Photo AI
A Write notes on photosynthesis under the following headings - Scottish Highers Biology - Question 16 - 2019
Question 16
A Write notes on photosynthesis under the following headings. (i) Use of energy absorbed by photosynthetic pigments (ii) Carbon fixation OR B Write notes on the ... show full transcript
Worked Solution & Example Answer:A Write notes on photosynthesis under the following headings - Scottish Highers Biology - Question 16 - 2019
Step 1
Use of energy absorbed by photosynthetic pigments
Answer
Photosynthesis begins when light energy is absorbed by pigments in the chloroplasts, particularly chlorophyll.
- Energy absorbed by carotenoids is passed to chlorophyll, where it excites electrons in the pigment molecules.
- These excited electrons are transferred along the electron transport chain, leading to a release of energy.
- The energy released is utilized by ATP synthase to produce ATP.
- Additionally, some of this energy is used for photolysis, splitting water molecules to release oxygen.
Step 2
Carbon fixation
Answer
Carbon fixation occurs during the Calvin cycle, where ATP and NADPH generated in the light-dependent reactions are utilized.
- Carbon dioxide is first joined to ribulose bisphosphate (RuBP) by the enzyme RuBisCO.
- This reaction produces 3-phosphoglycerate (3PG).
- The 3PG is then phosphorylated by ATP to form glyceraldehyde-3-phosphate (G3P).
- Hydrogen and NADPH are necessary for this step.
- G3P can then be utilized to synthesize glucose, and some G3P molecules are used to regenerate RuBP.