Because during digestion, blood is needed to execute the process.
Swimming also requires blood so it takes the blood that was initially being used for digestion away.
Hope it helped!
Meiosis does not occur in archaea or bacteria, which reproduce via asexual processes such as mitosis or binary fission. ... Because the chromosomes of each parent undergo genetic recombination during meiosis, each gamete, and thus each zygote, will have a unique genetic blueprint encoded in its DNA.
Nucleic acids also typically contain phosphorous, and nitrogen plays an important structural role in nucleic and proteins. The proteins, being made up a diverse set of amino acids, have, in addition to carbon, hydrogen, oxygen, and nitrogen, the elements sulfur and selenium.