Explain the process of photosynthesis, using a recipe format so the children can understand how plants eat, drink and grow. The ingredients are light from the sun, water from the soil, carbon dioxide from the air and chlorophyll from the cells in the plants. Explain how the chlorophyll absorbs the light, the water then is split into hydrogen and oxygen, hydrogen and carbon dioxide make food for the plant, and extra oxygen is released into the air.
Leaves on plants and trees can't change color unless they are exposed to light. Choose a tree with large leaves that changes color in the fall, such as maple. In late summer or early fall, before the leaves are changing color, have the children put a piece of aluminum foil over part of a leaf that is still on a tree and tape it on with masking tape. They can then write their names on the tape. When the leaves have changed color, have them carefully remove the foil and see the color difference.
Have the children collect a variety of leaves that have fallen on the ground, particularly ones with deep ribs on the leaves. They can then place the leaves under a piece of paper and rub over them with the side of a crayon. Ask them to choose colors that leaves are in summer as well as what they change to in the fall. They should come up with a variety of greens, from light to dark, as well as yellow, brown, orange and red.
To illustrate the effect of light on plants during photosynthesis, have each child plant two seedlings in separate cups, such as beans or peas. They should write their names on the containers, and place one in the sunlight and the other in complete darkness, such as in a closet. In a week to 10 days, remove the plants from the dark and compare the differences, from root structure to color to health.