The Fundamental Unit of Life Class 9 Science Chapter 5 Important Questions, Download PDF

The Fundamental Unit of Life Class 9 Science Chapter 5 Important Questions PDF

This chapter explains that the cell is the basic building block of all living things. Each cell can perform important life activities on its own, which is why it is called the fundamental unit of life. The chapter also covers different parts of the cell, like the nucleus, cytoplasm, and cell membrane, and their functions. By studying these important questions, students can understand how living organisms are made and how cells work to keep them alive. Below is the PDF of important questions: 

CBSE Important Questions The Fundamental Unit of Life 

Multiple Choice Questions (1 Mark)

1. The process by which water moves through a semi-permeable membrane from a region of high concentration to a region of lower concentration, thereby equalizing water concentration is called:
   (A) Evaporation
   (B) Diffusion
   (C) Osmosis
   (D) All of the above
   Ans: (C)

2. Identify the function that the vacuole in plants does not perform from the following options.
   (A) They store toxic metabolic wastes.
   (B) They help with the process of cell division.
   (C) They help to maintain turgidity.
   (D) They provide structural support.
   Ans: (B)

3. Which of the following statements best defines plasmolysis?
   (A) The shrinkage of contents of a living cell away from the cell wall due to exosmosis caused by a hypertonic solution.
   (B) The shrinkage of protoplast of a non-living cell from the cell wall due to exosmosis caused by hypertonic solution.
   (C) The process of shrinkage of protoplast from the cell wall due to exosmosis caused by a hypotonic solution.
   (D) The process of swelling of the cytoplasm due to endosmosis caused by a hypertonic solution.
   Ans: (A)

4. Which of the following options are associated with mitochondria?
   (i) These are the sites of cellular respiration.
   (ii) These are the sites of protein synthesis.
   (iii) These are also called powerhouses of the cell.
   (iv) These are double membranous organelles.
   (A) (i) and (iii)
   (B) (iii) and (iv)
   (C) (i), (iii) and (iv)
   (D) Only (ii)
   Ans: (C)

5. Select the incorrect statement(s) regarding the nucleus.
   (i) It has a double-layered outer membrane.
   (ii) It contains chromosomes.
   (iii) Its outer membrane is porous.
   (iv) It plays a central role in cellular reproduction.
   (A) Only (iii)
   (B) (i) and (ii)
   (C) (ii) and (iv)
   (D) None of the above
   Ans: (D)

6. Which of the following cell organelles can make complex sugars from simple sugars?
   (A) Vacuoles
   (B) Lysosomes
   (C) Chloroplast
   (D) Golgi apparatus
   Ans: (D)

7. The transportation of materials in the cell is done by:
   (A) Golgi complex
   (B) Lysosomes
   (C) Mitochondria
   (D) Endoplasmic reticulum
   Ans: (D)

8. Chromosomes are composed of:
   (A) DNA and protein
   (B) DNA and Sugar
   (C) Sugar and protein
   (D) Chromatin
   Ans: (A)

9. Which of the following components of cell are absent in prokaryotes?
   (i) Nucleoid
   (ii) Plastids
   (iii) Vesicles
   (iv) Nuclear membrane
   (v) Chromosomes
   (vi) Mitochondria
   (A) (i), (ii) and (iii)
   (B) (ii), (iv) and (v)
   (C) (ii), (iv) and (vi)
   (D) (iii), (iv) and (v)
   Ans: (C)

10. Select the correct pair that comprises of unicellular organisms only.
    (A) Amoeba and Rhizopus
    (B) Paramecium and Chlamydomonas
    (C) Bacteria and Fungi
    (D) Plants and animals
    Ans: (B)

11. Match the following columns:

(A) P-3, Q-4, R-1, S-2
(B) P-1, Q-2, R-3, S-4
(C) P-2, Q-4, R-1, S-3
(D) P-4, Q-3, R-1, S-2
Ans: (D)
Sol: Robert Hooke discovered the cell in 1665. Schleiden and Schwann proposed the cell theory. Robert Brown discovered the nucleus in 1831, and Purkinje coined the term 'protoplasm' in 1839.

12. Match the following columns:

(A) P-3, Q-2, R-1
(B) P-1, Q-2, R-3
(C) P-3, Q-1, R-2
(D) P-2, Q-1, R-3
Ans: (D)

In a hypotonic solution, the surrounding medium  has a higher concentration of water than that of the  cell. The cell will gain water by osmosis  (endosmosis). The cell is likely swell up.  The medium surrounding the cell is hypertonic if it  has lower water concentration than the cell. The  will lose water by osmosis (exosmosis). Therefore,  the cell will shrink. In an isotonic solution, the medium has exactly the  same water concentration as the cell, there will be  no net movement of water across the cell  membrane. The cell will stay the same size.

Very Short Answer Type Questions (1 Mark)

13. What are the functional regions of a cell?
Sol: There are three major functional regions of cells: • cell membrane or plasma membrane, nucleus and cytoplasm.

14. Why do animal cells not have a cell wall?

Sol. Animals do not have rigid walls because cell walls are incompatible with the way in which an animal moves and grow. The flaccid cell membrane provides the animal cell freedom of mobility and formation of different tissues which is not present in plants.

15. How are chromatin, chromatid and chromosomes related to each other?
Sol. Chromatin is a thin thread-like structure which is composed of DNA (deoxy ribonucleic acid) and proteins to form a rod-like chromatid. Two similar chromatids attach to a centromere to form a chromosome.

16. Name the cell organelle which plays an important role in detoxifying many poisons and drugs in the liver cells of vertebrates.
Sol. Smooth endoplasmic reticulum (SER)

17. What is the full form of ATP?
Sol. Adenosine triphosphate

18. What are the two components of the plasma membrane?
Sol. The main components of the plasma membrane are proteins and lipids.

19. The cell wall of a plant cell is made up of which component?
Sol. In a plant cell, the cell wall is mainly made up of cellulose. Cellulose is a complex substance which gives the structural strength to the plants. It is permeable to water, solutes and gases.

Short Answer Type Questions (2 Marks)

20. What is cell division? Types?
    Sol: The process by which a parent cell divides into two or more daughter cells is called cell division.
    There are two main types of cell division:
    (i) Mitosis: The process of cell division by which most of the cell divide for growth is called mitosis:
    (ii) Meiosis: Specific cells of reproductive organs or tissues in animals and plants divide to form gametes by meiosis.

21. Why is the plasma membrane called selectively permeable?
    Sol: The plasma membrane permits the entry and exit of selective materials in and out of the cells. It also prevents the movement of selective materials. Therefore, the plasma membrane is called a selectively permeable membrane.

22. Which cell organelle is called "suicide bags"? Why is this organelle called so?
    Sol. Lysosomes contain digestive enzymes that are capable of digesting the whole cell when the situation so demands. Since a cell in itself contains an organelle through which it can kill itself, thus the lysosome is called the suicide bag of the cell.

23. Who first described the Golgi apparatus? Write down the functions of the Golgi apparatus.
    Sol. The Golgi apparatus was first described by the Camillo Golgi. Its function includes the storage, modification and packaging of products in vesicles. In some cases, complex sugars may be made from simple sugars in the Golgi apparatus. The Golgi apparatus is also involved in the formation of lysosomes.

24. Why is the cell called the structural and functional unit of life?
    Sol. All living organisms are made up of cells so cell is the basic building unit of a living organism and all the activities performed by a living organism are sum total of activities performed by its cells hence cell is called the structural and functional unit of life.

25. Which organelle is known as the powerhouse of the cell? Why?
    Sol. It is mitochondria of the cell also known as the power house of the cell because it synthesizes energy in the form of ATP during respiration which is vital for various life activities.

26. Where do the lipids and proteins constituting the cell membrane get synthesised?
    Sol. The endoplasmic reticulum is of two types:
    (i) Smooth endoplasmic reticulum (SER): It is responsible for the synthesis of lipids constituting cell membrane.
    (ii) Rough endoplasmic reticulum (RER): It bears the ribosomes and is therefore responsible for the synthesis of proteins constituting cell membrane.

27. What are genes? Why nucleus is called the director of the cell?
    Sol. Genes are the functional units of DNA that carries genetic information. These are the hereditary units. The nucleus controls cell metabolism and other activities of the cell, hence, it is also called master or director of the cell.

28. Write two similarities and one dissimilarity between mitochondria and plastids.
    Sol. Two similarities between mitochondria and plastids are:
    (i) Both are double membrane structures.
    (ii) Both of them have their own genetic material (DNA).
    Dissimilarity between mitochondria and plastids is that mitochondria is the site of production of energy whereas plastid is the site of photosynthesis.

Short Answer (3 Marks)

29. Differences between animal and plant cells:

 

 

 

30. Answer the following questions.

(A) Why are mitochondria and chloroplast known as semi-autonomous organelles?
Sol: "Chloroplast and mitochondria" are termed to be the "semi-autonomous organelles" in "eukaryotic cells". This is because in eukaryotic cells, the mitochondria and the chloroplast are seen to possess DNA of their own. Chloroplasts are the organelles that are seen to contain chlorophyll in plants. Mitochondria, commonly known as the "energy currency of the cell", produces energy in the form of ATP that is required by the body to perform various actions. The DNA of these organelles codes for most of the proteins that are needed for these organelles. It is for this reason that "chloroplast and mitochondria" are termed to be the semi-autonomous organelles.
(B) Write a short note on cytoplasm.
Sol. It is a gel-like substance that fills the cell and occurs between the plasma membrane and the nucleus. It is made up of about 80% water and is usually clear and colourless. Cell organelles such as mitochondria, ribosomes, Golgi bodies, etc. are suspended in the cytoplasm.
(C) Name the only cell organelle seen in prokaryotic cells.
Sol. Ribosomes are cell organelles without a membrane enclosing it, so-called membraneless or membranous organelle. These are the only cell organelle found in both prokaryotic and eukaryotic cells.

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

 

 

32. (a) Distinguish between nucleolus and nucleus. (b) What is endosmosis and exosmosis?
Sol. (a) The nucleolus is RNA rich, rounded, darkly stained structure present inside the nucleus. Its function is to synthesise ribosomes and store RNA.
Nucleus is the DNA rich part of eukaryotic cell that contains chromosomes. It remains separated from cytoplasm by a double membraned nuclear envelope.
(b) The inward diffusion of water through a semipermeable membrane when the surrounding solution is less concentrated is called endosmosis (endo: inward).
Endosmosis leads to swelling up of the cells.
The outward diffusion of water through a semipermeable membrane when the surrounding solution is more concentrated is called exosmosis (exo: outward). Exosmosis leads to the shrinking up of cells.

33. Explain in brief the different mechanisms by which movement of substances takes place across the cell membrane.
Sol. Movement of substances across the cell membrane occurs through a number of mechanisms like: Diffusion, osmosis, active transport, endocytosis and exocytosis.
(i) Diffusion is the process of movement of molecules of a substance from a region of their higher concentration to a region of their lower concentration. Waste material like carbon dioxide moves out of the cell through diffusion. Similarly, oxygen enters the cell through diffusion.
(ii) Osmosis is the passive movement of water or any other solvent molecules from a region of higher water concentration to a region of lower water concentration through a semipermeable membrane.
(iii) In active transport, molecules move uphill against the forces of passive diffusion. Active transport always involves the expenditure of energy (from ATP) because materials are pumped against the concentration gradient.

34. What will happen if we put an animal cell into the following:
(a) Hypotonic Solution
(b) Isotonic solution
(c) Hypertonic solution
Sol. (a) If the medium surrounding the cell has a higher water concentration than the cell, meaning that the outside solution is very dilute, the cell will gain water by osmosis (endosmosis). Such a solution is known as a hypotonic solution. Water molecules are free to pass across the cell membrane in both directions, but more water will come into the cell than will leave. The net (overall) result is that water enters the cell. The cell is likely to swell up.
(b) If the medium has exactly the same water concentration as the cell, there will be no net movement of water across the cell membrane. Such a solution is known as an isotonic solution. Water crosses the cell membrane in both directions, but the amount going in is the same as the amount going out, so there is no overall movement of water. The cell will stay the same size.
(c) If the medium has a lower concentration of water than the cell, meaning that it is a very concentrated solution, the cell will lose water by osmosis (exosmosis). Such a solution is known as a hypertonic solution. Again, water crosses the cell membrane in both directions, but this time more water leaves the cell than enters it. Therefore, the cell will shrink.

Long Answer Questions (5 Marks)

35. Explain the structure and function of nucleus of a cell with neat labelled diagram.
    Sol:

     

    Sol. Nucleus is formed of four components:
    (i) Nuclear membrane: It is porous (with nuclear pores) and semipermeable membrane. Outer membrane is studded with ribosomes and may be continuous with RER. It regulates the exchange of materials between nucleoplasm and cytoplasm.
    (ii) Nucleoplasm or nuclear sap: It is a transparent, semifluid, colloidal ground substance in which nucleoli and chromatin fibres are present.
    (iii) Nucleolus: It is dense, spherical, naked (membrane less) and darkly stained structure and is the site of formation and storehouse of rRNAs so helps in the synthesis of ribosomes.
    (iv) Nuclear chromatin: It is a darkly stained network of long and fine threads called chromatin fibres which, during cell division, condense by dehydration and spiralling to form a species specific number of rods, called chromosomes. The DNA possesses all the necessary information for the cell to function, grow and divide properly. The specific segments of DNA are termed genes. These are the hereditary units.
    Functions of nucleus are:
    (i) The nucleus controls cell metabolism and other activities of the cell, hence, it is also called Master or Director of the cell.
    (ii) Chromatin part of the nucleus possesses all the genetic information that is required for growth and development of the organism, its reproduction, metabolism and behaviour.
    (iii) Nucleus plays a central role in the cellular reproduction (division of single cell to form two cells).
    (iv) Along with environment, nucleus also directs the chemical activities of the cell. This determines the development and future form of the cell.

36. (a) What would happen if the plasma membrane ruptures or breaks down?
    (b) What would happen to the life of a cell if there were no Golgi apparatus?
    (c) Name the materials of which the cell membrane and cell wall are composed.

    Sol. (a) Plasma membrane is the selective permeable membrane that surrounds the cell and allows the entry and exit of selected materials of the cell. If it ruptures, the contents of the cell will come in direct contact with the surrounding medium and not only unwanted materials will be able to enter freely into the cell, but useful material will also find its way out of the cell easily. This will seriously disrupt various metabolic activities of the cell and will result in its eminent death.
    (b) If there were no golgi apparatus, the material synthesized by endoplasmic reticulum would not be carried to the various parts inside and outside the cell. Also as the Golgi apparatus performs the function of storage and modification of the material synthesised in the cell, these materials could not be stored and modified further. Moreover, there will be no production of lysosomes which will cause the accumulation of waste material, viz. worn out and dead cell organelles within the cell which will ultimately lead to cell death.
    (c) Cell wall is composed of cellulose and cell membrane is composed of lipids and proteins.

37. Write down the functions of:
    (a) Lysosomes
    (b) Endoplasmic reticulum
    (c) Vacuole

    Sol. (a) Functions of lysosomes:
    • Extracellular digestion: Sometimes lysosomal enzymes are released outside the cell to break down extracellular material. So, they are known as digestive bags.
    • Digestion of foreign material: Lysosomes also destroy any foreign material such as bacteria, entering the cell.
    • Cellular digestion: Lysosomes get ruptured and enzymes are released free in damaged cells, ageing cells, poorly working cell organelles to digest them. So, they are also known as suicide bags. Thus lysosomes help in the waste disposal of the cell and keep the cell clean of any unwanted waste material.
    (b) Functions of endoplasmic reticulum:
    • The network of ER separates cytoplasm of the cell into several small compartments.
    This compartmentalization of cytoplasm helps a cell to perform specific functions within specific chambers excluding others.
    • The ER gives mechanical support to the cytoplasm by providing a kind of cytoskeleton to maintain the shape of cell.
    • The ER offers extensive surface for the synthesis of proteins and lipids. It also helps in the transport of materials (especially proteins) from one part of the cell to another or between the cytoplasm and the nucleus.
    • The SER brings about detoxification in the liver of vertebrates, i.e., it converts harmful poisons and drugs into harmless substances for excretion by the cell.
    (c) Functions of Vacuole:
    • Vacuoles are meant for the storage of food, water and other substances.
    • They help in the elimination of excess water from the cell (osmoregulation), and maintains internal pressure of the cell.
    • They help the cells to remain turgid.

38. How is a bacterial cell different from an onion peel  cell?

39. Answer the following questions:

1. (i) What is cell sap? Give its composition.
   (ii) If all the ribosomes of a cell are destroyed, what happens in the cell?
   (iii) What are the locations of proteins synthesized in cells?
   (iv) Who discovered cells, and how?
   (v) Write the names of different plant parts in which chromoplast, chloroplast, and leucoplast are present.

   Sol. (i) Cell sap is the fluid present inside the large sap vacuoles of the plant cell. It comprises salts, sugars, amino acids and mainly water. It provides buoyancy and support to the cell. It also helps in the storage of many materials. Cell sap maintains the osmosis of the cell. It also helps in colouration due to dissolved pigments in it.
   (ii) Ribosomes are the protein factory of the cell. Ribosomes work as a structural unit in protein synthesis. If all the ribosomes of a cell are destroyed then protein synthesis will stop.
   (iii) The ribosomes are responsible for protein synthesis within cells. Ribosomes can also be called protein factories.
   (iv) Robert Hooke, an English scientist, discovered cells in 1665. While examining a tiny slice of cork under his self-designed microscope, he saw a honeycomb-like structure.
   (v) Chromoplasts are present in flowers, fruits or any other coloured part of the plant (other than green part).
   Chloroplasts are present in leaves and stem of plant (green part).
   Leucoplasts are present anywhere in plant as they are colourless and stores food.

Benefits of Solving Important Questions Class 9 Science Chapter 5 

Enhanced Understanding : Important Questions Class 9 Science Chapter 5 reinforces key concepts about cell structure and function, helping students grasp fundamental biological principles.

Improved Retention : Regular practice aids memory retention, making it easier to recall information during exams.

Exam Preparation : Familiarity with Important Questions Class 9 Science Chapter 5 boosts confidence and equips students for various question formats they might encounter in assessments.

Critical Thinking : Engaging with these questions encourages analytical thinking and problem-solving skills, essential for scientific inquiry.

Identifying Weak Areas : Practicing important questions helps identify topics that need further review, allowing for targeted study.

Application of Knowledge : It promotes the application of theoretical knowledge to practical scenarios, deepening overall comprehension of the subject.

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