Photosynthesis : 12th Class Biology Question Answer Lesson 11 – NIOS

Photosynthesis : 12th Class Biology Question Answer Lesson 11 – NIOS

Photosynthesis : 12th Class Biology Question Answer Lesson 11 - NIOS


  1. (i) Define photosynthesis
    Ans. It is the process by which green plants produce food (carbohydrates)
    from simple substances like CO2 and water in presence of sun light
    and chlorophyll.

    (ii) Give the overall general chemical equation of photosynthesis. Plants and animals
    Ans. 6CO2 + 12 H2O Chlorophyll ⎯⎯⎯⎯⎯ Sunlight → C6H12O6 + 6H2O + 6O2
  1. (i) List the two categories of photosynthetic pigments.
    Ans. Chlorophylls and carotenoids.
    (ii) Which pigments are known as accessory pigments?
    Ans. Carotenoids and chlorophyll b
  1. (i) What does chlorophyll do to the light falling on it?
    Ans. Absorb it and then convert it into chemical energy.
    (ii) Which pigment system absorbs maximally the red wavelength of light
    Ans. Chlorophyll a and b
  1. Answer the following
    (i) In which colour of light, rate of photosynthesis is minimum and in whichcolour of light it is maximum?
    Ans. Minimum in green and yellow light and maximum in blue and red

    (ii) Name the type of energy that is used in the process of photosynthesis.In which form does this energy get stored in plant body?
    Ans. light energy; chemical energy
  1. Which molecule is the source of evolution of oxygen in photosyntheisis— CO2or H2O?
    Ans. From photolysis of water in PSII


  1. What is the role of NADP?
    Ans. NADP acts as an electron acceptor and H+ acceptor and finally, it gets reduced to NADPH2.
  2. Why is dark reaction called so?
    Ans. It is called dark reaction because it can occur independent of light i.e.
    can occur both in light and in dark.
  3. What is the role of the enzymes (i) rubisco and (ii) PEPCo and where are they present?
    Ans. Rubisco is a part of C3 cycle and combines with CO2 to producea C3 compound called PGA.
    PEPCo is a part of C4 path way and combines with CO2 to form a C4 compound called OAA.
    Rubisco is present in the mesophyll cells of C Plants and animals 3 plants and in the bundle sheath cells of C4 plants.
    PEPCo is found only in mesophyll cells of C4 plants.
  4. Explain Kranz anatomy.
    Ans. The leaves of C4 plants show presence of dimorphic chloroplasts, called Kranz anatomy. In these plants, the vascular bundles have a sheath of large parenchyma cells aroundthem in the form of a wreath, thus the name Kranz anatomy.
  5. Differentiate between the chloroplasts present in the mesophyll cells and in thebundle sheath cells of the leaf of a C4 plant.
  6. Why are C4 plants more efficient than C3 plants?
    Ans. C4 plants have no photorespiration and thus there is no loss of additional carbon dioxide, due to breakdown of RuBP to Glycolate and CO2.
  7. Name the two sets of reactions in photosynthesis in which light energy is required.
    Ans. i. Photolysis of water


  1. List the internal factors that influence the rate of photosynthesis?
    Ans. leaf age, chlorophyll content, leaf anatomy (size, internal structure, stomatal distribution)
  2. State the principle of limiting factor.
    Ans. See text
  3. Give an example of chemosynthetic bacteria.
    Ans. Nitrosomonass and Nitrobacter.
  4. Why are prokaryotes not able to produce ATP by chemiosmosis?
    Ans. Because they are not able to maintain H+ gradient across a membranein the absence of membrane bound organelles in their cytoplasm.


  1. Describe briefly the process of photosynthesis.
  2. Write short notes on (i) Ultrastructure of chloroplast and (ii) Pigments involvedin photosynthesis.
  3. What are accessory pigments? Why they are called so?
  4. Mention path of electrons in the light reaction of photosynthesis.
  5. What do you understand by photophosphorylation.
  6. Discuss photolysis of water and its significance.
  7. Describe the reactions occurring during dark reaction of photosynthesis.
  8. Differentiate between C3 and C4 plants.
  9. Differentiate between PSI and PSII.
  10. What are the products of light reactions. What is the fate of these products?
  11. Why is cyclic photophosphorylation called so?
  12. What is Kranz anatomy?
  13. Name the two carboxylase enzymes in C4 cycle.
  14. What are chemosynthetic autotrophs?
  15. How does CO2 concentration affect the rate of photosynthesis?
  16. What is the effect of excess of oxyygen on the rate of photosynthesis?
  17. Whether light absorbed by green plants, on global basis is limiting factor forphotosynthesis or not! Explain

NIOS 12th class biology Q Ans

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