In the small intestine, the products of digestion are absorbed by both diffusion and active transport (including carrier-mediated and co- transport mechanisms).

Quick Scoop

  • Many small molecules (like some lipids) move into intestinal cells simply by diffusion down their concentration gradient.
  • Most key nutrients (such as glucose, amino acids, and many ions) need active transport, which uses membrane carriers and cellular energy to move them against a gradient.
  • Textbooks often summarize this by saying that absorption occurs by diffusion, facilitated diffusion, and active transport, but exam-style questions usually pair “diffusion and active transport” as the expected answer.

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