Micro-organisms

CA 2005

Micro-organisms include…..

BacteriaFungi Viruses

Bacteria All bacteria are single-celled microbes. They all have the following parts:

CytoplasmA cell membrane

A cell wall

A single chromosome. (that is not inside a

nucleus)

They may also have:

A Flagellum (for movement)

A Slime Capsule (for protection against viruses)

Fungi

Fungi may be multicellular (the moulds)

Or unicellular (the yeasts)

Moulds

Moulds are made up of a network of

threads. Each thread is called a

Hypha.All the hyphae

together are called the Mycelium

The reproductive structure is the Sporangium. It holds the spores.

Mushrooms and toadstools are just the reproductive structures (sporangia) of a mould fungus. The main mycelium of hyphae

is hidden underground.

Each mushroom contains millions of tiny spores. Spores are like seeds except that the don’t have any internal food store. So they have to start growing as soon as they land.

Yeast

The Chromosomes are in a proper

Nucleus

Cytoplasm

Cell membrane

Cell wall

Viruses

Viruses are very simple structures.

They have no nucleus, cytoplasm, cell membrane, or cell wall!

They consist of just:

A protein coat

A few genes

Alive or not?

Bacteria and fungi perform all of the seven characteristics of life –

so they are living organisms.

Viruses do not perform any of the characteristics of life - so they

cannot be classed as living organisms.

Movement

Feeding

Respiration

Growth

Sensitivity

Excretion

Reproduction

Culturing Micro-organisms

Bacteria and Fungi can be grown on a petri dish containing agar jelly.

Agar jelly contain the nutrients required by the microbes to grow.

Adding the microbes to the agar is called inoculation.

It is critical to avoid contamination with the wrong microbes. After incubation at the

correct temperature the individual microbes have grown into colonies.

Life Processes of Micro-organisms.

1. Nutrition

Bacteria and fungi both secrete enzymes onto their food.

The enzymes digest (break down) the food into simpler particles which the microbe then absorbs into its cell or cells.

Because the digestion takes place outside the microbe itself it is called extracellular digestion.

Moulds secrete their enzymes from the tips of their hyphae. They then absorb the products and use them to provide the energy for the hyphae to grow onto the next

bit of food.

Respiration

Respiration is the release of energy from food.

It is a chemical reaction that takes place in all living cells.

Respiration that uses oxygen is called Aerobic respiration.

Respiration that doesn’t use oxygen is called Anaerobic respiration.

Bacteria and Fungi respire, viruses do not.

Aerobic Respiration

The formula is:

Glucose + oxygen carbon dioxide + water + Energy

Aerobic respiration is the most efficient way of getting energy out of food.

It doesn’t change much between animals, plants or microbes.

Microbes that live in the air are generally aerobic.

Anaerobic RespirationAnaerobic respiration doesn’t produce as much energy as

aerobic respiration and changes a lot between different organisms.

Bacteria.

One of the most famous bacteria that uses anaerobic respiration is the one that

produces yoghurt.

Glucose lactic acid + CO2

Many pathogens are anaerobes.

Yeast

Yeast can respire anaerobically.

Glucose alcohol + CO2

This is important in baking and brewing. It is commonly

called Fermentation

Brewing(Fermentation)

The yeast respires the sugar solution anaerobically,

producing alcohol and CO2

The CO2 bubbles up to

the top

The air-trap allows the CO2 to escape,

but prevents oxygen from

entering. (In other words, it keeps the

yeast respiring anaerobically.)

Eventually the alcohol produced will kill the yeast and the fermentation will stop. This happens at about 12% for wine yeast.

BakingTo bake bread the yeast is mixed with flour and sugar to make a dough.

The yeast respires the sugar and the CO2 given off makes the dough rise.

Any alcohol made inside the dough by anaerobic respiration evaporates off when the bread is baked.

Growth and Reproduction.

As they feed bacteria cells grow.

When they are fully grown the bacteria simply split in two to make two new bacteria.

This simple form of reproduction is called Binary Fission.

1. Bacteria

2. Yeast.

Like bacteria, yeast cells grow as they feed.

Unlike bacteria, they do not split in half though.

Instead they grow new yeast cells from their tips.

This is called Budding.

3. Moulds

As moulds grow their mycelium of hyphae spread over the food.

They send up vertical shoots called sporangia for reproduction.

Each sporangium is packed with thousands of tiny spores.

On larger moulds it is the sporangia that we pick and call mushrooms!

4. Virus ReplicationViruses do not grow or reproduce – they replicate.

That is, they take over other cells and force them to make new viruses. This is called the Lytic Cycle.

1. A virus attaches to a

host cell.

2. It injects its genes.

3. The genes force the host cell to make new viruses.

4. The host cell then bursts,

releasing the new viruses.

Excretion

• Bacteria and fungi produce waste products. This is called excretion.

• These waste products can be helpful or harmful.

Helpful waste products.

• yoghurt (bacteria)

•vinegar (bacteria)

• alcohol (yeast)

•antibiotics (moulds)

Harmful waste products

• food spoilage (i.e bad taste) – mostly from

bacteria.

• toxins from pathogens (bacteria).

Factors affecting microbes.

To grow their best microbes need:

• the correct temperature.

• moisture

• the correct pH

• the correct nutrients

• aerobic microbes also need a supply of oxygen.

Changing any of these will slow down or stop the microbes that cause decay.

Cold Temperatures

Cold temperatures (about 4oC) slow down the rate at which microbes grow and reproduce so food will last for several days.

Freezing food stops them reproducing, but it doesn’t completely stop their respiration – so toxins can still build up.

Cold Temperatures (b)

This baby mammoth and frozen person remained trapped in ice for thousands of years without decaying.

High TemperaturesCooking destroys microbes.

Food in cans remains edible for years as the

heat used in their manufacture kills all the microbes inside

Pasteurised milk has been heated to 60oC. This doesn’t change the taste of the milk, but it does kill most of the microbes in it.

MoistureMicrobes cannot move without water

Dried food and sugary food have both had all their moisture removed so they last a long time.

Moisture (b)

Without moisture organisms can be preserved for thousands of years.

PH

Pickling makes conditions too acid for microbes, particularly bacteria, to survive in.

Oxygen

Without oxygen, vacuum-packed food will last

indefinitely.

Coal was formed when trees fell into anaerobic peat marshes

Saprophytes.• A saprophyte is an organism that feeds on

dead material.

•All fungi and many bacteria are saprophytes.

• In nature they are critically important for recycling nutrients.

Microbes are essential at this stage – recycling dead and decaying material

The nitrogen cycle is complicated – but again, microbes play an essential role in the recycling stage of it.

Man uses these saprophytes for his own recycling….

The bacteria in a sewage works feed on the sewage and respire it, leaving just CO2 and water afterwards.

In the wrong place, however, these same

saprophytes can be a menace!

Pathogens

Pathogens are microbes that cause disease.

Viruses are always pathogens

As are many bacteria

Pathogens can cause damage in two ways:

1. By destroying your own cells.

2. By releasing poisons, called toxins, into your blood.

Remember: There are plant pathogens too:

In the late 1800s, potato blight caused over 1 million Irish to starve. Another 2 million were

forced to emigrate

Black spot is a pathogen of many crop and garden plants.

Preventing Infection by Microbes.

1. Keep infection away from uninfected people – if you’re ill, stay home!

2. Use good, basic hygiene – wash your hands before you prepare food, cover your mouth when sneezing or coughing etc.

3. Prevent cross-contamination – don’t keep cooked food and fresh food together in your fridge.

4. Disinfect surfaces before preparing food on them. (Disinfectants kill microbes.)

Antibiotics.Some moulds produce antibiotics – chemicals that destroy bacteria.

This mould is Penicillium, which produces penicillin.

In the picture the penicillin has destroyed the bacteria colonies near to the fungus.

Remember: Antibiotics only destroy bacteria. They don’t work on viruses.

Antibiotic Resistance.Originally antibiotics killed

99% of all bacteria!

The trouble is 1% survived because they were resistant to

the antibiotic used.

These resistant bacteria spread to take the place of those that the

antibiotic had killed.

As more and more bacteria are becoming resistant to antibiotics its becoming harder and harder to find new ones to kill them!