What physiological effects should divers be aware of when underwater?

The correct choice pertains to the physiological effects that divers experience when underwater, particularly regarding buoyancy and nitrogen absorption in the blood. As a diver descends, the pressure increases, affecting how gases are dissolved in the body, particularly nitrogen. According to Henry's Law, the amount of gas that can be dissolved in a liquid is proportional to the pressure of the gas above it. Consequently, the deeper a diver goes, the more nitrogen is absorbed into their bloodstream.

Increased buoyancy refers to the more pronounced effect of buoyancy forces as divers interact with water. This can lead to a need for careful management of buoyancy through the use of buoyancy control devices to maintain desired depths. Divers must also monitor their nitrogen intake since excessive nitrogen absorption can lead to decompression sickness, commonly known as "the bends," upon surfacing, making it vital for divers to manage their depth and time underwater effectively.

The other choices, while they may touch on common experiences or concepts regarding diving and physiological changes, do not capture the critical interactions that occur with pressure, gas absorption, and the resulting implications for safety and buoyancy control underwater.