Molecular Biology - Photosynthesis

Photosynthesis is the metabolic process by which light energy is converted into chemical energy, involving the production of carbon compounds such as glucose ($C_6H_{12}O_6$).

Visible light has a range of wavelengths between $400\text{ nm}$ (violet) and $700\text{ nm}$ (red). Chlorophyll is the main photosynthetic pigment, absorbing red and blue light while reflecting green light.

The process occurs in two main stages: the light-dependent reactions (in the thylakoid membranes) and the light-independent reactions (in the stroma).

Photolysis of water occurs during the light-dependent reactions where light energy splits water molecules: $2H_2O \rightarrow 4e^- + 4H^+ + O_2$. This provides electrons for the electron transport chain and releases oxygen as a waste product.

The Calvin cycle (light-independent reaction) uses $ATP$ and reduced $NADP$ (NADPH) to fix $CO_2$ into organic molecules, catalyzed by the enzyme Rubisco.

Limiting factors of photosynthesis include temperature, light intensity, and $CO_2$ concentration. Any of these factors, if in short supply, will limit the rate of reaction according to Liebig's Law of the Minimum.

Chromatography is used to separate photosynthetic pigments (chlorophyll $a$, chlorophyll $b$, carotene, and xanthophyll) based on their solubility in a solvent.

The change in Earth's atmosphere, specifically the 'Great Oxidation Event' approximately $2.4$ billion years ago, was caused by the evolution of oxygenic photosynthesis in cyanobacteria.