(c) Xanthophyll (d) Carotenoid These carbohydrates are subsequently used for plant growth. Ans: a. Lumen of the thylakoids. Transformants showed a 50 times increase in PEPC activity compared with that in the wild type. The enzyme contains two different subunits known as A and B with a quaternary structural configuration of A8B8 in higher plants (Figure 11.9), although this may differ in some bacteria. In C 4 plants (see C4 pathway) the bundle sheath cells contain chloroplasts and are the site of the Calvin cycle.The initial fixation of carbon dioxide to form malic acid takes place in the palisade mesophyll cells, which in C 4 plants form a circle around the bundle sheath. Q12.What is the basis for designating C3 and C4 pathways of photosynthesis? d. Photorespiration involves a complex network of enzyme reactions that exchange metabolites between chloroplasts, leaf peroxisomes and mitochondria. Thus, due to RuBisCO’s low affinity for CO2 and its oxygenase activity, the major limitation of C3 photosynthesis is the fact that at present atmospheric CO2 concentrations, the net photosynthetic capacity of the Calvin cycle is reduced from that that can operate at elevated levels of CO2 (see Chapter 4.13 and references therein). nomenclature of 3 – phospho-D-glycerate carboxylase – E.C. However, overexpression of PEPC in transgenic rice may cause a decrease in CO2 fixation and an increase in respiration under light conditions [46]. The effects of CO2 enrichment may be different for plants when they are grown in competition with plants of different species. He also contributed to working out the complete biosynthetic pathway; hence, it was called Calvin cycle after him. Ans: a. Grana-lamellae. The C4 enzyme also exhibits regulatory properties, with sugar phosphates acting as apparent allosteric regulators. e. Synthesis of starch _________ Q11. The majority of photorespiratory gene expression, with some important exceptions, is restricted to the bundle sheath. (b) Lumen of thylakoid During the synthesis of subunit B the precursor is transported across the chloroplastic membrane and, after cleavage of an extra peptide molecule in the stroma, it is eventually assembled with the large subunit to produce the holoenzyme. A study by Mckinley et al. Crops both allocate a larger proportion of biomass to reproduction than wild species and respond more in fruit and seed production than wild species to CO2 enrichment (Jablonski et al. Ans :ATP and NADPH are used to drive the processes leading to the synthesis of food, more accurately, sugars. High values, reflecting a low affinity for CO2, have now been ascribed to problems with both isolation of the enzyme and assay under conditions which prevented its reactivation. The concentration of RUBISCO can reach 10 mg protein per gram fresh weight of leaf, resulting in an estimated concentration of some 240 mg of enzyme per ml of chloroplast stroma or 0.4 to 0.5 nM enzyme. Many attempts have been made, by mutation or selection, to isolate varieties containing RUBISCO with a more favourable carboxylase/oxygenase ratio; so far without result. Bundle sheath cells in barley are capable of photosynthesis, since bundle sheath cells can reduce tetrazolium blue, indicating photosystem II activity (Williams et al., 1989), can synthesize starch in the light, and single-cell immunoblotting from lateral bundle sheath cells shows that they contain amounts of Rubisco protein similar to those of single mesophyll cells (Koroleva et al., 2000). c. Fixation of C02: Stroma of chloroplast The enzyme from C4 plants shows higher maximum velocity, has a lower affinity for HCO3 (higher Km value) and is present in greater amounts than is the case for the other forms. Ku et al. However, the waste-less Aloe skin is known to have bioactive substances and for the potential use in industry as well. In addition, the greater availability of nitrogen often prevents at least some of the decrease in nitrogen concentrations seen in other plants grown under elevated CO2. Q12. a. Photorespiration in C3–C4 intermediate species may be suppressed by different means. Assertion: In `C_(4)` plants, the bundle sheath cells are rich in an enzyme phosphoate carboxylase-oxygenase (RuBisCO). 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. Vitamin B and choline (concerned with the production of energy, amino acid metabolism and developing muscle mass). Such high protein concentration is needed in order to achieve reasonable rates of CO2 fixation since the carboxylating activity of the enzyme has a slow turnover rate; a maximum of around 200 molecules of substrate per active site per minute. C. High density of chloroplasts. The photosynthetic process in C4 plants is more efficient than in C3 plants, and several food crops are C4 such as maize and sorghum. Fig. This gradient is important because it is the breakdown of this gradient that leads to release of energy. chyma cell of the bundle sheath. 2002). Ans: Photosynthetic organisms occur at different depths in the ocean. During summer season flowers blossom on a spike up to 90 cm (35 inch) in height and each flower is pendulous with a yellow tubular corolla 2–3 cm (0.8–1.2 inch) long. This discrimination is strongest in C3 plants, with C3 biomass being typically 25‰ depleted in 13C (i.e., δ13C=−22 to −30‰ compared to the VPDB carbonate standard; see Glossary), while in C4 and CAM plants the depletion is typically δ13C ≈ −8 to −11‰. 8.2 (Ni et al., 2004). These three components of the inner leaf pulp have been shown to be distinctive from each other both in terms of morphology and sugar composition as shown in Fig. Plant cell. b. In addition these plants show tolerance to higher temperatures. Multiple Choice Questions These protons are also removed from the stroma. 5.1 illustrates the wide diversity of bioenergy crop types that utilise differing photosynthetic machinery to fix CO2. D.R. Consequences for other plastid functions are not well understood but are addressed here through a quantitative comparative proteome analysis of purified M and BS chloroplast stroma. In the leaves of the NAD‐malic enzyme (NAD‐ME)‐type C 4 dicot Amaranthus viridis L., there are chloroplasts in the vascular parenchyma cells (VPC), companion cells (CC), ordinary epidermal cells (EC), and guard cells (GC), as well as in the mesophyll cells (MC) and the bundle sheath cells (BSC). It has been shown to exhibit anti-inflammatory function These are organic compounds containing anthracene-9, 10-quinone, an anthracene derivative with two ketone groups attached to the central benzene ring, 7-hydroxy-5-methyl-2-(2-oxopropyl)-8-[(2S,3R,4R,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]chromen-4-one, 6-[4-hydroxy-2-methyl-6-[(2S,3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxyphenyl]-4-methoxypyran-2-one, 2-[6-[4,5-dihydroxy-2-(hydroxymethyl)-6-[4,5,6-trihydroxy-2-(hydroxymethyl)oxan-3-yl]oxyoxan-3-yl]oxy-4,5-dihydroxy-2-(hydroxymethyl)oxan-3-yl]oxy-6-(hydroxymethyl)oxane-3,4,5-triol, It is a polysaccharide consisting of mannose units. C4 plants collect CO2 in mesophyll cells, which are close to the leaf surface, then transfer it to bundle-sheath cells, which are rich in RuBP carboxylase and surround the “veins” that deliver water to the leaf tissue. Whether bioenergy crops, forests, or arable crops, plants have the potential to sequester large amounts of carbon from the atmosphere and into the soil. sis of isolated mesophyll and bundle sheath cells in the C 4 grass Sorghum bicolor. Ans: ATP and NADPH. These bacteria are capable of a process known as nitrogen fixation, in which atmospheric nitrogen is chemically reduced to a form in which it can enter into metabolism by the bacterium or plant and become incorporated into molecules such as proteins and nucleic acids. Fig. In the green tissue, the enzyme is part of a cyclic mechanism which pumps CO2 to the PCR cycle as described above. Besides, A. vera skin also includes a variety of mineral elements, such as calcium, iron, zinc, manganese whose content is higher than that of the gel (Zhen et al., 2011). The main difference between CAM and C4 fixation is that whereas C4 metabolism is based on synergistic operation in the light with spatial separation of the PEPase and RuBisCO, in CAM, the CCM is based on temporal separation of the synthesis and decarboxylation of a C4 intermediate and refixation of the CO2 by the action of RuBisCO in the light (Figure 2). It forms a protective covering on leaf vein, and consist of one or more cell layers, usually parenchyma. Modified from Yamori W, Hikosaka K, Way DA. These higher CO2 concentrations also contribute to increases in water- and nitrogen-use efficiencies [6]. Superoxide dismutase (SOD) is an enzyme that is able to engulf and digest bacteria, protozoa, and cell wastes, and it is important to a functional, immune system. Cyanobacteria and some other photosynthetic bacteria do not have chloroplasts. The C4 cycle is a key part of the high drought tolerance of B. aralocaspica, allowing it to grow in dry desert conditions. 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.) (a) PSII, plastoquinone, cytochromes, PSI, ferredoxin in the blue and the red regions, also shows higher rate of photosynthesis. Stephen A. Rackley, in Carbon Capture and Storage (Second Edition), 2017. (b)     PEP Carboxylase ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. URL: https://www.sciencedirect.com/science/article/pii/B9780080319995500182, URL: https://www.sciencedirect.com/science/article/pii/B9780080885049002439, URL: https://www.sciencedirect.com/science/article/pii/B9780080885049002415, URL: https://www.sciencedirect.com/science/article/pii/B9780128120415000210, URL: https://www.sciencedirect.com/science/article/pii/B9780128202449000044, URL: https://www.sciencedirect.com/science/article/pii/B9780123847034004044, URL: https://www.sciencedirect.com/science/article/pii/B9780081010365000057, URL: https://www.sciencedirect.com/science/article/pii/B9780081020715000088, URL: https://www.sciencedirect.com/science/article/pii/B9780080319995500212, Comprehensive Biotechnology (Second Edition), 2011, SHOOT MORPHOLOGY AND LEAF ANATOMY IN RELATION TO PHOTOSYNTHESIS, Techniques in Bioproductivity and Photosynthesis (Second Edition), pathway the vascular tissue is surrounded by two bundle sheaths. b. In C4 plants, CO2 is initially fixed by an enzyme with a much higher affinity for CO2 (phosphoenolpyruvate (PEP) carboxylase) with no oxygenase activity. Perhaps the two most important determinants of plant species’ responses to elevated CO2 are (1) the variant of photosynthetic physiology that a species uses and (2) whether the species is a legume. Does moonlight support photosynthesis? However, in some C4 plants, such as species of the Chenopodiaceae, the Kranz-syndrome is not clearly evident1. David E. Reichle, in The Global Carbon Cycle and Climate Change, 2020. [6] on biomass partitioning in Sorghum grown as a bioenergy crop found biomass, primarily leaves, leaf sheaths, and roots, accumulated predominantly until floral initiation, then stems dominated until anthesis (the opening of the flower buds), then panicles (branching cluster of flowers) until grain maturation. The C4 species are classified into three subtypes according to the decarboxylation enzyme: Nicotinamide adenine dinucleotide phosphate (NADP)-dependant malic enzyme (NADP-ME subtype); NAD-dependant malic enzyme (NAD-ME subtype); and phosphoenolpyruvate carboxykinase (PEP-CK subtype) [17]. Q13. According to the mechanism by which they reduce photorespiration, they can be classified into type I or type II C3–C4 intermediates. Q4. Photorespiration is a wasteful reaction that occurs when plants take in oxygen and give out carbon dioxide instead of taking in carbon dioxide and releasing oxygen. The difference between C3 and CAM vs. C4 plants is that C4 plants make a four-carbon sugar during the Calvin cycle instead of two three-carbon sugars as in C3 plants. Assertion: In `C_(4)` plants, the bundle sheath cells are rich in an enzyme phosphoate carboxylase-oxygenase (RuBisCO). (d)     ATP synthase Ans: a. Photorespiration C4 photosynthesis relies on cooperation between mesophyll cells for the initial fixation of bicarbonate, but not CO2, and bundle sheath cells for fixation of CO2 concentrated by the C4 cycle [41]. The mesophyll cells of leaves Cotrufo et al. If you have any query regarding NCERT Exemplar Class 11 Biology Chapter 13 Photosynthesis in Higher Plants, drop a comment below and we will get back to you at the earliest. 31. i.One portion called F0 is imbedded in the membrane and forms a transmembrane channel that carries out facilitated diffusion of protons across the membrane. The nutritional components of Aloe are equally distributed between the pulp and the cortex of the leaf (Hatano, 2005). They have a special type of leaf anatomy. Group 15Muhammad Rashidi Bin MdYusofMuhammad Amirul Bin JamaludinHaznul Bin Hamzah 2. (a) ATP and sugar                                  The. The carbon-fixation pathway begins in the mesophyll cells, where carbon dioxide is converted into bicarbonate, which is then added to the three-carbon acid phosphoenolpyruvate (PEP) by an enzyme called phosphoenolpyruvate carboxylase. 15,000) by nuclear DNA. However there are important differences in response to CO2 among different types of plants. e. Synthesis of starch: Stroma of chloroplast. High concentration of CO 2 near Rubisco enhances carboxylation and reduces photorespiration.. C 4 photosynthetic Carbon Cycle: . Ans: No, this plant cannot photosynthesise in the absence of light. (b) PSI, plastoquinone, cytochromes, PSII, ferredoxin They can photosynthesise in very low light conditions. Overall, in FACE experiments, C4 plants show approximately one-third of the increase of photosynthetic rates experienced by C3 species, and little enhancement of growth (Ainsworth and Long 2005). 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