<span>A retrovirus is anything of a group of RNA viruses that insert a DNA copy of their genome into the host cell to replicate.
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The energy before and after a process must be the same.
<span>The importance of the G0 phase is that during cell division when the cell get a signal that there are enough of cells (not more required) or there is a mutation in the cell that need to be fixed before they differentiate fully or the cell during its division gets damage then it is signalled to rest, and it is this phase that cell leave the cycle and quit dividing. It could be temporary resting period (so when cell again required, or damaged got fixed) then the cells will again join the cycle and continue to divide again or it can also be permanent for example neurons, which are resting in G0 phase and never divides again.</span>
The notable
hardness of bone is attributed to the presence of inorganic hydroxyapatites.
Due to the calcium salts deposited in it, resulting to the hardness. The
abnormal hardness of bone, which allows it
to resist the compression.