Life Processes

  • Question 53

    List the events that occur during photosynthesis in brief.


    During photosynthesis the following events occur:
    (i) Absorption of light energy by the chlorophyll pigment.
    (ii) Conversion of light energy into chemical energy.
    (iii) Splitting of water molecules into hydrogen and oxygen.
    (iv) Reduction of carbon dioxide into carbohydrates.

    Question 54

    Do all events during photosynthesis take place one after the other immediately? Give an example.

    Not necessarily. For example, desert plants take up carbon dioxide at night and prepare an intermediate compound. This intermediate compound is acted upon by the energy absorbed during the day by the chlorophyll.
    Question 55

    State the part played by each of the following in photosynthesis:
    (a) Water (b)Chlorophyll (c) Stomata.


    (a) Water: Water (H2O) undergo photosynthesis in light reaction.

    H2O → 2H+ + O + 2e
    O + O → O2 ↑

    As a result ATP and NADPH are formed which are used in formation of carbohydrates from CO2

    Water also releases O2 which is given out during photosynthesis.

    (b) Chlorophyll: It traps solar (light) energy and utilises it in fixing oxides of carbon (CO2) and hydrogen (H2O) as carbohydrates.

    (c) Stomata: They help in exchange of gases. Carbon dioxide needed in photosynthesis is taken in through stomata. Oxygen produced in photosynthesis is given out through stomata. 

    Question 56

    Draw a labelled diagram of cross-section of a leaf lamina to show chloroplasts.


     Cross-section of a leaf

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