Concept explainers
The water necessary for photosynthesis
- a. is split into H2 and O2.
- b. is directly involved in the synthesis of carbohydrates.
- c. provides the electrons to replace those lost in photosystem II.
- d. provides the H + needed to synthesize G3P.
- e. does none of the above.
Introduction: The water molecule is essential in photosynthesis. It splits into hydrogen ions and oxygen, and provide electrons to replace the lost electrons from the photosystem II during the light reaction. This reaction is called photolysis of water. The protons can be used to produce ATP through ATP synthase.
Answer to Problem 1TY
Correct answer: The water present in the photosynthesis provides the electrons to replace the loss of electrons in the photosystem II. Hence, the correct answer is option c.
Explanation of Solution
Reason for correct answer:
Option c. is given as “provides the electrons to replace those lost in photosystem II”.
The photolysis of water provides electrons to replace the lost electrons in the photosystem II. It dissociates into hydrogen ions and oxygen. During this reaction, the electrons produced from the hydrogen ions are used to replace the electrons lost in the photosystem II. Hence, the correct answer is option c.
Reasons for the incorrect answer:
Option a. is given as “is split into H2 and O2”.
The water is split into oxygen and hydrogen ions and not hydrogen gas. This is because the electrons gained from the formation of hydrogen ions are provided to replace lost electrons in the photosystem II. Hence, option a. is incorrect.
Option b. is given as “is directly involved in the synthesis of carbohydrates”.
The water molecule is not directly involved in the synthesis of carbohydrates. It only provides electrons for the photosystem II. The molecule of carbon dioxide serves as the direct fuel for the production of carbohydrates. Hence, option b. is incorrect.
Option d. is given as “provides the H+ needed to synthesize G3P”.
Water provides electrons to the photosystem II. G3P is synthesized by the reduction and dephosphorylation of 1,3 biphosphoglycerate which is further coupled with the oxidation of NADH. Hence, option d. is incorrect.
Option e. is given as “does none of the above”.
Water does provide an electron to the reaction centre and it is used for the production of energy using light. It also splits into hydrogen ions and single oxygen atoms which then forms oxygen gas. The oxygen produced is liberated as the by-product of photosynthesis. Hence, option e. is incorrect.
Hence, the options a., b., d., and e. are incorrect.
Water dissociates into the single oxygen atom and hydrogen ions liberates electron. The released electron is captured by the photosystem II. The electron then passes to the primary electron acceptor and finally to the photosystem I. Photosystem I uses it to produce energy in the form of ATP and NADPH.
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