Question

Which of the following statements is correct?
A) Photorespiration is useful process
B) $C4$ plants are more efficient than $C3$ plants
C) $C3$ plants are more efficient than $C4$ plants
D) Photorespiration is absent in $C3$ plants but present in $C4$ plants

Answer 1

Hint: The evolution of carbon dioxide in the presence of light is referred to as the photorespiration. However, the carbon is fixed in plants via three major processes known as the $C3$, $C4$ and CAM pathways. $C4$ Plants have a unique anatomy of leaf and biochemistry that further helps in fixing carbon dioxide.

Complete answer:
$C3$ Plants derive its name from the first three carbon compounds it produces during the dark reaction of photosynthesis. Majority of the plants undergo the $C3$ cycle and hence are called the $C3$ plants. However, in conditions of high temperature, $C3$ plants undergo photorespiration because at high temperature, the affinity of oxygen for the enzyme RUBISCO is high therefore in place of carbon dioxide, oxygen can bind to RUBISCO. This binding of oxygen to enzyme RUBISCO reduces the water use efficiency as well as the photosynthetic efficiency of the plants. Therefore, some of the plants have evolved a different mechanism of carbon fixation which is known as the $C4$ pathway. It is characterized by a special leaf anatomy and biochemistry which allows or facilitates the binding of carbon dioxide in conditions of high temperature also. In this case, the first product produced is the 4 carbon compound therefore the plants are called the $C4$ plants. This compound helps in concentrating and transferring carbon dioxide towards the RUBISCO enzyme present in the specific cell. This improves the photosynthetic efficiency as well as the water use efficiency of the plant resulting in more productivity.
However, the photorespiration involves the consumption of high-energy molecules (ATP and NADPH), that are formed during the light reaction. This in-turn prevents the use of these high-energy molecules by the plants for production of carbohydrates. Thus, photorespiration is a wasteful process.

So, the correct answer is option “B” that is $C4$ plants are more efficient than $C3$ plants.

Note:
The carbon dioxide present in the atmosphere can be removed via fixation of carbon that takes place during the dark reaction of photosynthesis through various pathways like, $C3$ and $C4$ .Examples of $C3$ plants are rice, barley, cotton, sunflower, potato, soybean, etc. $C4$ Plants are however found in hot and humid climates examples include millet, sugarcane, maize, sorghum, etc.