Bacteria and Viruses - Ambition, Respect, Care and...

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Bacteria and Viruses

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Comparing cell sizes

Most plant and animal cells are between 10µm and 100µm

in size – around the diameter of a human hair – and too

small to see without a microscope.

The largest cell in the human body

is the female egg cell, at around

100µm in diameter.

The smallest human cell is the

sperm cell – the head is around

5µm long.

Bacteria are single celled

organisms and are around 1µm in

diameter, even smaller than sperm.

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How big are micro-organisms?

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Microscopes

Due to advances in microscope technology, micro-organisms

can be magnified, allowing us to see them in greater detail.

size of image

actual size of the objectmagnification =

Now, with electron microscopes, scientists

can attain a magnification as high as 2×106. bacteria

When Antonie van Leeuwenhoek discovered

single-celled organisms in 1676, his microscope

could magnify an image up to 500 times.

Magnification is the measure of how many times bigger the

image is than the object being studied.

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Virtual microscope

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What are bacteria?

Bacteria can be classified according to their shape

under a microscope:

spherical spiral rod curved rod

Bacteria lack mitochondria and chloroplasts. As they also

have no distinct nucleus, their genetic material is contained

within a coiled cluster of chromosomal DNA and a single

circular strand of plasmid DNA.

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What do bacteria contain?

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How do bacteria feed?

A large number of different species of bacteria exist and

exploit a very wide range of habitats. Different species of

bacteria can survive on a range of energy sources:

Using photosynthesis to

produce their own food.

Consuming organic

compounds from the

environment, e.g. from dead

organisms, to obtain energy.

Using carbon dioxide and inorganic chemicals, such

as ammonia and nitrate, to produce their own food.

This method of obtaining food allows bacteria to survive

extreme conditions, such as boiling sulphur-rich water.

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Energy from decaying substances

Many species of bacteria can obtain energy from organic

compounds through the process of decomposition or decay.

A warm, moist, oxygen-rich environment is the most

favourable for decay to occur.

Which of the following might you

expect to decay at a faster rate:

cubes of bread that are

kept in a dry environment

cubes of bread that are

exposed to moisture?

The conditions in which bacteria reproduce and feed will

therefore affect the rate of food spoilage.

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Rates of decay experiment

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How bacteria reproduce

Bacteria can reproduce rapidly via asexual reproduction,

where a single bacterium makes a copy of itself with exactly

the same genetic code.

In particular, bacteria

use a special type of

asexual reproduction

called binary fission.

This involves

one bacteria

splitting in two.

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The growth rate of pathogens

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What do micro-organisms need to grow?

Bacteria can be grown in a liquid broth

or on solid agar. To reproduce at the

optimum growth rate, bacteria need to

be kept in ideal conditions, involving:

a continuous supply of food

the optimum pH

the removal of products

For example, when the pH or

temperature is above the optimum,

bacterial growth rates decline.

gro

wth

ra

te

pH or temperature

optimum

the optimum temperature.

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Culturing bacteria

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Virus fact file

Micro-organism: Virus (e.g. flu virus and HIV)

Size: They are smaller than bacteria

and fungi, between 10 nm and 100 nm.

Shape: Viruses have regular and

geometric shapes.

Structure: A virus is a simple

organism that does not display all

the characteristics of a living thing.

It is made up of a protein coating

and some genetic material.

Reproduction: Viruses can only grow

and reproduce within other living things.

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Structure of a virus

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A virus cannot read its own genes but it can make a host

cell copy them and make the proteins.

Using viruses

The virus on the right is a bacteriophage.

It infects bacteria by injecting its genetic

material down a special tube.

protein

coat

genetic

material

injection tube

Viruses can also attack some plant

cells and some animal cells.

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Human immunodeficiency virus (HIV)

HIV is a virus that causes acquired immunodeficiency

syndrome (AIDS) – a deterioration of the immune system.

In 2007, 33.2 million

people were estimated

to be living with HIV.

There is currently no

cure; however, antiviral

drugs have been

developed to help delay

the onset of AIDS.

The process of how the HIV infects a cell and reproduces

within the living cell is typical of a virus.

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How do viruses replicate?

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Glossary

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Multiple-choice quiz