Sample 1Medium
A figure shows a leaf in vertical section. Each vascular bundle is surrounded by a ring of large cells (A) with many chloroplasts, thick walls impervious to gaseous exchange and no intercellular spaces. Loosely packed cells (B) lie around this ring. Which statement about this leaf is correct?
- A
RuBisCO in B fixes CO2, and A only stores starch
- B
The Calvin cycle runs only in B, and A carries out the C4 cycle
- C
This is a C3 leaf, and its first stable product is a 3-carbon acid
- D
B fixes CO2 with PEP carboxylase, and the Calvin cycle runs in A
Show the answer
The answer is D.Large bundle sheath cells around the vascular bundles are Kranz anatomy, found in C4 plants. Mesophyll cells fix CO2 with PEP carboxylase into oxaloacetic acid. The C4 acid reaches the bundle sheath, where it releases CO2 to RuBisCO and the Calvin cycle.
- A.
The mesophyll cells (B) of a C4 plant lack RuBisCO. Their first CO2 acceptor is PEP, fixed by PEP carboxylase.
- B.
In C4 plants the Calvin cycle runs in the bundle sheath cells (A). The initial fixation into C4 acids happens in the mesophyll (B).
- C.
A ring of large bundle sheath cells around each vascular bundle is Kranz anatomy, the mark of a C4 plant. Its first product is a 4-carbon acid, OAA.
NCERT: Class 11 Biology, Chapter 11
Sample 2NEET level
Consider the following statements about C4 plants: I. Their leaves have Kranz anatomy, with bundle sheath cells that have a large number of chloroplasts. II. The primary CO2 acceptor in their mesophyll cells is a three-carbon molecule, phosphoenol pyruvate. III. RuBisCO is abundant in their mesophyll cells. IV. Photorespiration does not occur in them. Which of the statements above are correct?
- A
I and III only
- B
II and III only
- C
I, II and III only
- D
I, II and IV only
Show the answer
The answer is D.C4 leaves have Kranz anatomy, PEP (a 3-carbon compound) fixes CO2 in the mesophyll, and photorespiration does not occur. RuBisCO is absent from the mesophyll cells and is found in the bundle sheath cells, so III is wrong.
- A.
Includes III and leaves out II and IV, both correct.
- B.
Includes III: the mesophyll cells of C4 plants lack RuBisCO.
- C.
Includes III, which is wrong, and leaves out IV.
NCERT: Class 11 Biology, Chapter 11 (Photosynthesis in Higher Plants), The C4 Pathway