Answer the following regarding the light independent reactions: In a plant cell,
ID: 202338 • Letter: A
Question
Answer the following regarding the light independent reactions: In a plant cell, where does the Calvin cycle occur? Stroma T0 The enzyme Rubisco is protons. effectively stop the light-dependent reactions when p the light-independent reactions to proceed when plants are ibited by protons. How does this inhibition of Rubisco ants are in the dark and allow in the light? When does carbon fixation occur? DcCuisia the stoma and resuHs What enzyme is needed for carbon fixation during the Calvin cvdle? the pradu Con of glucose Ribloze bisphosphote (alboxylase (Rueisco) What are electrons used for in the Calvin cycle? What is the final electron acceptor in photosynthesis? How many turns of the Calvin cycle are needed to produce one glucose Explain your answer. What is the role of the enzyme Rubsico in the Calvin cycle? What is the role of NADPH in the Calvin cycle? What can a plant cell make from G3P?Explanation / Answer
1) In plants, the CO2 molecules are used to make 3-carbon sugar, glyceraldehydes-3-phosphate (G3P). The sequence of reactions that results in this carbon fixation is called as the Calvin cycle. It occurs in the stroma of chloroplasts.
2) When the plant is illuminated, the light-dependent reactions occur, and this produces ATP and NADPH. This process involves the production of a proton gradient across the thylakoid membrane by expelling proton from the stroma into thylakoid lumen. The resulting decrease in H+ concentration activates Rubisco, and so light independent reactions take place when the plant is exposed to light.
3) Carbon fixation occurs during the day, in the presence of light. This process utilizes the products of light-dependent reactions of photosynthesis, and the key enzyme Rubisco is activated by these products (ATP. NADPH, and higher levels of H+).
4) The key enzyme in the whole process is Rubisco.
5) NADPH provides the electrons. NADPH is oxidized to NADP+ to convert 1,3 bisphosphoglycerate into glyceraldehyde-3-phosphate.
6) In photosynthesis, the final electron acceptor is NADP. The net reaction of light-dependent reactions is the following.
2H2O + 2NADP+ + 3ADP + 3Pi O 2 + 2NADPH + 3ATP
The light energy absorbed by chlorophyll pigments resulting in excitation of electrons to higher energy levels and subsequent transfer to a series of molecules and complexes like PSII and PSI in the electron transport chain (ETC). This eventually ends with NADP getting oxidized to NADPH.
7) It takes six rounds of Calvin cycle to produce one glucose molecule. Each cycle fixes one molecule of CO2 into 3-ribulose bisphosphate towards the generation of 3-phosphoglycerate and subsequently glyceraldehyde-3-phosphate.
3 CO2 + 6 NADPH + 6 H+ + 9 ATP glyceraldehyde-3-phosphate (G3P) + 6 NADP+ + 9 ADP + 3 H2O + 8 Pi
Three molecules of CO2 is needed to produce one molecule of 3-carbon glyceraldehydes-3-phosphate effectively. So, six rounds are needed to generate one glucose molecule.
8) Ribulose-1,5-bisphosphate carboxylase captures a CO2 molecule by carboxylation of a 5-carbon sugar, Ribulose-1, 5-bisphosphate to generate two molecules of 3-phosphoglycerate.
9) NADPH is required to convert 1,3 bisphosphoglycerate into glyceraldehyde-3-phosphate by the enzyme glyceraldehydes-3-phosphate dehydrogenase. NADPH, generated from the light-dependent reaction is reduced to NADP+, which can then be utilized for photosynthesis again.
10) G3P is used by the plant cells to produce six carbon sugars like glucose, and 5 out of 6 molecules produced from Calvin cycle is utilized for regeneration of ribulose-5-phosphate.
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