Q4. C3 plants use the Calvin cycle, but are relatively inefficient since RuBisCO can also react with O2 in a process called photorespiration. Thus, we find that C 4 plants undergo carboxylation twice, ie in mesophyll, through the C 4 Cycle and in bundle sheath cells via the Calvin Cycle. This can be an acute problem for plants growing in hot arid environments. (b) C3 plants Then, OAA is reduced to malate by NADP+-dependent malate dehydrogenase (NADP+-MDH) or aminated to aspartate by aspartate aminotransferase. Aloe skin is regarded as the main byproduct of processing, with a lot of quantity and high value for nutrition and health. ‘ The initial fixation by PEP carboxylase in the mesophyll cells is a mechanism for concentrating CO2 in the bundle sheath cells to inhibit RuBP oxygenation. He also contributed to working out the complete biosynthetic pathway; hence, it was called Calvin cycle after him. Most estimates suggest that the correct Km for CO2 is around 10 to 20 μM and the Km for RuBP around 20 to 50 μM. The expression of NADP+-ME in rice caused grana degradation and bleaching of leaves. The mechanism and possible regulation of C4 acid decarboxylation in NAD-malic enzyme-type C4 plants was studied using isolated bundle sheath cells and mitochondria from Panicum miliaceum. Ans: (a) Chlorophyll a pigment acts directly to convert light energy to chemical energy. 2. In leaves, mesophyll cells are not differentiated in the spongy layer and palisade layer. Q9. 1999). Q16. Q5. A third type of photosynthesis, Crassulacean acid metabolism (CAM) photosynthesis, is much less common and is mostly only found in succulents. The pigments are organised into two discrete photochemical light harvesting complexes (LHC) within the Photosystem I (PS I) and Photosystem II (PS II). b. If a green plant is kept in dark with proper ventilation, can this plant carry out photosynthesis? b. Maize (as it is a C4 plant) C3 plants tend to originate from temperate regions and fix CO2 directly using Ribulose- 1,5-bisphosphate carboxylase oxygenase (RuBisCO) to produce two 3-carbon molecules, hence ‘C3 plants’ (Fig. In this book the enzyme is referred to as RUBISCO, this abbreviation being the least unwieldy of the many alternatives, which include the Enzyme Commission (E.C.) The mestome sheath is encircled by a second, parenchymatic sheath containing only a few chloroplasts which are sometimes smaller than those in the mesophyll. Because of the key role of RUBISCO in the production of p-glycollate, the first intermediate of the photorespiratory pathway, this enzyme has attracted considerable research interest during the last 10 years. Ans: (c) During light reaction in photosynthesis the following are formed ATP, hydrogen donor/(NADPH) and 02. The nutritional components of Aloe are equally distributed between the pulp and the cortex of the leaf (Hatano, 2005). Ans: ATP and NADPH. Q15. This creates a proton gradient across the thylakoid membrane as well as a measurable decrease in pH in the lumen. Carbon sequestration can be natural where the natural processes of the carbon cycle are utilised, such as biological fixation described above, or artificial sequestration where carbon is compressed and stored, known as carbon capture and storage (CCS; discussed in more detail in Section 5.2). Cross sections are (a) a C3 species, F. robusta; (b) a C3–C4 intermediate species, F. floridana; and (c) a C4 species, F. trinervia. Wild and crop species are different in many ways, particularly in the traits that have been subject to intensive selection by humans. The sheath is without intercellular space. Its pH is 4.5. are capable of utilizing aspartate as a Hill oxidant. In defining leaf source strength, its photosynthesis rate is only one parameter of interest. This reaction is catalysed by the enzyme RuBP carboxylase which results in the formation of two molecules of 3-PGA. This strong purging action is closely related to the chemical structure of the molecule. Based on the above equation, answer the following questions: Assertion: In `C_(4)` plants, the bundle sheath cells are rich in an enzyme phosphoate carboxylase-oxygenase (RuBisCO). In plants with the C4 pathway either a single or a double layered sheath may be developed. Yes, through female gametes. Ans: (a) Energy required for ATP synthesis in PSII comes from proton gradient. Understanding how such a spatial arrangement of enzymes is accomplished and maintained is important to recreate a functional C4 pathway in C3 plants. Mesophyll cells and bundle sheath strands isolated from leaves of the C 4 plant Digitaria sanguinalis (L.) Scop. They are seen around leaf veins surrounding the vascular bundles. Is it a catabolic or an anabolic process? iii. The Calvin cycle reactions only occur in bundle sheath cells in a C4 plant. a. Synthesis of ATP and NADPH _________ It turns out that the C 4 metabolism of Sorghum is based solely on the NADP-dependent malic enzyme pathway. This is the biosynthetic phase or dark reaction of photosynthesis. Can anything be given as a supplement to maintain its growth or survival? It is closely related to other members of the Lily family such as onions, leeks, garlic, tulips, turnips, and asparagus. Tomatoes, carrots and chillies are red in colour due to the presence of one pigment. d. found in bundle sheath cells. The bundle sheath in a leaf is a layer of compactly arranged parenchyma surrounding the vasculature (Esau, 1965) and is a conduit between the vasculature and the mesophyll cells. Pure mannan, acetylated mannan, acetylated glucomannan, galactomannan, galactan, galactogalacturan, arabinogalactan, galactoglucoarabinomannan, pectic substance, xylan, cellulose, chromones, isoaloeresin-D, isoarabaichromone and neoaloesin A. Saccharides: Mannose, Glucose, They aid in proper digestion, maintain cholesterol levels, improve liver functions, and promote the strengthening of bones, Phosphatase, amylase, carboxypeptidase, catalase, cyclooxidase, cyclooxigenase, lipase, oxidase, phosphoenolpyruvate carboxylase, superoxide dismutase, and peroxidase, Enzymes are natural protein molecules with highly specialized catalytic functions in biochemical reactions produced by all living organisms (microorganisms, plants, animals, and human beings). Both processes take place in double membrane bound organelles. • One intemode long phylloclade or stem which is leaf like is called cladode. Leaves of C4 plants – maize or sorghum lack photorespiration. Explain. Find out. i. Start studying 13. Although the heavier 13C isotope has a natural abundance of ~1% in the atmosphere, when CO2 availability is not the limiting factor for primary production, photosynthesis discriminates against the heavier isotope with the result that carbon-fixed plant biomass is relatively depleted in 13C. The light-independent reactions of photosynthesis or the Calvin cycle take place in bundle sheath cells. Q12.What is the basis for designating C3 and C4 pathways of photosynthesis? (a) 100-390 (b) 390-430 (c) 400-700 (d) 760-10000 The reaction that is responsible for the primary fixation C02 is catalysed by Calvin pathway in C 4 plants takes place only in bundle sheath cells (because RuBisCO is present) but does not take place in the mesophyll cells because lack of RuBisCO enzyme in mesophyll cells of C 4 plants like maize, sorghum, sugarcane, Jowar, Euphorbia, Atriplex, Q9. RuBisCO is spatially isolated in specialist cells and CO2 is re-fixed in these bundle sheath cells (Fig. How do they conduct photosynthesis? Ans: a. b. Copyright © 2020 Elsevier B.V. or its licensors or contributors. The bundle sheath cells are rich in RuBisCO enzyme (necessary for the C 3 or the Calvin cycle), but lack PEPcase. The C4 enzyme also exhibits regulatory properties, with sugar phosphates acting as apparent allosteric regulators. Hence these factors are related to the balance between the rates of beneficial carboxylation and degradative production of p-glycollate. First, the full genome sequence for the maize PEPC was expressed in rice. Carbon-concentrating mechanisms have evolved in plants to make them more efficient and C4 photosynthesis is one such carbon-concentrating mechanism. Bundle sheath cells are surrounded by thick cell walls containing suberins and other hydrocarbons that limit the diffusion of CO2 to confine it within the cells [42]. 5.1). As already mentioned above, CO2 is not only a substrate for the enzyme but also functions as an activator or regulator of the carboxylation reactions. BOLHAR-NORDENKAMPF, in Techniques in Bioproductivity and Photosynthesis (Second Edition), 1985. After senescence and/or when the whole plant dies, the carbon within the plant is sequestered into the soil. This gradient is important because it is the breakdown of this gradient that leads to release of energy. What does the action spectrum indicate? The Km for CO2 is equivalent to the concentration of carbon dioxide in water equilibrated with the atmosphere. Appropriate compartmentalization of C4-cycle enzymes within the leaf and a mechanism to confine the CO2 until it is fixed by RuBisCO may be essential for the cycle to operate successfully. Ans: On studying vertical sections of leaves, one of a C3 plant and the other of a C4 plant. b. These have agranal chloroplasts and contain starch grains. Rates of C4 acid-dependent photosynthetic O2 evolution equalled those observed with saturating NaHCO3; the rates ranged from 3 to 5 mumol min-1 (mg chlorophyll)-1. These cell thick walls cannot be exchanged for gasses. In particular, photosynthetic functions are divided between mesophyll and bundle-sheath leaf cells. We hope the NCERT Exemplar Class 11 Biology Chapter 13 Photosynthesis in Higher Plants help you. Enrichment of fumarase is consistent with the larger number of mitochondria in bundle-sheath cells relative to mesophyll cells. The leaf has two external membranes which are green and leathery. Understanding how such a spatial arrangement of enzymes is accomplished intracellularly versus intercellulary and maintained is very important in developing strategies to genetically engineer a functional C4 pathway in selected C3 plants (see Chapter 4.13). Some of these terms/chemicals are associated with the C4 Explain. Using a Mutator transposable element as a molecular probe, we identified a tightly linked restriction fragment length polymorphism that cosegregated with the bsd2 -conferred phenotype. As we have discussed, for most plants elevated CO2 alters the balance between internal concentrations of carbon and nitrogen. The large (A) subunit (M.W. In C3 plants RUBISCO is located in the stroma of all chloroplasts. Hence, the action spectrum and absorption spectrum not overlap. 11.11. Ans: a. Plant cell. a. Loosely arranged mesophyll cells lie between the bundle sheath and the leaf surface. b. Stroma of chloroplast. This resulted in a slightly increased CO2 fixation rate, and partial suppression of O2 inhibition of photosynthesis [43]. Q9.Why does the rate of photosynthesis decrease at higher temperatures? The leaf structure of C3 and C4 plants shows clear anatomical and ultrastructural differences: in most C3 species the leaf anatomy corresponds to the description above (Section 8.1), but C4 plants have a highly specialised anatomy corresponding to their different CO2 fixation pathways. However, the waste-less Aloe skin is known to have bioactive substances and for the potential use in industry as well. The activities of nitrate-assimilating enzymes, except for nitrate reductase, were high enough to account for the proposed in vivo rates of nitrate assimilation. (a) C4 plants Fig. a. This minimizes opening of stomata during the warmer daytime hours. In both processes electron transport system requires. Most C4 plants have a unique Kranz structure and distribute C4 enzymes efficiently among mesophyll and bundle sheath cells. The particularly large cells around the vascular bundles of the C4 pathway plants are called bundle sheath cells, and the leaves which have such anatomy are said to have ‘Kranz’ anatomy. C3 plants carry out the entire Calvin cycle in mesophyll cells and have relatively fewer bundle-sheath cells. This combination of anatomical and metabolic features suits C4 plants to hot and arid habitats with high irradiation; it may also be an adaptation to short vegetation periods, but only when in conjunction with optimal growing conditions8. The rate of turnover of the oxygenase reaction is an order of magnitude lower. In tropical rain forests, the canopy is thick and shorter plants growing below it, receive filtered light. X 1200. C4 plants also show much less of a response of nitrogen and protein concentrations to elevated CO2 than do C3 plants (Cotrufo et al. The gradient is broken down due to the movement of protons across the membrane to the stroma through the transmembrane channel of the F0 of the ATPase. A schematic of the major photosynthetic pathways (C3, CAM, C4, and C3–C4 subtypes) showing the intracellular flow of C from the atmosphere to the phloem in source leaves of vascular plants. Table 8.2. From: Comprehensive Biotechnology (Second Edition), 2011, H.R. Chemical composition of A. vera leaf pulp and exudates was reported (Femenia et al., 1999) and is summarized in Table 8.1. C4 Pathway. (c) C2-plants absorption by chlorophyll a, i.e. Q1. [46] reported that a quadruple transfomant rice line harboring PEPC, PPDK, MDH, and NADP+-ME showed a slight increase in CO2 fixation rate. They have a special type of leaf anatomy. C. High density of chloroplasts. 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