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$C_4$ plants are more efficient in photosynthesis than $C_3$ plants due to
A
Lower rate of photorespiration
B
Higher leaf area
C
Presence of larger number of chloroplasts in the leaf cells
D
Presence of thin cuticle
Detailed Solution
In $C_3$ plants RuBisCO also acts as an oxygenase: when $O_2$ binds to it, RuBP is broken down in photorespiration, which fixes no $CO_2$, forms no ATP or NADPH and releases already fixed $CO_2$. This lowers productivity.
In $C_4$ plants $CO_2$ is first fixed in the mesophyll cells by PEP carboxylase into a $C_4$ acid, which is transported to the bundle sheath cells and decarboxylated there.
This raises the $CO_2$ concentration around RuBisCO in the bundle sheath, so RuBisCO works as a carboxylase and its oxygenase activity is minimised.
As a result photorespiration does not occur (is negligible) in $C_4$ plants, so their productivity and yields are better; they also tolerate higher temperatures and high light intensities.
Hence $C_4$ plants are more efficient due to a lower rate of photorespiration.
Note: the answer line in the source PDF prints (3), but its own explanation ('Photorespiration does not occur in C4 plants') and NCERT support 'lower rate of photorespiration', which is taken as the answer here.
In $C_4$ plants $CO_2$ is first fixed in the mesophyll cells by PEP carboxylase into a $C_4$ acid, which is transported to the bundle sheath cells and decarboxylated there.
This raises the $CO_2$ concentration around RuBisCO in the bundle sheath, so RuBisCO works as a carboxylase and its oxygenase activity is minimised.
As a result photorespiration does not occur (is negligible) in $C_4$ plants, so their productivity and yields are better; they also tolerate higher temperatures and high light intensities.
Hence $C_4$ plants are more efficient due to a lower rate of photorespiration.
Note: the answer line in the source PDF prints (3), but its own explanation ('Photorespiration does not occur in C4 plants') and NCERT support 'lower rate of photorespiration', which is taken as the answer here.