Building with Light
Source:Den of Airlie, expedition pack (SNH & Wildwood Designs)
- To understand that all green plants depend on sunlight for food
- To understand that different plants grow in different light conditions
You will need
- sketch books or paper
- trees to lie under
- jackets or mats to lie on if the ground is damp
Did you know?Photosynthesis means 'building with light'. It comes from two greek words: phos - light; synthesis - putting together. Green plants make carbohydrates using carbon dioxide as a source of carbon and water as a source of hydrogen. Green plants contain little factories called 'chloroplasts' which trap the energy from sunlight in pigments called chlorophyll. Enzymes then cause a chemical reaction which creates carbohydrates, and oxygen is formed as a waste product.
Before the ActivityDiscuss food chains with the children and introduce the idea that (nearly) all food chains start with the energy from the Sun being captured by green plants and that the green plants use this energy to grow and make leaves, roots and fruit etc. Animals then eat the plants to get their energy to grow. Introduce the children to the three main chemicals involved in photosynthesis, water (H2O), Carbon dioxide (CO2) and Oxygen (O2). Explain that photosynthesis has been called ''The Greatest Deal on Earth''.
- Take the children to an area where they can lie under trees and also lie in an open sunny area. Get them to hold up a green leaf to the sky (with it still attached to the tree, if possible). Let them look closely at it for a minute and think about how green it is. Then get the children to lie down under the trees, arranged like spokes in a wheel. Remind them that the green colour all around them is 'chlorophyll' the mysterious substance which traps sunlight energy. Tell them that we are going to think about the Greatest Deal on Earth! Ask them why it is shady under the trees. As they breathe in ask them what gas their body needs from the air. As they breathe out, ask them what gas they are putting into the air. Remind them what the trees leaves will do with this carbon dioxide.
- Ask them to close their eyes and imagine they are leaves on a forest floor plant. Tell them that if they could photosynthesise they wouldn't need to eat meals! Ask them to think about how much light is reaching them and whether they feel exposed or sheltered, damp or dry.
- Get them to move out from under the trees to an area of more direct light. Get them to lie in their circles again and close their eyes and look up at the sky. Imagine that they are a plant out in the open, how do they feel now. Where would they rather be a plant?
- See if the children can point out different plants which are growing in the open, to the ones which are growing in the shade of the trees. Discuss why some woodland plants like bluebells and primroses will grow and flower quickly in the Spring and then die back (what has happened to their supply of sunlight by mid-summer?).
Suggested Follow up
- The Light and Shade sampling activity in the Woodland Ways section
- The Viewfinders activity in the Woodland Ways section
- The Tree Theatre activity in the Woodland Ways section
- Photosynthesis(and transpiration) made easy from the Cornwall Wildlife Trust
- See the upd8 sitefor games and activities which explore photosynthesis in more depth
- Bitesize revision from the BBC - photosynthesis pages