Current Affairs 11th Class

Many external and internal factors affecting the rate of respiration are as follows : (1) External factors (i) Temperature : With every \[10{}^\circ C\] rise of temperature from \[0{}^\circ C\] to \[30{}^\circ C\]the rate of respiration increases 2 to 2.5 times (i.e., temperature coefficient \[({{Q}_{10}}{}^\circ )\] is = 2 to 2.5), following Vant Hoff’s Law. Maximum rate of respiration takes place at \[{{30}^{o}}C,\]there is an initial rise, soon followed by a decline. Higher the temperature above this limit, more is the initial rise but more is the decline and earlier is the decline in the rate of respiration. Probably this is due to denaturation of enzymes at high temperature. Below \[0{}^\circ C\]the rate of respiration is greatly reduced although in some plants respiration takes place even at \[-20{}^\circ C.\] Dormant seeds kept at \[{{50}^{o}}C\]survive. (ii) Supply of oxidisable food : Increase in soluble food content readily available for utilization as respiratory substrate, generally leads to an increase in the rate of respiration upto a certain point when some other factor becomes limiting.  (iii) Oxygen concentration of the atmosphere : The amount of oxygen in the environment of plants is increased or reduced upto quite low values the rate of respiration is not effected. On decreasing the amount of oxygen to 1.9% in the environment aerobic respiration become negligible (extinction point of aerobic respiration) but anaerobic respiration takes place. (iv) Oxygen poisoning : The significant fall in respiration rate was observed in many tissues in pure \[{{O}_{2}},\]even at N.T.P. This inhibiting effect was also observed in green peas when they are exposed to pure oxygen exerting a pressure of 5 atm- the respiration rate fall rapidly. The oxygen poisoning effect was reversible, if the exposure to high oxygen pressure was not too prolonged. (v) Water : With increase in the amount of water the rate of respiration increases. In dry seeds, which have \[8-12%\] of water the rate of respiration is very low but as the seeds imbibe water the respiration increases. As water is necessary for activity of enzymes. (vi) Light : Respiration takes place in night also which shows that light is not essential for respiration. But light effects the rate of respiration indirectly by increasing the rate of photosynthesis due to which concentration of respiratory substrates is increased. More the respiratory substrate more is the rate of respiration. (vii) Carbon dioxide\[(C{{O}_{2}})\]:  If the amount of CO2 in the air is more than the usual rate of respiration is decreased. Germination of seeds is reduced and rate of growth falls down. Heath, (1950) has shown that the stomata are closed at higher cone. of \[C{{O}_{2}},\] due to which oxygen does not penetrate the leaf and rate of respiration is lowered. (viii) Inorganic salts : The chlorides of alkali cations of Na  and K, as also the divalent cations of Li, and Ca and Mg, generally increase the rate of respiration as measured by the amount of \[C{{O}_{2}}\]evolved. Monovalent chlorides of K and Na increases the rate of respiration, while more...

Chloroplast (The site of photosynthesis) : Chloroplast are green plastids which function as the site of photosynthesis in eukaryotic photoautotrops. Photosynthetic unit can be defined as number of pigment molecules required to affect a photochemical act, that is the release of a molecule of oxygen. Park and Biggins (1964) gave the term quantasome for photosynthetic units is equivalent to 230 chlorophyll molecules. Chloroplast pigments : Pigments are the organic molecules that absorb light of specific wavelengths in the visible region due to presence of conjugated double bonds in their structures. The chloroplast pigments are fat soluble and are located in the lipid part of the thylakoid membranes. There is a wide range of chloroplastic pigments which constitute more than 5% of the total dry weight of the chloroplast. They are grouped under two main categories : (1) Chlorophylls : Chlorophyll 'a' is found in all the oxygen evolving photosynthetic plants except photosynthetic bacteria. Reaction centre of photosynthesis is formed of chlorophyll a. It occurs in several spectrally distinct forms which perform distinct roles in photosynthesis (e.g., \[Chl{{a}_{680}}\,\,or\,\,{{P}_{680}},\text{ }Chl{{a}_{700}}\,\,or\,\,{{P}_{700}},\]etc.). It directly takes part in photochemical reaction. Hence, it is termed as primary photosynthetic pigment. Other photosynthetic pigments including chlorophyll b, c, d and e ; carotenoids and phycobilins are called accessory pigments because they do not directly take part in photochemical act. They absorb specific wavelengths of light and transfer energy finally to chlorophyll a through electron spin resonance. Chlorophyll a is bluish-green while chlorophyll b is olive-green. Both are soluble in organic solvents like alcohol, acetone etc. Chlorophyll is a green pigment because it does not absorb green light (but reflect green light) Chlorophyll \[a\,\,({{C}_{55}}{{H}_{72}}{{O}_{5}}{{N}_{4}}Mg)\] possesses \[C{{H}_{3}}\](methyl group), which is replaced by \[CHO\](an aldehyde) group in chlorophyll \[b\,\,({{C}_{55}}{{H}_{70}}{{O}_{6}}{{N}_{4}}Mg).\] Chlorophyll molecule is made up of a squarish tetrapyrrolic ring known as head and a phytol alcohol called tail. The magnesium atom is present in the central position of tetrapyrrolic ring. The four pyrrole rings of porphyrin head are linked together by methine \[(CH=)\] groups forming a ring system. When central Mg is replaced by Fe, the chlorophyll becomes a green pigment called 'cytochrome' which is used in photosynthesis (Photophosphorylation) and respiration both. (2) Carotenoids : They are sometimes called lipochromes due to their fat soluble nature. They are lipids and found in non-green parts of plants. Light is not necessary for their biosynthesis. Carotenoids absorb light energy and transfer it to Chl. a and thus act as accessory pigments. They protect the chlorophyll molecules from photo-oxidation by picking up nascent oxygen and converting it into harmless molecular stage. Carotenoids can be classified into two groups namely carotenes and xanthophyll. (i) Carotenes : They are orange red in colour and have general formula \[{{C}_{40}}{{H}_{56}}.\]They are isolated from carrot. They are found in all groups of plants i.e., from algae to angiosperms. Some of the common carotenes are \[\alpha ,\beta ,\gamma \]  and \[\delta \] carotene; phytotene, lycopene, neurosporene etc. The lycopene is a red pigment found in ripe tomato and red pepper more...

Decker and Tio (1959) reported that light induces oxidation of photosynthetic intermediates with the help of oxygen in tobacco. It is called as photorespiration. The photorespiration is defined by Krotkov (1963) as an extra input of \[{{O}_{2}}\] and extra release of \[C{{O}_{2}}\] by green plants is light. Photorespiration is the uptake of \[{{O}_{2}}\] and release of \[C{{O}_{2}}\] in light and results from the biosynthesis of glycolate in chloroplasts and subsequent metabolism of glycolate acid in the same leaf cell. Biochemical mechanism for photorespiration is also called glycolate metabolism. Loss of energy occurs during this process. The process of photorespiration involves the involvement of chloroplasts, peroxisomes and mitochondria. RuBP carboxylase also catalyses another reaction which interferes with the successful functioning of Calvin cycle.     Biochemical mechanism (1) Ribulose-1, 5-biphosphate \[\xrightarrow{{{O}_{2}}}\] 2 Phoshoglycolic acid + 3 Phoshoglyceric acid   (2) 2 Phosphoglycolic acid \[+{{H}_{2}}O\xrightarrow{Phosphatase}\] Glycolic acid + Phosphoric acid. (3) Glycolic acid \[+{{O}_{2}}\underset{\text{Oxidase}}{\mathop{\xrightarrow{\text{Glycolic}\,\text{acid}}}}\,\] Glyoxylic acid\[+{{H}_{2}}{{O}_{2}}\] \[2{{H}_{2}}{{O}_{2}}\xrightarrow{\text{Catalase}}2{{H}_{2}}O+{{O}_{2}}\] (4) Glyoxylic acid + Glutamic acid \[\underset{\text{transaminase}}{\mathop{\xrightarrow{\text{Glutamate}-\text{glyoxylate}}}}\,\] Glycine \[+\,\,\alpha -\]keto glutaric acid (5) 2 Glycine \[+{{H}_{2}}O+NA{{D}^{+}}\xrightarrow{{}}\]Serine\[+C{{O}_{2}}+N{{H}_{3}}+NADH\] (6) Serine + Glyoxylic acid \[\xrightarrow{{}}\] Hydroxypyruvic acid + Glycine Hydroxypyruvic acid \[\xrightarrow{{}}\] Glyceric acid (7) Glyceric acid + ATP ® 3 phosphoglyceric acid + ADP + phosphate Importance of photorespiration : Photorespiration is quite different from respiration as no ATP or NADH are produced. Moreover, the process is harmful to plants because as much as half the photosynthetically fixed carbon dioxide (in the form of RuBP) may be lost into the atmosphere through this process. Any increase in \[{{O}_{2}}\] concentration would favour the uptake of \[{{O}_{2}}\] rather than \[C{{O}_{2}}\] and thus, inhibit photosynthesis for this rubisco functions as RuBP oxygenase. Photorespiration is closely related to \[C{{O}_{2}}\] compensation point and occurs only in those plants which have high \[C{{O}_{2}}\] compensation point such as \[{{C}_{3}}\] plants. Photorespiration generally occurs in temperate plants. Few photorespiring plants are : Rice, bean, wheat, barley etc. Inhibitors of glycolic acid oxidase such as hydroxy sulphonates inhibit the process of photorespiration. Unlike usual mitochondria respiration neither reduced coenzymes are generated in photorespiration nor the oxidation of glycolate is coupled with the formation of ATP molecules. Photorespiration (\[{{C}_{2}}\] cycle) is enhanced by bright light, high temperature, high oxygen and low \[C{{O}_{2}}\]concentration.

Photosynthesis is an oxidation reduction process in which water is oxidised to release O2 and CO2 is reduced to form starch and sugars. Scientists have shown that photosynthesis is completed in two phases. (1) Light phase or Photochemical reactions or Light dependent reactions or Hill's reactions : During this stage energy from sunlight is absorbed and converted to chemical energy which is stored in ATP and \[NADPH+{{H}^{+}}.\] (2) Dark phase or Chemical dark reactions or Light independent reactions or Blackman reaction or Biosynthetic phase : During this stage carbohydrates are synthesized from carbon dioxide using the energy stored in the ATP and NADPH formed in the light dependent reactions. Evidence for light and dark reactions in photosynthesis : (1) Physical separation of chloroplast into grana and stroma fractions : It is now possible to separate grana and stroma fractions of chloroplast. If light is given to grana fraction in presence of suitable H-acceptor and in complete absence of \[C{{O}_{2}},\]then ATP and \[NADP{{H}_{2}}\]are produced (i.e., assimilatory powers). If these assimilatory powers (ATP and\[NADP{{H}_{2}}\]) are given to stroma fraction in presence of \[C{{O}_{2}}\]and absence of light, then carbohydrates are formed. (2) Experiments with intermittent light or Discontinuous light : Rate of photosynthesis is faster in intermittent light (Alternate light and dark periods) than in continuous light. It is because light reaction is much faster than dark reaction, so in continuous light, there is accumulation of ATP and \[NADP{{H}_{2}}\]and hence reduction in rate of photosynthesis but in discontinuous light, ATP and \[NADP{{H}_{2}}\]formed in light are fully consumed during dark in reduction of \[C{{O}_{2}}\] to carbohydrates. Accumulation of \[NADP{{H}_{2}}\] and ATP is prevented because they are not produced during dark periods. (3) Temperature coefficient studies : Blackman found that \[{{Q}_{10}}\] was greater than 2 in experiment when photosynthesis was rapid and that \[{{Q}_{10}}\] dropped from 2 often reaching unity, i.e., 1 when the rate of photosynthesis was low. These results show that in photosynthesis there is a dark reaction (\[{{Q}_{10}}\] more than 2) and a photochemical or light reaction (with \[{{Q}_{10}}\] being unity). \[{{Q}_{10}}=\frac{\text{Reaction}\,\text{rate}\,\text{of}\,(t+10){}^\circ C}{\text{Reaction}\,\text{at}\,t{}^\circ C}\] Light reaction (Photochemical reactions) : Light reaction occurs in grana fraction of chloroplast and in this reaction are included those activities, which are dependent on light. Assimilatory powers (ATP and\[NADP{{H}_{2}}\]) are mainly produced in this light reaction. Robin Hill (1939) first of all showed that if chloroplasts extracted from leaves of Stellaria media and Lamium album are suspended in a test tube containing suitable electron acceptors, e.g., Potassium ferroxalate (Some plants require only this chemical) and potassium ferricyanide, oxygen is released due to photochemical splitting of water. Under these conditions, no \[C{{O}_{2}}\]was consumed and no carbohydrate was produced, but light-driven reduction of the electron acceptors was accompained, by \[{{O}_{2}}\] evolution.    \[\underset{\begin{smallmatrix} \text{Electron} \\\text{acceptor} \end{smallmatrix}}{\mathop{4F{{e}^{3+}}}}\,+\underset{\begin{smallmatrix} \text{Electron} \\\,\,\text{donor} \end{smallmatrix}}{\mathop{2{{H}_{2}}O}}\,\overset{\,\,\,\,\,\,\,}{\longleftrightarrow}\underset{\begin{smallmatrix} \text{Reduced} \\\,\text{Product}\end{smallmatrix}}{\mathop{4F{{e}^{2+}}}}\,+4{{H}^{+}}+{{O}_{2}}\uparrow \]   The splitting of water during photosynthesis is called photolysis. This reaction on the name of its discoverer is known as Hill reaction. Hill reaction proves that (1) In photosynthesis oxygen is released from water. (2) Electrons more...

On the basis of discovery of Nicolas de Saussure that "The amount of \[{{O}_{2}}\] released from plants is equal to the amount of \[C{{O}_{2}}\] absorbed by plants", it was considered that \[{{O}_{2}}\] released in photosynthesis comes from \[C{{O}_{2}},\] but Ruben proved that this concept is wrong. In 1930, C.B. Van Niel proved that, sulphur bacteria use \[{{H}_{2}}S\](in place of water) and \[C{{O}_{2}}\] to synthesize carbohydrates as follows: \[6C{{O}_{2}}+12{{H}_{2}}S\xrightarrow{\,\,\,\,}{{C}_{6}}{{H}_{12}}{{O}_{6}}+6{{H}_{2}}O+12S\] This led Van Niel to the postulation that in green plants, water \[({{H}_{2}}O)\] is utilized in place of \[{{H}_{2}}S\] and \[{{O}_{2}}\] is evolved in place of sulphur (S). He indicated that water is electron donar in photosynthesis. \[6C{{O}_{2}}+12{{H}_{2}}O\xrightarrow{\,\,\,\,}{{C}_{6}}{{H}_{12}}{{O}_{6}}+6{{H}_{2}}O+6{{O}_{2}}\] This was confirmed by Ruben and Kamen in 1941 using Chlorella a green alga. They used isotopes of oxygen in water, i.e., \[{{H}_{2}}^{18}O\] instead of \[{{H}_{2}}O\] (normal) and noticed that liberated oxygen contains \[^{18}O\] of water and not of \[C{{O}_{2}}.\] The overall reaction can be given as under : \[6C{{O}_{2}}+12{{H}_{2}}^{18}O\underset{\text{Chlorophyll}}{\mathop{\xrightarrow{\text{Light}}}}\,{{C}_{6}}{{H}_{12}}{{O}_{6}}+{{6}^{18}}{{O}_{2}}+6{{H}_{2}}O\]

Before seventeenth century it was considered that plants take their food from the soil.
  • Van Helmont (1648) concluded that all food of the plant is derived from water and not from soil.
  • Stephen Hales (Father of Plant Physiology) (1727) reported that plants obtain a part of their nutrition from air and light may also play a role in this process.
  • Joseph Priestley (1772) demonstrated that green plants (mint plant) purify the foul air (i.e., Phlogiston), produced by burning of candle, and convert it into pure air (i.e., Dephlogiston).
  • Jan Ingen-Housz (1779) concluded by his experiment that purification of air was done by green parts of plant only and that too in the presence of sunlight. Green leaves and stalks liberate dephlogisticated air (Having \[{{O}_{2}}\]) during sunlight and phlogisticated air (Having \[C{{O}_{2}}\]) during dark.
  • Jean Senebier (1782) proved that plants absorb \[C{{O}_{2}}\]and release \[{{O}_{2}}\] in presence of light. He also showed that the rate of \[{{O}_{2}}\] evolution depends upon the rate of \[C{{O}_{2}}\]consumption.
  • Nicolus de Saussure (1804) showed the importance of water in the process of photosynthesis. He further showed that the amount of \[C{{O}_{2}}\]absorbed is equal to the amount of \[{{O}_{2}}\] released.
  • Julius Robert Mayer (1845) proposed that light has radiant energy and this radiant energy is converted to chemical energy by plants, which serves to maintain life of the plants and also animals.
  • Liebig (1845) indicated that main source of carbon in plants is \[C{{O}_{2}}.\]
  • Bousingault (1860) reported that the volume of \[C{{O}_{2}}\] absorbed is equal to volume of \[{{O}_{2}}\] evolved and that \[C{{O}_{2}}\] absorption and \[{{O}_{2}}\] evolution get start immediately after the plant was exposed to sunlight.
  • Julius Von Sachs (1862) demonstrated that first visible product of photosynthesis is starch. He also showed that chlorophyll is confined to the chloroplasts.
  • Melvin Calvin (1954) traced the path of carbon in photosynthesis (Associated with dark reactions) and gave the \[{{C}_{3}}\] cycle (Now named Calvin cycle). He was awarded Nobel prize in 1961 for the technique to trace metabolic pathway by using radioactive isotope.
  • Huber, Michel and Deisenhofer (1985) crystallised the photosynthetic reaction center from the purple photosynthetic bacterium, Rhodopseudomonas viridis. They analysed its structure by X-ray diffraction technique. In 1988 they were awarded Nobel prize in chemistry for this work.

Blackmann's law of limiting factors F.F. Blackmann (1905) proposed the law of limiting factors according to which 'when process is conditioned to its rapidity by a number of factors, the rate of process is limited by the pace of the slowest factor'.  is usually a limiting factor in photosynthesis under field conditions particularly on clear summer days under adequate water supply. Blackmann's law of limiting factor is modification of Liebig's law of minimum, which states that rate of process controlled by several factors is only as rapid as the slowest factor permits. Theory of three cardinal points was given by Sachs in 1860. According to this concept, there is minimum, optimum and maximum for each factor. For every factor, there is a minimum value when photosynthesis starts, an optimum value showing highest rate and a maximum value, above which photosynthesis fails to take place. Factors : The rate of photosynthetic process is affected by several external (Environmental) and internal factors. External factors (1) Light : The ultimate source of light for photosynthesis in green plants is solar radiation, which moves in the form of electromagnetic waves. Out of the total solar energy reaching to the earth about 2% is used in photosynthesis and about 10% is used in other metabolic activities. Light varies in intensity, quality (Wavelength) and duration. The effect of light on photosynthesis can be studied under these three headings. (i) Light intensity : The total light perceived by a plant depends on its general form (viz., height, size of leaves, etc.) and arrangement of leaves. Of the total light falling on a leaf, about 80% is absorbed, 10% is reflected and 10% is transmitted. In general, rate of photosynthesis is more in intense light than diffused light. (Upto 10% light is utilized in sugarcane, i.e., Most efficient converter). Another photosynthetic superstar of field growing plants is Oenothera claviformis (Winter evening-primrose), which utilizes about 8% light. However, this light intensity varies from plant to plant, e.g., more in heliophytes (sun loving plants) and less in sciophytes (shade loving plants). For a complete plant, rate of photosynthesis increases with increase in light intensity, except very high light intensity where 'Solarization' phenomenon occurs, i.e., photo-oxidation of different cellular components including chlorophyll occurs. It also affects the opening and closing of stomata thereby affecting the gaseous exchange. The value of light saturation at which further increase is not accompanied by an increase in uptake is called light saturation point. (ii) Light quality : Photosynthetic pigments absorb visible part of the radiation i.e.,  to For example, chlorophyll absorbs blue and red light. Usually plants show high rate of photosynthesis in the blue and red light. Maximum photosynthesis has been observed in red light than in blue light. The green light has minimum effect. On the other hand, red algae shows maximum photosynthesis in green light and brown algae in blue light. (iii) Duration of light : Longer duration of light period favours photosynthesis. Generally, if the plants get 10 to 12hrs light per more...

Some forms of bacteria obtain energy by chemosynthesis. This process of carbohydrate formation in which organisms use chemical reactions to obtain energy from inorganic compounds is called chemosynthesis. Such chemoautotrophic bacteria do not require light and synthesize all organic cell requirements from \[C{{O}_{2}}\] and \[{{H}_{2}}O\] and salts at the expense of oxidation of inorganic substances like (\[{{H}_{2}},N{{O}_{3}}^{},S{{O}_{4}}\]or carbonate). Some examples of chemosynthesis are : (1) Nitrifying bacteria : e.g., Nitrosomonas, Nitrosococcus, Nitrobacter etc. (2) Sulphur bacteria : e.g., Beggiatoa, Thiothrix and Thiobacillus. (3) Iron bacteria : e.g., Ferrobacillus, Leptothrix and Cladothrix. (4) Hydrogen bacteria : e.g., Bacillus pentotrophus (5) Carbon bacteria : e.g., Carboxydomonas, Bacillus oligocarbophilus.

Like green plants, some purple and green sulphur bacteria are capable of synthesizing their organic food in presence of light and in absence of \[{{O}_{2}},\]which is known as bacterial photosynthesis. Van Niel was the first to point out these similarities. Oxygen is not liberated in bacteria during process of photosynthesis. Their photosynthesis is non-oxygenic. Because bacteria use \[{{H}_{2}}S\]in place of water \[({{H}_{2}}O)\] as hydrogen donor. Photosynthetic bacteria are anaerobic. Only one type of pigment system (PSI) is found in bacteria except cyanobacteria which possess both PSI and PSII. Bacteria has two type of photosynthetic pigments. Bacteriochlorophyll and Bacterioviridin. The photosynthetic bacteria fall under three categories (1) Green sulphur bacteria : It contains chlorobium chlorophyll, which absorb 720-750nm (far red light) of wavelength of light. e.g., Chlorobium. (2) Purple sulphur bacteria : e.g., Chromatium. (3) Purple non-sulphur bacteria : e.g., Rhodospirillum, Rhodopseudomonas. Characteristics of bacterial photosynthesis are : (1) No definite chloroplasts but contain simple structures having pigments called chromatophores (term coined by Schmitz). (2) Contain chlorobium chlorophyll or bacterio-chlorophyll. (3) Use longer wavelengths of light \[(720-950nm).\] (4) No utilization of \[{{H}_{2}}O\](but use \[{{H}_{2}}S\]or other reduced organic and inorganic substances). (5) No evolution of \[{{O}_{2}}.\] (6) Photoreductant is \[NAD{{H}_{2}}(Not\,\,NADP{{H}_{2}}).\] (7) Only one photoact and hence one pigment system and thus one reaction centre, i.e., \[{{P}_{890}}.\] (8) Cyclic photophosphorylation is dominant. (9) It occurs in presence of light and in absence of \[{{O}_{2}}.\]

(1) Iron Source : It is present in the form of oxides in the soil. It is absorbed by the plants in ferric as well as ferrous state but metabolically it is active in ferrous state. Its requirement is intermediate between macro and micro-nutrients. Functions (i) Iron is a structural component of ferredoxin, flavoproteins, iron prophyrin proteins (Cytochromes, peroxidases, catalases, etc.) (ii) It plays important roles in energy conversion reactions of photosynthesis (phosphorylation) and respiration. (iii) It acts as activator of nitrate reductase and aconitase. (iv) It is essential for the synthesis of chlorophyll. Deficiency symptoms (i) Chlorosis particularly in younger leaves, the mature leaves remain unaffected. (ii) It inhibits chloroplast formation due to inhibition of protein synthesis. (iii) Stalks remain short and slender. (iv) Extensive interveinal white chlorosis in leaves. (v) It may develop necrosis aerobic respiration severely affected. (vi) In extreme deficiency scorching of leaf margins and tips may occur. (2) Manganese Source : Like iron, the oxide forms of manganese are common in soil. However, manganese dioxide (highly oxidised form) is not easily available to plants. It is absorbed from the soil in bivalent form \[(M{{n}^{++}}).\] Increased acidity leads to increase in solubility of manganese. In strong acidic soils, manganese may be present in toxic concentrations. Oxidising bacteria in soils render manganese unavailable to plants at pH ranging from 6.5 to 7.8. Functions (i) It acts as activator of enzymes of respiration (malic dehydrogenase and oxalosuccinic decarboxylase) and nitrogen metabolism (nitrite reductase). (ii) It is essential for the synthesis of chlorophyll. (iii) It is required in photosynthesis during photolysis of water. (iv) It decreases the solubility of iron by oxidation. Hence, abundance of manganese can lead to iron deficiency in plants. Deficiency symptoms (i) Chlorosis (interveinal) and necrosis of leaves. (ii) Chloroplasts lose chlorophyll, turn yellow green, vacuolated and finally perish. (iii) 'Grey spot disease' in oat appears due to the deficiency of manganese, which leads to total failure of crop. (iv) 'Marsh spot's in seeds of pea. (v) Deficiency symptoms develop in older leaves. (3) Copper Source : Copper occurs in almost every type of soil in the form of complex organic compounds. A very small amount of copper is found dissolved in the soil solution. It is found in natural deposits of chalcopyrite (CuFeS2). Functions   (i) It activates many enzymes and is a component of phenolases, ascorbic acid oxidase, tyrosinase, cytochrome oxidase. (ii) Copper is a constituent of plastocyanin, hence plays a role in photophosphorylation. (iii) It also maintains carbohydrate nitrogen balance. Deficiency symptoms (i) Both vegetative and reproductive growth are reduced. (ii) The most common symptoms of copper deficiency include a disease of fruit trees called 'exanthema' in which trees start yielding gums on bark and 'reclamation of crop plants', found in cereals and legumes. (iii) It also causes necrosis of the tip of the young leaves (e.g., Citrus). The disease is called 'die back'. (iv) Carbon dioxide absorption is decreased in copper deficient trees. (v) Wilting of entire plant occurs under acute more...


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