Which is not essential for seed germination in most cases?
Water, air and suitable temperature are necessary for seed germination. Water is necesssary for germination because food is stored in the seeds in dry condition, but the developing embryo cannot utilize this dry food. Food can be utilized in liquid form only and seeds can utilize only dissolved oxygen. Excess water stops germination because once all the dissolved oxygen is utilised by the seed, further germination is not possible as the life supporting oxygen is now lacking. During germination rapid cell division takes place. Energy is required for cell division. This energy is obtained from oxidation. The oxygen required for oxidation is supplied by the air. So, air is necessary for seed germination. Suitable temperature is necessary because low temperature retards the embryo activity and high temperature destroys the delicate embryo tissue. So, the correct answer is 'Light'.