Q21. Which phase of the cell cycle involves the replication of DNA?
a) G1 phase
b) S phase
c) G2 phase
d) M phase
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Correct Answer: b) S phase
Explanation: The S phase, or synthesis phase, is the phase of the cell cycle during which DNA replication occurs. This phase precedes cell division and is crucial for ensuring that each daughter cell receives a complete and identical copy of the genetic material.
Q22. During which phase of mitosis do the chromosomes become visible under a light microscope?
a) Prophase
b) Metaphase
c) Anaphase
d) Telophase
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Correct Answer: a) Prophase
Explanation: Prophase is the stage of mitosis where the chromatin condenses into visible chromosomes. At this stage, the chromosomes appear as distinct structures under a light microscope, marking the beginning of mitotic division.
Q23. Which of the following is a characteristic of metaphase of mitosis?
a) Chromatids separate and move towards opposite poles
b) Chromosomes align along the equatorial plane of the cell
c) Nuclear envelope reforms around the separated chromosomes
d) Chromosomes condense and become visible
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Correct Answer: b) Chromosomes align along the equatorial plane of the cell
Explanation: Metaphase of mitosis is characterized by the alignment of chromosomes along the equatorial plane (metaphase plate) of the cell. This alignment ensures that each daughter cell receives an equal and complete set of chromosomes during cell division.
Q24. What is the main difference between anaphase I and anaphase II of meiosis?
a) Anaphase I involves the separation of sister chromatids, while anaphase II involves the separation of homologous chromosomes.
b) Anaphase I occurs in diploid cells, while anaphase II occurs in haploid cells.
c) Anaphase I results in the formation of two daughter cells, while anaphase II results in the formation of four daughter cells.
d) There is no difference between anaphase I and anaphase II.
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Correct Answer: a) Anaphase I involves the separation of sister chromatids, while anaphase II involves the separation of homologous chromosomes.
Explanation: Anaphase I of meiosis involves the separation of homologous chromosomes, while anaphase II involves the separation of sister chromatids. This distinction is essential for reducing the chromosome number and producing genetically diverse haploid cells during meiosis.
Q25. Which of the following occurs during telophase II of meiosis?
a) Homologous chromosomes separate and move towards opposite poles
b) Nuclear envelope reforms around the separated chromosomes
c) Chromosomes align along the equatorial plane of the cell
d) Sister chromatids separate and move towards opposite poles
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Correct Answer: b) Nuclear envelope reforms around the separated chromosomes
Explanation: Telophase II of meiosis is the final stage of meiotic division, where the nuclear envelope reforms around the separated chromosomes in each of the four haploid daughter cells. This process marks the completion of meiosis and the formation of genetically diverse gametes.
Q26. Which of the following statements about cytokinesis is true?
a) Cytokinesis involves the division of the nucleus.
b) Cytokinesis occurs simultaneously with telophase.
c) Cytokinesis occurs before the completion of mitosis.
d) Cytokinesis is the same process as karyokinesis.
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Correct Answer: b) Cytokinesis occurs simultaneously with telophase.
Explanation: Cytokinesis is the process of dividing the cytoplasm and organelles between daughter cells. It typically begins during telophase of mitosis, although the exact timing may vary depending on the cell type. During cytokinesis, a cleavage furrow forms in animal cells, while a cell plate forms in plant cells, ultimately resulting in the formation of two separate daughter cells.
Q27. What is the significance of crossing over during meiosis?
a) It ensures the separation of homologous chromosomes during anaphase I.
b) It increases genetic diversity among offspring.
c) It prevents errors in DNA replication.
d) It occurs only in prophase II of meiosis.
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Correct Answer: b) It increases genetic diversity among offspring.
Explanation: Crossing over, which occurs during prophase I of meiosis, involves the exchange of genetic material between homologous chromosomes. This process results in the reshuffling of genetic combinations, leading to increased genetic diversity among offspring. It contributes to the variability observed in traits within a population.
Q28. What is the role of spindle fibers during cell division?
a) Spindle fibers help to replicate DNA.
b) Spindle fibers help to separate sister chromatids during anaphase.
c) Spindle fibers form the nuclear envelope.
d) Spindle fibers synthesize proteins.
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Correct Answer: b) Spindle fibers help to separate sister chromatids during anaphase.
Explanation: Spindle fibers are microtubular structures that are involved in the movement and segregation of chromosomes during cell division. During anaphase of mitosis or anaphase II of meiosis, spindle fibers attach to the centromeres of sister chromatids and pull them towards opposite poles of the cell, ensuring that each daughter cell receives a complete set of chromosomes.
Q29. How many daughter cells are produced at the end of meiosis II?
a) Two
b) Four
c) One
d) None
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Correct Answer: b) Four
Explanation: At the end of meiosis II, four haploid daughter cells are produced from the two haploid cells formed during meiosis I. Each of these daughter cells contains a unique combination of chromosomes due to the random assortment of homologous chromosomes and crossing over during meiosis I, followed by the separation of sister chromatids during meiosis II.
Q30. What is the significance of the spindle checkpoint during mitosis?
a) It ensures that the DNA is replicated accurately.
b) It prevents the cell from entering anaphase prematurely.
c) It initiates the process of cytokinesis.
d) It facilitates the attachment of spindle fibers to chromosomes.
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Correct Answer: b) It prevents the cell from entering anaphase prematurely.
Explanation: The spindle checkpoint, also known as the metaphase checkpoint, is a regulatory mechanism that ensures proper chromosome alignment on the metaphase plate before the onset of anaphase. It monitors the attachment of spindle fibers to the kinetochores of chromosomes and prevents the cell from progressing into anaphase until all chromosomes are properly attached and aligned. This helps to maintain chromosomal stability and prevent errors in chromosome segregation.