Question 1

Which of the following best explains the structural similarity between mitochondria and chloroplasts according to the endosymbiotic theory?

Accepted Answer

Both organelles originated from the fusion of prokaryotic cells with eukaryotic cells, leading to a shared double-membrane structure.

Question 2

In the light-harvesting phase of photosynthesis, what is the primary function of the reaction center within a photosystem?

Accepted Answer

To excite and eject an electron from chlorophyll, initiating charge separation.

Question 3

Which equation correctly represents the net synthesis of one triose phosphate molecule during the Calvin cycle?

Accepted Answer

$$3CO_2 + 9ATP + 6NADPH + 5H_2O \rightarrow G3P + 9ADP + 6NADP^+ + 8P_i$$

Question 4

Which of the following statements about the electron transport chain in chloroplasts is correct?

Accepted Answer

Electron flow between photosystem II and photosystem I passes through a cytochrome complex, which pumps protons into the thylakoid lumen.

Question 5

What is the main regulatory mechanism for key enzymes of the Calvin cycle in photosynthetic tissues?

Accepted Answer

Activation by high stromal pH and magnesium concentrations in the light.

Question 6

Which of the following best describes the role of thioredoxin in the regulation of the Calvin cycle?

Accepted Answer

Thioredoxin senses the redox state of the cell and activates enzymes by reducing disulfide bonds.

Question 7

Rubisco’s oxygenase activity leads to the production of phosphoglycolate. What is the consequence of this reaction for photosynthetic efficiency?

Accepted Answer

Phosphoglycolate cannot be used in the Calvin cycle, leading to decreased photosynthetic efficiency.

Question 8

Which organelles are involved in the glycolate pathway (photorespiration) in plants?

Accepted Answer

Chloroplast, leaf peroxisome, and mitochondrion.

Question 9

How do C4 and CAM plants minimize photorespiration and increase photosynthetic efficiency?

Accepted Answer

By fixing CO2 via a preliminary carboxylation that does not involve rubisco, followed by decarboxylation under low oxygen and concentrated CO2 conditions.

Question 10

Which of the following equations represents the ATP synthesis reaction catalyzed by the CF$$_{0}CF$_{1}$$ complex in the chloroplast?

Accepted Answer

$$ADP + P_i \rightarrow ATP$$

Question 11

Which molecule is the initial product of carbon dioxide fixation in the Calvin cycle?

Accepted Answer

3-phosphoglycerate

Question 12

What is the main function of the cytochrome b$$_6/f $$complex in the photosynthetic electron transport chain?

Accepted Answer

To pump protons into the thylakoid lumen, generating a proton gradient.

Question 13

Which of the following is a real-world consequence of rubisco’s oxygenase activity in agricultural crops?

Accepted Answer

Reduced yield due to increased photorespiration under high temperature and low CO$$_2$$ conditions.

Question 14

Which of the following best describes the role of ATP and NADPH produced in the chloroplast?

Accepted Answer

They are used for carbon fixation and reduction in the Calvin cycle, as well as for biosynthesis of fatty acids, chlorophyll, and nitrogen/sulfur assimilation.

Question 15

Which of the following statements about cyanobacteria is correct?

Accepted Answer

Cyanobacteria have internal membranes that function like thylakoids and contain carboxysomes for carbon fixation.

Question 16

Which of the following is a plausible outcome if the proton gradient across the thylakoid membrane is disrupted?

Accepted Answer

ATP synthesis by the CF$$_{0}CF$_{1}$$ complex would decrease significantly.

Question 17

Which of the following best explains why C4 plants are more efficient in hot, dry climates compared to C3 plants?

Accepted Answer

C4 plants spatially separate carbon fixation and the Calvin cycle, reducing photorespiration and increasing efficiency under low CO$$_2$$ and high O$$_2$$ conditions.

Question 18

Which of the following is a multi-step process that integrates light reactions and carbon assimilation in photosynthesis?

Accepted Answer

Light energy is converted to chemical energy (ATP and NADPH) in the thylakoid membrane, which is then used in the stroma for carbon fixation and reduction in the Calvin cycle.

Ch 11 - Photosynthetic Energy Metabolism: Photosynthesis (Cell Biology Study Notes)

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