INTEXT QUESTION
1. Who discovered cells, and how?
Answer: Cells were discovered by Robert Hooke in 1665. He examined a thin slice of cork with a self-designed primitive microscope and saw honeycomb-like compartments, which he named cells.
2. Why is the cell called the structural and functional unit of life?
Answer: The cell is called the structural and functional unit of life because every living cell can perform basic functions needed for life. Inside a cell, different organelles perform special jobs like making material or removing waste. Thus, all life processes depend on cells.
INTEXT QUESTION
1. How do substances like CO₂ and water move in and out of the cell? Discuss.
Answer: Substances like carbon dioxide and oxygen move across the cell membrane by diffusion, that is, from high concentration to low concentration. For example, CO₂ formed inside the cell moves out, and oxygen enters when its level decreases inside. Water also moves by diffusion, but through a selectively permeable membrane. This special case of diffusion of water is called osmosis.
2. Why is the plasma membrane called a selectively permeable membrane?
Answer: The plasma membrane is the outermost covering of the cell. It allows the entry and exit of some materials while preventing the movement of others. Because it permits only selected substances to pass through, it is called a selectively permeable membrane.
INTEXT QUESTION
1. Can you name the two organelles we have studied that contain their own genetic material?
Answer: The two organelles that contain their own genetic material are mitochondria and plastids.
2. If the organization of a cell is destroyed due to some physical or chemical influence, what will happen?
Answer: If the organisation of a cell is destroyed, the cell will lose its proper functioning and finally die. This is because the damaged cell cannot perform its life processes. In such cases, lysosomes may also burst, and their enzymes digest the cell completely, leading to its death.
3. Why are lysosomes known as suicide bags?
Answer: Lysosomes are called suicide bags because they contain powerful digestive enzymes. When a cell is damaged, these lysosomes may burst and their enzymes digest the entire cell, causing its death.
4. Where are proteins synthesised inside the cell?
Answer: Proteins are synthesised in the ribosomes, which are present on the surface of the Rough Endoplasmic Reticulum (RER)
EXERCISES
1. Make a comparison and write down ways in which plant cells are different from animal cells.
Answer:
3. What would happen if the plasma membrane ruptured or broke down?
Answer: If the plasma membrane ruptured or broke down, the cell would die. This is because the plasma membrane controls the entry and exit of materials, and without it, the life of the cell cannot be maintained.
4. What would happen to the life of a cell if there were no Golgi apparatus?
Answer: If there were no Golgi apparatus, the cell would not be able to store, modify, and package the materials made in it. The formation of lysosomes would also stop. As a result, the cell would not be able to function properly.
5. Which organelle is known as the powerhouse of the cell? Why?
Answer: The mitochondria are known as the powerhouse of the cell because they release energy in the form of ATP (Adenosine Triphosphate). This ATP is used by the cell for making new compounds and for mechanical work, so it is called the energy currency of the cell.
6. Where do the lipids and proteins constituting the cell membrane get synthesised?
Answer: The lipids and proteins of the cell membrane are synthesised in the Endoplasmic Reticulum (ER). The Smooth ER (SER) makes lipids, while the Rough ER (RER) with ribosomes helps in protein synthesis.
7. How does an Amoeba obtain its food?
Answer: Amoeba takes its food by using its flexible cell membrane. The cell membrane bends and engulfs the food material from the outside environment. This process is called endocytosis.
8. What is osmosis?
Answer: Osmosis is the passage of water from a region of high water concentration to a region of low water concentration through a selectively permeable membrane, until equilibrium is reached.
9. Carry out the following osmosis experiment:
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,
(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.
Answer: (i) In cups B and C, sugar and salt are present, so the solution inside the potato cup becomes concentrated. Water from outside (where the concentration of water is higher) enters inside by osmosis, and that is why water gathers in B and C.
(ii) Potato A is kept empty to act as a control. It helps to compare and prove that osmosis occurs only when a solute (like sugar or salt) is present.
(iii) In cup A, there is no solute, so no concentration difference is created, and water does not enter. In cup D (boiled potato), cells are dead, so osmosis cannot occur, and water does not gather.
10.Which type of cell division is required for the growth and repair of the body, and which type is involved in the formation of gametes?
Answer: The type of cell division required for growth and repair of the body is mitosis.
The type of cell division involved in the formation of gametes is meiosis.
2. How is a prokaryotic cell different from a eukaryotic cell?
Answer:
