CBSE Class 9 Science The Fundamental Unit of Life Assignment Set A

Question. Who discovered cells and how?
Answer: An English Botanist, Robert Hooke discovered cells. In 1665, he used self-designed microscope to observe cells in a cork slice.

Question. Why cell is 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 and also all the functions taking place inside the body of organisms are performed by cells.

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

Question. Why is the plasma membrane called a selectively permeable membrane?
Answer: Plasma membrane called a selectively permeable membrane because it regulates the movement of substances in and out of the cell. This means that the plasma membrane allows the entry of only some substances and prevents the movement of some other materials.

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

Answer

Question. Can you name the two organelles we have studied that contain their own genetic material?
Answer: Mitochondria and plastids

Question. If the organization of a cell is destroyed due to some physical or chemical influence, what will happen?
Answer: If the organization of a cell is destroyed due to some physical or chemical influence then cell will not be able to perform the basic functions like respiration, nutrition, excretion etc. This may stop all the life activities and may result in its death.

Question. 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.

Question. Where are proteins synthesized inside the cell?
Answer: The proteins are synthesized in the Ribosome inside the cell.

EXERCISE

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

Question. How is a prokaryotic cell different from a eukaryotic cell?
Answer:

Question. What would happen if the plasma membrane ruptures or breaks down?
Answer: If the plasma membrane ruptures or breakdown then the cell will not be able to exchange material from it’s surrounding by diffusion or osmosis. Thereafter the protoplasmic material will be disappeared and the cell will die.

Question. What would happen to the life of a cell if there was no Golgi apparatus?
Answer: Golgi apparatus has the function of storage modification and packaging of the products. If there is no Golgi apparatus then the packaging and transporting of materials synthesized by cell will not happen.

Question. Which organelle is known as the powerhouse of the cell? Why?
Answer: Mitochondria are known as the powerhouse of cells because energy required for various chemical activities needed for life is released by mitochondria in the form of ATP (Adenosine triphosphate) molecules.

Question. Where do the lipids and proteins constituting the cell membrane get synthesized?
Answer: Lipids are synthesized in Smooth endoplasmic reticulum (SER) and the proteins are synthesized in rough endoplasmic reticulum (RER).

Question. How does an Amoeba obtain its food?
Answer: Amoeba takes in food using temporary finger-like extensions of the cell surface which fuse over the food particle forming a food-vacuole as shown in figure. Inside the food vacuole, Complex substances are broken down into simpler ones which then diffuse into the cytoplasm. The remaining undigested material is moved to the surface of the cell and thrown out.

Question. What is osmosis?
Answer: Osmosis is the process in which water molecules moves from the region of highconcentration to a region of low concentration through a semi permeable membrane.

Question. Carry out the following osmosis experiment:
Take four peeled potato halves and scoop 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) Water gathers in the hollowed portions of set-up B and C because water enters the potato as a result of osmosis. Since the medium surrounding the cell has a higher water concentration than the cell, the water moves inside by osmosis. Hence, water gathers in the hollowed portions of the potato cup.
(ii) Potato A in the experiment acts as a control set-up. No water gathers in the hollowed portions of potato A.
(iii) Water does not gather in the hollowed portions of potato A because potato cup A is empty. It is a control set-up in the experiment.
Water is not able to enter potato D because the potato used here is boiled. Boiling denatures the proteins present in the cell membrane and thus, disrupts the cell membrane. For osmosis, a semipermeable membrane is required, which is disrupted in this case. Therefore, osmosis will not occur. Hence, water does not enter the boiled potato cup.

Exam Questions NCERT Class 9 Science Chapter 5 The Fundamental Unit of Life

Question. What is the function of ribosome?
Ans : Ribosome helps in protein synthesis.

Question. What is the function of cell wall and plasma membrane?
Ans : Cell Wall : Gives rigidity, shape and protection to plant cell.
Cell Membrane : Allows only selected materials to move in and out of the cell.

Question. Give the function of nuclear membrane.
Ans : The nuclear membrane present as outer covering of nucleus allows transfer of material inside and also out of the nucleus to cytoplasm.

Question. Write the functions of cell wall in plant cell.
Ans : (i) It provides rigidity and strength to the cell.
(ii) It gives a definite shape to the cell.
(iii) It withstands the osmotic pressure which is developed by cell contents.
(iv) It protects the inner cell organelles bounding the cell from outside.

Question. How many types of proteins are present in cell structure?
Ans : There are two types of protein molecules : intrinsic proteins, which completely covers the lipid bilayer and extrinsic proteins, which occur either on the outer surface or on the inner surface of the lipid membrane.

Question. What are vacuoles?
Ans : Vacuoles are fluid-filled structures surrounded by a membrane. The fluid in the vacuoles is called cell sap.
In animal cells, either they are absent or are very small in size.

Question. List any six functions of nucleus of a cell.
Ans :(i) Nucleus plays a central role in cellular reproduction.
(ii) It plays an important role in determining the way the cell will develop.
(iii) It also determines what form the cell will exhibit at maturity.
(iv) It contains chromosome thus inherits characters.
(v) It is the control centre of the cell.
(vi) It directs chemical activities of the cell.

Question. Name some organelles which are found only in animal cells and those which occur only in plant cells.
Ans : (i) Structures found only in animal cells : centrosomes, lysosome.
(ii) Structures found only in plant cells : cell wall, plastids and big vacuoles.

Question. (i) What will happen when eukaryotic cells are placed in hypotonic solution?
(ii) What will happen if eukaryotic cells are placed in hypertonic solution?
(iii) What will happen if eukaryotic cells are placed in isotonic solution?
Ans :
(i) When eukaryotic cells are placed in hypotonic solution, the water molecules will enter into the cell and the cell will swell up.
(ii) If eukaryotic cells are placed in hypertonic solution, the water molecules will come out of the cell and the cell will shrink.
(iii) If the eukaryotic cell is placed in isotonic solution, the amount of water molecule will remain the same; it will neither move out nor will go inside.
The cell will remain same sized.