Question

${{C}_{4}}$ plants are more efficient in photosynthesis at higher temperature due to presence of
A. Bundle sheath
B. Pyruvate phosphate dikinase
C. Well differentiated mesoph
D. Agranal plastids in bundle sheath

Answer 1

${{C}_{4}}$ plants are adapted to tropical regions and they minimize photorespiration, a wasteful process where rubisco reacts with ${{O}_{2}}$ instead of $C{{O}_{2}}$.They also recycle their $C{{O}_{2}}$. In these ways they increase the efficiency of photosynthesis.

Complete answer:
Let us analyse the options one by one.

Option A: Bundle sheath cells are large cells around vascular bundles of ${{C}_{4}}$ plants and are absent in ${{C}_{3}}$ plants. In ${{C}_{4}}$ plants, Calvin cycle takes places in bundle sheaths.Bundle sheath cells are where rubisco enzyme is concentrated and hence avoid its reaction with ${{O}_{2}}$ which is present in the mesophyll cells. Only $C{{O}_{2}}$ which gets concentrated in bundle sheaths reacts with rubisco which increases the efficiency of photosynthesis.
Option B: Pyruvate phosphate dikinase is an enzyme which catalyse the conversion of pyruvate to phosphoenolpyruvate (PEP). PEP is the primary $C{{O}_{2}}$ acceptor in ${{C}_{4}}$ plants which adds to the increased efficiency.
Option C: The well distinguished mesophyll helps only $C{{O}_{2}}$ to concentrate in the bundle sheath cells. This restricts rubisco from reacting with ${{O}_{2}}$ which in turn results in prevention of photorespiration
Option D: Chloroplasts of bundle sheath cells lack grana and they are deficient in photosystem I activity. This is called chloroplast dimorphism and adds to the efficiency of photosynthesis.Therefore, this is the correct option.

Thus, the correct answer is option (D) Agranal plastids in bundle sheath.

Note: The advantages of ${{C}_{4}}$ plants are as follows,
i) They are able to keep their stomata closed for higher periods of time, thereby minimizing water loss.
ii) They are also very efficient in dry and hot climates.
iii) They can produce a lot of energy.
iv) Examples include: Corn, Pineapple, sugarcane, etc.