Why do viruses need living hosts, such as bacteria or eukaryote cells?

Astudent visits the beach during a very hot day she steps on the santa and jumps because it is so hot what type of heat transfer is demonstrated by the sand in this example

What re the two main phrases of the cell cycle.

The concept of keystone species is controversial among ecologists because most organisms are highly interdependent. if each of the trophic levels is dependant on all others how can we say one is most important