Final answer:
To increase O₂ delivery during exercise, human blood O₂ transport involves greater cardiac output and optimal usage of hemoglobin, while squids use hemocyanin to adjust their O₂ levels effectively.
Step-by-step explanation:
During exercise, compared to rest, several aspects of blood O₂ transport are modified to increase O₂ delivery to the exercising muscles. These include increasing the heart rate and stroke volume to boost cardiac output, dilating blood vessels to enhance blood flow to muscles, and maximizing the oxygen extraction by tissues (use of hemoglobin in vertebrates). To facilitate this, our bodies utilize hemoglobin within red blood cells to transport oxygen from the lungs to the cells and myoglobin for temporary storage in the tissues.
In squids, which differ from vertebrates, they use a different oxygen-carrying protein called hemocyanin, which is copper-based instead of iron-based like hemoglobin. This hemocyanin is found freely in their hemolymph (the invertebrate equivalent of blood) and not within cells. During periods of increased activity, squids can modulate their respiratory rate and cardiac output to increase O₂ delivery effectively. The concentration of hemocyanin and its affinity for oxygen can be adapted to varying oxygen levels in the water, providing squids with the ability to sustain high metabolic rates during activities like jet propulsion.