The Fundamental Unit of Life| NCERT Solutions| Class 9

NCERT Solutions of  Chapter: The Fundamental Unit of Life. NCERT Solutions along with worksheets and notes for Class 9.

Page 59

(1) Who discovered cells, and how?

Ans- Robert Hooke invented the cell when he was observing slices of cork under the microscope in 1665. He noticed compartments or boxes which looks like honey comb. He called each box cell. But, it took 150 years to know more about the cell after Robert Cook.

 

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

Ans- The organisation of cells membrane and organelles acquire its structure and ability to function. Therefore, cell has basic structural organisation. This helps the cell to perform functions like respiration, obtaining nutrition and clearing of waste material, or forming new proteins. Therefore, the cell is a fundamental structural unit of living organisms.

 

Page 61

(1) How do substances like Co2 and water move in and out of the cell? Discuss.

Ans- CO2 is a cellular waste and requires to be excreted out by the cell. The CO2 is accumulated in high concentration in side the cell. The concentration of the CO2 is very low outside the cell. Therefore, Co2 moves out from the cell by process of diffusion.

 

(2) Why is the plasma membrane called a selectively permeable membrane?

Ans- The plasma membrane is flexible, porous, made up of organic molecules (lipids and proteins) and allows the movement of substance or material both inward and outward of the cell. Therefore it is called semipermeable membrane. But, it also prevents the movement of some other materials. Therefore, cell membrane is also called selectively permeable membrane.

 

Page 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 m)

1 m = 10-6m

 

1. Size: generally large (5 – 100 m)
2. Nuclear region: _________and 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 absent 4. _____________________

Ans-

Prokaryotic Cell Eukaryotic Cell
1. Size: generally small (1 – 10 m)

1 m = 10-6m

 

1. Size: generally large (5 – 100 m)
2. Nuclear region: Poorly defined because of absence of nuclear membrane and 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 absent 4. Membrane – bound cell organelles present

 

(3) Why are lysosomes known as sucide bags?

Ans- When a cell gets burst the cell is digested by strong enzymes of the lysosomes. Therefore, lysosomes are called suicide bags.

 

(4) Where are proteins synthesized inside the cell?

Ans- Proteins are synthesized inside the cell by ribosomes.

 

Exercise-

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

Ans-

SN Plant cells Animal cells
1. Very lrage Small in size
2. Have chloroplast Chloroplast absent
3. Plastids present Plastids absent
4. Large vacuoles Small size vacuoles
5. Cell wall present Cell wall absent

 

(2) How is a prokaryotic cell different from a eukaryotic cell?

Ans- The cells having well organised nucleus with a nuclear membrane are called as eukaryotic cells. The cells having nuclear material without nuclear membrane are termed prokaryotic cells.

SN Prokaryotic Cell Eukaryotic Cell
1. Generally small size(1 – 10 m)

1 m = 10-6m

 

Generally large size (5 – 100 m)
2. Nuclear region is poorly defined because of absence of nuclear membrane and known as nucleoid.  Nuclear region is well defined and surrounded by a nuclear membrane
3. Has single chromosome: Have more than one chromosome
4. Membrane  – bound cell organelles absent Membrane – bound cell organelles present

 

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

Ans- The plasma membrane is flexible, porous, made up of organic molecules (lipids and proteins) and allows the movement of substance or material both inward and outward of the cell by diffusion and osmosis. If plasma membrane ruptures or break down the movement of the food and proteins will stop and cell will die.

 

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

Ans- The material synthesised near the ER is packaged and dispatched to various targets inside and outside the cell through Golgi apparatus. In some cases complex sugars may be made from the simple sugars in the Golgi apparatus. If there is no Golgi apparatus there will be no food dispatching inside and outside the cell.

 

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

Ans- ATP (Adenosine triphosphate) molecules are the form of energy released by mitochondria needed for various chemical activities necessary for life.

ATP is known as “energy currency for the cell. The stored ATP energy is used in making new compounds and for mechanical work. Therefore, Mitochondria is known as the power house of the cell.

 

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

Ans- The lipids are synthesized in smooth endoplasmic reticulum and proteins get synthesised in rough endoplasmic reticulum.

 

(7) How does an Amoeba obtain its food?

Ans- In single celled organisms like Amoeba, the food vacuoles contain the food items that Amoeba has consumed.

 

(8)What is osmosis?

Ans- Osmosis is another process by which substances can move across the cell membrane. In osmosis, solvent moves through a selectively permeable membrane towards high concentration of solute (low concentration of solvent) from low concentration of solute. Osmosis is special case of diffusion through a selectively permeable membrane.

 

(9) Carry out the following osmosis experiment:

Take four peeled potatoes 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.

Ans-

(i) Cup B and C has solute concentrated solution. Water starts to move inside the cup through osmosis.

(ii) Potato A is necessary for this experiment because without it we are not able to decide that solutes are necessary for process of osmosis in cells.

(iii) Cup A has no solute. Hence water does not get inside through osmosis.

Cup D is made up of boiled potato which makes it inactive. Therefore, process of osmosis is not possible.

 

(10) Which type of cell division is required for growth and repair of body and which type is involved in formation of gametes?

Ans- Mitosis cell division is required for growth and repair of body and which type is involved in formation of gametes.

Meiosis cell division is involved in formation of gametes.

Helping Topics

The Fundamental Unit of Life

Worksheet Class 9

 

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