CAPE Biology Photosynthesis Part 1

Introduction to Photosynthesis

Definition: Photosynthesis is the process through which autotrophic organisms, primarily plants, convert light energy into chemical energy in the form of glucose, using carbon dioxide and water, while releasing oxygen as a byproduct.
Basic equation: Due to misconceptions, it's essential to clarify that carbon dioxide and water do not directly meet during the process. The simplified equation is:6CO2 + 6H2O + Light energy → Glucose + 6O2

Photosynthesis consists of two stages:
- Light-dependent Stage: Requires light.
- Light-independent Stage: Does not require light.

Purpose: Produces ATP and NADPH, essential for the light-independent stage. Oxygen is also released during this process.
When it Happens: Primarily during periods of bright light (e.g., daytime).
Where it Happens:
- Location: Inside chloroplasts, specifically on the thylakoid membranes.
- Thylakoids: Membrane structures within chloroplasts that contain photosynthetic pigments necessary for absorbing light.
- Stroma: Gel-like substance surrounding thylakoids, containing enzymes and proteins supporting photosynthesis.

Light Harvesting:
- Pigments in chloroplasts include chlorophyll a, chlorophyll b, carotenoids, and xanthophylls.
- Pigments are structured in a photosystem that forms a light-harvesting complex within thylakoid membranes.
Photophosphorylation: Clip attached to capturing light energy and converting it into chemical energy.
Chemiosmosis: Process of ATP generation through proton gradients across the thylakoid membrane.

Photosystem II: P680 absorbs light energy.
- Upon excitation, it loses two electrons to the primary electron acceptor.
- Electrons are replenished by splitting water (Photolysis).
- This process releases oxygen gas and hydrogen ions.
Photosystem I: P700 captures light energy following Photosystem II.
- Like P680, it loses two electrons that can be replaced by electrons coming from the electron transport chain.
- Final acceptor is NADP, creating NADPH which holds high energy for the next stage.

Hydrogen ions accumulate in the thylakoid lumen leading passive diffusion through ATP synthase to generate ATP.
The energy stored in NADPH and ATP will be used in the light-independent reactions of photosynthesis.

Critical for the production of ATP and NADPH, which are necessary for the synthesis of glucose during the light-independent stage.
Contributes significantly to the oxygen levels in the atmosphere through the liberation of molecular oxygen as a byproduct of water splitting.