1. 8.2 Photosynthesis: An Overview

2. Photosynthesis
- The process by which plants use the energy from sunlight to convert water and carbon dioxide into high energy carbohydrates, oxygen.
The formula:
6H2O + 6CO2  C6H12O6 + 6O2

3. Photosynthesis: History
Van Helmont (1643)
Devised an experiment that led him to conclude:
That a tree gains most of it’s mass from water
J. Priestley (1771)
Using a bell jar, candle, and a plant he concluded:
The plant releases oxygen

4. J. Ingenhousz (1779)
Found that aquatic plants release bubble of oxygen in the light but not in the dark concluding:
Plants need sunlight to produce oxygen
The above scientists, led others to discover that in the presence of light, plants transform carbon dioxide into carbohydrates and they also release oxygen.

5. The Photosynthesis Equation
6H2O + 6CO2  C6H12O6 + 6O2
Photosynthesis is a series of reactions that use light energy from the sun to convert water and carbon dioxide into sugars and oxygen.

6. Lights and Pigments
In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll, a molecule in chloroplasts.
Cliff notes on light
White = all color wavelengths being reflected back at you.
Black = all color wavelengths being absorbed and none being reflected back at you.
The color you see is not absorbed but is reflected

7. Lights and Pigments Pigment – light absorbing molecules
Chlorophyll – plant’s primary pigment
Chlorphyll α
Chlorophyll b
When plants absorb light, the energy is transferred directly to electrons in the chlorophyll, powering photosynthesis.

8. Section Assessment
1.  Key Concept What did van Helmont, Priestley, and Ingenhousz discover about plants?
2.  Key Concept Describe the process of photosynthesis, including the reactants and products.
3.  Key Concept Why are light and chlorophyll needed for photosynthesis?
4. Describe the relationship between chlorophyll and the color of plants.
5. Critical Thinking Predicting How well would a plant grow under pure yellow light? Explain your answer.