HL Paper 3
Sodium alginate beads were prepared containing a suspension of Chlorella algae. These beads were placed in nine small jars containing hydrogencarbonate indicator solution. Hydrogencarbonate indicator is commonly used to detect changes in pH.
The jars were placed at different distances from a lamp, which was the only light source. The distances ranged from 40 to 130 centimetres. Jars were placed one at a time to avoid the jars from shading each other. Colour changes were observed.
[Source: © International Baccalaureate Organization 2020.]
State the name of the process which occurs in the chloroplasts of Chlorella, that uses CO2.
The colours of the indicator in the jars ranged from yellow to purple after five hours.
Predict the distribution of indicator colours in jars 1 to 9.
Explain the scientific reasoning for your hypothesis.
Suggest one other factor that has to be kept constant in all the jars during the experiment.