Photosynthesis and why leaves change color

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

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)

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

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

Why are plants green? Reflected light Transmitted light

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

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.

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.

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?