Viruses are very small pathogens that can only reproduce inside host cells. They have either DNA or RNA surrounded by a protein coat. Viruses cause many common diseases but cannot be treated with antibiotics since they are not technically living things. Bacteria are single-celled organisms that have cell membranes and walls but no nucleus. While some bacteria are helpful, others can cause diseases and are treated with antibiotics. Fungi form their own kingdom and come in both single and multi-celled forms. They feed by secreting enzymes and absorbing nutrients and act as decomposers by breaking down dead material.

1. Microorganisms
extended

2. Viruses
 Viruses are very, very small; they are only
seen with an electron microscope
These are
viruses like the
ones that
cause
influenza

3. This is a type of virus
that attacks bacterial
cells; it is called a
Bacteriophage.
Don’t be fooled by the
complex structure –
viruses are only made
of protein coat and of
genetic material

4. Genetic
material
Protein coat
with surface
proteins
This is a drawing of
a Virus
Note the simple
structure – its really
easy to draw
They are NOT cells
Make sure you have this diagram in
your notes

5. Viruses are not living organisms
They do not move, respire, respond to
stimuli, grow, excrete or feed!
They can only reproduce by taking
over a host cell
So all viruses are pathogens; they
cause disease
We cannot kill viruses with antibiotics
because they are not living cells

6. Viral Diseases:
 HIV causes AIDS
 Colds and Influenza are viral
 Measles, chicken pox and mumps
are all caused by viruses

7. Bacteria
Bacteria belong
to their own
Kingdom
They may be very
small, about the
size of a
mitochondrion,
but there are
millions of different
types of bacteria

8. Structure of a bacterial cell
Non-cellulose cell wall
Cell membrane
Flagellum (in some)
Plasmid (genetic material)
Loop of DNA
Slime capsule
(in some) Draw this in your notes

9.  Note that bacteria do not have a nucleus, the
DNA strand lies free in the cytoplasm
 Bacteria reproduce by dividing. This is called
asexual reproductions. It happens quickly.
 One cell becomes two, then four and so on…

10. Some bacteria are useful:
 Gut bacteria help digestion
 Some bacteria in the soil convert nitrogen gas to
nitrates. This makes soil more fertile.
 Bacteria cause decay to recycle nutrients
 We use bacteria to make food like yoghurt and
cheese – we will learn more about this later in the
term
This is Lactobacillus
It is used to make
yoghurt

11. Some bacteria are harmful:
 They are parasitic and cause diseases
when they invade a host
 Cholera, Tuberculosis and Salmonella are
caused by bacteria
 We can treat these with antibiotic drugs
This is Vibrio cholerae
It causes Cholera
when it is ingested with
contaminated water
or food

12. Fungi
 Fungi belong to their own Kingdom
 They are not plants or animals
 They have a cell walls made of Chitin
 They may be unicellular or multicellular

13.  They feed saprotrophically
 This means they secrete enzymes over the
food on which they grow to digest the
food
 Digested particles are they absorbed
 Fungi are decomposers; they feed on
dead organic matter and bring about
decay

14. If you look at bread mould, Rhizopus
nigricans, with a hand lens it looks like this:

15. Long threads called hyphae grow over
the bread
They form a carpet called a mycelium
Sporangia grow at the
top of vertical hyphae
These release spores
that will be carried in
the air to a new food
source

16. Yeast is a unicellular
fungus
Yeast cells can
reproduce asexually
to form a colony
Yeast is used to make
bread and alcoholic
beverages – we will
study this later in the
year

17.  Remember that
mushrooms and
toadstools are also fungi
 They are actually made
of compact hyphae
 The sporangia are on the
underside of the
umbrella-like part. These
release spores.