Name the major nutrient which we get from fish.

$(a)$ State three ways by which pests attack the plants.
$(b)$ Name the chemical used to control pests.
$(c)$ Explain why excessive use of such chemicals should be avoided.

Once Ravi and Aman were cooking rice in the kitchen and accidentally Aman's hand got a severe burn while opening the lid of the cooking vessel. Immediately,Ravi applied ice on his hand,then applied an ointment,and told him to cook carefully as he had been hurt by steam,and steam causes more severe burns. Aman thanked Ravi and smiled.
$(a)$ According to you,what kind of qualities are shown by Ravi?
$(b)$ How does steam produce more severe burns than boiling water?

In India,about $45 \%$ of the cultivated area is unirrigated,and scarce rainfall often causes crop failure,leading to drought-like conditions. This situation motivated villagers to use rainwater harvesting and watershed management.
$(i)$ What is meant by irrigation?
$(ii)$ List two different kinds of irrigation systems which can be adopted to supply water to agricultural land.
$(iii)$ What values does Rajan possess which helped villagers overcome their problem?

Ram tried hard to push the wall of a room. In the process of pushing the wall,he begins to perspire and feels exhausted although the wall does not move. Ram feels that he has done a lot of work and spent a lot of energy. Do you think that Ram was justified in making the statement that he has done a lot of work? Justify your answer and give the conditions under which work is done.

How is mariculture different from aquaculture?