The group of crop plant that are vegetatively propagated is:

 

The process accounts for species diversity is Meiosis. Meiosis is termed as a specialized cell division which reduces chromosomes number by half and then creates for haploid cells.

Cytokinins is a Plant hormone which helps in cell division and leads to Growth & formation of shoots, roots & bud.

An approach to studying biology that aims to model the dynamic behavior of whole biological systems based on a study of the interactions among the system's parts.

Urea is a by product of amino acid catabolism, Which occurs in the liver. The nitrogen in the  amino acid becomes converted to ammonia and this is further converted by the liver into urea

Study of Life in outer space or search of life external to Earth is known as Exobiology.