Photosynthesis and why Photosynthesis and why leaves change colorleaves 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

Different wavelengths of visible light are seen by the human eye as different colors.

WHYWHY ARE ARE PLA PLANTS NTS GREGREEN?EN?

Gammarays

X-rays UV Infrared Micro-waves

Radiowaves

Visible light

Wavelength (nm)

WHYWHY ARE ARE PLA PLANTS NTS GREGREEN? EN?

Plant Cells have Green Chloroplasts

The thylakoid membrane of the chloroplast is impregnated with photosynthetic pigments (i.e., chlorophylls, carotenoids).

Chloroplasts Chloroplasts absorb light absorb light energy and energy and convert it to convert it to chemical energychemical energy

LightReflected

light

Absorbedlight

Transmittedlight

Chloroplast

THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED

Why are plants green?

Reflected lig

ht

Transmitted light

PhotosynthesisPhotosynthesis Occurs in Occurs in chloroplastschloroplasts found in green parts of plants, found in green parts of plants,

primarily leavesprimarily leaves First light energy is absorbed (energy is captured from First light energy is absorbed (energy is captured from

sunlight)sunlight) PigmentsPigments – found in cholorplasts absorb light. Different – found in cholorplasts absorb light. Different

pigments absorb/reflect different wavelengths of lightpigments absorb/reflect different wavelengths of light ChlorophyllChlorophyll – primary pigment. Absorbs mostly blue – primary pigment. Absorbs mostly blue

and red light; reflects green and yellow light. and red light; reflects green and yellow light. CarotenoidsCarotenoids- pigments that reflect yellow and orange - pigments that reflect yellow and orange

colors. colors. Where in chloroplasts? Clusters of pigments called Where in chloroplasts? Clusters of pigments called

ThylakoidsThylakoids

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.

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?

Why do leaves change color?