Question 1

Which enzyme is responsible for the initial fixation of CO$$_2 in $$the Calvin Cycle of C$$_3$$ plants?

Accepted Answer

RuBP carboxylase/oxygenase (Rubisco)

Question 2

During the Calvin Cycle, what is the primary product that exits the cycle and can be used to synthesize glucose?

Accepted Answer

Glyceraldehyde-3-phosphate (G3P)

Question 3

Photorespiration is considered wasteful for plants because:

Accepted Answer

It consumes O$$_2$$ and releases CO$$_2$$ without producing sugars

Question 4

Which of the following best describes the main difference between C$$_3$$ and C$$_4$$ photosynthetic pathways?

Accepted Answer

C$$_3$$ plants fix CO$$_2$$ into a 3-carbon compound, while C$$_4$$ plants initially fix CO$$_2$$ into a 4-carbon compound

Question 5

In CAM plants, how is the timing of carbon fixation different from that in C$$_3$$ plants?

Accepted Answer

CAM plants fix CO$$_2 at $$night and perform the Calvin Cycle during the day

Question 6

Which of the following is a correct summary of the overall chemical equation for photosynthesis?

Accepted Answer

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

Question 7

A plant is exposed to hot, dry conditions. Which adaptation would most likely help it minimize photorespiration?

Accepted Answer

Using the C$$_4$$ pathway to concentrate CO$$_2 in $$bundle sheath cells

Question 8

Which of the following statements about the light-independent reactions (Calvin Cycle) is correct?

Accepted Answer

They use ATP and NADPH produced by the light-dependent reactions

Question 9

If a plant's chloroplasts are unable to regenerate RuBP, what would be the immediate consequence for the Calvin Cycle?

Accepted Answer

CO$$_2$$ fixation would stop

Question 10

Which of the following is a key reason why photorespiration is more likely to occur in C$$_3$$ plants under hot, dry conditions?

Accepted Answer

Stomata close to conserve water, reducing CO$$_2$$ availability and increasing O$$_2$$ concentration

Question 11

A scientist is studying a plant that opens its stomata at night and stores CO$$_2 as an $$organic acid. During the day, it closes its stomata and releases CO$$_2$$ internally for the Calvin Cycle. What type of plant is this?

Accepted Answer

CAM plant

Question 12

Which of the following is NOT an input required for the Calvin Cycle?

Accepted Answer

O$$_2$$

Question 13

In the Calvin Cycle, how many molecules of ATP and NADPH are required to produce one molecule of G3P (glyceraldehyde-3-phosphate)?

Accepted Answer

9 ATP and 6 NADPH

Question 14

Which of the following best explains why C$$_4$$ and CAM plants have evolved in certain environments?

Accepted Answer

To reduce photorespiration and increase efficiency of carbon fixation under stress conditions

Question 15

A mutation causes a plant to lack the enzyme PEP carboxylase. Which process would be most directly affected?

Accepted Answer

Initial CO$$_2$$ fixation in C$$_4$$ and CAM pathways

Question 16

Which of the following statements about the spatial separation of steps in C$$_4$$ photosynthesis is correct?

Accepted Answer

CO$$_2 is $$initially fixed in mesophyll cells and then released in bundle sheath cells for the Calvin Cycle

Question 17

Which of the following is a direct output of the Calvin Cycle that can be used to synthesize other organic molecules?

Accepted Answer

Glyceraldehyde-3-phosphate (G3P)

Question 18

A plant is genetically engineered to have Rubisco with a much higher affinity for CO$$_2$$ than for O$$_2. $$What would be the most likely result?

Accepted Answer

Photorespiration would decrease

Question 19

Which of the following best describes the role of ATP and NADPH in the Calvin Cycle?

Accepted Answer

They provide energy and reducing power for carbon fixation and reduction steps

Question 20

If a plant is placed in an environment with very high O$$_2$$ and low CO$$_2$$ concentrations, what is the most likely effect on its photosynthetic efficiency?

Accepted Answer

Photorespiration will increase, reducing photosynthetic efficiency

Calvin Cycle and Alternative Photosynthetic Pathways

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