Question

ME LIIL URE alternative that best completes the statement or answers the question. 1) Plants that fix CO2 into organic acids at night when the stoma are open and carry out the Calvin cycle during the day when the stoma are closed are called 1). A) C3 plants. E) A, B, and Care correct. B) C4 plants. C) CAM plants. D) Only A and B are correct. 2) Photorespiration lowers the efficiency of photosynthesis by removing which of the following from the Calvin cycle? A) glyceraldehyde phosphate molecules B) ribulose bisphosphate molecules C) RuBP carboxylase molecules D) carbon dioxide molecules E) ATP molecules 3) Assume a thylakoid is somehow punctured so that the interior of the thylakoid is no longer separated from the stroma. This damage will have the most direct effect on which of the following processes A) the splitting of water B) the reduction of NADP+ C) the absorption of light energy by chlorophyll D) the synthesis of ATP E) the flow of electrons from photosystem II to photosystem atadura o 4) Why are C4 plants able to photosynthesize with no apparent photorespiration? A) They conserve water more efficiently. B) They exclude oxygen from their tissues. C) They do not carry out the Calvin cycle. D) They are adapted to cold, wet climates. E) They use a more efficient enzyme to initially fix CO2. WH A SA 5) Which of the following statements is TRUE of fermentation? A) It produces more energy per glucose molecule than does aerobic respiration. B) It produces a net gain of NADH. C) It produces a net gain of ATP. D) It is an aerobic process. E) It can be performed only by bacteria.

Answer 1

1) The correct answer is C

Reason : In CAM plants, the absorption of sunlight energy takes place during the day and stomata is closed. During the night, stomata is opened and CO2 diffuses inside it. Then this CO2 is converted into organic acid ( generally malate) and is stored in the vacuoles till next morning. During day, this malate comes out and breaks down into CO2 and then Calvin Cycle begins.

2) The correct answer is D

Reason : Sometimes instead of fixing CO2, rubisco binds to O2 and fixes it. It ultimately leads to loss of 3 CO2 molecules per cycle. In photorespiration, phosphoglycolate is formed along with 3-PGA. This phosphoglycolate is then broken down into CO2 through Salvage Pathway, ultimately leading to the loss of 3 fixed C atoms from the reaction per cycle.

3) The correct answer is D

Reason : The synthesis of ATP occurs due to the proton gradient across the thylakoid membrane. When there is a H+ concentration difference between thylakoid lumen and stroma, then ATP is synthesized by the enzyme ATP synthase by utilising this gradient.

4) The correct answer is B

Reason : The major cause of photorespiration is the presence of high concentration of O2 at the site of RUBISCO enzyme. C4 plants dodge this by pumping only CO2 to the reaction, and keeping O2 away from the cells where the reaction occurs. Thus by maintaining high local levels of CO2, and keeping O2 away, C4 plants are able to dodge photorespiration.

5) The correct answer is C

Reason : In fermentation reaction, there is a net gain of ATP molecules. During the conversion of Glucose to Pyruvate, ADP is converted into ATP which is then consequently released. On the other hand, the other four options are incorrect. NADH is not gained, neither lost. It keeps on interconverting between NAD+ and NADH. Fermentation usually occurs in absence of oxygen and it is not restricted to bacterial cells. Our muscle cells also do fermentation reactions and fungi can also do it. The net energy produced in comparison to aerobic respiration per glucose molecule is very less due to incomplete breakdown of glucose.

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