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

Hello students and welcome to the wonders of biology! We have answered all in-text questions, exercise questions and in-text activities in this solution material, so you can access the answers to everything in one place. The solutions have been presented logically and lucidly to help you grasp these fundamental concepts well. We have also provided a set of extra questions which will give you sufficient practice.

Solutions to In Text Questions of NCERT Class 9 Science Chapter 5 The Fundamental Unit of Life –

Page 51:

1. Who discovered cells, and how?
Answer:
Robert Hooke discovered cells in the year 1665. He examined a thin slice of cork through a self-designed microscope and noticed it resembled the structure of a honeycomb consisting of many little compartments. He called these compartments ‘cells’.

2. Why is the cell called the structural and functional unit of life?
Answer:
The cell is called the structural unit of life because is it the smallest building block of living organisms and all organisms are made up of cells. The cell is called the functional unit of life because it carries out vital functions such as metabolism, growth, reproduction, energy production which are essential for survival.

Page 53:

1. How do substances like CO₂ and water move in and out of the cell? Discuss.
Answer:
Substances like carbon dioxide (CO₂) and water move in and out of cells through diffusion, moving from areas of high concentration to areas of low concentration. When the concentration of CO₂ and water is higher outside the cell, they move inside. When the concentration of CO₂ and water is higher inside the cell, they move outside.

2. Why is the plasma membrane called a selectively permeable membrane?
Answer:
The plasma membrane is called a selectively permeable membrane. This is because it permits the entry and exit of some materials in and out of the cell and also prevents movement of some other materials.

Page 55:


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 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._______________ _______________ _______________

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 due to the absence of a 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.

Page 57:

1. Can you name the two organelles we have studied that contain their own genetic material?
Answer:
The two organelles we have studied that contain their own genetic material are mitochondria and plastids. Both organelles contain their own DNA and ribosomes.

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 due to some physical or chemical influence, then the cell will not be able to perform functions like respiration, obtaining nutrition, clearing of waste material, forming new proteins and eventually die.

3. Why are lysosomes known as suicide bags?
Answer:
Lysosomes are known as suicide bags of the cell because when the cells gets damaged they release powerful digestive enzymes which digest the cell. This leads to the death of the cell.

4. Where are proteins synthesised inside the cell?
Answer:
Proteins are synthesised inside the animal cell in ribosomes which are attached to the rough endoplasmic reticulum and also present in mitochondria. Proteins are synthesized in the plant cell in ribosomes present in plastids.

Solutions to Exercises (Page No 59) of NCERT Class 9 Science Chapter 5 The Fundamental Unit of Life –

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

Plant Cell	Animal Cell
(i) Cell wall is present in addition to plasma membrane.	(i) Cell wall is absent, only plasma membrane is present.
(ii) Due to the hardiness of the cell wall, the cells can absorb more water without bursting.	(ii) The cell wall is absent and cannot protect the cell from bursting by absorbing water.
(iii) Plastids are present.	(iii) Plastids are not present.
(iv) Have large centrally located vacuoles.	(iv) Have small vacuoles.
(v) Can perform photosynthesis.	(v) Cannot perform photosynthesis.
(vi) Centriole is not present.	(vi) Centriole is present.
(vii) Rectangular or box-shaped.	(vii) Come in various shapes, including round, irregular, and elongated shapes.

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

Prokaryotic cell	Eukaryotic cell
(i) Size: generally small (1-10 µm) 1 µm = 10-6 m.	(i) Size: generally large (5-100 µm)
(ii) Nuclear region: Poorly defined due to the absence of a nuclear membrane and known as nucleoid.	(ii) Nuclear region: Well defined and surrounded by a nuclear membrane
(iii) Has a single chromosome.	(iii) Has more than one chromosome.
(iv) Membrane-bound cell organelles absent.	(iv) Membrane-bound cell organelles present.

3. What would happen if the plasma membrane ruptures or breaks down?
Answer:
If the plasma membrane ruptures or breaks down then the contents of the cell will leak out and the cell would die. The plasma membrane selectively allows materials to move in and out of the cell and keeps harmful substances out. This function of the plasma membrane would also be hampered.

4. What would happen to the life of a cell if there was no Golgi apparatus?
Answer:
If there was no Golgi apparatus, essential materials would not get sent to various targets inside and outside the cell. Also, lysosomes would not get produced and there would be accumulation of waste materials inside the cell. Due to the combination of these factors the cell would eventually die.

5. Which organelle is known as the powerhouse of the cell? Why?
Answer:
Mitochondria is the organelle that is known as the powerhouse of the cell because it generates energy in the form of ATP (Adenosine triphosphate) molecules. The body uses ATP for making new chemical compounds and for mechanical work. ATP is known as the energy currency of the cell.

6. Where do the lipids and proteins constituting the cell membrane get synthesised?
Answer:
Lipids and proteins constituting the cell membrane get synthesised in the endoplasmic reticulum. Specifically, lipids are synthesized in the smooth endoplasmic reticulum (SER) and proteins are synthesized in ribosomes attached to the surface of the rough endoplasmic reticulum (RER).

7. How does an Amoeba obtain its food?
Answer:
An Amoeba obtains its food by engulfing it using the flexible cell membrane. This process is known as endocytosis. It then traps the food in a food vacuole and digests it using digestive enzymes.

8. What is osmosis?
Answer:
The movement of water molecules through such a selectively permeable membrane from a region of higher concentration to a region of lower concentration is called osmosis. Even gases can undergo osmosis.

9. Carry out the following osmosis experiment:

• Take four peeled potato halves and scoops 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) Explain why water gathers in the hollowed portion of B and C.

Water gathers in the hollowed portion of B and C because of osmosis.

The medium inside potato cup B contains a higher concentration of sugar than the water in the trough outside. Therefore, concentration of water outside the potato cup is higher than the concentration of water inside and so water flows inside the cup due to osmosis.

The medium inside potato cup C contains a higher concentration of salt than the water in the trough outside. Therefore, concentration of water outside the potato cup is higher than the concentration of water inside and so water flows inside the cup due to osmosis.

(ii) Why is potato A necessary for this experiment?

Potato A is necessary for this experiment because it acts as the control of the experiment. It shows that the potato cup by itself cannot bring about water movement and allows us to see the difference between the different cases.

(iii) Explain why water does not gather in the hollowed out portions of A and D.

There is no salt/sugar inside cup A and hence there is no difference in concentration of water between the outside and inside of cup A. As a result, osmosis cannot occur and water cannot gather inside cup A.

The potato cup D has been boiled which killed the cells and their plasma membranes. Hence, there is no selectively permeable membrane for osmosis to occur. As a result, water cannot gather inside 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 the type of cell division that is required for growth and repair of the body and meiosis is the type of cell division that is involved in the formation of gametes.

Solutions to All Activities of NCERT Class 9 Science Chapter 5 The Fundamental Unit of Life –

1. Complete Activity 5.1 (Page 49).

• Let us take a small piece from an onion bulb. With the help of a pair of forceps, we can peel off the skin (called epidermis) from the concave side (inner layer) of the onion. This layer can be put immediately in a watch-glass containing water. This will prevent the peel from getting folded or getting dry. What do we do with this peel?

• Let us take a glass slide, put a drop of water on it and transfer a small piece of the peel from the watch glass to the slide. Make sure that the peel is perfectly flat on the slide. A thin camel hair paintbrush might be necessary to help transfer the peel. Now we put a drop of safranin solution on this piece followed by a cover slip. Take care to avoid air bubbles while putting the cover slip with the help of a mounting needle. Ask your teacher for help. We have prepared a temporary mount of onion peel. We can observe this slide under low power followed by high powers of a compound microscope.

What do we observe as we look through the lens? Can we draw the structures that we are able to see through the microscope, on an observation sheet? Does it look like Fig. 5.2?We can try preparing temporary mounts of peels of onions of different sizes. What do we observe? Do we see similar structures or different structures?

Answer:

Solution to Activity 5.1

2. Complete Activity 5.2 (Page 50).

• We can try preparing temporary mounts of leaf peels, tip of roots of onion or even peels of onions of different sizes.

• After performing the above activity, let us see what the answers to the following questions would be:

(a) Do all cells look alike in terms of shape and size?

(b) Do all cells look alike in structure?

(c) Could we find differences among cells from different parts of a plant body?

(d) What similarities could we find?

Answer:

Solution to Activity 5.2

3. Complete Activity 5.3 (Page 52).

Osmosis with an egg

(a) Remove the shell of an egg by dissolving it in dilute hydrochloric acid. The shell is mostly calcium carbonate. A thin outer skin now encloses the egg. Put the egg in pure water and observe after 5 minutes. What do we observe?

(b) Place a similar de-shelled egg in a concentrated salt solution and observe for 5 minutes. The egg shrinks. Why?

Answer:

Solution to Activity 5.3

4. Complete Activity 5.4 (Page 52).

• Put dried raisins or apricots in plain water and leave them for some time. Then place them into a concentrated solution of sugar or salt.

Answer:

Solution to Activity 5.4

5. Complete Activity 5.5 (Page 53).

• Find out about electron microscopes from resources in the school library or through the internet. Discuss it with your teacher.

Answer:

Solution to Activity 5.5

6. Complete Activity 5.6 (Page 53).

• Mount the peel of a Rhoeo leaf in water on a slide and examine cells under the high power of a microscope. Note the small green granules, called chloroplasts. They contain a green substance called chlorophyll. Put a strong solution of sugar or salt on the mounted leaf on the slide. Wait for a minute and observe under a microscope. What do we see?

• Now place some Rhoeo leaves in boiling water for a few minutes. This kills the cells. Then mount one leaf on a slide and observe it under a microscope. Put a strong solution of sugar or salt on the mounted leaf on the slide. Wait for a minute and observe it again. What do we find? Did plasmolysis occur now?

Answer:

Solution to Activity 5.6

7. Complete Activity 5.7 (Page 53).

• Let us take a glass slide with a drop of water on it. Using an ice-cream spoon gently scrape the inside surface of the cheek. Does any material get stuck on the spoon? With the help of a needle we can transfer this material and spread it evenly on the glass slide kept ready for this. To colour the material we can put a drop of methylene blue solution on it. Now the material is ready for observation under microscope. Do not forget to put a cover-slip on it!

• What do we observe? What is the shape of the cells we see? Draw it on the observation sheet.

Was there a darkly coloured, spherical or oval, dot-like structure near the centre of each cell? This structure is called nucleus. Were there similar structures in onion peel cells?

Answer:

Solution to Activity 5.7

Extra Questions to Complement Solutions to NCERT Class 9 Science Chapter 5 The Fundamental Unit of Life –

Very Short Answer Type Questions:

1. Who discovered cells?
Answer:
Robert Hooke.

2. Cell theory was proposed by whom?
Answer:
Schleiden and Schwann.

3. Which scientist proposed that cells arise from pre-existing cells?
Answer:
Virchow.

4. Name two cells in the human body which are associated with reproduction.
Answer:
Ovum and sperm cell.

5. Name a selectively permeable membrane in the cell.
Answer:
Plasma membrane.

6. Give an example of osmosis in plants.
Answer:
Absorption of water by plants roots.

7. Which part of the nucleus carries hereditary information?
Answer:
DNA present inside chromosomes.

8. Give the general name of organisms in which nucleoid is present.
Answer:
Prokaryotes.

9. Name the cell organelle which forms an extended network with the endoplasmic reticulum.
Answer:
Golgi apparatus.

10. Name the scientist who won the Nobel Prize for their work on the structure of the nervous system.
Answer:
Camillo Golgi.

11. Name an organelle which is only present in plant cells?
Answer:
Plastids.

Multiple Choice Questions (MCQ):

1. Which cell in the human body is only present in females?

(A) Sperm
(B) Ovum
(C) Nerve cell
(D) Fat cell

Answer: (B) Ovum

2. Which of the following is not a single-celled organism?

(A) Amoeba
(B) Chlamydomonas
(C) Paramoecium
(D) Onion plant

Answer: (D) Onion plant

3. Which is suitable for absorption of water by the cell?

(A) Isotonic solution
(B) Hypotonic solution
(C) Hypertonic solution
(D) Saturated solution

Answer: (B) Hypotonic solution

Hypotonic solution has a higher water concentration than the cell. Therefore, the cell will gain water by osmosis.

4. Which of the following solutions cannot be used to stain cells?

(A) Iodine solution
(B) Safranin solution
(C) Methylene blue
(D) Dilute sulphuric acid

Answer: (D) Dilute sulphuric acid

5. We put iodine solution on a temporary mount of onion peel to stain it. Looking through the microscope, we observe that a region of the cell contains little or not stain. Name the region.

(A) Nucleus
(B) Cytoplasm
(C) Cell wall
(D) Cell membrane

Answer: (B) Cytoplasm

6. What is the chemical used in the technique called ‘black reaction’?

(A) Dilute silver nitrate
(B) Concentrated silver nitrate
(C) Nitric acid (concentrated)
(D) Nitric acid (dilute)

Answer: (A) Dilute silver nitrate

7. Which organelle is responsible for generating energy which is needed by the body to carry out essential activities?

(A) Golgi apparatus
(B) Lysosomes
(C) Mitochondria
(D) Vacoules

Answer: (C) Mitochondria

The energy required for various chemical activities needed for life is released by mitochondria in the form of ATP (Adenosine triphosphate) molecules.

Short Answer Type Questions:

1. All multi-cellular organisms come from a single cell. Explain.
Answer:
Cells divide by the process of cell division to produce more cells of their own kind. All cells thus originate from a single cell by the process of cell division.

2. Division of labour is seen within a single cell. Explain.
Answer:
Each cell has specific components known as cell organelles. Each organelle has its own specific function such as making new material, clearing up waste material, producing energy and so on. The organelles carry out their own specific functions and make the cell work as a whole. Thus, division of labour is seen within a single cell.

3. How do waste substances like CO₂ get excreted out from the cell?
Answer:
When CO₂ accumulates in high concentrations inside the cell, the concentration of CO₂ outside the cell becomes low as compared to that inside the cell. Due to the difference of concentration of CO₂ inside and outside a cell, CO₂ moves out of the cell, from a region of high concentration, to a region of low concentration outside the cell by the process of diffusion.

4. Water is unable to enter a cell resulting in dehydration of the cell. What could be the problem?
Answer:
It could be that the plasma membrane is damaged due to which osmosis cannot occur even though there is a higher concentration of water outside the cell.

5. Plant cells do not explode on absorbing a lot of water. Explain.
Answer:
As the plant cell absorbs water, it swells and exerts pressure on the cell wall. The cell wall exerts an equal and opposite pressure on the swollen cell. This prevents it from bursting.

6. What happens to chromatin when the cell is about to divide?
Answer:
The entangled mass of thread-like structures called chromatin gets organised into rod-shaped structures called chromosomes when the cell is about to divide.

7. What are the functions of the nucleus of the cell?
Answer:
Nucleus contains the hereditary material DNA and plays an important role in cellular reproduction. It also directs the chemical activities of the cell and determines the way the cell will develop and what form it will exhibit at maturity.

8. Give one difference between cytoplasm and protoplasm.
Answer:
Cytoplasm refers to the fluid-like substance that fills the interior of a cell, excluding the nucleus. Protoplasm encompasses all living components of the cell, including both the cytoplasm and the nucleus.

9. What enables lysosomes to act as the waste disposal mechanism of the cell?
Answer:
Lysosomes contain powerful digestive enzymes capable of breaking down all organic waste material into simpler substances.

10. Name the white coloured plastid in plant cells. Give its function.
Answer:
The white coloured plastid in plant cells is called leucoplast. Materials such as starch, oils and protein granules are stored in the leucoplast.

11. What is the primary function of a vacuole?
Answer:
The primary function of the vacuole is storage of amino acids, sugars, various organic acids and proteins.

Long Answer Type Questions:

1. What are the functions of the endoplasmic reticulum?
Answer:
The functions of the endoplasmic reticulum are as follows:

(i) The rough endoplasmic reticulum (RER) contains ribosomes which manufacture proteins.

(ii) The smooth endoplasmic reticulum (SER) helps in manufacture of fat molecules or lipids.

(iii) The ER forms a network which serves as channels for transport of materials such as proteins between various regions of the cytoplasm or between the cytoplasm and the nucleus.

(iv) The ER also provides a surface for carrying out the various biochemical activities of the cell.

(v) In the liver cells of vertebrates, SER plays a crucial role in detoxifying many poisons and drugs.

2. Give the differences between mitosis and meiosis.
Answer:
The differences between mitosis and meiosis are as follows:

Mitosis	Meiosis
(i) Cells divide for growth and repair of tissues in organisms.	(i) Cells divide to form gametes required for reproduction.
(ii) One division occurs.	(ii) Two consecutive divisions occur.
(iii) Mother cell divides to form two identical daughter cells.	(iii) When a cell divides by meiosis it produces four new daughter cells instead of just two.
(iv) Daughter cells have the same number of chromosomes as the mother cell.	(iv) Daughter cells only have half the number of chromosomes as the mother cell.

Fill in the Blanks:

(a) Purkinje in 1839 coined the term __________.

(b) __________ is a cell which changes shape.

(c) The plasma membrane is made up of organic molecules called _________ and _________.

(d) The plant cell was is composed of __________.

(e) The nucleus has a double layered covering called __________.

Answers:

(a) Purkinje in 1839 coined the term protoplasm.

(b) Amoeba is a cell which changes shape.

(c) The plasma membrane is made up of organic molecules called lipids and proteins.

(d) The plant cell was is composed of cellulose.

(e) The nucleus has a double layered covering called nuclear membrane.

Match and Pair:

Column A	Column B
(i) Fungi	(a) Unicellular
(ii) Bacteria	(b) Photosynthesis
(iii) Chlorophyll	(c) Multicellular
(iv) Cell wall	(d) Genes
(v) DNA	(e) Plant cells

Answers:

Column A	Column B
(i) Fungi	(c) Multicellular
(ii) Bacteria	(a) Unicellular
(iii) Chlorophyll	(b) Photosynthesis
(iv) Cell wall	(e) Plant cells
(v) DNA	(d) Genes

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