NCERT Solutions for Class 11 Biology Chapter 10 - Cell Cycle And Cell Division

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

Ans: The average cell cycle span for a mammalian cell is \[24\] Hours.

2. Distinguish between cytokinesis and karyokinesis.

Ans: The differences between cytokinesis and karyokinesis are—

3. Explain the events that take place throughout the inter-phase.

Ans: Below mentioned are the events that take place during the inter-phase:

• The interphase is also known as the preparatory phase of the cell cycle. 

• During this period although the cell is said to be in a resting phase, it is metabolically quite active. 

• It is the time during which the cell prepares itself for division by enduring both DNA replication and cell growth in a sequential and orderly manner and it is completed in three steps.

(i) G1 (Gap 1) phase- This phase basically involves the synthesis of RNA and protein.

(ii) S (Synthesis) phase – It involves DNA replication. Throughout this time the amount of DNA doubled per cell. In animal cells, during the S phase DNA replication takes place in the nucleus, and the centriole replicates in the cytoplasm.

(iii) G2 (Gap 2) phase – It also involves RNA and protein synthesis.

Diagram showing Interphase of the cell cycle

4. What is the G0 (quiescent phase) of the cell cycle?

Ans: Quiescent Phase-

• The G0 phase is characterised by the inactivation of the cell cycle due to the lack of mitogens and energy-rich substances.

• Cells during this phase tend to stay metabolically active however they no longer proliferate. i.e., do not undergo splitting unless called on to do so dependent on the requirement of the organism. 

• For example, the Nerve and heart cells of chordates are in the permanent Go phase.

5. Why is mitosis called equational division?

Ans: Mitosis is called equational division as:-

• Mitosis is a cell division process wherein chromosomes multiply and become evenly distributed in two daughter nuclei, resulting in the daughter cells having the same number and kind of chromosomes as that of the mother cell. 

• So mitosis is called equational division.

6. Name the phase of the cell cycle at which each one of the following events takes place:

i. When chromosomes are transferred to the spindle equator.

Ans: Metaphase

ii. When a centromere splits and chromatids separate.

Ans: Anaphase

iii. When a pairing between homologous chromosomes takes place.

Ans: Zygotene of prophase-I  of meiosis

iv. When a crossing over among homologous chromosomes occurs.

Ans: Pachytene of prophase-I of meiosis

7. Describe the following. 

(a) Synapsis

• During the zygotene phase of prophase-I of meiosis, homologous chromosomes begin to join up, a process known as synapsis.

• Electron micrographs of this phase reveal that chromosome synapsis is accompanied by the formation of a complex structure known as synaptonemal complex among the synapsed chromosomes. 

• Pairing is taking place in a zipper-like fashion.

(b) Bivalent

• The complex established by a pair of synapsed homologous chromosomes is known as a tetrad or a bivalent i.e., a pair of chromosomes or four chromatids. 

• A bivalent contains two centromeres and four chromatids.

(c) Chiasmata

• Chiasmata are cross-like structures that appear in synapsed chromosomes. They characterize sites at which crossing over has taken place. 

• Crossing over is the exchange of gene segments among non-sister chromatids of homologous chromosomes. 

• Crossing over takes place at the pachytene stage, however, chiasmata are visible in the diplotene stage of prophase 1 of meiosis.

Draw a diagram to illustrate your answer.

Ans: Following diagram shows the synapsis, bivalent and chiasma formation.

8. In what way does cytokinesis in animal cells vary from that in plant cells?

Ans: Cytokinesis in animal cells vary from that in plant cells:-

• Cytokinesis in plant cells takes place by cell plate formation whereas in animal cells cytokinesis is accomplished by furrow formation. 

• Plant cells have a rigid cell wall. So In-plant cell wall development begins in the middle of the cell and develops outward to connect the existing lateral walls.

• This involves the laying of a cell plate that characterises the middle lamella among the cell walls of adjacent cells. 

• Cell plate develops centrifugally. Animal cells lack a cell wall. Hence cytokinesis involves the development of a furrow in the cell membrane. This grows centripetally and connects ultimately in the centre of the cell and the cytoplasm is split into two.

Diagram showing differences between animal and plant cell cytokinesis

9. Illustrate with examples where the four daughter cells from meiosis are equivalent in size and where they are found uneven in size.

Ans: The four daughter cells created during meiosis during the generation of male gametes (i.e. spermatozoa) in a human being are similar in size. Then, during the creation of a female gamete (i.e., ovum), in a human being, the four daughter cells are unequal in size.

10. Is DNA replication possible without cell division?

Ans: Yes. DNA replication is possible without cell decisions. Endomitosis is the proliferation of chromosomes found in a set in the nucleus without cytokinesis and karyokinesis leads to several copies within each cell.  It is of two kinds, which are described below.

i. Polyteny:

• Here chromosomes split and redivide without partition of chromatids so that such chromosomes turned into multi-stranded with several copies of DNA. 

• Such polytene (several stranded) chromosomes persist in the permanent prophase stage and do not endure the cell cycle e.g., polytene salivary glands) the chromosome of Drosophila. 

• Here several sets of chromosomes do not change.

ii. Polyploidy (endo-duplication)

• Here all chromosomes in a set split and its chromatids are isolated but the nucleus does not split. 

• This raises the number of sets of chromosomes in the nucleus (\[4\]x, \[8\]x…..). 

• This rise in sets of chromosomes is known as polyploidy. It can be stimulated by colchicine (alkaloid obtained from Colchicum autumnale (family –Liliaceae). These chromosomes are normal and endure a cell cycle.

11. List the major differences between meiosis and mitosis.

Ans: Differences between meiosis and mitosis:

12. Distinguish anaphase of mitosis from anaphase 1 of meiosis.

Ans: Difference between anaphase of mitosis from anaphase 1 of meiosis:

• During mitosis, chromatids separate from one another, but during meiosis, synapsed homologous chromosomes split from one another during anaphase I.

• It is important to recollect here that during the metaphase stage of prophase chromosomes lie on the equator with their centromere lying on the metaphase plate. The centromere separates and the chromatids travel to opposite poles throughout anaphase.

• In metaphase I of Meiosis, the bivalents arrange themselves on the equator, and centromeres of synapsed homologous chromosomes do not lie on the equator. 

• Anaphase I involves the separation of paired homologous chromosomes to the opposite poles of the equator. This is known as a disjunction of chromosomes.

Diagram showing anaphase I of Meiosis 

Diagram showing anaphase of Mitosis 

13. What is the significance of meiosis?

Ans: The significance of meiosis is given below:

• Formation of gametes: Meiosis is a process that produces gametes, which are necessary for sexual reproduction.

• Genetic information: It activates genetic information for the production of gametophytes or gametes while turning off saprophytic information.

• Maintenance of chromosome number: Meiosis maintains the fixed number of chromosomes in sexually reproducing organisms by producing gametes that have half of the chromosomes as compared to the mother cell. It is vital since the chromosome number develops into a double after fertilization

• Assortment of chromosomes: In meiosis maternal and paternal chromosomes separate independently. It leads to the reordering of chromosomes and the characteristics controlled by them. The variations help the breeders in enhancing the races of domesticated animals and plants.

• Crossing over: It leads to the recombination of genes that brings about variations.

• Mutations: Chromosomal and genomic mutations can occur by irregularities of meiotic divisions. Some of these mutations are useful to the organism and are propagated by natural selection.

• Evidence of basic relationship of organisms: Details of meiosis are basically similar in the vast majority of organisms indicating their basic resemblance and relationship.

14. Discuss with your teacher about:

i. Haploid insects and lower plants where cell division occurs, and

Ans: Cell division tends to happen in haploid insects, including drones of the honey bee and lower plant-like gametophytes of bryophytes, algae, and pteridophytes.

ii. Some haploid cells in higher plants where cell division does not occur.

Ans: Synergids and antipodals in the embryo sac of the ovule are haploid cells where cell division does not occur.

15. Can there be mitosis without DNA replication in the ‘S’ phase?

Ans: No, there cannot be any mitotic division without – DNA replication in the ‘S’ phase. 

16. Analyze events that took place during each phase of the cell cycle and observe in what way the following two parameters change.

i. A number of chromosomes (N) per cell.

Ans: Number of chromosomes (N) per cell:

• In mitotic division, the number of chromosomes remains the same as the parent cell at prophase and metaphase. At the anaphase stage of mitosis when the sister chromatids separate and form two nuclei in telophase, each of them contains the same number of chromosomes as the parent cell. 

• In meiotic division, the homologous chromosomes get separated into two different poles during anaphase-I. Thus during prophase-I, metaphase-I and anaphase-I, the cell contains the same chromosome number as the parent cell. As two separate nuclei are formed in telophase, each contains half the number of chromosomes compared to the parent cell.

• During meiosis-II, the sister chromatids are separated in anaphase-II. Thus the daughter cells retain their chromosome number the same as cells after meiosis I. So, the daughter cells contain N number of chromosomes if the parent cell has \[2\]N chromosomes.  

ii. Amount of DNA content (C) per cell.

Ans: Amount of DNA content (C) per cell:

• S or synthesis phase indicates the period during which DNA replication or synthesis takes place. Throughout this time the amount of DNA per cell becomes double. 

• If the initial amount of DNA is signified as \[2\]C then it rises to \[4\]C. During prophase, metaphase and anaphase of mitosis, the DNA content remains \[4\]C.

• After the telophase, as the sister chromatids are separated into two separate nuclei, each nucleus contains \[2\]C amount of DNA same as the parent cell in G\[1\]phase. 

• In meiosis, the daughter cells after first division contain \[2\]C volume of DNA which gets halved i.e., C after second division.  

Chapter 10 Bio Class 11 Cell Cycle and Cell Division NCERT Solutions PDF Download

The free pdf download for NCERT solutions will help you to gain an insight into Cell Cycle and Cell Division.The topics covered in NCERT solutions for Class 11 Biology Chapter 10 cell cycle and cell division are an important part of the syllabus. NCERT Solutions provide an easy outlook on the topic and helps the student to secure good marks in their exams. The Ncert solutions for Class 11 Biology Cell Cycle and Cell Division is available on this page for download in a pdf form. It is easy to understand and will clarify all doubts the students can have.

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

NCERT Solutions Ch 10 Biology Class 11 Cell Cycle and Cell Division defines the phases in which a cell develops. Firstly, the chromosomes are moved to the shaft equator in the Metaphase. Then, the centrosomes split, and chromatids separate in the Anaphase Pairing between homologous chromosomes occur in the Zygotene phase of prophase 1 in meiosis. Lastly, crossing over between homologous chromosomes happens during the Pachytene phase of prophase 1 in Meiosis.

An important part of this chapter provides the significance of Meiosis. It preserves the explicit chromosome number of every species accomplished across age. It also helps to improve the hereditary changeability in the number of inhabitants in living beings from age to ages. These variables are critical for the advancement cycle. Meiosis produces gametes for a sexual generation. It advances Crossovers and presents another mix of varieties or attributes. Chromosomal changes can happen because of variations from the norm during Meiosis. Most of these are extremely important in building an organism.

Mitosis and Meiosis are two important aspects of this chapter. The difference between Mitosis and Meiosis is that it occurs in somatic cells, forming two daughter cells and germ cells, forming four daughter cells, respectively. Chromosomes replicate before mitotic division but not before meiotic division. The number of chromosomes stays the same as the parent cell in case of Mitosis and gets halved in case of Meiosis.

CBSE Class 11 Biology Chapter 10 NCERT Solutions Weightage Marks

Class 11 Biology Cell Cycle and Cell Division NCERT solutions includes a total of 9 per cent in the NEET examinations and 15 marks in CBSE examinations. The topic included in Biology Class 11 Chapter 10 Ncert solutions are as follows:

• Cell Cycle.

• Phases of a Cell Cycle.

• M Phase.

• Prophase.

• Metaphase.

• Anaphase.

• Telophase.

• Cytokinesis.

• Significance of Mitosis.

• Meiosis.

• Meiosis 2.

• Significance of Meiosis.

Benefits of Chapter 10 Biology Class 11 NCERT Solutions

The benefits of NCERT Solution for Class 11 Biology Chapter Cell Cycle and Cell Division are endless. The solutions will clear doubts for every candidate, and all prospective questions on these topics are answered here. Chapter 10 Bio Class 11 NCERT Solutions provide a clear insight into the Cell Cycle and Cell Division. The solutions are given in simple language and can be understood by all students. The solutions are given by teachers who are regarded as experts on this subject. These are prepared with the sole objective of helping the students to gain the maximum marks on these topics. The solutions also contain practical examples of Cells and Cell Divisions so that the students can handle any problem without any difficulty in the subject. All probable topics that can appear in the exams are covered thoroughly in these solutions for the students to gain more marks in the examination.