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3 light energy (�� )

4 chlorophyll (��)

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4. Use the words in the box to complete the following.

Photosynthesis is the production of carbohydrates from carbon dioxide and water using light energy from the sun and chlorophyll which exists in the cells of green plants.

A. Energy moves along the food chain from one life form to another. Some animals eat plants to get energy. Other animals then eat these animals to obtain the energy they need. Plants, on the other hand, produce their own food using energy from the sun. They do this through a process called 'photosynthesis'.

B. Photosynthesis uses energy from the sun to change carbon dioxide (C02) and water (H20) into carbohydrates. Carbohydrates are chemicals that contain hydrogen, carbon and oxygen and they are the plant's food. To start the process, the plant absorbs carbon dioxide through tiny holes in its leaves and sucks up water from the soil through its roots. A green substance in the plant's leaves called chlorophyll absorbs energy from the sun. The plant now has all it needs for photosynthesis to begin.

C. There are two stages to the photosynthesis process. In the first stage, called the light reaction, light energy from the sun is converted into chemical energy. This energy is stored in a chemical called ATP (adenosine triphosphate). The second stage of the process is the dark reaction. In this reaction, the plant converts the carbon dioxide and water into carbohydrates. Carbohydrates provide the plant with the energy it needs in order to grow.

D. The chemical reaction involved in photosynthesis can be summarised by this equation.

E. The equation shows how important photosynthesis is for life. As well as providing food for the plant from the sun's energy, the equation shows that the reaction also produces the oxygen that animals need to breathe. Without photosynthesis, our planet could not support life as we know it.

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