To vary the influence of the unique stimulus gravity, different experimental and technical approaches have been followed and developed. Today, we are in the ideal situation to perform gravitational biological experiments on the ground — by means of, for example, clinostats and centrifuges — and in real microgravity using different facilities in dependence of the time of free fall needed. Comparative studies between simulated and real microgravity reveal similar results, though the response in actual microgravity appears to be more pronounced and faster. The methods that are used to answer questions in gravitational biology are presented, explained, and discussed within this chapter.

In their natural environment, swimming microorganisms are confronted with a large number of interacting stimuli, which, after a complex signal processing, result in behavioral responses. To understand the impact of a single stimulus, such as gravity, the behavior has to be studied under controlled and defined conditions. Experimenters had to learn that the behavior of microorganisms also depends on parameters such as geometry of the observation chamber, cell density, thermo-convection, time of measurement with respect to circadian rhythm, and that the responses are “full of surprises” (Kessler, 1985b). To study the responses with respect to gravity, an observation chamber should be completely filled and air bubbles should be excluded to avoid chemotactic responses (cf. Section 7.3) and shearing forces.