1. Bacteria, Viruses and Fungi
Microorganisms
Bacteria, Viruses and Fungi

2. Bacteria Structure The structure of a typical bacterium is shown here.
Capsule
Flagellae
Cell wall
Cell membrane
Cytoplasm
Nuclear material (DNA)

3. Bacteria reproduce by binary fission, which means that they split in two and their offspring all have identical genes.

4. Reproduction A single bacterium just before
The DNA replicates and divides
Cell membrane pinches together
Two bacteria are formed

5. Reproduction In ideal conditions they can reproduce every 20 minutes.
This rapid increase in numbers is called exponential growth.
Bacteria will not increase forever as eventually a lack of food or space or the build up of toxins in the form of waste products will cause the numbers to level off and then decrease.

6. Growth of bacteria with time.
1.0
Number of bacteria (millions)
0.5
100
200
300
400
Time since infection (minutes)

7. Modes of life
Most bacteria are consumers – they do not make their own food.
Parasitic bacteria feed off living material while saprophytic bacteria live on dead matter.
Bacteria feed by producing enzymes, which pass through the cell membrane and break food down outside the cell membrane.
The broken down food then enters the bacteria through the cell membrane.
This is called extra cellular digestion – means out of the cell digestion.

8. Bacteria and food particle
Enzymes secreted outside
Food enters the bacteria
Enzymes digest food particle

9. Viruses How do you kill something that is not alive?
They are non-cellular.
Lack the complex structures found in cells.
Show only some of the characteristics of living things.
What are these?
Mrs Gren
A philosophical problem follows
How do you kill something that is not alive?

10. What are viruses?
Viruses are much smaller than bacteria. They do not feed or move and can only reproduce by taking over living cells.
Viruses are not cells, nor are they alive.
A virus consists of a string of genes coiled up inside a protein coat. This can form different shapes and there are thousands of different viruses.
Viruses are very efficient at reproduction.

11. Virus structure Genetic material Protein coat
Remember – they can take on any shape – an example only!!

12. Virus reproduction
When a virus lands on the surface of a cell, it inserts its genes into the host cell.
The virus takes over the cell and makes it assemble thousands of copies of the virus in a process called replication.
The cell then bursts, releasing the new viruses, which spread to other cells or organisms.
The genes of viruses readily mutate, which is why new strains of viruses regularly emerge – SARS good example of this.

13. 2. Genetic material from the virus
enters the host cell.
1. Virus attaches to host cell
3. Contents of the host cell is used to make viral genetic material and protein coats.
4. Host cell bursts and new viruses are released. Old cell dies and viruses are free to attach to new cells.

14. Harmful viruses
All viruses are pathogens and they cause many human ailments from colds, flu, polio, hepatitis and AIDS.
They are NOT affected by antibiotics and few, if any drugs are successful against viral infections.
They also infect plants, damaging crops.
Viruses cannot be cultured on an agar plate and are usually cultured inside living cells, like fertilised hens eggs.

15. Fungi (yeasts, moulds, mushrooms...)
Fungi include unicellular yeasts as well as multi-cellular moulds , mushrooms and toadstools.
Fungi are immobile but, unlike plants, they cannot make their own food. They are saprophytes. They live of dead organisms or their products.
Multicellular fungi are made up of a mass of fine threads called hyphae, which invade the tissue of the host organism or dead matter.

16. Fungi Structure
Sporangium
Spores
Hyphae
Food

17. Feeding
Fungi feed like bacteria by releasing digestive enzymes onto food – extra cellular digestion.
Hyphae expand into food
Enzymes are secreted into the food
and it is digested on the spot.
Nutrients are absorbed into the
hyphae

18. Reproduction
Fungi are spread by microscopic cells called spores that have tough walls.
Special spore capsules or cases called sporangia develop and produce the spores. Millions of spores are released to float in the air.
When the spores settle on dead or living tissue, they germinate, sending out hyphae that rapidly branch and invade the new host.
When spores are produced by a single parent, this is a form of asexual reproduction giving genetically identical offspring. Fungi can also reproduce sexually which produces variation amongst the offspring.

19. Spores land on food
Hyphae grow
Sporangia grow, mature and
make spores which disperse.

20. Ever eaten a ripe sporangium?
Tasty with butter and garlic or
just plain!!