Solved examples for class 8 science : Chapter 8

    Cell Structure and Functions

    I. Multiple Choice Questions (MCQs).
    Q.1. Cell is the structural and functional unit of complex structure of
    a) life
    b) animal
    c) plant
    d) none of these
    Answer. a) life

    Q.2. Shape of a cell is due to the
    a) cell membrane
    b) cell wall
    c) both (a) and (b)
    d) none of these

    Answer. (c) (c) both (a) and (b)
    Q.3. Which of the following is not a function of a cell membrane?
    a) It provides protection to the cell
    b) It gives shape to the cell
    c) It allows transport of materials
    d) It brings about cell division

    Answer.(d) It brings about cell division

    Q.4. The living component of the cell is
    a) protoplasm
    b) cytoplasm
    c) nucleus
    d) none of these

    Answer. (a) protoplasm

    Q.5. Various life functions performed by the cell organelles takes place inside………………………. .
    a) cell wall
    b) nucleoplasm
    c) cytoplasm
    d) cell membrane

    Answer. (c) cytoplasm

    II. Fill in the blanks by selecting appropriate words from the given list : List : membrane, cells, microscopic, Genes, nerve cell

    Q.1. ………………………..are assembled to make up the body of every living organism.
    Q.2. Majority of cells are……………………………. in size and are not visible to the naked eyes.
    Q.3. The……………………………… separates the cells from one another and also the cell from the surrounding medium.
    Q.4. The largest cell in the human body is the ……………………….
    Q.5. ……………………………………contain message in the form of genetic code.

    Answer. 1- cells, 2- microscopic, 3- membrane, 4- nerve cell, 5- Genes

    III. Match the items of Column A with those of Column B.


    Answer. 1-e, 2-a, 3-d, 4-b, 5- c

    Write ‘T’ for the true and ‘F’ for the false statements.
    Q.1. Living organisms differ from one another but all of them are made up of cells.
    Q.2. Every organism begins life as a single cell which is the fertilised egg.
    Q.3. Cells are generally found in elongated shape.
    Q.4. Nuclear material lies scattered without a nuclear membrane in a prokaryotic cell.
    Q.5. Vacoules are large in animal cells and small in plant cells.

    Answer. 1-T, 2-T, 3-F, 4-T, 5- F

    V. Very Short Answer Questions.

    Q.1. Who observed the cells for the first time?
    Answer: Robert Hooke observed the cells for the first time.

    Q.2. What does it make easy to study the detailed structure of a cell?

    Answer: Dyeing or colouring

    Q.3. Write the different shapes of the cells.

    Answer: Cells are found in a variety of shapes. They may be round, spherical, oval, elongated, spindle shaped, branched, etc.

    Q.4. Name a dense fluid present in the nucleus.
    Answer: Nucleoplasm

    Q.5. Name the unit of heredity.
    Answer: Genes

    VI. Short Answer Questions.

    Q.1. What are the functions of cell wall?
    Answer: Functions of cell walls:
    (i) It provides protection against variation in temperature, high wind speed, atmospheric moisture, etc.
    (ii) It provides mechanical strength.
    (iii) It controls the shape and size of the cell.

    Q.2. What are the functions of nucleus?
    Answer: Functions of nucleus:
    (i) Nucleus brings about cell division.
    (ii) It is responsible for transmission of hereditary materials from one generation to the other.
    (iii) It acts as a control centre of all the activities of the cell.

    Q.3. Define genes and their uses.
    Answer: Genes are the units of heredity. They control the transfer of characteristics from parents to the offspring. Certain characteristics which we acquire from our father and mother are carried by these genes. Our physical and genetic make-up is a result of combination and recombination of these genes. Genes contain message in the form of genetic codes.

    Q.4. Describe types of organisms based on the number of cells. Explain shape and size of cells with proper examples.

    Answer: Types of Organisms based on the Number of Cells
    • Unicellular and
    • Multicellular

    (i) Unicellular organisms: Organisms Like Amoeba and Paramecium are made up of a single cell which carries out all the Life processes for these organisms. They are single-celled or unicellular organisms.

    (ii) Multicellular organisms: Organisms made up of more than one cell are called multicellular organisms. The number of cells in a multicellular organism may be as large as billions and trillions as in human body. Cells in such organisms form groups to perform a variety of functions.

    Q.5. Describe differences between animal and plant cells.
    Answer: Differences between Animal Cell and Plant Cell


    Q.6. Describe how to observe the basic components of the onion peel cell through an activity.

    Answer: To observe the basic components of the onion peel cell.

    Requirements: Onion, glass slides, forceps, dropper, water, coverslip, compound microscope and methylene blue.

    Procedure: Take a glass slide and coverslip and clean it properly. Take an onion bulb and remove the dry pink coverings. Now, separate the fleshy white layers of bulb with the help of forceps. Place a small piece of the thin layers of onion peel in a drop of water on a slide. Add a drop of methylene blue solution to the layer and place a coverslip on it. While placing coverslip ensure that there should be no air bubbles under the coverslip. Now observe the slide under the microscope. Observation: Onion peel consists of many cells. All cells have a boundary. Inside the cell some darkly stained round bodies are also seen.

    Conclusion: The onion cells surrounded by cell membrane are covered by another thick layer called cell wall. The dense rounded body present at the centre of the cells is called nucleus.

    VII. Long Answer Questions.

    Q.1. Discuss the main parts of cell and their functions briefly.
    Answer: A cell can be divided into three basic components-
    i. Cell membrane
    ii. Cytoplasm
    iii. Nucleus
    In addition to these an outermost layer called cell wall is present in all the plant cells.

    Cell Wall: It is a thick rigid layer present outside the cell membrane of the plant cell. It is made up of cellulose, calcium pectate and magnesium pectate. Cell wall is non-living in nature. Functions:
    (i) It provides protection against variation in temperature, high wind speed, atmospheric moisture, etc.
    (ii) It provides mechanical strength.
    (iii) It controls the shape and size of the cell.

    Cell Membrane: It is thin outer protective covering enclosing the cytoplasm and other cell organelles. It is also known as plasma membrane. The membrane separates the cells from one another and also the cell from the surrounding medium. It is made up of lipids and proteins. Plasma membrane is porous and allows the movement of certain substances in and out of the cell. It is semipermeable or selectively permeable in nature and allows transport of specific molecules only.

    Functions:
    (i) It provides protection to the cell.
    (ii) It gives shape to the cell.
    (iii) It allows transport of materials in and out of the cell.

    Cytoplasm: It is a jelly-like substance present between the cell membrane and the nucleus. Various other living components known as cell organelles are present in the cytoplasm. Various life functions performed by the cell organelles take place inside the cytoplasm.

    Nucleus : It is an important component of the living cell. It is generally spherical, dense, granular and located in the centre of the cell. It can be stained and observed easily with the help of a microscope.
    A nucleus consists of the following parts :
    (i) Nuclear membrane :
    (ii) Nucleoplasm :
    (iii) Nucleolus :
    (iv) Chromosomes :
    Functions:
    (i) Nucleus brings about cell division.
    (ii) It is responsible for transmission of hereditary materials from one generation to the other.
    (iii) It acts as a control centre of all the activities of the cell.

    Q.2. Write main differences between prokaryotic and eukaryotic cells.
    Answer: Differences between prokaryotic and eukaryotic cells

    Prokaryotic Cell: Nucleus in a bacterial cell is not well organised Like multicellular organisms. Nuclear material Lies scattered in the cell without a nuclear membrane. This cell does not have any well differentiated cell organelles. Because of their primitive structure they are known as prokaryotes e.g., bacteria, blue green algae (cyanobacteria).

    Eukaryotic Cell: Multicellular organisms have cells with well organised nucleus and other well organised cell organelles. These cells are known as eukaryotic cells and the organisms as eukaryotes.

    Q.3. Discuss the main cell organelles and their functions briefly.

    Answer: Following are the main cell organelles and their functions:
    i. Mitochondria : They are oval shaped organelles which produce energy during respiration. They are known as powerhouses of the cell. They are present both in animal cell and plant cell.
    ii. Endoplasmic Reticulum : They are tube Like structures that extend from nuclear membrane to the cell membrane. They help in transportation of substances within the cell.
    iii. Ribosomes : They are small granular organelles which help in protein synthesis. They are found free in surface of cytoplasm or located on the endoplasmic reticulum.
    iv. Golgi Bodies which perform are found only They are the organelles secretory functions and in animal cells.
    v. 5. Centrosomes: They are rounded bodies found in animal cells which help in cell division.
    vi. Lysosomes: They are sac like structures containing digestive enzymes to digest microbes, food particles and worn out cells.
    vii. Plastids: They are the coloured organelles found scattered in the cytoplasm of leaf cell. Plant cells have three types of plastids-
    (a) Chloroplast: Green coloured organelle, due to the presence of chlorophyll. They help in photosynthesis.
    (b) Leucoplast: They are colourless and help in storing food.
    (c) Chromoplast: These plastids have pigments other than green e.g., red, yellow, etc. chromoplast commonly found in tomato, carrots, beetroot, etc.

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