Elena wanted to investigate how net gas exchange in immobilized green algae, Chlorella vulgaris, is affected by different light conditions.
She set up four glass vials, each containing the same volume of red hydrogencarbonate indicator solution. She added 20 uniform alginate beads containing Chlorella to vials A, B, and C. Vial D was left with only the indicator solution and no algae beads. Each vial was sealed with an airtight cap.
The vials were then placed under the following conditions for three hours:
Suggest a hypothesis for Elena's investigation.
State two variables that Elena should keep constant in her investigation.
State the purpose of Vial D in this investigation.
Elena recorded her results in the table below:
| Vial | Colour of indicator at start | Colour of indicator after three hours |
|---|---|---|
| A | red | purple |
| B | red | yellow |
| C | red | red |
| D | red | red |
Explain the change in colour of the indicator in Vial A.
Explain the change in colour of the indicator in Vial B.
Suggest why the indicator did not change colour in: Vial C
Suggest why the indicator did not change colour in: Vial D
Baryta water is a reagent that forms a white benchmark when carbon dioxide concentration increases. Suggest why baryta water would not be a suitable indicator for use in this investigation.
