8-2 Overview of Photosynthesis Biology I

Photosynthesis Photosynthesis – process by which plants and some other organisms use light energy to convert water and carbon dioxide into sugars/starches and oxygen Sunlight + CO 2 + H 2 O glucose + Oxygen

Experiments Vanhelmonts Experiment Put seedling in soil Tree Grew Soil Did not change Conclusion: Water gave mass to the plant

Experiments Cont. Priestleys Experiment: Placed candle under a bell jar Fire became extinguished Then placed candle and plant twig under bell jar Flame stayed lit Conclusion: plants produce oxygen!

Experiments Cont. Ingenhousz – Concluded that Priestlys findings are only true when the plant is exposed to light NO oxygen is produced when the plant is placed in the dark. Final Conclusions: In the presence of light, plants transform CO 2 and H 2 O into carbohydrates and also release oxygen.

Photosynthesis Equation 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 Occurs in the presence of light!

Light and Pigments Not only does photosynthesis require light and CO 2, but it also requires chlorophyll. Chlorophyll is a pigment located in the chloroplast Pigments – light absorbing pigments The plants main pigment is chlorophyll (Types A and B)

Chlorophyll Cont. Chlorophyll absorbs blue and red light and does not absorb green – result is the green color in plants Plants also have other pigments carotenoids and xanthophylls that reflect other wavelengths of light.