BioInteractive Photorespiration and Alternative Carbon Fixation 1 — Questions and Answers
Question 1: What is photorespiration?
- A process where RuBisCO fixes O2 instead of CO2, releasing CO2 and reducing photosynthetic efficiency (Correct answer)
- A process that produces ATP from light
- An alternative way to split water
- A method of cyclic electron flow
Correct answer: A process where RuBisCO fixes O2 instead of CO2, releasing CO2 and reducing photosynthetic efficiency
Photorespiration occurs when RuBisCO oxygenates RuBP instead of carboxylating it, wasting energy and releasing CO2 without fixing carbon.
Question 2: Under what conditions is photorespiration most likely to occur?
- High O2, low CO2, and high temperature (Correct answer)
- Low O2, high CO2, and low temperature
- Darkness and cool temperatures
- High humidity and low light
Correct answer: High O2, low CO2, and high temperature
Photorespiration is favored when O2 concentrations are high relative to CO2 and temperatures are elevated, causing RuBisCO to act as an oxygenase.
Question 3: How do C4 plants reduce photorespiration?
- They concentrate CO2 around RuBisCO in bundle sheath cells using a CO2 pump (Correct answer)
- They lack RuBisCO entirely
- They fix carbon only at night
- They use a different electron transport chain
Correct answer: They concentrate CO2 around RuBisCO in bundle sheath cells using a CO2 pump
C4 plants initially fix CO2 into 4-carbon acids in mesophyll cells and transport them to bundle sheath cells, where CO2 is released in high concentrations for RuBisCO.
Question 4: What enzyme initially fixes CO2 in C4 plants?
- PEP carboxylase (Correct answer)
- RuBisCO
- Rubisco activase
- Carbonic anhydrase
Correct answer: PEP carboxylase
PEP carboxylase (PEPC) fixes CO2 into oxaloacetate in the mesophyll cells of C4 plants; it has a much higher affinity for CO2 than RuBisCO.
Question 5: What is the 4-carbon compound first produced when CO2 is fixed in C4 plants?
- Oxaloacetate (Correct answer)
- 3-phosphoglycerate
- Pyruvate
- Malate
Correct answer: Oxaloacetate
PEP carboxylase combines CO2 with phosphoenolpyruvate (PEP) to form oxaloacetate, a 4-carbon compound, in the mesophyll cells.
Question 6: Which type of plants are best adapted to hot, sunny, arid environments due to reduced photorespiration?
- C4 plants (Correct answer)
- C3 plants
- Bryophytes
- Shade-adapted ferns
Correct answer: C4 plants
C4 plants minimize photorespiration in hot, sunny conditions by concentrating CO2 around RuBisCO, making them highly efficient in such environments.
BioInteractive Photorespiration and Alternative Carbon Fixation 1
What is photorespiration?