Absorption of digestion productsAQA A-Level Biology: Mind map

Exam questions on Absorption of digestion products

1. Cells lining the ileum absorb glucose from the gut lumen after a meal. As digestion proceeds, the concentration of glucose in the lumen can fall below that inside the epithelial cells. Glucose enters the cells together with sodium ions through a co-transporter protein in the cell-surface membrane.
   Explain how glucose can be absorbed into the epithelial cells when its concentration in the lumen is lower than in the cells.2 marks
2. After a meal containing fat, triglycerides in the small intestine are hydrolysed by lipase to monoglycerides and fatty acids. Bile salts, secreted by the liver, mix with these products and form tiny spherical structures that move to the surface of the epithelial cells lining the ileum.
   Explain how these structures increase the rate at which monoglycerides and fatty acids are absorbed.2 marks
3. Pieces of ileum from a rat were placed in a solution containing glucose and sodium ions, and the rate of glucose uptake was measured. In the normal solution, uptake was 100 arbitrary units. When sodium ions were removed from the solution, uptake fell to 8 units. When the normal solution was supplemented with ouabain, a substance that inhibits the sodium-potassium pump but does not bind to the glucose co-transporter, uptake fell gradually to 15 units over 30 minutes.
   Use the information to explain the role of sodium ions in the absorption of glucose.3 marks