Question

State the MAJOR steps for Malus domestica to harvest light energy and convert to sugar during photosynthesis. (Details of the biochemical pathways are NOT required.)

Answer 1

Photosynthesis is the process by which a plant prepare their food in the presence of carbon dioxide (through stomata), sunlight (taken up by the chlorophyll) and water (through soil via roots).

This process consists of two Phenomenons :

1) Light reaction or Photochemical reaction occurs during day time

2) Dark reaction or Biochemical reaction occurs during night time

Steps during Light reaction or Photochemical reaction:

a) Absorption of CO2 with the help of stomata which open during day.

b) Absorption of water with the help of roots from the soil.

c) Absorption of sunlight in the presence of chlorophyll.

d) Photolysis of water as follow:

2H2O   4H+ + O2 this reaction is carried out in the presence of sunlight during day time.

e) Removal of oxygen gas from the stomata.

f) 4H+ and light energy stored in the form of ATP and NADPH + H+ (that can be used in the dark reaction) by the help of process electron transport chain .

These all steps are carried out in the thylakoid membrane where photosystem I ( P700) and photosystem II (P680) used to harvest the solar energy.

Steps during Dark reaction or Biochemical reaction

During night, plant use light reaction products to form their food.

Reduction of CO2 using H+ and ATP/NADPH + H+ form of stored energy, convert it into the glucose with the help of Calvin or C3 cycle.

Excess of glucose is stored in the vacuole for Futcher use