Topic: B2bLesson: 2Title: 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 Simple sugars

• Proteins Amino acids

• Lipids (fats) 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 intestineb) Proteins stomach and small intestinec) Fats small intestine2. What are the following broken down into by

digestive enzymes?a) Carbohydrates simple sugarsb) Proteins amino acidsc) Fats fatty acids + glycerol3. 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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