The Science of Their CHANGING COLOURS

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 clorophyll 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 oxygem to live. Their bodies use oxygen, and what do you think they produce? Yes, carbon dioxide. When animals and humans breath out, they let the carbon dioxide go.

It's easy to see that plants, animals, and humans help each other in this way. In countries where the wheather cools down in autumn, plants lose their chlorophyll, and their 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.

DID YOU KNOW...??

Deciduous forests are one of the world's six major life zones: the often frozen tundra, the mostly evergreen taiga, temperate (mild) deciduous forest, topical rain forest, grassland and savanna, and desert.

The power of Life

Without energy in our bodies, we wouldn't be able to do anything. We couldn't walk, talk, or even play. Energy is usable power. And all energy is related to some kind of motion.

All living things need energy, no matter what they do. Plants get their energy from sunlight. The energy is stored in chemicals inside the plant. This happens in a process is called 'photosynthesis'.

Animals that eat plants take in the energy stored in plants. The energy is stored then stored in chemicals inside the animals as 'food energy'. The same happen when animals eat other animals.

Plants and animals use food energy every day as they grow and do the work of being a plant or an animal. So plants have to keep absorbing sunlight, and animals have to keep eating plants or other animals.

It isn't only living things that have energy. A dead tree has hidden energy. When we burn its wood it gives off warmth, or 'heat energy'. The sun also makes heat energy as it constantly burns.

The sun gives off not just heat but also light, as 'light energy'. The battery in a tourch makes it shine, generating light energy. But if we put the same battery in a radio, we get music. A batter's energy is known as 'eletrical energy'. And in a toy car that eletrical energy produces movement, or 'kinetic energy'.

If we couldn't use heat, light, or eletrical energy, we wouldn't be able to drive cars or cook food. We wouldn't have light at night. Basically, we'd have to use the energy of our own bodies. And that would mean eating a lot more and doing a lot less.

DID YOU KNOW..?

Energy from food is measured in calories, An adult needs to take in about 2,000 to 2,5000 calories a day. Bicyclists in a major race eat three to five times that much, and still some times run out of energy.