Q11. The nucleolus is primarily involved in the synthesis of:
[A] DNA
[B] mRNA
[C] tRNA
[D] rRNA
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Correct Answer: [D] rRNA
Explanation: The nucleolus is a prominent structure within the nucleus and is the primary site for the synthesis of ribosomal RNA (rRNA). rRNA is a crucial component of ribosomes, which are essential for protein synthesis. DNA is synthesized during replication, mRNA during transcription, and tRNA during transcription, but nucleolus is specifically for rRNA synthesis and ribosome biogenesis.
Q12. Chromosomes are composed of:
[A] DNA only
[B] Protein only
[C] DNA and proteins
[D] RNA and proteins
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Correct Answer: [C] DNA and proteins
Q13. The longest phase of the cell cycle is:
[A] Prophase
[B] Metaphase
[C] Anaphase
[D] Interphase
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Correct Answer: [D] Interphase
Explanation: Interphase is the longest phase of the cell cycle, constituting about 95% of the cell cycle duration. During interphase, the cell grows, synthesizes new organelles and biomolecules, and replicates its DNA in preparation for cell division (M phase). Prophase, metaphase, and anaphase are stages of mitosis or meiosis, which are relatively shorter compared to interphase.
Q14. The stage of mitosis where chromosomes align at the equatorial plate is:
[A] Prophase
[B] Metaphase
[C] Anaphase
[D] Telophase
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Correct Answer: [B] Metaphase
Q15. Separation of sister chromatids occurs during which phase of mitosis?
[A] Prophase
[B] Metaphase
[C] Anaphase
[D] Telophase
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Correct Answer: [C] Anaphase
Q16. Cytokinesis in animal cells is achieved by:
[A] Cell plate formation
[B] Furrow formation
[C] Spindle fiber elongation
[D] Kinetochore separation
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Correct Answer: [B] Furrow formation
Explanation: Cytokinesis, the division of cytoplasm, in animal cells typically occurs by furrow formation or cleavage furrow. A cleavage furrow forms in the cell membrane and gradually deepens to constrict and divide the cytoplasm into two daughter cells. In plant cells, cytokinesis is by cell plate formation. Spindle elongation and kinetochore separation are part of chromosome segregation during mitosis/meiosis, not cytokinesis itself.
Q17. Cell plate formation is characteristic of cytokinesis in:
[A] Animal cells
[B] Plant cells
[C] Bacteria
[D] Fungi
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Correct Answer: [B] Plant cells
Q18. Meiosis results in the production of:
[A] Two diploid daughter cells
[B] Four diploid daughter cells
[C] Two haploid daughter cells
[D] Four haploid daughter cells
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Correct Answer: [D] Four haploid daughter cells
Q19. Crossing over, a key event in genetic recombination, occurs during:
[A] Leptotene
[B] Zygotene
[C] Pachytene
[D] Diplotene
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Correct Answer: [C] Pachytene
Explanation: Crossing over, the exchange of genetic material between non-sister chromatids of homologous chromosomes, occurs during pachytene stage of prophase I in meiosis. It leads to genetic recombination and increases genetic diversity. Leptotene is chromosome condensation, zygotene is synapsis, and diplotene is chiasmata formation, pachytene is the actual stage of crossing over.
Q20. Synapsis, the pairing of homologous chromosomes, occurs during:
[A] Leptotene
[B] Zygotene
[C] Pachytene
[D] Diplotene
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Correct Answer: [B] Zygotene
Explanation: Synapsis is the pairing of homologous chromosomes to form synaptonemal complex, which occurs during zygotene stage of prophase I in meiosis. This pairing is essential for crossing over to occur in the next stage (pachytene). Leptotene is chromosome condensation, pachytene is crossing over, and diplotene is chiasmata formation.