NEET Biology Cell Cycle and Cell Division MCQs Set 36

Answer: (d) Metaphase

Explanation:
1. Spindle fibres attach to the kinetochores of chromosomes, which are aligned on the equatorial plate at metaphase, and this attachment becomes clearly evident then.
2. Anaphase follows with the separation of chromatids, and telophase is the reformation stage.

Teacher's Note:
1. Metaphase is the stage of chromosome alignment and spindle attachment.
2. Chromosomes are most condensed and easiest to count here.

Answer: (b) G1, S, G2, M

Explanation:
1. The mitotic cell cycle runs in the sequence G1, S, G2 and M.
2. Interphase (G1, S, G2) prepares the cell for division, and M phase includes mitosis and cytokinesis.

Teacher's Note:
1. G1 then S then G2 then M.
2. Remember it as Gap, Synthesis, Gap, Mitosis.

Answer: (b) Zygotene

Explanation:
1. Synapsis, the pairing of homologous chromosomes, takes place during zygotene of prophase I.
2. The synaptonemal complex forms at this stage.

Teacher's Note:
1. Zygotene means pairing.
2. Pachytene is crossing over.

Answer: (d) (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)

Explanation:
1. G1 is the phase of cell growth and organelle duplication, S phase is DNA replication and chromosome duplication, G2 is further cytoplasmic growth and protein synthesis, and metaphase of M phase aligns the chromosomes.
2. The correct matching is a-i, b-ii, c-iii, d-iv.

Teacher's Note:
1. DNA content doubles in S phase.
2. Cytoplasmic growth continues through G1 and G2.

Answer: (c) (iv) (iii) (ii) (i)

Explanation:
1. Zygotene shows synapsis, pachytene shows crossing over, diplotene shows chiasmata and diakinesis shows terminalization of chiasmata.
2. Hence a-iv, b-iii, c-ii, d-i.

Teacher's Note:
1. Remember the order of prophase I: leptotene, zygotene, pachytene, diplotene, diakinesis.
2. Associate each substage with its main event.

Answer: (d) Cell is metabolically active, grows but does not replicate its DNA.

Explanation:
1. In G1 phase the cell is metabolically active and grows continuously but does not replicate its DNA.
2. DNA replication occurs in S phase and nuclear division in M phase.

Teacher's Note:
1. G1 is the first gap phase.
2. Cells that stop here may enter G0.

Answer: (c) G1 phase

Explanation:
1. Some cells exit the cell cycle after G1 and enter a quiescent stage called G0.
2. They are metabolically active but do not proliferate unless required.

Teacher's Note:
1. Cells in G0 leave from G1 phase.
2. Heart cells are an example.

Answer: (d) Diplotene

Explanation:
1. The synaptonemal complex is formed during zygotene, complete at pachytene and dissolved by the end of diplotene as the homologous chromosomes start to separate.

Teacher's Note:
1. Chiasmata become visible when the complex dissolves at diplotene.
2. Bivalents separate except at chiasmata.

Answer: (b) Twice the amount of DNA in comparison to haploid gamete.

Explanation:
1. After meiosis I the daughter cells are haploid in chromosome number, but each chromosome still has two chromatids, so the DNA content is twice that of a haploid gamete.
2. After meiosis II it equals that of the gamete.

Teacher's Note:
1. Meiosis I is reductional in chromosome number only.
2. DNA content halves again in meiosis II.

Answer: (b) Non-sister chromatids of homologous chromosomes at Pachytene stage of prophase I.

Explanation:
1. Crossing over is the exchange of segments between non-sister chromatids of homologous chromosomes.
2. It occurs at pachytene of prophase I, when the bivalents are fully synapsed.

Teacher's Note:
1. Crossing over involves the enzyme recombinase.
2. Recombination nodules mark the sites.

Answer: (d) G1® S ® G2® M 84

Explanation:
1. The correct sequence of phases of the cell cycle is G1, S, G2 and M.
2. Option d follows this sequence, while the others violate it.

Teacher's Note:
1. DNA replication always comes before mitosis.
2. G1, S, G2 are collectively interphase.

Answer: (a) exit the cell cycle

Explanation:
1. Cells in G0 have left the cycle after G1 and are quiescent: they are metabolically active but do not divide unless stimulated.
2. So the cells exit the cell cycle.

Teacher's Note:
1. G0 is a resting state, not termination.
2. Many differentiated cells stay in G0 for life.

Answer: (b) Meiocyte

Explanation:
1. Meiosis takes place in meiocytes, the meiosis-capable diploid cells such as spore mother cells and gamete mother cells.
2. A megaspore, conidium or gemmule is already a product or a propagule.

Teacher's Note:
1. Meiocyte means meiosis-undergoing cell.
2. Spore mother cells divide meiotically in plants.