Hydrogencarbonate indicator is a water-soluble solution that can act as a source of carbon dioxide for aquatic photosynthetic organisms. The solution changes colour depending on the concentration of carbon dioxide in the solution. These colours are related to different pH values, as shown in Table 1.1. Table 1.1 colour of hydrogencarbonate indicator solution | pH | concentration of carbon dioxide in the solution yellow | 7.6 | increasing carbon dioxide concentration yellow-orange | 7.8 | orange | 8.0 | orange-red | 8.2 | red | 8.4 | atmospheric concentration red-magenta | 8.6 | decreasing carbon dioxide concentration magenta | 8.8 | magenta-purple | 9.0 | purple | 9.2 | Chlorella vulgaris is a protoctist that is single-celled, aquatic and photosynthetic. It can be immobilised in alginate beads. Alginate beads with immobilised C. vulgaris can be used to measure the rate of photosynthesis. [Figure 1.1] [Figure 1.2] [Figure 1.3] [Figure 1.4] [Figure 1.5]