Valentina, Alexandru, and Elizabeth present…

Every autumn some leaves change

COLOR

Green leaves turn to various shades of yellow, orange, red...

But WHY does thishappen???

Well, chemistry can explain it!!!

•First, we should know why the leaves are green

•The green pigment in leaves is chlorophyll

•Absorbs red and blue light from the sunlight

•The light reflected by the leaves is diminished in red and blue and appears green

•Chlorophyll molecule is large

(C55H70MgN4O6)

•It is not water soluble

•Chlorophyll molecules are attached to chloroplasts inside the cells.

•Chloroplasts are the site of photosynthesis

x CO2 + y H2O x O2 + Cx(H2O)y

light

chlorophyll

•The energy of the light absorbed by chlorophyll is converted into chemical energy stored in carbohydrates.

•It causes plants to grow, flower, and produce seed

•The synthesis of chlorophyll requires sunlight and warm temperatures.

Another pigment

found in the leaves

is carotene

•Carotene absorbs blue-green and blue light

•The light reflected from carotene makes the leaves appear yellow

The formula for carotene is C40H36

This large molecule is located in the chloroplasts of many plants

•Carotene is a more stable compound than chlorophyll

•It is the remaining carotene which causes the leaf to appear yellow

•When carotene and chlorophyll are present in the same leaf, the light reflected appears green

The third class of pigments are the

anthocyanins

•Anthocyanins are responsible for the beautiful red color of the maple leaves

•Anthocyanins are also found in ripe apples and grapes

•The red color is determined also by the acidity of the cell sap

•The more acidic the sap is, the brighter the red of the leaf is

•Anthocyanins are formed by a reaction between sugar and certain proteins

•In the autumn the concentration of sugars in the leaves increases so…

•More anthocyanins that will turn the leaf red are produced

There are six different kinds of anthocyanins!

The shortening days and cool nights of autumn trigger changes in the tree…

•A corky membrane between the branch and the leaf stem grows.

•The production of the chlorophyll in the leaf declines, so the other pigments take over

•Weather also influences the intensity of autumn colors.

•Dry, cold sunny weather destroys chlorophyll and enhances anthocyanin production

•The brightest colors are produced when dry sunny days are followed by cool, dry nights

Now you know why the colors

of the leaves change!!!

http://www.brainpop.com/science/ecology/autumnleaves