B2 - Foundations in biology Flashcards
1
Q
What is the cell theory?
A
- both plant/animal tissue is composed of cells
- cells are the basic unit of all life
- cells only develop from existing cells
2
Q
What are the two lenses of a compound light microscope?
A
- objective (near specimen)
- eyepiece (specimen viewed)
3
Q
How are samples prepared for light microscopy?
A
- dry mount:
- solid specimens are viewed whole/cut into very thin slices (sectioning)
- cover slip is placed over the sample
- wet mount:
- specimens are suspended in liquid (water/immersion oil)
- cover slip is placed at an angle to prevent any air bubbles
- ** living organisms can be viewed this way **
- squash slides:
- wet mount prepared first and lens tissue is used to press down cover slip
- can be used for soft samples (e.g. root tip squashes)
- smear slides:
- edge of slide is used to smear a sample
- creates a thin, even coating on another slide
- cover slip is placed on top (can be used for blood samples)
4
Q
What are the types of electron microscopes?
A
- transmission electron (TEM)
- scanning electron (SEM
5
Q
What is a TEM?
A
- beam of electrons is transmitted through the specimen
- resolving power = 0.5 nm
- (2D images)
6
Q
What is a SEM?
A
- beam of electrons is sent across the surface of the specimen
- the reflected electrons are collected
- resolving power = 3-10 nm
- (3D images)
7
Q
What are the differences between a light and electron microscope?
A
- l = cheap/easy to use
- e = expensive/difficult to use
- l = no sample distortion
- e = sample prep causes distortion
- l = no vacuum required
- e = vacuum required
- l = natural colour/staining
- e = b/w images
- l = x2000 mag
- e = x 500 000 mag
- l = 200 nm (resolving power)
- e = 0.5/3-10 nm (resolving power)
- l = living/dead specimen
- e = dead specimen
8
Q
What is laser confocal microscopy?
A
- single spot of focused light is moved across specimen
- causes fluorescence from components labelled with a dye
- emitted light is filtered through pinhole (only light from close to focal plane is detected)
- non-invasive and used to diagnose eye diseases
- produces 2D/3D images
9
Q
Why is staining used for light microscopy?
A
- increases the contrast of cells
- different cells take up stains to different degrees
- allows for the cell components to be more visible
10
Q
What are the types of stains?
A
- crystal violet/methylene blue:
- positively charged
- attracted to negatively charged materials in cytoplasm (cell components)
- nigrosin/Congo red:
- negatively charged
- repelled by the cytosol (stay outside the cells)
- stand out against the stained background
11
Q
What is differential staining?
A
- helps to distinguish between two types of organisms
- gram stain technique
- acid-fast technique
12
Q
What is the gram stain technique?
A
- separates bacteria into gram +ve and -ve
- crystal violet is added, then iodine (fixes dye)
- it is then washed with alcohol
- the gram +ve retains the stain (blue/purple)
- gram -ve have thinner cell walls so they lose the stain
- (then stained with safranin dye)
- gram +ve are more susceptible to penicillin (inhibits cell wall formation)
- gram -ve are not susceptible
13
Q
What is the acid-fast technique?
A
- used to differentiate species of Mycobacterium from other bacteria
- lipid solvent carries carbolfuchsin dye into cells
- cells are washed with dilute acid-alcohol solution
- Mycobacterium are able to retain the carbolfuchsin stain (bright red)
14
Q
What are the stages of producing pre-prepared slides?
A
- fixing
- sectioning
- staining
- mounting
15
Q
What is magnification?
A
- how many times larger the image is than the actual size of the object
16
Q
What is resolution?
A
- the ability to distinguish between two close points of an object
17
Q
How do you calculate magnification?
A
- size of image / actual size of object
18
Q
What is an eyepiece graticule?
A
- glass marked with fine scale from 1 to 100 (no units)
