4.4.1.2
Photosynthesis
Photosynthesis is the process by which green plants produce food. When plants photosynthesise, they absorb light energy to power the reaction. They use carbon dioxide and water to produce glucose and oxygen. The rate of photosynthesis is affected by many factors, such as:
light intensity light wavelength.
You are going to investigate the effect of light intensity on the rate of photosynthesis using an aquatic organism such as pondweed. The effect of light intensity can be investigated by varying the distance between the pondweed and a light source. The closer the light source, the greater the light intensity. Learning outcomes
Maths skills required
Develop a hypothesis based on your understanding of photosynthesis.
Calculate the mean of a set of figures. Understand inverse proportions •HT•
Change one variable and observe the effect.
Present information graphically
Control variables to ensure the data you collect is valid. Apparatus list test tube
stopwatch
0.2% solution of sodium hydrogencarbonate
freshly cut 10 cm piece of pondweed (Elodea works well)
funnel
250 cm3 beaker
eye protection
light source ruler
Safety notes Be careful with the lamps – they might get hot enough to burn your skin. Turn off any lamps when they are not in use. Clean up any spills immediately.
Do not handle lamps, plugs, sockets or switches with wet hands and do not let water splash on the bulbs. Common mistakes LEDs work better than lamps for this practical as they don’t give out as much thermal energy. If you only have traditional lamps, put a large beaker of water in front of the hot light source; this will absorb the thermal energy but let the light pass through. If you do this, you may have difficulty getting the lamp close enough for your initial readings – see below. If there aren’t any bubbles from the cut end of the pondweed, cut a few millimetres off the end and put it right next to the light source. It should then start bubbling and allow you to do your experiment.
AQA GCSE (9–1) Combined Science: Trilogy Required Practicals Lab Book
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