2.1 - Basic Components of Living Systems Flashcards
Define magnification
How many times larger an image is than the actual size of the object
Define resolution
The closest distance between two points where they are both still clear and distinguishable
How does a compound light microscope work?
Has 2 lenses:
• objective lens - placed near specimen
• eyepiece lens - through which specimen is viewed
Both magnify the specimen
Double lens configuration allows for much higher magnification and reduced chromatic aberration
Illumination usually provided by light underneath samples, but some microscopes allow form opaque objects to be illuminated from above
What are the different types of sample preparation?
- dry mount
- wet mount
- squash slides
- smear slides
What is a dry mount?
Solid specimens are viewed whole or cut into very thin slices with a sharp blade (called SECTIONING)
Specimen is placed on the centre off the slide and a cover slip is placed over the sample
Eg hair, pollen, dust, insect parts can be viewed whole
Muscle tissue or plants can be sectioned and viewed this way
What is a wet mount?
Specimens are suspended in liquid eg water, immersion oil
A cover slip is placed on from an angle
Eg aquatic samples and other living organisms cam be viewed this way
What are squash slides?
A wet mount is first prepared, then a lens tissue is used to press down the cover slip
Potential damage to the cover slip can be avoided by squashing the sample between 2 microscope slides
Care needs to be taken so that the cover slip doesn’t break when being pressed
Eg root tip squashes are used to look at cell division
What are smear slides?
The edge of a slide is used to smear the sample, creating a thin, even coating on another slide.
A cover slip is then placed over the sample
Eg smearing blood on a slide to look at cells in the blood
Why do we use stains?
The cytoskeleton and other cell structures are often transparent
Stains increase contrast as different components within a cell take up stains to different degrees
The increase in contrast allows components to become visible so they can be identified
What are crystal violet and methylene blue?
Positively charged dyes
Attracted to negatively charged materials in the cytoplasm, leading to the staining of cell components
What are nigrosin and Congo red?
Negatively charged dyes
Repelled by negatively charged cytosol
These dyes stay outside cells , leaving fresh cells unstained, which then stand out against the stained background
This is a negative stain technique
What is differential staining?
Using specific stains to distinguish between different types of cells or between different organelles of a single organism
What is the gram-staining technique?
Used to differentiate bacteria into Gram-positive and Gram-negative bacteria.
Gram-positive bacteria take up a crystal violet stain and look blue/purple
Gram-negative bacteria don’t retain crystal violet stain and are then counter stained with safranin dye, turning it red
What processes may be involved in the production of pre-prepared slides?
- fixing - chemicals like formaldehyde are used to preserve specimens in as near-natural state as possible
- sectioning - specimens are dehydrated with alcohols to form a hard block and then placed in a mould with wax or resin to form a hard block, which can then be sliced thinly with a microtome
- staining - specimens are often treated with multiple stains to show different structures
- mounting - specimens are secured to a microscope slide and a cover slip placed on top
What are the features of a proper biological drawing?
- title
- state magnification
- use sharp pencil for drawing and labels
- use white, unlined paper
- use as much paper as possible for drawing
- draw smooth, continuous lines
- no shading
- draw clearly defined structures
- ensure proportions are correct
- label lines shouldn’t cross and shouldn’t have arrowheads
- label lines should be parallel to the top of he page and drawn with a ruler
What’s the equation for magnification?
M = I/A
M = magnification I = size of image A = actual size
What is an eyepiece graticule?
A glass disc marked with a scale 1-100
Doesn’t have units
Found on the objective lens of a microscope
What is a stage micrometer?
A microscope with a very accurate scale in micrometers (um) engraved on it
The scale marked is usually 100 divisions = 1mm, so 1 division = 10 um
It is used to calibrate the eyepiece graticule for each magnification separately
What is a transmission electron microscope (TEM)?
- a beam of electrons is transmitted through a specimen and focused to produce an image (similar to light microscopy)
- produces a 2D image
• resolution = 0.5nm
magnification = x 500,000
What is a scanning electron microscope (SEM)?
- a beam of electrons is sent across the surface of the specimen, and reflected electrons are detected
- produces a 3D image
•resolution = 3-10nm
magnification = x100,000
What is an artefact?
An object or structure seen through the microscope that have been created during the processing of a specimen (eg an air bubble)
Features of light microscopy
- inexpensive to buy and operate
- small and portable
- simple sample preparation
- sample preparation doesn’t usually lead to distortion
- natural colour of sample can be seen
- vacuum not required
- specimen can be alive or dead
- resolution = 200nm
- magnification = up to x2000
Features of electron microscopy
- expensive to buy and operate
- large and not portable (must be installed)
- complex sample preparation
- sample preparation can lead to distortion/artefacts
- black and white images produced (but can be coloured digitally)
- vacuum required
- specimen must be dead
- resolution = 0.5 nm (TEM) or 3-10nm (SEM)
- magnification = over x500 000
What are laser scanning confocal microscopes?
- moves a single spot of focused light across a specimen (point illumination)
- this causes fluorescence from the components labelled with a ‘dye’
- the emitted light from the specimen is filtered through a pinhole aperture
- only light radiated form very close to the focal plane (the distance that gives the sharpest image) is detected
