The main function of the respiratory system is to allow the exchange of gases between the atmosphere and the lungs.
Hence,the only structure that carries out this function is the alveoli as other structures such as the nose,trachea and pharynx transport gases to the alveoli just so that it can can out its function.
The outer layer of the skin covering the exterior body surface<span> of vertebrates ... the primary tissue of higher plants composed of </span>thin<span>-walled </span>cells<span> that remain capable of ... a swelling on a plant stem consisting of overlapping immature </span>leaves<span> or petals ... Older xylem </span>near<span> the center of a woody stem that no longer conducts water.</span>
Answer: B. Closed
In a closed circulatory system is the one in which the blood is circulated to all the parts of the body of the organism through vessels of different length and width. In this system the blood is pumped from the heart through blood vessels where it is transported to different organs and cells of the body instead of filling up the body cavity.
I think it'd be change in allele frequencies & microevolution.
