Crassulacean acid metabolism
Crassulacean acid metabolism, known as CAM photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions. In a plant using full CAM, the stomata in the leaves remain shut during the day to reduce evapotranspiration, the pre-collected CO2 is concentrated around the enzyme RuBisCO, increasing photosynthetic efficiency. This metabolism was first studied in plants of the Crassulaceae family, the first time it was studied, Crassula was used as a model organism. The term CAM may have coined by Ranson and Thomas in 1940. It was observed by the botanists Ranson and Thomas, in the Crassulaceae family of succulents and its name refers to acid metabolism in Crassulaceae, not the metabolism of crassulacean acid. CAM is an adaptation for increased efficiency in the use of water, during the night, a plant employing CAM has its stomata open, allowing CO2 to enter and be fixed as organic acids that are stored in vacuoles. During the day the stomata are closed, and the carbon is released to the Calvin cycle so that photosynthesis may take place, the carbon dioxide is fixed in the cytoplasm of mesophyll cells by a PEP reaction similar to that of C4 pathway.
But, unlike the C4 mechanism, the organic acids are stored in vacuoles for use. The latter cannot operate during the night because the reactions that provide it with ATP. The most important benefit of CAM to the plant is the ability to leave most leaf stomata closed during the day, plants employing CAM are most common in arid environments, where water comes at a premium. Plants using only C3 carbon fixation, for example, lose 97% of the water they uptake through the roots to transpiration - a high cost avoided by plants able to employ CAM. The C4 pathway bears resemblance to CAM, both act to concentrate CO2 around RuBisCO, thereby increasing its efficiency, CAM concentrates it temporally, providing CO2 during the day, and not at night, when respiration is the dominant reaction. C4 plants, in contrast, concentrate CO2 spatially, with a RuBisCO reaction centre in a bundle sheath cell being inundated with CO2, at low temperatures, plants using CAM open their stomata, CO2 molecules diffuse into the spongy mesophylls intracellular spaces and into the cytoplasm.
Here, they can meet phosphoenolpyruvate, which is a phosphorylated triose, during this time, the plants are synthesizing a protein called PEP carboxylase kinase, whose expression can be inhibited by high temperatures and the presence of malate. PEP-C kinase phosphorylates its target enzyme PEP carboxylase, phosphorylation dramatically enhances the enzymes capability to catalyze the formation of oxalacetate, which can be subsequently transformed into malate by NAD+ malate dehydrogenase. Malate is transported via malate shuttles into the vacuole, where it is converted into the storage form malic acid, in contrast to PEP-C kinase, PEP-C is synthesized all the time but almost inhibited at daylight either by dephosphorylation via PEP-C phosphatase or directly by binding malate. The latter is not possible at low temperatures, since malate is efficiently transported into the vacuole, in daylight, plants using CAM close their guard cells and discharge malate that is subsequently transported into chloroplasts.
There, depending on plant species, it is cleaved into pyruvate, CO2 is introduced into the Calvin cycle, a coupled and self-recovering enzyme system, which is used to build branched carbohydrates
Guttation is the exudation of drops of xylem sap on the tips or edges of leaves of some vascular plants, such as grasses. Guttation is not to be confused with dew, which condenses from the atmosphere onto the plant surface, at night, transpiration usually does not occur because most plants have their stomata closed. When there is a soil moisture level, water will enter plant roots. The water will accumulate in the plant, creating a slight root pressure, the root pressure forces some water to exude through special leaf tip or edge structures, hydathodes or water glands, forming drops. Root pressure provides the impetus for this flow, rather than transpirational pull, guttation is most noticeable when transpiration is suppressed and the relative humidity is high, such as during the night. Guttation fluid may contain a variety of organic and inorganic compounds, mainly sugars, on drying, a white crust remains on the leaf surface. Concentrations this high are near those of active ingredients applied in field sprays for pest control and it was found that when bees consume guttation drops collected from plants grown from neonicotinoid-coated seeds, they die within a few minutes.
This phenomenon may be a factor in bee deaths and, consequently, if high levels of nitrogen appear in the fluid, it is a sign of fertilizer burn. Excess nitrogen must be leached from the soil by addition of large quantities of water and this is the best way to restore soil fertility, but it may result in water pollution. Homeostasis Osmosis Soil plant atmosphere continuum Transpiration
A cactus is a member of the plant family Cactaceae, a family comprising about 127 genera with some 1750 known species of the order Caryophyllales. The word cactus derives, through Latin, from the Ancient Greek κάκτος, Cacti occur in a wide range of shapes and sizes. Most cacti live in habitats subject to at least some drought, many live in extremely dry environments, even being found in the Atacama Desert, one of the driest places on earth. Cacti show many adaptations to conserve water, almost all cacti are succulents, meaning they have thickened, fleshy parts adapted to store water. Unlike many other succulents, the stem is the part of most cacti where this vital process takes place. Most species of cacti have lost true leaves, retaining only spines, as well as defending against herbivores, spines help prevent water loss by reducing air flow close to the cactus and providing some shade. In the absence of leaves, enlarged stems carry out photosynthesis, Cacti are native to the Americas, ranging from Patagonia in the south to parts of western Canada in the north—except for Rhipsalis baccifera, which grows in Africa and Sri Lanka.
Cactus spines are produced from specialized structures called areoles, a kind of highly reduced branch, areoles are an identifying feature of cacti. As well as spines, areoles give rise to flowers, which are usually tubular, Cactus stems are often ribbed or fluted, which allows them to expand and contract easily for quick water absorption after rain, followed by long drought periods. Like other succulent plants, most cacti employ a mechanism called crassulacean acid metabolism as part of photosynthesis. Transpiration, during which carbon enters the plant and water escapes, does not take place during the day at the same time as photosynthesis. The plant stores the carbon dioxide it takes in as malic acid, retaining it until daylight returns, because transpiration takes place during the cooler, more humid night hours, water loss is significantly reduced. Many smaller cacti have globe-shaped stems, combining the highest possible volume for water storage, the tallest free-standing cactus is Pachycereus pringlei, with a maximum recorded height of 19.2 m, and the smallest is Blossfeldia liliputiana, only about 1 cm in diameter at maturity. A fully grown saguaro is said to be able to absorb as much as 200 U. S. gallons of water during a rainstorm, a few species differ significantly in appearance from most of the family.
At least superficially, plants of the genus Pereskia resemble other trees and they have persistent leaves, and when older, bark-covered stems. Their areoles identify them as cacti, and in spite of their appearance, Pereskia is considered close to the ancestral species from which all cacti evolved. In tropical regions, other cacti grow as forest climbers and epiphytes and their stems are typically flattened, almost leaf-like in appearance, with fewer or even no spines, such as the well-known Christmas cactus or Thanksgiving cactus. Cacti have a variety of uses, many species are used as ornamental plants, others are grown for fodder or forage, cochineal is the product of an insect that lives on some cacti
A cuticle /ˈkjuːtɪkəl/, or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of cuticle are non-homologous, differing in their origin, function, in human anatomy, cuticle refers to several structures. In zoology, the cuticle or cuticula is a multi-layered structure outside the epidermis of many invertebrates, notably roundworms and arthropods. The main structural components of the cuticle are proteins, highly cross-linked collagens and specialised insoluble proteins known as cuticlins, together with glycoproteins. The rigidity is a function of the types of proteins and the quantity of chitin, the more acidic the protein is, the softer the cuticle. It is believed that the cells and hemocytes produce protein and monitors the timing. Often, in the cuticle of arthropods, structural coloration-producing nanostructures are observed, in botany, plant cuticles are protective, waxy coverings produced by the epidermal cells of leaves, young shoots and all other aerial plant organs.
Cuticles minimize water loss and effectively reduce pathogen entry due to their waxy secretion, the main structural components of plant cuticles are the unique polymers cutin and/or cutan, impregnated with wax. The cuticles of plants function as permeability barriers for water and water-soluble materials, the cuticle both prevents plant surfaces from becoming wet and helps to prevent plants from drying out. Xerophytic plants such as cactus have very thick cuticles to help them survive in their arid climates, plants that live in range of seas spray may have thicker cuticles that protect them from the toxic effects of salt. Some plants, particularly adapted to life in damp or aquatic environments, have an extreme resistance to wetting. A well-known example is the Sacred Lotus and this adaptation is not purely the physical and chemical effect of a waxy coating, however, it depends largely on the microscopic shape of the surface. The effect is to reduce wetting of the surface substantially, structural coloration is observed in the cuticles of plants (see, as an example, the so-called marble berry, Pollia condensata.
Cuticle is one used for the outer layer of tissue of a mushrooms basidiocarp. The alternative term pileipellis, Latin for skin of a cap might be technically preferable and it is the part removed in peeling mushrooms. On the other hand, some terminology in mycology makes finer distinctions. Be that as it may, the pileipellis is distinct from the trama, the fleshy tissue of a mushroom or similar fruiting body, and from the spore-bearing tissue layer
In botany, shoots consist of stems including their appendages, the leaves and lateral buds, flowering stems and flower buds. The new growth from seed germination that grows upward is a shoot where leaves will develop, in the spring, perennial plant shoots are the new growth that grows from the ground in herbaceous plants or the new stem or flower growth that grows on woody plants. In everyday speech, shoots are often synonymous with stems, which are an integral component of shoots, provide an axis for buds and leaves. Young shoots are eaten by animals because the fibres in the new growth have not yet completed secondary cell wall development, making the young shoots softer and easier to chew. As shoots grow and age, the cells develop secondary cell walls that have a hard, some plants produce toxins that make their shoots inedible or less palatable. Many woody plants have distinct short shoots and long shoots, in some angiosperms, the short shoots, called spur shoots or fruit spurs, produce the majority of flowers and fruit.
A similar pattern occurs in some conifers and in Ginkgo, although the short shoots of some such as Picea are so small that they can be mistaken for part of the leaf that they have produced. A related phenomenon is seasonal heterophylly, which involves visibly different leaves from spring growth, whereas spring growth mostly comes from buds formed the previous season, and often includes flowers, lammas growth often involves long shoots
A xerophyte is a species of plant that has adapted to survive in an environment with little liquid water, such as a desert or an ice- or snow-covered region in the Alps or the Arctic. The morphology and physiology of xerophytes are variously adapted to conserve water, other species may be adapted to survive long periods of desiccation of their tissues, during which their metabolic activity may effectively shut down. Plants with such morphological and physiological adaptations are xeromorphic, Plants absorb water from the soil, which evaporates from their outer surfaces, this process is known as transpiration. In dry environments, a plant would evaporate water faster than the rate at which water was replaced in the soil. To reduce this effect, xerophytic plants exhibit a variety of specialized adaptations to survive in such conditions and other succulents are commonly found in deserts, where there is little rainfall. Likewise, chaparral plants are adapted to Mediterranean climates, which have wet winters, Plants that live under arctic conditions have a need for xerophytic adaptations, since water is unavailable for uptake when the ground is frozen.
Succulent plants store water in their stems or leaves and they include the Cactaceae family, which has round stems and can store a lot of water. The leaves are vestigial, as in the case of cacti, wherein the leaves are reduced to spines. Xerophytes are commonly found in environments, where plants such as pineapples. Water is stored in the bulbs of plants, at or below ground level. They may be dormant during drought conditions and are, therefore, if the water potential inside a leaf is higher than outside, the water vapour will diffuse out of the leaf down this gradient. This loss of water vapour from the leaves is called transpiration, transpiration is natural and inevitable for plants, and much water is lost through this process. However, it is vital that plants living in dry conditions are adapted so as to reduce water loss and decrease the size of the open stomata. It is important for a plant living in conditions to conserve water because, without enough water. If the plant loses too much water, it will pass its permanent wilting point and it is important to note, that whilst it is vital to keep stomata closed, they have to be opened for gaseous exchange in photosynthesis.
Xerophytic plants may have similar shapes and structures and look similar, even if the plants are not very closely related. For example, some species of cacti, which evolved only in the Americas, may similar to Euphorbias. An unrelated species of caudiciforms, plants with swollen bases that are used to store water, xerophytic plants can have less overall surface area than other plants, so reducing the area that is exposed to the air and reducing water loss by evaporation
Scanning electron microscope
A scanning electron microscope is a type of electron microscope that produces images of a sample by scanning it with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that contain information about the surface topography. The electron beam is scanned in a raster scan pattern. SEM can achieve better than 1 nanometer. Specimens can be observed in vacuum, in low vacuum, in wet conditions. The most common SEM mode is detection of electrons emitted by atoms excited by the electron beam. The number of electrons that can be detected depends, among other things. By scanning the sample and collecting the electrons that are emitted using a special detector. An account of the history of SEM has been presented by McMullan. Ardenne applied the principle not only to achieve magnification but to purposefully eliminate the chromatic aberration otherwise inherent in the electron microscope. He further discussed the various modes and theory of SEM. The types of produced by an SEM include secondary electrons, reflected or back-scattered electrons, photons of characteristic X-rays and light, absorbed current.
Secondary electron detectors are standard equipment in all SEMs, but it is rare that a machine would have detectors for all other possible signals. The signals result from interactions of the beam with atoms at various depths within the sample. In the most common or standard detection mode, ie secondary electron imaging or SEI, consequently, SEM can produce very high-resolution images of a sample surface, revealing details less than 1 nm in size. Back-scattered electrons are beam electrons that are reflected from the sample by elastic scattering and they emerge from deeper locations within the specimen and consequently the resolution of BSE images is generally poorer than SE images. BSE images can provide information about the distribution of different elements in the sample, characteristic X-rays are emitted when the electron beam removes an inner shell electron from the sample, causing a higher-energy electron to fill the shell and release energy. These characteristic X-rays are used to identify the composition and measure the abundance of elements in the sample, due to the very narrow electron beam, SEM micrographs have a large depth of field yielding a characteristic three-dimensional appearance useful for understanding the surface structure of a sample
The tomato is the edible fruit of Solanum lycopersicum, commonly known as a tomato plant, which belongs to the nightshade family, Solanaceae. The species originated in Central and South America, the Nahuatl word tomatl gave rise to the Spanish word tomate, from which the English word tomato originates. Numerous varieties of tomato are widely grown in temperate climates across the world, with greenhouses allowing its production throughout the year, the plants typically grow to 1–3 meters in height and have a weak stem that often sprawls over the ground and vines over other plants. It is a perennial in its habitat, and grown as an annual in temperate climates. An average common tomato weighs approximately 100 grams and its use as a food originated in Mexico, and spread throughout the world following the Spanish colonization of the Americas. Tomato is consumed in diverse ways, including raw, as an ingredient in dishes, salads. While tomatoes are botanically fruits, they are considered culinary vegetables.
The word tomato comes from the Spanish tomate, which in turn comes from the Nahuatl word tomatl and it first appeared in print in 1595. The native Mexican tomatillo is tomate, meaning fat water or fat thing), when Aztecs started to cultivate the Andean fruit and red, they called the new species xitomatl. It first appeared in print in 1595, the scientific species epithet lycopersicum means wolf peach, and comes from German werewolf myths. The Italian word, pomodoro was borrowed into Polish, and via Russian, the usual pronunciations of tomato are /təˈmeɪtoʊ/ and /təˈmɑːtoʊ/. The words dual pronunciations were immortalized in Ira and George Gershwins 1937 song Lets Call the Whole Thing Off and have become a symbol for nitpicking pronunciation disputes. In this capacity, it has become an American and British slang term. Or Its all the same to me, botanically, a tomato is a fruit, a berry, consisting of the ovary, together with its seeds, of a flowering plant. However, the tomato has a lower sugar content than other edible fruits.
Typically served as part of a salad or main course of a meal, rather than at dessert, it is, in the US, considered a culinary vegetable. One exception is that tomatoes are treated as a fruit in home canning practices, they are acidic enough to process in a water bath rather than a pressure cooker as vegetables require. Tomatoes are not the food source with this ambiguity, bell peppers, green beans, avocados
A stem is one of two main structural axes of a vascular plant, the other being the root. The stem is divided into nodes and internodes, The nodes hold one or more leaves. Adventitious roots may be produced from the nodes, the internodes distance one node from another. The term shoots is often confused with stems, shoots generally refers to new plant growth including both stems and other structures like leaves or flowers. In most plants stems are located above the surface but some plants have underground stems. Stems have four main functions which are, Support for and the elevation of leaves, the stems keep the leaves in the light and provide a place for the plant to keep its flowers and fruits. Transport of fluids between the roots and the shoots in the xylem and phloem Storage of nutrients Production of new living tissue, the normal lifespan of plant cells is one to three years. Stems have cells called meristems that annually generate new living tissue, Stems are often specialized for storage, asexual reproduction, protection or photosynthesis, including the following, Acaulescent – used to describe stems in plants that appear to be stemless.
Actually these stems are just extremely short, the leaves appearing to rise out of the ground. Arborescent – tree like with woody stems normally with a single trunk, branched – aerial stems are described as being branched or unbranched Bud – an embryonic shoot with immature stem tip. Bulb – a short underground stem with fleshy storage leaves attached, e. g. onion, daffodil. Bulbs often function in reproduction by splitting to form new bulbs or producing small new bulbs termed bulblets, bulbs are a combination of stem and leaves so may better be considered as leaves because the leaves make up the greater part. Caespitose – when stems grow in a mass or clump or in low growing mats. Cladode – a flattened stem that appears more-or-less leaf like and is specialized for photosynthesis, climbing – stems that cling or wrap around other plants or structures. Corm – a short enlarged underground, storage stem, e. g. taro, decumbent – stems that lie flat on the ground and turn upwards at the ends. Fruticose – stems that grow shrublike with woody like habit, herbaceous – non woody, they die at the end of the growing season.
Pedicel – stems that serve as the stalk of a flower in an inflorescence or infrutescence. Peduncle – a stem that supports an inflorescence Prickle – a sharpened extension of the outer layers
A desert is a barren area of land where little precipitation occurs and consequently living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to the processes of denudation, about one third of the land surface of the world is arid or semi-arid. This includes much of the regions where little precipitation occurs. Deserts can be classified by the amount of precipitation falls, by the temperature that prevails. Deserts are formed by weathering processes as large variations in temperature between day and night put strains on the rocks which consequently break in pieces, although rain seldom occurs in deserts, there are occasional downpours that can result in flash floods. Rain falling on hot rocks can cause them to shatter and the resulting fragments and this picks up particles of sand and dust and wafts them aloft in sand or dust storms. Wind-blown sand grains striking any solid object in their path can abrade the surface, rocks are smoothed down, and the wind sorts sand into uniform deposits.
The grains end up as level sheets of sand or are piled high in billowing sand dunes, other deserts are flat, stony plains where all the fine material has been blown away and the surface consists of a mosaic of smooth stones. These areas are known as desert pavements and little further erosion takes place, other desert features include rock outcrops, exposed bedrock and clays once deposited by flowing water. Temporary lakes may form and salt pans may be left when waters evaporate, there may be underground sources of water in the form of springs and seepages from aquifers. Where these are found, oases can occur and animals living in the desert need special adaptations to survive in the harsh environment. Plants tend to be tough and wiry with small or no leaves, water-resistant cuticles, some annual plants germinate and die in the course of a few weeks after rainfall while other long-lived plants survive for years and have deep root systems able to tap underground moisture. Animals need to cool and find enough food and water to survive.
Many are nocturnal and stay in the shade or underground during the heat of the day and they tend to be efficient at conserving water, extracting most of their needs from their food and concentrating their urine. Some animals remain in a state of dormancy for long periods and they reproduce rapidly while conditions are favorable before returning to dormancy. People have struggled to live in deserts and the surrounding lands for millennia. Nomads have moved their flocks and herds to wherever grazing is available, the cultivation of semi-arid regions encourages erosion of soil and is one of the causes of increased desertification. Many trade routes have been forged across deserts, especially across the Sahara Desert, large numbers of slaves were taken northwards across the Sahara
Xylem is one of the two types of transport tissue in vascular plants, phloem being the other. The basic function of xylem is to water from roots to shoots and leaves. The word xylem is derived from the Greek word ξύλον, meaning wood, the most distinctive xylem cells are the long tracheary elements that transport water. Tracheids and vessel elements are distinguished by their shape, vessel elements are shorter, Xylem contains two other cell types and fibers. In transitional stages of plants with secondary growth, the first two categories are not mutually exclusive, although usually a vascular bundle will contain primary xylem only, the branching pattern exhibited by xylem follows Murrays law. Primary xylem is formed during growth from procambium. Metaxylem develops after the protoxylem but before secondary xylem, metaxylem has wider vessels and tracheids than protoxylem. Secondary xylem is formed during growth from vascular cambium. All species have secondary xylem, which is uniform in structure throughout this group.
Many conifers become tall trees, the xylem of such trees is used and marketed as softwood. Angiosperms, there are some quarter of a million to four hundred species of angiosperms. Within this group secondary xylem is rare in the monocots, many non-monocot angiosperms become trees, and the secondary xylem of these is used and marketed as hardwood. The xylem transports water and soluble mineral nutrients from the throughout the plant. It is used to replace water lost during transpiration and photosynthesis, Xylem sap consists mainly of water and inorganic ions, although it can contain a number of organic chemicals as well. The transport is passive, not powered by energy spent by the elements themselves. Transporting sap upwards becomes more difficult as the height of a plant increases, the phloem pressure can rise to several MPa, far higher than atmospheric pressure. Selective inter-connection between these systems allows this high concentration in the phloem to draw xylem fluid upwards by negative pressure.
Transpirational pull, the evaporation of water from the surfaces of cells to the atmosphere creates a negative pressure at the top of a plant
A temperature is an objective comparative measurement of hot or cold. It is measured by a thermometer, several scales and units exist for measuring temperature, the most common being Celsius, and, especially in science, Kelvin. Absolute zero is denoted as 0 K on the Kelvin scale, −273.15 °C on the Celsius scale, the kinetic theory offers a valuable but limited account of the behavior of the materials of macroscopic bodies, especially of fluids. Temperature is important in all fields of science including physics, chemistry, atmospheric sciences, medicine. The Celsius scale is used for temperature measurements in most of the world. Because of the 100 degree interval, it is called a centigrade scale.15, the United States commonly uses the Fahrenheit scale, on which water freezes at 32°F and boils at 212°F at sea-level atmospheric pressure. Many scientific measurements use the Kelvin temperature scale, named in honor of the Scottish physicist who first defined it and it is a thermodynamic or absolute temperature scale.
Its zero point, 0K, is defined to coincide with the coldest physically-possible temperature and its degrees are defined through thermodynamics. The temperature of zero occurs at 0K = −273. 15°C. For historical reasons, the triple point temperature of water is fixed at 273.16 units of the measurement increment, Temperature is one of the principal quantities in the study of thermodynamics. There is a variety of kinds of temperature scale and it may be convenient to classify them as empirically and theoretically based. Empirical temperature scales are historically older, while theoretically based scales arose in the middle of the nineteenth century, empirically based temperature scales rely directly on measurements of simple physical properties of materials. For example, the length of a column of mercury, confined in a capillary tube, is dependent largely on temperature. Such scales are only within convenient ranges of temperature. For example, above the point of mercury, a mercury-in-glass thermometer is impracticable. A material is of no use as a thermometer near one of its phase-change temperatures, in spite of these restrictions, most generally used practical thermometers are of the empirically based kind.
Especially, it was used for calorimetry, which contributed greatly to the discovery of thermodynamics, empirical thermometry has serious drawbacks when judged as a basis for theoretical physics. Theoretically based temperature scales are based directly on theoretical arguments, especially those of thermodynamics, kinetic theory and they rely on theoretical properties of idealized devices and materials