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)
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.
Closer lamp → more bubbles (faster photosynthesis). Rate levels off at high light.
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.