NCERT Solutions for Class 9 Science Chapter 5 The Fundamental Unit of Life

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

Answer:

Animal Cell	Plant Cell
In general, animal cells are of small size.	Plant cells are larger than animal cells
Cell wall is absent in animal cell	Cell was is present in plant cell
Plastids is absent in animal cells except euglena	Plastids are present
Vacuoles are smaller in size	Vacuoles are larger in size

2. How is a prokaryotic cell different from a eukaryotic cell?

Answer:

Prokaryotic Cell	Eukaryotic Cell
Nucleus is absent	Nucleus is present
Do not contain membrane bound organelles	Contains membrane bound organelles
Are mostly unicellular	Are multicellular
E.g. E.coli, Streptococcus,etc.	E.g. Plants, animals, etc.

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

Answer: Plasma membrane is responsible for movement of substance inside and outside the cell through diffusion. If plasma membrane breaks down, then material from the cell will leak causing the death of the cell.

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

Answer: If golgi complex is not present then

• Packaging, modification and storage process will not happen.
• Formation of complex sugars with simple sugars will not be possible
• Formation of lysosomes will not be possible

5. Which organelle is known as the powerhouse of the cell? Why?

Answer: Mitochondria is known as powerhouse of the cell. This is because, it creates energy for the cell through cellular respiration. Mitochondria releases energy in the form of ATP, which is used for various chemical activities essential for life. Therefore, mitochondria is called as powerhouse of the cell.

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

Answer: Lipids and proteins are synthesised in endoplasmic reticulum. In smooth endoplasmic reticulum lipids are synthesised. In rough endoplasmic reticulum, proteins are synthesised on the site called ribosomes.

7. How does an Amoeba obtain its food?

Answer: By the process of endocytosis, amoeba obtains its food. Cell membrane of amoeba is flexible enough to engulf food inside its body, thereby, forming a food vacuole.

8. What is osmosis?

Answer: Movement of molecules of water from region of higher concentration to lower concentration through semipermeable membrane is known as osmosis. If medium surrounding the cell has high water concentration, more amount of water moves inside cell by the process of osmosis. Such a solution is called hypotonic solution. If the water concentration of medium and cell is same, equal amount of water travels on both side. Hence, there is no net movement across the cell. Such a solution is isotonic solution. If medium surrounding the cell is of low water concentration, more water moves out of cell. Such a solution is called as hypertonic solution.

9. Carry out the following osmosis experiment:

Take four peeled potato halves and scoos 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 hollowed portion of B and C.

Answer: Water is collected in hollowed portion of B and C because of osmosis. Through the process of osmosis, water is collected in potato. Medium surrounding the cell of potato has higher water concentration as compared to the cell. Therefore, water moves inside the cell through osmosis.

(ii) Why is potato A necessary for this experiment?

Answer: Potato A is acting as control setup.

(iii) Explain why water does not gather in the hollowed out portions of A and D.

Answer: Water does not gather in hollowed out portions of A because potato cup A is empty. In this experiment it is control set up. Water does not enter in potato D because potato used here is boiled potato. Boiling disrupts the cell membrane and for osmosis cell membrane is necessary. Thus, osmosis doesn’t occur due to which water doesn’t enter in potato D.

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