1. Photosynthesis and why leaves change color

2. PHOTOSYNTHESIS – process by which green plants, some bacteria and some protist change light energy and use carbon dioxide and water to produce carbohydrates

3. WHY ARE PLANTS GREEN?
Different wavelengths of visible light are seen by the human eye as different colors.
Gamma rays
Micro- waves
Radio
waves
X-rays UV
Infrared
Visible light
Wavelength (nm)

4. WHY ARE PLANTS GREEN? Plant Cells have Green Chloroplasts
The thylakoid membrane of the chloroplast is impregnated with photosynthetic pigments (i.e., chlorophylls, carotenoids).

5. THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED
Chloroplasts absorb light energy and convert it to chemical energy
Reflected
light
Light
Absorbed
light
Transmitted
light
Chloroplast

6. Why are plants green?
Reflected light
Transmitted light

7. Photosynthesis
Occurs in chloroplasts found in green parts of plants, primarily leaves
First light energy is absorbed (energy is captured from sunlight)
Pigments – found in cholorplasts absorb light. Different pigments absorb/reflect different wavelengths of light
Chlorophyll – primary pigment. Absorbs mostly blue and red light; reflects green and yellow light.
Carotenoids- pigments that reflect yellow and orange colors.
Where in chloroplasts? Clusters of pigments called Thylakoids

9. Why do leaves change color?
Summer - trees are very actively making sugars with the process of photosynthesis. There is a lot of green chlorophyll and it is being used to capture the energy of sunlight. There is some yellow and orange pigments present too, but there is so much green chlorophyll we don’t see the small amounts of yellow and orange.

10. Why do leaves change color?
Fall- trees begin to shut down their chloroplast (food-making organelles) to get ready for winter. The green chlorophyll disappears from the leaves.
As the bright green fades away, we begin to see the yellow and orange in the leaves. In some trees, like maples, glucose is trapped in the leaves after photosynthesis stops. Sunlight and the cool nights of autumn cause the leaves turn this glucose into a red color. The brown color of trees like oaks is made from wastes left in the leaves.

11. Spring- what do you think happens?
Why do leaves change color?
Winter- there is not enough light or water for photosynthesis. Trees become dormant (greatly reduced metabolic rate) and live off the food they stored during the summer
Spring- what do you think happens?