Light Intensity D. Crowley, 2008

Friday, April 21, 2017 Light Intensity To understand how light intensity affects photosynthesis

carbon dioxide + water  glucose + oxygen Talking Why can you argue that it is good for your plants to talk to them?! Remember, when plants grow they do so via photosynthesis – for this to occur plants need carbon dioxide, water and light (and when you speak, you exhale carbon dioxide)! chlorophyll light energy carbon dioxide + water  glucose + oxygen 6CO2 + 6H2O  C6H12O6 + 6O2

Rate Of Photosynthesis What can affect the rate of photosynthesis? Photosynthesis needs carbon dioxide, water and light (as well as a variety of nutrients) If any of these are taken away, they become a limiting factor of photosynthesis – reducing the amount of photosynthesis which can take place…

Light Intensity Experiment How could you measure how light intensity affects the rate of photosynthesis? Hydrogen carbonate indicator reacts when carbon dioxide is present: - In normal atmospheric conditions, the indicator is orange/red When there is lots of carbon dioxide the indicator is yellow When there is not much carbon dioxide the indicator is purple So we can set up an experiment, changing the light intensity, and then measure the hydrogen carbonate indicator to see how the CO2 levels vary…

Experiment Take 2 similar pieces of elodea Place 1 piece of elodea in a test tube and submerge with hydrogen carbonate indicator Place 1 piece of black paper around the test tube, ensuring the top is sealed (use the rubber band) Repeat this experiment, this time placing 1 piece of tracing paper around the test tube Finally set up a control – a test tube with only hydrogen carbonate indicator and no elodea in it or paper around it! Leave test tubes in a rack, by the window for >20 mins…

carbon dioxide + water  glucose + oxygen Prediction Write down your prediction – remember the photosynthesis equation and the colour changes of the hydrogen carbonate indicator… carbon dioxide + water  glucose + oxygen Hydrogen carbonate indicator reacts when carbon dioxide is present: - In normal atmospheric conditions, the indicator is orange/red When there is lots of carbon dioxide the indicator is yellow When there is not much carbon dioxide the indicator is purple

Prediction We should find the test tube with tracing paper (most light availability) should have photosynthesised the most – used up most of the CO2 so the indicator should be purple The test tube with black paper should have stopped most of the light getting through, so not much photosynthesis would have taken place (respiration would actually increase CO2 content) – used least CO2 so the indicator should be yellow Our control should remain orange/red