This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Chloroplast Function – Photophosphorylation”.
1. What is photophosphorylation?
a) Addition of phosphate without light
b) Removal of phosphate without light
c) Addition of phosphate with light
d) Addition of phosphate with light
Explanation: Photophosphorylation is the process of addition of phosphate group with the presence of light, which happens as a part of the photosynthesis reactions. In this reaction the ADP molecule is phosphorylated to ATP molecule.
2. Who discovered photophosphorylation?
a) D David
b) D Benjamin
c) D Arnon
d) D Robert
Explanation: D Arnon and his coworkers found photophosphorylation in the bacterial cells. He also found the cyclic and non-cyclic photophosphorylation reactions.
3. Cyclic photophosphorylation has both photosystem I and II.
Explanation: Photophosphorylation contains only photosystem I. Because there is only a transfer of electrons, but there’s no reduction of NADP+.
4. The site of photophosphorylation is __________
c) Endoplasmic reticulum
Explanation: The photophosphorylation occurs in the thylakoids of chloroplast. Because photophosphorylation requires sunlight to occur and chloroplast is the site for absorption of light.
5. Which enzyme helps in the flow of protons from the thylakoid to the stroma?
a) ADP synthase
b) ATP synthase
c) ADP hydrolase
d) ADP hydrolase
Explanation: ATP synthase helps in the flow of protons from thylakoids to the stroma. It also helps in the production of ATP. It yields 1 molecule of ATP for every 2 photons.
6. How many micromoles of CO2 is fixed per milligram of chloroplast in an hour?
Explanation: For one milligram of chloroplast 3.5 micromoles of CO2 is fixed in an hour. This reaction is also known as the “dark reaction”.
7. Which of the following organisms contain chromosome?
a) Green Sulphur bacteria
b) Blue green bacteria
c) Purple bacteria
d) Plant cells
Explanation: A photosynthetic antenna complex found in Green Sulphur bacteria is known as chromosome. They are smaller than the usual antennas in bacteria and lack some protein complexes that aids support for the pigments required for photosynthesis.
8. Which of the following organisms lack photophosphorylation?
Explanation: Yeast is a heterotroph which cannot synthesize its own food by the use of sunlight. It is devoid of the photosynthetic pigments and photophosphorylation requires these pigments.
9. In the conversion of ADP to ATP by the enzyme ATP synthase, which reaction helps in the movement of H+ across the membranes?
a) Redox reaction
b) Oxidation reaction
d) Redox reaction
Explanation: The chemiosmosis is the process by which H+ ions move from thylakoids to stroma. It is simultaneous process of osmosis with chemical reactions.
10. Which of the following protein is disrupted due to the disorder in photophosphorylation reaction?
Explanation: The disorder in photophosphorylation due to high intensity light causes an accumulation of reactive oxygen species. This causes them to bind with D1 protein and inactivates them.
11. The inactivation of photosynthesis is known as photo inhibition.
Explanation: When there is a high intensity of light, the photosynthesis inhibition happens due to the block in the electron transport chain. This is known as photo inhibition. This photosynthetic capacity is reduced, which in turn reduces the normal metabolism of all plants.
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