NEET Biology Cell Cycle and Cell Division Important Questions Set 01

These Class 11 NEET Biology important questions on Cell Cycle and Cell Division give 45 questions with step-by-step answers, arranged as very short, short and long answer types, as asked in school and board examinations. They help NEET aspirants revise the definitions, structures, differences and key terms of the chapter.

Very Short Answer Type Questions

Question 1. How many meiotic divisions are required to produce 32 microspores?
Answer: Eight

Question 2. Name the stage which connects meiosis I and meiosis II.
Answer: Interkinesis

Question 3. Name the first stage of the interphase in which active synthesis of RNA and protein occurs.
Answer: G₁ phase

Question 4. What percentage of duration of cell cycle does interphase last?
Answer: More than 95%

Question 5. Name the last stage of prophase I.
Answer: Diakinesis

Question 6. Name the phase in which the chromatids move apart in mitosis and meiosis.

Answer:

Mitosis – Anaphase

Meiosis – Anaphase II

Question 7. Which process changes the long, fine chromatin fibres into chromosomes?
Answer: Condensation of chromosomes

Question 8. How does the cell plate divide the plant cell into two daughter cells?
Answer: The cell plate starts from the centre of the cell and moves or grow outwards, centrifugally to meet the lateral cell wall. It therefore, divides the cell into two halves.

Question 9. Name the three sub-stages of interphase.
Answer: G₁ phase, S phase, G₂ phase

Question 10. Which type of cell division produces new cells for regeneration?
Answer: Mitosis

Short Answer Type Questions

Question 11. Why is DNA duplicated well before cell division?
Answer: DNA is duplicated well before cell division to ensure that daughter cells have identical genetic information about their structure and functioning. It is to ensure that both the daughter cells have intact genome.

Question 12. Differentiate between anaphase I and anaphase II of meiosis.
Answer: Anaphase I Anaphase II
1. The homologous chromosomes separate The chromatids of the chromosomes from each other and start moving towards separate from each other and start the poles. moving towards the opposite poles.
2. The centromere holding the two The centromere holding the two chromatids do not break and the entire chromatids breaks and the chromatids chromosome move towards the pole. move towards the opposite poles.
3. It reduces the number of chromosomes to It does not reduce the chromosome half. number.

Question 13. Mention the significance of crossing over phenomenon occurring during meiosis I.
Answer: Crossing over introduces new combinations of genes which results into variations. Thus, exchange of genetic material produces variations.

Question 14. What is the difference between S phase and G₂ phase?
Answer: S Phase G₂ Phase
1. It is a phase where synthesis of DNA takes It is a phase where RNA and proteins required place. during the Mphase are synthesized.
2. It lasts for6–8 hours in humans. It lasts for2–5 hours in humans.

Question 15. Write the names of two cells which do not divide after attaining fully differentiated state.
Answer: RBC, nerve cell.

Question 16. What is meant by metaphasic plate?
Answer: The plane of alignment of the chromosomes at metaphase is referred to as the metaphase plate.

Question 17. What is M phase? Which two processes are involved during M phase?

Answer:

M phase or mitotic phase is the phase where actual cell division occurs. It consists of two processes namely :

(i) Karyokinesis – Division of nucleus

(ii) Cytokinesis – Division of cytoplasm.

Question 18. What are the four major stages of karyokinesis?
Answer: Prophase, metaphase, anaphase, telophase.

Question 19. Define cell plate.
Answer: The formation of the new cell wall begins with the formation of a simple precursor, called the cell plate that represent the middle lamella between the walls of two adjacent cells.

Question 20. What happens to the somatic cell if its surface area to volume ratio decreases?
Answer: If the surface area volume ratio of a cell decreases, then the cell undergoes mitosis or cell division. It maintains the size of the cell which is essential for proper functioning of the cell.

Question 21. In which phase of the cell cycle, the following take place?
(i) Replication or duplication of DNA
(ii) Separation of chromatids

Answer:

(i) Interphase (S-phase)

(ii) M phase (Anaphase)

Question 22. Schematically show the following :
(i) Centromere
(ii) Spindle fibres

Answer:

Centromere

Sister chromatids

(i) Centromere

Spindle fibres

(ii) Spindle fibres

Question 23. What is the major difference between S phase and M phase of the cell cycle?
Answer: S phase is the phase where synthesis or duplication of DNA occurs and M phase is the phase where the DNA duplicated during S phase is distributed between the two daughter cells.

Question 24. What will happen to the lizards whose tail is surgically removed (cut)?
Answer: The cells present at the tail of the lizard undergo mitosis to produce new cells which regenerate the new tail.

Question 25. Draw the diagram of the following :
(i) Interphase
(ii) Diakinesis
(iii) Telophase II

Answer:

A well-labelled diagram should show these parts: Centrioles; Centrosomes; Centrosphere; Cell membrane; Daughter; Nuclear cells membrane; Chromatin; Nucleolus.

INTERPHASE DIAKINESIS TELOPHASE II

Question 26. Diagrammatically explain the behaviour of chromosome during the following phases.
(i) G₁ phase
(ii) S phase
(iii) G₂ phase
Answer: G₁-Phase S-Phase G₂-Phase

Question 27. Which is the event that occurs during anaphase II?
Answer: The event which occurs during anaphase II is the separation of the chromatids of the univalent chromosomes present in the daughter cell formed after meiosis I. The chromatids present in the univalent chromosomes differ from each other due to crossing over.

Question 28. Why are haploid gametes important for the sexual reproduction?
Answer: During sexual reproduction, two gametes fuse together to form a fertilized egg. If the gametes are diploid (2n), then the offspring produced would be (4n) and when it would reproduce, the new offspring would have 8n condition and so on. This would disturb the stability of the organism, so in order to maintain the diploid condition in the offsprings, meiosis produces two haploid gametes which fuse together to form a diploid offspring.

Question 29. Write the major events occurring during prophase II.

Answer:

(i) It is a short phase where the chromatids of the univalent condenses.

(ii) The chromatin material becomes compact.

(iii) The nucleolus and nuclear membrane disintegrates and disappears.

Question 30. What is the role of mitosis in repair, reproduction, healing and regeneration?

Answer:

(i) Repair : Mitosis is a mechanism for replacing old, dead and worn out cells by new cells.

(ii) Reproduction : Mitosis brings about reproduction in unicellular organisms.

(iii) Healing and regeneration : Mitosis produces new cells for healing the wounds and for regeneration.

Long Answer Type Questions

Question 31. Define :
(i) Synapsis
(ii) Synaptonemal complex
(iii) Bivalent
(iv) Dyad
(v) Metaphasic plate

Answer:

(i) Synapsis : The pairing of homologous chromosomes during zygotene of prophase I of meiosis is called synapsis.

(ii) Synaptonemal complex : Chromosome synapsis is accompanied by the formation of complex structure called synaptonemal complex.

(iii) Bivalent : The complex formed by a pair of synapsed homologous chromosomes. The two homologous chromosome pair together and thus form a bivalent.

(iv) Dyad : The sister chromatids of homologous chromosomes which become visible during cell division are called dyads.

(v) Metaphasic plate : The plane of alignment of the centromere of all the chromosomes of the cell at the equator during metaphase, is called metaphasic plate.

Question 32. Give the scientific term for each of the following :
(i) An inactive stage shown by the cells which does not proliferate unless called on to do so.
(ii) A disc-like structure surrounding the centromere.
(iii) The stage which lasts for months or years in the oocytes of some vertebrates.
(iv) A unicellular organism whose cell cycle time is 90 min.

Answer:

(i) Quiescent or G₀ stage.

(ii) Kinetochore

(iii) Diplotene

(iv) Yeast

Question 33. Describe prophase of mitosis.

Answer:

Pro means first and phase means stage, therefore prophase is the first stage of mitosis which follows the interphase of the cell cycle. The following events occur during prophase :

(i) Initiation of condensation of chromosomal material : The condensation of this chromatin material takes place and during condensation, the DNA strands unwind or untangles to form compact mitotic chromosomes.

(ii) The centrioles in the animal cells, begins to move towards the opposite poles of the cell.

(iii) Initiation of mitotic spindle occurs during prophase.

(iv) Cells at the end of prophase, when viewed under the microscope, do not show golgi complexes, endoplasmic reticulum, nuclear membrane and nucleolus.

Question 34. Draw the diagram of different phases of mitosis.

Answer:

A well-labelled diagram should show these parts: Metaphase.

Question 35. When does each of the following occur in meiosis II?
(i) The nuclear membrane reappears.
(ii) The centromere divides into two.
(iii) The chromosomes are thickest and shortest.
(iv) The chromosomes align at the equator.

Answer:

(i) Telophase II

(ii) Anaphase II

(iii) Metaphase II

(iv) Metaphase II

Question 36. Name the last stage of karyokinesis of meiosis I. Mention the events that occur during this stage and also represent this stage with the help of a diagram.

Answer:

Telophase I is the final stage of reductional division, i.e., meiosis I. It is characterised by following events :

(i) The chromosomes reach the poles. The spindle fibres completely disappear.

(ii) The nucleolus and nuclear membrane reappear.

(iii) The chromosomes uncoil and elongate but remain straight in this phase. They do not reach the extremely extended state of the interphase nucleus.

(iv) It produces two daughter cells each containing a single nucleus. The nucleus of the daughter cell receives only one chromosome from each homologous pair and thus it has half the number of chromosome. The separation of the two chromatids Telophase I occurs during meiosis II.

Question 37. Describe the second stage of meiosis I.

Answer:

After completing prophase I, the chromosomes enter metaphase I. Following events occur during metaphase I :

(i) The bivalent chromosomes align themselves at the equator on the equatorial plate. The centromeres of the two chromosomes are arranged in two rows at the equator.

(ii) The distribution of the bivalent chromosomes are at random. The two chromosomes can face either of the two poles. There is no fixed direction in which paternal or maternal chromosomes would face.

(iii) The microtubules of the spindle fibres from opposite poles attach to the centromere of the chromosome facing towards it.

Question 38. Draw the diagram of following stages :
(i) Metaphase II
(ii) Leptotene
(iii) Cell plate formation
(iv) Diplotene

Answer:

A well-labelled diagram should show these parts: Centrioles; Chromo- somes; (i) Metaphase-II; (ii) Leptotene; Plasma membrane; Nuclear; Cell Plate membrane; (Disappearing); Nucleolus.

(iii) Cell plate formation (iv) Diplotene

Question 39. Explain the stage/phase of cell cycle where you would find nerve cells.

Answer:

The non-dividing cells such as nerve cells enter the quiescent stage or G₀ stage of the cell cycle. In this phase, the cell 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 rather start differentiating into specific types of cells. These cells do not go beyond the G₁ phase.

Question 40. Describe the process of cytokinesis which occurs by the centripetal movement of the plasma membrane.

Answer:

In animal cells, cytokinesis is achieved by the formation of a furrow. The furrow forms in the plasma membrane of the cell which deepens gradually. It moves centripetally and ultimately joins in the centre dividing the cell cytoplasm into two. The ingrowing constriction of the plasma membrane moves inside the cell which finally joins and divide the animal cell into two daughter cells.

Centrioles Daughter nucleus

cells

A B C

Question 41. Explain the diplotene stage of meiosis.

Answer:

(i) The synaptonemal complex formed during the zygotene dissolves partially during the diplotene. Therefore, the homologous chromosomes separate excepts in the region of crossing over.

(ii) The point of attachment between the homologous chromosomes after the partial dissolution of the synaptonemal complex is called chiasmata. It becomes visible during diplotene stage. The two homologous chromosomes begin to separate from each but remain attached at the chiasmata. Chiasmata marks the sites where crossing over occurred during pachytene. The homologous chromosomes do not separate at chiasmata, and hence they are seen as a X-shaped structure.

Question 42. Diagrammatically represent different phases of the cell cycle.

Answer:

G₁ G₀ S

Cytokinesis phase Telo hase se ap hase An tapha

G₂ as e

Question 43. What is the significance of pachytene?

Answer:

Pachytene : It is the third stage of prophase I. It occurs after zygotene and the following events occur during pachytene :

(i) The synapsed chromosomes continue to become thick and short. The chromatids of the homologous chromosomes now become clearly visible and are referred as dyad. The two chromatids of the same chromosome are called sister chromatids and two chromatids of the two different homologous chromosomes is called as non-sister chromatids.
(ii) During pachytene, crossing over occurs between non-sister chromatids of the homologous chromosomes. The exchange of genetic material (DNA) between the non-sister chromatids of the homologous chromosomes is known as crossing over.

(iii) Crossing over leads to recombination of genetic material which involves a mutual exchange of the corresponding segments of non-sister chromatids of homologous chromosomes. It takes place by breakage and reunion of chromatid segments.

Question 44. Why is G₁ phase important during cell cycle?
Answer: G₁ phase corresponds to the interval between mitosis and initiation of DNA replication. In this phase, cell replicate DNA and remain metabolically active. The cell grows in size continuously and synthesizes nucleotides, ATP, proteins, amino acids, RNAs etc. (required during S phase) during this phase. The G₁ phase synthesize the enzymes and other things required during S phase. It is the Gap phase which occur prior to the S phase and prepare or synthesizes components required during the next phase, i.e., S phase. If G₁ phase does not occur the DNA replication would not occur.

Question 45. What will happen if zygotene stage is skipped by the cells?

Answer:

Zygotene is the second stage of prophase I. It occurs after leptotene. A diploid cell contains two set of chromosomes. The two chromosomes which are similar in form, size, structure are called homologous chromosomes. One of the homologous chromosomes is paternal chromosome and the other is maternal chromosome.

During zygotene, these homologous chromosomes start pairing together. These homologous chromosome come to lie side by side in pairs and this pairing is known as synapsis. The complex formed by a pair of synapsed chromosome is called bivalent. If zygotene is skipped, then crossing over, recombinations would not occur. Meiosis would not occur and gamete would not be properly formed.