Digestion & absorption 6.1 30'

Digestion & absorption (The human digestive system)

This subsection looks at the Human Digestive System, its parts and functions. You will also be learning about digestive enzymes, their conditions, substrates and products, methods of absoprtion as well as looking in more detail at villi and microvilli structures in the small intestine. 

Key words 

Learn and test your biological vocabulary for 6.1 digestion and absorption using these flashards 

Clean sweep - quick revision through the whole topic

These slides summarise the essential understanding and skills in this topic. 
They contain short explanations in text and images - good revision for all students.

Read the slides and look up any words or details you find difficult to understand.

Video tutoral

Watch the Screencast of a teacher drawing the diagram below.
This shows how to draw a simple diagram of the digestive system that can be drawn quickly and used in IB exams.

Revision summary list for 6.1 Digestion and absorption

  • The outline structure of the digestive system. (skill - annotated diagram)
  • Food is mixed with enzymes and moved along by the contraction of circular and longitudinal muscle of the small intestine.
  • Enzymes (amylase, lipase and an endopeptidase) are secreted by the pancreas into the small intestine where they digest macromolecules ( starch, glycogen, lipids and nucleic acids) in food into monomers.
  • Tissue layers in the intestines include longitudinal and circular muscles, mucosa and epithelium.
  • The presence of Villi in the small intestines increases the surface area of epithelium and helps absorb the monomers formed by digestion and mineral ions and vitamins.
  • Different nutrients are absorbed into epithelial cells by different membrane transport mechanisms.


  • Apply knowledge of the process or digestion and absorption in the small intestine to the digestion of starch and the transport of maltose and glucose to the liver.
  • Describe your experience of the use of dialysis tubing as a model of the intestines.
  • Draw an annotated diagram of the digestive system.
  • Identify tissue layers in transverse sections of the small intestine

Revision mind maps

Review questions

This is a self marking quiz containing questions covering the topic outlined above.
Try the questions to check your understanding


1. Drag the labels to the gorrect place on the diagram below

mouth esophagus liver stomach pancreas small intestine large intestine anus









Write a list of the ones you got wrong.

Try to sketch a diagram and place these organs into the digestive system.

Then try this question again.


2. Which row in the following list gives the correct functions of the enzymes named?

Amylase breaks down starch

Endopeptidase breaks the peptide bonds in polypeptides

Lipase breaks down triglycerides into fatty acids and glycerol


3. Which of the following best describes the process of peristalsis?

Circular muscles tighten and close the lumen of the intestines, then longitudinal muscles in the wall of the intestines contract pushing the partly digested food along the tube.


4. Which of the following best describes the role of the villi in the small intesines

Villi absorb nutrient molecules in a variety of ways including, diffusion, facillitated diffusion and active transport. The also increase the surface area of the epithelium of the small intestines. Goblet cells within this epithelium produce mucus, but it is not moved along by the villi.

Food is moved along the digestive tract by peristalsis

Which of the following are involved in producing the process of peristalsis?

The contraction of circular and longitudinal muscle moves food along the digestive system


Peristalsis moves food, as it is being digested, along the intestines.

How does this movement help digestion?

As well as moving food along the digestive tract, peristalsis helps to mix the food with enzymes.


Which of the enzymes below are secreted by the pancreas?

The pancreas secretes digestive enzymes, including protease (trypsinogen), lipase, and amylase.

Interestingly - the pancreas also produces an enzyme, "phospholipase" which catalyses breakdown of phospholipids. (not required for IB)

The islets of the pancreas are involved in glucose control, but this is not a role in digestion.


What is the advantage of villi and microvilli increasing the surface area of epithelium in the small intestines?

The larger the surface area of epithelium the faster the rate of absorption is..


Which of the following statements best describes the molecules which are absorbed by villi, in the small intestines?

Large macromolecules cannot be absorbed by villi. Monomers are smaller molecules and are absorbed by the villi.

The term nutrients includes both monomers and macromolecues, so is less precise.


The diagram shows a representation of several layers in the wall of human intestines.

What is the name of the layer labelled X.

Villi are found in the layer called mucosa, and the layer beneath the mucosa is the submucosa.


What is the fate of cellulose in the human digestive system?

Humans don't make enzymes to digest cellulose. Bacteria can digest cellulose in the human intestines, but much of the cellulose eaten is undigested. It is sometimes called 'Fibre'.

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Fun revision activity

A little bit of fun to revise the digestion topic. Can you make it to the leaderboard?
If you can't see the content below, please click this link to Digestion card match game