Biology- 2.1: Cell structure

2.1 - Cell Structure

What is the maximum resolution of light microscopes?

The maximum resolution of light microscopes is approximately 200 nanometres

What is the maximum magnification of light microscopes

The maximum magnification of light microscopes is typically around x1500

What can light microscopes observe ?

Larger structures:

>entire cells

>nuclei

>mitochondria and chloroplast

Advantages of light microscopes

>Cheap and small

>Specimen preparation is straightforward

>coloured images produced

>can observe living specimens

Disadvantages of light microscopes

>Low magnification and resolution

>Can only see large structures

> Cannot see small internal structures

What do electron microscopes use to form an image

Electrons through the specimens

What is the maximum resolution of electron microscopes

0.2 nanometers

What is the maximum magnification of electron microscopes

x1,000,000

What can electron microscopes observe

Small internal structures:

>Cell membranes

>ribosomes

>the endoplasmic reticulum (ER)

>Lysosomes

Disadvantages of electron microscopes

>Large and expensive

>Specimens prepared using complex processes

>Specimens must be viewed in a vacuum so they must be dead

>images are always black and white

Two types of electron microscopes

Transmission electron microscope (TEM)

Scanning electron microscopes (SEM)

How does TEMs work

They use electromagnets to transmit a beam of electrons through a specimens

Why does denser parts of cells appear darker in TEMs

Denser parts of the specimen absorb more electrons, therefore appear darker.

Describe the images produced from TEM

>high resolution

>shows the internal structure of the cell and within organelles

>2D

How does SEMs work?

A beam of electrons pass across the surface of a specimen and then detect the rate at which the electrons bounce back

Describe the images produced from SEM

>3D

>only shows the surface of specimens

>lower maximium resolution compared the TEM

How do you work out magnification?

Magnification = image size/ actual size

How do the 5 unite of measures relate (nm, µm , m, mm , cm )

nm → µm → mm → m (divide by 1000) smallest to biggest

mm → cm (divide by 10)