Question

Some cells in the adult animal do not divide. They exit \[{G_1}\] phase and enter an inactive stage which is called as
A. \[{G_2}\] phase
B. \[{G_0}\] phase
C. S-phase
D. M-phase

Answer 1

Hint:Cell division is a very important process in all living organisms. During the division of a cell, place cell cycle is divided into phases:
(i) Interphase
(ii) M phase (Mitosis phase)
(i) Interphase is divided into three further phases: (i) \[{G_1}\]phase (Gap 1), (ii) S phase (synthesis), (iii) \[{G_2}\] phase (Gap2)
(ii) Important process of M phase are karyokinesis (Nuclear division), Cytokinesis (Division of cytoplasm)

Complete answer
A. \[{G_2}\] phase: During \[{G_2}\] phase, proteins are synthesized in preparation for mitosis while cell growth continues. The cytoplasmic organelles, such as centrioles, mitochondria and Golgi apparatus are doubled.
B. \[{G_0}\] Phase: some cells do not divide further, do not proceed beyond \[{G_1}\] phase and start undergoing such cells are said to be in quiescent stage or G0 phase of cell cycle to distinguish them from \[{G_1}\] cells which will soon enter S-phase cells in this stage remains metabolically active but no longer proliferate. Some of the cells in \[{G_0}\] phase are fibroblasts that help in healing wounds, grow and divide again on demand of the body.
C. S-phase: In this period DNA synthesis or replication takes place. During this time the amount of DNA per cell doubles. However there is no increase in the chromosome number.
D. M-phase: It is the mitotic phase. Since the number of chromosomes in the parent cell and progeny cells are the same, it is also called educational division. This phase is further divided into four stages:
(i) prophase
(ii) Metaphare
(iii) Anaphase
(iv) Telophase

Hence the correct answer is option B: \[{G_0}\] phase.

Note: (i) \[{G_1}\]phase corresponds to the internal between mitosis and initiation of DNA replication.
(ii) Mammalian (human) cells divide in approximately 24 hours.
(iii) Yeast cells divide in about 90 minutes
(iv) The most important event in the regulation of cell cycle occurs in the G1 phase A \[{G_1}\] cell commits whether to restart a new cell cycle or to enter the \[{G_0}\] phase.