NCERT Solutions of Ch 5 The Fundamental Unit of Life Class 9th Science

Question

Can you provide me NCERT Solutions of Ch 5 The Fundamental Unit of Life Class 9th Science Textbook

Answer 1

Page No: 59

 

1. Who discovered cells, and how?

Answer

An English Botanist, Robert Hooke discovered cells in 1665. While examining a thin slice of cork under a microscope, he noticed that the thin slice of cork resembled the structure of a honey comb consisting of many hexagonal compartments known as 'cells'.

 

2. Why is the cell 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. All the functions taking place inside the body of organisms are performed by cells.

 

Page No. 61

 

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

Answer

Substances such as carbon dioxide move in and out of cells by the process of diffusion. In this process, there is a spontaneous movement of substances from a region of higher concentration to a region of their lower concentration.

Movement of water occurs by the process of osmosis. In this process, there is spontaneous movement of water from a region of higher concentration to a region of lower concentration across a selectively permeable membrane.

 

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

Answer

Plasma membrane permits the entry and exit of selected materials in and out of the cell. It also prevents movement of some other materials. Hence, it is called a selectively permeable membrane.

 

Page No: 63

 

1. Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.

	Prokaryotic cell	.	Eukaryotic cell
1.	Size: generally small ( 1-10 µm) 1 µm= 10-6 m	1.	Size: generally large (5-100 µm)
2.	Nuclear region: _____________________________ and is known as ________.	2.	Nuclear region: well-defined and surrounded by a nuclear membrane
3.	Chromosome: single	3.	More than one chromosome
4.	Membrane-bound cell organelles are absent	4.	_________________________________

Answer

	Prokaryotic cell		Eukaryotic cell
1.	Size: generally small ( 1-10 µm) 1 µm== 10-6 m	1.	Size: generally large (5-100 µm)
2.	Nuclear region: poorly defined because of the absence of a nuclear membrane, and is known as nucleoid	2.	Nuclear region: well-defined and surrounded by a nuclear membrane
3.	Chromosome: single	3.	More than one chromosome
4.	Membrane-bound cell organelles are absent	4.	Membrane-bound cell organelles such as mitochondria, plastids, etc., are present

Page No: 65

 

1. Can you name the two organelles we have studied that contain their own genetic material?

Answer

Mitochondria and plastids

 

2. If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?

Answer

If the organisation of a cell is destroyed, it will stop performing basic functions and will ultimately die. Lysosomes present inside the cell will burst to release enzyme which will digest the cell.

 

3. Why are lysosomes known as suicide bags?

Answer

Lysosomes are called suicide bags because in case of disturbance of their cellular metabolism they digest their own cell by releasing own enzymes.

 

4. Where are proteins synthesized inside the cell?

Answer

In the Ribosome inside the cell.

Answer 2

Exercises

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

Answer

Animal Cell	Plant Cell
Animal cells are generally small in size.	Plant cells are larger in size.
A cell wall is absent in animal cells.	A cell wall is present outside the plasma membrane of a plant cell.
Many small vacuoles are present in an animal cell.	A large central vacuole is present in a plant cell.
Plastids are absent in an animal cell.	Plastids are present in a plant cell.

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

Answer

Prokaryotic cell	Eukaryotic Cell
Eukaryotic cells are larger in size as compared to prokaryotic cells.	Prokaryotic cells are generally small in size.
A well-defined nucleus is absent and the nuclear region is not surrounded by  nuclear membrane.	A well defined nucleus is present.
A single chromosome is present.	More than one chromosome is present.
Membrane-bound organelles such as mitochondria, plastids, endoplasmic reticulum, golgi apparatus, lysosomes etc. are absent.	Membrane bound organelles are present.
Cell division takes place by fission or budding.	Cell divsion take place by mitosis or meiosis.

3. What would happen if the plasma membrane ruptures or breaks down?
Answer
Plasma membrane is responsible for regulating the movement of contents inside and outside of the cell as well as it is also responsible for the exchange of gases. Apart from this plasma membrane also enables the cell to engulf food from its external environment, rupturing or breakdown of plasma membrane will lead to all these functions being affected as the result of which cell can die.
 

4. What would happen to the life of a cell if there was no Golgi apparatus?
Answer
The absence of Golgi apparatus will affect the life of a cell in following ways:
(i) Formation of Lysosomes will be affected
(ii) Packaging and Dispatching of Material synthesized near Endoplasmic Reticulum to various targets inside/outside cells will be affected
(iii) The formation of cell plate and cell membrane will not take place. 
(iv) Storage, Modification and Packaging of Products in Vesicles will be affected.
 

5. Which organelle is known as the powerhouse of the cell? Why?
Answer
Mitochondria are known as powerhouse of the cell. They are the sites for the synthesis, storage and transport of ATP (Adenosine triphosphate), commonly called 'energy currency of the cell.
 

6. Where do the lipids and proteins constituting the cell membrane get synthesised?
Answer
(i) Proteins are synthesised by the ribosomes attached to rough endoplasmic reticulum. 
(ii) Lipids are synthesised by the smooth endoplasmic reticulum. 
(iii) These proteins and lipids are modified by the Golgi apparatus to form the plasma membrane.
 

7. How does an Amoeba obtain its food?
Answer
Amoeba obtain its food through the process of endocytosis. The plasma membrane of Amoeba is flexible which help to engulfits food particles and other material from its external environment.
 

8. What is osmosis?
Answer
Osmosis is a special case of diffusion of water molecules from a region of higher concentration to a region of lower concentration through a semi-permeable membrane. 
 

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.
(ii) Why is potato A necessary for this experiment?
(iii) Explain why water does not gather in the hollowed out portions of A and D.
Answer
(i) The water gathers in the hollowed portion of potato cups B and C due to osmosis. 
(ii) Cup A is necessary because it shows that if two solutions have the same concentration, there is no net movement of water molecules. 
(iii) Water does not gather in the hollowed portion of A because there is no change in the concentration of water. For osmosis to occur, one of the concentrations must be higher.
(iv) Cup D was made of dead cells and their cell membranes were no more selectively permeable membranes. Therefore, no osmosis takes place and water does not get collected in cup D.
 

10. Which type of cell division is required for growth and repair of body and which type is involved in formation of gametes?
Answer
Mitosis is used for growth and repair of body and produces diploid cells identical to each other and the parent cell. 
Meiosis is used for sexual reproduction and produces haploid cells different to each other and the parent cell. Thus, meiosis results in formation of gametes.