NEET Biology: Cell Cycle and Cell Division questions with solutions

Q1. Cell division can not be stopped in phase of the cell cycle.

1. Gi phase
2. Ga phase
3. s phase
4. Prophase

Answer: Prophase

Prophase is part of mitosis, when chromosomes condense and the cell is already engaged in division. In contrast, interphase stages like G1 and S are more controllable checkpoints where the cycle can be halted.

Q2. Some dividing cells exit the cell cycle and enter vegetative inactive stage. This is called quiescent stage (G₀). This process occurs at the end of

1. G₁ phase
2. S phase
3. G₂ phase
4. M phase

Answer: G₁ phase

Quiescence (G₀) is entered from G₁, when a cell can either continue toward DNA synthesis or exit the cycle. This is why the transition to the inactive state occurs at the end of G₁ phase.

Q3. Identify the correct statement with regard to G₁ phase (Gap 1) of interphase.

1. Reorganisation of all cell components takes place.
2. Cell is metabolically active, grows but does not replicate its DNA.
3. Nuclear Division takes place.
4. DNA synthesis or replication takes place.

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

G₁ is the first gap phase of interphase, when the cell is metabolically active and grows while preparing for DNA synthesis. DNA replication happens in S phase, and nuclear division occurs later in mitosis.

Q4. In ‘S’ phase of the cell cycle:

1. Amount of DNA doubles in each cell.
2. Amount of DNA remains same in each cell.
3. Chromosome number is increased.
4. Amount of DNA is reduced to half in each cell.

Answer: Amount of DNA doubles in each cell.

In S phase, the cell replicates its DNA in preparation for division. This doubles the DNA content in each cell, while the chromosome number stays the same until sister chromatids separate.

Q5. During which phase(s) of cell cycle, amount of DNA in a cell remains at 4C level if the initial amount is denoted as 2C?

1. G0 and G1
2. G1 and S
3. Only G2
4. G2 and M

Answer: G2 and M

After S phase, each chromosome has been replicated, so the cell contains 4C DNA. This 4C amount persists through G2 and remains until the end of M phase, when division produces two daughter cells and the DNA per cell returns to 2C.

Q6. A somatic cell that has just completed the S phase of its cell cycle, as compared to gamete of the same species, has:

1. same number of chromosomes but twice the amount of DNA
2. twice the number of chromosomes and four times the amount of DNA
3. four times the number of chromosomes and twice the amount of DNA
4. twice the number of chromosomes and twice the amount of DNA

Answer: same number of chromosomes but twice the amount of DNA

After S phase, each chromosome has been duplicated into two sister chromatids, but the chromosome number is still counted by centromeres, so it stays the same. A gamete is haploid, so the somatic cell has the same chromosome count as before replication relative to itself, but twice the DNA compared with the unreplicated state.

Q7. In the somatic cell cycle:

1. In G1 phase DNA content is double the amount of DNA present in the original cell
2. DNA replication takes place in S-phase
3. A short interphase is followed by a long mitotic phase
4. G2 phase follows mitotic phase

Answer: DNA replication takes place in S-phase

S phase is the synthesis phase of interphase, and it is when DNA is replicated. The other options misstate the amount of DNA in G1 or the order and length of cell-cycle phases.

Q8. At what stage of the cell cycle are histone proteins synthesized in a eukaryotic cell?

1. During G2 stage of prophase
2. During S-phase
3. During entire prophase
4. During telophase

Answer: During S-phase

Histone proteins are synthesized during S-phase because DNA replication occurs then, and the newly made DNA must be immediately packaged into nucleosomes. This timing ensures histones are available in step with DNA synthesis.

Q9. In cell cycle, DNA replication takes place in

1. G1 phase
2. G2 phase
3. Mitotic metaphase
4. S phase

Answer: S phase

DNA replication occurs during the synthesis (S) phase of interphase, when the cell duplicates its genetic material in preparation for cell division. G1 is growth, G2 is preparation for mitosis, and metaphase is a mitotic stage after replication is complete.

Q10. Which one of the following structures will not be common to mitotic cells of higher plants?

1. Cell plate
2. Centriole
3. Centromere
4. Spindle fibres

Answer: Centriole

Higher plant cells do not generally contain centrioles, even though they still form a spindle using other microtubule-organizing regions. Cell plates, centromeres, and spindle fibres are all involved in plant mitosis.

Q11. Match the following with respect to meiosis: (A) Zygotene - (i) Terminalization (B) Pachytene - (ii) Chiasmata (C) Diplotene - (iii) Crossing over (D) Diakinesis - (iv) Synapsis Select the correct option from the following:

1. (a) (iv) (iii) (ii) (i)
2. (b) (i) (ii) (iii) (iv)
3. (c) (ii) (iv) (iii) (i)
4. (d) (iii) (iv) (i) (ii)

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

In zygotene, homologous chromosomes undergo synapsis. Pachytene is when crossing over occurs, diplotene shows chiasmata, and diakinesis is marked by terminalization of chiasmata.

Q12. Dissolution of the synaptonemal complex occurs during

1. Zygotene
2. Diplotene
3. Leptotene
4. Pachytene

Answer: Diplotene

Diplotene is the stage of prophase I when the synaptonemal complex disassembles and homologous chromosomes start to separate, while remaining connected at chiasmata. Zygotene is when synapsis begins, and pachytene is when synapsis is complete and crossing over occurs.

Q13. Which of the following options gives the correct sequence of events during mitosis?

1. Condensation → nuclear membrane disassembly → arrangement at equator → centromere division → segregation → telophase
2. Condensation → crossing over → nuclear membrane disassembly → segregation → telophase
3. Condensation → arrangement at equator → centromere division → segregation → telophase
4. Condensation → nuclear membrane disassembly → crossing over → segregation → telophase

Answer: Condensation → nuclear membrane disassembly → arrangement at equator → centromere division → segregation → telophase

The correct order follows the main mitotic phases: chromosomes condense, the nuclear membrane breaks down, chromosomes align at the equator, centromeres split, sister chromatids separate, and telophase begins. Crossing over is not part of mitosis; it occurs in meiosis.

Q14. Anaphase Promoting Complex (APC) is a protein degradation machinery necessary for proper mitosis of animal cells. If APC is defective in a human cell, which of the following is expected to occur?

1. Chromosomes will be fragmented
2. Chromosomes will not segregate
3. Recombination of chromosome arms will occur
4. Chromosomes will not condense

Answer: Chromosomes will not segregate

APC promotes progression into anaphase by targeting key regulators for degradation, which allows sister chromatids to separate. If APC is defective, the cell cannot properly initiate chromatid separation, so chromosomes will not segregate.

Q15. Centromere is required for:

1. movement of chromosomes towards poles
2. cytoplasmic cleavage
3. crossing over
4. transcription

Answer: movement of chromosomes towards poles

The centromere is the chromosome region where the kinetochore forms and spindle fibers attach, allowing sister chromatids or chromosomes to be pulled to opposite poles. It is not involved in cleavage, crossing over, or transcription.

Q16. Mitotic spindle is mainly composed of which protein?

1. Actin
2. Myosin
3. Tubulin
4. Myoglobin

Answer: Tubulin

The mitotic spindle is made of microtubules, and microtubules are polymers of tubulin. Actin and myosin are mainly involved in muscle contraction and cell movement, while myoglobin stores oxygen in muscle.

Q17. A bivalent consists of

1. two chromatids and one centromere
2. two chromatids and two centromeres
3. four chromatids and two centromeres
4. four chromatids and four centromeres

Answer: four chromatids and two centromeres

A bivalent is formed when two homologous chromosomes pair up in prophase I of meiosis. Since each homolog has two sister chromatids and one centromere, the pair contains four chromatids and two centromeres.

Q18. The correct sequence of phases of cell cycle is:

1. M → G₁ → G₂ → S
2. G₁ → G₂ → S → M
3. S → G₁ → G₂ → M
4. G₁ → S → G₂ → M

Answer: G₁ → S → G₂ → M

The cell cycle proceeds through G₁ for growth, S for DNA replication, G₂ for final preparation, and M for mitosis/cytokinesis. This is the standard sequence of events in a dividing eukaryotic cell.

Q19. Spindle fibres attach on to

1. Telomere of the chromosome
2. Kinetochore of the chromosome
3. Centromere of the chromosome
4. Kinetosome of the chromosome

Answer: Kinetochore of the chromosome

Spindle fibres attach to the kinetochore, a protein complex assembled on the centromere. This is the site that connects chromosomes to the mitotic spindle for proper separation.

Q20. Cells in G₀ phase:

1. exit the cell cycle
2. enter the cell cycle
3. suspend the cell cycle
4. terminate the cell cycle

Answer: exit the cell cycle

G₀ is the quiescent state where cells are not progressing through the active cell-cycle phases. They have exited the cycle, rather than merely pausing within it.