6.1 Digestion and absorption

Essential idea: The structure of the wall of the small intestine allows it to move, digest and absorb food.

The images above show sections of a small intestine under increasing (left to right) magnification. On the left a cross section of the ileum shows both the folded nature of the inner wall (increasing the surface area in contact with digested food to make absorption more effecient) and the outer muscular layers (which both move the digested food along by peristalsis and again help absorption as the muscular contractions force digested food into contact with the walls). Next under increasing magnification the intricate folded nature of the walls becomes clear. The third image shows the cross section an individual villus. The villus and it's specialised cells are key in both the processes of digestion and absorption (goblet cells secrete enzymes into the lumen, immobilised enzymes on the walls further aid digestion, channels and pumps facilitate absorption). The final image is an electron micrograph which shows the incredibly small microvilli on the surface of the villi (which further increase the surface area available for digestion and absorption).

Understandings, applications and skills

6.1.U1	The contraction of circular and longitudinal muscle of the small intestine mixes the food with enzymes and moves it along the gut.
6.1.U2	The pancreas secretes enzymes into the lumen of the small intestine. [Students should know that amylase, lipase and an endopeptidase are secreted by the pancreas. The name trypsin and the method used to activate it are not required.]
6.1.U3	Enzymes digest most macromolecules in food into monomers in the small intestine. [Students should know that starch, glycogen, lipids and nucleic acids are digested into monomers and that cellulose remains undigested.]
6.1.U4	Villi increase the surface area of epithelium over which absorption is carried out.
6.1.U5	Villi absorb monomers formed by digestion as well as mineral ions and vitamins.
6.1.U6	Different methods of membrane transport are required to absorb different nutrients.
6.1.A1	Processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the liver.
6.1.A2	Use of dialysis tubing to model absorption of digested food in the intestine.
6.1.S1	Production of an annotated diagram of the digestive system.
6.1.S2	Identification of tissue layers in transverse sections of the small intestine viewed with a microscope or in a micrograph. [Tissue layers should include longitudinal and circular muscles, mucosa and epithelium.]

[Text in square brackets indicates guidance notes]

Starter

Drawing the digestive system
How well do you know the structure of the digestive system? Try drawing it and then watch the video to check your understanding. Practise makes perfect expect to be tested on this at the start and end of lessons.

video by Stephanie Castle of IB Biology Review

Understanding the digestive system
A musical introduction to the structure and processes involved by Mr W

Now test your learning from the video using the interactive quizzes and flashcards on Mr W's website

Presentation and Notes

The presentation is designed to help your understanding.

Activity Ideas

Display Board Wars
Research and summarise your understanding of digestion and absorption by constructing a display:

Teams will consist of 3 - 4 individuals
Each team has an A0 sized space on which they can display their work
Each display should aim to answer/satisfy all the learning statements (above)
Teams will be marked on: Creativity (5 max), Organisation/Clarity (5 max),
Accuracy and completeness (10 max) and Presentation (5 max)
Your teacher is a valuable source of information use them well during this part of the process

Teams can potentially gain 10 bonus marks by answering questions on digestion and absorption:

Each team will have 5 questions to answer
if a question can be answered (in 30 seconds) without referring to the display 2 marks are gained, if the display is referred to 1 mark is awarded.
Questions are created by students from other groups, the questioner nominate which student will answer a given question - students cannot be nominated more than twice

The winning team is the one that gains the most points in total from the quiz and the display itself. Prizes for winners/runners up will be decided by your teacher.

Use the Cornell style template to collate your own notes for Topic 6.1 - Digestion and absoprtion

Quick quiz

Quick quiz Use the BioK Quick Quiz on 6.1 Digestion and absorption (as directed) to check your understanding of the topic.

Nature of science

Use models as representations of the real world—dialysis tubing can be used to model absorption in the intestine. (1.10)