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Class IX Biology: Cell Basics

The plasma membrane is selectively permeable, allowing some materials to enter and exit the cell while preventing the movement of others. A hypotonic solution has a higher water concentration than the cell, an isotonic solution has the same water concentration, and a hypertonic solution has a lower water concentration than the cell. The plasma membrane is made of lipids and proteins. Endocytosis is the process by which the cell engulfs food and materials from the outside. Plasmolysis occurs when a plant cell loses water through osmosis and the cell contents shrink away from the cell wall. The nucleus contains DNA and controls the cell's activities. It plays a central role in cell division. A nucleoid is the undefined nuclear region in

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72 views3 pages

Class IX Biology: Cell Basics

The plasma membrane is selectively permeable, allowing some materials to enter and exit the cell while preventing the movement of others. A hypotonic solution has a higher water concentration than the cell, an isotonic solution has the same water concentration, and a hypertonic solution has a lower water concentration than the cell. The plasma membrane is made of lipids and proteins. Endocytosis is the process by which the cell engulfs food and materials from the outside. Plasmolysis occurs when a plant cell loses water through osmosis and the cell contents shrink away from the cell wall. The nucleus contains DNA and controls the cell's activities. It plays a central role in cell division. A nucleoid is the undefined nuclear region in

Uploaded by

Perajothi Palaniraja
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CLASS: IX – BIOLOGY

Chapter: 5 - The Fundamental unit of life

1. Why is the plasma membrane selectively permeable?


Ans. The plasma membrane allows the entry and exit of some materials in and out of the cell.
It also prevents the movement of some other materials. Thus the cell membrane is said
to be selectively permeable.

2. Define the following:


a. Hypotonic solution
b. Isotonic solution
c. Hypertonic solution

Ans. (a) If the medium surrounding the cell has a higher water concentration than the cell
meaning that the outside solution is very dilute, the cell will gain water by osmosis.
Such a solution is called a hypotonic solution.
(b) If the medium has exactly the same water concentration as the cell, there will be no
net movement of water across the cell membrane. Such a solution is known as an
isotonic solution.
(c) If the medium has a lower concentration of water than the cell , meaning that it is a
very concentrated solution, the cell will lose water by osmosis. Such a solution is
known as a hypertonic solution.

3. What is the plasma membrane made up of?


Ans. The plasma membrane is flexible and is made up of organic molecules called lipids and
proteins.

4. What is endocytosis?
Ans. The flexibility of the cell membrane enables the cell to engulf in food and other material
from its external environment. This process is known as endocytosis.
E.g. - Amoeba acquires its food by endocytosis.

5. What is plasmolysis?
Ans. When a living plant cell loses water through osmosis, there is shrinkage or contraction
of the contents of the cell away from the cell wall. This phenomenon is known as
plasmolysis.
6. What are the functions of the nucleus?
Ans. (i) The nucleus contains chromosomes which have the information for inheritance of
features from parents to next generation in the form of DNA (Deoxy ribonucleic acid)
molecules.
(ii) The nucleus plays a central role in cellular reproduction.
(iii) It helps to control and coordinate the chemical activities of the cell.

7. Draw the diagram of a well-developed nucleus before and during the cell division.

Nucleus

Nucleus during cell division

8. What is nucleoid?
Ans. An undefined nuclear region containing only nucleic acids is called a nucleoid. They
are present in prokaryotic cells. E.g. - Bacteria
9. Draw diagrams of the followings:
a) Various cells from the human body - NCERT, fig.5.3:

b) A prokaryotic cell (a bacterial cell) - NCERT, Fig. 5.4

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