Cambridge Secondary (7-9). Stage 9. Science. Learner's Book - Unit 1: Photosynthesis and the carbon cycle - Question 54

Tubes A and B contain water plant; C and D contain small animals; E and F contain both. A, C and E are kept dark; B, D and F receive light. Each tube has hydrogencarbonate indicator and the same small platform.

All organisms respire all the time. In which tubes were organisms respiring?