Fig. 1. shows the apparatus used by some students during an investigation.
The apparatus is drawn as seen from above.

Some arthropods were placed in the container.
A drop of red dye was inserted into the capillary tube.
The drop of red dye in the capillary tube gradually moved towards the arthropods.
(i) Explain why the drop of red dye moved towards the arthropods.
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The investigation shown in Fig. 1 was repeated at different temperatures.
Fig. 2 shows the results.

(ii) State the trend shown in Fig. 2.
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(iii) Calculate the percentage increase in the rate of dye movement between 10°C and 20°C.
Show your working.

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(i) When the red dye was inserted in the capillary tube , it moves towards the arthropods because of the aerobic respiration. The oxygen present in the container was used by the arthropods and carbon dioxide/ water vapour was released by the process of aerobic respiration. As the container is sealed, carbon dioxide/ water vapour is absorbed by the chemical present in the container for the absorption of CO${}_2$ / water vapour. So, the volume of air and pressure present in the container decreases. As there is no oxygen left in the container, now arthropods will have to take oxygen from outside through the capillary tube. Hence, the dye present in the capillary tube will move towards the arthropods.
(ii) The Fig. 2, explains the graph, rate of dye movement/ mm per hour versus temperature (${}^o$C). At low temperature, the dye movement is slow and at high temperature dye movement is fast. So, we can conclude that, as the temperature increases the rate of dye movement increases.
(iii) Movement of dye at 10 ${}^o$C = 5 mm per hour
Movement of dye at 20 ${}^o$C = 5.9 per hour
Percentage increase in the rate of dye movement between 10°C and 20°C = 5 - 5.9
= 0.9
= 0.9 × 100
= 90 %