Answer: The main differences between plant cells and animal cells are summarized in the table below:
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell Wall | Present (made up of cellulose). | Absent. |
| Plastids | Present (e.g., Chloroplasts). | Absent. |
| Vacuoles | Large, central, and permanent vacuole. | Small and temporary vacuoles. |
| Centrosomes | Absent (except in lower plants). | Present. |
| Shape | Fixed and rectangular. | Irregular and flexible. |
Answer:
Cells which do not have a true nucleus and membrane-bound organelles are called prokaryotic cells (e.g., bacteria and cyanobacteria). These cells are very primitive, and membrane-bound organelles such as ER, mitochondria, and Golgi apparatus are absent.
On the other hand, cells which have a true and well-developed nucleus are called eukaryotic cells (e.g., cells of higher plants and animals). In these cells, all membrane-bound organelles are present.
Answer: Plasma membrane is the outer limiting membrane of the cell. If it ruptures or breaks down, the selective permeability is lost, all cellular contents (protoplasm) would spill out, and the cell would ultimately die.
Answer: Golgi apparatus is responsible for the packaging, modification, and dispatching of cellular materials. It is also involved in the formation of lysosomes. If there is no Golgi apparatus, these essential storage and packaging functions would stop, and cellular materials would not be transported.
Answer: Mitochondria are known as the powerhouse of the cell because they are responsible for the oxidation of food molecules and the synthesis of energy in the form of ATP (Adenosine Triphosphate) molecules.
Answer: Lipids are synthesised by the Smooth Endoplasmic Reticulum (SER), while proteins constituting the cell membrane are synthesised by the Rough Endoplasmic Reticulum (RER) with the help of ribosomes attached to it.
Answer: An Amoeba obtains its food through a process called endocytosis. Due to the flexibility of its cell membrane, it extends finger-like temporary projections called pseudopodia around the food particle. The pseudopodia merge to form a food vacuole (phagosome) inside which food is digested.
Answer: Osmosis is the movement of water molecules from a region of higher water concentration (lower solute concentration) to a region of lower water concentration (higher solute concentration) through a selectively permeable membrane.
Take four peeled potato halves and scoop 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:
- Keep cup A empty
- Put one teaspoon sugar in cup B
- Put one teaspoon salt in cup C
- 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:
-
Explain why water gathers in the hollowed portion of B and C.
Answer: Water gathers in cups B and C because of osmosis. Since the cavity contains sugar/salt (a hypertonic solution) and the outer trough has water, water moves from the outside into the hollowed portion across the living cells of the potato. -
Why is potato A necessary for this experiment?
Answer: Potato A acts as a control experiment. It proves that the accumulation of water in B and C occurs specifically due to the presence of solute (sugar/salt) inside the cups and not merely due to the presence of the cavity. -
Explain why water does not gather in the hollowed out portions of A and D.
Answer:- In cup A: No solute (sugar or salt) is added, so there is no concentration difference to drive osmosis.
- In cup D: Boiling kills the cells of the potato, destroying the cell membrane. Since a selectively permeable membrane is essential for osmosis, no movement of water takes place.
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