Question

Some cells in the adult animal do not divide. They exit G1 phase and enter an inactive stage which is called as ____________
(A) $G_2$ phase
(B) $G_0$ phase
(C) S phase
(D) M

Answer 1

Cell division is referred to as a very important process in all living organisms. During the division of a cell, the complete set of events are called cell cycle and cell cycle is divided into phases:
(i) Interphase (ii) M phase (Mitosis phase)

Complete answer:
Interphase is categorised into three further phases:
G1 phase (Gap 1), (ii) S phase (synthesis), and last is (iii) G2 phase (Gap2)
Important process that takes place in M phase are karyokinesis (Nuclear division), Cytokinesis (Division of cytoplasm)
Now let us find solution from given options:

$G_2$ phase: At the time of $G_2$ phase, proteins are produced in preparation for mitosis while cell growth continues. The cytoplasmic organelles, for instance as centrioles, mitochondria and Golgi apparatus are doubled.

$G_0$ Phase: some cells do not show active division further, do not proceed after the $G_1$ phase and begin undergoing such cells are known to be in quiescent stage or $G_O$ phase of cell cycle to varied them from $G_1$ cells which will soon enter S-phase cells in this stage remains metabolically active but these cell then do not proliferate. Some of the cells in Go phase are fibroblasts that play a role in healing wounds, growing and dividing again on demand of the body.

S-phase: In this period DNA synthesis or replication occurs. At the time of this the amount of DNA per cell doubles. But there is no increase in the chromosome number.
M-phase: It is also termed as the mitotic phase. Since the number of chromosomes in the parent cell and progeny cells are the equal, it is also termed as educational division.

This phase is further categorised into four stages:
1)Prophase
2)Metaphase
3)Anaphase
4)Telophase

Hence, the correct answer is option (B)

Note: $G_1$ phases are intermediate to the internal between mitosis and initiation of DNA replication.
Mammalian (human) cells division in 24 hours.
Yeast cells completes division in about 90 minutes
The most essential event in the regulation of cell cycle takes place in the $G_1$ phase $G_1$ cell commits whether to restart a new cell cycle or to enter the Go phase.