The Fundamental Unit of Life
Science Class Ninth
In-text questions & Solution
Question (1) Who discovered cells, and how?
Answer
Robert Hooke an English scientist discovered the cell in the year 1665. He examined the cork using his own designed microscope and found that the cork has a similar structure to a honeycomb which has little compartments. He called these boxes "cells".
Question (2) Why is the cell called the structural and functional unit of life?
Answer
All living organisms are made up of cells. And all basic processes that are required to be live are performed at the cellular level, i.e. respiration, synthesis of proteins and fats, clearing the waste materials, and forming new cells.
Thus, it is called that the cell is the structural and functional unit of life.
Question (3) How do substances like CO2 and water move in and out of the cell? Discuss.
Answer
Substances like CO2 and water move in and out of the cell through the process of diffusion and osmosis.
When the concentration of the CO2 increases in the cell, it goes out through the process of diffusion and is finally expelled through exhalation.
Similarly, whenever the concentration of water increases on either side, i.e. in or out of the cell, it passes to the region of low concentration.
Question (4) Why is the plasma membrane called a selectively permeable membrane?
Answer
The plasma membrane allows only certain substances to pass through it, i.e. only selected substances can pass through the plasma membrane. This is the cause of why the plasma membrane is called a selectively permeable membrane.
The plasma membrane is known as a semi-permeable membrane also.
Question (5) Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.
| Question Table | |
|---|---|
| Prokaryotic Cell | Eukaryotic Cell |
| (1) Size: Generally small (1 – 10 μm) 1 μm = 10–6 m | (1) Size: Generally large (5 – 100 μm) |
| (2) Nuclear region: _______ and known as ____ | (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 | (2) _ _ _ _ |
Answer
| Answer Table | |
|---|---|
| Prokaryotic Cell | Eukaryotic Cell |
| (1) Size: Generally small (1 – 10 μm) 1 μm = 10–6 m | (1) Size: Generally large (5 – 100 μm) |
| (2) Nuclear region: are poorly defined due to the absence of nuclear membrane and known as 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 | (2) All organelles are membrane bound including nucleus. |
Question (6) Can you name the two organelles we have studied that contain their own genetic material?
Answer
In animal cells mitochondria contain their own genetic materials and in plant cells, plastids especially chloroplasts contain their own genetic materials and ribosomes.
Question (7) If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?
Answer
The cell will die if the organisation of a cell is destroyed due to any influence. And if this would have happened to all the cells of an organism, the organism will die
Question (8) Why are lysosomes known as suicide bags?
Answer
The lysosomes contain digestive enzymes that can destroy or digest even the whole of the cell. The lysosomes act as cleaning organelles, it cleans unwanted materials and pathogens by acting as digestive material over it. If a cell gets damaged, lysosomes may burst and the enzymes digest their own cell. Because of this, the lysosomes are known as suicide bags.
Question (9) Where are proteins synthesised inside the cell?
Answer
Proteins are synthesised in Endoplasmic Reticulum, especially in Rough Endoplasmic Reticulum. Endoplasmic Reticulum is membrane bound organelle found at the outer circumference of the nucleus.
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