Question

Explain why respiration is said to be the reverse of photosynthesis?

Answer 1

Photosynthesis is the process by which green plants produce organic matter (starch) by entrapping sunlight and carbon dioxide. It is an anabolic process. On the other hand, respiration is a catabolic process. The processes in which ‘synthesis’ of new compounds occur are known as anabolic reactions. The process involving ‘destruction’ of molecules to release the energy stored in them are known as catabolic processes.

Complete answer:
Photosynthesis and respiration (particularly cellular respiration) are completely two different processes having different roles.
Photosynthesis is the process which involves production of organic matter (starch or glucose) which is the main food for the green plants. Thus, this process works on storing energy in the form of food.
Respiration involves the breakdown of this starch or glucose to release the energy within it which is used for various metabolic processes.
We may understand a little bit more why photosynthesis and respiration are reverse processes by looking at the following comparison:

PHOTOSYNTHESIS	RESPIRATION
It only occurs in green plants, i.e., autotrophs and some chemosynthetic bacteria.	It is a process that occurs in all living organisms.
It is an endothermic reaction as it requires energy.	It is an exothermic reaction as it liberates energy.
It produces energy (ATP) by producing light energy.	It produces energy (ATP) by liberation of energy from oxidation of food substrates.
The net chemical reaction of photosynthesis is as follows: $6CO_2+6H_2O \xrightarrow{\text{light energy}} C_6H_{12}O_6+ 6O_2$	The net chemical reaction of respiration is as follows:$C_6H_{12}+6O_2 \to 6CO_2 + 6H_2O$

Note:
It should be noted that the two processes- photosynthesis and respiration are mutually beneficial to each other. The energy released by respiration in turns drives photosynthesis.
Not in all autotrophs where photosynthesis occurs, oxygen is liberated. There are certain microbes which do not evolve oxygen, and this type of photosynthesis is known as anoxygenic photosynthesis. The chemosynthetic sulfur bacteria are of this type. These bacteria use sulfur and the electron donor rather than oxygen. So these bacteria do not liberate oxygen during photosynthesis.