Digestive system

Chapter overview

1.5 weeks

Learners have already been introduced to the digestive system in Chapter 2. This chapter focuses more on a healthy diet and the different components making up a healthy diet. Learners will be required to conduct some food tests to investigate which foods contain which components, such as starch and fats. The chapter will also look at the alimentary canal and digestion in more detail to see how the food we eat becomes a form which can be absorbed into our bodies. In Gr 6 CAPS, learners do an introduction to nutrition and learn about the basic food groups.

5.1 Healthy diet (3 hours)




Activity: Comparing healthy and unhealthy foods

Working in pairs, comparing, describing, categorising


Activity: Comparing meals

Comparing, describing, explaining


Investigation: Which foods contain starch and fats and oils?

Investigating, observing, interpreting, describing, writing, explaining

CAPS suggested

Activity: How does your diet affect your health in the short and long term?

Researching, interpreting, predicting, explaining

CAPS suggested

5.2 The alimentary canal and digestion (1.5 hours)




Activity: The different organs in the digestive system



Activity: A digestion simulation

Working in groups, observing, describing, interpreting, comparing, writing


  • Why do we need to follow a healthy diet? What does a healthy diet consist of?
  • What makes one type of food healthy and another type of food unhealthy?
  • Is it possible to prevent things like diarrhoea or constipation? What about ulcers?
  • Why do we need to digest food?
  • How is food digested in our bodies?
  • Where does the digested food go?

In this chapter we are going to look more closely at the food we eat to see why certain foods are considered healthy and others unhealthy. We will then investigate how the food from our plates gets to our cells and why our digestive system is so well adapted for its job.

A healthy diet

  • balanced diet
  • dehydration
  • diet
  • enzymes
  • iodine solution
  • nutrients
  • starch
  • sugars

Our human bodies are very active. Our bodies need a huge variety of different nutrients and substances in order to perform all these processes. We obtain these nutrients from the food we eat. The human body needs a balanced, healthy diet to keep functioning property.

Comparing healthy and unhealthy foods


  1. Work with a partner.
  2. We often know if a food is healthy or unhealthy. List at least 10 healthy and 10 unhealthy foods in the following table.

Healthy food

Unhealthy food

When you are done share your food list with the class and record the class' ideas of healthy and unhealthy foods on a large sheet of paper or on the board. Display this in the class.

Study the list of healthy and unhealthy food.

What common characteristics can you identify in the food that the class listed as healthy?

Learner-dependent answer

What common characteristics can you identify in the food that the class listed as unhealthy?

Learner-dependent answer

A simulation about eating and exercise http://phet.colorado.edu/en/simulation/eating-and-exercise

Let's take a closer look at what makes up a healthy diet.

The seven building blocks of a healthy diet

  • protein
  • carbohydrates
  • fats
  • fibre
  • glucose
  • vitamins
  • minerals

The foods that we eat can be divided into different groups:

  • proteins
  • carbohydrates
  • fats and oils
  • vitamins
  • minerals
  • fibre (non-digestible carbohydrates)
  • water

A healthy diet consists of foods from all of these groups.


Proteins are our bodies' building blocks. They build and repair body cells and tissues. Foods rich in protein are: fish, meat, poultry, eggs, cheese and other food from animal sources. There are also many sources of protein from plants. For example: products made from soya beans, peas and beans, nuts and seeds.

Almond nuts.


Carbohydrates are the main supply of energy for our bodies. They break down in our digestive system to form glucose (which is a sugar). Examples of foods that contain carbohydrates are: whole grain bread, potatoes, pasta, rice, fruit, vegetables, maize and legumes.

Unfortunately many people eat too many carbohydrates, especially processed carbohydrates like sweets and biscuits, chips, pastries, soft drinks and sweetened fruit juices.

Often, fruit juice is not the healthiest choice of drink as some fruit juices contain the same amount or more sugar than the average soft drink. The best choice is water!

Whole wheat bread.
Mealies (corn) contain a lot of carbohydrate.

Fats and oils

Fats and oils are important for many body processes:

  • Fat protects and insulates your organs
  • They help maintaining healthy hair and nails.
  • Some vitamins can only be absorbed and transported when attached to fat molecules.
  • Fats and oils also provide the body with energy.

However, some fats are better than others and having too much of any type is not a good idea.

Olive oil and canola oil are both healthy oils.
Sardines are high in healthy fats.


Our sources of vitamins are from fruit...
...and vegetables.

Vitamins help with the different chemical reactions in our bodies:

  • vitamin A helps strengthen our immune system and is good for eyesight in the dark
  • B vitamins help us process energy from food
  • vitamin C helps to keep your skin and gums healthy and improves the immune system
  • vitamin D helps to build strong bones and teeth

Our main sources of vitamins are from fruit and vegetables. The following diagram summarises some of these sources for various vitamins. You do not need to know all of these.

Many people take large amounts of supplements to ensure they get enough vitamins and minerals. However it is rather wasteful as the body excretes any excess vitamins and minerals and only stores a few vitamins like Vitamin A, D, E and K.

Food sources of different vitamins.


Our bodies cannot produce minerals and we therefore need to include these in our diets. Some of the minerals we should include in our diets are:

  • calcium which is essential for strong bones and teeth.
  • iron which is needed for healthy blood.
  • magnesium which is used for building strong bones, teeth and muscles.
  • sodium which is also needed for muscle and nerve function, and more importantly it helps regulate the amount of water in the blood.

There are a variety of sources of minerals. For example, high levels of calcium are found in dairy products, meat is a high source of iron, and magnesium is found in lots of foods such as bananas, nuts, green leafy vegetables and milk. The most common source of sodium is in sodium chloride, which is table salt.


Fibre found in the skins of fruit and vegetables, and in wholegrain cereals, cannot be digested. It therefore travels through the alimentary canal. We need fibre in our diet as it helps us to have regular bowel movements and avoid constipation. .

Beans are a good source of fibre.
High fibre breakfast cereal. http://www.flickr.com/photos/trekkyandy/3316748814/


Our bodies are made up of more than 50 percent water. Water is necessary to help our blood carry nutrients and waste around the body and to help the chemical reactions that occur in our cells. Water forms most of sweat, saliva and tears.

You need to drink water daily.

Find out more and get a special dietary plan worked out just for you http://www.choosemyplate.gov/

Comparing meals

This is an optional activity, and can also be done as a class discussion if you do not have time in class.


  1. Below are photographs of different meals for breakfast, lunch and dinner.
  2. One of the meals is healthier than the other.
  3. Choose which is the healthier option and explain why.


Option 1: Fruit loops

Option 2: Fruit salad

The fruit salad is healthier as it contains a variety of fresh fruits which are high in fibre and packed with healthy vitamins. Fruit salad will satisfy some of your requirement of fruit and vegetables for the day. The fruit loops are unhealthy as they contain a lot of sugars and artificial colourants and flavourants. They have limited nutritional value in terms of vitamins and minerals.


Option 1: Hamburger

Option 2: Omelette with salad

The omelette is the healthier option. As with the egg salad, this meal contains fresh salad and the eggs are a source of protein. The omelette possibly has meat or mushrooms and cheese which also adds to the nutritional content. The hamburger is unhealthy as although it contains meat, starch and cheese, the way it was probably prepared is unhealthy as the meat is fried in oil. There is also no fresh fruit or vegetables.


Option 1: Chicken pieces

Option 2: Beef, peas and rice

The beef, peas and rice is the healthier option for supper as the meal contains starch (rice), meat for protein (beef) as well as vegetables (peas). The other meal is less healthy as it only contains one food group, namely protein from the chicken pieces.

Different cultures and religions follow different diets. Some cultures will only eat certain types of food and will avoid other combinations. Some religions might restrict their followers to only certain foods while others have no real dietary laws. Within South Africa, we have a very diverse population with people from many cultures, backgrounds and religions. This makes our country a truly unique, diverse and interesting place in which to live!

Testing food

  • emulsion

There are various chemical tests which are used to easily identify the type of food molecules present in different foods.

Once such test is the starch test. We can also test for the presences of fats and oils using the emulsion test.

In lower grades you might recall doing the starch test on plants to see which leaves store starch from the glucose produced in photosynthesis.

Which foods contain starch and fats and oils?

In this investigation, learners will be provided with the background information and basic instructions. They will have to design the investigation themselves and then write up their findings in an experimental report.

Before the lesson starts, set up each workbench with the materials and apparatus the learners will require to do the food tests.

The materials required are (per learner or group):

  • various food items to test for starch: for example, pieces of bread, apple, tomato, boiled egg, cheese, cucumber, potato, yoghurt, ham (some substances must contain starch and some not)
  • various food items to test for fats and oil: for example, the above food items can be used, and in addition, you could also provide peanut butter and butter
  • petri dish per group or learner for the starch test
  • bottle of iodine solution and dropper
  • several test tubes for the fat emulsion test
  • water
  • glass rod (or any other suitable round hard item) for crushing food substances for fat emulsion test
  • bottle of ethanol
  • forceps


  1. You need to conduct an investigation to test whether the food substances you have been provided with contain starch or fats and oils or both.
  2. A summary of each test is given below. You will need to design your investigation and conduct it.
  3. Before starting, think about how you will record your results and write out your proposed method.

Starch iodine test:

Iodine solution is an orange-brown colour. When iodine is added to a substance which has starch in it, the iodine reacts with the starch to produce a blue-black colour. The blue-black colour indicates the presence of starch.

Learners will need to use the dropper to add a couple drops of the iodine solution to the food substance to be tested in a petri dish. Let them practise on a small piece of white paper, so they see the colour change before trying it on the food. Starch hold the fibres in paper together.

Fat emulsion test:

To conduct the test, crush a piece of the food (or liquid) in a small amount of ethanol. Pour some of the mixture onto paper. Once the ethanol has evaporated, oil stains on the paper will indicate the presence of fats or oils in the food.

If you are allergic to iodine rather observe this experiment and do not participate.


What is the aim of your investigation?

To find out whether starch or fats and oils, or both are present in certain foods.


What is your hypothesis for this investigation?

Learner-dependent answer

This will vary depending on what food substances you provide to learners. An example of a hypothesis for this investigation is: "The iodine solution will turn blue-black when added to the potato, bread and apple, indicating these foods contain starch. The emulsion from the cheese, yoghurt, butter and peanut butter will turn milky white, indicating the presence of fats".


List the materials and apparatus you used in this investigation.

Learner-dependent answer

An example that learners could provide:

  • samples (small) of the following foods - learners identify which foods they are testing for starch and fats.
  • iodine solution with dropper
  • petri dish
  • forceps
  • test tubes
  • paper
  • ethanol


Write down the method which you followed in this investigation.

Learner-dependent answer

Learners need to write the method in a list of numbered steps. Learners need to indicate that they collected the food samples and placed them in different petri dishes (bowls if these were not available). They then dropped iodine solution in turn on each of these samples observing and recording the results. They must then indicate how they did the fat emulsion test, by placing small pieces of the food substances in a test tube, adding ethanol and crushing and stirring with the rod or another rounded, hard object. They should then pour the mixture onto paper and allowed the ethanol to evaporate and record the results.


Use the following space to record your results and observations from this investigation.

Learner-dependent answer

Learners could draw a table to record their results and observations, or just list the foods which tested positive or negative for each substance. An example of the layout for a learners table could be:

Table to indicate the presence of starch or fats and oils in various food substances

Food substance

Result of iodine test

Contains starch?

Result of emulsion test

Contains fats?


Turned blue-black


No murky, white colour



Parts of apple turned blue-black


No murky, white colour



Remained orange-brown/did not turn blue-black


Emulsion turned murky, white colour




Discuss and evaluate your results and findings and the importance of food tests.

Learner-dependent answer

Learners should discuss which types of foods contained starch and fats and which did not. They could note that plant material in particular contains starch because the plants photosynthesize specifically to produce glucose that are the building blocks for carbohydrates. Animal products (such as the ham and boiled egg) do not contain starch. Learners should also discuss any unusual findings which they did not expect and whether this could be a result of inaccuracy or contamination. Learners should also evaluate their results and whether they could have done anything to improve the investigation, such as possibly repeating the tests.


What do you conclude from this investigation?

Learner-dependent answer

Learners must refer back to their hypothesis in the conclusion and either reject or accept it.

Health problems relating to diet

In Chapter 2 this term, we looked at some of the health issues relating to the digestive system, such as ulcers, diarrhoea and eating disorders. There are also health issues which arise directly due to your diet. The following activity will introduce you to some of these health concerns.

How does your diet affect your health in the short and long term?

Learners could do this as a quick class discussion as you go through the different conditions.


  1. Below is a table with descriptions of several health issues relating to a poor diet.

  2. You need to read the descriptions and use your knowledge of the food groups to then classify what the diet of the person is deficient in, or else has a surplus of in their diet.

  3. For some conditions, there may be a variety of causes, but this activity is focusing on the causes related to diet.

Name of health issue


What does this person have a deficiency or surplus of in their diet?


Osteoporosis is a disease, most common in older women, where the bones become fragile and are more likely to break. Usually the bones lose density and become porous.


Anaemia is a condition of the blood when there are not enough healthy red blood cells. A patient feels tired and weak as the tissues and organs in the body are not able to get enough oxygen so respiration slows down.


This is a severe form of malnutrition dues to starvation. The person becomes extremely thin (emaciated).


A person has constipation when they have a bowel movement less than 3 times per week. The person may have hard stools and difficulty and pain when passing stools.

Name of health issue


What does this person have a deficiency or surplus of in their diet?


Osteoporosis is a disease, most common in older women, where the bones become fragile and are more likely to break. Usually the bones lose density and become porous.

The main contributing factor is not enough calcium or Vitamin D in the diet. This can also be a genetic, inherited trait.


Anemia is a condition of the blood when there are not enough healthy red blood cells. A patient feels tired and weak as the tissues and organs in the body are not able to get enough oxygen.

Too little iron in the diet. Iron is needed for healthy red blood cells to deliver oxygen to the tissues. Blood loss can also result in anemia, but this does not refer to diet.


This is a severe form of malnutrition due to starvation. The person becomes extremely thin (emaciated).

A severe deficiency of nearly all nutrients, especially protein and carbohydrates.


A person has constipation when they have a bowel movement less than 3 times per week. The person may have hard stools and difficulty and pain when passing stools.

A diet lacking fibre. Fibre helps to produce stools and stimulate the digestive system. Not drinking enough fluids (water) can also cause constipation.

Digestion and the alimentary canal

  • digestion
  • dissolve
  • enzymes
  • faeces
  • gastric

What is digestion?

Digestion involves a variety of complex processes that turn the food that you eat into tiny molecules that can then be absorbed and transported to the cells of the body.

There are two types of digestion:

  1. Mechanical digestion occurs when food is physically broken down through chewing, churning and mashing. Mechanical digestion takes place in your mouth and in your stomach.

Mechanical digestion does not change the chemical properties of the food. Rather, it changes the physical properties by breaking large pieces up into small pieces, therefore it can also be called physical digestion.

  1. Chemical digestion takes place when different digestive enzyme sbreak down the bits of food into smaller molecules. Enzymes are special proteins that speed up certain chemical reactions in the body. Chemical digestion starts in the mouth where enzymes in your saliva start to break down starch. Chemical digestion also takes place in the stomach and small intestine.

The alimentary canal

  • peristalsis

We already studied the alimentary canal in Chapter 2 so we'll start by reviewing what we learnt there.

Dr William Beaumont (1785 - 1853) discovered how food is digested in the stomach. He dropped food, attached to silk threads, into the stomach of a patient who had a gunshot wound to the stomach that would not close, and examined what happened.

The different organs in the digestive system


  1. Label the following diagram.
  2. The labels have been provided for you. There are some which you might not have come across yet, as they are not the main components in the digestive system, but still play important roles.

Labels to include:

  • large intestine
  • anus
  • oesophagus
  • rectum
  • stomach
  • mouth
  • small intestine
  • liver
  • gallbladder
  • pancreas

Learners must draw straight, parallel label lines with a ruler and labels should be written one underneath the other. In this image, the liver is the large red organ next to the stomach, and the gallbladder is the small green part in front of it. The liver produces bile which it then secretes into the gallbladder to be stored before it enters the digestive tract. Bile helps with fat digestion. The pancreas, the yellow organ below the stomach in the diagram, is another organ which plays an important role in digestion as it produces the enzymes for chemical digestion which are secreted into the small intestine. The liver, pancreas and gallbladder are accessory organs to the digestive system. However, they are not part of the alimentary canal. Make learners aware that there is a difference in discussing the digestive system (including these accessory organs) and the alimentary canal (which only focuses on the organs and structures through which food passes and not the liver, pancreas and gallbladder).

Take a virtual tour through the alimentary canal http://nature.ca/discover/exm/blddgstvsystm/index_e.cfm

Learning how to link the structural adaptations of an organ, tissue or cell to its function is a very important skill to start developing.

Let us make a model of the alimentary canal that can demonstrate mechanical and chemical digestion in the different parts, and also learn about how the different parts are structurally adapted to suit their function.

Although CAPS states that no detail of how the different parts of the alimentary canal are structurally adapted to suit their function, some of this information has been included in the following activity. It was felt that it is necessary to start developing this skill as learners will often have to describe structural adaptations for function in Life Sciences Gr. 10-12. This skill is often poorly developed in learners and so it is beneficial to start introducing learner to this kind of reasoning and explanations of biological structures from early on. This is an optional activity.

A digestion simulation

Objectives for this activity:

  • Learn about how the different parts are structurally adapted to their function.
  • Describe the parts of the alimentary canal and what each part's functions are.
  • Understand physical and chemical digestion.
  • Discuss how food travels from ingestion to digestion to absorption and egestion.
  • Make observations regarding the process of digestion.

A suggestion is to make learners work in groups and produce one model per group. This way they will be able to discuss the model with each other as they are going along and there might also be less mess. Set up a workstation for each group prior to the lesson with the required materials laid out. The materials below are suggestions to be used to create a model of each part. However, you can also use other materials if you have more appropriate ideas or access to other materials in your classroom.

Alternatively, you could also do this activity as a demonstration in the front of the class, discussing the model and structures as you go along.

If you are not able to physically produce the model of digestion with your learners in class, you can still read through the activity and learners can still answer the questions and you can discuss the structural adaptations.


Each group will need the following:

  • large dish to work over, or black bags and newspaper
  • crackers, white bread or viennas
  • mixing bowl
  • scissors, pestle and potato masher
  • water bottle that can squirt water through a small hole
  • the inner tube of a kitchen paper towel roll or toilet paper roll
  • a clear plastic Ziplock bag
  • 30 - 40 ml of lemon juice, vinegar or a fizzy drink
  • full length stocking with the toe section cut open - it helps if one leg is put inside the other to form a double layer
  • bicarbonate of soda dissolved in water in syringes (10ml)
  • large bowl


  1. Work in groups and construct a model to demonstrate the different processes that food goes through in the different parts of the alimentary canal.
  2. Make careful observations and describe in detail what happens at each stage.
  3. Work over a large bowl or tray or sheets of newspaper and black bag to contain the mess which might be produced during this activity.

An interactive animation showing how different foods are digested and absorbed http://kitses.com/animation/swfs/digestion.swf

Stage 1 - The mouth

The function of the mouth is to ingest food and to start to digest the food. The mouth is specifically adapted for its function as follows:

  • The lips keep the food in the mouth while chewing.
  • Food is bitten off with the front teeth.
  • Food is cut, torn and mashed into smaller parts by the different teeth in the mouth - this is mechanical digestion.
  • The tongue moves the food around the mouth while it is being chewed. It also prepares the food for swallowing.
  • Salivary glands secrete saliva. Saliva coats the food in the mouth making it easier to swallow. Saliva also contains enzymes which start to chemically digest.

Learners need to cut up the food with the scissors, break it up with the pestle and mash it with the potato masher. They then squirt water all over it and use their hands to make the food into a ball.

Using the mixing bowl to represent the mouth and the scissors, pestle and potato masher to represent and simulate the digestion of your food type that occurs in the mouth.

Squirt some water onto the mixture as you are 'digesting' the food.

Describe what is happening to the food at this point.

The scissors, pestle and potato masher is mechanically breaking down the food into smaller particles (mechanical digestion). The water (saliva) sprayed on the food is covering it and starting to digest some of it (chemical digestion).

Compare the model to the actual process in your mouth and what each part and action you are performing in the simulation represents.

The scissors are like the incisors that cut the food, the pestle is the pre-molars and the potato masher represents the molars. The water sprayed on the food is the saliva that starts chemical digestion. The hands making the ball with the food represents the action of the tongue and soft palate in making the bolus.

Our bodies produce about 1.7 litres of salivaeach day.

Stage 2 - The oesophagus

The pharynx (the throat) moves food from the mouth to the oesophagus. The oesophagus transports food from the pharynx to the stomach.

  • A flap in the pharynx covers the trachea (windpipe) to prevent food from accidentally going into the trachea and causing the person to choke.
  • The oesophagus is a muscular tube that moves the food by contracting in sections and relaxing in other sections. This is called peristalsis.
  • A special circular muscle shuts the entrance of the stomach. It prevents the contents of the stomach from pushing back into the oesophagus which may lead to vomiting.

One learner should hold the cardboard roll/tube with the one end in the bag while another learner tips the mixing bowl so that the food bolus rolls down the tube and into the bag.

Roll the ball of food you created in the mouth down the cardboard tube and into the clear Ziplock bag.

Describe what is happening to the food at this point.

The ball of food is being transported from the mouth to the stomach.

Compare the model to the actual process in your oesophagus. Can you think of a better way of simulating the action of moving the food from the mouth to the stomach?

Learner-dependent answer

In the human body, the oesophagus transports the food (bolus) from the mouth to the stomach just like the cardboard tube allows the ball of food to travel from the mixing bowl representing the mouth to the Ziplock bag representing the stomach. Learners should note the downfall of this part of the model as food does not 'roll' down the oesophagus as they have done here in the simulation. Rather, the food is moved down by the peristaltic actions of the muscles surrounding the oesophagus. Learners should think up alternative ways to simulate or represent this action, such as using a plastic tube which is not hard and using your hands to squeeze the food down the tube and out the other side into the bag.

Stage 3 - The stomach

The stomach is specifically adapted for its function as follows:

  • The stomach has strong muscles which help churn the food to break it up further. This also mixes the pieces of food with the digestive gastric juices.
  • Since the stomach has to store food and liquid, it has many folds and ridges in the wall that help to expand the stomach further.
  • The lining of the stomach is replaced to prevent the stomach from digesting itself.
  • The stomach secretes gastric juices when food is present. This helps the functioning of the enzymes in the chemical digestion of proteins.
  • Cells in the stomach lining are adapted to absorb water.
  • The lower end of the stomach has muscles which can control the emptying of the stomach contents.

Learners need to pour the digestive juices onto the food and then seal the stomach / Ziplock bag. They then simulate the stomach churning by shaking and churning the Ziplock bag with the food inside. This should go on for quite a while as the food often remains in the stomach for long periods.

The Ziplock bag represents the stomach. After the food has entered the stomach, pour one of the digestive juices (lemon juice, vinegar or Coca Cola) into the bag over the ball of food.

In your body, a special circular muscle closes and seals the stomach and digestive juices from the oesophagus. Seal the Ziplock as if you were sealing the actual upper end of the stomach.

Squeeze the bag to show the churning of food in the stomach.

Describe what is happening to the food at this point.

The churning and shaking is physically breaking up the food through mechanical digestion. The coke, vinegar or lemon juice aids chemical digestion.

Compare the model to the actual process in your stomach.

The stomach muscles churn and move the food around to break it up through mechanical digestion just like your hands when they are churning and moving the food to break it up in the bag. The coke, vinegar or lemon juice added to the stomach represent the gastric juices which the stomach secretes from its walls to cause chemical digestion.

Stage 4 - The small intestine

In the small intestine, the digestion of proteins, carbohydrates and fats is completed and the end-products of these digestion processes are absorbed. The small intestine is specifically adapted for its function as follows:

  • Since most of the digestion and absorption process takes place in the small intestines, it is especially long and folded to create an even bigger absorption area.
  • The inner layer of the small intestine is lined with small finger like structures called villi which aid absorption and increases the area for absorption.
  • The small intestine has a large network of capillaries surrounding it to transport the absorbed food away.
  • The muscles of the small intestine control the direction in which the food flows through peristalsis.

Learners need to let the food mixed with the digestive juices, run from the Ziplock into the stocking. It shouldn't be excessively runny but make sure they are working over a large dish to catch the excess liquid. They should be squirting small amounts of bicarbonate dissolved in water into the syringe to simulate the digestive enzymes being added to the small intestine.

You may want to explain how peristalsis works by showing how the muscles around the small intestine squeeze rhythmically to push the food from the stomach through the entire intestine. Let learners use their hands to simulate peristalsis - if one hand is squeezing tightly around the small intestine the other releases and relaxes around the small intestine.

The stocking that you have been provided with represents the small intestine. Cut a small corner off the bottom of the Ziplock bag and insert this end into the stocking.

Work over a large dish or black plastic bags for this part. While one learner is holding the stocking, the other learner should squeeze the food mixture into the stocking.

Use the syringes with the dissolved bicarbonate of soda and squirt the bicarbonate of soda into the food as it enters the stocking.

Simulate the action that takes place in the small intestine to move the food mixture through.

Describe what is happening to the food at this point.

The food is mixing with the bicarbonate of soda dissolved in water and moving through the small intestine. The food takes a very long time to move through the small intestine and the liquid is running through the stockings and into the large dish or onto the table.

Compare the model to the actual process in your small intestine.

When food arrives in the small intestine digestive enzymes are secreted from the pancreas and bile from the gallbladder. This is represented by the bicarbonate of soda mixture which is squirted into the stocking. These enzymes digest the food particles that are then able to be absorbed by the cells in the walls of the small intestine. The molecules move into the capillaries and blood stream that surrounds the small intestine. As learners squeeze the food along, some of the liquid runs out of the stocking and this represents the molecules being absorbed into the bloodstream. Learners could also compare the length of the small intestine to the long stocking being used. At the end of the process the food that is left is dryer and can move out of the small intestine as undigested waste that gets egested. In the same way the food that is left in the stocking is moved to the open end of the stocking and released.

Stage 5 - The large intestine

The large intestine absorbs water and mineral salts, to make some vitamins, and to decay the undigested food materials to form faeces. The large intestine is specifically adapted for its function as follows:

  • Undigested waste remains in the large intestine for up to 24 hours in order to maximise the absorption of water from this region.
  • The muscles in the large intestine are able to turn the waste material into faeces preparing it for egestion.
  • When it is time to egest waste, the muscles in the large intestine create strong peristaltic movements to force the faeces out of the body via the rectum and anus.
  • Circular muscles in the anus control the emptying of the waste materials.

Was this a worthwhile activity for you? Explain what you learnt from this activity and whether you think it was a worthwhile activity or not, giving reasons for your opinion.

Learner generated answer.

Watch a video with some fascinating facts about the digestive system

In exams and tests you will be asked how a specific structure is adapted to its function. Remember when you see such a question to break it down into four separate steps:

  1. Outline: Give a brief explanation of the the main point you will discuss, i.e. structure, function and specific adaption(s).
  2. Structure: Here you need to specify what the structure looks like.
  3. Function: What does it need to do? What role does it play or purpose does it fulfil?
  4. Adaptation: This is where you put together structure and function - it has X, so it can do Y. For example, it is thin, so gases diffuse through it quickly.


  • There are seven buildings blocks in a healthy diet: proteins, carbohydrates, fats and oils, vitamins, minerals, fibre and water.
  • A healthy diet includes the correct proportions of the seven building blocks.
  • Problems in our digestive system can be related to an inappropriate diet that does not give our bodies the correct nutrients.
  • Our alimentary canal is composed of the mouth, oesophagus, stomach, small intestine, large intestine, rectum and anus.
  • Digestion is the breaking down of food into usable, dissolvable forms that can be absorbed.
  • There are two types of digestion: mechanical (or physical) and chemical digestion.
  • Each structure in the alimentary canal is specifically adapted to suit its purpose.

Concept map

The alimentary canal is made of several parts linked together - two of these parts are missing in the concept map. We also looked at two types of digestion in this chapter. What are these? When filling them in on the concept map, you need to decide which space to put them in by looking at the concepts which come after to describe each type.

Teacher's version

Revision questions

Describe what you understand the term 'healthy diet' means. [2 marks]

A healthy diet provides all the nutrients, such as carbohydrates, proteins, fats, vitamins, minerals and fibre that are needed for well-being, and contains them in correct amounts/ proportions.

For each of the following food items, classify what nutrients you can get from them (i.e. protein, carbohydrates, vitamins, etc). Some food items provide more than one class of nutrient. [10 marks]

Food item


Food item


Fried chips.


Chicken pieces.

Bran biscuits.



Assorted nuts.

Split peas and lentils.

Green beans.


Food item


Food item


Fried chips.

Carbohydrates (starch), oil from frying.


Vitamins (especially vitamin C) and minerals, carbohydrates (sugar), water.

Chicken pieces.

Protein and fats.

Digestive biscuits.

Carbohydrates, fibre.


Vitamins and minerals, starch.


Minerals (calcium), protein, fats, water.

Assorted nuts.

Fats and oils, protein, vitamins and minerals.

Split peas and lentils.

Protein, fibre, starch, vitamins and minerals.

Green beans.

Vitamins and minerals, protein, carbohydrates, fibre


Fats and oils.

Which of the foods in Question 2 contain starch? How can you test if they contain starch? [9 marks]

The starch test will indicate whether a food contains starch - if you drop iodine solution on the food and the iodine turns from brownish-orange to blue-black then the food contains starch. Food that will possibly test positive for starch in the above examples are: green beans, split peas and lentils, butternut, digestive biscuits, fried chips.

Why is it important to limit your intake of take-aways? [3 marks]

Take-away food is usually cooked in large quantities of oil and contain many additives and fats to make it last longer and taste stronger which might not be good for the body.

Give at least 2 reasons why we should eat raw fruit and vegetables. [2 marks]

Heat can break down some vitamins and boiling dissolves them and minerals out of the food, so it's better to eat them raw.

Some food may take up to 24 to 36 hours to digest and be fully absorbed. Why do you think this process takes so long and why is this a good thing? [2 marks]

Food that is digested over a long period of time has all the beneficial nutrients removed from it rather than travelling through the digestive system really fast and having only a part of the nutritional value of the food absorbed from it.

Total [28 marks]