Chapter 8.7: Photorespiration

Question 1

Define photorespiration

Answer 1

action of the enzyme rubisco, which catalyzes the oxidation of RuBP, releasing CO₂; this reverses carbon fixation and can reduce the yield of photosynthesis

Question 2

What is the first step of C₄ photosynthesis?

Answer 2

o Initially fix carbon using PEP carboxylase in mesophyll cells

Question 3

Define • Crassulacean Acid Metabolism

Answer 3

a mode of carbon dioxide fixation by which CO₂ enters open leaf stomata at night and is used in photosynthesis during the day, when stomata are closed to prevent water loss

Question 4

Why do stomata close?

Answer 4

o Under hot, arid conditions, specialized openings in the leaf called stomata close to conserve water  As a result, low-CO₂ and high-O₂ conditions within the leaf favor photorespiration

Question 5

After o CAM plants initially fix CO₂ using PEP carboxylase to produce oxaloacetate, what is the next step of CAM photosynthesis?

Answer 5

o The oxaloacetate is often converted into other organic acids  These organic compounds accumulate during the night and are stored in the vacuole

Question 7

What is the first step of CAM photosynthesis?

Answer 7

o CAM plants initially fix CO₂ using PEP carboxylase to produce oxaloacetate

Question 8

After o Produces the organic acid oxaloacetate, which is converted to malate and transported to bundle-sheath cells that surround the leaf veins, what is the next step of C₄ photosynthesis?

Answer 8

o Within the bundle-sheath cells, malate is decarboxylated to produce pyruvate and CO₂  Because the bundle-sheath cells are impermeable to CO₂, the local level of CO₂ is high and carbon fixation by rubisco and the Calvin cycle is efficient

Question 9

After o Initially fix carbon using PEP carboxylase in mesophyll cells, what is the next step of C₄ photosynthesis?

Answer 9

o Produces the organic acid oxaloacetate, which is converted to malate and transported to bundle-sheath cells that surround the leaf veins

Question 10

Define CAM plants

Answer 10

plants that use C₄ carbon fixation at night, then used the stored malate to generate CO₂ during the day to minimize desiccation

Question 11

What are plants that use C₄ carbon fixation at night, then used the stored malate to generate CO₂ during the day to minimize desiccation?

Answer 11

CAM plants

Question 12

What is the advantage of the C₄ pathway?

Answer 12

o Advantageous in hot dry climates where photorespiration would remove more than half of the carbon fixed by the usual C₃ pathway alone

Question 13

After oWithin the bundle-sheath cells, malate is decarboxylated to produce pyruvate and CO₂, what is the next step of C₄ photosynthesis?

Answer 13

o The pyruvate produced by decarboxylation is transported back to the mesophyll cells

Question 14

What is the action of the enzyme rubisco, which catalyzes the oxidation of RuBP, releasing CO₂; this reverses carbon fixation and can reduce the yield of photosynthesis?

Answer 14

photorespiration

Question 15

After The oxaloacetate is often converted into other organic acid, what is the last step of CAM photosynthesis?

Answer 15

o During the day, when the stomata are close, the organic acids are decarboxylated to yield high levels of CO₂  These high levels of CO₂ drive the Calvin cycle and minimize

Question 16

What is the disadvantage of the C₄ pathway?

Answer 16

o The C₄ pathway requires 12 additional ATP compared to the Calvin cycle in order to produce a single glucose

Question 17

What is a mode of carbon dioxide fixation by which CO₂ enters open leaf stomata at night and is used in photosynthesis during the day, when stomata are closed to prevent water loss?

Answer 17

• Crassulacean Acid Metabolism