(i) Nutrition is necessary because:
(a) it helps in the growth of new cells and repair of older ones.
(b) it is needed to develop resistance against diseases.
(c) it providies energy for metabolic processes
(ii) Disappearance of green plants from earth means a total disaster of the ecosystem. Green plants are the source of energy for all organisms. All other organisms directly or indirectly depend on them for food.So, if they disappear from the earth, all the herbivoures will die due to starvation and so will the carnivore, i.e. it would result in extinction of life from the earth.