Chapter overview

2 weeks

As an introduction, refer learners to the classification of living organisms that they would have done in Gr. 7 Life and Living. They should be familiar with the range of living organisms classified into the five kingdoms, namely plants, animals, bacteria, protists and fungi. Ask learners to explain what they understand about bacteria, protists and fungi. In previous chapters and grades, we have dealt extensively with organisms from the two kingdoms plants and animals. However, those that are not seen at a macroscopic level have not yet been studied in much detail. A more in-depth look at microorganisms is the focus of this chapter. In addition we will look at which of these are harmful and which are useful. Learners have not yet been introduced to cells (which will follow in Gr. 9) so the classification should not go to cellular level. An excellent resource for teachers to use is: http://ideasforteachers.wordpress.com/2010/03/22/microorganisms/ where Interactive Whiteboard lessons, videos, worksheets, etc. on microorganisms are available.

Note: Although CAPS spells 'micro-organisms' with a hyphen, which is accepted, it is not the most commonly used spelling. We have therefore used the spelling without the hyphen, namely 'microorganism' as this is what learners will mostly encounter in other resources, especially online.

3.1 Types of microorganisms (2 hours)




Activity: What does 'microscopic' mean?

Observing, describing, writing

CAPS suggested

Activity: Classifying organisms

Classifying, writing

Optional (revision)

Activity: Calculating the size of an organism using a scale bar

Examining, analysing, calculating

CAPS suggested

3.2 Harmful microorganisms (2 hours)




Activity: Where are pathogens found?

Identifying, writing


Activity: How easily do viruses spread?

Group work, analysing, discussing


Activity: HIV Research

Researching, discussing

CAPS suggested

Activity: Preventing the spread of diseases

Researching, writing

Optional (Extension)

Activity: Typhoid Mary

Researching, writing, discussing

Optional (Extension)

Activity: Research an infectious disease

Researching, writing

CAPS suggested

3.3 Useful microorganisms (2 hours)




Investigation: Investigating the growth of yeast

Hypothesising, investigating, observing, measuring, recording, analysing, writing, group work

CAPS suggested

Activity: Careers as a natural scientist

Researching, discussing

CAPS suggested

  • What are microorganisms?
  • Why do we need microorganisms on Earth?
  • Are there microorganisms living in my body?
  • How do we study microorganisms?
  • What causes your body to get sick?
  • Are microorganisms of any use to us?

Microorganisms have been on Earth for billions of years and have adapted to live in extreme conditions. They are found in almost all areas of the Earth's biosphere and new microorganisms are still being discovered all the time. Some can be harmful, causing disease and illnesses, while others are useful to us and are a vital part of ecosystems. Let's take a closer look!

Types of microorganisms

  • bacteria
  • disease
  • fungi
  • infect
  • protist
  • virus

Bacterium is singular and bacteria is plural.

The prefix 'micro' comes from the Greek word mikros meaning small. How many words can you think of which contain the prefix micro? What do they all have in common?

Microorganisms are extremely small living organisms. People did not even know they existed until the invention of microscopes in the 1600s! We say that we cannot see microorganisms with the 'naked eye'. We have to view them under a microscope.

A basic light microscope.

Antonie van Leeuwenhoek designed and built his own microscopes. In 1674 he became the first person to see and describe microscopic organisms like bacteria, yeast and many other microorganisms.

Antonie van Leeuwenhoek is considered to be the first microbiologist.
Some of the microorganisms which van Leeuwenhoek observed and first described. He called them 'animalcules'.

Someone who studies microorganisms is amicrobiologist.

What does 'microscopic' mean?

The intention of this short activity is to familiarise learners with the idea of microscopic objects and what this means. To be microscopic means that they need to be viewed under a microscope. The purpose is to show learners that many objects can be viewed under a microscope to see the detail, and there are many objects which can only be viewed under a microscope in order to be seen at all.


  • hand lens or magnifying glass
  • newspaper print
  • other small objects with detail

Provide learners with a range of different objects with fine detail, for example, newspaper, a cloth to view the individual threads, and if possible, grow some bread mould by leaving out a damp piece of bread in an enclosed container for a couple days prior to starting this activity.


  1. Your teachers will provide you with a range of different objects to view.
  2. First observe the objects with your naked eye.
  3. Then use the hand lens to view the objects again.
  4. Take note of the differences in the detail you can observe.


The use of corrective glasses or contact lenses still constitutes 'naked eye' as it merely corrects vision to normal human accuracy. Make sure that learners requiring corrective glasses or contact lenses understand that they may keep their glasses on and it will still constitute a 'naked eye' observation.

What do we mean by the term 'naked eye'?

It means viewing something using only your eyes; with nothing in front of your eyes to help you view something.

Describe some of the differences when you viewed the objects using just your eyes and when you used a hand lens.

Learners should note that they were able to view more detail when viewing something using a hand lens and that things looked bigger.

  1. The following images show different views of the same object. One image shows what we would see with our naked eye. We call this the macroscopic view. The other photo shows what we would see if we viewed the object under a microscope. This is called the microscopic view. For each object, identify which is the microscopic view and which is the macroscopic view.

In the last activity we saw that you can view objects under a microscope allowing you to see much more detail than if you just viewed them with your naked eyes. There are many organisms on Earth however, which we cannot see at all with our naked eye. We can only see them when we look under a microscope. These are microorganisms.

The living organisms on Earth can be grouped in many ways. You have learnt about classification before. Let's revise our classification system for all organisms on Earth.

Classifying organisms

This is optional revision of what learners have already covered in Gr. 7 on Biodiversity, and briefly mentioned in Chapter 2 this term.


  1. Study the following diagram showing how we classify organisms on Earth.
  2. Answer the questions that follow.


Do you see that the organisms in the diagram are divided into five groups? What do we call these five groups?


Write the names of these five groups in the spaces on the diagram.

The five kingdoms are: Animals, Plants, Bacteria, Fungi and Protists.

Which groups do you think contain organisms which can be classified as microorganisms?

Bacteria, Fungi and Protists.

Do you think microorganisms are living or non-living? Give a reason for your answer.

They are living. They perform all seven life processes (moving, respiring, sensing, growing, reproducing, excreting, feeding).

As discussed in this chapter, viruses are also microorganisms. There is much debate as to whether viruses are living or non-living. Viruses do not perform all seven life processes so they are not included in one of the five kingdoms.

Microorganisms include viruses, bacteria, protists and some types of fungi (although many fungi can be seen without the use of a microscope). Let's have a closer look at the different types of microorganisms, before looking at how they can impact our lives in a positive or negative way.

Bacteria are a large kingdom of microorganisms. Many bacteria are responsible for causing diseases in humans, however some are also useful as we will see later. Viruses are also tiny organisms, much smaller than bacteria even. They can infect all types of organisms, such as plants, animals and also bacteria. Viruses need to infect other organisms in order to replicate (reproduce).

There is much debate amongst scientists about whether we can classify viruses as living or not!

Mycobacterium tuberculosis bacteria which cause Tuberculosis (TB) in people. http://www.flickr.com/photos/niaid/5149398656/
H1N1 influenza virus particles which cause flu symptoms in people. http://www.flickr.com/photos/niaid/8411599236/

Fungi are also one of the five kingdoms of organisms. Many different varieties of fungi exist. Some are large enough for us to see without the help of a microscope, like mushrooms and bread mould. They are macroscopic. There are others which are microscopic and can only be seen under a microscope, for example yeast.

Not all fungi are microscopic, such as mushrooms. http://www.flickr.com/photos/78428166@N00/6107931302/
Millions of yeast cells viewed under the microscope. http://www.flickr.com/photos/tessawatson/384591931/

Watch how yeast reproduce

Protists are a very diverse group of microorganisms. The organisms in this kingdom do not fit easily into any of the other four kingdoms, namely animals, plants, fungi or bacteria. However, some protists are plant-like and others are animal-like. Most protists are microscopic and live in water. The only macroscopic members are the algae or seaweeds.

A protists living in freshwater.
A protist found in the gut of many animals.

As you might have noticed from some of the microorganisms mentioned here, some of them can be harmful to humans and other organisms as they cause diseases and illnesses.

Calculating the size of an organism using a scale bar

How do you know the size of a microorganism? You will notice that many pictures of microorganisms have a scale bar. A scale bar is a very useful tool that allows us to calculate the actual size of objects. Follow the instructions below to figure out the length of this Oxytricha trifallax protist.

A micrograph ofOxytricha trifallax.


Measure the length of Oxytricha trifallax using your ruler. (Express your answer in mm.)

Learner-dependent answer.

Note: The answer will depend on the format in which the image is viewed (printed, photocopied, online, etc.) and the exact point that learners choose for the start and end of the organism. A small amount of variability is expected.

Measure the length of the scale bar with your ruler. (Express your answer in mm.)

Learner-dependent answer

Note: This will depend on the format in which the image is viewed (printed, photocopied, online, etc.)

Divide the size of the object (in mm) by the size of the scale bar (in mm) and round off. Your answer will be a ratio and will not have units, since you divided mm by mm.

The answer should be approximately 3.

Note: The ratio should be constant no matter what size the image was printed! This is the power of using a scale bar. Encourage learners to round-off their answers to one decimal point in order to make their calculations easier. You can discuss with the class why learners may have slightly different answers.

To find the actual size of the organisms, take your answer and multiply it by the number on the scale bar. The units on the scale bar are in μm and so your answer must be in μm. How big is Oxytricha trifallax?

The length of the organism is approximately 150μm.

Note: teachers should accept any answers that are within the range of 120 -180 μm. Learner's answers may differ. You may use this opportunity to discuss with learners why they think there is variation in their answers. Ask them to compare the length they measured to the length of their friends. Maybe some learners measured from the tips of the cilia and have a larger answer than others who chose not to include the cilia in their measurements.

How many μm are there in a mm?

There are 1000 μm in 1 mm.

How many Oxytricha trifallax could lie end to end in 1 mm?

Approximately 6.67 Oxytricha trifallax could lie end to end.

Note: The answer is arrived at by dividing 1000 by the size of one Oxytricha trifallax. Teachers should accept answers between 6 and 8.

  1. Using the same method you practised before, calculate the size of the following organisms:


    Approximately 110 μm

    Note: Accept answers between 100 and 120 μm

    A fossilised diatom.

    Approximately 57 μm (0.057 mm)

    Note: Accept answers between 50-60 μm

Scientists know what size to make the scale bar because they know what magnification they are using on their microscopes. You will learn about magnification, field of view and how to create your own scale bar if you continue with Life Sciences in Gr. 10.

Harmful microorganisms

  • contaminate
  • fever
  • immune system
  • pathogen
  • transmitted

Some microorganisms cause diseases which may result in death. Microorganisms that cause diseases are called pathogens. These pathogens infect other organisms and cause various signs and symptoms in the organism.

Where are pathogens found?


  1. Discuss the question asked in the title of this activity with your group or class.
  2. Use the following photos in your discussion.
A handrail. http://www.flickr.com/photos/lunchtimemama/99886586/
Public pay phones. http://www.flickr.com/photos/v1ctor/7805728128/
A basin and toilet. http://www.flickr.com/photos/editor/2084672070/
An ATM keypad. http://www.flickr.com/photos/redspotted/272104/
Rubbish. http://www.flickr.com/photos/creativecomputer/415482865/in/photostream/
Drains and pipes. http://www.flickr.com/photos/tauntingpanda/6240242/


What can you conclude about where disease-causing microorganisms are found?

Microorganisms that cause disease are found on many surfaces which come into contact with humans regularly, such as handrails, public keypads, etc. They are also found in places which are unclean. Learners should be able to see that disease-causing microorganisms are found almost everywhere.

How do you think diseases spread from one person to the next?

Learners need to come up with their own answers here based on the discussion about where pathogens are mostly found. They could conclude that they spread by humans coming into contact with surfaces and objects which have the pathogens on them.

Find out what it means to 'sterilise' an object, and write your own definition.

To sterilise something means to make something very clean so that any microorganisms on the surface of an object or in a fluid are removed or killed.

Transmission of infectious diseases

These diseases are called infectious diseases as they can be passed from one organisms to the next.

We can come into contact with various dangerous microorganisms each and every day, whether it is when you open the door handle of a toilet or use a trolley at the shopping centre. Pathogens can spread between humans and other organisms in many different ways, for example:

  1. In droplets from the air that we breathe: When an infected person sneezes or coughs, the pathogen travels in the drops of spit or mucus to another person.

  2. In untreated and contaminated water: The pathogen is transmitted in contaminated water, especially if it has been in contact with human sewage. These diseases are called waterborne diseases, such as cholera and typhoid, and cause diarrhoea.

  3. In contaminated food: Sometimes people prepare food without washing and disinfecting their hands properly and the food can become contaminated.

  4. Through cuts or wounds: Many pathogens enter our bodies via cuts or wounds. For example, tetanus bacteria live in the soil and when someone hurts themselves on a piece of rusty metal, this pathogen can infect the person.

  5. Through bites from animals: Some pathogens can spread via bites from infected animals. For example, the rabies virus from infected animals and malaria is transmitted to humans through mosquitoes.

One of the best ways to prevent the spread of harmful pathogens is by washing your hands regularly with soap and warm water.

How easily do viruses spread?

This is anoptional activity, but it is suggested if you have time in class.

This activity develops from the previous text about the spread of diseases. We will be looking at how viruses spread, and in particular sexually transmitted diseases (STD's). The aim of this activity is to open up discussion about choices of protection to prevent STD's, and importantly the freedom to say "no" and mean "no". Once the activity is completed it is very important to have a detailed discussion about the wider issues involved and the importance of learners having a clear concept of what they want before embarking in sexual activity. It provides the opportunity to discuss the issues and realities of both STD's and preventing unwanted pregnancies.

Birth control or contraception are methods or devices used to prevent pregnancy. However, some contraceptives (pills) may not prevent STDs, whereas some (condoms) may also PROTECT individuals from contracting STDs.

You are using acid to track the spread of STD's - the acid represents a microorganism that causes an STD. One person will be passing acid in the form of vinegar, as the children share their water. The water should be shared by pouring water into each other's cups, not by drinking! If they have been acidified they will pass the acid on to whoever they share their water with. By the end of the activity only those who do not accept from others will remain "disease free". This can either be related to abstinence, or could equally represent people who had safe sex and used protection to prevent the exchange of bodily fluids that may contain the microorganisms which cause STDs.

We are going to have a look at how some viruses spread by acting it out.


  • paper cups or beakers (one per learner)
  • white vinegar (dilute)
  • water
  • dropper
  • liquid indicator

If possible, use a universal indicator


  1. Your teacher will divide your class into three groups: A, B and C.
  2. Each group will be given specific instructions. You must obey the instruction that your teacher gives to your group for the activity.
  3. After the activity, answer the questions.

Instructions for the activity:

  1. Divide the class into three groups: A, B and C. Each group will be given different instructions to carry out.
  2. Brief each of the groups in private as follows (the other groups must not be able to hear the instructions given):

    1. Group A: Instruct them that no matter who offers to share their water with them, they must be very firm and polite but say "No". However, they should offer their water to people they want to give some to. They must NOT let anyone give them water.

    2. Group B: Instruct them they can share their water with whoever they want and they can choose if they wish to receive water from other members of the class. They can say yes or no.

    3. Group C: Instruct them that if anybody offers them water they should say "Yes". They must also try very hard to give a little of their water to as many people as they can. They must try to convince those that say no they should have some. (They are not allowed to give water if the person is definite about "no".)

    4. All groups should be encouraged to try to share a little water with as many people as they can but if someone is very firm about "no" they have to respect this.

  3. You (the teacher) must also take part in the activity. Your cup must have acidified water (vinegar) in it. Make sure you get as many pupils as possible to have some, or target pupils you know have strong persuasive skills.
  4. Once everyone has their instructions and a cup of water, go outside or in an open space to perform the activity.
  5. Allow everyone to sensibly walk round, mingling all groups, offering to share their water.
  6. After about 10 minutes ask the groups to gather into their designated groups A, B or C again. Place the cups in groups (A, B, C) on a table keeping the groups separate.
  7. Now carefully add a few drops of indicator to every person's cup.
  8. Get your class to observe patterns in colour and discuss what each group's secret instructions were.
  9. What you should find is all those in group A should turn green if you used universal indicator. (If someone was persuaded to share you may have the odd red cup, this is really useful because it shows even more clearly the power of NO). Group B will have a mix of red and green liquid in cups depending if they said yes to some or no to everybody. All of group C should be red, i.e. contaminated with acid.


At this point, discuss what the different colours mean. You can use the following questions to guide the discussion, or else learners can answer them by themselves or in small groups.

Point out that only one person had the disease to start with but now everyone who has red liquid in their cup has it. Encourage discussion about how even your best friend may have slept with someone else and thus could pass the disease on to you. Therefore the only safe way to prevent getting a STD is to abstain from sexual intercourse or from the use of male condoms and female condoms. It is useful to stress that girls have as much, if not even more right, to protect themselves from disease and pregnancy, and that it should be their choice as well, which must be equally respected.

You will get a lot of laughter but it is a really dynamic way to generate discussion around this very important topic. Stress the importance of each person's right to choose whether they do or don't want to take part in sex at school age. Stress the benefits of waiting but also balance it with the sensible option of protected sex not just to prevent pregnancy. It is also important to stress that even if a girl is on contraception pills, these will not provide protection against STD's - only a condom will do this.

Which group had the most cups with red liquid? What does this mean?

Group C should have the most red cups. This means that they were contaminated. They did not say 'No'.

The activity that you just acted out can be used to describe the spread of one of the most devastating viruses in the world today, especially Southern Africa. Which virus is this?

The Human Immunodeficiency Virus (HIV).

Note: Learners must not say AIDS here. AIDS is not a virus- it is a syndrome that can result from infection with HIV.

How does this virus spread? What action did you do in the activity to represent this?

HIV spreads by sexual intercourse without protection or by coming into contact with an infected person's blood through an open wound. In the activity this was represented by mixing water with someone else.

Note: HIV can also be transmitted from mother to child during pregnancy.

How can you prevent the spread of this virus? Discuss this with your class.

The virus can be prevented from spreading by abstinence (saying "No") or by using male or female condoms.

The Human Immunodeficiency Virus (HIV) is one of the most devastating viruses in our world today. The HI virus causes Acquired Immunodeficiency Syndrome (AIDS) in humans. It is a condition where the immune system starts to fail and is ultimately life-threatening. HIV infects white blood cells in the human immune system.

White blood cell (stained blue) infected with tiny HI viruses (stained yellow). http://www.flickr.com/photos/niaid/5613410125/

HIV Research

This can be done as a homework activity and then learners can report back to the class. A suggestion is to get different learners to research the different questions and then report back to the class and have a class discussion.

You must warn your learners to be sensitive about this topic. Encourage the use of scientific terms, great sensitivity to each other, and they must not laugh at what anyone says.


  1. Below is a list of questions about HIV. You will be allocated a question to research.
  2. Write your findings in the space provided and then you will report back to the class in a discussion.


  1. What organism causes HIV/AIDS?
  2. What are the symptoms of the disease?
  3. What are the dangers of having many sexual partners and unprotected sex?
  4. How can the spread of the virus be prevented/minimised?
  5. What is the current treatment for this condition?
  6. How is mother-to-child infection prevented?
  7. Why is pre- and post- natal treatment and monitoring important for pregnant mothers?

Write about what you found in the following space.

South Africa is one of the world leaders in the treatment of HIV/AIDS and better ways of living with the syndrome are being developed all the time. You must continue to do your own reading about the latest developments.

As we saw, the spread of HIV can be prevented by abstinence and having protected sex. HIV can also spread if one uses an infected needle, for example. This is why it is very important that doctors always use sterilised needles and equipment in their practise. Other diseases spread in different ways.

Preventing the spread of diseases

The Anopheles mosquitoes that cause malaria have their abdomens pointing up, whereas normal mosquitoes have their abdomens pointing down?

Malaria is a disease caused by a protist. The protist enters the human body via the bloodstream when an infected female Anopheles mosquito bites a person. The protist travels to the liver of the person and starts to reproduce. Malaria causes high fever and severe headaches, and can lead to a coma and death.

The Anopheles mosquito which spreads the protist that causes malaria in humans. http://www.flickr.com/photos/prep4md/3029599900/ http://www.flickr.com/photos/prep4md/3029599900/
The protist (purple) that causes malaria is moving through the gut of the mosquito in this image.


Find out how the spread of malaria can be prevented. Write about this in the space below and what you should do if you are travelling to an area where there is a high risk of malaria.

There are various ways to prevent malaria. Several different medicines are available which can be taken before going to a high-risk area, which prevents someone from contracting the disease. One way to prevent the spread is to also minimise the bites that you are likely to get by using mosquito repellents and sleeping underneath mosquito nets at night. Another method is to actually eradicate the infected mosquitoes, for example by spraying breeding grounds. You can also regularly empty out containers that could could collect rain water and allow mosquitoes to breed.

Airborne diseases such as tuberculosis (TB) caused by a bacteria, and influenza (flu) caused by a virus, can spread very easily. How do these disease spread and how can we reduce the transmission of these diseases?

The symptoms of these diseases include coughing and sneezing. So, when an infected person coughs or speaks, they spray out drops which can carry the microorganisms and spread them to another person. the infected person could wipe their mouth or eyes and then wipe another surface, thus also spreading the disease. Ways to prevent the spread are to cover your mouth when coughing or sneezing, washing your hands, and there are also various vaccinations available to prevent one from getting these diseases.

Typhoid Mary

This can be done as an extension activity if you have time or else as a homework task.

Typhoid is a disease caused by a bacterial infection. Some people can have these bacteria inside their bodies without realising it, and without ever getting ill from it. They are called 'carriers'. This was the case with Mary Mallon or Typhoid Mary who was a carrier of the disease.


Research typhoid. Find out what causes the disease and what its symptoms are, and find out about treatment.

Learners should include: typhoid is generally spread through food and water that is contaminated with the faeces of an infected person, that contains Salmonella bacteria. It is a life-threatening illness that causes high fevers, weakness, stomach pains and headaches, and a loss of appetite; with a red rash in some patients. The only way to know for sure whether someone has typhoid is to test their blood or faeces for the bacteria Salmonella typhi. Typhoid is treated with antibiotics and there is a vaccine against it.

Share your research with the class.

Read Mary's story below and then answer the questions that follow.

Typhoid Mary

Mary Mallon emigrated from Ireland to America at the age of 15. When she arrived she became a servant, and soon discovered a talent for cooking. Since the cook in households earned a higher salary, she was happy to change from a simple servant to this role. She worked in 8 households from 1900-1907 as the cook, leaving a trail of 51 people seriously ill with typhoid, one of whom, a small girl, died of the disease.

When she was eventually identified as the cause of the many illnesses, authorities at first tried to persuade her to volunteer samples of her faeces, blood and urine to be tested. She refused, although she did admit that she seldom washed her hands when working with food. She didn't think it was necessary. Eventually, after putting up a tremendous fight, she was taken with the help of 5 policemen, to the nearby hospital where the samples were removed. These proved that she was in fact infected with typhoid although she was not sick at all. The authorities sent her to a small island near the city where she was kept away from others for fear of infecting them too. Apart from a short 'parole period', she remained on this island, in full health, until her death.

Mary Mallon. also known as 'Typhoid Mary', was a carrier of typhoid without knowing it.


Why do you think the newspaper article from more than 100 years ago shows Mary breaking skulls into a frying pan?

They were showing how each time she made a meal she was transmitting typhoid to the family and people who would eat the food, and could potentially die from the disease.

Explain how you think the disease was most probably spread from Mary to the people in the home where she worked? Tip: We know that handwashing was not a common practice at this time.

She might not have washed her hands after going to the toilet and might in this way have spread the disease to the food she was preparing. The people eating the food would then have contracted the illness.

Do you think Mary believed the accusations against her? What could have been her reasons for this?

Learner-dependent answer but could include: No, she did not show any symptoms so she probably thought that they were accusing her of something that was not true. Yes, she did because she saw so many people getting sick around her but she was afraid to admit it.

Imagine being Mary and refusing to give authorities samples of your faeces, urine and blood. Why would you not want to give these?

If she did not believe the accusations then she probably thought that they were on a witchhunt and wanted to make her look guilty, so she refused. If she thought that she was in fact making people sick she might have been really scared that the truth would come out and she would have caused all the people to be sick. Either way she knew that they would use the results to take action against her, banishing her to a quarantine colony.

Do you think authorities acted against Mary's basic human rights? Explain your answer.

Yes and no. Yes they could have taken more care in explaining the dangers and getting her to understand the problem of her 'carrier status' (she carried the disease without getting sick), and No, she was infecting many others and making them sick so they were right to protect these people. The authorities had to weigh up Mary's basic right to privacy against those of all the other people who could potentially be harmed by her.

If you were the doctor in charge of the investigation against Mary, how would you have acted in the same situation? Explain why you would have done this.

Learner-dependent answer.

Note: This question was included to allow learners to think how they would have managed the situation differently and requires them to think about the ethical issues of the case.

Discuss with your class possible alternative courses of action that we, as a society, can take when faced with such a dangerous microorganism that can potentially kill millions of people.

Learner-dependent answer.

As we have seen, many microorganisms can be harmful and cause dangerous diseases around the world.

Research an infectious disease

To make sure that all learners do not research the same diseases, a suggestion is to put everyone's names in a hat and then draw them out and assign the names to the various diseases as you go down the list. Learners can either prepare a written report, a poster or an oral presentation for this task. Learners may work in groups of 2-3 for this task.


Your teacher will assign the following viruses, bacteria, protist or fungal diseases to different learners in the class.

Use sources from the library, the internet and interviews with healthcare professionals, to find out more the diseases. Remember to list your sources in a bibliography.

Write a report, prepare a poster or oral depending on your teacher's instruction on the disease.

  1. You must include information on:

    The causes of the disease

    Symptoms of the disease

    At least 3-4 major symptoms.

    Treatment of the disease

    Tell learners that they do not need to know the exact names or dosages of medications.

    How communities react to people with the disease

Diseases or illnesses caused by viruses

Diseases or illnesses caused by bacteria

Diseases from fungi and/or protist

chicken pox or shingles


genital herpes

infectious hepatitis

influenza (flu)






rubella (German measles)


yellow fever

Marburg Virus Disease (MVD)



bubonic plague



some strains of dysentery









typhoid fever

whooping cough


African sleeping sickness


amoebic dysentery




athlete's foot

Note that pneumonia appears in both the viral and bacterial column as the infection can be caused either by virus or bacterial infections.

Many scientists around the world are continually doing research to find and develop cures or vaccinations for infectious diseases, as well as ways to prevent the spread and transmission. One of the most important scientists in medical microbiology was Louis Pasteur. He was a French chemist and microbiologist. He discovered a way to reduce death rate in many diseases and also created the first vaccines for rabies and anthrax.

Louis Pasteur (1822 - 1895), a famous French microbiologist.

Would you like to make a difference to the lives of people in the world? Perhaps you also want to contribute to the research going on to find cures for some of the devastating infectious diseases, such as HIV/AIDS? Or develop a vaccine against a certain strain of influenza? If so, find out what subjects you need to do in Gr. 10 and what and where you can study after school! Be curious and discover the possibilities!

Useful microorganisms

  • antibiotic
  • fermentation
  • fixed
  • legumes
  • nitrogen

In Chapter 2 we looked at the interactions and interdependence of organisms within an ecosystem. Do you remember discussing food chains and decomposers? What was the role of decomposers in the environment?

Decomposers break down dead, organic matter so that it does not clutter up an ecosystem and cause diseases, and in the process they recycle (return) nutrients to the ecosystem.

Many decomposers are microorganisms. These microorganisms play a very important role in ecosystems as they break down dead plant and animal matter. They help to return the nutrients to the soil so that they are recycled. Some bacteria remove nitrogen (N2) from the air and convert it to nitrogen compounds that animals and plants can use. In plants such as legumes, the roots actually contain nodules with the bacteria inside of them. These nitrogen-fixing bacteria, called Rhizobia, cannot live independently and need a plant host. The bacteria get glucose from the plant and the plant benefits by getting the nitrogen compounds which the bacteria fixed from the soil. What is this kind of symbiotic relationship called?

It is a mutualistic symbiotic relationship as both organisms benefit from the relationship. This links back to what learners covered in Chapter 2 and acts as a revision. Learners must be encouraged to take notes in class for these kinds of discussions.

Nitrogen-fixing bacteria form root nodules in some plants, such as legumes. http://www.flickr.com/photos/ricephotos/8566704879/
Can you see the white root nodules on these roots, which containRhizobia bacteria? http://www.flickr.com/photos/plant-trees/4833252601/

We also have bacteria which live inside of us and help the functioning of our bodies! Escherichia coli is found in the lower intestine of many warm-blooded animals. They are part of the natural flora of the gut. They can actually help the animal by producing vitamin K2 and also help prevent other harmful bacteria from growing in the gut.

An interesting article on a newly discovered species of microorganism that lives in symbiosis in the digestive tract of termites. http://www.huffingtonpost.com/2013/04/06/cthulhu-microbes-termite_n_3022887.html

Escherichia coli bacteria found in the gut of many warm-blooded animals.

Humans have also found ways to use microorganisms to do things for us. This dates back throughout our history. Let's find out!

Microorganisms used by people

You might be surprised at how many of our day to day experiences are somehow due to microorganisms.

Have you ever seen the side of a yoghurt container which says it contains 'live cultures'? This refers to the bacteria inside the yoghurt. People use microorganisms for processing foods, such as when brewing beer, making wine, baking bread and pickling food. Microorganisms are also used in the fermentation process when producing dairy products, such as yoghurt and cheese.

Yeast is one of the microorganisms humans have used for food-processing. The most common uses of yeast are in producing alcoholic beverages, such as beer and wine, and in baking, as yeast is used to make dough rise.

The first records of using of yeast to make bread dates back to Ancient Egypt.

Yeast grows under specific conditions. As it grows it uses sugar for energy and converts it into carbon dioxide and alcohol. This process is called fermentation. We can measure the amount of carbon dioxide that is produced to see how well the process works.

What are the best conditions for this to take place? Is there an optimal amount of sugar and what about the best temperature? These are all questions which curious people have asked over time! Let's do an investigation to find out.

We will look more at fermentation next term in Matter and Materials when we do chemical reactions.

Investigating the growth of yeast

You will conduct two separate investigations to determine the optimal conditions for yeast to grow. The first will measure what sugar concentrations are necessary for yeast to grow best. You will receive some guidance and help with this part. The second part will require that you set up your own investigation to determine at what temperature the yeast will grow best. You will be required to plan, conduct and collect data from the investigation on your own.

Learners will investigate the conditions necessary for optimal yeast growth or fermentation. As learners have been exposed to similar investigations in this strand it is less guided as previous investigations.

  • This investigation should run over two periods. There should be at least 2 / 3 days between these periods.
  • The investigation will be done according to the scientific method
  • The activity works well with packets of dry yeast that are readily available from supermarkets.
  • The first part of the investigation will determine the sugar concentration needed for the yeast to grow and learners will receive more guidance.
  • The second part will require learners to plan and execute their own investigation to determine the optimal temperature at which the yeast will grow.
  • Teachers may therefore choose to use this for an informal practical assessment mark.
  • This lesson may be used for a cooperative learning task where the two pairs of learners within the team of 4 could be tasked to work independently to complete different tasks and complete the mass and volume measurements. Teachers should if possible encourage this as it also minimises the use of apparatus and scales.
  • If overflow pans are not available you can also use cake pans or foil pans that are readily available from supermarkets.

Before the investigation it might help learners to watch to see what happens when yeast and sugar are mixed.

Part 1: Yeast growth in different sugar concentrations


To determine the effect of different concentrations of sugar on the rate at which yeast grows.


Which concentration of sugar is best for yeast growth?


Learners should be able to explain that the yeast will use the sugar as a food source and produce carbon dioxide.


  • 6 balloons
  • 14 grams (2 packets) of dry yeast
  • white sugar
  • mass scale
  • funnel
  • 6 x 50 cm string
  • 2 - 50 ml graduated cylinders
  • 600 ml beaker
  • overflow pan
  • permanent markers
  • ice packs

There are different kinds of yeasts. The one we are using breaks down sugar in dough. Others break down wood and corn stalks and produce ethanol (alcohol) while another breaks down the sugar in fruits, nectar, molasses or sorghum.


  1. Work in groups of four.
  2. Use the permanent marker to label each balloon A, B, C, D, E and F.
  3. Each balloon will need to be filled with 2 g of yeast and a different quantity of sugar. Balloon A will need to get 2 g of sugar, B will get 3 g of sugar, C will get 4 g of sugar and so on. (See the table below.) Use a plastic spoon or spatula to place the yeast and sugar into the balloon.
  4. Use a funnel and pour 50 ml lukewarm tap water into each balloon.
  5. One person should hold the balloon and funnel while the other pours in the water.
  6. As soon as the balloon has been filled, take a piece of string and tie off the balloon as close as possible to the level of the water without trapping any air.
  7. Knot the balloon's rubber neck to ensure that no air can get in or water can get out.
  8. Place each prepared balloon on ice to prevent the fermentation process from starting.
  9. Before you allow the fermentation process to start, you need to determine the starting mass and volume of each balloon.
  10. MASS: Determine the mass of the tied balloon to the nearest 2 decimal places. Return it to the ice.
  11. VOLUME: Use the water displacement method to determine the volume of the balloon.

    1. Place water in a large jug level with the top of the jug.
    2. Completely submerge the balloon under the water in the jug: push the balloon and allow the water to flow over the sides into the overflow pan. You should stop when your fingers touch the water.
    3. The water in the overflow plan is therefore the volume of water that the balloon displaced.
    4. Carefully measure the water in the overflow pan. Record your measurements in the table below.
    5. Return the balloon to the ice as soon as possible.
  12. PREPARE FOAM COOLER BOX: You are going to place the balloons inside a foam cooler box with warm water in (the box should keep the water warm). Pour 40 oC water into the cooler box (as it normally cools down quite quickly).

  13. FERMENTATION INCUBATION: You are now ready to start the process of incubating the yeast.

    1. Place each balloon into the warm water.
    2. Record which balloons sink and which float.
    3. Leave the balloons in the warm water for 20 - 30 minutes during which time the yeast will ferment the sugar.
    4. Record the exact time that you used for incubation: _____ minutes.
  14. AFTER INCUBATION: Use a paper towel to dry the balloons.

    1. Determine the volume of each balloon.
    2. Determine the mass of each balloon.

Tip: It is really important that you work fast and accurately at this point. Your team should really consider letting one pair determine the mass and the other the volume of each balloon.

  1. Calculate what changes (if any) occurred during incubation to the mass and volume of each balloon.
  2. Hang your balloon on a clothesline or hanger in the class to dry.
  3. Clean up your work area and wash, dry and pack away all equipment that you used.

It would be an excellent data management activity to have learners record the different groups' data on the board in order to determine the mean (class average) for the class' balloon mass and volumes.

  1. THREE DAYS LATER: remove your balloons from the clothes line / hanger. Record all observations that you can make - remember to use ALL your senses.
  2. Use the same methods to determine the mass and volume of each balloon and record this on the table.
  3. AFTER measuring the mass and volume of each balloon, carefully cut it open. Make careful notes to describe your observations of the contents of each balloon.
  4. Use your table of measurements to draw a graph.


Complete the table with the correct information obtained from your work.


Amount of yeast (g)

Amount of sugar (g)

Balloon mass before ferment ation (g)

Balloon volume before ferment ation (g)

Sink/ Float

Balloon volume after fermentat ion (g)

Balloon mass after fermentat ion (g)

















Present the data you collected on a graph in the space below.


Describe the changes that you observed happening in your balloons from the start to the end of the incubation period.

The answer would depend on the results from the investigation but learners should be able to say that the balloons filled up and became bigger (some more than others).

Were the changes the same in each balloon?

The answer would depend on the results from the investigation but they should be able to observe that the balloons with the small amount of sugar only increased a little bit but the ones with more sugar in increased more in size.

Explain why you think these changes occurred differently in the contents of each of your balloons.

The answer would depend on the results from the investigation but learners should be able to say that the balloons with a greater concentration sugar were able to ferment more quickly or for a longer time than the ones with a smaller concentration of sugar.

How did you expect the balloons to react after 3 days?

Learner-dependent answer. Learners might indicate that they thought the balloons would just continue blowing up / increasing in size, or they may have hypothesised that once the sugar was used up the balloons would stay the same size (or even decrease).

Describe how each of the balloons actually looked after the 3 days.

The answer would depend on the results from the investigation but in most cases the balloons should have decreased in size.

Provide a possible explanation for your observations. Think for instance of what could possibly have been lost from the balloons.

The answer would depend on the results from the investigation but learners should be able to conclude that the sugar in the solution has all been used, so no new carbon dioxide was being made, and the carbon dioxide in the balloons slowly began to escape through the walls of the balloon.

At the start you added yeast, sugar granules and water. Describe how the contents of each of the balloons looked at the end of the investigation.

The answer would depend on the results from the investigation but learners should be able to describe the light brown fizzy contents that has a distinct sour smell and flavour.


What did you learn from doing this investigation?

Learners may conclude that the more sugar was added the more gas was produced.

A simplified version of this investigation can also be done:

  • Provide learners with 4 bottles.
  • Dissolve half a packet of instant yeast into each of the 4 bottles.
  • Mark the bottles A - D.
  • Bottle A should have normal tap water with only the yeast dissolved in it. Stretch a balloon over the top of the bottle.
  • Bottle B should have the yeast dissolved in lukewarm water (not too hot). Stretch a balloon over the top.
  • Bottle C should have normal tap water with 10 ml of sugar dissolved with the 7 g (half a packet) of yeast. Stretch a balloon over the top.
  • Bottle D should have 40 degree C water with 10 ml of sugar dissolved with the 7 g (half a packet) of yeast. Stretch a balloon over the top.
  • The balloons will of course fill with carbon dioxide - with Bottle D filling the fastest as the conditions are most perfect for this in that bottle.

Part 2: Yeast growth at different temperatures

Conduct this investigation again, but this time you need to find out the best temperature for yeast growth. A suggestion is to use 10 ml of sugar for each of the balloons and 7 g of instant yeast (or 2 teaspoons of sugar and 1 teaspoon of yeast). Why do you need to add the same amount of yeast and sugar to all containers? You will need to change the temperature of the water however to measure the optimum temperature for yeast to ferment.


Remember to evaluate your results and discuss any difficulties you might have had or ways to improve your experimental design. In your discussion, you will also need to do some extra research about the applications of this process and include this information. Do not forget to reference your sources in a bibliography at the end.

Besides the use of microorganisms in food and food-making processes, there are also other processes for which we use microorganisms. Specific microorganisms are used in water treatment, like when treating sewage on a large scale.

In biotechnology research, microorganisms are being used to produce alternative, renewable energy, for example, biogas and biofuels.

Microorganisms are used in the development of various medicines, for example, antibiotics. Penicillin is a group of antibiotics which come from Penicillium fungi. The discovery of penicillin and its uses to treat certain bacterial infections happened by chance. This was due to the curiosity of a scientist, Alexander Fleming, and this led to the discovery of many more antibiotics.

Sir Alexander Fleming, who discovered penicillin in 1928.

Microorganisms are also used in many fields of science and medical research. Scientists use yeast to learn more about many other types of organisms. The use of viruses is also currently being explored in many universities around the world to actually help with cures for various conditions, even cancer! The possibilities for discovery are endless!

An article on how a virus could potentially help to cure melanomas, a type of cancer. http://news.yale.edu/2013/06/14/fast-acting-virus-targets-melanoma-mice

Careers as a natural scientist

This is a suggested CAPS activity, but it is not for assessment purposes. Learners should start to learn about and explore various careers within the Natural Sciences. A variety of career options are suggested by this activity. Ideally all of the careers in the list should be represented by at least one student. This is a good chance for learners to explore their interests, so those who already have well-developed passions and interests should be encouraged to explore them further with this activity. If a learner has a career not on this list that is related to Natural Sciences they may talk about their choice instead.


  1. Examine the list of careers below and select one career that interests you.

    Environmental Scientist

    Nature conservationist







    Food Scientist







  2. Do some research about the career you have selected.
  3. Pretend it is 14 years in the future and you are about to attend your 10-year high school reunion!
  4. Break into groups and have a discussion as 28-30 year-olds!
  5. Use the questions below to guide your discussions.


What subjects did you take in Gr. 10?

Learner-dependent answer

Which university did you go to? What did you study?

Learner-dependent answer

Where do you live?

Learner-dependent answer

What does your "typical day" involve?

Learner-dependent answer

What is the best part of you job?

Learner-dependent answer

What is the worst part of your job?

Learner-dependent answer

10 reasons to love science (video).


Concept map

This concept map shows all that we have learnt about Microorganisms in this chapter. What types of microorganisms are there? Fill these into the 4 spaces below. How can we prevent the spread of harmful microorganisms? Fill in 2 of these actions in the spaces provided. In this chapter we learnt about useful microorganisms - what are two products we make using microorganisms? Fill these in.

Teacher's version

Revision questions

Explain in your own words why a microorganism is said to be 'microscopic'. [2 marks]

Microorganisms cannot be seen with the naked eye and they have to be viewed through a microscope.

Which groups of organisms are always microscopic? [3 marks]

Bacteria, viruses and protists.

Which kingdom contains organisms which can be microscopic or macroscopic? [1 mark]


Name 3 foods that are made using microorganisms. [3 marks]

Some examples are bread, yoghurt, cheese, wine and beer.

Draw a cartoon to show how someone in a shopping centre could possibly be contaminated by a virus or bacteria. [5 marks]

Learner-dependent answer.

Note: Learners should be able to show that the person might breathe in the virus/bacteria after someone has coughed without a hand or tissue in front of their mouths; touch another or touch an object where the bacteria is on; drink water that has not been sterilised; eat food that contains the virus / bacteria or have a mosquito or other insect bite the person.

More people seem to catch colds and the flu in winter than in summer. Explain a possible reason(s) for this. Hint: think of the different ways in which people behave in winter.) [2 marks]

People are indoors with windows and doors closed, and are more likely to huddle together, thus if someone sneezes it travels within the small confines of the room and fresh breezes do not come in from the windows and doors and blow the tiny droplets containing viruses away.

Describe how someone would typically contract a waterborne virus. [2 marks]

Either they would drink the water from a contaminated source without sterilising the water first, or they would eat fruit or vegetables that has been sprayed with this water and they might not wash it first before eating it and thus they get contaminated.

Why do you think certain diseases such as malaria, typhoid and cholera, are more serious and cause more deaths in third-world countries in Africa, especially in children, compared to first-world countries? [4 marks]

People in poverty cannot often get the medical help because they cannot afford to visit the doctor, live far away from clinics, have no transport or cannot travel fast enough to the hospitals to get their children treated in developing countries. The malaria in developing countries might be worsened by malnutrition and poor hygiene which might make the child too weak to survive. People living in developing countries might not be able to afford the preventative sprays that prevent the mosquitoes from biting them, and the soaps to wash away or kill bacteria .In poor communities, there is a huge lack in proper sanitation and sewage systems. This makes it much easier for disease-causing pathogens to travel in contaminated water and cause diarrhoea. Stagnant water areas are more common in third world countries which are ideal breeding grounds for mosquitoes.

List 3 important ways that we can prevent the spread of diseases. [3 marks]

You can wash your hands, sterilise or boil all utensils, don't leave food like meat and chicken out / in areas where bacteria can grow, take preventative measures such as using a condom during sex, having vaccinations.

Note: Teachers can use their discretion and accept any other relevant measures that learners may mention.

Describe the optimal conditions necessary for yeast to grow. [2 marks]

Correct sugar solution, correct temperature: (fairly warm).

Total [26 marks]