The Fundamental Unit of Life
NCERT Solutions • Class 9 Science • Chapter 5Chapter Exercises
[Image of detailed comparison between plant and animal cells]
1. Make a comparison and write down ways in which plant cells are different from animal cells.
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell Wall | Present (composed of cellulose). | Absent. |
| Plastids | Present (e.g., chloroplasts). | Absent (except in Euglena). |
| Vacuoles | Large permanent central vacuole. | Small temporary vacuoles. |
| Shape | Fixed and rigid due to cell wall. | Irregular or round. |
| Golgi Apparatus | Many simple units (Dictyosomes). | Single complex unit near nucleus. |
2. How is a prokaryotic cell different from a eukaryotic cell?
| Feature | Prokaryotic Cell | Eukaryotic Cell |
|---|---|---|
| Size | Generally small ($1-10 \mu m$). | Generally large ($5-100 \mu m$). |
| Nuclear Region | Undefined, no nuclear membrane (Nucleoid). | Well-defined, surrounded by nuclear membrane. |
| Chromosomes | Single chromosome. | More than one chromosome. |
| Organelles | Membrane-bound organelles absent. | Membrane-bound organelles present (mitochondria, etc.). |
3. What would happen if the plasma membrane ruptures or breaks down?
Diffusion & Homeostasis
The plasma membrane regulates the movement of substances in and out of the cell. If it ruptures:
1. The cell loses its ability to maintain internal chemical composition.
2. Essential cell components (protoplasm) will leak out.
3. Uncontrolled diffusion occurs, leading to cell death.
The plasma membrane regulates the movement of substances in and out of the cell. If it ruptures:
1. The cell loses its ability to maintain internal chemical composition.
2. Essential cell components (protoplasm) will leak out.
3. Uncontrolled diffusion occurs, leading to cell death.
4. What would happen to the life of a cell if there was no Golgi apparatus?
The Golgi apparatus is involved in the storage, modification, and packaging of products in vesicles. Without it:
• Substances synthesized by the ER would not be packaged and dispatched to targets.
• Formation of lysosomes would stop, causing waste accumulation.
• The cell would fail to function properly and eventually die.
• Substances synthesized by the ER would not be packaged and dispatched to targets.
• Formation of lysosomes would stop, causing waste accumulation.
• The cell would fail to function properly and eventually die.
5. Which organelle is known as the powerhouse of the cell? Why?
Organelle: Mitochondria.
Reason: They perform cellular respiration to release energy required for various life processes. This energy is released in the form of ATP (Adenosine Triphosphate) molecules, often called the “energy currency” of the cell.
Reason: They perform cellular respiration to release energy required for various life processes. This energy is released in the form of ATP (Adenosine Triphosphate) molecules, often called the “energy currency” of the cell.
6. Where do the lipids and proteins constituting the cell membrane get synthesised?
Proteins Synthesized in the Rough Endoplasmic Reticulum (RER) (due to presence of ribosomes).
Lipids Synthesized in the Smooth Endoplasmic Reticulum (SER).
Lipids Synthesized in the Smooth Endoplasmic Reticulum (SER).
[Image of phagocytosis in Amoeba]
7. How does an Amoeba obtain its food?
Endocytosis
Amoeba obtains food through a process called Endocytosis.
1. Its flexible cell membrane forms finger-like projections called pseudopodia.
2. It engulfs the food particle forming a food vacuole.
3. Digestion takes place inside the vacuole.
Amoeba obtains food through a process called Endocytosis.
1. Its flexible cell membrane forms finger-like projections called pseudopodia.
2. It engulfs the food particle forming a food vacuole.
3. Digestion takes place inside the vacuole.
8. What is osmosis?
Osmosis is the passage of water molecules from a region of high water concentration to a region of low water concentration through a selectively permeable membrane.
9. Carry out the following osmosis experiment… Observe the four potato cups and answer the following:
(i) Why water gathers in B and C:
Cups B (sugar) and C (salt) contain hypertonic solutes compared to the cells of the potato. Through endosmosis, water moves from the trough (high concentration) into the hollowed portion (low water concentration) through the semi-permeable membrane of potato cells.
(ii) Necessity of Potato A:
Potato A acts as a control setup. It remains empty to prove that water does not enter the cup simply due to the physical setup, but requires a concentration gradient (osmosis).
(iii) No water in A and D:
• Cup A: There is no solute (sugar/salt) to create a concentration gradient, so no osmosis occurs.
• Cup D: The potato was boiled, which destroys the semi-permeable membrane and kills the cells. Osmosis cannot occur in dead cells.
Cups B (sugar) and C (salt) contain hypertonic solutes compared to the cells of the potato. Through endosmosis, water moves from the trough (high concentration) into the hollowed portion (low water concentration) through the semi-permeable membrane of potato cells.
(ii) Necessity of Potato A:
Potato A acts as a control setup. It remains empty to prove that water does not enter the cup simply due to the physical setup, but requires a concentration gradient (osmosis).
(iii) No water in A and D:
• Cup A: There is no solute (sugar/salt) to create a concentration gradient, so no osmosis occurs.
• Cup D: The potato was boiled, which destroys the semi-permeable membrane and kills the cells. Osmosis cannot occur in dead cells.
[Image of mitosis vs meiosis stages]
10. Which type of cell division is required for growth and repair of body and which type is involved in formation of gametes?
Growth & Repair Mitosis. (Produces identical diploid cells).
Gamete Formation Meiosis. (Produces non-identical haploid cells).
Gamete Formation Meiosis. (Produces non-identical haploid cells).