Define the measured comparison, standardise samples and conditions, collect repeat quantitative data and explain how an added treatment, time or sample tests the extension.
The photograph shows a sea slug of the genus Aplysia, a marine animal.
external gills; © walkdragon/Shutterstock
Magnification ×1.0
Aplysia can be kept in tanks in a laboratory.
Aplysia absorb oxygen using external gills.
When the gills are touched, the gills are completely withdrawn into the body by a reflex action.
The gills re-emerge after some time.
The student formed the following hypothesis:
The more frequently the gills are touched the less time it takes them to re-emerge.
Plan an investigation to find evidence to support or reject this hypothesis.
Describe preliminary practical work that you might undertake to ensure your proposed method would provide quantitative results.