Different types of microscopes Lesson Element

Objectives Learners should be able to: explain how an electron microscope is different to a light microscope define the terms magnification and resolution convert units of measurement used in microscopy state with examples, when different microscopes are used.

What is the smallest thing you can see with your eyes? 3 What is the smallest thing you can see with your eyes? What is the smallest thing you can see with a light microscope?

Light Microscopes Light rays are focussed using glass lenses to magnify objects up to x1500 Eyepiece lens Coarse and fine Focusing Objective lenses Stage clips Stage Diaphragm Mirror

Cheek cell plasma membrane cytoplasm nucleus

Onion cells

To see more detail an electron microscope can be used Electron microscopes use an electron beam instead of light, which is focussed using electromagnets. The specimen has to be specially prepared and held inside a vacuum chamber from which the air has been pumped out (because electrons do not travel very far in air). The image is formed as a photograph (called an electron micrograph) or as an image on a TV screen.

Electron microscope Specimen is dead and dehydrated. high voltage electron gun Specimen is dead and dehydrated. Black and white image [or false colour]. Objects can be magnified up to x500 000! anode condenser lens objective aperture lens specimen Intermediate lens projector lens fluorescent screen

Which parts of this cell would be visible using a light microscope? Nucleus Cytoplasm Cell membrane Possibly mitochondria

Which parts of the cell would be visible using an transmission electron microscope (TEM) Nucleus Cytoplasm Cell membrane Possibly mitochondria

What can be seen with an electron Microscope?

Scanning electron microscope Work in a similar way but are designed to make images of the surfaces of objects.

Resolution Resolution means how close together 2 objects can be, and still be seen as separate objects. Resolution of a light microscope 0.250 µm Resolution of an electron microscope 0.25 nm Do you know how small µm and nm are?

Magnification Magnification is how many times bigger an object is in an image, than in real life. Magnification using light microscope – up to x1500 Magnification using an electron microscope – up to x500 000

Comparing light and electron microscopes Light microscope Electron microscope Magnification Resolution Type of radiation used Focussed by Type of material that can be viewed Size Preparation and cost of material

Comparing light and electron microscopes Light microscope Electron microscope Magnification x1500 X500,000 Resolution 250nm 0.25nm Type of radiation used Light Electrons Focussed by Glass lenses Electromagnets Type of material that can be viewed Living/moving/dead/abiotic Dead/abiotic Size Small and portable Large and static Preparation and cost of material Cheap and easy Difficult and expensive

How big are cells? Units for measurements mm Micrometers - µm Nanometers – nm 1mm = 1000µm 1µm = 1000nm

Cheek cell Approximately 60µm in diameter.

Onion cell Approximately 200µm in length.

Mitochondrion Approximately 2µm in diameter.

HIV Virus Approximately 2µm in diameter.

Put these in size order starting with the biggest Cilia 10µm Mitochondrion 2µm Sperm cell 55µm Ribosome 20nm Human kidney 13cm Nerve cell from a giraffes neck 3m Red blood cell 9µm HIV virus 100nm Human egg 100µm

Put these in size order starting with the biggest - answers Nerve cell from a giraffes neck 3m Human kidney 13cm Human egg 100µm Sperm cell 55µm Cilia 10µm Red blood cell 9µm Mitochondrion 2µm HIV virus 100nm Ribosome 20nm

Convert these measurements 10mm = µm 3mm = µm 670 µm = mm 0.75mm = µm 24 µm = nm 186nm = µm

Convert these measurements - answers 10mm = 10 000µm 3mm = 3 000µm 670 µm = 0.67mm 0.75mm = 750µm 24 µm = 24 000nm 186nm = 0.186µm

Quick quiz

What sort of microscope would you use to… study the internal structure of a mitochondria?

What sort of microscope would you use to… view sperm cells to see if they are moving?

What sort of microscope would you use to… look at organisms, cells or tissues that are alive?

What sort of microscope would you use to… view the surface of a bacterial cell?

What sort of microscope would you use to… observe the double membrane around a chloroplast?

What sort of microscope would you use to… look at a cross-section of a sample at high resolution? What do you think this is a picture of?

What sort of microscope would you use to… look at a viral cell?

What sort of microscope would you use to… look at the shape and surface of red blood cells in detail?

What have we learnt using electron microscopes? Cells contain organelles to carry out different functions. The internal structure of organelles and how they function. Structure of bacteria and viruses. Causes of medical conditions e.g. MS, HIV.

Objectives Can you: explain how an electron microscope is different to a light microscope define the terms magnification and resolution convert units of measurement used in microscopy state with examples, when different microscopes are used.

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