Question

3. (1) Draw a neat and well-labeled diagram of the chloroplast.
(1) List the events taking place in the photochemical phase of photosynthesis
In show the effect of light on photosynthesis​

Answer 1

Explanation:

(i) Structure of the chloroplast:

(ii) The photochemical phase of photosynthesis is light dependent. A series of chemical reactions occur in quick succession initiated by light; therefore, the phase is called the photochemical phase. It takes place in the chlorophyll-containing thylakoids of the chloroplast.

It occurs in the following steps:

1) Activation of chlorophyll: On exposure to light, chlorophyll becomes excited and absorbs photons (a photon is the smallest unit of light energy) to get activated.

2) Photolysis of water: The energy absorbed is used in the splitting of water molecules into hydrogen ion (H+) and hydroxide ion (OH−). During this process, electrons are released.

2H2O → 4H+ + O2 + 4e-

3) Production of the reducing agent: NADP, i.e. nicotinamide dinucleotide phosphate, picks up the hydrogen ion and is reduced to NADPH.

NADP + e− + H+ → NADPH

4) Formation of molecular oxygen: Hydroxide ion is oxidised to hydrogen peroxide which decomposes to form molecular oxygen (O2). Molecular oxygen is released during photosynthesis.

2O → O2

5) Photophosphorylation: Electrons are used to convert ADP (adenosine diphosphate) into an energy-rich compound ATP.

ADP + Phosphate → ATP

(inorganic)

(iii)

I would select white light because photosynthesis is maximum in white light, while it is minimum in green light as green light is reflected by green plants.

I would select a destarched plant because during the experiment, any starch formed in the leaf will indicate that the starch is synthesised by the plant during photosynthesis by using light.

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