NCERT Solutions For Class 11 Biology Chapter 10 Cell Cycle and Cell Division

Chapter 10 Biology Class 11 NCERT Solutions

Q1. What is the average cell cycle span for a mammalian cell?

Answer:

The average cell cycle span for a mammalian cell is 24 hours.

Q2. Distinguish cytokinesis from karyokinesis.

Answer:

The differences between cytokinesis and karyokinesis are as follows:

Q3. Describe the events taking place during interphase.

Answer:

Interphase refers to the phase in the cell cycle which prepares the cell and its nucleus for the division. Interphase is divided into three sub-phases like

1. G1 phase- It is the longest stage of interphase, also called the first growth phase or post-mitotic gap phase. Both the cell and its nucleus grow in size. There is the synthesis of RNA, proteins, nucleotides, amino acids for histones and energy-rich compounds. There is a checkpoint called G1 cyclin or CG1, where the decision about the entry in the G0 stage is taken. If the decision is made cell cycle goes on uninterrupted or the cell undergoes the G0 stage. It refers to the resting phase in which the cell is arrested and not allowed to divide.

2. S Phase- In this phase, chromosomes along with their DNA replicates. The content of DNA doubles up, however, the number of chromosomes remains the same. After replication, the daughter chromosomes remain attached in the region of the centromere. The centrosome, if present begins to divide.

3. G2 phase- This phase is characterised by increased synthesis of RNA and proteins. The cell organelles undergo multiplication in this phase while the cell grows in size. G2 phase is also called as second growth phase or pre-mitotic gap phase.

NCERT Solutions for Class 11 Biology Chapter 10 Cell Cycle and Cell Division:

Q4. What is Go (quiescent phase) of cell cycle?

Answer:

G _o (quiescent phase)- It refers to the stage of inactivation of cell cycle due to the absence of mitogens and energy-rich compounds. The cells of this stage are metabolically active and they act as reserve cells i.e. they undergo growth and differentiation for a specific function. E.g Cells in the quiescent centre of the root tip.

Cell Division Class 11 Exercise

Q5. Why is mitosis called equational division?

Answer:

Mitosis is called equational division because, at the end of mitosis, the numbers of chromosomes remain same in parental cells and daughter cells. Similarly, the ploidy of the parental and daughter cells also remain the same in mitosis.

Q6. Name the stage of cell cycle at which one of the following events occur:

(i) Chromosomes are moved to spindle equator.

Answer:

(i) Chromosomes are moved to spindle equator

During metaphase, the chromosomes move to the spindle equator and align themselves there.

Q6. Name the stage of cell cycle at which one of the following events occur:

(ii) Centromere splits and chromatids separate.

Answer:

(ii) Centromere splits and chromatids separate

During anaphase, the centromere splits and chromatids are separated. These chromatids after separation move to the opposite poles.

Q6. Name the stage of cell cycle at which one of the following events occur:

(iii) Pairing between homologous chromosomes takes place.

Answer:

(iii) Pairing between homologous chromosomes takes place

The pairing between homologous chromosomes takes place during zygotene of prophase I of meiosis I. As a result of this pairing bivalents are formed.

Q6. Name the stage of cell cycle at which one of the following events occur:

(iv) Crossing over between homologous chromosomes takes place.

Answer:

(iv) Crossing over between homologous chromosomes takes place

Crossing over between homologous chromosomes takes place during pachytene of prophase I of meiosis I.

Class 11 Biology Chapter 10 Question Answers

Q7. Describe the following:

(a) synapsis

Draw a diagram to illustrate your answer.

Answer:

Synapsis- The process of the pairing of homologous chromosomes during the zygotene stage of prophase I of meiosis I is called synapsis. During synapse, a synaptonemal complex is formed by the homologous chromosome which is referred to as a bivalent or a tetrad.

Q7. Describe the following:

(b) bivalent

Draw a diagram to illustrate your answer.

Answer:

Bivalent- it refers to the structure formed by a pair of the synapsed homologous chromosome.

Q7. Describe the following:

(c) chiasmata

Draw a diagram to illustrate your answer.

Answer:

Chiasmata- These are points of attachment between homologous chromosomes during their separation in diplotene to metaphase I stage of meiosis. Chiasmata are initially formed in the regions of crossing over between nonsister chromatids but later on, tend to shift sideways.

Q8. How does cytokinesis in plant cells differ from that in animal cells?

Answer:

The process of cytokinesis differs in plant and animal cells

CBSE NCERT solutions for class 11 biology chapter 10 cell cycle and cell division:

Q9. Find examples where the four daughter cells from meiosis are equal in size and where they are found unequal in size.

Answer:

Meiosis is the reductional division that leads to the formation of four daughter cells which have half the number of chromosomes than the parent cell. Meiosis takes place during spermatogenesis and oogenesis in humans. During spermatogenesis, the daughter cells or sperms formed are equal in size while during oogenesis the daughter cells are unequal in size.

Cell Cycle and Cell Division Class 11 Questions and Answers

Q10. Distinguish anaphase of mitosis from anaphase I of meiosis.

Answer:

Anaphase of mitosis	Anaphase I of meiosis
Anaphase of mitosis involves splitting of each chromosome at centromere into two sister chromatids which start moving towards the opposite poles.	Anaphase I of meiosis I involve the separation of homologous chromosomes, while the chromatids remain attached at their chromatids.

Q11. List the main differences between mitosis and meiosis.

Answer:

Q12. What is the significance of meiosis?

Answer:

The process of meiosis is essential for all sexually reproducing organisms. It occurs in reproductive cells to form gametes that have half the number of chromosomes of the reproductive cells. The two gametes from reproductive cells fuse with each other to form a zygote. As a result, the zygote comes to have a double number of chromosomes. Thus, meiosis maintains the chromosome number of organisms. apart from this, there are other significances of meiosis also. Some of these are as follows

1. Meiosis form gametes that are required for sexual reproduction

2. Meiosis maintains the fixed number of chromosomes in sexually reproducing organisms by having the same during gametogenesis

3. In meiosis, paternal and maternal chromosomes assort independently. It causes a reshuffling of chromosomes and the traits controlled by them. The variations help the breeders in improving the races of useful plants and animals.

4. Meiosis introduces a new combination of traits or variations.

5. Chromosomal and genomic mutations occur by irregularities of meiotic division. Some of these mutations are useful to the organism.

Solutions for NCERT Class 11 Biology Chapter 10 Cell Cycle and Cell Division:

Q13. Discuss with your teacher about

(i) haploid insects and lower plants where cell-division occurs

Answer:

In some lower plants and haploid insects such as drones of a honey bee, meiosis occurs in the zygote. This type of meiosis is called zygotic meiosis whereas this type of life cycle is called haplontic life cycle.

Q13. Discuss with your teacher about

(ii) some haploid cells in higher plants where cell-division does not occur.

Answer:

Synergids and antipodals are haploid cells in higher plants where cell division does not occur.

Q14. Can there be mitosis without DNA replication in 'S' phase?

Answer:

Without DNA replication in 'S' phase, mitosis cannot occur. During DNA replication, DNA duplicates and this is a very important step. If DNA duplication does not occur than even in mitosis, there will be a reduction in the number of chromosomes of daughter cells. Thus, mitosis cannot occur without DNA replication.

Q15. Can there be DNA replication without cell division?

Answer:

Yes, DNA replication can occur without being followed by cell division. For example, polyteny is a condition in which chromosomes repeatedly replicates but the cells do not divide and as a result of this, DNA accumulates in the cell.

NCERT Solutions for Class 11 Biology Chapter 10 Cell Cycle and Cell Division:

Q16. Analyse the events during every stage of cell cycle and notice how the following two parameters change

(i) number of chromosomes (N) per cell

Answer:

The number of chromosomes (N) per cell changes during the anaphase I stage of meiosis I. During this stage, the homologous chromosomes get separated and starts moving towards the opposite poles. Thus, the bivalents get divided into sister chromatids. This leads to a reduction of the number of chromosomes to half in daughter cells.

Q16. Analyse the events during every stage of cell cycle and notice how the following two parameters change

(ii) amount of DNA content (C) per cell

Answer:

The amount of DNA content per cell changes during 'S' phase and anaphase. In 'S' phase, the number of chromosomes remains the same but DNA replicates. Due to DNA replication, the content of DNA doubles up from 1C to 2C or from 2C to 4C depending on whether the cell is diploid or haploid. In anaphase II, the DNA Content decreases to one half from 2C to 1C.