Question

When $CO_2$ used is equal to $CO_2$ released, it is called as
A. Compensation point
B. Threshold point
C. Critical point
D. Danger threshold

Answer 1

Hint: Compensation point may be defined as light intensity on the light curve when rate of photosynthesis equals to rate of respiration.
Photosynthesis is a process which is used by plants to convert light energy into chemical energy. The raw materials in photosynthesis are water and carbon dioxide and products of photosynthesis are sugar and oxygen, leaving the leaf.
Respiration is a process in living organisms involving production of energy with the intake of oxygen and release of carbon dioxide.

Complete step by step answer:
At compensation point, the net assimilation of carbon dioxide is zero. Leaves produce $CO_2$ by photorespiration and cellular respiration, but $CO_2$ is converted into carbohydrate by photosynthesis. The net exchange of gases is also zero at this point. The compensation point is reached during early mornings and late evenings. Respiration is constant, while photosynthesis depends on the intensity of sunlight. The products of photosynthesis are used up in respiration so that the organism is neither consuming nor building biomass. When the rate of photosynthesis equals the rate of respiration, the compensation point occurs.

So the correct answer is compensation point.

Note: Threshold point- it is the point at which $CO_2$ is of sufficient intensity to produce an effect. Critical point- it is the amount of $CO_2$ beyond which there is no longer any difference.