Natural Sciences, Gr. 8 class notes
Main resource:
De Beer, J.J.J. et al. (2013). Via Afrika natural sciences CAPS: Gr 8: Learner's book.
Cape Town: Via Afrika Publishers.
Strand 1: Life and living
Topic 3: Micro-organisms
1. Types of microorganisms
Micro-organisms are tiny organism that are too small for the human eye to see.
These organisms make up the vast majority of life on Earth, and influence our lives
in unexpected ways.
Micro-organisms need energy to live like any other organism, therefore also make
use of respiration. They also need to reproduce, and can do this very rapidly; some
are able to duplicate and reproduce themselves every 20 minutes.
We can distinguish between most micro-organisms by the way that their genetic
material is contained:
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Prokaryotes = don’t have a true, fully formed nucleus; genetic material floats
around freely in the cytoplasm.
Eukaryotes = have a true nucleus, where genetic material is contained within
a nuclear membrane.
Prokaryotic micro-organisms are the oldest living organisms known to man, the very
first living organism on earth was probably a prokaryote. These microorganisms are
unicellular, and some can survive even in the most extreme living conditions. It is
suspected that eukaryotic micro-organisms evolved much later as life began to
become more complex and diverse. Eukaryotes made it possible for multicellular
organisms to exist.
Virus
Acellular
= doesn’t have a true, fully
formed cell structure and cannot
survive on its own).
Ultra-microscpic.
They are infectious agents.
= cause infections and disease.
They need a host to reproduce.
HIV/AIDS:
The Human Immunodeficiency Virus (HIV) attacks the immune system
of a healthy individual, increasing their vulnerability to infections and
cancer. In serious cases, the individual can develop Acquired
Immunodeficiency Syndrome (AIDS) where the immune system
completely shuts down, exposing the individual to a variety of mild to
serious infections that weaken the body and can be fatal.
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Bacteria
Unicellular
= consist of single cells.
Prokaryotic.
Found in every single habitat on
Earth (even inside multicellular
organisms)
Come in many different shapes
and sizes.
Tuberculosis:
A micro-organism called Mycobacterium tuberculosis causes
tuberculosis (TB), a very serious lung infection that causes more
deaths than any other bacterial disease. It gradually breaks down the
inner lining of the lungs, causing the individual to have severe
coughing fits, struggle to breathe, and in serious cases, cough up
blood. Left untreated, the individual will eventually die.
Protista
Mostly unicellular.
Eukaryotic.
Found in places with lots of
moisture.
Malaria:
This disease is very common in central and northern African countries.
Several different protist species cause malaria, all of which are
transferred to humans by mosquitoes that breed in the calm waters of
rivers and lakes. The protist enters the bloodstream and can travel to
the brain causing brain damage. Symptoms are very flu-like, including
chills, fever, sweating, and intense nausea. In severe cases, the
individual may experience seizures and slip into a coma.
Fungi
Eukaryotic.
Do not ingest (eat) food.
Instead, they secrete powerful
enzymes that break down
material outside their bodies,
which they then absorb.
They are often parasites
= organisms that take nutrients
from a host.
Many fungi produce poisonous chemicals that can cause mild to
severe medical conditions in the people who eat them. Consuming
some fungi can be fatal.
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Micro-organisms can be found in every environment and habitat on the planet, even
on things that we humans use every day, like phones, stationary, handrails of
staircases, toilet seats, etc. When we have contact with these surfaces, we can
potentially catch and spread all sorts of dangerous diseases.
Ways that we can prevent disease include:
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•
•
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Washing hands before eating.
Thoroughly cleaning eating utensils before and after mealtimes.
Boiling drinking water if we have doubts whether it is clean.
Practicing daily good hygiene, like showering/bathing, brushing teeth twice a
day, etc.
2. Microbiology
The study of micro-organisms is called Microbiology. Microbiologists are scientists
who specialise in studying micro-organisms. These scientists have played important
roles in developing cures for some diseases.
For example, Alexander Fleming was experimenting with bacteria, growing them on
special dishes called petri dishes. He accidentally left the lid off one of his petri
dishes, and found that a fungus had started to grow on it. Amazingly, he noticed that
where the fungus grew, no bacteria was able to grow. This lead him to discover
penicillin, which is one of the most common antibacterial medicines used today.
Small white paper discs were placed on a petri dish containing bacteria; each
disc was dipped in different solutions containing different concentrations of
antimicrobial agents. You can see some discs have clear zones around them,
indicating that these antimicrobial solutions were able to stop bacteria from
growing.
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3. Useful micro-organisms
Some micro-organisms play important roles in maintaining ecosystems. They often
act as important decomposers, thereby helping to recycle chemicals in nature. Other
micro-organisms can be very useful for humans in the development of foods,
medicines, and biotechnology.
Lactobacillus is a special bacteria used
to ferment milk, thereby producing
yoghurt, cheese, and other dairy
products.
Some micro-organisms produce
chemicals that stop other microorganisms from growing, which humans
can exploit to make antimicrobial
medicines.
Louis Pasteur was a French chemist
and microbiologist responsible for
creating the first vaccines to treat
diseases like rabies and anthrax. He
also was the first to develop “germ
theory”, identifying that microorganisms
are responsible for diseases.
Furthermore, “Pasteurisation” is a
process he developed which involves
heating liquids to a specific temperature
for a specific amount of time in order to
kill off any micro-organisms that grow
inside of it.
Alcoholic beverages such as beer and
wine are produced when yeast breaks
down the sugars in fruits to produce
alcohol. This process is anaerobic,
meaning it takes place when no oxygen
is present; instead of producing carbon
dioxide, like in respiration, the yeast
produces ethyl alcohol.
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