microscopy 2.1/2/3

How does a light microscope work

a light microscope is compounded as it has 2 lens: objective and eyepiece 

what is the advantage of having a compounded light microscope

it allows for a much higher magnification and reduces chromatic aberration

What is chromatic aberration

The distortion in lenses that causes the colours of light to not focus on a certain point causing blurred images

What is dry mounting

When solid specimens are cut into thin slices with a sharp blade know as sectioning

What specimens is dry mounting used for

Hair, pollen, dust can be viewed whole, muscle tissue and plants can be viewed whole

What is Wet mount

Specimens are suspended in water or an immersion oil and a cover slip is placed at an angle

What specimens are viewed using a wet mounting

Aquatic samples and other living organisms

What are squash slides

First a wet mount is prepared then a lens tissue is used to gently pressed down the cover slip

What are squash slides used for

Good technique for soft samples such as root tips

What are smear slides

The edge of a slide is used to smear the sample creating a thin even coating on the slide

What are smear slides used for

Used for blood smears to see blood cells

What is staining used for

It’s used to create a greater contrast between cell structures and more internal structures can be visible

What is differential staining

Used to distinguish different types of organisms or different organelles of a single organism

what is magnification

it’s how many times larger the image is than the actual size of the object

What is resolution

Resolution is the ability to see individual objects as separate entities

How can u calculate magnification

Size of object/ actual size of object

How does electron microscope work

A beam of electrons with a wavelength of less than 1 n is used to illuminate the image

What are disadvantages of using an electron microscope

It’s very expensive, specimens can get damaged by electron beam, preparation process is complex

How do TEM work

A beam of electrons is transmitter thru a specimen and focused to produce an image

How do SEM work

A beam of electrons is sent across the surface of a specimen and reflected electrons are collected

TEM resolution

0.5 nm

SEM resolution

3-10 nm

What are some key point to prepare a sample in electron microscope

It’s a vacuum so that the electron beams travel in a straight line. Specimens need to be fixed using chemicals or freezing

Sample preparation in TEM

They are set in resin then stained again

Sample preparation in SEM

May be fractured to expose the inside then coated in a heavy metal like gold or silver

How to calibrate an image

First using the eyepiece graticule then calibrate it using a stage micrometre measure the diameter on the nucleus in graticule units and then use the calibrated graticule to calculate the diameter in micro meters