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100-461: Not to be confused with Stoma . [REDACTED] Look up stroma in Wiktionary, the free dictionary. Stroma may refer to: Biology [ edit ] Stroma (tissue) , the connective, functionally supportive framework of a biological cell, tissue, or organ (in contrast, the parenchyma is the functional aspect of a tissue) Stroma of ovary ,

200-471: A are the partial pressures of water in the leaf and in the ambient air respectively, P is atmospheric pressure, and r is stomatal resistance. The inverse of r is conductance to water vapor ( g ), so the equation can be rearranged to and solved for g : Photosynthetic CO 2 assimilation ( A ) can be calculated from where C a and C i are the atmospheric and sub-stomatal partial pressures of CO 2 respectively . The rate of evaporation from

300-572: A cascade method, Swiss chemist and physicist Raoul Pierre Pictet evaporated liquid sulfur dioxide in order to liquefy carbon dioxide, which in turn was evaporated to cool oxygen gas enough to liquefy it. He sent a telegram on December 22, 1877, to the French Academy of Sciences in Paris announcing his discovery of liquid oxygen . Just two days later, French physicist Louis Paul Cailletet announced his own method of liquefying molecular oxygen. Only

400-425: A phenotypic plasticity in response to [CO 2 ] atm that may have been an adaptive trait in the evolution of plant respiration and function. Predicting how stomata perform during adaptation is useful for understanding the productivity of plant systems for both natural and agricultural systems . Plant breeders and farmers are beginning to work together using evolutionary and participatory plant breeding to find

500-447: A proton pump drives protons (H ) from the guard cells. This means that the cells' electrical potential becomes increasingly negative. The negative potential opens potassium voltage-gated channels and so an uptake of potassium ions (K ) occurs. To maintain this internal negative voltage so that entry of potassium ions does not stop, negative ions balance the influx of potassium. In some cases, chloride ions enter, while in other plants

600-477: A chemical element. The name oxygen was coined in 1777 by Antoine Lavoisier , who first recognized oxygen as a chemical element and correctly characterized the role it plays in combustion. Common industrial uses of oxygen include production of steel , plastics and textiles , brazing, welding and cutting of steels and other metals , rocket propellant , oxygen therapy , and life support systems in aircraft , submarines , spaceflight and diving . One of

700-434: A few drops of the liquid were produced in each case and no meaningful analysis could be conducted. Oxygen was liquefied in a stable state for the first time on March 29, 1883, by Polish scientists from Jagiellonian University , Zygmunt Wróblewski and Karol Olszewski . In 1891 Scottish chemist James Dewar was able to produce enough liquid oxygen for study. The first commercially viable process for producing liquid oxygen

800-482: A great degree of variation in size and frequency about species and genotypes. White ash and white birch leaves had fewer stomata but larger in size. On the other hand sugar maple and silver maple had small stomata that were more numerous. Different classifications of stoma types exist. One that is widely used is based on the types that Julien Joseph Vesque introduced in 1889, was further developed by Metcalfe and Chalk, and later complemented by other authors. It

900-562: A high carbon dioxide affinity, phosphoenolpyruvate carboxylase (PEPcase). Retrieving the products of carbon fixation from PEPCase is an energy-intensive process, however. As a result, the PEPCase alternative is preferable only where water is limiting but light is plentiful, or where high temperatures increase the solubility of oxygen relative to that of carbon dioxide, magnifying RuBisCo's oxygenation problem. A group of mostly desert plants called "C.A.M." plants ( crassulacean acid metabolism , after

1000-457: A leaf can be determined using a photosynthesis system . These scientific instruments measure the amount of water vapour leaving the leaf and the vapor pressure of the ambient air. Photosynthetic systems may calculate water use efficiency ( A / E ), g , intrinsic water use efficiency ( A / g ), and C i . These scientific instruments are commonly used by plant physiologists to measure CO 2 uptake and thus measure photosynthetic rate. There

1100-481: A light sky-blue color caused by absorption in the red (in contrast with the blue color of the sky, which is due to Rayleigh scattering of blue light). High-purity liquid O 2 is usually obtained by the fractional distillation of liquefied air. Liquid oxygen may also be condensed from air using liquid nitrogen as a coolant. Liquid oxygen is a highly reactive substance and must be segregated from combustible materials. The spectroscopy of molecular oxygen

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1200-560: A major role in absorbing energy from singlet oxygen and converting it to the unexcited ground state before it can cause harm to tissues. The common allotrope of elemental oxygen on Earth is called dioxygen , O 2 , the major part of the Earth's atmospheric oxygen (see Occurrence ). O 2 has a bond length of 121  pm and a bond energy of 498  kJ/mol . O 2 is used by complex forms of life, such as animals, in cellular respiration . Other aspects of O 2 are covered in

1300-438: A part of air that he called spiritus nitroaereus . In one experiment, he found that placing either a mouse or a lit candle in a closed container over water caused the water to rise and replace one-fourteenth of the air's volume before extinguishing the subjects. From this, he surmised that nitroaereus is consumed in both respiration and combustion. Mayow observed that antimony increased in weight when heated, and inferred that

1400-404: A process called eutrophication and the decay of these organisms and other biomaterials may reduce the O 2 content in eutrophic water bodies. Scientists assess this aspect of water quality by measuring the water's biochemical oxygen demand , or the amount of O 2 needed to restore it to a normal concentration. Paleoclimatologists measure the ratio of oxygen-18 and oxygen-16 in

1500-411: A significant effect on stomatal closure of its leaves. There are different mechanisms of stomatal closure. Low humidity stresses guard cells causing turgor loss, termed hydropassive closure. Hydroactive closure is contrasted as the whole leaf affected by drought stress, believed to be most likely triggered by abscisic acid . It is expected that [CO 2 ] atm will reach 500–1000 ppm by 2100. 96% of

1600-458: A small proportion of manganese dioxide. Oxygen levels in the atmosphere are trending slightly downward globally, possibly because of fossil-fuel burning. At standard temperature and pressure , oxygen is a colorless, odorless, and tasteless gas with the molecular formula O 2 , referred to as dioxygen. As dioxygen , two oxygen atoms are chemically bound to each other. The bond can be variously described based on level of theory, but

1700-438: A soft tissue, well supplied with blood, consisting of spindle-shaped cells with a small amount of connective tissue Stroma of iris , fibres and cells in the iris Stroma of cornea , plates of collagen fibrils in the cornea Lymph node stromal cell , cells which provide a scaffold for other lymph node cells Stroma of bone marrow Stroma (fungus) , a tissue structure of some ascomycete mushrooms Stroma (fluid) ,

1800-550: A stoma. This meristemoid then divides asymmetrically one to three times before differentiating into a guard mother cell. The guard mother cell then makes one symmetrical division, which forms a pair of guard cells. Cell division is inhibited in some cells so there is always at least one cell between stomata. Stomatal patterning is controlled by the interaction of many signal transduction components such as EPF (Epidermal Patterning Factor), ERL (ERecta Like) and YODA (a putative MAP kinase kinase kinase ). Mutations in any one of

1900-449: A triplet electronic ground state . An electron configuration with two unpaired electrons, as is found in dioxygen orbitals (see the filled π* orbitals in the diagram) that are of equal energy—i.e., degenerate —is a configuration termed a spin triplet state. Hence, the ground state of the O 2 molecule is referred to as triplet oxygen . The highest-energy, partially filled orbitals are antibonding , and so their filling weakens

2000-576: Is the most abundant element in Earth's crust , and the third-most abundant element in the universe after hydrogen and helium . At standard temperature and pressure , two oxygen atoms will bind covalently to form dioxygen , a colorless and odorless diatomic gas with the chemical formula O 2 . Dioxygen gas currently constitutes 20.95% molar fraction of the Earth's atmosphere , though this has changed considerably over long periods of time in Earth's history . Oxygen makes up almost half of

2100-570: Is a corrosive byproduct of smog and thus an air pollutant . Oxygen was isolated by Michael Sendivogius before 1604, but it is commonly believed that the element was discovered independently by Carl Wilhelm Scheele , in Uppsala , in 1773 or earlier, and Joseph Priestley in Wiltshire , in 1774. Priority is often given for Priestley because his work was published first. Priestley, however, called oxygen "dephlogisticated air", and did not recognize it as

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2200-477: Is absorbed by specialized respiratory organs called gills , through the skin or via the gut ; in terrestrial animals such as tetrapods , oxygen in air is actively taken into the body via specialized organs known as lungs , where gas exchange takes place to diffuse oxygen into the blood and carbon dioxide out, and the body's circulatory system then transports the oxygen to other tissues where cellular respiration takes place. However in insects ,

2300-454: Is also coordinated by the cellular peptide signal called stomagen, which signals the activation of the SPCH, resulting in increased number of stomata. Environmental and hormonal factors can affect stomatal development. Light increases stomatal development in plants; while, plants grown in the dark have a lower amount of stomata. Auxin represses stomatal development by affecting their development at

2400-508: Is associated with the atmospheric processes of aurora and airglow . The absorption in the Herzberg continuum and Schumann–Runge bands in the ultraviolet produces atomic oxygen that is important in the chemistry of the middle atmosphere. Excited-state singlet molecular oxygen is responsible for red chemiluminescence in solution. Table of thermal and physical properties of oxygen (O 2 ) at atmospheric pressure: Naturally occurring oxygen

2500-513: Is based on the size, shape and arrangement of the subsidiary cells that surround the two guard cells. They distinguish for dicots : In monocots , several different types of stomata occur such as: In ferns , four different types are distinguished: Stomatal crypts are sunken areas of the leaf epidermis which form a chamber-like structure that contains one or more stomata and sometimes trichomes or accumulations of wax . Stomatal crypts can be an adaption to drought and dry climate conditions when

2600-405: Is because the light response of stomata to blue light is independent of other leaf components like chlorophyll . Guard cell protoplasts swell under blue light provided there is sufficient availability of potassium . Multiple studies have found support that increasing potassium concentrations may increase stomatal opening in the mornings, before the photosynthesis process starts, but that later in

2700-469: Is composed of three stable isotopes , O , O , and O , with O being the most abundant (99.762% natural abundance ). Most O is synthesized at the end of the helium fusion process in massive stars but some is made in the neon burning process . O is primarily made by the burning of hydrogen into helium during the CNO cycle , making it a common isotope in the hydrogen burning zones of stars. Most O

2800-574: Is dependent on the diffusion resistance provided by the stomatal pores and also on the humidity gradient between the leaf's internal air spaces and the outside air. Stomatal resistance (or its inverse, stomatal conductance ) can therefore be calculated from the transpiration rate and humidity gradient. This allows scientists to investigate how stomata respond to changes in environmental conditions, such as light intensity and concentrations of gases such as water vapor, carbon dioxide, and ozone . Evaporation ( E ) can be calculated as where e i and e

2900-495: Is different from Wikidata All article disambiguation pages All disambiguation pages Stoma The term is usually used collectively to refer to the entire stomatal complex, consisting of the paired guard cells and the pore itself, which is referred to as the stomatal aperture. Air, containing oxygen , which is used in respiration , and carbon dioxide , which is used in photosynthesis , passes through stomata by gaseous diffusion . Water vapour diffuses through

3000-567: Is little evidence of the evolution of stomata in the fossil record, but they had appeared in land plants by the middle of the Silurian period. They may have evolved by the modification of conceptacles from plants' alga-like ancestors. However, the evolution of stomata must have happened at the same time as the waxy cuticle was evolving – these two traits together constituted a major advantage for early terrestrial plants. There are three major epidermal cell types which all ultimately derive from

3100-436: Is one way plants have responded to the increase in concentration of atmospheric CO 2 ([CO 2 ] atm ). Although changes in [CO 2 ] atm response is the least understood mechanistically, this stomatal response has begun to plateau where it is soon expected to impact transpiration and photosynthesis processes in plants. Drought inhibits stomatal opening, but research on soybeans suggests moderate drought does not have

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3200-447: Is oxygen as a component of water, the major constituent of lifeforms. Oxygen in Earth's atmosphere is produced by biotic photosynthesis , in which photon energy in sunlight is captured by chlorophyll to split water molecules and then react with carbon dioxide to produce carbohydrates and oxygen is released as a byproduct . Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by

3300-441: Is produced when N (made abundant from CNO burning) captures a He nucleus, making O common in the helium-rich zones of evolved, massive stars . Fifteen radioisotopes have been characterized, ranging from O to O. The most stable are O with a half-life of 122.24 seconds and O with a half-life of 70.606 seconds. All of the remaining radioactive isotopes have half-lives that are less than 27 seconds and

3400-408: Is reasonably and simply described as a covalent double bond that results from the filling of molecular orbitals formed from the atomic orbitals of the individual oxygen atoms, the filling of which results in a bond order of two. More specifically, the double bond is the result of sequential, low-to-high energy, or Aufbau , filling of orbitals, and the resulting cancellation of contributions from

3500-441: Is severely limited by the capacity to store fixed carbon in the vacuoles, so it is preferable only when water is severely limited. However, most plants do not have CAM and must therefore open and close their stomata during the daytime, in response to changing conditions, such as light intensity, humidity, and carbon dioxide concentration. When conditions are conducive to stomatal opening (e.g., high light intensity and high humidity),

3600-712: Is temperature-dependent, and about twice as much ( 14.6  mg/L ) dissolves at 0 °C than at 20 °C ( 7.6  mg/L ). At 25 °C and 1 standard atmosphere (101.3  kPa ) of air, freshwater can dissolve about 6.04  milliliters  (mL) of oxygen per liter , and seawater contains about 4.95 mL per liter. At 5 °C the solubility increases to 9.0 mL (50% more than at 25 °C) per liter for freshwater and 7.2 mL (45% more) per liter for sea water. Oxygen condenses at 90.20  K (−182.95 °C, −297.31 °F) and freezes at 54.36 K (−218.79 °C, −361.82 °F). Both liquid and solid O 2 are clear substances with

3700-435: Is the result of the oxygen cycle . This biogeochemical cycle describes the movement of oxygen within and between its three main reservoirs on Earth: the atmosphere, the biosphere, and the lithosphere . The main driving factor of the oxygen cycle is photosynthesis , which is responsible for modern Earth's atmosphere. Photosynthesis releases oxygen into the atmosphere, while respiration , decay , and combustion remove it from

3800-457: Is unusual among the planets of the Solar System in having such a high concentration of oxygen gas in its atmosphere: Mars (with 0.1% O 2 by volume) and Venus have much less. The O 2 surrounding those planets is produced solely by the action of ultraviolet radiation on oxygen-containing molecules such as carbon dioxide. The unusually high concentration of oxygen gas on Earth

3900-517: Is usually given priority in the discovery. The French chemist Antoine Laurent Lavoisier later claimed to have discovered the new substance independently. Priestley visited Lavoisier in October 1774 and told him about his experiment and how he liberated the new gas. Scheele had also dispatched a letter to Lavoisier on September 30, 1774, which described his discovery of the previously unknown substance, but Lavoisier never acknowledged receiving it (a copy of

4000-608: The Earth , the Moon , Mars , and meteorites , but were long unable to obtain reference values for the isotope ratios in the Sun , believed to be the same as those of the primordial solar nebula . Analysis of a silicon wafer exposed to the solar wind in space and returned by the crashed Genesis spacecraft has shown that the Sun has a higher proportion of oxygen-16 than does the Earth. The measurement implies that an unknown process depleted oxygen-16 from

4100-463: The Earth's crust in the form of various oxides such as water , carbon dioxide , iron oxides and silicates . All eukaryotic organisms , including plants , animals , fungi , algae and most protists , need oxygen for cellular respiration , which extracts chemical energy by the reaction of oxygen with organic molecules derived from food and releases carbon dioxide as a waste product. In aquatic animals , dissolved oxygen in water

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4200-556: The Greek roots ὀξύς (oxys) ( acid , literally 'sharp', from the taste of acids) and -γενής (-genēs) (producer, literally begetter), because he mistakenly believed that oxygen was a constituent of all acids. Chemists (such as Sir Humphry Davy in 1812) eventually determined that Lavoisier was wrong in this regard, but by then the name was too well established. Oxygen entered the English language despite opposition by English scientists and

4300-405: The leaf are saturated with water vapour , which exits the leaf through the stomata in a process known as transpiration . Therefore, plants cannot gain carbon dioxide without simultaneously losing water vapour. Ordinarily, carbon dioxide is fixed to ribulose 1,5-bisphosphate (RuBP) by the enzyme RuBisCO in mesophyll cells exposed directly to the air spaces inside the leaf. This exacerbates

4400-470: The shells and skeletons of marine organisms to determine the climate millions of years ago (see oxygen isotope ratio cycle ). Seawater molecules that contain the lighter isotope , oxygen-16, evaporate at a slightly faster rate than water molecules containing the 12% heavier oxygen-18, and this disparity increases at lower temperatures. During periods of lower global temperatures, snow and rain from that evaporated water tends to be higher in oxygen-16, and

4500-430: The thermal decomposition of potassium nitrate . In Bugaj's view, the isolation of oxygen and the proper association of the substance to that part of air which is required for life, provides sufficient evidence for the discovery of oxygen by Sendivogius. This discovery of Sendivogius was however frequently denied by the generations of scientists and chemists which succeeded him. It is also commonly claimed that oxygen

4600-553: The 17th and the 18th century but none of them recognized it as a chemical element . This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory , which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher , and modified by the chemist Georg Ernst Stahl by 1731, phlogiston theory stated that all combustible materials were made of two parts. One part, called phlogiston,

4700-531: The 2s electrons, after sequential filling of the low σ and σ orbitals; σ overlap of the two atomic 2p orbitals that lie along the O–O molecular axis and π overlap of two pairs of atomic 2p orbitals perpendicular to the O–O molecular axis, and then cancellation of contributions from the remaining two 2p electrons after their partial filling of the π orbitals. This combination of cancellations and σ and π overlaps results in dioxygen's double-bond character and reactivity, and

4800-527: The American scientist Robert H. Goddard became the first person to develop a rocket engine that burned liquid fuel; the engine used gasoline for fuel and liquid oxygen as the oxidizer . Goddard successfully flew a small liquid-fueled rocket 56 m at 97 km/h on March 16, 1926, in Auburn, Massachusetts , US. In academic laboratories, oxygen can be prepared by heating together potassium chlorate mixed with

4900-494: The Half-Blood Prince Stroma Buttrose (born 1929), Australian architect Other [ edit ] Stroma (musical group) , a New Zealand chamber music ensemble Island of Stroma , a now uninhabited island off the northern coast of Scotland See also [ edit ] Stromae (born 1985), Belgian singer Struma (disambiguation) Stromatolite , layered sedimentary structure formed by

5000-478: The Philosopher's Stone drawn from the source of nature and manual experience"] (1604) described a substance contained in air, referring to it as 'cibus vitae' (food of life, ) and according to Polish historian Roman Bugaj, this substance is identical with oxygen. Sendivogius, during his experiments performed between 1598 and 1604, properly recognized that the substance is equivalent to the gaseous byproduct released by

5100-438: The Sun's disk of protoplanetary material prior to the coalescence of dust grains that formed the Earth. Oxygen presents two spectrophotometric absorption bands peaking at the wavelengths 687 and 760  nm . Some remote sensing scientists have proposed using the measurement of the radiance coming from vegetation canopies in those bands to characterize plant health status from a satellite platform. This approach exploits

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5200-512: The atmosphere enhances photosynthesis, reduce transpiration, and increase water use efficiency (WUE). Increased biomass is one of the effects with simulations from experiments predicting a 5–20% increase in crop yields at 550 ppm of CO 2 . Rates of leaf photosynthesis were shown to increase by 30–50% in C3 plants, and 10–25% in C4 under doubled CO 2 levels. The existence of a feedback mechanism results

5300-493: The atmosphere. In the present equilibrium, production and consumption occur at the same rate. Free oxygen also occurs in solution in the world's water bodies. The increased solubility of O 2 at lower temperatures (see Physical properties ) has important implications for ocean life, as polar oceans support a much higher density of life due to their higher oxygen content. Water polluted with plant nutrients such as nitrates or phosphates may stimulate growth of algae by

5400-480: The best suited species such as heat and drought resistant crop varieties that could naturally evolve to the change in the face of food security challenges. Oxygen Oxygen is a chemical element with the symbol   O and atomic number 8. It is a member of the chalcogen group in the periodic table , a highly reactive nonmetal , and a potent oxidizing agent that readily forms oxides with most elements as well as with other compounds . Oxygen

5500-412: The bond order from three to two. Because of its unpaired electrons, triplet oxygen reacts only slowly with most organic molecules, which have paired electron spins; this prevents spontaneous combustion. In the triplet form, O 2 molecules are paramagnetic . That is, they impart magnetic character to oxygen when it is in the presence of a magnetic field, because of the spin magnetic moments of

5600-512: The day sucrose plays a larger role in regulating stomatal opening. Zeaxanthin in guard cells acts as a blue light photoreceptor which mediates the stomatal opening. The effect of blue light on guard cells is reversed by green light, which isomerizes zeaxanthin. Stomatal density and aperture (length of stomata) varies under a number of environmental factors such as atmospheric CO 2 concentration, light intensity, air temperature and photoperiod (daytime duration). Decreasing stomatal density

5700-444: The diatomic elemental molecules in those gases. The first commercial method of producing oxygen was chemical, the so-called Brin process involving a reversible reaction of barium oxide . It was invented in 1852 and commercialized in 1884, but was displaced by newer methods in early 20th century. By the late 19th century scientists realized that air could be liquefied and its components isolated by compressing and cooling it. Using

5800-404: The diffusion of water back out of the cell by osmosis . This makes the cell plasmolysed , which results in the closing of the stomatal pores. Guard cells have more chloroplasts than the other epidermal cells from which guard cells are derived. Their function is controversial. The degree of stomatal resistance can be determined by measuring leaf gas exchange of a leaf. The transpiration rate

5900-426: The dominant allele , but in the ‘wild type’ recessive allele showed a large increase, both in response to rising CO 2 levels in the atmosphere. These studies imply the plants response to changing CO 2 levels is largely controlled by genetics. The CO 2 fertiliser effect has been greatly overestimated during Free-Air Carbon dioxide Enrichment (FACE) experiments where results show increased CO 2 levels in

6000-466: The electron spins are paired. It is much more reactive with common organic molecules than is normal (triplet) molecular oxygen. In nature, singlet oxygen is commonly formed from water during photosynthesis, using the energy of sunlight. It is also produced in the troposphere by the photolysis of ozone by light of short wavelength and by the immune system as a source of active oxygen. Carotenoids in photosynthetic organisms (and possibly animals) play

6100-563: The fact that the Englishman Priestley had first isolated the gas and written about it. This is partly due to a poem praising the gas titled "Oxygen" in the popular book The Botanic Garden (1791) by Erasmus Darwin , grandfather of Charles Darwin . John Dalton 's original atomic hypothesis presumed that all elements were monatomic and that the atoms in compounds would normally have the simplest atomic ratios with respect to one another. For example, Dalton assumed that water's formula

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6200-569: The family Crassulaceae, which includes the species in which the CAM process was first discovered) open their stomata at night (when water evaporates more slowly from leaves for a given degree of stomatal opening), use PEPcase to fix carbon dioxide and store the products in large vacuoles. The following day, they close their stomata and release the carbon dioxide fixed the previous night into the presence of RuBisCO. This saturates RuBisCO with carbon dioxide, allowing minimal photorespiration. This approach, however,

6300-399: The first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium . In his work Pneumatica , Philo observed that inverting a vessel over a burning candle and surrounding the vessel's neck with water resulted in some water rising into the neck. Philo incorrectly surmised that parts of the air in

6400-527: The fluid between grana, where carbohydrate-forming reactions occur in the chloroplasts of photosynthetic plant cells Stromal cell , a connective tissue cell of any organ; supports the function of the parenchyma The nonmalignant cells which are present in the tumor microenvironment; see Tumor microenvironment § Stromal cells People [ edit ] Freddie Stroma (born 1987), British actor known for playing Cormac McLaggen in Harry Potter and

6500-645: The genes which encode these factors may alter the development of stomata in the epidermis. For example, a mutation in one gene causes more stomata that are clustered together, hence is called Too Many Mouths ( TMM ). Whereas, disruption of the SPCH (SPeecCHless) gene prevents stomatal development all together.  Inhibition of stomatal production can occur by the activation of EPF1, which activates TMM/ERL, which together activate YODA. YODA inhibits SPCH, causing SPCH activity to decrease, preventing asymmetrical cell division that initiates stomata formation. Stomatal development

6600-495: The growth of bacteria or algae Stromer (disambiguation) Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title Stroma . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Stroma&oldid=1218925728 " Category : Disambiguation pages Hidden categories: Short description

6700-400: The guard cells, whose ends are held firmly in place by surrounding epidermal cells, the two guard cells lengthen by bowing apart from one another, creating an open pore through which gas can diffuse. When the roots begin to sense a water shortage in the soil, abscisic acid (ABA) is released. ABA binds to receptor proteins in the guard cells' plasma membrane and cytosol, which first raises

6800-399: The idea; instead, it was based on observations of what happens when something burns, that most common objects appear to become lighter and seem to lose something in the process. Polish alchemist , philosopher , and physician Michael Sendivogius (Michał Sędziwój) in his work De Lapide Philosophorum Tractatus duodecim e naturae fonte et manuali experientia depromti ["Twelve Treatises on

6900-499: The letter was found in Scheele's belongings after his death). Lavoisier conducted the first adequate quantitative experiments on oxidation and gave the first correct explanation of how combustion works. He used these and similar experiments, all started in 1774, to discredit the phlogiston theory and to prove that the substance discovered by Priestley and Scheele was a chemical element . In one experiment, Lavoisier observed that there

7000-450: The lower surface are hypostomatous , and leaves with stomata only on the upper surface are epistomatous or hyperstomatous . Size varies across species, with end-to-end lengths ranging from 10 to 80 μm and width ranging from a few to 50 μm. Carbon dioxide , a key reactant in photosynthesis , is present in the atmosphere at a concentration of about 400 ppm. Most plants require the stomata to be open during daytime. The air spaces in

7100-428: The majority of these have half-lives that are less than 83 milliseconds. The most common decay mode of the isotopes lighter than O is β decay to yield nitrogen, and the most common mode for the isotopes heavier than O is beta decay to yield fluorine . Oxygen is the most abundant chemical element by mass in the Earth's biosphere , air, sea and land. Oxygen is the third most abundant chemical element in

7200-418: The most successful and biodiverse terrestrial clade , oxygen is directly conducted to the internal tissues via a deep network of airways . Many major classes of organic molecules in living organisms contain oxygen atoms, such as proteins , nucleic acids , carbohydrates and fats , as do the major constituent inorganic compounds of animal shells, teeth, and bone. Most of the mass of living organisms

7300-494: The nitroaereus must have combined with it. He also thought that the lungs separate nitroaereus from air and pass it into the blood and that animal heat and muscle movement result from the reaction of nitroaereus with certain substances in the body. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract "De respiratione". Robert Hooke , Ole Borch , Mikhail Lomonosov , and Pierre Bayen all produced oxygen in experiments in

7400-431: The organic ion malate is produced in guard cells. This increase in solute concentration lowers the water potential inside the cell, which results in the diffusion of water into the cell through osmosis . This increases the cell's volume and turgor pressure . Then, because of rings of cellulose microfibrils that prevent the width of the guard cells from swelling, and thus only allow the extra turgor pressure to elongate

7500-425: The outermost (L1) tissue layer of the shoot apical meristem , called protodermal cells: trichomes , pavement cells and guard cells, all of which are arranged in a non-random fashion. An asymmetrical cell division occurs in protodermal cells resulting in one large cell that is fated to become a pavement cell and a smaller cell called a meristemoid that will eventually differentiate into the guard cells that surround

7600-477: The pH of the cytosol of the cells and cause the concentration of free Ca to increase in the cytosol due to influx from outside the cell and release of Ca from internal stores such as the endoplasmic reticulum and vacuoles. This causes the chloride (Cl ) and organic ions to exit the cells. Second, this stops the uptake of any further K into the cells and, subsequently, the loss of K . The loss of these solutes causes an increase in water potential , which results in

7700-445: The past 400,000 years experienced below 280 ppm CO 2 . From this figure, it is highly probable that genotypes of today’s plants have diverged from their pre-industrial relatives. The gene HIC (high carbon dioxide) encodes a negative regulator for the development of stomata in plants. Research into the HIC gene using Arabidopsis thaliana found no increase of stomatal development in

7800-451: The photosynthetic activities of autotrophs such as cyanobacteria , chloroplast -bearing algae and plants. A much rarer triatomic allotrope of oxygen , ozone ( O 3 ), strongly absorbs the UVB and UVC wavelengths and forms a protective ozone layer at the lower stratosphere , which shields the biosphere from ionizing ultraviolet radiation . However, ozone present at the surface

7900-498: The presence of some, if not all, pathogens. However, pathogenic bacteria applied to Arabidopsis plant leaves can release the chemical coronatine , which induce the stomata to reopen. Photosynthesis , plant water transport ( xylem ) and gas exchange are regulated by stomatal function which is important in the functioning of plants. Stomata are responsive to light with blue light being almost 10 times as effective as red light in causing stomatal response. Research suggests this

8000-498: The receptor level like the ERL and TMM receptors. However, a low concentration of auxin allows for equal division of a guard mother cell and increases the chance of producing guard cells. Most angiosperm trees have stomata only on their lower leaf surface. Poplars and willows have them on both surfaces. When leaves develop stomata on both leaf surfaces, the stomata on the lower surface tend to be larger and more numerous, but there can be

8100-455: The remainder of this article. Trioxygen ( O 3 ) is usually known as ozone and is a very reactive allotrope of oxygen that is damaging to lung tissue. Ozone is produced in the upper atmosphere when O 2 combines with atomic oxygen made by the splitting of O 2 by ultraviolet (UV) radiation. Since ozone absorbs strongly in the UV region of the spectrum , the ozone layer of

8200-414: The seawater left behind tends to be higher in oxygen-18. Marine organisms then incorporate more oxygen-18 into their skeletons and shells than they would in a warmer climate. Paleoclimatologists also directly measure this ratio in the water molecules of ice core samples as old as hundreds of thousands of years. Planetary geologists have measured the relative quantities of oxygen isotopes in samples from

8300-406: The stomata into the atmosphere as part of a process called transpiration . Stomata are present in the sporophyte generation of the vast majority of land plants , with the exception of liverworts , as well as some mosses and hornworts . In vascular plants the number, size and distribution of stomata varies widely. Dicotyledons usually have more stomata on the lower surface of the leaves than

8400-417: The stomatal crypts are very pronounced. However, dry climates are not the only places where they can be found. The following plants are examples of species with stomatal crypts or antechambers: Nerium oleander , conifers, Hakea and Drimys winteri which is a species of plant found in the cloud forest . Stomata are holes in the leaf by which pathogens can enter unchallenged. However, stomata can sense

8500-455: The transpiration problem for two reasons: first, RuBisCo has a relatively low affinity for carbon dioxide, and second, it fixes oxygen to RuBP, wasting energy and carbon in a process called photorespiration . For both of these reasons, RuBisCo needs high carbon dioxide concentrations, which means wide stomatal apertures and, as a consequence, high water loss. Narrower stomatal apertures can be used in conjunction with an intermediary molecule with

8600-486: The universe, after hydrogen and helium. About 0.9% of the Sun 's mass is oxygen. Oxygen constitutes 49.2% of the Earth's crust by mass as part of oxide compounds such as silicon dioxide and is the most abundant element by mass in the Earth's crust . It is also the major component of the world's oceans (88.8% by mass). Oxygen gas is the second most common component of the Earth's atmosphere , taking up 20.8% of its volume and 23.1% of its mass (some 10 tonnes). Earth

8700-401: The unpaired electrons in the molecule, and the negative exchange energy between neighboring O 2 molecules. Liquid oxygen is so magnetic that, in laboratory demonstrations, a bridge of liquid oxygen may be supported against its own weight between the poles of a powerful magnet. Singlet oxygen is a name given to several higher-energy species of molecular O 2 in which all

8800-435: The upper atmosphere functions as a protective radiation shield for the planet. Near the Earth's surface, it is a pollutant formed as a by-product of automobile exhaust . At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft . The metastable molecule tetraoxygen ( O 4 ) was discovered in 2001, and was assumed to exist in one of the six phases of solid oxygen . It

8900-456: The upper surface. Monocotyledons such as onion , oat and maize may have about the same number of stomata on both leaf surfaces. In plants with floating leaves, stomata may be found only on the upper epidermis and submerged leaves may lack stomata entirely. Most tree species have stomata only on the lower leaf surface. Leaves with stomata on both the upper and lower leaf surfaces are called amphistomatous leaves; leaves with stomata only on

9000-451: The vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philo's work by observing that a portion of air is consumed during combustion and respiration . In the late 17th century, Robert Boyle proved that air is necessary for combustion. English chemist John Mayow (1641–1679) refined this work by showing that fire requires only

9100-428: Was HO, leading to the conclusion that the atomic mass of oxygen was 8 times that of hydrogen, instead of the modern value of about 16. In 1805, Joseph Louis Gay-Lussac and Alexander von Humboldt showed that water is formed of two volumes of hydrogen and one volume of oxygen; and by 1811 Amedeo Avogadro had arrived at the correct interpretation of water's composition, based on what is now called Avogadro's law and

9200-408: Was first discovered by Swedish pharmacist Carl Wilhelm Scheele . He had produced oxygen gas by heating mercuric oxide (HgO) and various nitrates in 1771–72. Scheele called the gas "fire air" because it was then the only known agent to support combustion. He wrote an account of this discovery in a manuscript titled Treatise on Air and Fire , which he sent to his publisher in 1775. That document

9300-451: Was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx . Highly combustible materials that leave little residue , such as wood or coal, were thought to be made mostly of phlogiston; non-combustible substances that corrode, such as iron, contained very little. Air did not play a role in phlogiston theory, nor were any initial quantitative experiments conducted to test

9400-491: Was independently developed in 1895 by German engineer Carl von Linde and British engineer William Hampson . Both men lowered the temperature of air until it liquefied and then distilled the component gases by boiling them off one at a time and capturing them separately. Later, in 1901, oxyacetylene welding was demonstrated for the first time by burning a mixture of acetylene and compressed O 2 . This method of welding and cutting metal later became common. In 1923,

9500-445: Was no overall increase in weight when tin and air were heated in a closed container. He noted that air rushed in when he opened the container, which indicated that part of the trapped air had been consumed. He also noted that the tin had increased in weight and that increase was the same as the weight of the air that rushed back in. This and other experiments on combustion were documented in his book Sur la combustion en général , which

9600-462: Was not sensibly different from that of common air , but I fancied that my breast felt peculiarly light and easy for some time afterwards." Priestley published his findings in 1775 in a paper titled "An Account of Further Discoveries in Air", which was included in the second volume of his book titled Experiments and Observations on Different Kinds of Air . Because he published his findings first, Priestley

9700-408: Was proven in 2006 that this phase, created by pressurizing O 2 to 20  GPa , is in fact a rhombohedral O 8 cluster . This cluster has the potential to be a much more powerful oxidizer than either O 2 or O 3 and may therefore be used in rocket fuel . A metallic phase was discovered in 1990 when solid oxygen is subjected to a pressure of above 96 GPa and it

9800-499: Was published in 1777. In the meantime, on August 1, 1774, an experiment conducted by the British clergyman Joseph Priestley focused sunlight on mercuric oxide contained in a glass tube, which liberated a gas he named "dephlogisticated air". He noted that candles burned brighter in the gas and that a mouse was more active and lived longer while breathing it. After breathing the gas himself, Priestley wrote: "The feeling of it to my lungs

9900-458: Was published in 1777. In that work, he proved that air is a mixture of two gases; 'vital air', which is essential to combustion and respiration, and azote (Gk. ἄζωτον "lifeless"), which did not support either. Azote later became nitrogen in English, although it has kept the earlier name in French and several other European languages. Lavoisier renamed 'vital air' to oxygène in 1777 from

10000-420: Was shown in 1998 that at very low temperatures, this phase becomes superconducting . Oxygen dissolves more readily in water than nitrogen, and in freshwater more readily than in seawater. Water in equilibrium with air contains approximately 1 molecule of dissolved O 2 for every 2 molecules of N 2 (1:2), compared with an atmospheric ratio of approximately 1:4. The solubility of oxygen in water

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