Core Practical: Investigating Light & Photosynthesis Flashcards
All 5 cards in this deck
What are the steps to investigate the effect of light intensity on the rate of photosynthesis using pondweed?
e.g. lamp at 10 cm- Put pondweed in a tube of pond water with the lamp 10 cm away, a water bath between lamp and tube.
- Count the oxygen bubbles given off in one minute = rate in bubbles per minute.
- Repeat at other distances, working out light intensity as .
Why is a water bath (tank of water) placed between the lamp and the pondweed?
To maintain a constant temperature — it acts as a heat shield, absorbing heat from the lamp.
Give three variables that must be controlled when investigating the effect of light intensity on the rate of photosynthesis.
Any three of: temperature; carbon dioxide concentration; volume of pond water; length/mass/type of pondweed; extraneous light (use the same light source).
Give one improvement that gives a more accurate measurement of the gas produced than counting bubbles by eye.
Collect the gas in a gas syringe or measuring cylinder to measure the volume of oxygen produced.
Or: film the bubbles with a video camera and count them in slow-motion playback.Why is sodium hydrogencarbonate added to the water in the pondweed experiment?
It releases carbon dioxide into the water, so carbon dioxide is not a limiting factor.