Photosynthesis Overview and Reactions

Study Notes

Photosynthesis is the process of capturing light energy to create food.
Plants, algae, and other chlorophyll-bearing organisms capture light energy and use it to produce energy-rich organic molecules from carbon dioxide.
The overall reaction for photosynthesis is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (carbon dioxide + water → glucose + oxygen)
Photosynthesis involves two sets of reactions: light-dependent and light-independent reactions.

These reactions only occur in the presence of light.
They capture solar energy and store it in molecules that will provide the energy for the next reactions.
Key steps are:
- Converting light energy into electron energy
- Splitting water molecules
- Converting electron energy into chemical energy in ATP.

These reactions do not directly require light.
They convert short-term energy storage (ATP) to long-term energy storage (sugar).
Key Steps:
- Carbon Dioxide Fixation: Carbon dioxide enters the leaf, and an enzyme combines it to RuBP (a 5-carbon compound).
- Carbon Dioxide Reduction: The 6-carbon molecule splits into two 3-carbon molecules (PGA). PGA is reduced to a three-carbon molecule called PGAL in a series of reactions (using ATP and NADPH).
- Glucose Formation: PGAL molecules rearrange to form a six-carbon sugar (glucose).
The Calvin Cycle is vital to converting inorganic carbon into organic molecules.

Chloroplasts are the organelles where photosynthesis takes place.
They have a double membrane.
The chloroplast contains grana (stacks of thylakoids) and stroma (fluid surrounding the grana).
Thylakoid membranes are where the light-dependent reactions occur.
Stroma is the site for the light-independent reactions (Calvin cycle).

Respiration is the process of making energy available in the cell.
Respiration involves breaking down complicated molecules (like glucose) into simpler molecules (like CO₂ and water).
The essential reaction for respiration is: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 36 ATP (glucose + oxygen → carbon dioxide + water + energy).
Respiration occurs mainly in mitochondria and the cytoplasm.
Cellular respiration has three main stages: Glycolysis, Krebs Cycle and the Electron transport system.

Photosynthesis uses light energy to convert carbon dioxide and water into glucose and oxygen.
Respiration converts glucose and oxygen into carbon dioxide, water, and energy in the form of ATP. Both processes are crucial for the survival of most life forms.