The water flea (Daphnia magna) is a small freshwater crustacean that exhibits vertical migration behavior in response to light to avoid predation.
Biologists used a choice chamber to investigate the effects of steady green light and pulsed blue light on the movement behavior of Daphnia magna.
Table 1 shows their results. The P values show results from a chi-squared statistical test.
Table 1 | Behaviour of Daphnia magna | Type of light used in choice chamber | | :--- | :---: | :---: | | | Steady green | Pulsed blue | | Moving towards the light | 38 | 27 | | Moving away from the light | 12 | 23 | | P value | 0.003 | 0.62 |
State a null hypothesis the biologists tested in this investigation.
The natural habitat of Daphnia magna is freshwater ponds. Suggest two abiotic factors (other than light) that should be kept constant in the choice chambers so that the water fleas display normal behavior.
A researcher studying Table 1 suggested that either type of light could be used to cause Daphnia magna to move towards the light source. Evaluate the researcher's suggestion.
At sunrise, Daphnia magna move rapidly away from light into deeper water to hide from visual predators. Table 2 shows the maximum speeds recorded of these water fleas.
Table 2
| Response to light | Maximum speed / mm min−1\text{mm min}^{-1}mm min−1 |
|---|---|
| Water fleas moving towards steady green light | 45 |
| Water fleas moving away from steady green light | 80 |
Calculate the shortest time one Daphnia magna would take to move from a shallow depth of 0.5 m0.5\text{ m}0.5 m to a deep refuge at 14.5 m14.5\text{ m}14.5 m depth at sunrise. Give your answer to the nearest hour.