Sec 8-2: Photosynthesis – An Overview

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