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How the Digestive Enzymes Work

In this worksheet, students will explain the conditions that enzymes require in order to function properly.

'How the Digestive Enzymes Work' worksheet

Key stage:  KS 3

Curriculum topic:   Biology: Structure and Function of Living Organisms

Curriculum subtopic:   Nutrition and Digestion

Difficulty level:  

Worksheet Overview

Enzymes are biological catalysts that help to speed up different processes in our body. The digestive process involves 3 main enzymes; however, these enzymes are very fussy and will only work if the temperature and pH are just right.  

 

So what is the best temperature?

 

For all digestive enzymes the optimum (best) temperature is always 37°C. Why 37°C, you ask?  Well 37°C is, in fact, body temperature.

The effect of temperature on the activity of an enzyme is shown in the graph below:

 

Enzyme temperature activity graph

 

As you can see from the graph, the enzymes activity gradually increases as the temperature reaches 37°C.  At temperatures greater than 37°C, the enzymes become denatured, meaning that they can no longer do their job, causing the reaction to slow down. 

 

What about pH?

 

The effect of pH on the activity of an enzyme varied depending on the enzyme in questions:

  • Amylase - the enzyme used to break down starch in to sugars, works best in acidic conditions which is why the mouth and stomach are the perfect place for amylase. 
  • Protease - the enzyme used to break down protein into amino acids can work under both acidic and slightly alkaline conditions which is why it is broken down in both the stomach (acidic) and the small intestine (slightly alkaline) . 
  • Lipase - the enzyme used to break down fats into fatty acids, works best in alkaline conditions which is why it is broken down in the small intestine and not in the mouth or stomach.  
     

 

The sharp change in pH between the acidic stomach and the slightly alkaline small intestine occurs thanks to the liver. The liver produces a substance called bile, which in stored in the gall bladder before being used to neutralise the stomach acid as it reaches the small intestine. 

 

Liver

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