Answer:
The correct answer is a Protein
Explanation:
Proteins are macromolecules consisting of amino acids which are joined by peptide bonds.
Protein molecule has two ends, amino(-NH2) group is present at one end that is known as amino terminal end or N terminal end whereas carboxyl group is present at the another end that is called carboxy terminal end or C terminal end.
In the human respiratory system, gas exchange occurs across the cells of the alveoli. Alveoli or an alveolus is the deepest part of the human respiratory system. This part of the respiratory system is a place where gas exchange between oxygen and carbon dioxide occurs from inhaled air to the blood cells<span>.</span>
