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How the Digestive Enzymes Work

This worksheet will explain the conditions that enzymes require in order to function properly.

Key stage:  KS 3

Curriculum topic:  Biology: Structure and Function of Living Organisms

Curriculum subtopic:  Nutrition and Digestion

Difficulty level:  

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QUESTION 1 of 10

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 temperatue on the activity of an enzyme is shown in the graph below:

 

 

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 not 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. 

 

Look at the diagram showing the human digestive system and then answer the question below:

 

 

 

In which parts of the digestive system would amylase be used? Tick two boxes.

salivary gland (mouth)

gall bladder

bile duct

liver

stomach

Look at the diagram showing the human digestive system and then answer the question below:

 

 

Which part of the digestive system produces bile?

salivary gland

gall bladder

pancreas

stomach

liver

Look at the diagram showing the human digestive system and then answer the question below:

 

 

 

Which part of the digestive system carries bile?

salivary gland

gall bladder

bile duct

rectum

stomach

Look at the diagram showing the human digestive system and then answer the question below:

 

 

 

In which part of the digestive system are conditions acidic?

stomach

small intestine

heart

Which of the following it the optimum temperature for all digestive enzymes?

15°C

27°C

37°C

45°C

A scientist isolated a protein-digesting enzyme from the stomach and another from the small intestine. He used them in this investigation:

 

 

In which of the following test tubes would the protein have been digested? Tick two boxes.

A

B

C

D

A scientist isolated a protein-digesting enzyme from the stomach and another from the small intestine. He used them in this investigation:

 

 

 

In which of the following test tubes would the fat have been digested?

A

B

C

D

 What is the role of bile in the digestion process?

To digest fats.

To digest proteins.

To make the conditions acidic.

To neutralise the stomach acid.

 

Where is bile stored before being used? 

liver

gall bladder

bile duct

What happens to enzymes when the temperture becomes greater than their optimum temperature? 

Nothing, enzymes will work at any temperature.

The enzyme activity will increase as the temperature increases.

The enzymes will become denatured and will no longer work.

  • Question 1

Look at the diagram showing the human digestive system and then answer the question below:

 

 

 

In which parts of the digestive system would amylase be used? Tick two boxes.

CORRECT ANSWER
salivary gland (mouth)
stomach
EDDIE SAYS
Amylase is used in the mouth and stomach, as it breaks starch into sugars and works best in acidic conditions.
  • Question 2

Look at the diagram showing the human digestive system and then answer the question below:

 

 

Which part of the digestive system produces bile?

CORRECT ANSWER
liver
EDDIE SAYS
Bile is produced in the liver, which is stored in the gall bladder before travelling to the small intestine and neutralising the stomach acid.
  • Question 3

Look at the diagram showing the human digestive system and then answer the question below:

 

 

 

Which part of the digestive system carries bile?

CORRECT ANSWER
bile duct
EDDIE SAYS
Bile travels down the bile duct into the small intestine, where it neutralises stomach acid.
  • Question 4

Look at the diagram showing the human digestive system and then answer the question below:

 

 

 

In which part of the digestive system are conditions acidic?

CORRECT ANSWER
stomach
EDDIE SAYS
The conditions in the stomach are acidic, as food is broken down into small molecules by enzymes which work best in acidic conditions, such as amylase.
  • Question 5

Which of the following it the optimum temperature for all digestive enzymes?

CORRECT ANSWER
37°C
EDDIE SAYS
The digestive enzymes work best at 37°C, which is body temperature.
  • Question 6

A scientist isolated a protein-digesting enzyme from the stomach and another from the small intestine. He used them in this investigation:

 

 

In which of the following test tubes would the protein have been digested? Tick two boxes.

CORRECT ANSWER
A
D
EDDIE SAYS
Protease is the enzyme which breaks down proteins. It works in both acidic and slightly alkaline conditions, and is found in the stomach and small intestine (which is slightly alkaline).
  • Question 7

A scientist isolated a protein-digesting enzyme from the stomach and another from the small intestine. He used them in this investigation:

 

 

 

In which of the following test tubes would the fat have been digested?

CORRECT ANSWER
D
EDDIE SAYS
Lipase is the enzyme used to break down fat into fatty acids. The fat in test tube D would have been digested, as lipase works in alkaline conditions, like those found in the small intestine.
  • Question 8

 What is the role of bile in the digestion process?

CORRECT ANSWER
To neutralise the stomach acid.
EDDIE SAYS
Bile is used in the digestion process to neutralise stomach acid in the small intestine.
  • Question 9

 

Where is bile stored before being used? 

CORRECT ANSWER
gall bladder
EDDIE SAYS
Bile is stored in the gall bladder before it travels down the bile duct to the intestine.
  • Question 10

What happens to enzymes when the temperture becomes greater than their optimum temperature? 

CORRECT ANSWER
The enzymes will become denatured and will no longer work.
EDDIE SAYS
The temperature is important as, if the temperature is greater than 37°C, the enzymes become denatured and can no longer work properly, so the reaction slows down rapidly.
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