What is a photomicrograph?
A photo taken through a microscope
Define magnification
The number of times greater an image is than the actual size of the object being observed.
Define resolution
The ability to distinguish between two structures/ points in an observable object.
- Refers to the clarity of the image
What are stains?
- coloured chemicals which bind to molecules on the specimen
- creates contrast
Why do we stain specimens before viewing?
- Many biological structures are colourless
- makes structures stand out so we can see them
What is differential staining?
- Using multiple stains to help distinguish between two ‘hard to identify’ organisms
Name 4 stains and what they bind to
Eosin= Stains cytoplasm pink or red
Acetic orcein= Binds to DNA, stains chromosomes red
Iodine in solution= stains cellulose yellow, starch grains appear blue/black
Sudan red= Stains lipids red
How are permanently fixed slides made in light microscopy?
- You fix the sample, preserve using chemicals
- Dehydrate them to remove water
- Embed in a block of wax or resin to slice without distortion
- Use a microtone (very sharp blade) to cut thin sections so light can pass through the sample.
- Stain the slide.
What are artefacts?
Visible details that aren’t part of the specimen, created during preparation of specimen. Can lead to misleading conclusions.
State the formula for magnification
M= Image size/ Object size
How do u convert mm —> um
x1000
Describe microfilaments
- Made of actin which is a contractile protein
- 7nm
- Responsible for cell movement and contraction
- Cytokenisis
Describe Microtubules
- Made from globular tubulin proteins
- 25nm
- polymerise to form tubes that determines the shape of a cell
- tracks of movement for organelles
- transports materials in cytoplasm
Describe intermediate fibres
- made from fibrous proteins
- 10nm
- provide mechanical strength, helps maintain the integrity of cell
- act as guide wires
What is the gram stain technique?
- Crystal violet dye is applied, then iodine to fix the slide
- Slide is washed with alcohol
- Gram pos= retain crystal violet stain
Gram neg= has thinner cell walls so it loses the stain - Stained with safranin dye which acts as a counterstain, bacteria will appear red.
Describe gram positive and gram negative bacteria
Positive
- susceptible to penicillin which inhibits formation of cell walls
Negative
- thinner cell walls not susceptible to penicillin
What is the acid fast technique?
Used to differentiate between species of mycobacterium from other bacteria
- lipid solvent is used to carry carbolfuschin dye into the cells being investigated.
- Cells are washed with a dilute acid-alcohol solution
- Mycobacterium are not affected by the acid alcohol solution and retains the carbolfuschin dye which is bright red.
- The other bacteria is exposed to methylene blue stain
What is diffraction?
The tendency for light waves to spread as they near to different physical structures in an organism
- depends on the wavelength of the light
How is resolution limited by diffraction?
- Structures in specimens are close together so the light reflected can overlap due to diffraction
- Causes structures to be no longer visible as separate entities, detail is lost
What is the resolution of a TEM and an SEM
TEM= 0.5nm
SEM= 3-10nm
What is the magnification of a TEM and an SEM?
TEM= 1,000,000
SEM= 1,000,000
Describe the image produced by a SEM
- 3D surface image
- Shows the surface texture of specimens
- black and white
- vacuum needed
- specimens can be thick or thin, dead
Describe the image produced by a TEM
- 2D surface image
- Intracellular structures visible
- black and white
- vacuum needed
- specimen must be dead and thin
Name disadvantages of electron microscopes
- Expensive
- vacuum required
- may require additional training
- complex and large to install
- images in black and white
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Biological membranes33
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Communicable diseases65
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Biological molecules54
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Nucleic acids33
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Enzymes32
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Exchange surfaces32
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Cell structure30
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Cell organelles22
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Cell division40
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Transport in animals57
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Transport in plants49
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Classification and evolution51
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Biodiversity57
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Homeostasis69
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Ecosystems31
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Plant hormones27
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Hormones67
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Photosynthesis33
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Nerves44
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Nerves- the brain regions6
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Respiration34
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Inheritance38
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Manipulating genomes23
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Cellular control33
