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

NCERT Solutions Notes Important Questions MCQ Quiz – 1 MCQ Quiz – 2

NCERT In-Text Questions Solutions

In-Text Questions Page 59

1. Who discovered cells, and how?
   Ans:-  Robert Hooke discovered cells in 1665 while examining a thin slice of cork through a self-designed microscope. He saw that the cork resembled the structure of a honey comb consisting of many little compartments. He called these small boxes cells.
   
2. Why is the cell called the structural and functional unit of life?
   Ans:- Cell is called the structural and functional unit of life because all the living organisms are made up of basic unit called cell and all the functions that take place inside the organisms are performed by the cell.

In-Text Questions Page 61

1. How do substances like CO₂ and water move in and out of the cell? Discuss.
   Ans:- The substances like CO₂and water move in and out of a cell by diffusion from the region of high concentration to low concentration . .When the concentration of CO₂and water is higher in external environment than that inside the cell, CO₂and water moves inside the cell. When the concentration outside the cell becomes low and it is high inside the cell, they moves out.
   
2. Why is the plasma membrane called a selectively permeable membrane?
   Ans:- Plasma membrane controls the entry & exit of the materials in & out of the cell. So, plasma membrane is called selectively permeable membrane.

In-Text Questions Page 63

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

Prokaryotic Cell	Eukaryotic Cell
Size : generally small ( 1-10 μm) 1 μm = 10–6 m	Size: generally large ( 5-100 μm)
Nuclear region: _________ and known as___	Nuclear region: well defined and surrounded by a nuclear membrane
Chromosome: single	More than one chromosome
Membrane-bound cell organelles absent	____________ ____________

Ans:-

Prokaryotic Cell	Eukaryotic Cell
Size : generally small ( 1-10 μm) 1 μm = 10–6 m	Size: generally large ( 5-100 μm)
Nuclear region: poorly defined because of the absence of nuclear membrane and known as nucleiod.	Nuclear region: well defined and surrounded by a nuclear membrane
Chromosome: single	More than one chromosome
Membrane-bound cell organelles absent	Membrane-bound cell organelles present

In-Text Questions Page 65

1. Can you name the two organelles we have studied that contain their own genetic material ?
   Ans:- Mitochondria and Plastids
   

2. If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?
   Ans:–  If the organization of a cell is destroyed due to some physical or chemical influence then cell will not be able to perform its basic functions like digestion, excretion, respiration etc. This may stop all the life activities and the life of an individual may come to an end.
   
3. Why are lysosomes known as suicide bags?
   Ans:- Lysosomes are known as suicide bags of a cell because if the cell gets damaged, lysosomes may burst and the enzymes will digest their own cell.
   
4. Where are proteins synthesised inside the cell?
   Ans:- Proteins are synthesized by ribosomes and ribosomes are present on the RER (rough endoplasmic reticulum), mitochondria and plastids inside the cell.
   

NCERT End Exercises Solutions

1. Make a comparison and write down ways in which plant cells are different from animal cells.
   Ans:-
   
   
2. How is a prokaryotic cell different from a eukaryotic cell?
   Ans:-
   
   
3. What would happen if the plasma membrane ruptures or breaks down?
   Ans:- If the plasma membrane ruptures or breaks down, all the useful substances will move out of the cell and there will be no difference between cell content and its external environment. Ultimately, the cell will die.
   
4. What would happen to the life of a cell if there was no Golgi apparatus?
   Ans:-  Golgi apparatus performs the function of storage, modification and packaging of products. If Golgi apparatus is not there then materials synthesized by cell will not be packaged and transported.
   
5. Which organelle is known as the powerhouse of the cell? Why?
   Ans:-  Mitochondria is known as the powerhouse of the cell because energy required for various chemical activities needed to support life is released by mitochondria in the form of ATP (Adenosine triphosphate) molecules.
   
6. Where do the lipids and proteins constituting the cell membrane get synthesised?
   Ans:- Lipids are synthesized on smooth endoplasmic reticulum (SER) and the proteins are synthesized on rough endoplasmic reticulum (RER).
   
7. How does an Amoeba obtain its food?
   Ans:- Amoeba engulfs its food by the process of endocytosis in which pseudopodia are formed due to the flexibility of the plasma membrane.
   
   
8. What is osmosis?
   Ans:- The movement of water from the region of higher water concentration to lower water concentration through a semi permeable membrane is called osmosis.
   
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.
   
   Ans:- (i) Osmosis is the process responsible for the gathering of water in the hollowed portion of B and C. Since, the concentration of solute (sugar in cup B and salt in cup C) is higher inside the cup as compared to the water, which is outside the cup. Hence, water from its higher concentration (outside the cup) will move towards the lower concentration (inside the cup). This process of osmosis (moving in of solvent) is called endosmosis.
   (ii) Potato A acts as a control for the experiment. This is required for comparing theresults of the experiment.
   (iii) Water does not gather in the hollowed out portions of A and D because of the following reasons:-
   • The hollowed portion of potato A is empty. So, because of no concentration difference, no osmosis can occur.
   • The hollowed portion of potato D contains sugar in it but it is boiled. So, osmosis cannot occur as its semipermeable membrane is destroyed by boiling.