Topic 2.2 - biology4friends

IB Biology
2 Cells
2.2 Prokaryotic cells
All syllabus statements ©IBO 2007
All images CC or public domain or link to original material.
Jason de Nys
2.2.1 Draw and label a diagram of the ultrastructure of Escherichia coli (E. coli) as an example of
a prokaryote.
A typical Bacterial cell, very
much like an individual E. coli
2.2.2 Annotate the diagram with the functions of each of the named structures.
The Flagellum (plural: flagella) consists of a molecular motor
embedded in the cell membrane and a long spiralling filament
that rotates. It propels the bacterium through it’s environment.
Flagella can move bacteria at up to
60 body lengths/second
By comparison, the fastest land
animal, the cheetah, manages only
25 body lengths/second. So slow!
I can still
bite your
face off!
The Capsule helps the bacteria by:
• Being fragile and slippery so that the bacterium is
harder to engulf by predators (prevents phagocytosis)
• Holding water and preventing desiccation
• Preventing infection by viruses
• Helping the bacteria to stick to surfaces and each other
When bacteria stick together they can
form biofilms such as plaque on teeth.
This cat on the right has plaque on the
tooth marked P3
The nucleoid is an irregularlyshaped region within the cell of
a prokaryote that contains all or
most of the genetic material.
Unlike the nucleus of a eukaryotic
cell, it is not surrounded by
a nuclear membrane.
The genome of prokaryotic
organisms generally is a circular,
double-stranded piece of DNA, of
which multiple copies may exist at
any time. (Wikipedia)
A Plasmid is a DNA molecule that is separate from, and can replicate
independently of, the chromosomal DNA in the nucleoid region.
They are double-stranded and, in many cases, circular.
Bacteria regularly exchange
plasmids through a process
called conjugation.
A pilus from one bacterium
attaches to another
bacterium and forms a
hollow tube that the plasmid
moves through.
Pili also have a rôle in
attaching bacteria to each
other and other surfaces and
in preventing phagocytosis
The Cell Membrane regulates the
passage of materials in and out of
the cell
The Cell Wall stops the cell from
bursting due to turgor pressure
caused by high concentrations of
solutes, proteins etc inside the cell
compared to outside
The 70S is the cellular machinery that synthesises proteins using
an mRNA template
(More about that in 3.5.4)
They are free-floating in the cytoplasm
So after absorbing all of that information, all you have to do
is put it in the diagram!
Annotate: to add brief
notes to a diagram or
2.2.3 Identify structures from 2.2.1 in electron micrographs of E. coli.
Hmmm… not much to
see here, just a bunch
of E. coli grown in
culture and stuck on
a cover slip
A bunch of E. coli from
the gut of a pig.
The strand-like things
might be flagella?
E. coli hiding out inside
a stoma on a lettuce
leaf. A quick wash isn’t
going to move those
More E. coli
Why have they been
different colours on
each slide?
The colours are
artificially added to aid
Here you can see pili
and flagellae
You may be able to
see a darker region;
the nucleolus
The cytoplasm
might also look
granular, due to all
of the ribosomes in
2.2.4 State that prokaryotic cells divide by binary fission.
Binary fission, also known as
Prokaryotic fission, is a form
of asexual reproduction
and cell division used by
all prokaryotes
(and by some organelles in eukaryotes)
↓ Just watch the first bit
Further information:
The presenter above uses Prezi (ooooh!)
Both she and the man below have used a diagram from
Wikimedia commons. It is acknowledged below, but not above.
Tsk tsk!