate cones, but some species are monoecious, a pollen cone contains hundreds of microsporangia carried on reproductive structures called sporophylls
