Practice free Photosynthesis (Botany) NEET multiple-choice questions online with instant answers and detailed explanations. No login required.
Which of the following are special features of the C4 plants?
I. They have a special type of leaf anatomy.
II. They tolerate higher temperatures and show a response to high light intensities.
III. They lack photorespiration and have greater productivity of biomass.
Read page 218, XI NCERT
Consider the situation where photosynthesis is going on at a steady pace in a typical experiment with a light on, and carbon dioxide is being combined with ribulose-bisphosphate (RuBP) to produce 3-phosphoglycerate (3PG). Then suddenly the source of carbon dioxide is eliminated. What changes in the concentrations of 3PG and RuBP would occur?
Elimination of a source of CO2 would block the action of RUBISCO, which required CO2 as a subtrate. There would be no further production of 3-phosphoglycerate (3PG).
The remaining reactions of the Clavin Cycle are not block by the absence of CO2. Intermediates in the cyclic pathway would be converted to ribulose-1,5-bisphosphate (RuBP) and the level of RuBP would rise.
Crops such as tomatoes and bell pepper, allowed to grow in a carbon dioxide rich environment, show higher yields because:
Read page 223, XI NCERT
At about what percentage of the full sunlight does light saturation occurs in photosynthesis?
Read page 222, XI NCERT
Suppose the interoir of the thylakoids of isolated chloroplasts and then transferred in the dark to a pH 8 solution. What would be likely to happen?
The proton gradient will lead to chemiosmosis and phosphorylation of ADP into ATP.
Consider the following two statements:
I. Except for plants in shade or in dense forests, light is rarely a limiting factor in nature for photosynthesis.
II. Light saturation occurs at 50% of the full sunlight.
Page 222, XI NCERT
For assimilation of one CO2 molecule via photosynthesis, the energy required in form of ATP and NADPH2 are:
In Clavin cycle, CO2 acceptor molecule is RuBP or RuDP. The enzyme catalyzing this reaction is RuBP carboxylase/oxygenase (Rubisco). As Clavin cycle takes in only one carbon (as CO2) at a time, so it takes six turns of the cycle to produce a net gain of six carbons )i.e., hexose or glucose). In this cycle, for formation of one mole of hexose sugar (Glucose), 18 ATP and 12 NADPH2 are used. For 6 molecules of CO2 it needs 18 ATP and 12 NADPH2 , molecules so for one molecule of CO2 it needs 3 ATP and 2 NADPH2 molecules.
Phosphoenol pyruvate (PEP) is the primary CO2 acceptor in
Phosphoenol Pyruvate (PEP) is found in the mesophyll cell, which accepts the atmospheric CO2 in C4 -plants and converts it to oxaloacetate — a C4 compound. It is the first stable compound of C4 -plants.
Concept Enhancer C4 -plants possess special adaptation anatomy in their leaves to cope up the photorespiratory losses. There are dimorphic chloroplast present in them—agranal in bundle sheath cells and granal in mesophyll cells.
With reference to factors affecting the rate of photosynthesis, which of the following statements is not correct?
In C4 -plants, the initial fixation of CO2 occurs in mesophyll cells. The primary acceptor of CO2 is Phosphoenol Pyruvate (PEP). It combines with CO2 in the presence of enzyme PEP carboxylase to form the first stable product, i.e., oxaloacetic Acid (OAA). C3 plants lack PEPcaboxylase enzyme. They posses RuBisCO enzyme. This enzyme can work as both carboxylase (fixation of CO2) and oxygenase (fixation of O2). RuBisCO has much greater affinity for CO2 than for O2 and the binding is competitive. At higher temperature, its ffinity for CO2 decrease and it works as oxygenase.
Therefore, at higher temperature photosynthesis decrease in C3 -plants, while in C4 -plants increases.
The process which makes major difference between C3 and C4 Plants is
Photorespiration is the process which makes a different between the C3 and C4 plants. In this process, there is a continuous loss of carbon fixed in the form of CO2. It occurs due to the high O2 content, high temperature conditions in which RuBP carboxylase starts working as RuBP oxygenate and normal photosynthesis does not occur.
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