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Large food molecules must be hydrolysed before their products cross intestinal cell membranes. Explain each enzyme’s substrate and the transport route of the resulting molecules.
What you'll be able to do
Amylase hydrolyses glycosidic bonds in starch, producing shorter sugars including maltose. Membrane-bound disaccharidases complete digestion of relevant disaccharides into monosaccharides close to the absorptive surface. Glucose can then enter epithelial cells by sodium-linked co-transport and leave towards tissue fluid through suitable transporters.
Endopeptidases hydrolyse internal peptide bonds, producing shorter peptides. Exopeptidases remove terminal amino acids; membrane-bound dipeptidases hydrolyse dipeptides. These complementary actions increase the production of absorbable amino acids. Do not say one protein enzyme simply converts every protein directly into glucose.
Bile salts emulsify lipid, forming smaller droplets and increasing the area available to lipase. This is a physical dispersion, not enzymatic hydrolysis by bile. Lipase hydrolyses ester bonds, producing absorbable fatty acids and monoglycerides in the intestinal process.
Bile salts help form micelles containing lipid digestion products. Micelles bring these products close to the epithelial membrane, where lipid components can leave the micelle and enter cells. The whole micelle does not need to pass intact through the cell membrane. Within cells, lipids can be reassembled and packaged for onward transport.
Villi increase intestinal surface area and microvilli further increase epithelial membrane area. Thin epithelium shortens the pathway, while capillary supply and lymphatic transport help move absorbed products away. Numerous transport proteins and an ATP supply support the relevant uptake mechanisms.
Monosaccharide and amino-acid absorption can use co-transport driven by maintained ion gradients. A model membrane such as dialysis tubing can demonstrate selective permeability and diffusion, but it lacks the full living epithelial transport machinery. Evaluate what such a model shows rather than assuming it reproduces active absorption or micelle handling completely.
Try each question before opening the worked response. Use precise biological terms, connect each cause to its effect, and check units and assumptions when interpreting data.
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Key takeaways
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.