(a) Mention any one harmful effect of using plastic bags on the environment. Suggest better alternatives to the usage of plastic bags.

(b) Paddy fields require a large amount of water. The pesticides and chemical fertilizers used are washed down into the soil or waterbodies. How do these chemicals reach our bodies? What is this phenomenon known as?

(a) Harmful effect of plastic bags and alternatives:

Plastic is non-biodegradable — it is not broken down by the enzymes of decomposer microorganisms (bacteria, fungi) and so persists in the environment for a very long time. One major harmful effect: plastic bags choke drains and soil, and when ingested by grazing animals (cattle, stray animals often eat plastic mixed with food waste), they block the digestive tract, causing illness or death of the animal. (Other valid effects: they clog soil pores and waterlogged drains, preventing water percolation and causing water-logging/flooding; they persist for hundreds of years, accumulating as permanent litter and polluting land and water bodies.)

Better alternatives: cloth bags, jute bags, paper bags — all made of natural, biodegradable materials that decomposers can break down, unlike plastic.

(b) How pesticides/fertilizers reach our bodies:

Paddy fields require large amounts of water, and pesticides and chemical fertilizers applied to the field are washed down by this water into the soil or into water bodies (rivers, ponds). From the soil, these chemicals are absorbed by plant roots along with water and minerals; from water bodies, they are taken up by aquatic plants and animals. In this way the chemicals enter the food chain at the producer level.

Since these chemicals are non-degradable, they are not excreted and instead get accumulated progressively at each successive trophic level as one organism eats another — herbivores accumulate more than plants, carnivores accumulate more than herbivores, and so on. Because human beings occupy the topmost level of most food chains, the maximum concentration of these harmful chemicals gets accumulated in the human body, through eating contaminated grains (wheat, rice), vegetables, fruits, and meat.

This phenomenon — the increasing concentration of a harmful, non-degradable chemical at successive trophic levels of a food chain — is known as biological magnification.