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SolveItNCERT · CBSE · NEET

NCERT Exemplar · Class 10 Science Life Processes

82 questions · 82 still being checked

Short Answer Questions 66–72 (part 8 of 9)

  1. Exercise 66

    Name the correct substrates for the following enzymes
    (a)
    Trypsin
    (b)
    Amylase
    (c)
    Pepsin
    (d)
    Lipase

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    NCERT’s answer
    (a)
    — Protein
    (b)
    — Starch
    (c)
    — Protein
    (d)
    — Fats
    Each enzyme acts on one class of food molecule. \[\text{(a) Trypsin: Proteins} \qquad \text{(b) Amylase: Starch} \] \[\text{(c) Pepsin: Proteins} \qquad \text{(d) Lipase: Fats (lipids)} \] Answer: (a) Proteins (b) Starch (c) Proteins (d) Fats.

  2. Exercise 67

    Why do veins have thin walls as compared to arteries?

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    NCERT’s answer
    Arteries carry blood from the heart to various organs of the body under high pressure so they have thick and elastic walls. Veins collect the blood from different organs and bring it back to the heart. The blood is no longer under pressure so the walls are thin with valves to ensure that blood flows only in one direction.
    Arteries carry blood away from the heart under high pumping pressure, so need thick, elastic, muscular walls to withstand it.\[P_{artery} \gg P_{vein} \] Veins carry blood back to the heart, its pressure already spent crossing the capillaries, so a thin wall suffices; internal valves stop the low-pressure blood from flowing backward. Answer: Veins carry low-pressure blood, so they need no thick elastic wall, only valves against backflow.

  3. Exercise 68

    What will happen if platelets were absent in the blood?

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    NCERT’s answer
    In the absence of platelets, the process of clotting will be affected.
    Platelets plug the cut and are the main source of thromboplastin, which starts clotting. \[\text{Cut} \Rightarrow \text{platelets (main) + injured tissue} \to \text{thromboplastin} \Rightarrow \text{prothrombin} \to \text{thrombin} \Rightarrow \text{fibrinogen} \to \text{fibrin (clot)} \] Without platelets there is no plug and little thromboplastin, so this chain is barely triggered. Answer: Clotting would be severely impaired, so even a small cut would bleed for a long time, risking serious blood loss.

  4. Exercise 69

    Plants have low energy needs as compared to animals. Explain.

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    NCERT’s answer
    Plants do not move. In a large plant body there are many dead cells like schlerenchyma as a result it requires less energy as compared to animals.
    Plants show no locomotion, so nothing is spent on muscular movement. Their few movements -- stomatal opening, tendril coiling, seismonastic folding -- are slow and localised. Much of the plant body, xylem and cork, is dead tissue needing no active metabolism. Answer: No locomotion, only slow localised movements, and dead supportive tissue keep a plant's energy demand low.

  5. Exercise 70

    Why and how does water enter continuously into the root xylem?

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    NCERT’s answer
    Cells of root are in close contact with soil and so actively take up ions. The ion-concentration, increases inside the root and hence osmotic pressure increases the movement of water from the soil into the root which occurs continuously.
    Active mineral uptake keeps a root hair's cell sap more concentrated than the soil solution around it.\[c_{\text{cell sap}} > c_{\text{soil solution}} \xrightarrow{\text{osmosis}} \text{soil} \to \text{root hair} \to \text{cortex} \to \text{endodermis} \to \text{xylem} \] Transpiration keeps drawing water out at the xylem's far end, so the gradient -- and the inflow -- never stops. Answer: Higher solute concentration in root cells draws soil water in by osmosis, cell to cell into the xylem; transpiration keeps removing it, so the flow is continuous.

  6. Exercise 71

    Why is transpiration important for plants?

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    NCERT’s answer
    Transpiration is important because
    (a)
    it helps in absorption and upward movement of water and minerals from roots to leaves
    (b)
    it prevents the plant parts from heating up.
    Water lost from the leaf sets up a suction that keeps water and minerals moving. \[\text{Leaf cells lose water vapour (out through stomata)} \Rightarrow \text{suction on xylem column} \Rightarrow \text{water + minerals rise from root} \] \[\text{Evaporation absorbs latent heat} \Rightarrow \text{leaf temperature}\downarrow \text{(cooling)} \] It also carries off water the roots absorb in excess of the plant's need. Answer: Transpiration pulls water and minerals up from the roots, cools the plant by evaporative loss, and removes water absorbed in excess.

  7. Exercise 72

    How do leaves of plants help in excretion?

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    NCERT’s answer
    Many plants store waste materials in the vacuoles of mesophyll cells and epidermal cells. When old leaves fall, the waste materials are excreted along with the leaves.
    Leaf cells lock wastes away in their vacuoles, for example as calcium oxalate crystals. \[\mathrm{Ca^{2+}(aq) + C_2O_4^{2-}(aq) \to CaC_2O_4(s)} \] Tannins are stored in leaf vacuoles too. Excess water leaves as vapour through stomata, and the stored waste leaves the plant when the leaf falls (abscission). Answer: Leaves store wastes such as calcium oxalate crystals and tannins in their vacuoles and remove them when shed (abscission); excess water is lost as vapour through stomata.