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NCERT Exemplar · Class 10 Science Life Processes

82 questions · 82 still being checked

Short Answer Questions 56–65 (part 7 of 9)

  1. Exercise 56

    Why is the rate of breathing in aquatic organisms much faster than in terrestrial organisms?

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    NCERT’s answer
    Aquatic organisms like fishes obtain oxygen from water present in dissolved state through their gills. Since the amount of dissolved oxygen is fairly low compared to the amount of oxygen in the air, the rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms.
    Water holds far less dissolved oxygen than an equal volume of air. \[[\mathrm{O_2}]_{\text{water}} \ll [\mathrm{O_2}]_{\text{air}} \;\Rightarrow\; \text{water moved over gills per unit time} \uparrow \;\Rightarrow\; \text{breathing rate} \uparrow \] Aquatic organisms must therefore ventilate their gills much faster to obtain sufficient oxygen for respiration. Answer: Because dissolved oxygen in water is far scarcer than oxygen in air, aquatic organisms breathe faster to meet their oxygen needs.

  2. Exercise 57

    Why is blood circulation in human heart called double circulation?

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    NCERT’s answer
    The blood circulation in human heart is called double circulation because the blood passes through the heart twice in one complete cycle of the body – once through the right half in the form of deoxygenated blood and once through the left half in the form of oxygenated blood.
    In one complete circuit of the body, blood passes through the heart twice.\[\text{Body (deoxy.)} \to \mathrm{RA} \to \mathrm{RV} \to \text{Lungs} \to \mathrm{LA} \to \mathrm{LV} \to \text{Body (oxy.)} \] The first pass oxygenates blood at the lungs; the second delivers it to body tissues. Answer: Blood passes through the heart twice in one complete circuit of the body -- once to the lungs (pulmonary) and once to the body (systemic) -- so it is called double circulation.

  3. Exercise 58

    What is the advantage of having four chambered heart?

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    NCERT’s answer
    In four chambered heart, left half is completely separated from right half by septa. This prevents oxygenated and deoxygenated blood from mixing. This allows a highly efficient supply of oxygenated blood to all parts of the body. This is useful in animals that have high energy needs, such as birds and mammals.
    A muscular septum fully divides the heart into left and right halves.\[\text{septum} \Rightarrow \text{no mixing of oxygenated \& deoxygenated blood} \Rightarrow \mathrm{O_2} \text{ delivery to tissues} \uparrow \] This efficient oxygen supply meets the high metabolic rate needed to keep body temperature constant. Answer: Complete separation of oxygenated and deoxygenated blood by the septum makes oxygen delivery highly efficient, supporting a high, steady metabolic rate.

  4. Exercise 59

    Mention the major events during photosynthesis

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    NCERT’s answer
    The major events during photosynthesis are
    (a)
    absorption of light energy by chlorophyll
    (b)
    conversion of light energy to chemical energy
    (c)
    splitting of \(\displaystyle \mathrm{H}_2 \mathrm{O}\) into \(\displaystyle \mathrm{H}_2, \mathrm{O}_2\) and \(\displaystyle \mathrm{e}^{-}\)
    (d)
    reduction of \(\displaystyle \mathrm{CO}_2\) to carbohydrates
    Major events:
    absorption of light energy by chlorophyll
    conversion of light energy to chemical energy (ATP, NADPH)
    splitting of water into hydrogen and oxygen (photolysis)
    reduction of carbon dioxide to carbohydrate
    \[6\mathrm{CO_2} + 12\mathrm{H_2O} \xrightarrow[\text{chlorophyll}]{\text{light}} \mathrm{C_6H_{12}O_6} + 6\mathrm{O_2} + 6\mathrm{H_2O} \] Answer: Light absorption by chlorophyll, conversion of light to chemical energy, photolysis of water, and reduction of \(\displaystyle \mathrm{CO_2}\) to carbohydrate.

  5. Exercise 60

    In each of the following situations what happens to the rate of photosynthesis?
    (a)
    Cloudy days
    (b)
    No rainfall in the area
    (c)
    Good manuring in the area
    (d)
    Stomata get blocked due to dust

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    NCERT’s answer
    (a)
    Decreases
    (b)
    Decreases
    (c)
    Increases
    (d)
    Decreases
    Each factor limits photosynthesis when it falls short. \[\text{(a) Cloudy days} \Rightarrow \text{light}\downarrow \Rightarrow \text{rate}\downarrow \] \[\text{(b) No rainfall} \Rightarrow \text{water}\downarrow,\ \text{stomata close} \Rightarrow \mathrm{CO_2}\ \text{uptake}\downarrow \Rightarrow \text{rate}\downarrow \] \[\text{(c) Good manuring} \Rightarrow \text{minerals (Mg, N)}\uparrow \Rightarrow \text{chlorophyll, growth}\uparrow \Rightarrow \text{rate}\uparrow \] \[\text{(d) Dust-blocked stomata} \Rightarrow \mathrm{CO_2}\ \text{entry}\downarrow \Rightarrow \text{rate}\downarrow \] Answer: Rate falls in (a), (b) and (d); rises in (c).

  6. Exercise 61

    Name the energy currency in the living organisms. When and where is it produced?

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    NCERT’s answer
    Adenosine triphosphate (ATP) produced during respiration in living organisms and also during photosynthesis in plants.
    ATP is the energy currency: cells store energy in it and spend it on work. \[\mathrm{ADP} + \mathrm{P_i} + \text{energy} \to \mathrm{ATP} \] \[\text{Respiration: } \mathrm{C_6H_{12}O_6} + 6\,\mathrm{O_2} \to 6\,\mathrm{CO_2} + 6\,\mathrm{H_2O} + \text{energy (ATP)} \] \[\text{Photosynthesis, light reaction: } \mathrm{ADP} + \mathrm{P_i} + \text{light energy} \to \mathrm{ATP} \] It is produced whenever a cell oxidises food during respiration: a little in the cytoplasm (glycolysis), most in the mitochondria. In green plants it is also made in daylight, in the chloroplasts. Answer: ATP, produced in respiration (cytoplasm, mitochondria) and, in plants, in the light reaction of photosynthesis (chloroplasts).

  7. Exercise 62

    What is common for cuscuta, ticks and leeches?

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    NCERT’s answer
    All are parasites, they derive nutrition from plants or animals without killing them.
    Cuscuta is a chlorophyll-less plant that taps a host plant's vascular tissue through haustoria; ticks and leeches attach to a host animal's skin and suck its blood. In all three, food is taken directly from a living host's body, without killing it. Answer: Parasitic mode of nutrition.

  8. Exercise 63

    Explain the role of mouth in digestion of food.

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    NCERT’s answer
    (a)
    Food is crushed into small pieces by the teeth.
    (b)
    It mixes with saliva and the enzyme amylase (found in saliva) breaks down starch into sugars.
    (c)
    Tongue helps in thorough mixing of food with saliva.
    Teeth masticate food into small pieces, raising the surface area for enzyme action; the tongue mixes it with saliva into a bolus. \[\text{Starch} \xrightarrow{\text{salivary amylase}} \text{Maltose} \] Saliva also moistens and lubricates the bolus for swallowing. Answer: The mouth breaks food down mechanically, starts starch digestion chemically (to maltose), and eases swallowing.

  9. Exercise 64

    What are the functions of gastric glands present in the wall of the stomach?

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    NCERT’s answer
    (a)
    Production of pepsin enzyme that digests proteins
    (b)
    Secretion of Mucus for protection of inner lining of stomach.
    Gastric glands secrete gastric juice: \(\displaystyle \mathrm{HCl}\), pepsin and mucus. \[\text{Pepsinogen} \xrightarrow{\mathrm{HCl}} \text{Pepsin}, \qquad \text{Proteins} \xrightarrow{\text{Pepsin, acidic pH}} \text{Peptones} \] \(\displaystyle \mathrm{HCl}\) kills ingested germs and gives pepsin the acidic medium it needs; mucus protects the stomach's own wall from this acid. Answer: They release HCl (kills germs, activates/aids pepsin), pepsin (digests protein) and protective mucus.

  10. Exercise 65

    Match the terms in Column (A) with those in Column (B)
    Column (A)Column (B)
    (a) Trypsin(i) Pancreas
    (b) Amylase(ii) Liver
    (c) Bile(iii) Gastric glands
    (d) Pepsin(iv) Saliva

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    NCERT’s answer
    (a)
    — i, (b) — iv, (c) — ii, (d) — iii
    Each secretion is matched to the organ that makes it. \[\text{(a) Trypsin} \to \text{(i) Pancreas} \qquad \text{(b) Amylase} \to \text{(iv) Saliva} \] \[\text{(c) Bile} \to \text{(ii) Liver} \qquad \text{(d) Pepsin} \to \text{(iii) Gastric glands} \] Answer: a-(i), b-(iv), c-(ii), d-(iii).