This MCQ module is based on: Prokaryotes, Eukaryotes and Cell Division
TOPIC 5 OF 50
Prokaryotes, Eukaryotes and Cell Division
🎓 Class 9
Science
CBSE
Theory
Ch 2 — Cell: The Building Block of Life
⏱ ~11 min
🌐 Language: [gtranslate]
🧠 AI-Powered MCQ Assessment
▲
📝 Worksheet / Assessment
▲
This assessment will be based on: Prokaryotes, Eukaryotes and Cell Division
Upload images, PDFs, or Word documents to include their content in assessment generation.
Prokaryotes, Eukaryotes and Cell Division
Class 9 Science · Chapter 2 · Part 3 — Cell Types, Comparisons & Cell Division
2.18 Two Great Categories: Prokaryotes and Eukaryotes
All cells fall into one of two big groups depending on whether they have a true nucleus or not.
🦠 Prokaryote vs Eukaryote — Click to compare strengths and limits L4 Analyse
Click each cell type to weigh how its design serves its lifestyle. Which one wins on speed of division? Which one wins on complexity?
Click either cell above to see how its simpler or more complex design becomes a strength or a limit.
| Feature | Prokaryotic Cell | Eukaryotic Cell |
|---|---|---|
| Size | Very small (1–10 µm) | Larger (10–100 µm) |
| Nucleus | Absent — DNA lies free in nucleoid | True nucleus with nuclear membrane |
| Membrane-bound organelles | Absent | Present (mitochondria, ER, Golgi, etc.) |
| Ribosomes | Smaller (70S) | Larger (80S) |
| Cell division | Binary fission | Mitosis / Meiosis |
| Examples | Bacteria, blue-green algae | Plants, animals, fungi, protists |
2.19 Plant Cell vs Animal Cell
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell wall | Present (cellulose) | Absent |
| Plastids | Present (chloroplasts) | Absent |
| Vacuole | One large central vacuole | Small or absent |
| Centrosome | Absent | Present (helps in division) |
| Shape | Fixed, rectangular | Variable, often round |
| Mode of nutrition | Autotrophic (makes own food) | Heterotrophic (eats food) |
2.20 Unicellular vs Multicellular Organisms
Some organisms manage their entire life with just one cell. Such unicellular organisms include amoeba, paramoecium, yeast, and most bacteria. That single cell does everything: feeding, breathing, moving, reproducing.
Multicellular organisms — like rose plants, mango trees, frogs, humans — are made of millions or trillions of cells. Different groups of cells specialise in different tasks: muscle cells contract, nerve cells carry signals, root hair cells absorb water. This division of work is called division of labour.
2.21 Cell Division
How does a single fertilised egg grow into a complete baby with trillions of cells? How do you heal a cut on your finger? The answer lies in cell division — the process by which a parent cell produces new daughter cells. Two types of cell division occur in eukaryotes: mitosis and meiosis.
Mitosis — the basic divider
Mitosis happens in all somatic (body) cells. It produces two daughter cells, each with the same number of chromosomes as the parent cell. Mitosis is responsible for:
- Growth of the body
- Replacement of dead/damaged cells (e.g., wound healing)
- Asexual reproduction in organisms like Hydra
Meiosis — making gametes
Meiosis happens only in the reproductive organs (ovaries, testes, anthers). It produces gametes (sperm and egg, or pollen and ovule). The most important point: meiosis halves the chromosome number, so when the gametes fuse during fertilisation the offspring gets back the original number.
Quick comparison:
| Mitosis | Meiosis |
|---|---|
| Body cells | Reproductive cells |
| 2 daughter cells | 4 daughter cells |
| Chromosome number stays same | Chromosome number halved |
| For growth and repair | For sexual reproduction |
2.22 When Cell Division Goes Wrong — Cancer
Cancer: Normally, cells divide only when needed and stop when enough cells are made. Sometimes a mutation in the DNA causes cells to divide uncontrollably, forming an abnormal mass called a tumour. If the tumour grows aggressively and spreads to other parts of the body (metastasis), it is called cancer. Cancer is a disease of uncontrolled cell division.
Activity 2.5 — Onion peel meets salt waterL3 Apply
Predict:
If you mount an onion peel on a slide and add a drop of strong salt solution, what do you think will happen to the cells?
- Peel a thin layer from an onion bulb and mount it on a glass slide with a drop of water.
- Stain with iodine. Observe the rectangular cells with their nuclei.
- Replace water with strong salt solution. Observe again after 5 minutes.
Water moves out of the onion cells (exosmosis) into the salt solution. The cytoplasm shrinks and pulls away from the rigid cell wall. This shrinkage is called plasmolysis and confirms that the cell membrane is selectively permeable.
Competency-Based Questions
Scenario: While preparing slides in the school lab, Aman observed three samples under the microscope: (i) a bacterial smear from yoghurt, (ii) onion peel cells, and (iii) human cheek cells. He noticed the bacteria had no visible nucleus, while the other two clearly did. He also noticed that only the onion cells had a thick wall.
Q1. Bacteria are classified as ____________. L1
(a) prokaryotes — they lack a true membrane-bound nucleus.
Q2. Why are onion cells rectangular while human cheek cells are roundish? L3
Onion cells (plant cells) have a rigid cellulose cell wall that gives them a fixed rectangular shape. Animal cells like cheek cells have only a flexible plasma membrane, so they take a roundish, irregular shape.
Q3. State true or false: Mitosis halves the number of chromosomes in the daughter cells. L1
False. Mitosis keeps the chromosome number the same. Meiosis halves it.
Q4. A wound on Aman's finger heals within a week. Which type of cell division is responsible? L2
Mitosis. Skin cells around the wound divide repeatedly, producing identical daughter cells that replace the damaged ones.
Q5. Explain how cancer is related to cell division. L4
In normal cells, division is tightly controlled — cells divide only when needed and stop when enough are produced. In cancer cells, this control mechanism breaks down due to mutations in the DNA. The cells keep dividing uncontrollably, forming a tumour that may invade nearby tissues and even spread to distant organs (metastasis).
Assertion–Reason Questions
Choose: (A) Both true, R explains A. (B) Both true, R does not explain A. (C) A true, R false. (D) A false, R true.
A: Plant cells have a fixed shape.
R: Plant cells possess a rigid cellulose cell wall outside the plasma membrane.
(A) — Both true; R is the correct explanation of A.
A: Meiosis is essential for sexual reproduction.
R: Meiosis doubles the number of chromosomes in gametes.
(C) — A is true, but R is false. Meiosis halves the chromosome number so that fertilisation can restore the original number.
A: Cancer is a disease of uncontrolled cell division.
R: Mutations in DNA can disturb the regulation of cell division.
(A) — Both true and R correctly explains A.
AI Tutor
Science Class 9 — Exploration
Ready