1. Food and Digestion Objectives
Identify and give reasons why some foods are not absorbed by the body
Recognise that sugars, vitamins and minerals are small molecules and can be absorbed by the body
Explain why large food molecules are need to be broken down
Explain why enzymes are necessary for digestion

2. FOOD AND DIGESTION Starter
Potatoes, rice and bread contain a lot of starch.
If starch stays as starch in the gut, what would happen to it?

3. FOOD AND DIGESTION
You have already discovered that starch cannot pass through the gut wall and be absorbed into the blood.
If starch stays as starch in the gut then you should have said it will be egested (can you remember the difference between egestion and excretion?)
You are going to see what happens when starch is mixed with saliva.

4. FOOD AND DIGESTION
Syringe 5 cm3 starch ‘meal’ saliva cm3 into a test tube.
Leave for 20 mins (Write up your method and prepare a results table in this time)
Remove a sample from the tube with a dropper and place it with a drop of iodine solution in a spotting tile
Test the remaining liquid for sugar by adding benedict’s reagent and boiling

5. Digestive enzymes
How do digestive enzymes help the process of digestion?
Digestive enzymes are the chemicals that break large insoluble food molecules into smaller soluble molecules.

6. Digestive enzyme animation

7. Enzymes and carbohydrate digestion
Carbohydrates are chains of identical sugar molecules.
The digestive enzymes called carbohydrases break the chemical bonds between the individual sugar molecules in each carbohydrate chain.
Carbohydrase
In saliva
long carbohydrate molecule
(starch meal)
sugar
molecules

8. Food and Digestion
What do your results show is in the liquid after 20 mins?
Explain what you have found out. Make sure you use the following words:-Higher ability pupils should be asked to explain the results including the following words:- saliva, amylase enzyme, breaks down, starch, glucose, molecules, large, smaller, digests. You may use the word more than once if you wish

9. absorbed, small,amylase enzyme, molecules, starch
Food and Digestion
Which type of food is in the liquid after 20 mins?
The _________ _________ has broken down the large ________ molecules into _____________ glucose ____________ which can now be __________ into the bloodstream.
absorbed, small,amylase enzyme, molecules, starch

10. FOOD AND DIGESTION Find out:
Proteins and fats are large insoluble food molecules.
They are digested by enzymes into small soluble molecules.
What are the products of digestion of proteins and fats?
Why should chewing speed up digestion?