The Science of Changing Colours. LEAVES.

The Science of Changing Colours. LEAVES.

    Trees that shed their leaves every year are called 'deciduous' trees. New leaves grow again in spring.
         Scientists think that plants get rid of things they can't use any more. After a flower has helped to make seeds for a plant, its petals fall off. And soon after leaves have lost their green material called 'chlorophyll', they also fall off.

        The chlorophyll in leaves uses sunlight to make sugar out of water and carbon dioxide, a gas in the air. Plants need carbon dioxide to live and grow. When leaves use carbon dioxide, another gas called 'oxygen' is produced. Plants don't need all the oxygen they produce, so they let most of it go.
         
       Animals and humans need oxygen to live. Their bodies use oxygen, and what do you think they produce? Yes, carbon dioxide. When animals and humans breathe out, they let the carbon dioxide go.

The Science of Changing Colours. LEAVES.

          It's easy to see that plants, animals, and humans help each other in this way. In countries where the weather cools down in autumn, plants lose their chlorophyll, and thein leaves may turn yellow or red. The yellow colour was in the leaves all summer, but there was so much green in the leaves that the yellow was hidden.

          Yellow leaves turn red only if they have lots of sugar in their sap and the sun shines on them. The more sugar a leaf has, the redder it becomes. If a leaf is kept in the shade, it will stay yellow, even if it has a lot of sugar.