CBSE/NCERT/Exercises/Class_11_Biology
Created by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
Created by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
NCERT Biology Exercises for Class 11 Biology - Cell Cycle and Cell Division - Class_11_Biology
Answer: The average cell cycle span for a mammalian cell is approximately 24 hours.
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Answer: Interphase is the "resting phase" where the cell prepares for division by undergoing growth and DNA replication. It consists of three stages:
Answer: The G₀ phase is an inactive stage where cells exit the G₁ phase and no longer proliferate. These cells remain metabolically active but do not divide unless specifically called upon by the organism to replace lost cells (e.g., heart cells).
Answer: Mitosis is called equational division because the number of chromosomes in the daughter cells is exactly the same as the number of chromosomes in the parent cell (both remain 2n).
(i) Chromosomes are moved to spindle equator. (ii) Centromere splits and chromatids separate. (iii) Pairing between homologous chromosomes takes place. (iv) Crossing over between homologous chromosomes takes place.
Answer: (i) Metaphase (ii) Anaphase (iii) Zygotene (Prophase I of Meiosis) (iv) Pachytene (Prophase I of Meiosis)
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| Feature | Mitosis | Meiosis |
|---|---|---|
| Type of Division | Equational (2n to 2n) | Reductional (2n to n) |
| Number of Divisions | One single division | Two sequential divisions (I & II) |
| Synapsis & Crossing Over | Absent | Present in Prophase I |
| Daughter Cells | Two diploid cells, identical | Four haploid cells, varied |
| Occurrence | Somatic cells | Germ cells (Gametogenesis) |
Answer: Meiosis ensures the conservation of the specific chromosome number of each species across generations in sexually reproducing organisms. It also increases genetic variability in populations through crossing over, which is crucial for evolution.
Answer: No. Mitosis requires the distribution of an exact copy of the genome to each daughter cell. Without DNA replication in the S phase, the chromosome number would be halved in each division, violating the principle of equational division.
Answer: Yes. In some organisms, karyokinesis is not followed by cytokinesis, leading to a multinucleate condition (e.g., liquid endosperm in coconut). In other cases, repeated DNA replication without division leads to polyploidy.
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/CBSE/NCERT/Exercises/Class_11_Biology/Chapter_10_Cell_Cycle_and_Cell_Division.mdx