The Digestive System  

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You need a basic understanding of the human digestive system at GCSE level:

 

Journey of Food:  

1. Mouth → chewed + amylase (in saliva) starts starch breakdown  

2. Oesophagus → peristalsis squeezes food down  

3. Stomach → acid + proteases break down proteins  

4. Small intestine → nutrients absorbed + enzymes finish digestion  

5. Large intestine → water absorbed → faeces formed  

6. Anus → waste exits  

 

Helper Organs:  

• Liver → makes bile  

• Gallbladder → stores bile  

• Pancreas → releases digestive enzymes

 

Enzymes

 

Enzymes are biological catalysts, meaning they speed up a reaction without being used up.

• Made of protein → active site has specific shape determined by the type of protein  

• Substrate fits like a key in a lock → reaction speeds up  

• Enzyme unchanged at the end → reusable

 

Lock & Key Model: Only the correct substrate fits the active site

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Digestive Enzymes  

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These break down products build new molecules or fuel respiration

 

Bile  

 

• Made in liver, stored in gallbladder  

• Alkaline → neutralises stomach acid  

• Emulsifies fats → breaks into tiny droplets → increases surface area for lipase

 

> Required Practical 4: Food tests (starch, sugar, protein, lipid)  

> Required Practical 5: Effect of pH on amylase activity