Grade 9 Science Ch 5 - Fundamental Unit of Life

Question 1.

Who discovered cells, and how?

Solution: Robert Hooke discovered the cell in 1665. He examined a thin slice of cork through a self designed primitive microscope and saw that the cork resembled the structure of a honey comb consisting of many tiny compartments. He called them cells which is derived from the Latin word “cell” meaning ‘a little room’.

Question 2.

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

Solution: All living organisms are made up of cells. Thus, cell is the structural unit of life.
Each cell is able to perform basic functions such as respiration, obtaining nutrition,
clearing of waste material, forming new proteins etc. The cell is, therefore, the basic

functional unit of living organisms.

Question 3.

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

Solution: CO2 moves in and out of the cells by the process of diffusion which involves movement of  molecules from higher concentration to lower concentration across the cell membrane.
Water moves in and out of the cells by osmosis. Osmosis involves the passive flow of
water or any other solvent from a region of higher water concentration to a region of lower

water concentration through a semi- permeable membrane.

Question 4.

Why the plasma membrane is called a selectively permeable membrane?

Solution: Plasma membrane permits the entry and exit of only selected materials in the cell. It also prevents movement of selected materials. Therefore, the plasma membrane is called a selectively permeable membrane.

Question 5.

What are the differences between prokaryotic and eukaryotic cells:

Solution:The differences between prokaryotic cell and eukaryotic cell are as follows:

Question 6.

Name the two organelles that contain their own genetic material?

Solution: Mitochondria and Plastids

Question 7.

If the organisation of a cell is destroyed due to some physical or chemical influence,

what will happen?
Solution: If the organisation of a cell gets destroyed due to any reason then lysis of the whole cell  will occur due to the enzymes released by lysosomes.

Question 8.

Why are lysosomes known as suicide bags?

Solution:Lysosomes contain digestive enzymes that are capable of digesting the whole cell. During breakdown of cell structure, when the cell gets damaged, lysosomes digest their own cells by releasing own enzymes. Therefore, they are known as suicide bags of a cell.

Question 9.

Where are proteins sythesised inside the cell?

Solution: The ribosomes attached to the endoplasmic reticulum as well as present freely in the cytoplasm of all active cells are the site for the synthesis of proteins.

Question 10.

Make a comparison and write down ways in which plant cells are different from

animal cells.
Solution: Differences between plant cells and animal cells are as follows

Question 11.

What would happen if the plasma membrane ruptures or breaks down?

Solution: The plasma membrane acts as a mechanical barrier to the protoplasm which regulates transport of materials into and out of cell maintaining the identity of the cell. In case of rupturing of the plasma membrane, the protoplasmic contents will get dispersed in the surrounding medium and thus cell will disintegrate.

Question 12.

What would happen to the life of a cell if there was no Golgi apparatus?

Solution: In the absence of Golgi apparatus, the following problems will arise:
(i)The material synthesised by Endoplasmic reticulum would not be carried to the various
parts inside and outside the cell.
(ii) Synthesised materials could not be stored and modified further

(iii) There will be no production of lysosomes .

Question 13.

Which organelle is known as the power house of the cell? Why?

Solution:Mitochondrion is known as the power house of the cell. It is because the mitochondrion is the site of cellular respiration where energy in the form of ATP (adenosine triphosphate) is generated as a consequence of oxidation of carbohydrates and fats (lipids).

Question 14.

Where do the lipids and proteins constituting the cell membrane get synthesised?

Solution: Smooth endoplasmic reticulum (SER) helps in the manufacturing of lipids which are important for the formation of cell membrane. Ribosomes are the site for protein synthesis.

Question 15.

How does an Amoeba obtain its food?

Solution: Amoeba is a unicellular organism. It obtain its food through the false feet called
pseudopodia. Whenever it sees food particle its flexible membrane protrudes and engulfs
the food. This food is then broken down into the food vacuole which contains digestive

enzymes. This process is known as endocytosis.

Question 16.

What is osmosis? What are the differences between Diffusion and Osmosis?

Solution: Osmosis involves the passive flow of water or any other solvent from a region of higher water, concentration to a region of lower water concentration through a semi- permeable membrane
Difference between Diffusion and Osmosis:

Question 17.

Which type of cell division is required for growth and repair of body and which type

is involved in formation of gametes?
Solution: For growth and repair mitotic division (mitosis) are involved as this type of division keep the chromosome number constant. For gamete formation, meiosis is involved as reduction of chromosome number is necessary.

Question 18. Draw labelled diagram of the following:
a)Nucleus b) Plant cell c) Animal cell
Solution: