#biology #lightenergy #photosynthesis #convertionofenergy #textbook #igcse
Pg:- 86,87,88
Ch:- 6
Leaves convert light energy into ATP and oxygen through photosynthesis, which primarily occurs in plant cells' chloroplasts. This process can be divided into two main stages: the light-dependent reactions and the Calvin cycle (light-independent reactions).
1. Light Absorption:
Chlorophyll and other pigments in the chloroplasts absorb light energy, primarily from the sun.
This light energy excites electrons in chlorophyll molecules, particularly in photosystem II.
2. Splitting of Water (Photolysis):
The absorbed light energy drives the splitting of water molecules (H2OH_2OH2O) into:
Oxygen gas (O2): Released into the atmosphere as a byproduct.
Protons (H+): Contribute to a proton gradient used for ATP production.
Electrons: Replenish the electrons lost by chlorophyll in photosystem II.
2H2O → 4H+ + 4e− + O2
3. Electron Transport Chain (ETC):
The excited electrons move through an electron transport chain, a series of protein complexes embedded in the thylakoid membrane.
As electrons travel through the ETC:
Their energy is used to pump protons (H+) into the thylakoid lumen, creating a proton gradient (high H+ concentration inside the thylakoid and low H+ in the stroma).
4. ATP Formation (Photophosphorylation):
The proton gradient drives protons back into the stroma through ATP synthase, a protein complex that acts like a turbine.
As protons flow through ATP synthase, ATP from ADP and inorganic phosphate (Pi ) is generated.
ADP + Pi → ATP
5. Production of NADPH:
Electrons reach photosystem I, where they are re-energized by light.
These high-energy electrons are transferred to NADP⁺, along with protons, to form NADPH. This molecule serves as an energy carrier for the Calvin cycle.
NADP+ + 2e− + H+ → NADPH
Summary:
In the light-dependent reactions:
Light energy is converted into chemical energy stored in ATP and NADPH.
Oxygen is produced as a byproduct of the splitting of water.
These products are then used in the Calvin cycle to synthesize glucose, completing the photosynthesis process.
How is light energy converted into chemical energy during photosynthesis?
What are the main stages of photosynthesis, and what happens in each stage?
How do leaves adapt to maximize light absorption?
What is the significance of the light-dependent reactions in photosynthesis?
How do the light-independent reactions (Calvin cycle) contribute to the synthesis of glucose?
What factors can affect the efficiency of photosynthesis in leaves?