Question 1

Which of the following statements best explains how photosynthesis and cellular respiration contribute to the cycling of carbon atoms on Earth?

Accepted Answer

Photosynthesis converts carbon dioxide into organic molecules, and cellular respiration breaks down those molecules to release carbon dioxide.

Question 2

Which of the following organisms are classified as photoautotrophs?

Accepted Answer

Plants, algae, and some bacteria

Question 3

What is the primary role of chlorophyll in photosynthesis?

Accepted Answer

To absorb light energy and convert it to chemical energy

Question 4

During photosynthesis, which molecule is oxidized and which is reduced?

Accepted Answer

H$$_2O is $$oxidized and CO$$_2 is $$reduced

Question 5

Which equation correctly represents the overall process of photosynthesis?

Accepted Answer

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

Question 6

Why do intact chloroplasts not release heat when illuminated, unlike a solution of isolated chlorophyll?

Accepted Answer

Because the energy from excited electrons is used to synthesize ATP and NADPH instead of being lost as heat

Question 7

Which color of light is least effective in driving photosynthesis and why?

Accepted Answer

Green, because chlorophyll reflects green light rather than absorbing it

Question 8

What is the function of the electron transport chain in the light reactions of photosynthesis?

Accepted Answer

To pump protons into the thylakoid space, creating a gradient that drives ATP synthesis

Question 9

Why are two photons of light required for the movement of electrons from water to NADP$$^+ in $$the light reactions?

Accepted Answer

Because electrons must be excited twice, once in photosystem II and once in photosystem I, to reach the energy level needed to reduce NADP$$^+$$

Question 10

Which of the following best describes the process of photophosphorylation?

Accepted Answer

The synthesis of ATP using the energy from light-driven electron transport and a proton gradient across the thylakoid membrane

Question 11

During the Calvin cycle, what is the role of ATP and NADPH?

Accepted Answer

They provide energy and electrons for the reduction of CO$$_2 to G3P$$

Question 12

Which step in the Calvin cycle involves the incorporation of CO$$_2$$ into organic molecules?

Accepted Answer

Carbon fixation

Question 13

Why does photorespiration occur more frequently in C$$_3$$ plants than in C$$_4 or $$CAM plants on hot, dry days?

Accepted Answer

C$$_3$$ plants do not have mechanisms to concentrate CO$$_2$$ around Rubisco, leading to increased oxygenation and photorespiration when stomata close

Question 14

Which of the following is a correct comparison between photophosphorylation in chloroplasts and oxidative phosphorylation in mitochondria?

Accepted Answer

Both use a proton gradient to drive ATP synthesis via ATP synthase

Question 15

Which of the following is NOT a product of the light reactions of photosynthesis?

Accepted Answer

Glucose

Question 16

In the context of the greenhouse effect, how does photosynthesis help moderate climate change?

Accepted Answer

By removing CO$$_2$$ from the atmosphere and storing it in organic molecules

Question 17

Which of the following statements about the structure of chloroplasts is correct?

Accepted Answer

Chloroplasts contain stacks of thylakoids surrounded by a double membrane and a fluid called stroma

Question 18

Which of the following best describes the fate of oxygen atoms during photosynthesis, as determined by isotope tracing experiments?

Accepted Answer

Oxygen released as O$$_2$$ comes from water, not CO$$_2$$

Question 19

Which of the following is a real-world consequence of photosynthesis for life on Earth?

Accepted Answer

It provides food and oxygen for almost all living organisms

Photosynthesis: Using Light to Make Food (Campbell Biology Chapter 7 Study Notes)

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