CBSE Class 9 Science The Fundamental Unit of Life Assignment Set A

CBSE Class 9 Science the fundamental unit of life. Students are advised to refer to the attached assignments and practise them regularly. This will help them to identify their weak areas and will help them to score better in examination. Parents should download and give the assignments to their children for practice.

1. Who discovered cells and how?

Answer: An English Botanist, Robert Hooke discovered cells. In 1665, he used self-designed microscope to observe cells in a cork slice.

2. Why cell is called the structural and functional unit of life?

Answer: 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 cells.

3. How do substances like CO₂ and water move in and out of the cell? Discuss.

Answer: The substances like CO₂ and water move in and out of a cell by diffusion from the region of high concentration to low concentration.

When the concentration of CO₂ and water is higher in external environment than that inside the cell, CO₂ and water moves inside the cell. When the concentration outside the cell becomes low and it is high inside the cell, they move out.

4. Why is the plasma membrane called a selectively permeable membrane?

Answer: Plasma membrane called a selectively permeable membrane because it regulates the movement of substances in and out of the cell. This means that the plasma membrane allows the entry of only some substances and prevents the movement of some other materials.

Exam Questions NCERT Class 9 Science Chapter 5 The Fundamental Unit of Life

Question. What is the function of ribosome?
Ans : Ribosome helps in protein synthesis.

Question. What is the function of cell wall and plasma membrane?
Ans : Cell Wall : Gives rigidity, shape and protection to plant cell.
Cell Membrane : Allows only selected materials to move in and out of the cell.

Question. Give the function of nuclear membrane.
Ans : The nuclear membrane present as outer covering of nucleus allows transfer of material inside and also out of the nucleus to cytoplasm.

Question. Write the functions of cell wall in plant cell.
Ans : (i) It provides rigidity and strength to the cell.
(ii) It gives a definite shape to the cell.
(iii) It withstands the osmotic pressure which is developed by cell contents.
(iv) It protects the inner cell organelles bounding the cell from outside.

Question. How many types of proteins are present in cell structure?
Ans : There are two types of protein molecules : intrinsic proteins, which completely covers the lipid bilayer and extrinsic proteins, which occur either on the outer surface or on the inner surface of the lipid membrane.

Question. What are vacuoles?
Ans : Vacuoles are fluid-filled structures surrounded by a membrane. The fluid in the vacuoles is called cell sap.
In animal cells, either they are absent or are very small in size.

Question. List any six functions of nucleus of a cell.
Ans :(i) Nucleus plays a central role in cellular reproduction.
(ii) It plays an important role in determining the way the cell will develop.
(iii) It also determines what form the cell will exhibit at maturity.
(iv) It contains chromosome thus inherits characters.
(v) It is the control centre of the cell.
(vi) It directs chemical activities of the cell.

Question. Name some organelles which are found only in animal cells and those which occur only in plant cells.
Ans : (i) Structures found only in animal cells : centrosomes, lysosome.
(ii) Structures found only in plant cells : cell wall, plastids and big vacuoles.

Question. (i) What will happen when eukaryotic cells are placed in hypotonic solution?
(ii) What will happen if eukaryotic cells are placed in hypertonic solution?
(iii) What will happen if eukaryotic cells are placed in isotonic solution?
Ans :
(i) When eukaryotic cells are placed in hypotonic solution, the water molecules will enter into the cell and the cell will swell up.
(ii) If eukaryotic cells are placed in hypertonic solution, the water molecules will come out of the cell and the cell will shrink.
(iii) If the eukaryotic cell is placed in isotonic solution, the amount of water molecule will remain the same; it will neither move out nor will go inside.
The cell will remain same sized.

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