The process of respiration is essential in the oxygen/carbon dioxide cycle. respiration removes from the atmosphere and produces and releases to the atmosphere.

Oxygen is breathed and carbon dioxide is expired during respiration process.

In physiology, respiration is the development of oxygen from the outside condition to the cells inside tissues, and the emission of carbon dioxide to the outer environment.

The physiological meaning of respiration varies from the biochemical definition, which alludes to a metabolic procedure by which a creature acquires vitality (as ATP and NADPH) by oxidizing supplements and discharging waste items.

Cell respiration occurs in individual cells of life form, while physiologic respiration concerns dissemination and transport of metabolic products between the living being and the outer condition.  

they float because they are less dense than the water itself

something denser than water, like a rock, will sink to the bottom