Question 23M.3.HL.TZ2.27
| Date | May 2023 | Marks available | [Maximum mark: 6] | Reference code | 23M.3.HL.TZ2.27 |
| Level | HL | Paper | 3 | Time zone | TZ2 |
| Command term | Explain | Question number | 27 | Adapted from | N/A |
Explain how the epithelium cells of intestinal villi are adapted for absorption and what happens to absorbed material when it reaches the liver.
[6]
Adaptations for absorption:
a. epithelial cells are one cell layer thick which facilitates transport (from the lumen to blood vessels);
b. (epithelial cells) joined by tight junctions prevents leakage/OWTTE;
c. (each cell has) microvilli/brush border to increase absorption surface
OR
microvilli provide large surface area:volume ratio to increase absorption rate;
d. epithelial cells close to capillaries for transport/OWTTE;
e. epithelial cells rich in mitochondria to provide energy/ATP (for active transport);
f. membranes contain protein channels used for co-transport/facilitated diffusion of substances;
g. vesicles in large numbers for absorption of larger molecules (by endocytosis);
Storage in liver:
h. glucose is stored as glycogen (in the liver/hepatocytes);
i. fatty acids/fats stored in hepatocytes;
j. excess Vitamin A/D stored in hepatocytes;
k. iron/minerals stored in hepatocytes;
l. detoxification/breakdown of toxins;
Allow maximum of 5 marks for absorption.
g. Accept correct examples.
i. Accept correct examples.
This question was generally well answered, and many correct and complete answers were seen. Many answers failed to include enough elements for a long essay question and more could have been written about the adaptations of the epithelium cells for absorption, such as channel proteins and vesicles, and the fate of absorbed material in the liver, most only mentioning storage of glucose as glycogen. Many irrelevant parts were included, although usually correct, such as details of the hepatic circulation or the regulation of blood glucose by pancreatic hormones.
