Answers to In-Text Questions
Chapter 5: The Fundamental Unit of Life
Page No. 51
Question 1:
Who discovered cells, and how?
Answer:
Cells were discovered by Robert Hooke in 1665. He observed a thin slice of cork under a self-designed microscope and noticed small box-like compartments, which he named cells.
Question 2:
Why is the cell called the structural and functional unit of life?
Answer:
The cell is called the structural unit of life because all living organisms are made up of cells.
It is called the functional unit of life because all vital life processes such as respiration, nutrition, growth, and reproduction take place within cells.
Page No. 53
Question 1:
How do substances like CO₂ and water move in and out of the cell? Discuss.
Answer:
-
Carbon dioxide (CO₂) moves in and out of the cell by diffusion.
It moves from a region of higher concentration to lower concentration across the plasma membrane. -
Water moves in and out of the cell by osmosis, which is the movement of water through a selectively permeable membrane from a region of higher water concentration to lower water concentration.
Thus, diffusion helps in gaseous exchange, while osmosis helps in the movement of water across the cell membrane.
Question 2:
Why is the plasma membrane called a selectively permeable membrane?
Answer:
The plasma membrane is called selectively permeable because it allows some substances (like gases and water) to pass through it while preventing the movement of other substances.
This property helps the cell to maintain its internal environment.
Page No. 55
Question:
Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.
| Prokaryotic Cell | Eukaryotic Cell |
|---|---|
| 1. Size: generally small (1–10 µm) |
1. Size: generally large (5–100 µm) |
| 2. Nuclear region: not well defined and not surrounded by a nuclear membrane |
2. Nuclear region: well defined and surrounded by a nuclear membrane |
|
3. Chromosome: single chromosome |
3. More than one chromosome |
|
4. Membrane-bound cell organelles: absent |
4. Present |
Answer (in words, for exams):
-
Prokaryotic cells have a poorly defined nuclear region, single chromosome, and lack membrane-bound organelles.
-
Eukaryotic cells have a well-defined nucleus, more than one chromosome, and membrane-bound organelles present.
Page No. 57
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 (DNA) are:
-
Mitochondria
-
Plastids (chloroplasts)
Question 2:
If the organisation 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 not be able to perform its vital functions.
As a result, the cell will die.
Question 3:
Why are lysosomes known as “suicide bags” of the cell?
Answer:
Lysosomes contain powerful digestive enzymes.
When a cell is damaged or old, lysosomes may burst and digest the cell itself, leading to cell death.
Hence, lysosomes are called the “suicide bags” of the cell.
Question 4:
Where are proteins synthesised inside the cell?
Answer:
Proteins are synthesised on ribosomes, which are present:
-
On the rough endoplasmic reticulum (RER)
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Freely in the cytoplasm