Pearson Edexcel (9-1) GCSE Combined Science & GCSE Biology core practical - light and photosynthesis

Mr. Osman, a science teacher, introduces a core practical experiment to investigate how light intensity affects the rate of photosynthesis. He defines photosynthesis as the process where green plants and some organisms use sunlight to synthesize glucose and oxygen from carbon dioxide and water with chlorophyll's help.

The experiment requires a shielded lab area, eye protection, bottles with caps, a beaker of algae balls, hydrogen carbonate indicator, a lamp and heat filter, a meter ruler, a 10ml measuring cylinder, kitchen foil, a stopwatch, plastic forceps or a spoon, and a pipette.

First, decide on the distances between the algae and the lamp (e.g., 30, 40, 50, and 60 cm). Place bottles at these measured distances, remove caps, add 10-15 algal balls to each, and then add the same volume of indicator solution using a measuring cylinder and pipette. Cap the bottles.

Set up a heat filter (a water-filled clear container) between the lamp and the tubes. For a negative control, cover one bottle with kitchen foil to keep it in the dark and place it next to the bottle closest to the lamp.

Turn on the lamp and time for 60 minutes or longer. Compare the colors of the solutions in all bottles with an indicator scale. Record the pH of the solutions in a suitable table. Calculate the change in pH per hour for each bottle and add these calculations to the table. Use knowledge of photosynthesis to explain the obtained data.