Question

when rob dunns researchers collected specimens from the belly buttons of volunteers, they noticed that anaerobes tended to be found deep in the belly button while aerobes tended to be near the opening. what is the best explanation for this observation? the aerobes were near the opening because they require light. the anaerobes were deeper because that is where there is less oxygen. the anaerobes were deeper because they prefer the darkness. the aerobes were near the opening because there is more air there.

Explanation:

Aerobes need oxygen to survive. The opening of the belly button has more air (and thus more oxygen). Anaerobes do not need oxygen (and some are even harmed by it). The deeper part of the belly button has less oxygen. So, aerobes are near the opening (more air/oxygen) and anaerobes are deep (less oxygen). The options about light and darkness are not relevant as the key difference between aerobes and anaerobes is their oxygen requirement.

Answer:

The anaerobes were deeper because that is where there is less oxygen. The aerobes were near the opening because there is more air there.