3. Water normally stops combustion from taking place while cells contain a lot of water and respiration still goes on.

What can you conclude from this?

Heat production was a feature of burning glucose or sugar as you observed earlier. Living animals and plants usually produce energy in the form of heat.

We feel warm when we wear sweater in winter season. We know that sweater prevents loss of heat energy produced by the body. Does this suggest any way in which our bodies lose heat to the surroundings/

What are the other ways in which our body loses heat?

Heat is constantly lost from the body surface thus it must be continuously generated within our bodies to replace what has been lost to keep the body temperature constant.

Is the rate of heat production always the same?

In the course of vigorous activity, a greater amount of heat is generated. We know that we feel hot after some form of strenuous exercise such as running.

During cellular respiration energy is released. Some part of energy is stored in the form of ATP. Some part of energy is utilised in our day to day life activities. And the excess amount of energy is released in the form of heat. But in case of vigorous activity like running we need more amount of energy. For this the rate of respiration is increased. So heat is also released in excess quantity. That's why we feel warm. If the oxygen is not sufficient during vigorous exersise muscles start anaerobic respiration. Hence, lactic acid is formed. We know that accumulation of lactic acid causes pain in muscle. We reach normal position after some rest. Deep breathing helps us to restore energy in our body. Refer in annexure about Yoga Asanas.

Exchange of gases is a common life process in all living organisms, but it is not same in all. Single celled organisms Amoeba or multicellular organisms like Hydra and Planarians roundworms and earthworms obtain oxygen and expel carbon dioxide directly from the body by the process of diffusion. In other multicellular animals special organs are evolved. Animals either terrestrial or aquatic adopted to different types of respiration and possess different types of respiratory organs mostly depending on the habitat in which they live. Body size, availability of water and the type of