Topic: B2b
Lesson: 2
Title: Enzymes and digestion
Aims: Explain how enzymes are involved in
digestion
Starter: Write down everything you can
remember from key stage 3 about digestion,
eg. what it is; where it takes place...
What is digestion?
Breaking down large, insoluble molecules
into smaller, soluble molecules that can be
absorbed through the wall of the small
intestine
What breaks down the large molecules?
Digestive enzymes made by specialised cells
inside glands
The enzymes involved...
• Carbohydrates
• Proteins
• Lipids (fats)
Simple sugars
Amino acids
Fatty acids + glycerol
Digestion animation (First 5 mins 15 secs)
Listen carefully and make notes in your book.
You will be quizzed after the animation so
listen!
Mini test on digestive enzymes...
1. Where are the following digested:
a) Carbohydrates
mouth and small intestine
b) Proteins
stomach and small intestine
c) Fats
small intestine
2. What are the following broken down into by
digestive enzymes?
a) Carbohydrates  simple sugars
b) Proteins  amino acids
c) Fats  fatty acids + glycerol
3. Where are most enzymes produced? Pancreas
Why do you think there is acid in the
stomach?
• Kills bacteria in food – protects us
• Denatures proteins – makes digestion easier
• Activates stomach enzymes – these only work in
acidic conditions
• Ever wondered why PEPSIN (stomach enzyme)
doesn’t digest our own stomach?
• Pepsin is inactive when first made and is only
activated by HCL to start digesting proteins.
What does bile do?
• Bile is produced in the liver and stored in the
gall bladder.
• The enzymes in the small intestine need an
alkaline pH to work best, so bile passes into
the small intestine and neutralises acid from
the stomach.
• Bile also emulsifies fat droplets to increase
their surface area
How are villi in the small intestine
adapted to absorb food?
• How are villi specialised to carry out their job
of absorbing digested foods?
Answers
• Millions provide large surface area
• Each villus has many microvilli to further increase
surface area
• Rich blood supply for absorbed nutrients to pass
into and be taken around body
• Branch of lymphatic system takes absorbed fatty
acids and glycerol away to be used or stored
• Villi wall one cell thick for rapid passing through
of nutrients
Digestive system summary
• Salivary glands produce
________
• Liver produces ______
• Stomach produces
________ + ________
• Gall bladder stores
________
• Pancreas and small
intestine both produce
________, ________,
and ________
Why do people have their stomachs
stapled?
• stomach band
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