Question

If you grow yeast in a sealed test tube filled with water and a food source, do you think these growth conditions are aerobic or anaerobic?

Answer 1

As there is some oxygen in water, at first your culture would be aerobic, after a while your cells grow and consume the oxygen, after that it would be anaerobic.

if you want to start an anaerobic culture, even during first hours of cultures, you should use a deoxygenated water for your media, you can deoxygenate water by some commercially available reagents.
so it would be aerobic!