Absorbing food Edexcel International GCSE Biology revision
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In plain words
Digested food is no use until it's in your blood. The wall of the small intestine is folded into millions of tiny fingers called villi. Unfolded, it would cover a tennis court, which is why absorption is so quick.
Three things to know
- Digested food is absorbed in the small intestine (the ileum). Most water is absorbed there too, and the rest in the colon.
- Villi give a very large surface area. Their walls are one cell thick, so there's a short distance to cross, and each has a network of capillaries to carry the food away.
- Each villus also has a lacteal, which absorbs fatty acids and glycerol. Microvilli on the surface cells increase the area even more.
Tips and tricks
- Three features of a villus, three reasons: large surface area, thin wall (short distance), good blood supply (keeps the concentration gradient steep).
- The same three features appear on every exchange surface, including the alveoli in the lungs.
It lands in your notebook with its questions as flashcards.
Absorbing food: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
What are the finger-like folds of the small intestine called?
They increase the surface area for absorption.
Why are the walls of the villi one cell thick?
A short distance means faster absorption.
What does the lacteal absorb?
Sugars and amino acids go into the capillaries.
Where is most water absorbed?
The colon absorbs most of what remains.
Why does a villus have a rich blood supply?
This keeps the concentration gradient steep.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 6 marks. Write your answers on paper, then check them.
Absorbing food
Edexcel International GCSE Biology 4BI1 · 6 marks · papermunch.org
Name ______________________________ Date ______________
Explain how villi are adapted for absorbing digested food.[3]
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They give a large surface area; their walls are one cell thick, so the diffusion distance is short; they have many blood capillaries (and a lacteal) to carry absorbed food away, keeping the concentration gradient steep.
Name the part of the alimentary canal where most water is absorbed.[1]
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The small intestine.
State what is absorbed into the capillaries and what is absorbed into the lacteal of a villus.[2]
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Capillaries: glucose and amino acids. Lacteal: fatty acids and glycerol.
Answers: Absorbing food
- 1. They give a large surface area; their walls are one cell thick, so the diffusion distance is short; they have many blood capillaries (and a lacteal) to carry absorbed food away, keeping the concentration gradient steep.
- 2. The small intestine.
- 3. Capillaries: glucose and amino acids. Lacteal: fatty acids and glycerol.