Photosynthesis: An Overview Chapter 8.2 Photosynthesis: An Overview

In photosynthesis plants use sunlight energy to convert water and carbon dioxide into sugars and starches and oxygen.

Investigating Photosynthesis Van Helmont wanted to find out if a plant got what it needed just from the soil. He weighed the soil and a seedling and after 5 years weighed the little tree and the soil and saw that the soil hadn’t changed mass but the tree did. He decided that water must be where a plant gets what it needs to survive.

Priestley’s Experiment He put a candle under a jar and found that after time the candle went out – he reasoned there needed to be something in the air to keep the candle burning. He then took a spring of mint and put it under the jar with the candle and found the candle stayed lit for a longer period of time. With this experiment he discovered that a plant released oxygen.

Jan Ingenhousz He found that what Priestley observed only happened when the plant was exposed to light. These 3 experiments let to the discovery that in the presence of light, plants transform carbon dioxide and water into carbohydrates, and release oxygen.

The Photosynthesis Equation The equation for photosynthesis is: light 6CO2 + 6H2O  C6H12O6 + 6O2 In other words: carbon dioxide + water  sugars + oxygen Photosynthesis uses the energy of sunlight to convert water and carbon dioxide to high energy sugars and oxygen.

Light and Pigments Plants have chlorophyll – this is a molecule in chloroplasts. Sunlight is actually made of many different colors of light (wavelengths). We see the different wavelengths as colors. Chlorophyll absorbs the sun’s energy with pigments – light absorbing molecules. There are 2 types of chlorophyll: chlorophyll a and chlorophyll b. Chlorophyll absorbs light in the blue-violet and the red wavelengths the best. It does not absorb green wavelength. This is why plants are green. They reflect they wavelength.