Part 4 — C₄ Pathway, Kranz Anatomy, Photorespiration (Q76–100)

Part 4 (Q76–100) of Chapter 13 – Photosynthesis in Higher Plants (Class 11 NCERT, NEET relevance).

This section covers C₄ Pathway (Hatch–Slack), Kranz Anatomy, and Photorespiration (C₂ cycle).

Part 4 — C₄ Pathway, Kranz Anatomy, Photorespiration (Q76–100)

Q76.

The first stable product of the C₄ pathway is:
A. 3-PGA
B. Oxaloacetate (OAA) ✅
C. Pyruvate
D. G3P

Explanation:

• A. First product in C₃ cycle.
• B. (Correct) OAA (a 4C compound) is first stable product in C₄ pathway.
• C/D. Later intermediates.

Q77.

The enzyme that fixes CO₂ in C₄ plants initially is:
A. Rubisco
B. PEP carboxylase ✅
C. Phosphoribulokinase
D. Carboxypeptidase

Explanation:

• A. Rubisco operates in bundle sheath cells.
• B. (Correct) PEP carboxylase fixes CO₂ to PEP → OAA in mesophyll cells.
• C/D. Not involved here.

Q78.

Kranz anatomy is a characteristic of:
A. C₃ plants
B. C₄ plants ✅
C. CAM plants only
D. Bryophytes

Explanation:

• A. C₃ plants lack Kranz anatomy.
• B. (Correct) C₄ plants show Kranz anatomy (bundle sheath + mesophyll specialization).
• C. CAM plants fix CO₂ differently but not via Kranz.
• D. Don’t show it.

Q79.

Bundle sheath cells in C₄ plants contain:
A. Only PSII
B. Only PSI
C. Rubisco and Calvin cycle enzymes ✅
D. No chloroplasts

Explanation:

• A/B. Both photosystems absent/reduced here.
• C. (Correct) Bundle sheath cells run Calvin cycle with Rubisco.
• D. Wrong—chloroplasts are present.

Q80.

The advantage of the C₄ pathway is:
A. Less ATP requirement
B. Elimination of photorespiration ✅
C. Higher efficiency at low light
D. Absence of Calvin cycle

Explanation:

• A. C₄ requires more ATP.
• B. (Correct) Spatial separation prevents O₂ binding to Rubisco → no photorespiration.
• C. Efficiency higher in high light and temperature.
• D. Calvin cycle still operates in bundle sheath.

Q81.

C₄ plants show high productivity in:
A. Cool, shady regions
B. Hot, dry tropical regions ✅
C. Polar regions
D. High altitudes

Explanation:

• A. C₃ plants are better adapted here.
• B. (Correct) C₄ plants thrive in high temp + light with low water availability.
• C/D. Not suitable.

Q82.

Which statement is true for C₄ plants?
A. They need less ATP per CO₂ fixed
B. They require more ATP than C₃ plants ✅
C. They show more photorespiration
D. They lack Kranz anatomy

Explanation:

• A. Opposite is true.
• B. (Correct) C₄ requires ~30 ATP vs 18 ATP for one glucose due to additional steps.
• C/D. Incorrect.

Q83.

Which enzyme is absent in mesophyll cells of C₄ plants?
A. PEP carboxylase
B. Rubisco ✅
C. Malate dehydrogenase
D. Pyruvate phosphate dikinase

Explanation:

• A/C/D. Present in mesophyll.
• B. (Correct) Rubisco is restricted to bundle sheath.

Q84.

C₄ pathway is also called:
A. CAM cycle
B. Hatch–Slack pathway ✅
C. C₂ pathway
D. Krebs cycle

Explanation:

• A. CAM is different.
• B. (Correct) C₄ pathway = Hatch–Slack pathway.
• C. C₂ = photorespiration.
• D. Respiration pathway.

Q85.

The C₄ cycle involves how many different cell types?
A. 1
B. 2 ✅
C. 3
D. 4

Explanation:

• A. C₃ cycle occurs in one cell type.
• B. (Correct) Mesophyll and bundle sheath cells both participate.
• C/D. Not correct.

Q86.

Which of the following C₄ plants is commonly cultivated?
A. Rice
B. Maize ✅
C. Wheat
D. Barley

Explanation:

• A/C/D. C₃ crops.
• B. (Correct) Maize, sugarcane, sorghum are typical C₄ plants.

Q87.

Photorespiration is negligible in C₄ plants because:
A. Rubisco has no oxygenase activity
B. CO₂ concentration is high around Rubisco ✅
C. They use only PSI
D. They lack Calvin cycle

Explanation:

• A. Rubisco still has oxygenase activity.
• B. (Correct) Bundle sheath cells have high CO₂ concentration → minimizes oxygenase activity.
• C/D. Not correct.

Q88.

In photorespiration, the substrate for oxygenase activity of Rubisco is:
A. 3-PGA
B. RuBP ✅
C. OAA
D. Malate

Explanation:

• A/C/D. Not substrates.
• B. (Correct) RuBP can bind O₂ instead of CO₂ in presence of high O₂.

Q89.

Which organelles are involved in photorespiration?
A. Chloroplast and mitochondria
B. Chloroplast, mitochondria, peroxisome ✅
C. Chloroplast only
D. Cytoplasm

Explanation:

• A. Incomplete.
• B. (Correct) Photorespiration spans chloroplast, peroxisome, mitochondria.
• C/D. Not true.

Q90.

The first product of photorespiration is:
A. 3-PGA
B. Phosphoglycolate ✅
C. G3P
D. Malate

Explanation:

• A. Carboxylation product.
• B. (Correct) Oxygenase reaction of RuBP → phosphoglycolate.
• C/D. Not products.

Q91.

What is the consequence of photorespiration?
A. ATP and NADPH are produced
B. CO₂ is released without ATP/NADPH generation ✅
C. O₂ is fixed efficiently
D. Glucose is formed

Explanation:

• A/D. False.
• B. (Correct) Photorespiration wastes energy and carbon.
• C. O₂ binding is wasteful.

Q92.

Why is photorespiration considered wasteful?
A. Consumes ATP but does not fix CO₂ ✅
B. Produces too much glucose
C. Produces excess NADPH
D. Enhances transpiration

Explanation:

• A. (Correct) It consumes ATP, releases CO₂ → net loss.
• B–D. Incorrect.

Q93.

The C₂ cycle is another name for:
A. Photorespiration ✅
B. C₃ pathway
C. C₄ pathway
D. CAM cycle

Explanation:

• A. (Correct) Photorespiration is also called C₂ cycle.
• B–D. Different pathways.

Q94.

Rubisco functions as:
A. Carboxylase only
B. Oxygenase only
C. Both carboxylase and oxygenase ✅
D. Neither

Explanation:

• A/B. Partial truth.
• C. (Correct) Rubisco has dual function → basis of photorespiration.
• D. Incorrect.

Q95.

At high O₂ and low CO₂ concentration, Rubisco favors:
A. Carboxylase activity
B. Oxygenase activity ✅
C. Both equally
D. None

Explanation:

• A. Occurs when CO₂ high.
• B. (Correct) Low CO₂ + high O₂ → oxygenase activity → photorespiration.
• C/D. Not true.

Q96.

Photorespiration results in net loss of:
A. Nitrogen
B. Carbon ✅
C. Sulphur
D. Water

Explanation:

• A/C/D. Not directly.
• B. (Correct) CO₂ is released without glucose formation → carbon loss.

Q97.

In which plants is photorespiration least?
A. C₃ plants
B. C₄ plants ✅
C. CAM plants
D. Algae

Explanation:

• A. High photorespiration.
• B. (Correct) C₄ suppresses photorespiration by CO₂ concentrating mechanism.
• C. Intermediate.
• D. Varies.

Q98.

Which statement about C₄ plants is incorrect?
A. They have Kranz anatomy
B. They produce more glucose with less water loss
C. They require less ATP than C₃ ✅
D. They minimize photorespiration

Explanation:

• A/B/D. True.
• C. (Correct) C₄ requires more ATP due to additional steps.

Q99.

In photorespiration, glycolate formed in chloroplast is oxidized in:
A. Mitochondria
B. Peroxisome ✅
C. Stroma
D. Nucleus

Explanation:

• A. Later stage.
• B. (Correct) Glycolate oxidized to glyoxylate in peroxisome.
• C/D. Not involved.

Q100.

Which of the following statements is true?
A. C₃ plants are more efficient in hot, dry climate
B. C₄ plants minimize photorespiration by concentrating CO₂ around Rubisco ✅
C. Photorespiration generates ATP
D. C₂ cycle operates only in bundle sheath cells

Explanation:

• A. False; C₃ suffer under such conditions.
• B. (Correct) C₄ spatially separate steps → high CO₂ in bundle sheath.
• C. False; it consumes ATP.
• D. Wrong; C₂ involves 3 organelles.

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