Why are gills, a heart, and a closed circulatory system a much more efficient way of getting oxygen to all the cells than that of insects?

Identify the composition of oceanic and continental crystal rocks.in a model of earth’s interior,where would these rocks appear?

Substances that can pass through cell membranes by diffusion include a. na ions. b. proteins c. glucose. d. oxygen.

In 1994, telomerase activity was discovered in human cancer cell lines. although telomerase activity is rarely present in human somatic tissue, this discovery indicated that humans do contain the genes for telomerase proteins and telomerase rna. since inappropriate activation of telomerase may contribute to cancer, why do you think the genes coding for this enzyme have been maintained in the human genome throughout evolution?