NCERT Solutions for Class 9 Science Chapter 5 Fundamental Unit of Life provides detailed answers for all in-text and exercise Questions. These solutions contain an in-depth explanation of each topic involved in the chapter. All these solutions are prepared by expert teachers and updated for the current academic session.
NCERT Solutions for Class 9 Science Chapter 5 Fundamental Unit of Life Pure help students to understand the fundamental concepts given in class 9 Science textbook. We have prepared the answers to all the questions in an easy and well-structured manner. It helps students to grasp the chapter easily.
Class 9 Science Fundamental Unit of Life Intext Questions (Solved)
Intext Questions (PAGE NO. 51)
Question 1: Who discovered cells and how?
Answer: Cells were discovered in 1665 by an English Botanist, Robert Hooke. He used a primitive microscope to observe a thin slice of cork. When he observed the cork under the microscope, Hooke saw small, box-like structures that looked like tiny rooms, so he called them “cells.” These were actually the cell walls of dead plant cells in the cork.
Question 2: Why is the cell called the structural and functional unit of life?
Answer: Cells are called the structural and functional unit of life because they are the basic building blocks that form the structure of all living organisms, and they are capable of performing all the necessary functions for life. Each cell functions independently, carrying out activities like taking in nutrients, converting them into energy, and reproducing. This means that cells not only create the physical structure of organisms but also keep them alive and functioning.
PAGE NO. 53
Question 1: How do substances like CO2 and water move in and out of the cell? Discuss.
Answer: The cell membrane is selectively permeable and regulates the movement of substances in and out of the cell.
Movement of CO2: CO2 is produced during cellular respiration. Therefore, it is present in high concentrations inside the cell. This CO2 must be excreted out of the cell. In the cell’s external environment, the concentration of CO2 is low as compared to that inside the cell. Therefore, according to the principle of diffusion, CO2 moves from a region of higher concentration (inside the cell) towards a region of lower concentration (outside the cell). Similarly, O2 enters the cell by the process of diffusion when the concentration of O2 inside the cell is low as compared to its surroundings.
Movement of water: Water moves from a region of high concentration to a region of low concentration through the plasma membrane. The plasma membrane acts as a semi-permeable membrane, and this movement of water is known as osmosis. However, the movement of water across the plasma membrane of the cell is affected by the amount of substance dissolved in water.
Question 2: Why is the plasma membrane called a selectively permeable membrane?
Answer: The plasma membrane is called a selectively permeable membrane because it controls and selectively allows certain substances to pass in and out of the cell, while blocking other substances, like certain ions and large molecules.
PAGE NO. 55
Question 1: Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.
| Prokaryotic Cell | Eukaryotic Cell |
| 1. Size: generally small (1-10μm) | 1. Size: generally large (5-100μm) |
| 2. Nuclear region: ______________________ and known as ___________________ | 2. Nuclear region: well defined and surround 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 (1-10μm) | 1. Size: generally large (5-100μm) |
| 2. Nuclear region: poorly defined because of absence of nuclear membrane and known as nucleoid | 2. Nuclear region: well defined and surround by a nuclear membrane and known as nucleoid. |
| 3. Chromosome: Single | 3. More than one chromosome |
| 4. Membrane-bound cell organelles absent | 4. Membrane-bound cell organelles such as Mitochondria, plastids, etc., are present. |
PAGE NO. 57
Question 1: Can you name the two organelles we have studied that contain their own genetic material?
Answer: Mitochondria and plastids are the two organelles that contain their own genetic material. Both these organelles have their own DNA and ribosomes.
Question 2: If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?
Answer: Cell is the smallest unit of life, which is capable of all living functions. If the organisation of a cell is destroyed due to some physical or chemical influence, then the ability of the cell to perform all living functions such as respiration, nutrition, excretion, etc. would be affected.
Question 3: Why are lysosomes known as suicide bags?
Answer: Lysosomes are membrane-bound vesicular structures that contain powerful digestive enzymes. These enzymes are capable of breaking down any foreign food particles or microbes entering the cell. Sometimes, lysosomes can cause self-destruction of a cell by releasing these digestive enzymes within the cells. Hence, they are also known as ‘suicidal bags’.
Question 4: Where are proteins synthesized inside the cell?
Answer: Ribosomes are the site for protein synthesis. Ribosomes are very small structures found either in a free state, suspended in the cytoplasm, or attached to the surface of the endoplasmic reticulum. They are composed of ribonucleic acids and proteins.
Class 9 Science Fundamental Unit of Life Exercise Questions (Solved)
Question 1: Make a comparison to write down ways in which plant cells are different from animal cells.
Answer: The cells of animals and plants have the following differences:
| Animal Cell | Plant Cell |
| 1. Animal cells are generally small in size. | 1. Plant cells are larger than animal cells. |
| 2. Cell wall is absent. | 2. The plasma membrane of plant cells is surrounded by a rigid cell wall of cellulose. |
| 3. Except the protozoan Euglena, no animal cell possesses plastids. | 3. Plastids are present. |
| 4. Vacuoles in animal cells are many, small and temporary. | 4. Most mature plant cells have a permanent and large central sap vacuole. |
| 5. Animal cells have a single highly complex and prominent Golgi apparatus. | 5. Plant cells have many simpler units of Golgi apparatus, called dictyosomes. |
| 6. Animal cells have centrosome and centrioles. | 6. Plant cells lack centrosome and centrioles. |
Question 2: How is a prokaryotic cell different from a eukaryotic cell?
Answer: Difference between prokaryotic cell and eukaryotic cell:
| Prokaryotic Cell | Eukaryotic Cell |
| 1. Cell size is generally small (1 – 10 µm). | 1. Cell is generally large (5 – 100 µm). |
| 2. Nuclear region is called nucleoid and is not surrounded by a nuclear membrane. | 2. Nuclear material is surrounded by a nuclear membrane. . |
| 3. Only a single chromosome is present. | 3. More than one chromosome is present. |
| 4. Nucleolus is absent. | 4. Nucleolus is present. |
| 5. Membrane bound cell organelles are absent. | 5. Membrane bound cell organelles. |
| 6. Cell division by fission or budding (no mitosis). | 6. Cell division mitotic or meiotic. |
Question 3: What would happen if the plasma membrane ruptures or breaks down?
Answer: If the plasma membrane of a cell ruptures or breaks down, the cell would likely die. This is because the plasma membrane controls what goes in and out of the cell. If it’s damaged, the cell can’t control this anymore, which means it can’t keep the right balance of nutrients and might let harmful substances in. The cell wouldn’t be able to function properly and would eventually break apart.
Question 4: What would happen to the life of a cell if there is no Golgi apparatus?
Answer: The absence of the Golgi apparatus would lead to significant problems in protein and lipid handling, secretion of important substances, cell maintenance and growth, and possibly the cell’s immune functions and waste removal. This would greatly impact the cell’s health and its ability to perform necessary functions.
Question 5: Which organelle is known as the powerhouse of the cell? Why?
Answer: Mitochondria are known as the powerhouse of the cell because they produce most of the cell’s supply of adenosine triphosphate (ATP), the energy currency of the cell. This process is known as cellular respiration. Mitochondria take nutrients, break them down, and create ATP, providing energy for the cell to carry out various functions. This crucial role in energy production is why mitochondria are often referred to as the powerhouse of the cell.
Question 6: Where do the lipids and proteins constituting the cell membrane get synthesised?
Answer: Rough Endoplasmic Reticulum (RER) – synthesizes proteins constituting cell membrane.
Smooth Endoplasmic Reticulum (SER) – synthesizes lipids constituting cell membrane.
Question 7: How does Amoeba obtain its food?
Answer: Amoeba obtains its food through a process called phagocytosis. The cell membrane of amoeba is projected into numerous finger-like outgrowths; called pseudopodia. Amoeba surrounds a food particle by pseudopodia and makes a food vacuole; after engulfing the food.
Question 8: What is osmosis?
Answer: Osmosis is the movement of water molecules through a semi-permeable membrane from a region of lower solute concentration to a region of higher solute concentration
Question 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.
Experimental set up
(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 semi-permeable membrane is required, which is disrupted in this case. Therefore, osmosis will not occur. Hence, water does not enter the boiled potato cup.
Question 10: Which type of cell division is required for growth and repair of body and which type is involved in formation of gametes?
Answer: 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.