An animated description of the process of photosynthesis. Carbon dioxide seeps into leaves through pores called stomata. It reaches the chloroplasts where chlorophyll uses energy from sunlight to bind the carbon dioxide with water brought up from the roots to form carbohydrates. Oxygen is produced as a by-product.
Discuss with the class what factors that are required for photosynthesis. They could do experiments to investigate how the absence or low level of any of these factors can limit the rate of photosynthesis. For example, a table lamp can be moved closer to a beaker containing pondweed and the bubbles of gas counted to see the relationship between light intensity and photosynthesis. Half of a leaf can be covered for several days and then the leaf tested for starch using iodine (after boiling) to prove that photosynthesis only occurs in the light.