Amino Acid Absorption in Small Intestine

Steps:

• Digestion breaks proteins into amino acids in stomach and small intestine.
• Amino acids are absorbed through villi in the small intestine's lining.
• This region has large surface area for efficient nutrient uptake.
• Assimilation occurs via bloodstream transport from small intestine.

Why A is correct:

• Small intestine is primary site for amino acid absorption due to microvilli increasing surface area for diffusion into blood, per nutrient absorption physiology.

Why the others are wrong:

• B: Large intestine mainly absorbs water and electrolytes, not amino acids.
• C: Stomach digests proteins but does not absorb amino acids significantly.
• D: Mouth performs mechanical breakdown, with no amino acid absorption.

Final answer: A