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Basic components
of living systems
Module 2
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Diffraction of light limits the resolution
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Measure the length of the scale bar
2
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Divide the length (image size) by the representational
length (actual size) to find the magnification
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Measure the length of the structure you want to find the actual length of and
divide this by the magnification to find the actual length
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Illumination is provided by a light underneath
the sample
Positives
Negatives
•The objective/eyepiece lens
•Structures closer
configuration allows for a higher
together than 200nm will
magnification than in a simple light
appear as one objectmicroscope
Ribosomes are too small to
•cheap & easy to use
see
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Stains increase contrast as different components within a cell take up
stains to different degrees
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This is then heat fixed by passing through a flame
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 Positively charged dyes are attracted to negatively charged materials in the
cytoplasm e
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eosin
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These
dyes stay outside the cells, leaving the cells unstained, which then stand out
against the stained background
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 Gram stain technique- used to separate bacteria in 2 groups – gram-positive &
gram-negative
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The slide is then washed with alcohol
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Gram-negative bacteria have
thinner cell walls, so lose the stain
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 Acid-fast technique- used to differentiate species of mycobacterium from
other bacteria
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the
cells are then washed with a dilute alcohol solution
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Sample preparation for light microscopy

Dry mount- solid specimens are viewed whole e
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hair or
sectioned (dehydrated with alcohols & sliced thinly with a knife
called a microtome) e
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Muscle tissue
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Wet mount- specimens are suspended in a liquid such as water
or immersion oil e
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aquatic samples
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Squash slides- a wet mount is first prepared, then a lens tissue
is used to gently press down the cover slip
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E
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blood
The samples may be fixed with chemicals like formaldehyde to
preserve specimens in as near-natural state as possible
An artefact is a visible structure caused by processing the
specimen & not a feature of the specimen
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g
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Laser scanning confocal microscope
A single spot of focused light is moved across a specimen (point illumination)
The specimen has been treated with a fluorescent ‘dye’ & the components
labelled with the ‘dye’ causes fluorescence (absorption & re-radiation of
light)
The emitted light from the specimen is filtered through a pinhole aperture
...

Light emitted from other part of the specimen would reduce the resolution ,
so this unwanted radiation doesn't pass through the pinhole & isn’t detected
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•Have depth selectivity & can focus on structures at
different depths within a specimen so can observe whole
living specimens Used in medicine to give swift diagnosis
•3D images can be produced by creating images at
different focal planes
•Non-invasive- used in diagnosis of disease of the eye
•Needs training to use

Electron microscopy

Electron microscopes have a magnification of over x500000, producing
black & white images (colour can be added electronically
Transmission electron microscope- a beam of electrons is transmitted
through a specimen & focused to produce an image
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5nm
Scanning electron microscope- a beam of electrons is sent across the
surface of a specimen & the reflected electrons are collected
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This means 3D
images can be produced
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Measuring objects seen with a light microscope
To work out the size of an object viewed with a microscope, a
graticule is used
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As the same sample may look to be different
sizes under different magnifications, the graticule must be
calibrated:
1
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g
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Place stage graticule onto stage & align stage & eyepiece
graticule at lowest magnification (x40)
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Used measured length to calculate the value of each eyepiece
division e
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if 24 subdivisions of stage graticule calibrate with
the eyepiece graticule then the eyepiece graticule is 2400µm
(100µmx24) so 1 division of the eyepiece graticule must be
24µm
4
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Eukaryotic cells

Ultrastructure eukaryotic cells

• Nucleus- Contains coded genetic information in the form of DNA
molecules
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DNA associates with histone proteins
to form chromatin
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• Nucleolus- dense non-membrane bound structure found in the nucleus,
composed of proteins & RNA
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• Nuclear Envelope- double membrane which protects the DNA from
damage in the cytoplasm
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(DNA is too large to exit)
• Mitochondria- double membrane bound organelles with a fluid filled
matrix
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Mitochondria are the site of the
final stages of cellular respiration They are self replicating & can produce
their own enzymes as they contain a small amount of mitochondrial DNA
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In
order to look at cells under a microscope a thin slice needs to be cut & so
the mitochondria may be seen in different shapes depending on how it was
sliced (long ways, across or obliquely)

• Cytoskeleton- networks of protein fibres that hold organelles in place,
necessary for shape, stability & movement of organelles
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• Microfilament- contractile fibres formed from the protein actin
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They also form the track
along which motor proteins walk and drag organelles from one part of
the cell to another
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• Intermediate fibres- fibres which give mechanical strength to cells &
help maintain their integrity
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They are
made of nine triplets of microtubules, arranged in a cylinder
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Before a cell
divides, the spindle, made of microtubules, forms from the centriole
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Microtubules sprout outwards from each centriole forming a cilium or
undulipodium
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Each cilia contains 2 central microtubules
surrounded by 9 pairs of microtubules (9+ 2 arrangement)
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• Ribosomes- non-membrane bound organelles constructed in the nucleolus,
they’re the site of protein synthesis
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Ribosomes that are free in the cytoplasm are primarily the site of
assembly proteins that will be used inside the cell
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Rough endoplasmic reticulum- has ribosomes bound to the surface (large
SA for ribosomes) & is responsible for the synthesis & transport of
proteins
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Contains enzymes
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Modifies (e
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adding sugar) & packages proteins
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Consist
of a single membrane with fluid inside
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They engulf old cell organelles &
foreign matter, digest them & return digested components to the cell to
reuse
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• Peroxisome- contain digestive enzymes
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(requires
lots of oxygen)

• Chloroplasts- large organelles which are the site of photosynthesis
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The inner membrane is
continuous stacks of flattened membrane sacs called thylakoids which
contain chlorophyll
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The fluid filled matrix is called the stroma
here hydrogen reduces CO2 using energy from ATP to make
carbohydrates
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The internal membranes provide a large SA needed for the enzymes,
proteins & pigment molecules
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The cell wall is strong & can prevent
plant cells from bursting when turgid
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Fungi have cell walls that contain chitin not cellulose
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The large permanent vacuole is
important in the maintenance of turgor, so that the contents of the cell
push against the cell wall & maintain a rigid framework for the cell
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• Amyloplast- organelles found in some plant cells responsible for the
storage of starch granules through the polymerisation of glucose
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The instructions to create a particular protein are found in a gene in the DNA of
a cell
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This is called transcription
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2
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There the sequence of amino acids are read & the
instructions are translated to assemble a protein
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The protein molecules are then ‘pinched off’ from the RER in vesicles & travel to
the Golgi apparatus
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Vesicles then fuse with the Golgi apparatus which modifies, processes & packages
the protein molecules ready for release
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Packaged protein molecules are ‘pinched off’ in vesicles from the Golgi apparatus
& move towards the plasma membrane
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Vesicles then fuse with the plasma membrane which opens to release protein
molecules outside
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Some vesicles
form lysosomes
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Prokaryotic cells

- ATP production takes place here
- area within the cytoplasm where DNA is sited
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• Small loops of DNA called
long whip like projections that enable them to
move
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Energy to
rotate the filament that forms the flagellum is supplied
by chemiosmosis
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• Pili- smaller hair like projections that enable the
bacteria to adhere to each other or host cells & allow
the passage of plasmid DNA from one cell to another
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(circular DNA)
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Reproduces by asexual or sexual reproduction Reproduces by binary fission

viruses
Living?

Not living?

They have genetic materialeither DNA or RNA (not
both)

They do not have a cell
structure- they have no
cytoplasm, membranes o
organelles
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They can only reproduce when
inside a living host cell



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