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NCERT Exemplar · Class 9 Science The Fundamental Unit of Life

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Short Answer Questions 40–52 (part 5 of 6)

  1. Exercise 40

    Match the following A and B
    (A)
    (B)(a)
    Smooth endoplasmic reticulum
    (i)
    Amoeba
    (b)
    Lysosome
    (ii)
    Nucleus
    (c)
    Nucleoid
    (iii)
    Bacteria
    (d)
    Food vacuoles
    (iv)
    Detoxification
    (e)
    Chromatin material
    (v)
    Suicidal bag
    and nucleolus

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    NCERT’s answer
    a—iv; b—v; c—iii; d—i; e—ii
    Smooth endoplasmic reticulum helps break down toxins in liver cells -- detoxification. A lysosome bursts and digests its own cell when the cell is damaged -- a suicidal bag. A nucleoid is the naked, membrane-less DNA region found in a bacterium. Food vacuoles digest food engulfed by Amoeba. Chromatin material and the nucleolus lie inside the nucleus. Answer: (a)-(iv), (b)-(v), (c)-(iii), (d)-(i), (e)-(ii).

  2. Exercise 41

    Write the name of different plant parts in which chromoplast, chloroplast and leucoplast are present.

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    NCERT’s answer
    Flower and Fruit— Chromoplast Leaves of the plant— Chloroplast Root of the plant— Leucoplast
    Chloroplast carries chlorophyll and colours green leaves and young green stems. Chromoplast carries the yellow, orange or red pigment of non-green parts -- flower petals and ripe fruit. Leucoplast is colourless and stores food -- found in roots, underground stems and seeds.Answer: Chloroplast in green leaves/young stems; chromoplast in petals/ripe fruit; leucoplast in roots/underground stems/seeds.

  3. Exercise 42

    Name the organelles which show the analogy written as under
    (a)
    Transporting channels of the cell——
    (b)
    Power house of the cell——
    (c)
    Packaging and dispatching unit of the cell——
    (d)
    Digestive bag of the cell——
    (e)
    Storage sacs of the cell——
    (f)
    Kitchen of the cell——
    (g)
    Control room of the cell——

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    NCERT’s answer
    (a)
    Endoplasmic reticulum (b) Mitochondria (c) Golgi body (d) Lysosome (e) Vacuole (f) Chloroplast (g) Nucleus
    (a)
    Endoplasmic reticulum -- channels for transport within the cell.
    (b)
    Mitochondria -- release energy by respiration.
    (c)
    Golgi apparatus -- packages and dispatches materials in vesicles.
    (d)
    Lysosome -- enzymes digest worn-out organelles and invaders.
    (e)
    Vacuole -- stores water, ions and waste.
    (f)
    Chloroplast -- traps light energy, makes food.
    (g)
    Nucleus -- holds DNA, directs cell activity.
    Answer: (a) Endoplasmic reticulum (b) Mitochondria (c) Golgi apparatus (d) Lysosome (e) Vacuole (f) Chloroplast (g) Nucleus.

  4. Exercise 43

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

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    NCERT’s answer
    Hint— Bacterial cell is a prokaryote Onion peel cell is a plant cell— an eukaryote
    A bacterial cell is prokaryotic -- no nuclear membrane; its DNA lies free as a nucleoid, with no membrane-bound organelles. An onion peel cell is eukaryotic -- DNA inside a true nucleus, with membrane-bound organelles (ER, Golgi body, mitochondria, plastids).Answer: Bacterial cell -- prokaryote, no true nucleus. Onion peel cell -- eukaryote, true nucleus with membrane-bound organelles.

  5. Exercise 44

    How do substances like carbon dioxide (CO2\displaystyle CO_{2}) and water (H2\displaystyle H_{2}O) move in and out of the cell?

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    NCERT’s answer
    Hint—Diffusion and osmosis
    \(\displaystyle \text{CO}_2\), small and uncharged, diffuses across the membrane down its own concentration gradient. \[[\text{CO}_2]_{\text{inside}} > [\text{CO}_2]_{\text{outside}} \Rightarrow \text{CO}_2 \text{ diffuses out} \] Water crosses the same membrane by osmosis, from the more dilute side to the more concentrated side. \[[\text{H}_2\text{O}]_{\text{outside}} > [\text{H}_2\text{O}]_{\text{inside}} \Rightarrow \text{H}_2\text{O enters by osmosis} \] Respiration keeps \(\displaystyle \text{CO}_2\) higher inside, so it diffuses out; osmosis runs either way, depending on which side is more dilute.Answer: \(\displaystyle \text{CO}_2\) moves by diffusion; \(\displaystyle \text{H}_2\text{O}\) moves by osmosis -- both down a concentration gradient.

  6. Exercise 45

    How does amoeba obtain its food?

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    NCERT’s answer
    Hint—Endocytosis
    Amoeba has no fixed shape or mouth; it pushes out temporary pseudopodia that surround a food particle from all sides, engulfing it into a food vacuole by endocytosis (phagocytosis, since the engulfed particle is solid). Enzymes in the vacuole digest the food, and the digested nutrients pass into the cytoplasm.Answer: By endocytosis (phagocytosis) -- pseudopodia trap food in a vacuole, where it is digested.

  7. Exercise 46

    Name the two organelles in a plant cell that contain their own genetic material and ribosomes.

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    NCERT’s answer
    Hint—Mitochondria and plastids
    Mitochondria and plastids carry their own DNA and ribosomes, so each makes some of its own proteins -- though most of their proteins are still coded by the nucleus, so they are only semi-autonomous, never fully independent. Answer: Mitochondria and plastids.

  8. Exercise 47

    Why are lysosomes also known as “scavengers of the cells”?

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    NCERT’s answer
    Hint—Remove debris of the cell
    Lysosomes carry hydrolytic enzymes (proteases, lipases, nucleases) active at acidic pH: \[\text{worn-out organelle or foreign particle} \xrightarrow{\text{lysosomal enzymes}} \text{digested, reusable fragments} \] On membrane rupture the same enzymes digest the whole cell (autolysis). Answer: They digest worn-out organelles and foreign matter, and the cell itself when damaged — the cell's scavengers.

  9. Exercise 48

    Which cell organelle controls most of the activities of the cell? THE FUNDAMENTAL UNIT OF LIFE

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    NCERT’s answer
    Hint—Nucleus
    The nucleus carries the cell's DNA, which codes for the enzymes and proteins that run every activity, and it directs division by organising the chromosomes. Answer: The nucleus.

  10. Exercise 49

    Which kind of plastid is more common in
    (a)
    roots of the plant
    (b)
    leaves of the plant
    (c)
    flowers and fruits

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    NCERT’s answer
    Hint—(a) Leucoplast (b) Chloroplast (c) Chromoplast
    (a)
    Roots: leucoplasts -- no light reaches them, so they store starch rather than photosynthesise.
    (b)
    Leaves: chloroplasts -- chlorophyll traps light for photosynthesis.
    (c)
    Flowers and fruits: chromoplasts -- carotenoid pigments colour them to attract pollinators and dispersers.
    Answer: (a) Leucoplasts (b) Chloroplasts (c) Chromoplasts.

  11. Exercise 50

    Why do plant cells possess large sized vacuole?

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    NCERT’s answer
    Hint—Vacuoles not only store many important substances, they also contain cell sap that give turgidity to cell.
    \[\text{vacuole absorbs water} \Rightarrow \text{cell-sap volume}\uparrow \Rightarrow \text{turgor pressure}\uparrow \text{ against the wall} \]A single large central vacuole keeps the cell turgid and rigid, supporting non-woody parts, and stores water, wastes, ions and pigments. Answer: To build turgor pressure that keeps the cell rigid, and to store water, wastes, ions and pigments.

  12. Exercise 51

    How are chromatin, chromatid and chromosomes related to each other?

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    NCERT’s answer
    Hint—Chromosomes are made up of chromatids and chromatids are made up of chromatin
    \[\text{chromatin (loose DNA–protein thread)} \xrightarrow{\text{coiling, condensation}} \text{chromosome} \]Each of the two identical, full-length strands formed when chromatin condenses into a chromosome is a chromatid; the two sister chromatids stay joined at one point along their length, the centromere. Answer: Chromatin condenses into a chromosome; its two full-length identical strands are sister chromatids, joined at the centromere.

  13. Exercise 52

    What are the consequences of the following conditions?
    (a)
    A cell containing higher water concentration than the surrounding
    medium
    (b)
    A cell having low water concentration than the surrounding medium.
    (c)
    A cell having equal water concentration to its surrounding medium.

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    NCERT’s answer
    (a)
    Exosmosis (b) Endosmosis (c) No effect Long Answer Type Questions
    Water moves down its own concentration gradient, from where it is more concentrated to less: \[W_{\text{cell}} > W_{\text{medium}} \Rightarrow \text{exosmosis} \Rightarrow \text{cell shrinks (plasmolysis)} \] \[W_{\text{cell}} < W_{\text{medium}} \Rightarrow \text{endosmosis} \Rightarrow \text{cell swells, turgid or bursts} \] \[W_{\text{cell}} = W_{\text{medium}} \Rightarrow \text{no net flow} \Rightarrow \text{size unchanged} \]Answer: (a) Shrinks by exosmosis (plasmolysis). (b) Swells by endosmosis, may burst. (c) Size unchanged, no net flow.