Topics to revise
Photosynthesis
Bonding
Space (this is the only week with 3 topics as its triple)
Required practical - Photosynthesis
2026 - You are getting there, well done! Remember, if you have followed our program, you are on track to finish all topics. You could try a past paper over the holiday, but make sure you do the topics first. Once the exams start, you can use that time to check your understanding and try more papers.
We have created a series of short papers with Videos explaining how to answer each question. These are a good way to practice exam technique.
Photosynthesis
Investigate how light intensity affects the rate of photosynthesis by counting bubbles from pondweed.
Check your understanding with these quick common questions. Use the drop down boxes to see the correct answers.
Independent: distance of lamp from pondweed (light intensity).
Dependent: number of bubbles produced per minute.
Control: same pondweed, same time, same water temperature.
Lamp, metre ruler, pondweed (e.g. Elodea), beaker.
Sodium hydrogen carbonate (baking powder)
Lamp, metre ruler, pondweed (e.g. Elodea), beaker.
Sodium hydrogen carbonate (baking powder)
Measure distance carefully, use same pondweed length, repeat counts.
Improve accuracy my measuring volume of gas produced with a gas syringe
Control temperature with a water bath or LED light to improve Validity
Control CO2 concentration by using a solution of sodium hydrogen carbonate to improve validity.
Describe : Closer lamp, the higher the light intensity → more bubbles (faster photosynthesis). Rate levels off at high light.
Explain: This is because plants need light for photosynthesis. When the rate levels off, this is because another factor has become limiting (temperature or CO2).
Cut pond weed with a sharp blade
Measure 10cm of pond weed with a ruler
Place pondweed in a solution of sodium hydrogen carbonate (bicarb/baking powder)
Set lamp at fixed distance.
Count bubbles for 1 min.
Repeat at different distances.
Plot graph of rate vs distance.