Chapter 05 The Fundamental Unit of Life Exercise
Exercises
1. Make a comparison and write down ways in which plant cells are different from animal cells.
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Answer
Comparison of plant cell and animal cell
| Plant Cell | Animal Cell |
|---|---|
| Cell wall is present outside the plasma membrane. | Cell wall is absent. |
| Generally regular in shape. | Generally irregular in shape. |
| Larger in size than animal cells | Smaller in size than animal cells. |
| Plastids are present. | Plastids are absent except in Euglena. |
| A permanent and large vacuole is present. | Vacuoles are many, small and temporary. |
2. How is a prokaryotic cell different from a eukaryotic cell?
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Answer
| Prokaryotic Cell | Eukaryotic Cell |
|---|---|
| 1. Size : generally small $(1-10 \mu m)$ $1 \mu m=10^{-6} m$ | 1. Size: generally large ( $5-100 \mu m$ ) |
| 2. Nuclear region is poorly defined due to the absence of a nuclear membrane and known as the nucleoid | 2. Nuclear region: well defined and surrounded by a nuclear membrane |
| 3. Chromosome: single | 3. More than one chromosome |
| 4. Membrane-bound cell organelles absent | 4. Memberane-bound cell organelles present |
3. What would happen if the plasma membrane ruptures or breaks down?
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Answer
In case of plasma membrane ruptures or breaks down:
All the useful substances will move out of the cell
There will be no difference between cell content and its external environment.
The cell will close its normal shape.
4. What would happen to the life of a cell if there was no Golgi apparatus?
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Answer
Effect of absence of Golgi apparatus on life of a cell
(i) The packaging and dispatching of different types of proteins to various targets inside and outside the cell will be influenced.
(ii) The products of cell cannot be stored and modified later.
(iii) There will be effect on lysosomes formation. This will cause accumulation of worn out and dead cell organelles within the cell which may cause cell death.
5. Which organelle is known as the powerhouse of the cell? Why?
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Answer
The organelle mitochondria known as the power house of the cell. Process of cellular respiration takes place in mitochondria to generate energy required for various chemical activities in the form of ATP. This is the reason that mitochondria is known as power house of the cell.
6. Where do the lipids and proteins constituting the cell membrane get synthesised?
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Answer
Lipids and proteins are synthesised in the ER (Endoplasmic Reticulum).
7. How does an Amoeba obtain its food?
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Answer
Through the process of endocytosis, an Amoeba obtains its food. As its cell membrane is flexible enough, food particles are engulfed, forming a food vacuole girdling it, which is assisted by the pseudopodia. Amoeba secretes digestive enzymes to bring about digestion of the engulfed particle once the food is trapped.
8. What is osmosis?
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Answer
The movement of solvent from a region of its high concentration to a region of its low concentration through a semipermeable membrane is called osmosis. During osmosis, the water molecules (solvent) are free to cross the plasma membrane in both the directions.
9. Carry out the following osmosis experiment:
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Take four peeled potato halves and scoos each one out to make potato cups. One of these potato cups should be made from a boiled potato. Put each potato cup in a trough containing water. Now,
(a) Keep cup A empty
(b) Put one teaspoon sugar in cup B
(c) Put one teaspoon salt in cup $C$
(d) Put one teaspoon sugar in the boiled potato cup D.
Keep these for two hours. Then observe the four potato cups and answer the following:
(i) Explain why water gathers in the hollowed portion of $B$ and $C$.
(ii) Why is potato A necessary for this experiment?
(iii) Explain why water does not gather in the hollowed out portions of $A$ and $D$.
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Answer
(i) Osmosis is the process responsible for the gathering of water in the hollowed portion of B and C. Since, the concentration of solute (sugar in cup Band salt in cup C) is higher inside the cup as compared to the water, which is outside the cup. Hence, water from its higher concentration (outside the cup) will move towards the lower concentration (inside the cup). This process of osmosis (moving in of solvent) is called endosmosis.
(ii) Potato $A$ acts as a control for the experiment. This is required for comparing the results of the experiment.
(iii) Water does not gather in the hollowed out portions of $A$ and $D$ because of the following reasons:
- The hollowed portion of potato A is empty. So, because of no concentration difference, no osmosis can occur.
- The hollowed portion of potato D contains sugar in it but it is boiled.
So, osmosis cannot occur as its semipermeable membrane is destroyed by boiling.
10. Which type of cell division is required for growth and repair of body and which type is involved in formation of gametes?
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Answer
There are two ways in which a cell divides:
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Mitosis
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Meiosis
Mitosis is the type of cell division that is involved in the growth and repair of the body, whereas meiosis is a type of cell division which results in the formation of gametes.
