Class 9 Science Chapter 5 The Fundamental Unit of Life
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The Fundamental Unit of Life
Answers to Questions Within the Lesson(1)
1. Who discovered the cell and how?
Ans: The cell was discovered by Robert Hooke. He examined a thin slice of cork with a self-designed microscope and observed small compartments like a honeycomb. These compartments were called cells.
2. Why is the cell called the basic unit of structure and function?
Ans: The cell is the structural and functional unit of life. All living organisms are made up of cells. Due to the organized structure of cells, various biological functions are carried out efficiently. The coordination of these functions enables a living organism to exhibit its own characteristics. Therefore, the cell is called the basic unit of structure and function.
Answers to Questions Within the Lesson(2)
1. Discuss how substances like CO2 and water move in and out of the cell.
Ans: Molecules of all substances possess kinetic energy. Substances move from a region of higher concentration to a region of lower concentration. This movement can occur in any medium and is called diffusion. Through this process, waste substances like CO2 move out of the cell. Similarly, through osmosis, water enters the cell.
2. Why is the cell membrane called a selectively permeable membrane?
Ans: The cell membrane allows only certain substances to pass through it while restricting others from entering the cell. Therefore, it is called a selectively permeable membrane.
Answers to Questions Within the Lesson(3)
1. Show the differences between prokaryotic and eukaryotic cells and complete the table.
Ans: Show the differences between prokaryotic and eukaryotic cells and complete the table.
Answers to Questions Within the Lesson(4)
1. Name two cell organelles which contain genetic material.
Ans: Plastids and mitochondria.
2. What will happen if the organization of a cell is damaged due to physical and chemical factors?
Ans: Proper organization of the cell is essential for carrying out various biological functions in a living body. Through this organization, functions such as nutrition, respiration, reproduction, and growth are efficiently performed. If the cell organization is damaged, these biological functions will be disrupted.
3. Why are lysosomes called the “suicide bags” of the cell?
Ans: When there is any disturbance in cellular metabolism or when cells, like those of mucus membrane or skin die, lysosomes release digestive enzymes and destroy the cell itself. Therefore, lysosomes are called “suicide bags.”
4. Where does protein synthesis occur in the cell?
Ans: Protein synthesis occurs in ribosomes.
Exercise: Questions and Answers
1. Compare plant cells and animal cells, and mention the aspects in which a plant cell differs from an animal cell.
Ans: Plant cells and animal cells comparison:“Both plant and animal cells are eukaryotic and have a nucleus, cytoplasm, and cell membrane. A plant cell differs from an animal cell by having a cell wall, chloroplasts for photosynthesis, and a large central vacuole, which give it a fixed shape. Animal cells do not have these structures and are usually more flexible in shape.
2. Mention the aspects in which prokaryotic cells differ from eukaryotic cells.
Ans: Prokaryotic cells are smaller and simpler, without a true nucleus or membrane-bound organelles, and their DNA is present in a nucleoid region. Eukaryotic cells are larger and more complex, with a true nucleus and membrane-bound organelles, and their DNA is organized inside the nucleus.
3. What will happen if the cell membrane of a cell bursts?
Ans: The entire protoplasmic content of a cell is covered by a living, thin, and semipermeable membrane. If this membrane bursts, the protoplasmic materials will spread into the surrounding medium.
4. If a cell does not have a Golgi apparatus, what effect will it have on the life of the cell?
Ans: The Golgi apparatus performs cellular secretion functions such as secreting protease, lipase, etc., and helps in various biological processes. It also helps in the formation of the cell wall after cell division and in the formation of lysosomes and vacuoles. Therefore, if the Golgi apparatus is absent, these functions and the synthesis of substances will stop.
5. Which cell organelle is called the powerhouse of the cell and why?
Ans: Mitochondria are called the powerhouse of the cell. Mitochondria are the center of cellular respiration in living cells. They release enzymes and, through respiration, release the energy stored in carbohydrates, fats, and proteins. This energy converts ADP molecules into ATP molecules, which are stored in the mitochondria and used as needed. Hence, mitochondria are called the powerhouse of the cell.
6. Where are the lipids and proteins required for the formation of the cell membrane synthesized?
Ans: Proteins are synthesized in ribosomes and lipids are synthesized in the endoplasmic reticulum.
7. How does Amoeba take in food?
Ans: Amoeba lives by feeding on microscopic plant-like organisms. It forms pseudopodia to engulf food and creates a food vacuole. After ingestion, the food is completely enclosed within the vacuole. It then turns into a food vacuole where digestive juices act on the enclosed food and complete the digestion process.
8. What is osmosis?
Ans: Osmosis is the process by which water diffuses through a semipermeable membrane.
9. Perform the following experiment to observe osmosis. Take four peeled potato pieces and scoop out the middle of each piece to make them like small cups. One of these pieces should be taken from a boiled potato. Label them as (A, B, C, D).
(A) Keep cup “A” empty.
(B) Put one teaspoon of sugar in cup ‘B’.
(C) Put one teaspoon of salt in cup ‘C’.
(D) In cup “D” (made from boiled potato), also add one teaspoon of sugar. Keep all of them undisturbed for about two hours and then observe and answer the following questions.
(i) Why did the empty portions of cups ‘B’ and ‘C’ get filled with water?
(ii) Why is cup “A” necessary for this experiment?
(iii) Why did the empty portions of cups ‘A’ and ‘D’ not get filled with water? Explain the reason.
Ans: (i) The reason water appeared in cups ‘B’ and ‘C’ is that sugar and salt were present in them, and through the process of osmosis, water entered into the cups and filled them.
(ii) Cup ‘A’ is required in this experiment because it acts as a control experiment.
(iii) Cups ‘A and ‘D’ did not get filled with water. This is because ‘A’ is the control setup and ‘D’ is made from a boiled potato. The cell membrane of the boiled potato is dead, and osmosis does not occur in dead cells.
Additional Questions & Answers
1. What is a cell organelle? Mention one function of it.
Ans: Inside a cell, there are some structures that perform specific functions. These are called cell organelles. Function of cell organelles: Production of new substances in the cell and removal of waste materials from the cell.
2. How many components does a cell have and what are they?
Ans: A cell has three components: cell membrane, nucleus, and cytoplasm.
3. What is the cell membrane?
Ans: The cell membrane is a living, thin, and porous covering made of proteins and lipids. In animal cells, the cell membrane forms the outer boundary of the cell.
4. What is the cell membrane made of?
Ans: The cell membrane is made up of biomolecules called lipids and proteins.
5. What is cytoplasm?
Ans: The jelly-like substances present between the nucleus are called cytoplasm.
6. What is the cell wall? What is it made of?
Ans: In plant cells, apart from the cell membrane, there is a thick outer covering called the cell wall. The cell wall is made of cellulose.
7. What is plasmolysis?
Ans: When water leaves a plant cell through osmosis, the cell contents shrink and move away from the cell membrane. This phenomenon is called plasmolysis.
8. What is the nuclear membrane? Mention one function of it.
Ans: The double-layered covering surrounding the nucleus is called the nuclear membrane.
Function: It allows materials to pass out from the nucleus.
9. What is the full form of DNA?
Ans: DNA = Deoxyribo Nucleic Acid
10. What is a gene?
Ans: A gene is the unit of heredity in living organisms. It transfers characteristics from parents to offspring.
11. What are eukaryotic and prokaryotic cells? Give examples.
Ans: Cells of organisms that have a well-defined and organized nucleus are called eukaryotic cells. Example: humans, horses, etc. Cells of organisms that do not have a nuclear membrane or have an undefined nucleus are called prokaryotic cells. Example: bacteria, blue-green algae, etc.
12. What is the full form of RNA?
Ans: RNA = Ribo Nucleic Acid
13. Write short notes on:
(a) Endoplasmic Reticulum
Ans: The endoplasmic reticulum is a large network composed of membrane-bound tubules and vesicles. Its membrane is single-layered. These structures are irregularly spread throughout the cytoplasm forming a network. Ribosomes are attached to these tubules. The endoplasmic reticulum is of two types: smooth and rough. The smooth endoplasmic reticulum helps in the synthesis of lipids required for cellular functions. Proteins and lipids help in the formation of the cell membrane.
(b) Mitochondria
Ans: Mitochondria are known as the powerhouse of the cell. They produce ATP molecules which store energy required for various chemical reactions in living organisms. Structurally, mitochondria have a double membrane. The outer membrane is porous, while the inner membrane is highly folded. A significant feature is that mitochondria have their own DNA and ribosomes, enabling them to synthesize their own proteins.
(c) Plastids
Ans: Plastids are found only in plant cells. They are oval or rod-shaped organelles with a double membrane and two compartments. Plastids are of two types: chromoplasts and leucoplasts. Those plastids that contain chlorophyll are called chloroplasts, which are important for photosynthesis. Chloroplasts also contain yellow and orange pigments. Leucoplasts generally store starch, oils, and proteins. Plastids also have their own DNA and ribosomes.
(d) Lysosomes
Ans: Lysosomes are organelles involved in the removal of cellular waste materials. They appear as small sac-like structures. Lysosomes digest unwanted substances entering the cell and waste materials produced within the cell, thereby keeping the cell clean. They convert foreign materials such as bacteria, food particles, and dead cell organelles into simpler substances. If any abnormality occurs in cellular metabolism, lysosomes release enzymes that
can destroy the cell.
Multiple Choice Questions (MCQ)
1. What is the basic structural and functional unit of life?
(a) Tissue
(b) Cell
(c) Organ
(d) Organ system
Ans: (b)
2. Who discovered the cell for the first time?
(a) Robert Hooke
(b) Anton van Leeuwenhoek
(c) Robert Brown
(d) Schleiden
Ans: (a)
3. In which year was the cell discovered by Robert Hooke?
(a) 1665
(b) 1674
(c) 1831
(d) 1855
Ans: (a)
4. Which instrument is used to study cells?
(a) Telescope
(b) Microscope
(c) Barometer
(d) Thermometer
Ans: (b)
5. Who discovered the nucleus of the cell?
(a) Robert Hooke
(b) Robert Brown
(c) Virchow
(d) Darwin
Ans: (b)
6. Which cell organelle is known as the powerhouse of the cell?
(a) Nucleus
(b) Ribosome
(c) Mitochondria
(d) Golgi apparatus
Ans: (c)
7. Which organelle controls all activities of the cell?
(a) Cytoplasm
(b) Nucleus
(c) Cell wall
(d) Lysosome
Ans: (b)
8. What is the outermost covering of an animal cell?
(a) Cell wall
(b) Cytoplasm
(c) Cell membrane
(d) Nucleus
Ans: (c)
9. Which structure is present only in plant cells?
(a) Cell membrane
(b) Cytoplasm
(c) Cell wall
(d) Nucleus
Ans: (c)
10. What is the jelly-like substance inside the cell called?
(a) Nucleus
(b) Cytoplasm
(c) Cell wall
(d) Plastid
Ans: (b)
11. Which organelle is responsible for protein synthesis?
(a) Ribosome
(b) Lysosome
(c) Golgi apparatus
(d) Vacuole
Ans: (a)
12. Which organelle is known as the “suicide bag” of the cell?
(a) Ribosome
(b) Lysosome
(c) Nucleus
(d) Plastid
Ans: (b)
13. Which cell organelle helps in packaging and secretion?
(a) Ribosome
(b) Golgi apparatus
(c) Mitochondria
(d) Nucleus
Ans: (b)
14. What is the function of vacuole in plant cells?
(a) Protein synthesis
(b) Storage of substances
(c) Energy production
(d) Cell division
Ans: (b)
15. Which plastid contains chlorophyll?
(a) Leucoplast
(b) Chromoplast
(c) Chloroplast
(d) Amyloplast
Ans: (c)
16. What is the main function of chloroplast?
(a) Respiration
(b) Digestion
(c) Photosynthesis
(d) Excretion
Ans: (c)
17. Which structure is responsible for selective permeability?
(a) Cell wall
(b) Cell membrane
(c) Cytoplasm
(d) Nucleus
Ans: (b)
18. What is osmosis?
(a) Movement of solute
(b) Movement of water through a semipermeable membrane
(c) Movement of gases
(d) Movement of ions
Ans: (b)
19. What is diffusion?
(a) Movement of water only
(b) Movement of particles from high to low concentration
(c) Movement of particles from low to high concentration
(d) Movement of solids
Ans: (b)
20. Which cell organelle contains DNA?
(a) Ribosome
(b) Nucleus
(c) Lysosome
(d) Vacuole
Ans: (b)
21. What is the full form of DNA?
(a) Deoxyribo Nucleic Acid
(b) Dynamic Nucleic Acid
(c) Double Nucleic Acid
(d) Deoxy Nuclear Acid
Ans: (a)
22. What is the full form of RNA?
(a) Ribo Nucleic Acid
(b) Rapid Nucleic Acid
(c) Reactive Nucleic Acid
(d) Ribose Nuclear Acid
Ans: (a)
23. What is a gene?
(a) Unit of respiration
(b) Unit of heredity
(c) Unit of digestion
(d) Unit of excretion
Ans: (b)
24. Which type of cell has a well-defined nucleus?
(a) Prokaryotic
(b) Eukaryotic
(c) Bacterial
(d) Viral
Ans: (b)
25. Which organisms have prokaryotic cells?
(a) Plants
(b) Animals
(c) Bacteria
(d) Fungi
Ans: (c)
26. What is plasmolysis?
(a) Swelling of cell
(b) Shrinking of cell contents due to water loss
(c) Division of cell
(d) Growth of cell
Ans: (b)
27. Which organelle helps in lipid synthesis?
(a) Rough ER
(b) Smooth ER
(c) Ribosome
(d) Nucleus
Ans: (b)
28. Which organelle is involved in transport within the cell?
(a) Golgi apparatus
(b) Endoplasmic reticulum
(c) Nucleus
(d) Lysosome
Ans: (b)
29. What is the function of mitochondria?
(a) Digestion
(b) Energy production
(c) Storage
(d) Protection
Ans: (b)
30. Which organelle has its own DNA?
(a) Lysosome
(b) Mitochondria
(c) Ribosome
(d) Vacuole
Ans: (b)
31. What is the main component of cell wall?
(a) Protein
(b) Lipid
(c) Cellulose
(d) Starch
Ans: (c)
32. Which part of the cell contains enzymes for digestion?
(a) Ribosome
(b) Lysosome
(c) Nucleus
(d) Vacuole
Ans: (b)
33. What is the function of ribosomes?
(a) Lipid synthesis
(b) Protein synthesis
(c) Energy production
(d) Transport
Ans: (b)
34. Which organelle modifies proteins?
(a) Golgi apparatus
(b) Ribosome
(c) Nucleus
(d) Vacuole
Ans: (a)
35. What is the nature of the cell membrane?
(a) Fully permeable
(b) Impermeable
(c) Semi-permeable
(d) Rigid
Ans: (c)
36. Which cell organelle is absent in prokaryotic cells?
(a) Cell membrane
(b) Cytoplasm
(c) Nucleus
(d) Ribosome
Ans: (c)
37. What is the function of nucleus?
(a) Storage of food
(b) Control of cell activities
(c) Energy production
(d) Digestion
Ans: (b)
38. Which organelle helps in detoxification?
(a) Smooth ER
(b) Ribosome
(c) Lysosome
(d) Nucleus
Ans: (a)
39. Which cell is generally larger?
(a) Prokaryotic cell
(b) Eukaryotic cell
(c) Bacterial cell
(d) Viral cell
Ans: (b)
40. Which structure gives shape and rigidity to plant cells?
(a) Cell membrane
(b) Cytoplasm
(c) Cell wall
(d) Nucleus
Ans: (c)
