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>
Answer should be A system
When an athlete eats more protein or amino acids than he or she needs, the extra amino acids are either used in building the muscle tissues or are used in energy expenditure.
Proteins are the macromolecules composed of amino acid as polymers. Protein is an essential food component because it helps in the synthesis and repair of body parts, it help in growth and development, and also provides fuel to the body.
Muscle tissues are the ones responsible for the movement of the complete body. The tissues are rich in blood supply. They are of three categories: skeletal, cardiac and smooth. Any movement in body is possible only because of the contractions and relaxations of muscles.
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