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

The class 11 biology NCERT solutions chapter 10 Cell Cycle and Cell Division cover every back-exercise question, according to the latest 2026-27 CBSE syllabus, and help students prepare for the CBSE Boards, NEET and CUET. Each answer is worked step by step, from the 24-hour mammalian cell cycle and the three phases of interphase to why mitosis is equational, why meiosis is reductional, and how chromosome number and DNA content change at every stage.

This chapter sits in the Cell: Structure and Function unit, and the way a cell copies its genome and shares it out is one of the most heavily tested ideas in the whole of Class 11 Biology.

• CBSE Weightage: 3 to 4 marks, part of the Cell: Structure and Function unit and a high-frequency NEET topic.
• Topics covered: the cell cycle and its phases, interphase (G₁, S, G₂), the G₀ quiescent phase, mitosis and karyokinesis, cytokinesis in plant and animal cells, meiosis and prophase I, chromosome number and DNA content, and the significance of meiosis.
• Exercise count: 16 back-exercise questions, a mix of definitions, distinctions, a graph-free numerical on N and C, and diagram-based answers on synapsis and chiasmata.

These class 11 biology NCERT solutions chapter 10 Cell Cycle and Cell Division are curated by subject experts, based on the 2026-27 NCERT textbook, and checked against the last five years of CBSE Board and NEET papers.

Why Cell Cycle and Cell Division Matters and What the Chapter Covers

Every organism that grows, heals a wound or makes gametes does so by cell division, and this chapter is where students first learn the rules that keep the process orderly. It follows one cell as it becomes two, then explains how a second kind of division halves the chromosome number so that sexual reproduction does not double it every generation. The vocabulary set here carries straight into reproduction and genetics later in the course.

• Everyday role: mitosis replaces the epidermis, gut lining and blood cells that the body loses constantly, while meiosis makes the eggs and sperm that carry heredity.
• Core skill: tracking two separate quantities, the chromosome number (N) and the DNA content (C), through every stage of the cycle without merging them.
• Why it is tested so often: the equational-versus-reductional contrast and the five sub-stages of prophase I are staple NEET questions that reward exact wording.

The single most valuable habit in this chapter is writing the 2n and 2C values beside each stage as you describe it. That one line converts a descriptive answer into one that also answers the numerical version of the same question. The class 11 biology NCERT solutions chapter 10 Cell Cycle and Cell Division below follow the same order as the NCERT textbook so students can check their working line by line.

The Cell Cycle and Its Two Basic Phases

The cell cycle is the sequence of events by which a cell duplicates its genome, synthesises the other constituents of the cell and finally divides into two daughter cells. NCERT illustrates it with human cells in culture, which divide once in approximately every 24 hours. The cycle splits into two basic phases, and the exercise opens by asking for the average span and how it is shared out.

• Interphase: the long preparation period, occupying more than 95% of the cycle, during which the cell grows and copies its DNA.
• M phase (mitosis phase): the actual division, which in a 24-hour human cycle lasts only about an hour.
• The arithmetic: 24 hours minus the 1-hour M phase leaves about 23 hours of interphase, and 23 ÷ 24 gives 0.9583, so interphase is about 95.83% of the cycle.

The 24-hour figure is an average, not a rule, and NCERT is explicit that it varies from organism to organism and from cell type to cell type. Yeast, for example, completes a cycle in only about 90 minutes, which is roughly 16 times faster than the human cell. Because interphase is so long, it was once wrongly called the resting phase, when in fact it is the busiest part of the cycle. Refer to Exercise Q1 for the full step-by-step split of the 24-hour span.

Interphase: The G₁, S and G₂ Sub-phases

Interphase is not a single block but three sub-phases, and describing the events of each is a common short-answer question. The logic runs in order: grow first (G₁), copy the genome next (S), then assemble the machinery for division (G₂). Each sub-phase hands the next one its raw material, which is why the order cannot be shuffled.

The key trap is the S phase: the DNA doubles from 2C to 4C, but the chromosome number stays at 2n, because each chromosome simply gains a second sister chromatid and the two chromatids share one centromere. A chromosome is counted by its centromere, so twice the DNA still means the same count. Centriole duplication in S phase is an animal-cell event only, since plant cells lack centrioles and still build a spindle. Precision about that one word, animal, separates the top band from the middle in the NEET version of this question.

The G₀ Quiescent Phase

Some cells in adult animals do not appear to divide, and NCERT gives them a name and a place. Cells that will not divide further exit the G₁ phase and enter an inactive stage called the quiescent stage, or G₀. The word quiescent means quiet, not dead, and the whole answer hinges on that one contrast: metabolically active, but no longer proliferating.

• Where it is entered from: a cell steps into G₀ by exiting G₁, not from S, G₂ or M, because G₁ is the interval before DNA replication is committed to.
• What continues: normal cell function goes on, so a heart muscle cell keeps contracting and a nerve cell keeps conducting.
• What stops: there is no DNA replication and no M phase, so the cell makes no daughter cells unless called on to do so.

The exit is reversible: cells replacing tissue lost to injury or cell death are recalled from G₀ and divide only occasionally, as needed. This is why adult tissues differ so much in their ability to repair. Skin, gut lining and blood cells are replaced constantly, so few of their cells sit in G₀, while heart and nerve cells largely do, which is why those tissues recover so poorly after damage. The zero in G₀ records that the cell is at zero progress through the cycle, having left the sequence rather than advancing along it.

Mitosis, Karyokinesis and Why It Is Equational

The M phase begins with nuclear division, called karyokinesis, and usually ends with division of the cytoplasm, called cytokinesis. Karyokinesis runs through four stages, and NCERT is strict that cytokinesis is not one of them. Mitosis is described as the equational division because the number of chromosomes in the parent and progeny cells is the same.

Tracking a human cell where 2n = 46 shows why the count holds: 46 at G₁, 46 after S (two chromatids share one centromere), 46 at G₂, and 46 in each daughter, while the DNA runs 2C → 4C → 2C. An onion root tip cell with 16 chromosomes therefore gives daughter cells with 16 chromosomes each, not 8 and not 32. Contrast it in one line and the definition lands: mitosis is equational (2n → 2n), meiosis is reductional (2n → n). Work through Exercise Q5 for the full chromosome-count reasoning.

Cytokinesis in Plant Cells Versus Animal Cells

Karyokinesis runs the same way in plant and animal cells, but cytokinesis does not, because the cell's outer boundary forces the mechanism. An animal cell is bounded by a flexible plasma membrane, so it can be pinched, while a plant cell is enclosed by a relatively inextensible cell wall and cannot be. This is one of the cleanest distinguish questions in the chapter, and it rewards a table.

Direction is the single cleanest difference: the animal furrow moves inward from the outside, while the plant cell-plate grows outward from the centre. What both share is that at the time of cytoplasmic division, organelles like mitochondria and plastids get distributed between the two daughter cells, though nothing guarantees a perfect 50:50 split. Karyokinesis without cytokinesis produces a multinucleate syncytium, the classic NCERT example being the liquid endosperm of coconut. The reverse never happens, since the cytoplasm is not divided before the nucleus.

Meiosis and the Five Sub-stages of Prophase I

Meiosis is two divisions on a single round of DNA replication, and it is reductional because it takes a diploid cell to four haploid cells (2n → n). The heart of the process is prophase I, the longest and most complex prophase, subdivided into five sub-stages that carry the events NEET asks about most. Three key terms, synapsis, bivalent and chiasmata, all belong here.

The three terms in one line: synapsis is the pairing of homologous chromosomes, a bivalent (or tetrad) is the paired unit produced, holding 2 chromosomes and 4 chromatids, and chiasmata are the X-shaped joints left where the pair swapped material. A chiasma is not where crossing over happens now; it is the visible evidence, one stage later, of an exchange already completed by the end of pachytene. Crossing over occurs only between non-sister chromatids of the homologous chromosomes, so drawing the sister chromatids crossing is a costly error in Exercise Q7.

Tracking Chromosome Number (N) and DNA Content (C)

The final exercise question asks students to follow two parameters, the number of chromosomes (N) and the amount of DNA (C) per cell, across the whole cycle. The trap that catches most students is treating them as one quantity. They move independently: S phase adds chromatids, not chromosomes, so it doubles C while leaving N unchanged.

• Chromosome number (N): stays 2n through G₁, S and G₂; in mitosis it rises transiently to 4n at anaphase when centromeres split, then each daughter gets 2n.
• In meiosis: N falls to n per cell at telophase I as homologues separate, rises transiently to 2n at anaphase II, and each of the four final cells ends at n.
• DNA content (C): 2C at G₁, doubles to 4C during S, stays 4C through G₂; each mitotic daughter gets 2C, and each of the four meiotic products gets 1C.

Two related what-if questions test the same idea from the sides. Mitosis cannot happen without S phase, because a cell entering mitosis with single-chromatid chromosomes would hand each daughter only n and 1C, halving the number. DNA replication, however, can happen without cell division: in polyteny, the salivary gland chromosomes of Drosophila replicate to about 512 to 1024 strands (2⁹ to 2¹⁰) with no division, so C keeps doubling while N holds because all strands share one centromere. These two answers together prove that N and C are uncoupled quantities.

The Significance of Meiosis and Equal Versus Unequal Daughter Cells

Meiosis matters for two reasons the exercise draws out. First, it conserves the chromosome number of a species: it makes haploid gametes, and fertilisation restores the diploid number (n + n = 2n), so the number does not double each generation. Second, it generates variation, through crossing over and the independent assortment of homologues, so every gamete is genetically different. The chapter also asks where the four meiotic products are equal or unequal in size.

• Equal in size: spermatogenesis in animals gives four equal haploid spermatids, and microsporogenesis in plants gives four equal microspores.
• Unequal in size: oogenesis gives one large ovum and three small polar bodies that degenerate, so only one functional gamete results.
• Haploid cells that still divide: the male honey bee (drone) develops from an unfertilised egg and its cells divide by mitosis (n → n), never meiosis, since a haploid cell has no homologous pairs to separate.

Anaphase is where the equational and reductional labels are earned. In anaphase of mitosis the centromere splits and sister chromatids separate, so each pole gets 2n. In anaphase I of meiosis the whole homologous chromosomes separate while sister chromatids stay attached, the centromere does not split, and each pole gets n chromosomes of two chromatids each. Splitting sisters gives identical sets and holds the number; separating homologues gives varied sets and halves it. Same cell, two different things pulled apart, two different outcomes.

Cell Cycle and Cell Division Exercise-wise Breakdown

The NCERT back exercise has 16 questions, ranging from one-word stage names to a full analysis of how N and C change across the cycle. The table below maps the question blocks to their topics so students can plan their practice and revise by theme.

The marks in this chapter sit in exact stage names, clean distinctions and correctly tracked numbers rather than in long descriptions. Learn the five sub-stages of prophase I in order and the 2n, 2C values at each stage, then attach a named example. Every question in the class 11 biology NCERT solutions chapter 10 Cell Cycle and Cell Division PDF is solved with each step of reasoning shown, so students can compare their answers against the model working.

Common Mistakes Students Make in Cell Cycle and Cell Division

Most marks in this chapter are lost on small slips of counting and naming, not on hard ideas. Each mistake below costs 1 to 2 marks, so watch for it at the exact step.

Student Feedback on Cell Cycle and Cell Division Solutions

Other Cell Cycle and Cell Division Class 11 Biology Resources

Pair these solutions with the revision notes, formula sheet and NCERT textbook PDF for the same chapter.

NCERT Solutions for Class 11 Biology: All Chapters

Jump to the step-by-step solutions for any other Class 11 Biology chapter below.

FAQs on Cell Cycle and Cell Division Class 11 NCERT Solutions