Respiration vs photosynthesis - results

The liquid in these sealed tubes is a dilute non-poisonous substance: hydrogencarbonate indicator solution, the colour of which shows the amount of (dissolved) carbon dioxide in the liquid.
The colour of the indicator is normally orange, when in equilibrium with normal "fresh" air (carbon dioxide 0.04%).
In the presence of extra carbon dioxide ( > 0.04%), this changes from orangey towards yellow.
It turns towards pinkish-purple when the concentration of carbon dioxide is reduced below normal atmospheric levels ( < 0.04%).
These tubes contain either water snails, pondweed or both. This is to symbolise animals, plants and a balanced combination of life.
The 3 tubes on the left have been exposed to light, and the 3 tubes on the right have been kept in the dark.
In effect the tubes therefore show the ecological relationship between different forms of life on this planet, as it revolves in space!

The picture below shows the results after 24 hours, and the table beneath summarises the experimental treatments, results and conclusions.
Tube Number Kept in: Contents of tube Colour at start Colour at end Conclusion/explanation
1 (left) light snails orange yellow respiration only - by animals
2 snails and pondweed orange respiration by animals and plants balanced by photosynthesis by plants
3 pondweed red photosynthesis exceeds plant respiration
4 dark snails yellow animal respiration only
5 snails and pondweed yellow both plant and animal respiration
6 (right) pondweed yellow plant respiration only
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