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NCERT Exemplar · Class 9 Science The Fundamental Unit of Life

59 questions · 59 still being checked

Short Answer Questions 30–39 (part 4 of 6)

  1. Exercise 30

    Why are lysosomes known as ‘suicide-bags’ of a cell?

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    Lysosomes are known as ‘suicide-bags’ because when cell gets damaged during the disturbance in cellular metabolism, lysosomes may burst and the digestive enzymes thus released digest their own cell.
    Lysosomes hold powerful digestive (hydrolytic) enzymes, enclosed within a single membrane. \[\text{lysosomal membrane ruptures} \Rightarrow \text{enzymes released into the cytoplasm} \Rightarrow \text{autolysis: the cell digests itself} \] Answer: Ruptured lysosomes release digestive enzymes that break down the entire cell, so they are called suicide bags.

  2. Exercise 31

    Do you agree that “A cell is a building unit of an organism”. If yes, explain why?

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    NCERT’s answer
    Hint— Cell→ tissue → organ → organ system → organism
    Yes -- the cell is the smallest unit that can carry out all life processes on its own. \[\text{cell} \rightarrow \text{tissue} \rightarrow \text{organ} \rightarrow \text{organ system} \rightarrow \text{organism} \] Answer: Yes; the cell is the basic structural and functional unit from which the organism is built.

  3. Exercise 32

    Why does the skin of your finger shrink when you wash clothes for a long time?

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    The soap solution used for washing clothes is hypertonic to the cytoplasm of the epidermal (skin) cells. \[\text{soap solution hypertonic} \Rightarrow \text{exosmosis} \Rightarrow \text{water leaves epidermal cells} \Rightarrow \text{cells shrink} \] Answer: Exosmosis — water passes out of the skin cells into the hypertonic soap solution, so the cells shrink, wrinkling the skin.

  4. Exercise 33

    Why is endocytosis found in animals only?

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    NCERT’s answer
    Hint— Cell wall is absent in animals
    Endocytosis needs the plasma membrane to fold inward around a particle and pinch off as a vesicle. \[\text{no rigid cell wall} \Rightarrow \text{plasma membrane free to fold} \Rightarrow \text{particle engulfed (endocytosis)} \] Answer: Animal cells have no rigid cell wall, so their flexible plasma membrane can fold around and engulf material; a cell wall prevents this in plants.

  5. Exercise 34

    A person takes concentrated solution of salt, after sometime, he starts vomiting. What is the phenomenon responsible for such situation? Explain.

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    NCERT’s answer
    Exosmosis in intestine causes dehydration
    The concentrated salt solution is hypertonic compared with the cytoplasm of the cells lining the stomach and intestine. \[\text{concentrated salt solution (hypertonic)} \Rightarrow \text{exosmosis from mucosal cells} \Rightarrow \text{cells lose water, get irritated} \Rightarrow \text{vomiting} \] The rapid water loss irritates the stomach lining, and vomiting expels the concentrated solution. Answer: Exosmosis — water moves out of the stomach/intestinal cells into the concentrated salt solution, irritating them and causing vomiting.

  6. Exercise 35

    Name any cell organelle which is non membranous.

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    Ribosomes
    Answer: Ribosome — it has no surrounding membrane.

  7. Exercise 36

    We eat food composed of all the nutrients like carbohydrates, proteins, fats, vitamins, minerals and water. After digestion, these are absorbed in the form of glucose, aminoacids, fatty acids, glycerol etc. What mechanisms are involved in absorption of digested food and water?

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    NCERT’s answer
    Diffusion and osmosis respectively
    Digested food and water cross the intestinal wall by two processes. \[\text{glucose, amino acids, fatty acids, glycerol (high in lumen)} \xrightarrow{\text{diffusion}} \text{blood and lymph (low concentration)} \] \[\text{water (lumen)} \xrightarrow{\text{osmosis, across the cell membrane}} \text{blood} \] Answer: Diffusion carries the digested food molecules and osmosis carries water, both down their concentration gradients, across the intestinal wall into the blood and lymph.

  8. Exercise 37

    If you are provided with some vegetables to cook. You generally add salt into the vegetables during cooking process. After adding salt, vegetables release water. What mechanism is responsible for this?

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    NCERT’s answer
    Exosmosis
    Salt sprinkled on the vegetable dissolves in its surface moisture and makes the surrounding layer hypertonic to the cell's cytoplasm. \[\text{salt layer outside (hypertonic)} \Rightarrow \text{exosmosis from vegetable cells} \Rightarrow \text{water released, vegetable softens} \] Water keeps leaving the cells until the concentrations tend to equalise, so the vegetable appears wet. Answer: Exosmosis — the hypertonic salt layer outside draws water out of the vegetable cells.

  9. Exercise 38

    If cells of onion peel and RBC are separately kept in hypotonic solution,
    what among the following will take place? Explain the reason for your
    answer.
    (a)
    Both the cells will swell.
    (b)
    RBC will burst easily while cells of onion peel will resist the bursting to
    some extent.
    (c)
    a and b both are correct.
    (d)
    RBC and onion peel cells will behave similarly.

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    NCERT’s answer
    Hint— (b) Onion peel has cell wall and RBC does not have cell wall
    Hypotonic solution has more water outside than inside the cell. \[\text{outside hypotonic} \Rightarrow \text{water enters by endosmosis} \Rightarrow \text{cell swells} \] RBC has only a plasma membrane, so unchecked swelling bursts it. The onion peel cell's rigid wall limits its swelling, so it resists bursting instead.Answer: (b) RBC bursts easily; the onion peel cell's wall lets it resist bursting to some extent.

  10. Exercise 39

    Bacteria do not have chloroplast but some bacteria are photoautorophic in nature and perform photosynthesis. Which part of bacterial cell performs this?

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    NCERT’s answer
    Hint— Small vesicles associated with plasma membrane
    Photoautotrophic bacteria lack a chloroplast, but their plasma membrane carries the photosynthetic pigment. The membrane folds inward into extensions called chromatophores; these membranous folds hold the pigment and carry out the light-driven reactions of photosynthesis in place of a chloroplast.Answer: The plasma membrane, through its chromatophore infoldings.