The major groups of activities for improving crop yields can be classified as:

On what factors do the growth of plants and flowering depend?

Which one of the following nutrients is not available in fertilizers?

On a voyage in their yacht,John and his father came across an iceberg. John advised his father to keep away from the iceberg. His father said that it is just a small piece of ice jutting out of the sea and there is nothing to bother. John told his father that icebergs are dangerous and narrated the story of the ship $Titanic$,which was sunk by an iceberg. John explained to his father why the iceberg was dangerous. This convinced his father,and they steered clear of the iceberg.
$(a)$ Why are icebergs in the sea dangerous?
$(b)$ What values are possessed by John and his father?

$(a)$ 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.

How is mariculture different from aquaculture?