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Compare the Role of Enzymes in the Digestive System

Worksheet Overview

QUESTION 1 of 10

Did you know that our saliva contains something called enzymes? And did you know that without these enzymes digestion wouldn't be able to occur? So what are these enzymes anyway, and how do we use them in digestion?

Enzymes are proteins. They are biological catalysts that speed up a chemical reaction without being used up in the reaction. Enzymes have a complex 3D shape. The specific shape that allows molecules to fit in is called the active site. It's here that large insoluble food substances are broken into smaller soluble molecules. Smaller molecules are easily absorbed by the blood. These smaller molecules might be used for different processes, for example, glucose can be used for respiration. Some smaller molecules will be used to build and make new products. Proteins can be broken down into peptides, which are short chains of amino acids, and then further broken down into amino acids. These amino acids can be used to build new proteins needed for growth and repair.

 

The lock and key theory 

The shape of the active site of an enzyme matches the shape of the food molecule (substrate). A bit like a key is specific to the lock it opens,  a substrate will only match a specific enzyme. This is called the lock and key theory. 

 

Image showing enzyme in action

 

Different types of food are broken down by different enzymes.  Digestive enzymes are classified by the type of food that they affect. There are three main types:

carbohydrase – breaks carbohydrate into smaller sugars

protease – breaks protein into amino acids

lipase – breaks fat into fatty acids and glycerol

 

Carbohydrates

Carbohydrates are chains of identical sugar molecules. The digestive enzyme called carbohydrase breaks the chemical bonds between the sugar molecules in each carbohydrate chain. An example is amylase. Amylase is found in saliva and pancreatic juices. Amylase breaks starch down into small sugar molecules called maltose. Maltose can be further converted to glucose by another enzyme called maltase in the small intestine.

 

Image of starch broken into maltose by amylase enzyme

 

 

Proteins 

Proteins are made up of amino acids. There are over 20 different types of amino acids. Proteins are digested by digestive enzymes called proteases. These enzymes break proteins into smaller peptides and individual amino acids. Amino acids can be built up to make new proteins for growth and repair. Proteases can be found in the stomach, pancreas and small intestine.

 

Image of protein into amino acid by protease enzyme

 

Fats

Fats are digested in two stages:

Firstly, bile (made by the liver) emulsifies fat into smaller droplets called an emulsion. This increases the surface area of the fat. 

Secondly, the digestive enzyme lipase breaks each fat molecule into the smaller glycerol and fatty acid molecules. These can now be absorbed by the blood and can be used by the body for energy storage, and building cell structures like cell membranes. Bile is alkaline and helps to neutralise the acidic food leaving the stomach.

Lipases are found in the pancreas and small intestine.

 

Image of fats being broken down by bile and enzyme lipase 

 

In the following activity, you will compare the different enzymes in the digestive system.  

Enzymes are super important and without them digestion can't occur.

 

What are enzymes?

Enzymes are very specific. They have active sites that only bind with specific food molecules, also known as substrates.

 

Compare the different types of digestive enzymes by matching them with their substrates.

Column A

Column B

Carbohydrase
Breaks fat into fatty acids and glycerol
Protease
Breaks protein into amino acids
Lipase
Breaks carbohydrate into smaller sugars

Below are three different images of enzymes and their substrates.

 

Which of the three images could be showing activity in the acidic conditions of the stomach?

 

A B C
 Image of starch broken into maltose by amylase enzyme Image of protein into amino acid by protease enzyme Image of fats being broken down by bile and enzyme lipase

 

A

B

C

Enzymes break down larger insoluble food molecules to smaller soluble food molecules. Starch is a carbohydrate that will often get broken down into glucose.

 

What is the glucose used for? 

Digestive enzymes are essential for digestion to occur.

 

Where are the main enzymes found and what do they digest? 

The picture below shows an enzyme and three substrate molecules. 


Which substrate will react with the enzyme? 

 

Image of enzyme and three different substrates

Proteases are enzymes that catalyse proteins.

 

Label A. 

 

Image of protein broken down into peptides and amino acids

Amino acids

Peptides

Glucose

Carbohydrates, proteins and lipids are major nutrients. These are needed by the body and we get these nutrients by eating them. 

 

What do these nutrients provide? 


 

Image of food groups

 

Column A

Column B

Carbohydrates
Source of energy
Proteins
Essential part of cell membranes as well as a sour...
Lipids
Growth and repair

All digestive enzymes have some similarities.

 

Select the similarities below. 

Catalyse lipids

Biological catalysts

Catalyse proteins

Catalyse specific substrates

Have specific active sites

Bile and lipase both play an important role in the digestion of fats.

 

Compare bile and lipase by filling in the blanks below.

Catalyse lipids

Biological catalysts

Catalyse proteins

Catalyse specific substrates

Have specific active sites

The table below shows a summary of the digestive enzymes and their specific functions.

 

Match up A, B and C.

 

Carbohydrase Protease
A  proteins → amino acids  lipids → glycerol + fatty acids
 energy, respiration B  energy, cell membranes
salivary glands, pancreas, small intestine stomach, pancreas, small intestine pancreas, small intestine

Column A

Column B

A
Carbohydrates → sugars
B
Growth and repair
C
Lipase
  • Question 1

Enzymes are super important and without them digestion can't occur.

 

What are enzymes?

CORRECT ANSWER
EDDIE SAYS
How did you get on with filling in all these blanks? It is vital that you understand what an enzyme is and their importance in digestion. A common misconception is that enzymes get used up in reactions. Enzymes help to speed up reactions but don't take part in the actual reaction, so don't get used up.
  • Question 2

Enzymes are very specific. They have active sites that only bind with specific food molecules, also known as substrates.

 

Compare the different types of digestive enzymes by matching them with their substrates.

CORRECT ANSWER

Column A

Column B

Carbohydrase
Breaks carbohydrate into smaller ...
Protease
Breaks protein into amino acids
Lipase
Breaks fat into fatty acids and g...
EDDIE SAYS
Did you get them all correct? This is another really important thing to know, so take some time to learn them! To help you remember the name of these enzymes and their substrates, remember the clue is in the name: Carbohydrase → Carbohydrates Protease → Proteins Lipase → Lipids (another name for fats)
  • Question 3

Below are three different images of enzymes and their substrates.

 

Which of the three images could be showing activity in the acidic conditions of the stomach?

 

A B C
 Image of starch broken into maltose by amylase enzyme Image of protein into amino acid by protease enzyme Image of fats being broken down by bile and enzyme lipase

 

CORRECT ANSWER
B
EDDIE SAYS
Well done if you got this one correct! You might well have thought that there wasn't enough information to be able to work this one out, but this is where you needed to think back to all you know about digestion! Image A is showing amylase at work on carbohydrates - this happens in the mouth and the small intestine, but not in the stomach. This means that this cannot be showing the acidic conditions found in the stomach. Image B shows proteases breaking down proteins. This can happen in the stomach, pancreas and small intestine. It isn't obvious which of these areas are being shown here, but it could be the stomach. Image C is showing fat being emulsified into smaller droplets by bile and lipase. Bile is alkaline and is added to food leaving the acidic conditions of the stomach, neutralising it. This means that the environment has now become alkaline and it cannot be showing the stomach. This means that the only image that could possibly be showing activity in the stomach is image B.
  • Question 4

Enzymes break down larger insoluble food molecules to smaller soluble food molecules. Starch is a carbohydrate that will often get broken down into glucose.

 

What is the glucose used for? 

CORRECT ANSWER
respiration
EDDIE SAYS
Digestion allows smaller molecules to be used by the body for important processes. Often these smaller glucose molecules will be used to build new carbohydrates. The most important use for glucose is in the process of respiration where it is converted into energy.
  • Question 5

Digestive enzymes are essential for digestion to occur.

 

Where are the main enzymes found and what do they digest? 

CORRECT ANSWER
EDDIE SAYS
Well done if you got them all!! This activity is a great summary for revision purposes. Try this question a few times to consolidate your knowledge.
  • Question 6

The picture below shows an enzyme and three substrate molecules. 


Which substrate will react with the enzyme? 

 

Image of enzyme and three different substrates

CORRECT ANSWER
c
EDDIE SAYS
How are your puzzle-solving skills? Active sites have a specific shape that is complementary to a particular substrate. Like a puzzle piece, the substrate and the active site have to be complementary, or the substrate won't be broken down. C is the only substrate that has a complementary shape to the enzyme's active site.
  • Question 7

Proteases are enzymes that catalyse proteins.

 

Label A. 

 

Image of protein broken down into peptides and amino acids

CORRECT ANSWER
Peptides
EDDIE SAYS
This image is showing proteases at work on proteins. The first stage of this is the breaking down of protein into peptides, which are short chains of amino acids. These are then broken down to amino acids - the individual compounds that can make up proteins.
  • Question 8

Carbohydrates, proteins and lipids are major nutrients. These are needed by the body and we get these nutrients by eating them. 

 

What do these nutrients provide? 


 

Image of food groups

 

CORRECT ANSWER

Column A

Column B

Carbohydrates
Source of energy
Proteins
Growth and repair
Lipids
Essential part of cell membranes ...
EDDIE SAYS
Did you hesitate over the two options concerning energy sources? Both carbohydrates and lipids (another word for fats) are good sources of energy, but lipids are also essential for the maintenance of cell membranes. Having a varied and balanced diet is important - it means the body will get a mixture of nutrients. The body will reassemble these nutrients depending on what the body needs.
  • Question 9

All digestive enzymes have some similarities.

 

Select the similarities below. 

CORRECT ANSWER
Biological catalysts
Catalyse specific substrates
Have specific active sites
EDDIE SAYS
There were three options correct in this question. Did you get them all? Enzymes are catalysts, meaning that they speed up reactions without being changed by them. They are also highly specific - they only work on specific food molecules. They have active sites which have a specific shape for specific substrates.
  • Question 10

Bile and lipase both play an important role in the digestion of fats.

 

Compare bile and lipase by filling in the blanks below.

CORRECT ANSWER
EDDIE SAYS
How did you get on with this one? As well as getting the facts right in questions like this, you might like to think about the style of writing. When making comparisons in longer answers in your exams, remember to use comparative words, such as however, conversely, whereas, in contrast, or similarly.
  • Question 11

The table below shows a summary of the digestive enzymes and their specific functions.

 

Match up A, B and C.

 

Carbohydrase Protease
A  proteins → amino acids  lipids → glycerol + fatty acids
 energy, respiration B  energy, cell membranes
salivary glands, pancreas, small intestine stomach, pancreas, small intestine pancreas, small intestine
CORRECT ANSWER

Column A

Column B

A
Carbohydrates → sugars
B
Growth and repair
C
Lipase
EDDIE SAYS
All three enzymes are specific to the nutrient they catalyse. One similarity you might have spotted in the table is that they are all found in the pancreas (as well as other locations). Well done for reaching the end of this activity. Hopefully, you feel more confident about the topic of enzymes now.
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