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NCERT Exemplar · Class 10 Science Life Processes

82 questions · 82 still being checked

Short Answer Questions 36–45 (part 5 of 9)

  1. Exercise 36

    Name the following
    (a)
    The process in plants that links light energy with chemical energy
    (b)
    Organisms that can prepare their own food
    (c)
    The cell organelle where photosynthesis occurs
    (d)
    Cells that surround a stomatal pore
    (e)
    Organisms that cannot prepare their own food
    (f)
    An enzyme secreted from gastric glands in stomach that acts on proteins.

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    NCERT’s answer
    (a)
    Photosynthesis
    (b)
    Autotrophs
    (c)
    Chloroplast
    (d)
    Guard Cells
    (e)
    Heterotrophs
    (f)
    Pepsin
    (a) Photosynthesis (b) Autotrophs (c) Chloroplast (d) Guard cells (e) Heterotrophs (f) Pepsin

  2. Exercise 37

    "All plants give out oxygen during day and carbon dioxide during night". Do you agree with this statement? Give reason.

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    NCERT’s answer
    During day time, as the rate of photosynthesis is more than the rate of respiration, the net result is evolution of oxygen. At night there is no photosynthesis, so they give out carbon dioxide due to respiration.
    Respiration runs continuously, day and night, releasing \(\displaystyle \mathrm{CO_2}\). Photosynthesis needs light, so it runs only by day: \[6\mathrm{CO_2} + 6\mathrm{H_2O} \xrightarrow{\text{light, chlorophyll}} \mathrm{C_6H_{12}O_6} + 6\mathrm{O_2} \] By day photosynthesis outpaces respiration, so net \(\displaystyle \mathrm{O_2}\) is released; at night only respiration continues, so net \(\displaystyle \mathrm{CO_2}\) is released. Respiration itself never stops. Answer: Not fully — plants respire (and release \(\displaystyle \mathrm{CO_2}\)) at all times; only the net gas exchange flips with light.

  3. Exercise 38

    How do the guard cells regulate opening and closing of stomatal pores?

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    NCERT’s answer
    The swelling of guard cells due to absorption of water causes opening of stomatal pores while shrinking of guard cells closes the pores. Opening and closing of stomata occurs due to turgor changes in guard cells. When guard cells are turgid, stomatal pore is open while in flaccid conditions, the stomatal aperture closes.
    Each pore is flanked by two bean-shaped guard cells; the inner (pore-side) wall is thick, the outer wall thin.\[\text{water enters (osmosis)} \Rightarrow \text{turgor}\uparrow \Rightarrow \text{thin outer wall bulges outward} \Rightarrow \text{cells curve apart} \Rightarrow \text{pore opens} \] \[\text{water leaves} \Rightarrow \text{turgor}\downarrow \Rightarrow \text{cells go flaccid and straighten} \Rightarrow \text{pore closes} \] Answer: Turgid guard cells open the stomatal pore; flaccid guard cells close it.

  4. Exercise 39

    Two green plants are kept separately in oxygen free containers, one in the dark and the other in continuous light. Which one will live longer? Give reasons.

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    NCERT’s answer
    Plant kept in continuous light will live longer, because it will be able to produce oxygen required for its respiration by the process of photosynthesis.
    Photosynthesis needs light and yields \(\displaystyle \mathrm{O_2}\); respiration needs \(\displaystyle \mathrm{O_2}\) and runs regardless of light. \[\text{Lit plant: } 6\mathrm{CO_2}+6\mathrm{H_2O} \xrightarrow{\text{light}} \mathrm{C_6H_{12}O_6}+6\mathrm{O_2} \ \Rightarrow\ \mathrm{O_2}\text{ generated, feeds its own respiration} \] \[\text{Dark plant: no photosynthesis} \Rightarrow \text{no O}_2\text{ source in an O}_2\text{-free jar} \Rightarrow \text{respiration starved of O}_2 \] Answer: The plant kept in continuous light lives longer — it manufactures its own \(\displaystyle \mathrm{O_2}\) by photosynthesis and uses it for respiration, while the plant in the dark has no \(\displaystyle \mathrm{O_2}\) source and is starved sooner.

  5. Exercise 40

    If a plant is releasing carbon dioxide and taking in oxygen during the day, does it mean that there is no photosynthesis occurring? Justify your answer.

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    NCERT’s answer
    Release of \(\displaystyle \mathrm{CO}_2\) and intake of \(\displaystyle \mathrm{O}_2\) gives evidence that either photosynthesis is not taking place or its rate is too low. Normally during day time, the rate of photosynthesis is much more than the rate of respiration. So, \(\displaystyle \mathrm{CO}_2\) produced during respiration is used up for photosynthesis hence \(\displaystyle \mathrm{CO}_2\) is not released.
    Released \(\displaystyle \mathrm{CO_2}\) and absorbed \(\displaystyle \mathrm{O_2}\) show only that respiration outpaces any photosynthesis; two cases fit: \[\text{net }\mathrm{O_2}\text{ release} = \text{photosynthesis rate} - \text{respiration rate} < 0 \] \[\text{Case 1: photosynthesis rate} = 0 \quad(\text{plant kept in the dark, or a non-green plant}) \] \[\text{Case 2: } 0 < \text{photosynthesis rate} < \text{respiration rate} \quad(\text{dim light}) \] Answer: Not necessarily; photosynthesis may be absent, or occurring more slowly than respiration.

  6. Exercise 41

    Why do fishes die when taken out of water?

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    NCERT’s answer
    Fishes respire with the help of gills. Gills are richly supplied with blood capillaries and can readily absorb oxygen dissolved in water. Since fishes cannot absorb gaseous oxygen they die soon after they are taken out of water.
    Gills absorb only \(\displaystyle \mathrm{O_2}\) dissolved in water, not the \(\displaystyle \mathrm{O_2}\) of air, and water is what holds the filaments apart.\[\text{in water: filaments spread} \Rightarrow \text{large moist surface} \Rightarrow \text{dissolved }\mathrm{O_2}\text{ absorbed} \] \[\text{in air: filaments collapse, stick together, dry} \Rightarrow \text{surface}\downarrow\downarrow \Rightarrow \mathrm{O_2}\text{ uptake fails} \] Answer: Gills use only dissolved \(\displaystyle \mathrm{O_2}\); in air the filaments collapse and dry, so the fish cannot take in \(\displaystyle \mathrm{O_2}\) and suffocates.

  7. Exercise 42

    Differentiate between an autotroph and a heterotroph.

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    NCERT’s answer
    AutotrophHeterotroph
    1. Organisms that prepare their own food.1. Organisms that are dependent on other organisms for food.
    2. They have chlorophyll.2. They lack chlorophyll.
    Autotroph: has chlorophyll; builds its own organic food from \(\displaystyle \mathrm{CO_2}\) and \(\displaystyle \mathrm{H_2O}\) using light energy (photosynthesis); e.g. green plants, cyanobacteria. Heterotroph: no chlorophyll; cannot make its own food, depends on other organisms (as herbivore, carnivore, saprophyte or parasite) for ready-made organic matter; e.g. animals, fungi. Answer: Autotrophs synthesise their own food from inorganic raw materials using light energy; heterotrophs obtain food from other organisms.

  8. Exercise 43

    Is 'nutrition' a necessity for an organism? Discuss.

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    NCERT’s answer
    Food is required for the following purposes
    (a)
    It provides energy for the various metabolic processes in the body.
    (b)
    It is essential for the growth of new cells and repair or replacement of worn out cells.
    (c)
    It is needed to develop resistance against various diseases.
    Yes. Nutrition is the source of what every life process needs: \[\text{nutrition} \Rightarrow \text{energy for metabolism and movement} + \text{growth and repair of tissues} + \text{resistance against disease} \] \[\text{no nutrition} \Rightarrow \text{no energy, growth, repair or defence} \Rightarrow \text{organism cannot survive} \] Answer: Yes; without nutrition an organism gets no energy, cannot grow or repair itself, and cannot resist disease.

  9. Exercise 44

    What would happen if green plants disappear from earth?

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    NCERT’s answer
    Green plants are the sources of energy for all organisms. If all green plants disappear from the earth, all the herbivores will die due to starvation and so will the carnivores.
    Photosynthesis stops entirely. \[\text{No plants} \Rightarrow \text{no photosynthesis} \Rightarrow O_2 \downarrow,\ CO_2 \uparrow \] Since plants are the primary producers, every food chain collapses -- herbivores starve, then the carnivores that depend on them. Raw materials such as wood, fibre and many medicines would also vanish.

  10. Exercise 45

    Leaves of a healthy potted plant were coated with vaseline. Will this plant remain healthy for long? Give reasons for your answer.

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    NCERT’s answer
    This plant will not remain healthy for a long time because
    (a)
    it will not get oxygen for respiration.
    (b)
    it will not get carbon dioxide for photosynthesis.
    (c)
    Upward movement of water and minerals would be hampered due to lack of transpiration.
    Vaseline coating blocks the stomata on the leaf surface: \[\text{Stomata blocked} \Rightarrow CO_2 \text{ uptake} \downarrow,\ O_2/CO_2 \text{ exchange} \downarrow,\ \text{transpiration} \downarrow \] With photosynthesis and respiration both starved of gas exchange, and the transpiration pull gone, water and minerals stop rising through the xylem.