a. Pollination

Pollination is a process of transfer of pollen grains from anther to stigma of a flower. This process involves role of insect, butterflies, honey bees and birds.

b. water,air

A Forest is a purifier of water and air because it helps in bringing rain and helps in maintaining ground water and provides fresh water. Moreover, forests are responsible for maintaining a balance between oxygen and carbon dioxide gas in the atmosphere and provide fresh air.

c. ground

Giant trees form the top layer in the forest followed by shrubs and tall grasses. Herbs form the ground layer in the forest.

d. soil.

The decaying leaves and animal droppings in a forest enrich the soil because they are highly nutritious when they get converted to humus by decomposers and hence provides enrichment in nutrients to the soil.