Q: Which of the following equations correctly represents the overall process of photosynthesis?

$$6\ \mathrm{CO}_2 + 6\ \mathrm{H}_2\mathrm{O} + \text{light energy} \rightarrow \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6\ \mathrm{O}_2$$

Question 1

Which of the following best describes the relationship between photosynthesis and cellular respiration in the ecosystem, as shown in the first image?

Accepted Answer

Photosynthesis transforms light energy into chemical energy stored in organic molecules, which are then broken down by cellular respiration to produce ATP and release heat.

Question 2

In the context of the chemical cycling diagram (second image), what is the primary fate of the energy captured by plants from sunlight?

Accepted Answer

It is converted to chemical energy, which is used by organisms to do work and eventually lost as heat.

Question 3

Which of the following equations correctly represents the overall process of photosynthesis?

Accepted Answer

$$6\ \mathrm{CO}_2 + 6\ \mathrm{H}_2\mathrm{O} + 	ext{light energy} ightarrow \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6\ \mathrm{O}_2$$

Question 4

Which structure in the chloroplast is the primary site of the light-dependent reactions, and why is its structure important?

Accepted Answer

The thylakoid membrane, because its large surface area allows for the organization of photosystems and electron transport chains.

Question 5

What is the main function of Photosystem II (PSII) in the light reactions of photosynthesis?

Accepted Answer

To split water molecules, releasing oxygen and providing electrons to the electron transport chain.

Question 6

If water ($$\mathrm{H}_2\mathrm{O}) is $$not available to the chloroplast, what would be the immediate effect on the light reactions?

Accepted Answer

Both ATP and NADPH production would decrease because electrons from water are required to drive the electron transport chain.

Question 7

Which of the following best explains why the absorption spectrum of chlorophyll a and b peaks in the blue and red regions of the spectrum (see fifth image)?

Accepted Answer

Chlorophyll molecules absorb blue and red light most efficiently, which drives the light reactions of photosynthesis.

Question 8

What is the primary purpose of the Calvin cycle in photosynthesis?

Accepted Answer

To use ATP and NADPH to reduce $$\mathrm{CO}_2 to $$sugar.

Question 9

Which of the following would most likely occur if the supply of NADPH to the Calvin cycle were interrupted?

Accepted Answer

The reduction of $$\mathrm{CO}_2 to G3P $$would slow or stop, decreasing sugar production.

Question 10

A herbicide blocks electron flow between Photosystem II and Photosystem I. What is the most likely effect on ATP and NADPH production?

Accepted Answer

Both ATP and NADPH production decrease because the electron transport chain is disrupted.

Question 11

Why do plants require both chloroplasts and mitochondria?

Accepted Answer

Chloroplasts capture light energy to produce sugars, while mitochondria break down sugars to generate ATP for cellular work.

Question 12

Which of the following best describes the role of ATP synthase in the light reactions?

Accepted Answer

It synthesizes ATP from ADP and inorganic phosphate using the energy of a proton gradient across the thylakoid membrane.

Question 13

How does increasing light intensity affect the rate of the light reactions up to a certain point?

Accepted Answer

The rate of the light reactions increases with light intensity until it reaches a plateau due to saturation of the photosynthetic machinery.

Question 14

Which molecule is oxidized and which is reduced in the overall equation for photosynthesis?

Accepted Answer

$$\mathrm{H}_2\mathrm{O} is $$oxidized to $$\mathrm{O}_2$$, and $$\mathrm{CO}_2 is $$reduced to glucose.

Question 15

What would happen to a plant if Photosystem II stopped functioning but Photosystem I remained active?

Accepted Answer

ATP and NADPH production would decrease, and oxygen would not be produced.

Question 16

Why is the Calvin cycle considered an anabolic pathway?

Accepted Answer

It uses energy to build complex molecules like sugars from simpler molecules such as $$\mathrm{CO}_2.$$

Question 17

Which of the following best explains why treated weeds in the herbicide case study showed yellow leaves?

Accepted Answer

The herbicide disrupted the light reactions, reducing chlorophyll content and impairing photosynthesis.

Question 18

How does the structure of the thylakoid membrane facilitate the light reactions of photosynthesis?

Accepted Answer

It provides a large surface area for the arrangement of photosystems, electron transport chains, and ATP synthase, enabling efficient light capture and ATP/NADPH production.

Question 19

Which of the following is a direct input to the Calvin cycle?

Accepted Answer

Carbon dioxide ($$\mathrm{CO}_2)$$

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