Question

What is $G_0$ (quiescent phase) of cell cycle?

Answer 1

Some cells in the adult animals do not appear to exhibit division (e.g., heart cells) and many other cells divide only occasionally. These cells that do not divide further exist $G_1$ phase to enter an inactive stage called quiescent stage $\left(G_0\right)$ of the cell cycle. Cells in this stage remain metabolically active but no longer proliferate unless called on to do so depending on the requirement of the organism.