Digestion for 3.2

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Digestion

Find out about:

The physical breakdown of foodThe chemical breakdown of foodThe role of salivaThe oesophagusThe stomachThe duodenum, liver and the pancreasDigestion in the small intestineThe large intestine

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Starter:

Use the diagram below to describe what happens to food when you eat it

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Breaking down food

Objectives:

• Know that food is broken down by physical and chemical actions

• Know how these two processes happen

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The model digestive system

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Digestion

ingestion = taking in nutrients

egestion = removal of undigested food

Oesophagus

Stomach

Liver

Pancreas

Small intestine Large intestine(Colon)

Anus

Gall bladder

Rectum

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M

R

S

GRE

N NUTRITION

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Incisor - chisel shape. Used for biting soft foods like fruit.

Canine - pointed. Used for biting and tearing tough food.

Premolars - Large, flat surface. Large surface area for crushing and grinding food.

Molars - Larger, flat surface. Larger surface area.

Physical breakdown

Physical breakdown - Teeth

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Chemical breakdown

Remember that proteins, carbohydrates and fats are made from smaller molecules.

These large molecules do not easily dissolve into water but when they are broken into smaller molecules they will dissolve into water.

(Remember, we are made of about 70% water)

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Smaller pieces have a larger combined surface area

Each small cube has a surface area of 1cm2

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11 1

2 X 2 = 4

1

1

46X

1 X 6 = 6

68X

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Starch

To break down the large molecules we use special proteins called enzymes. Enzymes speed up the chemical reactions without being used up. They are called catalysts.

Amylase breaks this bond

Maltose

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Mouth-watering!

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Peristalsis in the gullet

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To oesophagus

Stomach

Valve

To duodenum

The stomach - an acid attack!

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Digestion continues in the stomach with acid that helps kill bacteria. Another enzyme, pepsin, breaks down proteins into smaller protein chains

Pepsinbreaks this bond

Protein chains of 2 amino acids

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The duodenum, liver and pancreas - the great escape

Lipids (fats) are broken down into fatty acids and glycerol

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The final stage of digestion now occurs

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Digestion in the small intestine

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The fate of undigested food

Anus

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Region of production

Type of enzyme Notes

salivary glands in the mouth

gastric glands in the stomach

pancreas

Enzymes - an overview

Type of food digested general name of enzyme

carbohydrate carbohydraseprotein

fat

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Ingestion

Egestion

Digestion

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Label the digestive system and describe the journey of a hotdog as it goes through the digestive system.

Key words: Sort these words into the correct order as they occur from the start to the end of the digestive process

• ingest• digest• egest• physical digestion• chemical digestion• teeth• alimentary canal• peristalsis• bolus• enzymes• amylase• pepsin• lipase

• oesophaugus• stomach• duodenum• liver• gall bladder• pancreas• bile• small intestine• large intestine• rectum• anus• gullet• fibre

• starch• protein• fat• amino acids

Creative writing:

mark scheme:1 mark per two words used (30 words)

5 marks for effort

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