Q: Which of the following best describes the overall chemical equation for photosynthesis in plants?

$$6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6$ + 6O_2$$

Question 1

Which of the following best describes the overall chemical equation for photosynthesis in plants?

Accepted Answer

$$6CO_2 + 6H_2O + 	ext{light energy} ightarrow C_6H_{12}O_6$ + 6O_2$$

Question 2

Which structure within the chloroplast is the primary site of the light reactions of photosynthesis?

Accepted Answer

Thylakoid membrane

Question 3

What is the main function of the pigment chlorophyll a in photosynthesis?

Accepted Answer

It directly participates in the light reactions by transferring excited electrons to the primary electron acceptor.

Question 4

Which of the following best explains why plants appear green to the human eye?

Accepted Answer

Chlorophyll reflects and transmits green wavelengths of light.

Question 5

During the light reactions, what is the immediate source of electrons for the electron transport chain in photosystem II?

Accepted Answer

Water ($$H_2O)$$

Question 6

Which of the following is a product of the linear electron flow in the light reactions of photosynthesis?

Accepted Answer

ATP and NADPH

Question 7

How does chemiosmosis in chloroplasts differ from chemiosmosis in mitochondria?

Accepted Answer

In chloroplasts, protons are pumped into the thylakoid space and diffuse back into the stroma to drive ATP synthesis; in mitochondria, protons are pumped into the intermembrane space and diffuse back into the matrix.

Question 8

Which enzyme catalyzes the fixation of carbon dioxide in the Calvin cycle?

Accepted Answer

Rubisco (Ribulose bisphosphate carboxylase/oxygenase)

Question 9

A plant growing in a hot, arid environment closes its stomata during the day and fixes CO$$_2 at $$night into organic acids. What type of plant is this and what is the advantage of this adaptation?

Accepted Answer

CAM plant; it reduces water loss by separating carbon fixation and the Calvin cycle in time.

Question 10

Which of the following statements about photorespiration is correct?

Accepted Answer

Photorespiration occurs when rubisco binds O$$_2$$ instead of CO$$_2$$, leading to the consumption of energy without producing sugar.

Question 11

Which of the following best describes the role of accessory pigments such as chlorophyll b and carotenoids in photosynthesis?

Accepted Answer

They broaden the spectrum of light that can be used for photosynthesis by absorbing wavelengths not absorbed by chlorophyll a.

Question 12

In the Calvin cycle, for the net synthesis of one molecule of glyceraldehyde 3-phosphate (G3P), how many molecules of ATP and NADPH are consumed?

Accepted Answer

$$9$$ ATP and $$6$$ NADPH

Question 13

Which of the following is a key difference between C$$_3$$ and C$$_4$$ plants?

Accepted Answer

C$$_4$$ plants initially fix CO$$_2$$ into a four-carbon compound in mesophyll cells, while C$$_3$$ plants fix CO$$_2$$ directly via rubisco.

Question 14

A scientist uses a spectrophotometer to analyze a pigment extract from a plant leaf. What information can be obtained from the absorption spectrum produced?

Accepted Answer

The wavelengths of light absorbed by the pigment, indicating which wavelengths are most effective for photosynthesis.

Question 15

Which of the following best explains why the action spectrum for photosynthesis is broader than the absorption spectrum of chlorophyll a alone?

Accepted Answer

Accessory pigments such as chlorophyll b and carotenoids absorb additional wavelengths of light.

Question 16

Which of the following is a direct product of cyclic electron flow in the light reactions of photosynthesis?

Accepted Answer

ATP

Question 17

A mutation disables the enzyme NADP$$^+$$ reductase in a plant cell. Which of the following would be the most immediate effect on the light reactions?

Accepted Answer

The plant would be unable to produce NADPH from NADP$$^+.$$

Question 18

Which of the following best describes the relationship between the light reactions and the Calvin cycle?

Accepted Answer

The light reactions provide ATP and NADPH to the Calvin cycle, which uses them to fix carbon dioxide into sugar.

Question 19

Which of the following is a real-world consequence of photorespiration in crop plants under hot, dry conditions?

Accepted Answer

Reduced crop yield due to loss of fixed carbon and energy.

Photosynthesis: Mechanisms, Pathways, and Adaptations

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