There are three different types of observation methods for the purpose of research. These three methods include the structured observation, participant observation, and the field experiments.
The structured observation is the method of data collection which is done without the direct involvement of the researcher with the participants. the participant observation is the type of observation which is used in the experiments involving qualitative research. The field experiment is the method of observation when the experiment rules are applied in the real world.
Among the given three types of observations, the structured observation is the type of observation that is used while observing the bacteria once a week for a period of a month.
Hence, the answer is structured observation.