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Biology · May / June 2025 · Paper 62 · Question 3

0610

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Hydrogencarbonate indicator can be used to determine the concentration of carbon dioxide in a solution. The table shows the colour of the indicator at different concentrations of carbon dioxide. carbon dioxide concentration hydrogencarbonate indicator colour high yellow medium red low purple Aquatic plants photosynthesise and use up carbon dioxide when in the light. Aquatic plants respire and produce carbon dioxide in the light and in the dark. When the carbon dioxide produced is equal to carbon dioxide used, hydrogencarbonate indicator is red. Using an aquatic plant, plan an investigation to determine the light intensity at which the rate of p [6]

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independent variable

1

at least three different light intensities ;

dependent variable

2

the colour of the indicator ;

3 and 4 details of the method ;;

method of changing light intensity e.g. different lamp

distances / dimmer switch altered / different bulbs / different lamps / different power lamps / detail of how to make one in the dark and one in the light

method to avoid heating effect of light e.g. heat shield / beaker of water between lamp and plant / use LED bulbs to prevent heating
keeping the plant under the water / weighting the plant down
sample the water around the plant and test with indicator 5 and 6 and 7 variables kept constant ;;;
colour / wavelength, of light
temperature
type / species / age, of plant
size / mass / length / height / surface area / number of leaves, of plant
volume of water (covering plant)
volume / number of drops, of (hydrogencarbonate) indicator
concentration of (hydrogencarbonate) indicator
set (stated) time for equilibration (to the new light intensity)
set (stated) time before noting colour

8

two or more repeats ;

9

relevant safety ;

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