© Boardworks Ltd 2004 1 of 39 Contents Describe what are microbes? Describe the structure of bacteria and viruses How do bacteria and viruses reproduce?

© Boardworks Ltd 20041 of 39

Contents

Describe what are microbes?

Describe the structure of bacteria and viruses

How do bacteria and viruses reproduce?

Summary quiz

Microbes


Starter activity

• Match the correct keyword to the definition

Pathogen

Infection

Disease

causes damage to the individual’s vital functions or systems.

the invasion and multiplication of pathogenic microbes in an individual or population.

a micro-organism that has the potential to cause disease.


Infection and disease

What is a pathogen?• A pathogen is a micro-organism that has

the potential to cause disease.

What is an infection?• An infection is the invasion and

multiplication of pathogenic microbes in an individual or population.

What is disease?• Disease is when the infection causes

damage to the individual’s vital functions or systems.

An infection does not always result in An infection does not always result in disease!disease!


Disease

• What is communicable? Communicable - able to be passed from one

person to the other

• What is non communicable? Non-Communicable - can’t be passed on from

one person to another


People who lead very unhealthy lifestyles sometimes become ill but it is also clear that people can become ill despite leading a healthy lifestyle. Why?

These were eventually discovered to be…

MICROBES

Therefore, rather than something being wrong with that person, perhaps something else changes the normal state of the body and causes disease.

What causes disease?

Why do people become ill?


As the name suggests, they are microscopic organisms.

They can only be seen using a microscope.

Microbes


Microbes

BACTERIA VIRUSES

The two kinds of microbe that we will be dealing with are:

Now it is important at this point to remember what it means to be living organism.

A living organism must be able to demonstrate that it can perform the seven life processes.


The seven signs of life


Microbes

The reason for looking back to these 7 characteristics is because although bacteria can perform all of these life processes, viruses cannot reproduce on their own.

Does this mean that viruses are

non-living?

This question is still hotly debated!


Micro-organisms are made from cell

• They are very small – so usually ONE cell

• Cells are the smallest unit of life – they can carry out the 7 characteristics of life

• Two types of cell:– Prokaryotic– Eukaryotic


Prokaryotes

• Prokaryotes are the oldest, simplest, and most abundant forms of life on earth.– abundant for over 2

billion years before the appearance of eukaryotes

– 5,000 different kinds currently recognized


Prokaryotic cells

• Single cell organisms• Two main types: bacteria and archaea• Relatively simple structure

Figure 1-7a


Bacteria

• These are tiny single celled organisms that cause a range of illnesses

Activity: Name some diseases caused by bacteria


Staphylococcus causing skin infections


Bacteria

As the bacteria breed successfully they begin to affect the body

Symptoms of infection appear Symptoms caused by remains of dead bacteria

or substances released by the living bacteria (toxins)

Toxins may cause fever Bacteria may directly damage body cells


Fungi - eukaryotes

• Can be single-celled organism to a 3.5-mile-wide mushroom.


Fungi

• These are tiny organisms that can cause a range of infections

• They release digestive chemicals onto the surface of the person they grow on.

Activity: Name some diseases caused by fungi


Athletes Foot


Fungi (yeast that causes thrush)


Viruses – living?

• Not a cell!

• Viruses can’t: – eat, – excrete wastes, – move around on their

own,– reproduce (unless they

are inside another organism’s cells)


Viruses

• Viruses are the smallest type of disease causes micro-organism

• They reproduce by taking over cells of the body and making these cells produce new viruses.

Viruses do not produce toxins but cause disease by damaging the cells they enter


What diseases do these viruses cause?

– Rhinovirus attacks cells in nose and throat

– HIV attacks cells of immune system

– Herpes Simplex

Can you think of any other diseases caused by a virus


Protoctista - eukaryotes

• Can be single-celled to multi-celled

• They’re not plants, animals or fungi

• Protoctistas fall into four general subgroups: unicellular algae, protozoa, slime moulds, and water moulds


Protozoa

This are single celled animal-like creatures

Cause diseases such as:

Malaria – transmitted through mosquito bites


Contents



How do microbes reproduce?

Summary quiz

Microbes


A single bacterium

cell wall

loose genetic material

absent from animal cells

cell membrane

cytoplasm

present in animal cells

Bacteria can be different shapes but this diagram can represent them.


Structure of a bacteria

Cell Wall – multi-layered structure

- 2 distinct types- slimy capsule surrounds cell wall

Cell Membrane– bilayer with proteins

floating in it-controls what goes in and out of

bacteria

Cytoplasm-circular chromosome of DNA

- few organelles- food storage granules

Flagella-one or more projection

from cell wall-Allow the bacterium to move

in liquids


Bacterium

The other major difference is the size of the cell.

To get an idea of how small these cells are, remember that the human body consists of approximately 100 million animal cells.

Bacteria cells are 10-1000 times smaller than animal cells.

So, the bacterium shares some structural characteristics with an animal cell but shows important differences. The most obvious differences are:

the absence of a distinct nucleus the presence of a cell wall


Bacterium

If we wanted to measure a single bacterium, its length would range from:

1

1000

1

20

mm mmto

Between 1000 and 20 bacteria would fit on a full stop!

If a full stop is 1mm wide how many bacteria could you line up along it?


Virus

Now let’s consider the structure of the virus.

protein coatinjection

tube

loose genetic material

tail plate

Absent in animal cells


Viruses - how small?

Viruses are very different to bacteria because they do not have a cellular structure and are much smaller.

Bacteria are 100 times smaller than a human cell.

Viruses are 1000 times smaller than a bacteria.

So how small are viruses compared to a human cell?

100 000 times smaller!100 000 times smaller!


Viruses and tennis balls!

If a common cold virus was the size of a tennis ball, how big would a nose be?

Here’s another way to think about the size of viruses...

A. the size of a supermarket

B. the size of Birmingham

C. the size of Wales


Viruses – living or not?

Some scientists say that viruses are not ‘alive’ because of how they reproduce. Would you say a virus was living or not?

Viruses need to hijack a host cell, like a human body cell, in which to live and make more viruses.

Viruses cannot function if they are outside of a host cell.

If viruses are such tiny microbes, how do they cause so much havoc?


Virus and bacterium properties


Contents




Summary quiz

Microbes


Contents




Summary quiz

Microbes


Bacteria reproduction

Bacteria can reproduce quickly and independently .

One bacterium can divide into two new bacteria every 20 minutes!


Bacteria reproduction

This means that if 1 bacterium enters your body at 8.00am, 4 hours later, you would have 4096 bacteria within your body!

Do viruses reproduce in the same way as bacteria?

No!No!


Virus reproduction

This is a body cell, which will provide the machinery, and chemicals the virus requires to make copies of it.

virus

host celle.g. a human body cell

Viruses need a host cell to reproduce within.


Virus replicationVirus replicationVirus replicationVirus replication

Virus Replication


The process of host cell infection

Therefore the virus not only infects the body; it also infects the body cells.

1. Approach

The virus approaches the host cell

2. Attachment

The virus secures itself to the surface of the host cell.



3. Insertion

The virus injects its genetic material through the injection tube and into the host cell.

4. Replication

The genetic material makes multiple copies of itself.



5. Assembly

New viruses are assembled using chemicals from the host cell. The original virus dies and breaks down.

It is at this stage that the viruses within the host cell can remain dormant. In other words, they sit within the cell without killing it or breaking out. With some viruses such as HIV, this period can last a number of years.

This is why people can remain infected with HIV without realizing they are infected.


Virus reproduction

CELL LYSIS


Student task

• USE BIOVIEWERS AND OBSERVE SOME SLIDES.

• DRAW 2 BACTERIAL, VIRUS, PROTOZOA AND FUNGI CELLS AND WRITE ABOUT THEM USING THE BOOKLETS


Common illnesses

VIRUSES BACTERIA

Influenza (flu) Food poisoning

Mumps Sore throats

Chickenpox Tuberculosis (TB)

Smallpox Tetanus

Polio Cholera

Rabies Typhoid

German measles Whooping cough

So, how do these microscopic organisms actually cause illness in such a complex and relatively enormous organism like a human being?

Most people have suffered from at least one of these illnesses:


Virus reproduction - what’s the order?


Virus reproduction - explain it!


Microbes quiz

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© Boardworks Ltd 2004 1 of 39 Contents Describe what are microbes? Describe the structure of bacteria and viruses How do bacteria and viruses reproduce?