NCERT Solutions for Class 9 Science Chapter 5 The Fundamental Unit of Life
Chapter Name | NCERT Solutions for Class 9 Science Chapter 5 The Fundamental Unit of Life |
Topics Covered |
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Related Study |
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NCERT Intext Questions
1. Who discovered cells and how?
Solution
Robert Hooke discovered cells. He observed the cells in thin slices of cork through microscope. It looked like small compartments.
2. Why is the cell called structural and functional unit of life?
Solution
Cells are called the structural and functional unit of life because all the living organisms are made up of cells and also all the functions taking place inside the body of organisms are performed by cell.
3. How do substances like CO2 and water move in and out of the cell? Discuss.
Solution
Substances move in and out of the cell by diffusion. Diffusion is the spontaneous movement of particles in order to attain equilibrium in concentration. While the movement of water through a semi-permeable membrane is called osmosis. It is important to note that plasma membrane is a semi-permeable membrane. Water always moves from high water concentration to low water concentration.
4. Why is the plasma membrane called a selectively permeable membrane?
Solution
Plasma membrane permits passage to some selected substances only, that is why it is called a selectively permeable or semi-permeable membrane.
5. Fill in the gaps in the following table illustrating differences between prokaryotic cell and eukaryotic cell.
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Prokaryotic Cell |
Eukaryotic Cell |
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1. |
Size : generally small ( 1 -10μm) 1μm = 10-6 m |
Size : generally large (5 – 100)μm |
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2. |
Nuclear region : -------- and known as |
Nuclear region : well defined and surrounded by a nuclear membrane. |
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3. |
Chromosome : single |
More than one chromosome. |
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4. |
Membrane bound cell organelles alsent. |
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Solution
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Prokaryotic Cell |
Eukaryotic Cell |
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1. |
Size : generally small (1 – 10 μm) 1 μm = 10-6 m |
Size : generally large (5 – 100)μm |
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2. |
Nuclear region : not well defined and known as nucleoid. |
Nuclear region: well defined and surrounded by a nuclear membrane. |
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3. |
Chromosome : single |
More than one chromosome. |
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4. |
Membrane bound cell organelles absent. |
Membrane bound cell organelles are present. |
6. Can you name the two organelles we have studied that contain their own genetic material?
Solution
Mitochondria and chloroplast.
7. If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?
Solution
Various function, of a cell is done by various parts of the cell. They work to continue life in the cell. If the organization of a cell is destroyed due to some physical or chemical influence, the cell will die.
8. Why are lysosomes known as suicide bags?
Solution
Lysosomes contain digestive enzymes. The enzymes are released in the cytoplasm of the cell in case of a rupture in lysosome. This results in cell death. It is why lysosome is also known as suicide bags of cells.
9. Where are proteins synthesized inside the cell?
Solution
Proteins are synthesized in ribosome.
NCERT Exercises Solutions
1. Make a comparison between plant cells and animal cells.
Solution
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Plant Cell |
Animal Cell |
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1. |
A plant cell is usually larger in size. |
An animal cell is comparatively smaller in size. |
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2. |
It is enclosed by a rigid cellulose cell wall in addition to plasma membrane. |
It is enclosed by a thin, flexible plasma membrane only. |
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3. |
It cannot change its shape. |
An animal cell can often change its shape. |
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4. |
Plastids are present. |
Plastids are usually absent. |
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5. |
A mature plant cell contains a large cnetral vacuole. |
An animal cell often possesses many small vacuoles. |
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6. |
Nucleus lies on one side in te peripheral cytoplasm. |
Nucleus usually lies in the centre. |
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7. |
Centrioles are usually absent. |
Centrioles are practically present. |
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8. |
Lysosomes are rare. |
Lysosome always present in animal cells. |
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9. |
Glyoxysomes may be present. |
They are absent. |
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10. |
Plasmodesmata are present. |
Plasmodesmata are usually absent. |
2. How is a prokaryotic cell different from a eukaryotic cell?
Solution
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Prokaryotic Cell |
Eukaryotic Cell |
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1. |
Generally small in size. |
Generally large in size. |
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2. |
Membrane bound cell organcelles are absent. |
Membrane bound cell organelles are present. |
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3. |
There is a single chromosome present. |
There are more than one chromosome present. |
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4. |
Nuclear region is not surrounded by nuclear membrane and well defined. |
Nuclear region is surrounded by nuclear membrane and well defined. |
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5. |
Cell division by fission or budding. |
Cell division mitotic or meiotic. |
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6. |
Nucleolus is absent. |
Nucleolus is present. |
3. What would happen if the plasma membrane ruptures or breaks down?
Solution
Plasma membrane provides space for the cell organelles and cytoplasm. It protects the contents of a cell from external environment. The cell components would be exposed to the external environment in case the plasma membrane breaks down.
4. What would happen to the life of a cell if there was no Golgi apparatus?
Solution
Golgi apparatus plays the important role of packaging various substances for further use. Absence of Golgi apparatus can hinder the formation of new cells during cell division because protein and lipid are important for the formation of Plasma Membrane. If there were no Golgi bodies, packaging and dispatching of materials synthesised by the cell will be stocked.
5. Which organelle is known as the powerhouse of the cell? Why?
Solution
Mitochondria is the powerhouse of the cell because respiration in cell takes place in mitochondria and the energy is stored in the form of ATP. It releases this energy required for different activities of life.
6. Where do the lipids and proteins constituting the cell membrane get synthesised?
Solution
Lipids are synthesized in the SER and protein is synthesized in RER.
7. How does an amoeba obtain its food?
Solution
Amoeba obtains its food through temporary finger like projections of cell surface called pseudopodia. Amoeba surrounds a food particle by pseudopodia to engulf the food and makes a food vacuole after engulfing the food. This is called phagocytosis.
8. What is osmosis?
Solution
The movement of water from high concentration to low concentration through a semi-permeable membrane is called osmosis.
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 hollow portion of B and C?
(ii) Why is potato A necessary for this experiment?
(iii) Explain, why water does not gather in the hollow portions of A and D?
Solution
(i) Water gathers in the hollow portions of set-up B and C because water enters the potato due to osmosis. Since the Medium surrounding the cell has a higher water concentration than the cell, the water moves inside by osmosis. Thus, water gathers in the hollowed portions of the potato cup.
(ii) Potato A in the experiment performs as a control set-up. No water collects in the hollowed portions of potato A.
(iii) Water does not gather in the hollowed portions of potato A because potato cup A is empty. It is a control set-up in the experiment.
Entry of water is not possible in potato D because the potato used here is boiled. Boiling denatures the proteins present in the cell membrane, so disrupts the cell membrane. A permeable membrane is required for osmosis, which is not present in this case. Therefore, osmosis will not occur.
10. Which type of cell division is required for growth and repair of body and which type is involved in the formation of gametes?
Solution
Mitosis cell division is required for growth and repair and Meiosis cell division is required for the formation of gametes.
Explanation : There are two types of cell divisions Mitosis and Meosis namely. Mitosis is the simple and mostly occurred types of cell division where a cell is divided into two cells. This type of division plays a major role in growth and repair of the body.
Meosis is the second type of cell division usually occurred in the reproductive system of the body. In this type of division, sex chromosomes are essentially divided and is involved in gamete formation.