Photosynthesis and Chloroplast Function

Study Notes

Biochemical process where plants, algae and some bacteria convert light energy into chemical energy
Produces glucose and oxygen as byproducts
Foundation of life on Earth - powers most ecosystems and produces oxygen

Organelles where photosynthesis occurs
Contain chlorophyll - pigment that absorbs light (blue and red wavelengths)
Chlorophyll absorbs light energy and transfers it into a chemical form that the plant can use to make glucose.
Outer membrane, inner membrane and thylakoid membrane
Thylakoids are stacked into structures known as grana
Space around grana is called stroma
Light-dependent reactions occur in the thylakoid membranes
Light-independent reactions occur in the stroma

### Light-Dependent Reactions

First stage of photosynthesis and occurs in thylakoid membranes
Photons are absorbed by chlorophyll
Energy excites electrons which are passed along the electron transport chain
Water molecules are split (photolysis) releasing oxygen and provides the electrons to replace those lost by chlorophyll
Excited electrons are used to create ATP and NADPH, energy carriers for the next stage
These reactions require light

Second stage of photosynthesis and occurs in the stroma
Doesn't require light directly
RuBisCO fixes carbon dioxide from the atmosphere by attaching it to a 5-carbon sugar, RuBP
The resulting compound is broken down into two molecules of 3-phosphoglycerate (3-PGA)
3-PGA converted into glyceraldehyde-3-phosphate (G3P), a 3-carbon sugar.
Some G3P molecules exit to form glucose and other carbohydrates, while others are recycled to regenerate RuBP

Scientists often experiment with different variables to understand how photosynthesis works
Independent variable: factor you change or manipulate
Dependent variable: factor you measure in response to changes in the independent variable