Question

Compensation point means
A. When the rate of photosynthesis is equal to the rate of respiration
B. When there is neither photosynthesis or respiration
C. When the entire food manufactured in photosynthesis remains unutilized
D. When the availability of water equalized with necessity of the water

Answer 1

Hint: Aerobic cellular respiration splits glucose into carbon dioxide and drives the synthesis of the energy currency of cells, that is, ATP.

Complete answer:
We will first learn the basics of photosynthesis and respiration.
Photosynthesis is the process by which the green plants fix the atmospheric carbon dioxide into organic compounds, mainly glucose. Therefore, plants must acquire carbon dioxide for photosynthesis to occur. Plants use the part of the food for their growth and repair. The excess of the food is stored. For example, excess glucose is stored in the form of starch in the plants.
The other requirement for photosynthesis is sunlight. This is because the synthesis reactions require energy input and sunlight provides energy to make glucose (a more complex compound) from a relatively simpler substance, carbon dioxide.
Now, let’s talk about respiration. Respiration occurs continuously in all living beings. It includes the breakdown of nutrients, mainly glucose, to retrieve the energy stored in its chemical bonds. This energy is then stored in the form of ATP.
During the process of respiration, glucose is broken down into carbon dioxide and water.
So, we can say that photosynthesis and respiration are opposite pathways for their end products. Water is required for light reactions of photosynthesis but is produced during respiration. However, both processes depend on gaseous exchange.
Plants have tiny pores, mainly on the surface of leaves, through which the exchange of respiratory gases occurs. Stomata are also the site for the entry of carbon dioxide to facilitate the process of photosynthesis.
Now, as mentioned, plants require sunlight for photosynthesis to occur. However, respiration does not require the presence of sunlight. Therefore, when the light intensity is low, the rate of photosynthesis is also reduced. Under these conditions, the rate of the fixation of carbon dioxide by photosynthesis is exactly equal to the rate of its release by respiration. This point is called the compensation point.
So, the answer is option A: When the rate of photosynthesis is equal to the rate of respiration.

Note: Respiration includes breathing and cellular respiration. Breathing is the exchange of gases and cellular respiration is the breakdown of nutrients to obtain the energy stored in them. Breathing provides oxygen for cellular respiration. Therefore, respiration should not be taken as an “exchange of oxygen and carbon dioxide” only.