Bacteria, Fungi and Viruses
They have the usual
a prokaryote and a
eukaryote, Draw a
table highlighting the
Mode of nutrition
Diplo – pairs of cells
Staphylo – clusters of cells
Strepto – chains of cells
The gram stain reaction further divides bacteria into
+ve or –ve types, this is due to the cell wall structure
of that particular bacteria.
Those that are stained purple are Gram +ve and
those that are pink are Gram –ve.
The cell wall of a bacteria is made from a chemical
sometimes called murein or peptidoglycan. This is a
carbohydrate based substance.
Cell Wall Structure
Gram stain Procedure
• Make a smear of bacteria on slide and heat fix it.
• Stain with crystal violet stain for 30 seconds.
• Rinse with lugols iodine for 30 s.
• Rinse with distilled water.
• Flood with alcohol/acetone for 10 s, wash with water.
• Flood slide with (Counterstain) safrannin for 1 minute.
• Dry and add cover slip, observe under the microscope.
The peptidoglycans that make up the majority of the
gram+ve cell wall forms purple complexes with iodine
that remain lodged in this layer even after washing
Gram-ve bacteria have a relatively impermeable
outer membrane. So it is difficult for the purple dye to
complex (bond) with the peptidoglycan and iodine
and so is washed off by the alcohol. The counterstain
(pink) just makes them more visible.
Most widely distributed organism on the earth, ice caps
to hot springs
Some are photosynthetic
Majority are 0.5-1.0 mm wide and 1-5mm long
Many are harmless, some useful, some killers
Can double in numbers every 20 minutes
Many can live in the presence or absence of oxygen
Some can live on very strange food sources, e.g. waste
paper processing material to using the sulphur in coal to
Carbon source Most bacteria will
have specific growth
Nitrogen source (amino can be added to the
acids or nitrate/ammonium culture medium (an
agar plate) to make
Growth factors (vitamins)
Bacterial Survival Needs – source of food, a way to break it
down (respiration) to release energy, etc.
Autotrophs (some use photosynthesis, others in deep oceans
use chemical ways)
Heterotrophs (some make yogurt, cheese, apple cider)
Decomposers = (“recyclers”) that live in soil and break down
chemicals in dead animals and plants.
Endospore = a thick, rounded, thick-walled, resting cell
formed inside a bacterial cell.
* Some bacteria form this when the environment is to
harsh for growth. (Anthrax is an example.)
* Endospores can resist freezing, heating, and drying.
These are plates with different bacteria
Obligate aerobes- need free molecular oxygen for metabolism
and growth, e.g. oxygen gas.
Obligate anaerobes- need oxygen free environments and are
killed by oxygen gas. (The reason for this sensitivity is that in the
presence of oxygen bacteria produce hydrogen peroxide, which
is harmful. This group lacks the enzyme to break it down, so are
killed by oxygen’s presence. The other two types of bacteria do
have the enzyme.)
Facultative anaerobes- can grow and survive in aerobic
conditions, but can switch to anaerobic if oxygen supply is in
Asexual reproduction is called Binary Fission, the cell
basically splits in two
This results in genetically identical cells
This is often preferred when a bacterium needs to
colonise an area quickly.
Or because it has an adaptation to that particular
environment and so sexual reproduction may involve
the production of offspring that does not contain
similar genes to the parent, which would mean death.
If the growth of a
is measured at
of time and the
data plotted, a
Sigmoid or S-
shaped curve is
This is where the bacteria are becoming accustomed to the new
There is little increase in cell numbers
This time may be used to synthesise cell organelles such as
This can last different periods of time depending upon viability of
This is the stage of maximal growth, during which the population doubles.
At this point all variables are at their optimal conditions and so grows
Eventually food starts to run out and overcrowding and toxic waste
products build up so growth curve gradient starts to slow, but more cells
still produced than were dying
The population does not increase, the number dying is exactly balanced by
those being produced.
Substrates will be used up and toxic by products may accumulate and so
to conserve energy they stop multiplying, some may even start to form
The accumulation of toxic waste increases and the lack of oxygen or other
nutrients makes life unfavourable, cells start to lyse or break down.