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.
-DNA is the blueprint for proteins, which play many roles in the body. PROTEINS play many roles in the body and determine many traits. The section of DNA that codes for a specific trait is called a GENE. In fruit flies, straight wings are dominant and curly wings are recessive.
Carbon dioxide is a byproduct of respiration while oxygen is a byproduct of photosynthesis.
Remember that a byproduct is a secondary product that is made in the synthesis of another. It is unintended and excreted.
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Second Question:
If a doctor prescribes antibiotics, its because the you have developed a bacterial infetcion on top of your flu or HIV for example.
Explanation: