© KCL/PENTECH/WCED 2000 Day length Plants making food 1. Joe lives for basketball. He plays basketball every morning. He eats breakfast after playing, then goes to school. His mum says he needs the energy the food provides. At school he wrote down the food he had for breakfast. With the help of his teacher, he wrote down where the food came from. Here is what he wrote. Milk Butter CowGrassSun EggChickenCornSun Bread WheatSun EXPLAIN in your own words where the energy Joe uses comes from.

© KCL/PENTECH/WCED 2000 Day length Plants making food 2. Joe is still confused about how plants make food. Joe’s teacher says food with sugar and starch gives you a lot of energy. She shows Joe an experiment to test for starch seconds yellow iodine solution warm water DESCRIBE in your own words how to carry out the experiment. boiling water green plant green leaf white leaf 3 minutes 30 seconds leaf turns black hot alcohol in tube boiling water in beaker

© KCL/PENTECH/WCED 2000 Day length Plants making food 3. Joe’s teacher shows him plants that have been kept in different conditions. clear plastic box black plastic box Carbon dioxide removed EXPLAIN what the results of the starch test show. And then they do the starch test together with these results. black leafyellow leaf

© KCL/PENTECH/WCED 2000 Day length Plants making food 4. Photosynthesis literally means ‘light building’. Biologists talk of photosynthesis occuring in plants. Plants can absorb the energy in light using their green pigment called chlorophyll. Plants also absorb carbon dioxide from the air into their leaves and water from the soil through their roots. Plants use light energy to combine the carbon dioxide and water to make glucose. The glucose is used to make the sweet sugar found in nectar, fruits and stem (sugar cane). Some of the glucose is turned into starch and stored in different parts of the plant such as the leaves themselves, roots, seeds and stems. Plants absorb minerals, like nitrates and phosphates, from the soil through their roots. These chemicals are used to build protein which is stored in seeds and is needed for plant growth. During photosynthesis oxygen is produced and released into the air. DRAW a diagram to illustrate the process of photosynthesis. Joe found this in a book at the library

© KCL/PENTECH/WCED 2000 Day length Plants making food 5. Joe said he could not see the oxygen coming out from leaves on plants and trees. His teacher set up an experiment to show the oxygen. water pond weed COUNT the bubbles at different times of the day. DRAW a histogram for your results on the axes below. Number of bubbles Time of day 6am9am12 noon3pm6pm9pm oxygen bubbles Make a CONCLUSION Hint: which environmental factors will have changed over the course of the day to cause this effect on the rate of photosynthesis.