Question

question 9
scientists have believed for many years that less oxygen is dissolved in deeper layers of the ocean compared to shallower layers. what experimental method would best test this hypothesis, and why?
send a robot to measure how much oxygen is dissolved in ocean water at various depths, because the amount of oxygen dissolved in water changes with pressure
add oxygen into a sample of ocean water and measure the percentage of oxygen that stays dissolved, because this allows you to control how much oxygen is added
capture fish from various ocean depths and measure how much oxygen is found in their tissues, because this most directly measures the oxygen available to living systems
grow photosynthetic plants at various ocean depths and determine how much oxygen those plants, produce, because all oceanic oxygen has to come from plants

Explanation:

To test the hypothesis about oxygen levels at different ocean depths, the most direct method is to measure oxygen in water at various depths. Using a robot to measure dissolved oxygen at different depths directly addresses the hypothesis. The other options either add oxygen (not testing natural levels), measure oxygen in fish tissues (indirect, as fish metabolism affects results), or focus on plant - produced oxygen (not the dissolved oxygen in water as hypothesized).

Answer:

Send a robot to measure how much oxygen is dissolved in ocean water at various depths, because the amount of oxygen dissolved in water changes with pressure.