Find the best tutors and institutes for Class 11 Tuition
Q16(i):
Analyse the events during every stage of cell cycle and notice how the following two parameters change
(i) number of chromosomes ($N$) per cell
Solution :
1. Definitions and Baseline Parameters
To analyze the fluctuation of the number of chromosomes ($N$) per cell during the cell cycle, we must first distinguish between the chromatid count and the chromosome count. By convention, a chromosome is defined by the presence of a centromere. If two sister chromatids are joined by a single centromere, they constitute one chromosome ($N=1$). Upon the splitting of the centromere, each chromatid becomes an independent chromosome.
2. Analysis of Chromosome Number ($N$) Across Stages
| Stage | Process | Number of Chromosomes ($N$) |
|---|---|---|
| $G_1$ Phase | Cell growth and organelle duplication | $2n$ |
| S Phase | DNA replication | $2n$ |
| $G_2$ Phase | Preparation for mitosis | $2n$ |
| Prophase / Metaphase | Chromatin condensation; alignment at plate | $2n$ |
| Anaphase | Centromere splitting | $4n$ (temporary state) |
| Telophase / Cytokinesis | Separation into two daughter cells | $2n$ (in each cell) |
3. Sequential Derivation of Numerical Changes
Step 1: Interphase ($G_1$, S, $G_2$)
During the S-phase, DNA content doubles ($2C \rightarrow 4C$) due to replication, but the number of chromosomes ($N$) remains constant. This is because the sister chromatids remain attached at the centromere. [Per the definition of a chromosome based on centromere count].
Step 2: Prophase and Metaphase
The chromosome number remains $2n$. In Metaphase, chromosomes are at their maximum condensation, but $N$ is still consistent with the diploid state because each chromosome consists of two sister chromatids sharing one centromere.
Step 3: Anaphase (The Critical Point of Change)
The defining event of Anaphase is the splitting of the centromere. Once the centromeres split, each sister chromatid is pulled toward opposite poles. At this specific instant, the cell contains double the number of chromosomes ($4n$) because every former chromatid is now legally classified as an independent chromosome. [Per the Law of Segregation of Chromatids].
Step 4: Telophase and Cytokinesis
As the nuclear envelope reforms around the two distinct poles, the cell undergoes cytokinesis. The $4n$ chromosomes are partitioned into two nuclei, effectively resetting the chromosome number in each daughter cell to the original $2n$.
4. Visual Representation of Chromosome Dynamics
Final Solution: The number of chromosomes ($N$) remains constant ($2n$) throughout Interphase, Prophase, and Metaphase. During Anaphase, the number of chromosomes temporarily doubles ($4n$) due to the splitting of the centromere, before returning to the diploid state ($2n$) in the two daughter cells following Cytokinesis.
More Questions from Class 11 Biology Cell Cycle and Division EXERCISES
- Q1: What is the average cell cycle span for a mammalian cell?
- Q2: Distinguish cytokinesis from karyokinesis.
- Q3: Describe the events taking place during interphase.
- Q4: What is $G_0$ (quiescent phase) of cell cycle?
- Q5: Why is mitosis called equational division?
- Q6(i): Name the stage of cell cycle at which one of the following events occur: (i) Chromosomes are moved to spindle equator.
- Q6(ii): Name the stage of cell cycle at which one of the following events occur: (ii) Centromere splits and chromatids separate.
- Q6(iii): Name the stage of cell cycle at which one of the following events occur: (iii) Pairing between homologous chromosomes takes place.
- Q6(iv): Name the stage of cell cycle at which one of the following events occur: (iv) Crossing over between homologous chromosomes takes place.
- Q7(a): Describe the following: (a) synapsis Draw a diagram to illustrate your answer.
- Q7(b): Describe the following: (b) bivalent Draw a diagram to illustrate your answer.
- Q7(c): Describe the following: (c) chiasmata Draw a diagram to illustrate your answer.
- Q8: How does cytokinesis in plant cells differ from that in animal cells?
- Q9: Find examples where the four daughter cells from meiosis are equal in size and where they are found unequal in size.
- Q10: Distinguish anaphase of mitosis from anaphase I of meiosis.
- Q11: List the main differences between mitosis and meiosis.
- Q12: What is the significance of meiosis?
- Q13(i): Discuss with your teacher about (i) haploid insects and lower plants where cell-division occurs, and
- Q13(ii): Discuss with your teacher about (ii) some haploid cells in higher plants where cell-division does not occur.
- Q14: Can there be mitosis without DNA replication in ‘S’ phase?
- Q15: Can there be DNA replication without cell division?
- Q16(ii): 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
CBSE Solutions for Class 11 Biology Cell Cycle and Division
Chapters in CBSE - Class 11 Biology
- The Living World
- Biological Classification
- Plant Kingdom
- Animal Kingdom
- Morphology of Flowering Plants
- Anatomy of Flowering Plants
- Structural Organisation in Animals
- Cell – The Unit of Life
- Biomolecules
- Transport in Plants
- Mineral Nutrition
- Photosynthesis
- Respiration in Plants
- Plant Growth and Development
- Digestion and Absorption
- Breathing and Exchange of Gases
- Body Fluids and Circulation
- Excretory Products and Elimination
- Locomotion and Movement
- Neural Control and Coordination
- Chemical Coordination and Integration
Top Tutors who teach Cell Cycle and Division
Top Tutor
Sapna Nagar, Gandhidham
3 yrs of
Exp
1 student
13 hrs of classes completed
450
per hour
Online Classes
I have 3 years of experience providing one-on-one tuition to students from Classes 10 to 12. For Class 11, I focus on building strong fundamentals and ensuring students understand concepts rather than relying on rote learning. I explain topics in a simple, student-friendly manner and use practical, real-life examples wherever possible. I help students with regular studies, homework, assignments, revision, exam preparation, and problem-solving. Being a final-year B.Tech CSE student, I can also help students develop logical thinking and a strong foundation in computer-related subjects. My teaching style is interactive, patient, and adapted to the individual student's pace and learning needs.
An excellent teacher who explains Chemistry concepts clearly and makes learning easy and interesting.
Top Tutor
Tri Nagar, Delhi
20 yrs of
Exp
1 student
32 hrs of classes completed
1000
per hour
Online Classes
Tutor's home
I am Anshu Gupta. I was working at a reputed school in Delhi for 23 year before relocating to Singapore in 2021. I was teaching Physics to Grade 12 students. I have taught more than 3000 students in the last 24 years. I worked in Singapore as a freelance tutor for last 1.5 years I'm teaching Physics to the students of IB, IP, CBSE, CIE, ICSE, AP. I have a vast 24 year experience of teaching Physics to high school students I create individual based strategies for my students for best results I can create my own study material Good conceptual knowledge of my subject is my strength. I believe in creating a friendly and comfortable environment for free interaction. I have a lot of experience of online teaching ( 4 years ) So the online lessons are as effective as face to face lessons I'm teaching Physics to the students of IB(HL and SL), IP(H1 and H2), CBSE(11th and 12th), CIE(A and AS), ICSE, AP(Physics C). I am teaching 3 H2 and 3 IB students online at present
Top Tutor
Banswara, Banswara
17 yrs of
Exp
1 student
6 hrs of classes completed
400
per hour
Online Classes
Teaching learners is an imaginative world in itself in which you actually don't teach but let the learners visualize everything in their mind and see how world and everything works. It is different from primary classes which are mostly non interesting. I have been teaching to class 8 - 10 tuitions students since 2010. As my Husband is having transferable job I have got a opportunity to teach in more than one state boards eventually. But due to Covid, Currently I am taking online classes also along with my regular ICSE school classes I assure that I have wonderful methods and learning techniques so student don't need to murmur any question .Students generally got serious in December time when board exam are near. But results are not making in 2-3 months. Little bit struggle daily do the magic’s i have seen in my previous student’s experience. Even the normal student can score 90 if he/she join at earlier and 2 hour self-study daily will bring tremendous change .I just want to say that my teachings are not forgettable teachings as because in my teaching class I make my students to see the things practically and deeply so it should be made non forgettable by learning and make good percent so in future you don't have to regret. Whatever the teachings are the learners try to incorporate it in future in many things and this is what I want my learners to learn and experience practically as it happens in science subject always.
The way she teaches is amazing and we are able to understand the lesson properly and we are able to do the problems.
Top Tutor
BRS Nagar, Ludhiana
1 yrs of
Exp
27 hrs of classes completed
Online Classes
I was a student in one of the top colleges of Ludhiana. I have proficiency in English . I can teach all subjects to primary wing .
Top Tutor
Laxmi Vihar, Hisar
4 yrs of
Exp
3 students
267 hrs of classes completed
800
per hour
Online Classes
I've taught Mathematics of class 11th and 12th in an academy for 2 years. And now teaching on UrbanPro from last 4 years. I focus on letting the student reach the deepest level of concept and then do problems of reference books like RD Sharma and others. My main target is to make student learn how to approach a question so that he can do by himself should he face any new problem.
Saurabh sir is a good teacher, and is clearly very knowledgeable in Mathematics. He takes time to clarify each and every concept, and caters to any schedule requirements, etc. The classes are interactive and super helpful.
