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Cell structure flashcards – A level biology OCR A module 2
Give 2 examples of stains which are Crystal violet
positively charged dyes. Methylene blue
Give 2 examples of stains which are Nigrosin
negatively charged dyes. Congo red
How is a dry mount prepared for A solid specimen (whole or thinly sliced) is
microscopy? placed on the centre of the slide, and a
cover slip is placed on top.
How is a wet mount prepared for The specimen is suspended in liquid and a
microscopy? cover slip is placed on at an angle.
What type of animal is generally viewed Aquatic animals.
using a wet mount?
Why are stains used in light microscopy? They increase contrast between organelles,
the cytoplasm, and the background.
Define what is meant by magnification. The degree to which something is or can be
magnified.
Define what is meant by resolution. The ability to see individual objects as
separate entities clearly.
What is the equation generally used to magnification = image size / object size
calculate magnification?
What is the equation generally used to 1 eyepiece division length = visible stage
calculate 1 eyepiece division length? micrometre length / number of equivalent
eyepiece divisions
What is the maximum magnification and Maximum magnification = x1500
resolution of a light microscope? Maximum resolution = 200nm
What are the advantages of using a light inexpensive
microscope? easy to operate
small and portable
no vacuum is required
has a simple sample preparation,
which does not usually lead to
distortion, and the natural colour of
the sample can be seen
can be used on living samples
, Cell structure flashcards – A level biology OCR A module 2
What are the disadvantages of using light Compared to an electron microscope it has:
microscopes? - low magnification
- poor resolution
How does a laser scanning confocal It moves a single spot of focused light
microscope work? across a specimen, causing fluorescence
from the components labelled with a dye.
The emitted light is then filtered through a
pinhole aperture.
can laser scanning confocal microscopes be Yes they can.
used on living samples?
what are the maximum magnifications and maximum magnification = 1000x
resolutions for a laser scanning confocal
microscope? maximum resolution = 0.8 micrometres
what are the maximum magnification and maximum magnification = x500000
resolution of electron microscopes?
maximum resolution = 0.1nm
How does an electron scanning microscope a beam of electrons is sent across
work? the surface of a specimen and the
reflected electrons are collected.
3D images are produced.
How does a transmissions electron a beam of electrons is transmitted
microscope work? through a specimen and focused to
produce an image
produces 2D cross sections
What are the positives and negatives of pros - produces detailed images
using electron microscopes?
cons - expensive, a vacuum is used so only
dead specimens can be examined
What is an artefact? A visible structural detail caused by
processing the specimen and appear in
both electron and light microscopy.
e.g., bubbles produced in preparing the
sample.
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