Optical microscope

Question 1

Optical microscopes use …. to form a image

Answer 1

light

Question 2

Optical microscopes use light to form an image

This limits the ……. of optical microscopes

Answer 2

resolution

Question 3

Why does light limit resolution

Answer 3

This limits the resolution of optical microscopes
Using light, it is impossible to resolve (distinguish between) two objects that are closer than half the wavelength of light

The wavelength of visible light is between 500-650 nanometres (nm), so an optical microscope cannot be used to distinguish between objects closer than half of this value

Question 4

This means optical microscopes have a maximum resolution of around

and what can you see with the microscope

Answer 4

0.2 micrometres (µm) or 200 nm
This means optical microscopes can be used to observe eukaryotic cells, their nuclei and possibly mitochondria and chloroplasts

Question 5

What can you not see with the optical microscope

Answer 5

This also means that optical microscopes cannot be used to observe smaller organelles such as ribosomes, the endoplasmic reticulum or lysosome

Question 6

Maximum magnification of optical microscope

Answer 6

This also means that optical microscopes cannot be used to observe smaller organelles such as ribosomes, the endoplasmic reticulum or lysosome

Question 7

A light microscope has two types of lens

Answer 7

A light microscope has two types of lens:
An eyepiece lens, which often has a magnification of x10

A series of (usually 3) objective lenses, each with a different magnification

Question 8

The resolution of a light microscope is limited by the wavelength of light

As light passes through the specimen, it will be diffracted
The longer the wavelength of light, the more it is diffracted and the more that this diffraction will overlap as the points get closer together

Electron microscopes have a much higher resolution and magnification than a light microscope as electrons have a much smaller wavelength than visible light

This means that they can be much closer before the diffracted beams overlap

Question 9

The concept of resolution is why the phospholipid bilayer structure of the cell membrane cannot be observed under a light microscope

The width of the phospholipid bilayer is about 10nm

The maximum resolution of a light microscope is 200nm (half the smallest wavelength of visible light, 400nm)

Any points that are separated by a distance less than 200nm (such as the 10nm phospholipid bilayer) cannot be resolved by a light microscope and therefore will not be distinguishable as “separate”

Question 10

Light microscope

The specimens can be living (and therefore can be moving), or dead

Light microscopes are useful for looking at whole cells, small plant and animal organisms, tissues within organs such as in leaves or skin

Answer 10

Due to the higher frequency of electron waves (a much shorter wavelength) compared to visible light, the magnification and resolution of an electron microscope is much better than a light microscope

Electron microscopes are useful for looking at organelles, viruses and DNA as well as looking at whole cells in more detail

Electron microscopy requires the specimen to be dead however this can provide a snapshot in time of what is occurring in a cell eg. DNA can be seen replicating and chromosome position within the stages of mitosis are visible

Question 11

Electron needs vaccum

light microscope

Answer 11

doesnt

Question 12

Electron hard to set up

Answer 12

optical not same with price and sample preparation