NEET Biology Cell Cycle and Cell Division Important Questions Set 02

These Class 11 NEET Biology important questions on Cell Cycle and Cell Division give 23 questions with step-by-step answers, arranged as very short, short and long answer types, taken from a model test paper. They help NEET aspirants revise the definitions, structures, differences and key terms of the chapter.

Very Short Answer Type Questions

Question 1. Which type of cell division is involved in regeneration?
Answer: Mitosis

Question 2. What is the duration of M-phase in cell cycle?
Answer: < 5%

Question 3. In which cell, the cytokinesis occurs by formation of a furrow?
Answer: Animal cell

Question 4. If the amount of DNA after S phase is equal to 20 pg, then what was the amount of initial DNA?
Answer: After S phase, 2C amount of DNA = 20 pg. In G1 phase, it would be 1 C or 10 pg.

Question 5. Name the phase of mitosis when the chromosomes are thickest, smallest and easily studied.
Answer: Metaphase

Question 6. Name the stage of meiosis when bivalents or homologous chromosomes separate from each other.
Answer: Anaphase I

Question 7. If a plant cell containing 23 chromosomes at the end of S phase, then what number of chromosomes are present at G₁ phase?
Answer: 23

Question 8. Which type of cell division maintains the nucleocytoplasmic ratio?
Answer: Mitosis

Short Answer Type Questions

Question 9. Define cell cycle.
Answer: A sequence of events by which a cell duplicates its genome, synthesize other constituents of the cell which eventually distribute and divides into two daughter cells is known as cell cycle.

Question 10. Define the period between two successive mitosis.
Answer: Interphase is a phase where the cell prepares itself for division. It is a biosynthetic phase in which the cell duplicates its organelles and replicates its DNA or genetic material.

Question 11. Describe the structures surrounding the constriction holding the two sister chromatids.
Answer: Centromere is the constriction which holds the two sister chromatids. It is surrounded by kinetochore which serves as the point of attachment of the chromosomes where the microtubules constituting the spindle fibres attach themselves.

Question 12. Briefly describe why meiosis I is called reductional division and meiosis II is called equational division?
Answer: Meiosis I is called reductional division because during this division, the chromosome number is reduced to half and meiosis II is called equational division because during this division, the number of chromosome remains the same as produced at the end of meiosis I.

Question 13. What is synaptonemal complex? When is it formed and what is its role?
Answer: It is formed during zygotene of prophase I. It is thought that synaptonemal complex stabilizes the two homologous chromosomes till the crossing over is completed.

Question 14. What is chiasmata? Explain its significance.
Answer: The point of attachment between the homologous chromosomes after the partial dissolution of the synaptonemal complex is called chiasmata. Chiasmata marks the site where crossing over occur during pachytene. They hold the homologous chromosome together.

Question 15. Write the name of meristems in which mitotic divisions result in a continuous growth of plants throughout their life?
Answer: Apical meristem and lateral cambium.

Short Answer Type Questions

Question 16. Diagrammatically explain cytokinesis in an animal cell.

Answer:

Centrioles Daughter nucleus

cells

A B C

Question 17. What is crossing over? Explain with a diagram.

Answer:

The exchange of genetic material between the non-sister chromatids of the homologous chromosomes is called crossing over. Kinetochores Non-sister chromatids Tetrad

Non-sister non-cross over chromatid Cross over Tetrad chromatids Non-sister non-cross over chromatid CROSSING OVER (IN PACHYTENE)

Question 18. Why do chromosomes assume short, rod-like forms during mitosis?
Answer: The chromosome condenses to assume short, rod-like forms during mitosis because it is easier for short, compact chromosomes to move through the cytoplasm in anaphase than it is for a long, slender twisted interphase chromosomes.

Question 19. Explain the events occurring during telophase.

Answer:

Telophase : Telo means end and phase means stage, hence telophase is the end stage of mitosis. The following events occur during telophase :

(i) The chromosomes (sister chromatids) reach their respective poles. The mitotic spindle disappears.

(ii) After reaching the poles, the chromosomes gradually uncoil and become thin, slender, long and lose their identity. The decondensation of chromosomes occur and finally they become indistinguishable mass and collect at the poles.

(iii) Nucleolus, endoplasmic reticulum, golgi bodies, and other organelle reappear in the daughter cells.

(iv) The nuclear envelope assembles around the chromatin cluster.

Question 20. Explain the events occurring during metaphase II.
Answer: The univalents, i.e., chromosomes align themselves at the equator, (on the equatorial plane) in the metaphase II. The microtubules, from the opposite poles, extend towards the equator and attach at the kinetochore of the chromatids.

Question 21. Describe the quiescent stage of the cell cycle.
Answer: The non-dividing cells enter the quiescent stage or G₀ stage of the cell cycle. In this phase, the cells remain metabolically active but do not proliferate unless they are called on to do so. They proliferate depending upon the requirement of the cell. The cells which enter G₀, do not divide further and start differentiating into specific types of cells. These cells do not go beyond the G₁ phase, i.e., the cell cycle for such cells stops at this phase. The cells present in the G₀ phase have two fates. They can either re-enter into the cell cycle, i.e., G₁ phase or they can fully differentiate and die.

Long Answer Type Questions

Question 22. Diagrammatically explain the behaviour and structure of chromosome during interphase and mitosis.

Answer:

G₁-Phase

S-Phase Anaphase

G₂-Phase

Metaphase Prophase

Question 23. Write the significance of meiosis.

Answer:

(1) Formation of gametes : Meiosis produces gametes for sexual reproduction. Gametes are essential for sexual reproduction because in sexual reproduction an organism is formed by the fusion of two gametes.

(2) Maintenance of chromosome number : Meiosis reduces the chromosomal number to half in the gametes, so that fertilization restores the original diploid number in the zygote.

(3) Introduction of variations : Meiosis provides a chance for the formation of new combination of chromosomes. This brings out variations. The new combinations are produced by crossing over in prophase I.