Name the following:
The exchange of chromatid parts between the maternal and the paternal chromatids of a pair of homologous chromosomes during meiosis.

Name the following:

The number of individuals inhabiting per unit area.

Name the following:

The immunity acquired by providing readymade antibodies from outside for treating certain infectious diseases.

Name the following:

The pollutants that cannot be broken down to simple and harmless products.

Name the following:

The part of the brain that carries impulses from one hemisphere of the cerebellum to the other.