In a person with the coeliac condition, eating gluten, a protein found in wheat, causes the body's own defences to attack and damage these villi, making the...
Question 1 Report
In a person with the coeliac condition, eating gluten, a protein found in wheat, causes the body's own defences to attack and damage these villi, making them shorter and flatter than normal. Fig. 9.1 shows a healthy villus, with its thin covering of cells and its blood supply. To measure the effect of the condition, doctors gave a test meal and recorded the mass of glucose absorbed per hour: a healthy person absorbed 5.0 g per hour, while a person with the untreated coeliac condition absorbed only 1.5 g per hour.
Fig. 9.1
(a) State the process, other than diffusion, by which glucose can be absorbed into the blood. [1]
(b) Explain why this process needs energy from respiration. [3]
(c) Calculate the percentage decrease in the mass of glucose absorbed by the person with the coeliac condition compared with the healthy person. Show your working. [2]
(d) Explain why damaged, flattened villi reduce the absorption of glucose. [3]
(e) State two other substances, besides glucose, whose absorption would also be reduced. [2]
(f) Suggest how avoiding gluten could improve the person's absorption over time. [2]
Answer Details
This question tests absorption at the villus, active transport, a percentage-change calculation, and how surface area affects absorption.
(a) [1] Besides diffusion, glucose is absorbed by active transport [1].
(b) [3] Active transport moves glucose against its concentration gradient (from a lower to a higher glucose concentration) [1]; moving a substance against a gradient requires energy [1]; this energy is released by respiration in the epithelial cells of the villus (which is why these cells contain many mitochondria) [1].
(c) [2] Percentage decrease \( = \dfrac{5.0 - 1.5}{5.0} \times 100 \) [1] \( = \dfrac{3.5}{5.0} \times 100 = \mathbf{70\%} \) [1].
(d) [3] Damaged villi are shorter and flatter, so the surface area for absorption is smaller [1]; fewer villi/microvilli are in contact with the food [1]; so there is less diffusion and active transport of glucose into the blood [1].
(e) [2] Any two other absorbed nutrients, one mark each: amino acids; fatty acids/glycerol; water; mineral ions; vitamins [2].
(f) [2] If gluten is avoided, the villi recover / grow back to their normal shape [1], increasing the surface area so absorption improves over time [1].
Download The App On Google Playstore
Everything you need to excel in your exams
