Sarah wanted to investigate how net gas exchange in an aquatic plant, Cabomba, is affected by different light intensities.
She set up four boiling tubes, each containing the same volume of orange hydrogencarbonate indicator. She added a healthy sprig of Cabomba of equal length to tubes P, Q, and R. Tube S was left with only the indicator solution and no plant. Each tube was sealed with a rubber bung.
The tubes were then placed under the following conditions for two hours:
Suggest a hypothesis for Sarah's investigation.
Give two variables that Sarah should keep constant in her investigation.
State the purpose of Tube S in the investigation.
Sarah recorded her results in the table below:
| Tube | Colour of indicator at start | Colour of indicator after two hours |
|---|---|---|
| P | orange | purple |
| Q | orange | yellow |
| R | orange | orange |
| S | orange | orange |
Explain the change in colour of the indicator in Tube P.
Explain the change in colour of the indicator in Tube Q.
Suggest why the indicator did not change colour in Tube R
Suggest why the indicator did not change colour in Tube S
Limewater is an indicator that can be used to show an increase in the level of carbon dioxide. Suggest why it would not be a suitable indicator for use in this investigation.
