Question

 (i) Draw a neat and well-labelled diagram of the Chloroplast.
(ii) List the events taking place in the photo-chemical phase of Photosynthesis.
(iii) If you are planning an experiment to show the effect of light on photosynthesis :
(a) Will you select white light or green light? Justify your answer.
(b) Why would you select a destarched plant?

Answer 1

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

It occurs in the following steps :
(a) The chlorophyll on exposure to light energy becomes activated by absorbing photons.
(b) This energy is used in splitting the water molecules (photolysis) as below :
H₂O → H⁺ + OH^–
(c) OH^– ions through a series of steps produce water (H₂O) and oxygen (O₂). Water may be used inside the plant but O₂ released into the atmosphere.
(d) H⁺ combines with CO₂ in dark reaction to produce glucose.

(iii)
(a) I will select white light because photosynthesis is maximum in white light while it is minimum in green light as the green light is reflected by green plants.
(b) I will select the destarched plant so I can demonstrate the synthesis of starch through the iodine test.