10.4 plants have adapted photosynthesis to environmental conditions

Question 1

Photorespiration

Answer 1

• Rubisco, a key enzyme in photosynthesis, can act as an oxygenase under certain conditions.
• High oxygen and low carbon dioxide concentrations favor oxygenase activity.
• Occurs on hot, dry days when leaf stomata close to prevent water loss, leading to increased oxygen levels relative to carbon dioxide.

Question 2

Phosphoglycolate Formation

Answer 2

• Rubisco’s oxygenase activity leads to the formation of phosphoglycolate.
• Phosphoglycolate inhibits reactions in the Calvin cycle and must be eliminated.
• Series of reactions in peroxisomes and mitochondria convert phosphoglycolate to 3-phosphoglycerate, resulting in CO2 loss.

Question 3

C3 Plants

Answer 3

• C3 plants fix CO2 using the Calvin cycle, with the first product being 3-phosphoglycerate (3PG).
• Prone to photorespiration on hot days but have advantages in cooler conditions.

Question 4

C4 Plants

Answer 4

• C4 plants fix CO2 using a different pathway, with the first product being oxaloacetate (4 carbon).
• Less prone to photorespiration on hot days but have advantages in warm, dry climates.

Question 5

Crassulacean Acid Metabolism (CAM)

Answer 5

• CAM plants have a unique carbon fixation strategy to conserve water.
• Stomata open at night to fix CO2 and store malate in vacuoles.
• During the day, malate is decarboxylated in chloroplasts, releasing CO2 for the Calvin cycle.

Question 6

Rubisco

Answer 6

• Rubisco is a key enzyme in carbon fixation, catalyzing the reaction between carbon dioxide and ribulose-1,5-bisphosphate (RuBP).
• It can also catalyze oxygenation of RuBP under certain conditions, leading to photorespiration.

Question 7

Oxygenase Activity

Answer 7

• Rubisco’s oxygenase activity occurs when oxygen concentration is relatively high compared to carbon dioxide.
• This leads to the inefficient fixation of oxygen instead of carbon dioxide, resulting in photorespiration.

Question 8

Advantages of C3 Plants

Answer 8

• C3 plants have advantages in cooler conditions due to their efficient photosynthetic pathway under normal temperatures.
• However, they are susceptible to photorespiration under high temperatures.

Question 9

Advantages of C4 Plants

Answer 9

• C4 plants have advantages in warm, dry climates due to their reduced susceptibility to photorespiration.
• Their carbon fixation pathway allows them to thrive in environments with high temperatures and low water availability.

Question 10

Crassulacean Acid Metabolism (CAM) Strategy

Answer 10

• CAM plants open stomata at night to minimize water loss and fix carbon dioxide.
• They store carbon as malate during the night and utilize it during the day for photosynthesis, enabling them to adapt to arid environments.