Jan van Helmont’s • determined that most of the mass (carbohydrates) gained in a Willow tree came from water.
Joseph Priestly • concluded that a plant
releases oxygen by making observations using a bell jar, candle and a plant.
Jan Ingenhousz • discovered that
aquatic plants produce oxygen bubble in light, but not in the dark.
u Photosynthesis
- Process by which plants use sunlight to convert H2O & CO2 into sugar & O2.
6CO2 + 6H2O C6H12O6 + 6O2
Carbon Dioxide
Water Glucose Oxygen
NOTE: Photosynthesis is the process of making SUGARS/STARCHES…NOT ENERGY!!!
**The plant uses the sugars and starches to make ATP.**
u How does the plant capture the light?
- They use pigments (molecules that absorb sunlight).
**Chlorophyll = Main pigment used by plants**
u Photosynthesis takes place inside the chloroplast.
u Thylakoid – Saclike membranes responsible for absorbing light. (Contains chlorophyll)
u Grana – Stack of thylakoid membranes.
**Light-reactions take place here.
u Stroma – Region outside the grana.
**Dark Reactions take place here.
Thylakoid Grana
Stroma
Light-Dependent Reactions 1) Chlorophyll absorbs sunlight & water.
- Reaction breaks H2O into 2 H+ and 1 O 2) O2 released back into atmosphere. 3) H+ bind to NADP+ (high energy electron carrier) producing
NADPH and turns ADP into ATP.
Light-independent reactions 4) CO2 is absorbed by the stroma 5) CO2 interacts w/ ATP and NADPH to make glucose.
u Factors that affect photosynthesis:
1) Water shortages
- H2O required for light-dependent stage
2) Temperature
- Photosynthesis depends on enzymes that work best between 0-35C.
3) Light intensity
- Increased light intensity = more photosynthesis until plateau
4) CO2
- Increased CO2 = more photosynthesis until plateau