Question

${C_4}$ plants are more efficient in photosynthesis than ${C_3}$ plants due to
A. Lower rate of photorespiration
B. Higher leaf areas
C. Presence of large numbers of chloroplasts in the leaf cells.
D. Presence of thin cuticle.

Answer 1

Hint: Photosynthesis: It is the process by which green plants and certain other organisms transform light energy into chemical energy.
Plants contain a pigment known as chlorophyll which is very essential for photosynthesis.

Complete answer:
In order to solve this question we need to know more about photosynthesis and carbon fixation.
>Photosynthesis: It is a process in which organisms like green plants and some other organisms like prokaryotic bacteria convert light energy into chemical energy.
Light energy is used to convert water, carbon dioxide, and inorganic compounds into oxygen and energy richer organic compounds.

> Carbon fixation: Carbon fixation is an integral part of photosynthesis, and something that must be taken into account when engineering photosynthesis into a new host.
Carbon fixation can be used to reduce the host's dependency on organic material as a carbon source

${C_3}$ plant: ${C_3}$ plants are plants in which the primary product of the assimilation of carbon dioxide through photosynthesis is 3-phosphoglycerate, which consists of 3 carbon atoms.

${C_4}$ plant: ${C_4}$ plants are defined as the plants that use the ${C_4}$ pathway during the dark reaction.
In ${C_3}$​ plants, $C{O_2}$ ​is pumped directly into the Calvin cycle, leaving rubisco exposed to ${O_2}$.

Rubisco in a ${C_3}$​ will take up ${O_2}$ ​rather than $C{O_2}$ ​to undergo photorespiration.
 Photorespiration occurs under low concentrations of $C{O_2}$ and high concentrations of ${C_2}$.

This process reduces efficiency of photosynthesis, potentially reducing photosynthetic output by 25% in ${C_3}$plants.
${C_4}$​ plants capture carbon dioxide in their mesophyll cells forming oxaloacetate. This oxaloacetate is then converted to malate and is transported into the bundle sheath cells, where oxygen concentration is low to avoid photorespiration.
So, ${C_4}$plants are more efficient in photosynthesis than ${C_3}$​ plants.

Hence, The correct answer is option (C).

Note:
${C_3}$ Plants:
- Primary product is 3-phosphoglyceric acid.
- It occurs in mesophyll cells.
- Photorespiration rate is very high.
- Carbon fixation occurs only once.
- Carbon dioxide fixation is slow.

${C_4}$ Plants:
- Primary product is four carbon compounds oxaloacetate.
- It occurs in mesophyll and bundle sheath cells.
- Photorespiration rate is absent.
- Carbon fixation occurs twice.
- Carbon dioxide fixation is faster.