Important Questions for CBSE Class 11 Biology Chapter 10 - Cell Cycle and Cell Division

1 Marks Questions:

1. Name the stage of cell division in which paired homologous chromosomes get shortened and thickened?

Ans: Pachytene is the stage of cell division in which paired homologous chromosomes get shortened and thickened.

2. Which structure of animal cell forms the asters of the spindle?

Ans: The centrosome is the structure of an animal cell that forms the asters of the spindle.

3. Name the cells in which meiosis occurs?

Ans: Meiosis occurs in the reproductive cells or germ cells.

4. At which stage of meiosis crossing over of genetic material takes place?

Ans: Pachytene is the stage of meiosis in which the crossing over of genetic material takes place.

5. What is the Go phase?

Ans: A stage when the cell cycle is arrested during interphase is called the Go phase.

6. Name the cell division concerned with cancer?

Ans: Mitosis is the type of cell division that is concerned with cancer.

7. What are kinetochores? 

Ans: Kinetochores are small disc-shaped structures at the surface of the centromeres.

8. What is interkinesis?

Ans: Interkinesis is the stage between two meiotic divisions.

9. Why is mitosis called equational division?

Ans: The chromosome number in the daughter cells is equal to the number of chromosomes in the parent cell hence mitosis is called equational division.

10. Name the stage of meiosis during which synaptonemal complex is formed.

Ans: Zygotene is the stage of meiosis during which a synaptonemal complex is formed.

11. What is the Go phase of the cell cycle?

Ans: Go is that phase of a cell cycle where the cells are metabolically active but no longer proliferate. 

12. Where does mitosis take place in plants and animals?

Ans: In plants mitosis takes place in the meristematic tissues whereas, in animals, it occurs in the somatic cells.

2 Marks Questions:

1. What is the importance of chromosomes replication during interphase?

Ans: Interphase is a stage between successive cell divisions. It is considered as the resting stage of a nucleus because it does not show any changes in the morphology however, physiologically it is an active stage in the life of a cell as the cell prepares itself for division and other biochemical changes as well.

2. Distinguish between the metaphase of mitosis and metaphase I of meiosis?

Ans: The metaphase of mitosis and metaphase I of meiosis differ from each other as:

3. How does duration affect the cell cycle in an organism?

Ans: Duration depends on the type of cell and other external factors such as temperature, food, and oxygen. The time period for G, S, G, and M-phase in different species under specific environmental conditions is like 20 min for bacterial cells, 10 hours for intestinal epithelial cells, 20 hours for onion root tip cells, etc. This shows that the time required for each step has been pre-set within cells of each organism.

4. Why is meiosis called reductional division and mitosis called equational division?

Ans: In meiosis, the number of chromosomes gets reduced to half hence, it is known as reductional division. Gametes are formed in sexually reproducing organisms in the germ cell. In mitosis, the number of chromosomes remains constant after division therefore, it is called equational division.

5. Write three processes that take place in interphase?

Ans: The three processes in interphase are:

i. Replication of DNA with the synthesis of histones and nuclear proteins.

ii. Division of the centriole to new centriole which lies at right to each other.

iii. Synthesis of energy-rich compounds to provide energy for mitosis.

6. Enumerate the significance of mitosis?

Ans: The various significances of mitosis are:

i. The number of chromosomes in the mitosis cell division remains constant in daughter cells.

ii. Asexual reproduction occurs with the help of mitosis.

iii. The size of a cell is controlled by the process of mitosis.

iv. The growth and development of the zygote are maintained by the process of mitosis.

7. Differentiate between chromatin and chromate.

Ans: Chromatin and chromate differ from each other as:

8. Give the terms for the following: 

a. The pet between 2 successive mitotic divisions.

b. Colt division in which chromosome number is halved.

c. Phase in the cell cycle where DNA is synthesized. 

d. Division of nuclear material. 

Ans: 

a. Interphase

b. Meiosis 

c. S phase 

d. Karyokinesis

3 Marks Questions:

1. What is the significance of meiosis?

Ans: The significance of meiosis is:

a. Meiosis reduces the number of chromosomes to half in the daughter cells.

b. Meiosis is a process in sexually reproducing animals because it restores the fixed number of chromosomes.

c. Meiosis results in the formation of gametes. Each of these gametes possesses half the number of chromosomes present in the somatic cells.

d. Gametes avoid multiplication of chromosomes thus maintaining the stability and a constant number of chromosomes of the species.

e. During crossing over, the exchange of nuclear material, genetic variations within the species occurs resulting in a new combination of genetic material.

2. Differentiate between animal cell mitosis & plant cell mitosis?

Ans: Animal cell mitosis and plant cell mitosis differ from each other as:

3. Write six differences between mitosis & meiosis? 

Ans: Mitosis and meiosis differ from each other as:

4. What are homologous chromosomes? What happens to homologous chromosomes during meiosis? 

Ans: Homologous chromosomes are defined as pairs of similar chromosomes having corresponding genes governing the same set of traits. 

During the heterotypic division of meiosis in leptotene, the chromosomes are thread-shaped and are coiled. During zygotene, homologous chromosomes start pairing. In pachytene, chromosomes show both- thickening and shortening. Diplotene is marked by the cessation of attraction force between the two homologous chromosomes. Uncoiling of the homologous chromosomes separate them from each other but also remains attached at chiasmata. During diakinesis, the separation of the homologous chromosome is complete. Exchange of parts between chromatids of homologous chromosomes may take place. During Anaphase I, centromeres of homologous compounds of bivalents repel each other post the separation of the centromere. The homologous chromosomes start to move apart, in telophase-I, chromosomes reach poles and become shortened. 

5. What will be the DNA content of a cell at G1, after S and G2., if the content after the M phase is 2C.

Ans: 

• Before mitotic division, the cell is in the interphase. There are three phases in interphases G1, S, G2. The daughter cell grows in size and produces the enzyme required for replication in the G1 phase.

• In the S phase, DNA replicates and the content of the chromosome gets double. In the G2 phase, cells grow in size and prepare to move in mitosis.

• Hence, when DNA content after the M-phase of a cell is 2c then in the G1 phase it remains in 2c as no replication occurs in this phase.

• In the S phase, DNA content becomes 4c as DNA replication takes place in this stage, and in the G2 phase, the DNA content will remain 4c.

• Then, when this cell finishes mitosis, the DNA content gets reduced to half i.e, 2c.

G1-2C1S-4C, G2-4C

5 Marks Questions:

1. Explain the various phases of meiosis II division?

Ans: Stages of meiosis II are:

i. Prophase II: Meiosis II is initiated immediately after cytokinesis usually before chromosomes have fully elongated. The nuclear membrane disappears by the end of prophase-II. The chromosomes again become compact.

ii. Metaphase-II: At this stage, the chromosomes align at the equator & the microtubules from opposite poles of the spindle get attached to the kinetochores of sister chromatids.

iii. Anaphase-II: It begins with the simultaneous splitting of the centromere of each chromosome allowing them to move towards opposite poles of the cell.

iv. Telophase-II: Meiosis ends with telophase-II, in which two groups of chromosomes once again get enclosed by the nuclear envelope, cytokinesis follows resulting in the formation of the tetrad of cell i.e. four haploid daughter cells.

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2. What is mitosis? Give a brief account of mitosis in an animal cell?

Ans: Mitosis is an equational cell division in which the number of chromosomes in parent and, progeny cell remains the same.

Stages of mitosis:

i. Prophase: 

a. Chromosome material condenses to form compact mitotic chromosomes. Chromosomes are seen to be composed of two chromatids attached together at the centromere.

b. Initiation of assembly of the mitotic spindle, microtubules the protein components of the cell cytoplasm help in the process.

ii. Metaphase: 

a. Spindle fibers attach to kinetochores of chromosomes

b. Chromosomes are moved to the spindle equator and get aligned along with the metaphase plate through spindle fibers to both poles.

iii. Anaphase: 

a. Centromere splits and chromatids separate 

b. Chromatids move to the opposite poles.

iv. Telophase: 

a. Chromosomes cluster at opposite spindle poles and lose their identity.

b. The nuclear envelope assembles around the clusters of chromosomes. 

c. Nucleolus, Golgi complex, and the ER reform.

The different stages of mitosis.

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