Each of two test-tubes was topped up with hydrogencarbonate indicator. An aquatic plant was put into each test-tube, and the test-tubes were sealed with bungs, as shown. Test-tube X was exposed to light, whereas test-tube Y was left in the dark. The outcomes are shown. What causes the colour changes in the hydrogencarbonate indicator in X and Y?
- AX: a decrease in the concentration of carbon dioxide; Y: an increase in the concentration of carbon dioxide
- BX: a decrease in the concentration of oxygen; Y: an increase in the concentration of oxygen
- CX: an increase in the concentration of carbon dioxide; Y: a decrease in the concentration of carbon dioxide
- DX: an increase in the concentration of oxygen; Y: a decrease in the concentration of oxygen