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Microbes

KS4 Biology


Microbes

Contents

What are microbes?

Bacteria and viruses

How do microbes reproduce?

Microbes and disease

Summary quiz


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!


Microbes

Bacteria have a traditional cell structure, as with animals and plants. Viruses do not. Let us firstly consider what these microbes look like and how they compare to the structure of cells that we are familiar with.

We will firstly deal with the general structure of a bacterium (singular of bacteria).

Bacteria are amongst the smallest known to mankind.


Contents

What are microbes?




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.


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?


Bacterium – label the parts


Virus – label the parts


Virus and bacterium properties


Contents

What are microbes?




Summary quiz

Microbes


Viruses and bacteria

You probably know more about bacteria and viruses than you think.

The following illnesses are all caused by microbes infecting the human body. How many do you recognise?


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:


TOXINS

Firstly, as soon as a virus or bacterium enters the body, we are termed infectedinfected.

Illness results from the effects these microbes have on our body.

Bacteria and viruses have the ability to produce poisons known as...

This is not the same as being ill.

Under attack!


When the microbe enters the body, it begins releasing these toxins which can damage body tissue and prevent body systems working properly.

The body could probably cope with a small amount of poison, but microbes quickly reproduce themselves.

If the microbes reproduce…

our normal state of well being is affected…

Under attack!

more microbes mean that more toxin produced…

We are said to be diseased.


1Person is well. The microbe levels are very low and the toxin levels are very low.

Toxin Levels

Presence of microbes

3Person is ill and diseased. The microbe levels are high and the toxin levels are high.

2Person is infected. The microbe levels are low and the toxin levels are low.

Diagram of a microbe attack

These symbols and colours represent the process of becoming infected and then ill:


Which microbe causes which disease?


The process of disease


Contents

What are microbes?




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.


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.



6. Cell Lysis (cell breaks)

The host cell splits open and dies. The viruses escape and release toxins. Each virus will then start another round of replication.

- toxin


Virus reproduction - what’s the order?


Virus reproduction - explain it!


Contents

What are microbes?




Summary quiz

Microbes


Microbes quiz

Download - Ks4 microbes

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