Double fertilization was first observed by Nawaschin (1892) in Lilium and Fritillaria and confirmed by Grignard. It is characteristic of angiosperms. In double fertilization first fertilization is normal and second, as it involves three nuclei is known as triple fusion.

The bacterium-Agrobacterium acts as avehicle for transfer of DNA or genes from one organism to another organism because it infects all dicot plants.

Restriction enzyme are also known as molecular knifes or molecular scissors. They are isolated from bacteria. They recognize specific base sequence in DNA and cleave both strands of it.

Leucaena leucocephala is commonly known as subabool. It is a very fast growing leguminous plant and therefore is commonly used as social foresting species.

Bacteria are prokaryotic in nature, in which typical chromosomes are lacking. DNA is circular and naked as it is not surrounded by histones (basic proteins which are responsible for coiled structure of nucleosome).

In almost all ecosystem the maximum amount of energy is found in 1^st trophic level.

The enzyme needed for replication of DNA i.e. formation of DNA from DNA is DNA polymerase III. DNA replication is initiated by RNA primer which is later removed by DNA polymerase I.

DDT has been recently banned because it is non-biodegradable and biomagnifying pollutant. Biomagnification means the increase in amount of DDT in the body of organism along with the increase in trophic level. Hence, the amount of DDT in 1st trophic level will be minimum and in top consumer will be maximum.

When changes involve only a few chromosome say one or two and not the entire genome, the phenomenon is called aneuploidy. Monosomy is a case of aneuploidy, when there is loss of one chromosome from a pair of homologue.

Biosphere is the part of earth where life exists.