1. Bile
LQ: What does it do?

2. Learning outcomes All: must give the two uses of bile
Most: can explain what bile does to lipids
Some: can explain how bile increases the surface area of lipids
Grade 6: explain how surface area increases digestion and explain the terms emulsification micelle and increased digestion

3. Chewing breaks up large chunks of food into smaller chunks
Why do we chew our food?
Chewing breaks up large chunks of food into smaller chunks
Chewing mixes in saliva…
… which contains amylase.
Amylase is an enzyme which breaks down starch into simple sugars.
Amylase
Sugars
(maltose)
Starch molecule

4. Solid lumps of food can only be digested from the outside
If we break large lumps of food down into smaller pieces…
Lump of food
Chewing
Enzymes
… we increase the surface area for the enzymes to work on
This will speed up the rate of chemical digestion by the enzymes

5. Progress check What is the function of the teeth?
What enzyme is produced in the mouth?
What is the purpose of chewing your food?
How does this help amylase do its job?

6. The lining of the stomach produces gastric juice
The stomach is a muscular bag which mashes food into a watery paste called chyme
The lining of the stomach produces gastric juice
Pepsin &
Hydrochloric Acid
Gastric juice contains:
- water
- hydrochloric acid which kills microbes in the food and provides the optimum pH for…
- pepsin, an enzyme which breaks down proteins into amino acids

7. Progress check What does pepsin break down?
What does the stomach lining produce?
What two functions does hydrochloric acid have in the gut?
What is the protein broken down into?

8. Pepsin
Amino acids
Protein molecule

9. The lining of the small intestine produces enzymes
Once the stomach has reduced the food to a smooth paste, it passes into the small intestine
Pancreas
Digestive Enzymes
Pepsin &
Hydrochloric Acid
The lining of the small intestine produces enzymes
More enzymes are added by the pancreas
The enzymes in the small intestine have an optimum pH of 6 - 8
Why is this a problem?

10. Liver The pancreas produces sodium bicarbonate
Bile
Gall Bladder
The pancreas produces sodium bicarbonate
The liver produces bile salts…
… which are stored in the gall bladder until they are needed
Sodium bicarbonate and bile salts are alkali…
… so they neutralize the stomach acid

11. Progress check
Why are bile and sodium bicarbonate added to the small intestine?
What happens to the digested food in the small intestine?

12. The contents of the small intestine are mostly water
GLYCEROL
Lipase
Fat molecule
Fatty acids
The contents of the small intestine are mostly water
Fat
(e.g. Vegetable oil)
Digestive enzymes are water soluble, but…
Surface where fat and water meet
… fats do not dissolve in water, so…
… lipases can only digest fats at the surface of fat droplets
Lipase enzyme particles
Water

13. Adding bile salts cause fats to emulsify in water (emulsify-to become an emulsion, two liquids mixed together)
Micelle
Add bile
Shake
Water
Emulsion
The fat forms tiny droplets called micelles which will stay suspended in water and not separate out
This massively increases the surface area for the lipase enzymes to work on

14. Progress check
Why does the lipid have to be made into smaller pieces before it can be digested?
What is the term that describes the breaking down of lipids? (think “e”)
What is a small piece of lipid called?
What does this process increase? (think “s” “a”)

15. Bile 6 mk Q answer
Emulsifier – means to make two liquids mix together e.g. oil and water
Bile acts upon fats
Bile is produced in the liver and stored in the gall bladder
Increases surface areas of fat droplets so it can be digested easier by enzymes
Lipase enzyme digests the fat into fatty acids and glycerol