A doctor carried out an investigation to find out where glucose is absorbed along the small intestine. One hour after a person had eaten a meal of bread, th...
Question 1 Report
A doctor carried out an investigation to find out where glucose is absorbed along the small intestine. One hour after a person had eaten a meal of bread, the doctor took samples of fluid from the gut lumen and from a nearby blood capillary at three points along the small intestine: the duodenum, the middle region and the ileum. The glucose concentration of each sample was then measured. Fig. 5.1 shows the results that were obtained, and Fig. 5.2 shows the three regions of the gut from which the samples were taken.
| Region | Glucose in gut lumen (mg / 100 cm3) | Glucose in capillary blood (mg / 100 cm3) |
|---|---|---|
| Duodenum | 180 | 90 |
| Jejunum | 120 | 95 |
| Ileum | 40 | 98 |
Fig. 5.2
(a) Using Fig. 5.1, describe how the glucose concentration in the gut lumen changes from the duodenum to the ileum. [2]
(b) Name the region of the alimentary canal where most glucose is absorbed. [1]
(c) Suggest why the glucose concentration in the capillary blood rises along the gut. [2]
(d) State two features of the small intestine that make it efficient at absorbing glucose. [2]
(e) State the meaning of the term active transport. [1]
Answer Details
(a) How lumen glucose changes from duodenum to ileum [2]: the glucose concentration in the lumen falls / decreases [1]; from 180 down to 40 mg per 100 cm\(^3\) (any correct data quote) [1]. It drops as the food moves along because glucose is being taken out of the gut.
(b) Where most glucose is absorbed [1]: the small intestine (accept ileum) [1].
(c) Why capillary blood glucose rises along the gut [2]: glucose is absorbed from the lumen into the blood along the length of the gut [1]; so the further along the sample is taken, the more glucose has entered the capillary [1] (98 mg per 100 cm\(^3\) at the ileum compared with 90 at the duodenum).
(d) Two features making the small intestine efficient [2]: any two of: many villi / microvilli giving a large surface area; a thin (one-cell-thick) epithelium for a short diffusion distance; a dense capillary network / good blood supply to carry glucose away and maintain the gradient [1 each, max 2].
(e) Meaning of active transport [1]: the movement of molecules against a concentration gradient using energy released by respiration [1]. This lets the gut absorb glucose even when its concentration in the blood is already higher than in the lumen.
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