NCERT solutions Class 9 Science Chapter 5 The Fundamental Unit Of Life

NCERT solutions Class 9 Science Chapter 5 The Fundamental Unit Of Life (All in text and Exercise Questions solved) updated

Exercise-5.1 Page: 59

1. Who discovered cells, and how?

Solution:

in 1665, Robert Hooke discovered cells while examining a thin slice of cork through a self-designed microscope. He observed that the cork resembled the structure of a honeycomb consisting of numerous tiny compartments. The minuscule boxes are referred to as cells.

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

Solution:

Cells form the structure of an entity. A group of cells form a tissue, further an organ and ultimately an organ system. They perform fundamental functions and life processes such as respiration, digestion, excretion etc in both unicellular and multicellular entities. They perform all the activities independently. Hence, cells are referred to as structural and fundamental units of life.

Exercise-5.2.1 Page: 61

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

Solution:

CO₂ moves by diffusion – These cellular waste accumulates in high concentrations in the cell, whereas the concentration of CO₂ in the external surroundings is comparatively lower. This difference in the concentration level inside and out of the cell causes the CO₂ to diffuse from a region of higher(within the cell) to a lower concentration.

H₂O diffuses by osmosis through the cell membrane. It moves from a region of higher concentration to a lower concentrated region through a selectively permeable membrane until equilibrium is reached.

4. Why is the plasma membrane called a selectively permeable membrane?

Solution:

The plasma membrane is called as a selectively permeable membrane as it permits the movement of only a certain molecules in and out of the cells. Not all molecules are free to diffuse.

Exercise-5.2.2-5.2.4 Page: 63

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

Solution:

Exercise-5.2.5 Page: 65

6. Can you name the two organelles we have studied that contain their own genetic material?

Solution:

The two organelles which have their own genetic material are:

1. Mitochondria

2. Plastids

7. If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?

Solution:

In the event of any damage to cells and when revival of cells is not possible, Lysosomes burst and enzymes digest such cells. This is why lysosomes are often referred to as ‘suicide bags’.

8. Why are lysosomes known as suicide bags?

Solution:

When there is damage to the cell and when revival is not possible, lysosomes may burst, and the enzymes digest their own cell. Consequently, lysosomes are known as suicide bags.

9. Where are proteins synthesised inside the cell?

Solution:

Protein synthesis in cells takes place in ribosomes. Hence, ribosomes are also referred to as protein factories. Ribosomes are particles that are found attached to the rough endoplasmic reticulum.

Exercise Page: 67

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

Solution:

The following table depicts the differences between plant cells and animal cells.

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

Solution:

The following are the differences between prokaryotic and eukaryotic cells.

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

Solution:

If plasma membrane ruptures or breaks down then molecules of some substances will freely move in and out of the cells. As plasma membrane acts as a mechanical barrier, exchange of material from its surroundings through osmosis or diffusion in a cell won’t take place. Consequently, the cell would die due to the disappearance of the protoplasmic material.

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

Solution:

The Golgi apparatus consists of stacks of membrane-bound vesicles whose functions are as follows:

• storage of substances
• packaging of substances
• manufacture of substances

Without the golgi apparatus, the cells will be disabled from packing and dispatching materials that were produced by the cells. The golgi apparatus is also involved in the formation of cells. Hence, in the absence of golgi apparatus, cells will not be produced.

5. Which organelle is known as the powerhouse of the cell? Why?

Solution:

Mitochondria are known as the powerhouse of the cell. It is because it releases the energy required for different activities of life. Mitochondria releases energy in the form of ATP(Adenosine triphosphate) molecules, essential for numerous chemical activities of life. Hence ATP is often referred to as ‘energy currency of the cell’.

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

Solution:

Lipids and proteins are synthesised in the ER [Endoplasmic Reticulum].

How does an Amoeba obtain its food?

Solution:

Through the process of endocytosis, an Amoeba obtains its food. As its cell membrane is flexible enough, food particles are engulfed forming a food vacuole girdling it which is assisted by the pseudopodia. Amoeba secretes digestive enzymes to bring about digestion of the engulfed particle once food is trapped.

What is osmosis?

Solution:

The process of movement of a water molecule from a region of higher concentration to a region of lower concentration through a semipermeable membrane is known as osmosis.

9. 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.

Solution:

(i) Water accumulates in the hollowed portions of B and C as a difference in the water concentration

is observed. Thereby, endosmosis occurs as the cells act as a semipermeable membrane.

(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 its

own 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 no

existence 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?

Solution:

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.

PRACTICAL BASED 2 marks QUESTIONS

Question 1.
Three students ‘A’, ‘B’ and ‘C were given five raisins each of equal mass. The raisins were soaked in distilled water at room temperature. ‘A’ soaked the raisins for 10 minutes, ‘B’ for overnight and ‘C for 60 minutes. They calculated the percentage of water absorbed by raisins. Now answer the following question :
(a) Name the student whose raisins will show the maximum percentage of water absorbed.
(b) Name the student whose raisins will show the minimum percentage of water absorbed. (CCE 2013)
Answer:
(a) Maximum Percentage ofWater Absorbed. Raisins of ‘B’ student.
(b) Minimum Percentage of Water Absorbed. Raisins of ‘A’ student.

Question 2.
A teacher soaked 10 g raisins in 35 ml of distilled water in a beaker A and a similar amount in beaker B. She maintained the temperature of beaker A at 20°C and beaker B at 40°C. After an hour, compare the percentage of water absorbed by raisins in beakers A and B. (CCE 2013, 2014)
Answer:
More water was absorbed in beaker B where temperature was 40°C. Permeability of cell membrane increases from 0°C to 40°C beyond which dénaturation sets in.

Question 3.
5g of raisins were placed in distilled water for 24 hours. The mass of water soaked raisins was found to be 7g. Calculate the percentage of water absorbed by raisins. (CCE 2013)
Answer:

Question 4.
A student puts five raisins in two beakers A and B. Beaker A contained 50 ml of distilled water at room temperature and beaker B had 50 ml of ice cold water. After some time what will be the observation of the student ? State reason for this observation.
(CCE 2013, 2015)
Answer:
Raisins in beaker A swell up. Those of beaker B do not. Low temperature of B water reduced membrane permeability as well as kinetic energy of water for osmosis.

Question 5.
A student recorded a mass of dry raisins as 6.0 g and mass of raisins after soaking them in water for about four hours as 10.5 g. Calculate the percentage of water absorbed by raisins. (CCE 2013)
Answer:

Question 6.
Write the mathematic equation used to determine the mass percentage of water absorbed by raisins.
Answer:
If initial weight is W₁ and final weight after soaking is W₂

Question 7.
Ravi took weight of five dry raisins and five swollen raisins of approximately equal size. If the weight of dry raisins was 7 g and weight of swollen raisins is ‘X’ g, then
(i) Write the formula to calculate the percentage of water absorbed by the raisins and
(ii) If the value of ‘X’ is 10.5 g, then what will be the percentage of water absorbed by the raisins ? (CCE 2014)
Answer:

Question 8.
Write four main steps of the method involved in an experiment “On determination of the percentage of water absorbed by raisins in the laboratory”. (CCE 2014)
Answer:
(i) Selection of raisins with intact stalks and their weight as W₁
(ii) Soaking the raisins in water at room temperature for at least 1-2 hours
(iii) Taking out wet raisins, wiping out water with blotting paper and their final weight as W₂

Question 9.
In the experiment of determining the percentage of water absorbed by raisins, two students Samya and Zahira used the following formula respectively

Which student used wrong formula ? What are W₁ and W₂ in the correct formula ? (CCE 2014)
Answer:
Student (i) used the wrong formula.
W₁ is initial weight of dry raisins. W₂ is final weight of swollen raisins.

Question 10.
(a) A student recorded the mass of dry raisins as 4.0 g and mass of raisins after soaking as 7.0 g. Calculate the percentage of water absorbed by raisins. (CCE 2014, 2016)
(b) Mention one application of the phenomenon of osmosis in plants. (CCE 2016)
Answer:

(b) Application of Osmosis. Turgidity of cells, root absorption.

Question 11.
(a) Ram while doing an experiment to find out the percentage of water absorbed by raisins measured the mass of dry raisins as 50 g. He soaked the raisins in water for four hours and again measured the mass as 80 g. Calculate the percentage of water absorbed by the raisins.
(b) He then placed raisins in concentrated salt solution. What will he observe ? (CCE 2015)
Answer:

(b) After Placing in Concentrated Salt Solution. Raisins will lose water and shrink to the maximum.

Question 12.
A student recorded the mass of dry raisins as 6.0 g and mass of raisins after soaking them in water for about four hours as 10.5 g. Calculate the percentage of water absorbed by raisins. Why do raisins get swelled up ? (CCE 2015)
Answer:

The raisins swell up due to absorption of water through osmosis.

Question 13.
A student recorded the following observations in an experiment for finding the percentage of water absorbed by raisins.
(i) Mass of water taken in beaker – 50 g
(ii) Mass of dry raisins before soaking water – 20 g
(iii) Mass of raisins after soaking water – 30 g.
(iv) Mass of remaining water in beaker after experiment – 40 g
Calculate the percentage of water absorbed by raisins. ( CCE 2015)
Answer:

Question 14.
If ‘X’ is the initial mass of the raisins and ‘Y’ is the final mass of raisins after soaking in water, calculate the percentage of water absorbed by raisins. Name the process due to which raisins absorb water. (CBSE 2015, 2016)
Answer:

Question 15.
A group of students selected 10 raisins with stalks and weighed them using digital balance. Then, they soaked them for a few hours. The weight of the swollen raisins was 9.2 g which was 4.6 g more than weight of dry raisins. Calculate the water imbibed by the raisins. ( CCE 2015)
Answer:

Question 16.
In the experiment “To determine the mass percentage of water imbibed by raisins”, the raisins absorb water when kept in water for 5-6 hours. Why does water absorption take place ? What is the phenomenon called ? (CCE 2015, 2016)
Answer:
Water moves into raisins due to endosmosis. Endosmosis is entry of water into a system, cell or organ due to presence of hypertonic solution in it and its separation from pure water or dilute solution by a semipermeable membrance. Skin of raisins function as semipermeable membrane. There is high concentration of sugar inside them. Therefore, external water passes into raisins and cause their swelling.

Question 17.
Before placing the raisins in water, the raisins weighed 10 g. The raisins were taken out of water, wiped well and then the weight was found to be 12.5 g. Determine the percentage of water absorbed by raisins. Define the process due to which raisins absorb water. (CCE 2016)
Answer:

Osmosis: Osmosis is the diffusion of water or solvent across a semipermeable membrane (which does not allow passage of solutes) from a region of its higher concentration to the region of its lower concentration. Plasma membrane functions as semipermeable membrane. There will be osmotic entry of water into cell if the external solution is pure water or dilute as compared to cell sap.

Question 18.
(a) In the experiment to determine the percentage of water absorbed by raisins, the raisins are wiped before weighing. Why ?
(b) While preparing a temporary stained mount of onion peel, Veena added a drop of glycerine. Why ? ( CCE 2016)
Answer:
(a) To remove unabsorbed water sticking to the surface of raisins.
(b) To prevent drying of onion peel.

Question 19.
A student took x gram water in a beaker and dipped p gram raisins in it. After keeping raisins in water for 2 hours, he measured the mass of soaked raisins as q grams. He also measured the mass of water left in the beaker which was y grams. On the
Answer:

Solutions ncert Class 9 Science Chapter 5 Very Short Answer Type Questions

Question 1. What are plastids? Name the different types of plastids found in a plant cell.
Answer: Plastids are organelles found only in plants. They are:
(a) Chloroplast-Containing chlorophyll
(b) Chromoplast-Containing carotenoids and xanthophyll (coloured plastids)
(c) Leucoplast-Wllite or colourless plastids

Question 2. What is plasma membrane made up of?
Answer: Plasma membrane is made up of proteins and lipids.

Question 3. What did Robert Hooke observed first in cork cell?
Answer: Robert Hooke observed that cork consists of box like compartments which formed a honeycomb structure.

Question 4. Name the autonomous organelles in the cell.
Answer. Chloroplasts and mitochondria are the autonomous organelles in the cells.

Question.5. What does protoplasm refer to?
Answer: Protoplasm refer to cytoplasm and nucleus.

Question 6. Name two cells which keep changing their shape.
Answer: Amoeba and white blood cells.

Question 7. Name the smallest cell and the longest cell in human body.
Answer: The smallest cell is the red blood cell or sperm cell in male. Longest cell is the nerve cell.

Question 8. Name 3 features seen/present in almost every cell.
Answer: Plasma membrane, nucleus and cytoplasm.

Question 9.What is diffusion?
Answer: When gases like C0₂, 0₂, move across the cell membrane, this process is called diffusion.

Question 10.What is osmosis? This takes place from high water concentration to low water concentration.
Answer: The movement of water molecules through a selectively permeable membrane is called osmosis. This takes place from high water concentration to low water concentration.

Question 11. What is the full form of DNA?
Answer: DNA —> Deoxyribo Nucleic Acid.

Question 12. What is the Junction of chromosome?
Answer: Chromosomes contain information for the inheritance of features from parents to next generation in the form of DNA molecules.

Question 13. Name the organelles present in liver of animals for detoxifying many poisons and drugs. 
Answer: In the liver of animal cells smooth endoplasmic reticulum helps in detoxifying many poisons and drugs.

Question 14. What is the energy currency of the cell?
Answer: ATP—Adenosine Triphosphate.

Question 15. What is the function of ribosome?
Answer: Ribosomes help in protein synthesis.

Question 16. Where are genes located in the cell?
Answer: Genes are located in the chromosomes in the nucleus of the cell.

Question 17. Name the cell organelles that helps in packaging?
Answer: Golgi apparatus.

Question 18. Name the cell organelle which helps in the transportation of material.
Answer: Endoplasmic reticulum.

Question 19. Name the cell organelle due to which leaves, flowers and fruits get their colour.
Answer: Chromoplast.

Question 20. Name the cell organelle which helps in the formation of lysosome.
Answer: Golgi apparatus.

Question 21. Name the cleansing organelle in the cell.
Answer: Lysosomes.

Question 22. Name two cells with cell wall.
Answer: Onion cell (plant cell) and fungi.

Question 23. Why does mitochondria have largely folded inner membrane?
Answer: Mitochondria is the site for cellular respiration and provides energy to the cell. The largely folded inner membrane provides the increased surface area for ATP-generating chemical reactions.

Question 24. Which organelle makes the digestive enzyme of lysosome?
Answer: Rough endoplasmic reticulum makes the digestive enzyme of lysosomes.

Question 25. What are cisterns?
Answer: The golgi bodies consist Of a system of membrane-bound vesicles arranged in stacks called cisterns.

NCERT Solutions For Class 9 Science Chapter 5 Short Answer Type Questions

Question 1. State two conditions required for osmosis.
Answer: (i) The difference in the concentration of water, one should have higher concentration than the other.
(ii) Semi-permeable membrane is also required through which water will flow.

Question 2. What is plasmolysis?
Answer: When a living plant cell loses water through osmosis there is shrinkage or contraction of the contents of the cell away from the cell wall. This phenomenon is known as plasmolysis.

Question 3. How does fungi and bacteria can withstand much greater changes in the surrounding medium than animal cells?
Answer: The cell wall present in fungi and bacteria permits these cells to withstand very dilute external medium without bursting.
The cells take up water by osmosis, swells, and builds the pressure against the cell wall. The wall exerts an equal pressure against the swollen cell. It is because of the cell wall, such cells can withstand much greater changes in the surrounding medium than animal cells.

Question 4. Give the function of nuclear membrane.
Answer: The nuclear membrane present as outer covering in the nucleus allows the transfer of material inside and out of the nucleus to cytoplasm.

Question 5. Name the cell-organelles that have their own DNA and ribosomes.
Answer: The cell organelles with their own DNA and ribosomes are mitochondria and plastids.

Question 6. State the difference between smooth endoplasmic reticulum and rough endoplasmic reticulum.
Answer:

Question 7. What is endocytosis?
Answer: The cell membranes flexibility allows the cell engulf in food and other material from its external environment. This process is known as endocytosis. E.g., Amoeba acquires its food through such processes.

Question 8. What is the function of vacuoles?
Answer: Vacuoles are storage sacs for solid or liquid content. In plant cells it provides turgidity and rigidity to the cell. In single-celled organisms vacuoles store food, e.g., Amoeba.

Question 9. When we put raisins in water, why do they swell?
Answer: Raisins are dry with less water inside, when they are kept in water, osmosis takes place, water flows through the cell wall, cell membrane of the raisins and therefore it swells.

Question 10. Why are lysosomes called suicidal bags?
Answer: Lysosomes contain digestive enzymes in it and helps in the cleaning of cell by digesting any foreign materials entering the cell, such as bacteria, food and old cell organelles.
When the lysosomes burst, the digestive enzyme digest its own cell. Hence it is called as suicidal bag.

Question 11. What is nucleoid?
Answer: The nuclear region in some cells are poorly defined due to the absence of a nuclear membrane, it contains only nucleic acid. This undefined nuclear region with nucleic acid in it is called nucleoid.

Question 12. What is the role, of cell organelles in the cell?
Answer: Each kind of cell organelles performs a specific function such as making new material, clearing of the waste, transporting material, etc.

Question 13. Label the figure and answer the questions:
(i) A – It is the packaging organelle
(ii) B – Provides energy
(iii) C – helps in the transport of material
(iv) D – Carries the information.

Answer. (i) A – Golgi body (ii) B – Mitochondria
(iii) C – Endoplasmic reticulum (iv) D – Nucleus

Question 14. What is the function of nucleus in a cell?
Answer: The nucleus plays a very important role in the reproduction of cells. It also helps the single cell to divide and form two new daughter cells.
It plays an important role in determining how the cell will develop and what form it will exhibit at maturity, by directing the chemical activities of the cell.

Question 15. What is the Junction of plastids?
Answer: Plastids are present only in plant cells. There are two types of plastids chromoplasts (coloured plastids) and leucoplasts (white or colourless)
Chromoplast—Consists of coloured pigments and gives different colours to flowers, fruits and leaves. The green colour pigment present in leaf is called chlorophyll which helps in the photosynthesis and a plastid with chlorophyll is called chloroplast.
Leucoplast—It stores starch, oil and protein granules in it.

Question 16. Do vacuoles store some material? If yes, name them.
Answer: Yes, vacuoles also store some important substances required in life of the plant cell. These are amino acids, sugars, various organic acids and some proteins. In some unicellular organisms, e.g. Amoeba, vacuoles also store food.

Question 17. Explain the structure and function of Golgi bodies.
Answer: Structures: Golgi bodies consist of a system of membrane-bound vesicles arranged in stacks parallel to each other called cisterns. These membranes have connections with the membrane of endoplasmic reticulum (ER).
Functions:
(1) The material synthesised near the ER is packaged and dispatched to various target inside and outside the cell through Golgi apparatus.
(2) It also stores, modifies and helps in the packaging of products in vesicles.
(3) In some cases, complex sugars may be made from simple sugars in it.
(4) It also helps in the formation of lysosomes.

Question 18. What are ribosomes? Where are they located in the cell? What is their function?
Answer: Ribosomes are spherical organelles present in the cell which are either freely distributed in the cytoplasm or may be attached to the endoplasmic reticulum.
It consists of ribosomal RNA (Ribonucleic acid) and proteins.
Functions of Ribosomes: It helps in the synthesis of proteins.

Question 19. What is the difference in chromatin, chromosomes and gene?
Answer: (1) Chromatin: It is a fine network of thread-like structure made up of DNA or RNA. It gets condense to form chromosomes.
(2) Chromosome: The chromosomes are made from chromatin material and are located iri the cell.
(3) Genes are found in chromosomes.

Question 20. Why do plant cells have more in number and big-sized vacuoles as compared to the animal cells?
Answer: Plant cells attain turgidity and rigidity due to the more number of vacuoles as well as large-sized vacuoles help the plant cells to withstand the wear and tear, external environmental conditions.
They also help in the storage of essential material required by plants for their growth like amino acids, sugar and various organic substances.

Question 21. Explain the following terms:
(a) Plasma membrane
(b) Cytoplasm
(c) Nucleus.
Answer: (a) Plasma membrane: It is a thin membrane which controls the passage of materials in and out of the cell. It is also called as selectively permeable membrane. It makes the outer boundary of the cell and is made up of lipo-protein,
(b) Cytoplasm: It is transparent jelly-like thick substance present in the cell. It makes the ground of the cell in which all the cell organelles are suspended.
(c) Nucleus: It is a double-layered membrane structure which contains chromosomes required for the inheritance of characteristics from one generation to the other.

Question 22. What is membrane biogenesis?
Answer: The endoplasmic reticulum helps in the manufacture of proteins and fat molecules or lipids which are important for the cell function. These proteins and lipids help in the building of the cell membrane. This process is known as membrane biogenesis.

Question 23. Which organelle is known as powerhouse of the cell?
Answer: Mitochondria is known as powerhouse of the cell because they store energy in the form of ATP. [Adenosine Triphosphate]

Question 24. What are genes?
Answer: Gene is a segment of DNA. They are located on chromosomes in linear fashions. One gene may perform one or more function. Genes are carrier of genetic codes.