Biology Chapter: Energy in Cells & Photosynthesis

Study Notes

ATP (adenosine triphosphate) is the main energy molecule used by cells.
ATP is composed of adenine, ribose, and three phosphate groups.
When the third phosphate group is removed from ATP, energy is released, forming ADP (adenosine diphosphate) and a phosphate group.
This energy release powers almost all energy-requiring activities in cells like the sodium-potassium pump and movement of cell parts.
ATP is not suitable for long-term energy storage.
Glucose (C6H12O6) is a more efficient energy storage molecule, containing 90 times more energy than ATP.
Cells maintain a small amount of ATP and store the majority of their energy in molecules like glucose.

Photosynthesis is the process plants use to convert sunlight, water, and carbon dioxide into glucose, a stored form of energy.
The equation for photosynthesis is: 6CO2 + 6H2O → C6H12O6 + 6O2, where 6CO2 represents carbon dioxide, 6H2O represents water, C6H12O6 represents glucose, and 6O2 represents oxygen.
Chlorophyll is a pigment in plants that absorbs sunlight and facilitates the process of photosynthesis.

Chloroplasts are the organelles in plants where photosynthesis takes place.
Chloroplasts have a double membrane structure.
Thylakoids are green membranes within chloroplasts containing chlorophyll.
A stack of thylakoids is called a granum.
Light-dependent reactions of photosynthesis occur in the thylakoids.
The stroma is the fluid surrounding the grana, where the light-independent reactions (Calvin Cycle) occur.

Photosynthesis involves two sets of reactions:
- Light-dependent reactions: These reactions require sunlight and occur in the thylakoids.
- Light-independent reactions (Calvin Cycle): These reactions do not require sunlight and occur in the stroma.

NADPH is a molecule that carries excited electrons, similar to how ATP stores energy in its third phosphate group.
NADPH acts as a "babysitter" carrying electrons from the light-dependent reactions in thylakoids to the light-independent reactions in the stroma.

Light-dependent reactions utilize sunlight and chlorophyll to store energy in ATP and NADPH.
ATP and NADPH carry energy to power the light-independent reactions (Calvin Cycle).
Glucose is the main product of the light-independent reactions, representing the entire process's goal.
Oxygen (O2) is a byproduct of photosynthesis and is released into the air.

The light-dependent reactions involve two main photosystems, Photosystem II and Photosystem I:
- Photosystem II: Uses chlorophyll pigments to absorb light energy and generate ATP.
- Photosystem I: Produces NADPH by exciting electrons using light energy.
Hydrogen ions (H+) are pumped across the thylakoid membrane, contributing to ATP production.