Photorespiration — practice questions

Question 1 · difficulty L1 · recall

Which enzyme initiates photorespiration by acting as an oxygenase?

• A. RuBisCO
• B. PEP carboxylase
• C. ATP synthase
• D. NADP reductase

Question 2 · difficulty L2 · understanding

Which of the following statements about RuBisCO is true?

• A. It is an enzyme involved in the photolysis of water
• B. It catalyzes the carboxylation of RuBP
• C. It is active only in the dark
• D. It has higher affinity for oxygen than carbon dioxide

Question 3 · difficulty L2 · understanding

Why is photorespiration considered wasteful for a C3 plant?

• A. It produces large amounts of ATP and glucose
• B. Carbon loss without sugar or useful ATP gain
• C. It fixes extra carbon dioxide into four-carbon acids
• D. It replaces mitochondrial respiration completely

Question 4 · difficulty L3 · understanding

Given below are two statements: Statement I: In $$\mathrm{C}_3$$ plants, some $$\mathrm{O}_2$$ binds to $$\mathrm{RuBisCO}$$, hence $$\mathrm{CO}_2$$ fixation is decreased. Statement II: In $$\mathrm{C}_4$$ plants, mesophyll cells show very little photorespiration while bundle sheath cells do not show photorespiration. In the light of the above statements, choose the correct answer from the options given below:

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true but Statement II is false
• D. Statement I is false but Statement II is true

Question 5 · difficulty L3 · understanding

The oxygenation activity of RuBisCo enzyme in photorespiration leads to the formation of

• A. 1 molecule of 3-C compound and 1 molecule of 2-C compound
• B. 1 molecule of 3-C compound
• C. 1 molecule of 6-C compound
• D. 2 molecules of 3-C compound

Question 6 · difficulty L3 · application

Hot, dry weather causes a C3 plant to close its stomata. Why can this increase photorespiration?

• A. PEP carboxylase replaces RuBisCO
• B. Internal oxygen falls to zero
• C. Lower CO2:O2 favours RuBisCO oxygenation
• D. The light reactions stop completely as soon as the stomata close

Question 7 · difficulty L3 · application

A researcher inhibits RuBisCO oxygenase activity without reducing its carboxylase activity. Which process should decline most directly?

• A. Photorespiration
• B. Cyclic photophosphorylation
• C. Water photolysis
• D. PEP regeneration

Question 8 · difficulty L4 · analysis

Two plants are exposed to high temperature and strong light. Plant P maintains high carbon dioxide around RuBisCO in bundle-sheath cells, whereas plant Q does not. Which plant should lose less carbon through photorespiration?

• A. Neither can photosynthesise
• B. Plant Q
• C. Both lose equal amounts
• D. Plant P