Chapter 5
The Fundamental Unit of Life
Here is the answer of chapter 5 The Fundamental Unit of Life of NCERT science of class 9.The complete solution of CHAPTER 5 The Fundamental Unit of Life is given here which is prepared subject expert.
Block Questions.(page no.- 59)
Ques 1. Who discovered cell and how?
Ans. Robert Hooke discovered the cell. He observed the cell in a cork slice with the help of a primitive microscope.
Ques 2. Why is cell called the structural unit of life?
Ans. Cell constitute various component of plants and animals a cell is the smallest unit of life and is capable of all living functions. Cell are the building blocks of life. This is the reason why cell are referred to as the basic structural and functional unit of life. All cells varies in shape and size and activity they perform in fact, the shape and size of a cell is related to the specific functions they perform.
Block Questions Page no- 61
Ques 1.How do substance like CO2 and water move in and out of the cell? Discuss.
Ans.It is because of the diffusion and osmosis process in the cell. Through diffusion CO2 enters in the cell and by the process of Osmosis the water molecules moves from an area of high water concentration through a particle permeable membrane.
Ques 2. Why is plasma membrane called selectively permeable membrane?
Ans.The plasma membrane allows or permits the entry and exist of source material in and out of the cell. It also prevents movement of source other materials. The cell membrane therefore is called a selectively permeable membrane.
Page No. 63
Ques 1. Fill in the gaps in the following table illustrating difference between prokaryotic and eukaryotic cells.
Ans.
| Prokaryotic Cell | Eukaryotic Cell |
| 1. Size: Generally small (1-10 μm) 1 μm = 10-6m 2. Nuclear region: ______________________________ ______________________________ and known as ___________________ 3. Chromosome: single 4. Membrane-bound cell organelles absent. | 1. Size: Generally large (5-100 μm) 2. Nuclear region: well defined and surrounded by a nuclear membrane.
3. More than one chromosome. 4. ______________________________ ______________________________ ______________________________ |
Solution:
| Prokaryotic Cell | Eukaryotic Cell |
| 1. Size: Generally small (1-10 μm) 1 μm = 10-6m 2. The nuclear region is poorly defined due to the absence of a nuclear membrane and known as the nucleoid. 3. There is a single chromosome. 4. Membrane-bound cell organelles absent. | 1. Size: Generally large (5-100 μm) 2. Nuclear region: well defined and surrounded by a nuclear membrane. 3. There are more than one chromosomes. 4. Membrane-bound cell organelles present. |
Page no-65
Ques 1. Can you name two organelles we have studied that contain their own genetic material?
Ans. Mitochondria and Plastids are two Organelles that contain their own genetic material.
Ques 2. If the organism of a cell is destroyed due to some physical or chemical influence,what will be happen?
Ans. Cell is the smallest unit of life which is capable of all living functions if the organism of cell is destroyed due to some physical or chemical influence then the ability of the cell by to perform all living function such as respiration , nutrition, excretion etc.would be affected.
Ques 3. Why are lysosomes known as Suicidal bags?
Ans . Lysosomes are membrane bound vesicular structure that contain powerful digestive enzymes. These enzymes are capable of breaking down any foriegn food particle or microbes entering the cell. Some time,Lysosomes can cause self destruction of a cell by releasing these digestive enzymes within the cell. Hence, they are also known as Suicidal Bags.
Ques 4. Why are proteins synthesized in the cell.
Ans. Proteins are synthesized in the Ribosomes in the cell.
Exercise Questions-
Page No. 67
Ques 1. Make a comparison to write down ways in which plant cells are different from animal cells.
Ans. The cells of plant and animal have the following differences:-
Animal Cell-
a) Animal cells are generally small in size.
b) Cell wall is absent.
c) Except the protozoan ,euglena, no animal cell posses plastids.
d) Vacuoles in animal cells are many small and temporary.
e) Animal cells have a single, highly complex and permanent golgi apparatus.
f)Animal cells have centrosome and centrioles.
Plant Cell-
a) Plant cells are larger than animal cells.
b) The plasma membrane of plant cell is surrounded by a rigid cell wall of cellulose.
c) Plastids are present.
d) Most mature plant cells have a permanent and large central sap vacuoles.
e) Plant cells have many simple unit of Golgi apparatus called dictyosomes.
f) Plant cells lack centrosomes and centrioles.
Ques 2. How do prokaryotic cell different from eukaryotic cells?
Ans. Prokaryotic Cell
a) Cell size is generally small (1-10mm).
b) Nuclear region is called nucleoid and is not surrounded by a nuclear membrane.
c) Only a single chromosome is present.
d) Nucleolus is absent.
e) Membrane bound cell organelles are absent.
f) Cell division by fission or budding (no mitosis).
Eukaryotic Cell
a) Cell is generally large (5-100mm).
b) Nuclear material is surrounded by a nuclear membrane.
c) More than one chromosome present.
d) Nucleolus is present.
e) Membrane bound cell Organelles.
f) Cell division mitotic or meiotic.
Ques 3. What would happen if plasma membrane ruptures or breaks down?
Ans. Plasma membrane is selectively permeable membrane of the cell that maintain its homeostasis, i.e. constant internal composition of the cell. If it ruptures or break down the constant internal chemical composition of the cell will be last and it will not be able perform its basic function. Such a cell with ruptured plasma membrane is killed.
Ques 4. What would happen to the life of a cell if there is no Golgi apparatus?
Ans. The material synthesised in the ER are stored, modify, packaged and dispatched to various targets inside and outside the cell through Golgi apparatus packs products in vesicles,the secretary vesicles. In some cases complex sugar. example:- cellulose may be made from simple sugar in Golgi apparatus. The Golgi apparatus is also involved in the formation of the cell which will not be possible if Golgi apparatus is not there.
Ques 5. Which organelle is known as the power house of the cell? Why?
Ans. Mitochondria are known as the Powerhouse of the cell because they contain enzymes that are needed for stepwise oxidation of food stuffs. Carbohydrates,fats and lipids present in cell to CO2 and water oxidation of food release energy which is used to form high energy ATP(Adinosine triphosphate) molecules ATP is known as energy currency of the cell and it is used as cellular fuel. Energy stored in ATP is used to bring about energy requiring activities of the cell such as photosynthesis protein synthesis and muscles contraction.
Ques 6. Where do lipids and proteins constituting the cell membrane get synthesised?
Ans. Rough endoplasmic Reticulum (RER) :- Synthesise protein constituting cell membrane.
Smooth endoplasmic Reticulum (SER):- Synthesise lipid consulting cell membrane.
Ques 7. How does Amoeba obtain its food?
Ans. Amoeba has flexible cell membrane it enables amoeba to engulf food by the process called Endocytosis.
Ques 8. What is osmosis?
Ans. The diffusion of water or solvent through a semi permeable membrane from a solution of lower concentration of solutes to a solution of higher concentration of solutes to which the membrane is relatively impermeable is called Osmosis.
Ques 9. Carry out the following osmosis experiment:
Take four peeled potato halves and 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 B
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) Water accumulates hollowed in the portion of B and C as the difference in water concentration is observed. Therby, endosmosis occurs as the cell acts as a semi permeable memebrane.
ii)Potato A is essential in this experiment as it is significant to compare different scenarios seen in
potato cups B, C and D. The potato A in this experiment clearly shows that the potato cavity on itsown cannot bring about water movement.
iii)Cup in A does not show any change in the water flow concentration for osmosis to occur, which requires the concentration to be higher than the other. Cells in cup D are dead, thus there is noexistence of a semipermeable membrane for water flow. Consequently, osmosis does not occur.
10. Which type of cell division is required for growth and repair of body and which type is involved in formation of gametes?
Ans. There are two ways in which a cell divides:
Mitosis
Meiosis
Mitosis is the type of cell division that is involved in the growth and repair of body whereas meiosis is a type of cell division which results in the formation of gametes.
These are some extra Questions of Chapter 5 The Fundamental Unit of life of class 9 Science NCERT.
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