CELL CYCLE AND CELL DIVISION

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Question 1

What is the cell cycle?

A) The process by which cells replicate their DNA only

B) The sequence of events by which a cell duplicates its genome, synthesizes other constituents, and divides into two daughter cells

C) The period during which cells grow without any division

D) The process of cell death

Answer: B) The sequence of events by which a cell duplicates its genome, synthesizes other constituents, and divides into two daughter cells
Explanation:
The sequence of events by which a cell duplicates its genome, synthesizes the other constituents of the cell and eventually divides into two daughter cells is termed cell cycle.
Reference:
Pg.No 120 of NCERT.

Question 2

During which phase of the cell cycle does DNA replication occur?

A) G1 phase

B) S phase

C) G2 phase

D) M phase

Answer: B) S phase
Explanation:
S or synthesis phase marks the period during which DNA synthesis or replication takes place.
Reference:
Pg.No 121 of NCERT.

Question 3

What is the primary function of mitosis?

A) To reduce chromosome number by half

B) To increase genetic variability

C) To produce diploid daughter cells with identical genetic complement

D) To form haploid gametes

Answer: C) To produce diploid daughter cells with identical genetic complement
Explanation:
Mitosis usually results in the production of diploid daughter cells with identical genetic complement.
Reference:
Page 125 of NCERT.

Question 4

In which phase of mitosis do the chromosomes align at the equator of the cell?

A) Prophase

B) Metaphase

C) Anaphase

D) Telophase

Answer: B) Metaphase
Explanation:
Chromosomes are moved to spindle equator and get aligned along metaphase plate through spindle fibres to both poles during metaphase.
Reference:
Page 123 of NCERT.

Question 5

What characterizes the anaphase stage of mitosis?

A) Chromosomes condense and the nuclear envelope reforms

B) Chromosomes align at the metaphase plate

C) Centromeres split and chromatids move to opposite poles

D) Chromosomes decondense and nuclear envelope disappears

Answer: C) Centromeres split and chromatids move to opposite poles
Explanation:
At the onset of anaphase, each chromosome arranged at the metaphase plate is split simultaneously and the two daughter chromatids, now referred to as daughter chromosomes of the future daughter nuclei, begin their migration towards the two opposite poles.
Reference:
Page 123 of NCERT.

Question 6

How does cytokinesis differ between animal and plant cells?

A) Animal cells form a cell plate; plant cells form a cleavage furrow

B) Animal cells form a cleavage furrow; plant cells form a cell plate

C) Both animal and plant cells form a cell plate

D) Both animal and plant cells form a cleavage furrow

Answer: B) Animal cells form a cleavage furrow; plant cells form a cell plate
Explanation:
In an animal cell, cytokinesis is achieved by the appearance of a furrow in the plasma membrane. In plant cells, wall formation starts in the centre of the cell and grows outward to meet the existing lateral walls. The formation of the new cell wall begins with the formation of a simple precursor, called the cell-plate.
Reference:
Page 124 of NCERT.

Question 7

What happens during the pachytene stage of prophase I in meiosis?

A) Chromosomes become visible

B) Homologous chromosomes pair and exchange genetic material

C) Synaptonemal complex dissolves

D) Chromosomes fully condense and nuclear envelope breaks down

Answer: B) Homologous chromosomes pair and exchange genetic material
Explanation:
Crossing over leads to recombination of genetic material on the two chromosomes. Recombination between homologous chromosomes is completed by the end of pachytene, leaving the chromosomes linked at the sites of crossing over.
Reference:
Page 126 of NCERT.

Question 8

In which stage of meiosis II do sister chromatids separate?

A) Prophase II

B) Metaphase II

C) Anaphase II

D) Telophase II

Answer: C) Anaphase II
Explanation:
Anaphase II begins with the simultaneous splitting of the centromere of each chromosome which was holding the sister chromatids together, allowing them to move toward opposite poles of the cell by shortening of microtubules attached to kinetochores.
Reference:
Page 127 of NCERT.

Question 9

What is the significance of meiosis in sexually reproducing organisms?

A) It increases chromosome number

B) It decreases genetic variability

C) It maintains chromosome number across generations and increases genetic variability

D) It produces diploid cells with genetic variation

Answer: C) It maintains chromosome number across generations and increases genetic variability
Explanation:
Meiosis is the mechanism by which conservation of specific chromosome number of each species is achieved across generations in sexually reproducing organisms.
Reference:
Page 128 of NCERT.

Question 10

What is the primary role of the G1 phase in the cell cycle?

A) DNA replication

B) Cell growth and metabolism

C) Chromosome separation

D) Cytokinesis

Answer: B) Cell growth and metabolism
Explanation:
During G1 phase the cell is metabolically active and continuously grows but does not replicate its DNA.
Reference:
Page 121 of NCERT.

Question 11

During which phase of the cell cycle does the cell prepare for mitosis by synthesizing proteins?

A) G1 phase

B) S phase

C) G2 phase

D) M phase

Answer: C) G2 phase
Explanation:
During the G2 phase, proteins are synthesised in preparation for mitosis while cell growth continues.
Reference:
Page 121 of NCERT.

Question 12

What is the significance of the S phase in the cell cycle?

A) The cell undergoes cytokinesis

B) DNA replication occurs

C) Chromosomes align at the metaphase plate

D) The cell undergoes apoptosis

Answer: B) DNA replication occurs
Explanation:
S or synthesis phase marks the period during which DNA synthesis or replication takes place.
Reference:
Page 121 of NCERT.

Question 13

In which stage of mitosis are chromosomes most condensed and visible?

A) Telophase

B) Anaphase

C) Metaphase

D) Prophase

Answer: C) Metaphase
Explanation:
During metaphase, condensation of chromosomes is completed and they can be observed clearly under the microscope.
Reference:
Page 123 of NCERT.

Question 14

In which stage of meiosis does crossing over occur?

A) Prophase I

B) Metaphase I

C) Anaphase I

D) Telophase I

Answer: A) Prophase I
Explanation:
Crossing over is the exchange of genetic material between two homologous chromosomes during pachytene of prophase I.
Reference:
Page 126 of NCERT.

Question 15

How many total chromosomes are present at the end of meiosis II if the starting cell had 8 chromosomes?

A) 4

B) 8

C) 2

D) 16

Answer: A) 4
Explanation:
Starting (Parent) cell typically being a diploid and it 8 chromosomes .As the daughter cell has half the number of chromosomes as that of parent (haploid),it will be having 4 chromosomes.
Reference:
Page 125 of NCERT.

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