All the vital activities in a living system require a continuous supply of energy. The energy is continuously produced and utilized for the various activities in the body.
Plants have the ability to convert solar energy into chemical energy. All animals and plants utilize chemical energy for vital purposes.
It is now well known that neither energy is created nor destroyed, although chemical energy is often converted from one form to the other forms of energy.
Principle of Conservation of Energy
This principle may be stated as follows:
This is the basic law of nature and is universally accepted.
Physical Law of Entropy
This is also a universal law and is applicable to both living and non-living systems. This law can be stated as follows:
ATP (Adenosine Triphosphate)
The chemical name of this compound is adenosine triphosphate. It consists of a nitrogenous base called adenine linked to a five-carbon sugar called ribose. The latter is linked to a chain of three phosphate molecules. ATP is the form of energy found in living cells.
The Source of Energy in the cells
As stated already that plants synthesize sugar from CO2 and water during photosynthesis in the presence of sunlight.
Thus the primary source of energy is the sun. Animals utilized the synthetic product (sugar) of plants to obtain energy i.e ATP through the process of respiration. Thus photosynthesis converts the solar energy into chemical energy while respiration release is for vital activities.