NEET Biology Cell Cycle and Cell Division MCQs Set 05

Answer: (d) Chromosomes move to the spindle equator and get aligned along the equatorial plate in metaphase

Explanation:
1. Alignment on the metaphase plate is the hallmark of metaphase.
2. Separated chromatids move to the poles in anaphase, and Golgi and ER vanish by late prophase.

Teacher's Note:
1. Metaphase equals alignment at the equator.
2. Anaphase equals poleward movement.

Answer: (d) kinetochores

Explanation:
1. Kinetochores are disc-like protein structures on the centromere.
2. Spindle microtubules attach to them.

Teacher's Note:
1. Kinetochore is the actual attachment site.
2. It forms on the centromere.

Answer: (d) bivalent

Explanation:
1. Paired homologues form a bivalent.
2. It contains four chromatids, so it is also called a tetrad.

Teacher's Note:
1. Bivalent equals two chromosomes paired.
2. Kinetochore is a centromere protein disc.

Answer: (a) the amount of DNA doubles in each cell

Explanation:
1. S phase is DNA synthesis.
2. DNA content rises from 2C to 4C, but chromosome number is unchanged.

Teacher's Note:
1. DNA doubles, chromosome number does not.
2. This is a frequent question.

Answer: (a) Pachytene

Explanation:
1. Recombinase acts in crossing over.
2. Crossing over occurs at pachytene.

Teacher's Note:
1. Pachytene equals crossing over.
2. Chiasmata are visible later in diplotene.

Answer: (b) twice the number of chromosomes and four times the amount of DNA

Explanation:
1. The gamete is n with 1C of DNA.
2. The somatic cell after S is 2n (twice the chromosomes) with 4C of DNA (four times).

Teacher's Note:
1. After S the cell is 2n with 4C DNA.
2. Gametes are n with 1C.

Answer: (c) G1

Explanation:
1. In G1 the cell grows and makes organelles, RNA and proteins.
2. S is DNA synthesis and G2 prepares for mitosis.

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

Answer: (b) kinetochore of the chromosome

Explanation:
1. Spindle microtubules bind the kinetochore, a protein disc on the centromere.
2. Telomeres are chromosome ends and kinetosome is the basal body of a cilium.

Teacher's Note:
1. Kinetochore is the direct attachment site.
2. Do not confuse with kinetosome.

Answer: (a) pachytene

Explanation:
1. Crossing over occurs between non-sister chromatids of synapsed homologues.
2. This takes place in pachytene.

Teacher's Note:
1. Pachytene equals crossing over.
2. Chiasmata are seen in diplotene.

Answer: (c) S phase

Explanation:
1. DNA is replicated in the S phase of interphase.
2. G1 and G2 are gap phases with no replication.

Teacher's Note:
1. S means synthesis.
2. This is a basic NEET fact.

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

Explanation:
1. Pachytene has crossing over (a-iii).
2. Metaphase I has chromosomes at the equator (b-iv).
3. Diakinesis has terminalisation (c-ii), and zygotene has pairing (d-i).

Teacher's Note:
1. Each stage has one landmark event.
2. Only option c matches all four.

Answer: (a) Condensation, nuclear membrane disassembly, arrangement at the equator, centromere division, segregation, telophase

Explanation:
1. Chromosomes condense in prophase and the envelope breaks down.
2. They then align (metaphase), centromeres divide, chromatids segregate (anaphase) and telophase follows.
3. Crossing over does not occur in mitosis.

Teacher's Note:
1. Mitosis has no crossing over.
2. Follow the stage order carefully.

Answer: (b) Chromosomes will not segregate

Explanation:
1. APC degrades the proteins that hold sister chromatids together.
2. Without it, sister chromatids cannot separate at anaphase.

Teacher's Note:
1. APC triggers the metaphase to anaphase transition.
2. Defective APC arrests the cell at metaphase.

Answer: (a) G1, S and G2

Explanation:
1. Interphase is the period between two successive M phases and includes G1, S and G2.
2. The other options belong to M phase.

Teacher's Note:
1. Interphase equals G1 plus S plus G2.
2. M phase is the actual division.

Answer: (a) All are correct

Explanation:
1. G0 cells have exited the cycle and are quiescent.
2. They stay metabolically active and can re-enter the cycle when stimulated.

Teacher's Note:
1. G0 is a resting stage that can be reversible.
2. Some cells such as neurons remain in it permanently.

Answer: (d) DNA synthesis phase - doubling of the number of chromosomes in the cell

Explanation:
1. The S phase doubles the amount of DNA, not the number of chromosomes.
2. The other three matches are correct.

Teacher's Note:
1. DNA content doubles, chromosome number does not.
2. This is a classic trap.

Answer: (b) G1 phase

Explanation:
1. This interval is the first gap phase, G1.
2. The cell is metabolically active and grows during it.

Teacher's Note:
1. G1 is between M and S.
2. G2 is between S and M.

Answer: (d) a, b and c

Explanation:
1. Adult heart, skeletal muscle and nerve cells have exited the cycle into G0.
2. They do not divide under normal conditions.

Teacher's Note:
1. Heart cells are the textbook example.
2. These cells stay in G0.

Answer: (a) C, E, D, A, B

Explanation:
1. C is replication, so it belongs to interphase. E is condensation (prophase), D is alignment (metaphase), A is chromatid separation (anaphase) and B is reorganisation of nuclei (telophase).
2. So the sequence is C, E, D, A, B.

Teacher's Note:
1. Link each event to its stage name.
2. Prophase condenses, telophase reforms nuclei.

Answer: (d) C, B, E, A, D

Explanation:
1. Synapsis (zygotene) comes first, then crossing over (pachytene).
2. The complex dissolves in diplotene, chiasmata terminalise in diakinesis and homologues disjoin in anaphase I.

Teacher's Note:
1. Prophase I events come before anaphase I disjunction.
2. Follow zygotene, pachytene, diplotene, diakinesis.

Answer: (c) 92

Explanation:
1. Each pole has 46 chromosomes, so the parent cell had 46 chromosomes.
2. At metaphase every chromosome has two chromatids, giving 92 chromatids.

Teacher's Note:
1. Chromatids at metaphase are twice the chromosome number.
2. Chromosome number is 46 throughout.