Download unit 2 lesson 4

UNIT 2 LESSON 4
Aims
Pupils learn what happens to food in the small intestine linking to size of molecules and enzymes
Learning Objectives
Pupils should:
8A/3a Interpret the relationship between a model gut and the digestive system and explain
it
8A /3b Know that enzymes break down large insoluble molecules into smaller, soluble
molecules.
POSSIBLE ACTIVITIES
Activity 1 Objectives 8A/3a
Set up this practical as demo as it is difficult for pupils to do it - see U2.4W1 worksheet - A model
gut for instructions. You must set this up early in the lesson as it takes awhile for the results to
show. In discussions, pupils should be able to predict the results with explanations ie large
molecules (starch) cannot pass through the tiny holes in the visking tubing (like small intestine)
whereas sugar as small molecule can. The water represents the blood.
Activity 2 Objectives 8A/3a
Demonstrate ‘Making Poo’. U2.4W2. Use a pair of tights to demonstrate the guts and the processes
of reabsorption. Talk through the idea of eating breakfast:
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Banana, toast and yoghurt etc. Gets broken down by teeth (wooden spoon) and
you produce saliva (water) all in mouth (small bowl)
Tell class it is then swallowed and goes into the stomach were stomach acid is
added to continue digestion. (More water added).
Then put mixture into tights.
It enters the small intestine were all the nutrients are absorbed into the blood.
Demonstrate the movement along by peristalsis.
It then moves on to the large intestine where the water is reabsorbed into the
body and pupils can see water coming out and food solidifying.
Finally enters the rectum (squeeze all excess water out). Then cut a slit in tights
so the waste can be excreted.
Activity 3 Objectives 8A/3b
Demonstrate that starch powder in water does not dissolve but sugar will. Ask leading questions
like so what needs to happen to the starch so it can be absorbed into blood through the small
intestine? They should come up with starch needs to be broken down into smaller, soluble
molecules ie sugar.
Then ask how large, insoluble molecules can be broken down leading to idea of enzymes. Enzymes
are biological catalysts which speed up reactions.
Students write notes from discussions. A Choice of worksheets U2.4W3, U2.4W4 or U2.4W5.
Risk Assessment
Care when handling chemicals - safety glasses must be worn.
Suggested Homework Tasks
Write up practical
Resources:Lesson 4
Activity
1
2
3
Homework
Resources required
Demonstration
Softened visking tubing
String, sissors and sellotape
Starch suspension and strong glucose solution mixed
together
Pipettes
Benedict's solution
Iodine solution
Water bath at 90 C
Kettle
Demonstration
Tights
Scissors
Large beaker(1 litre)
Water jug
Small beaker
Spatula, large
Food: Bread, banana, yoghurt, coco pops all work well
(something brown essential)
Starch powder and sugar granules
A Choice of Worksheets U2.4W3-5