Magnification and Scale Calculations

Microscopy reveals objects beyond unaided vision. In a compound light microscope, an objective and an eyepiece enlarge the view together. Multiply their magnifications to calculate the total: x10 multiplied by x40 gives x400.

Light microscopes allow observation of living cells. However, the wavelength of visible light limits the detail they can distinguish.

Electron microscopes replace light with an electron beam. Its shorter wavelength allows finer resolution and greater useful magnification. These instruments can reveal structures within mitochondria or details on virus surfaces, but specimens generally cannot remain alive.

A scanning probe microscope maps a specimen's surface using a very fine tip. The tip moves across or just above the surface and detects local interactions, somewhat like fingers reading braille.

Match the instrument to the investigation. To follow a living cell as it moves or divides, choose light microscopy. To examine structures much smaller than visible light can resolve, electron microscopy offers finer detail.

Living organisms consist of cells, usually too small for unaided observation. Microscopes make cell study possible, but image size alone is not enough.

Magnification compares the size of an image with the size of its subject. Resolution determines whether nearby details can be distinguished. Contrast makes structures look different enough to tell apart.

A light microscope directs visible light through a specimen or onto its surface. Glass lenses enlarge the view, showing whole cells and some larger internal structures. Living specimens can be observed this way.

An electron microscope forms images using electrons. Their shorter wavelength supports finer resolution and greater useful magnification, revealing details such as mitochondrial folds.

Microscope observations helped establish cell theory: organisms contain at least one cell; cells are life's basic units; and new cells arise only from existing cells. Continued observation has supported these principles.

Cells are life's smallest units. Most require a microscope to be seen. Electron microscopy offers finer resolution and greater useful magnification than light microscopy, revealing very small internal structures. Light microscopes are easier to operate and can show living cells.

Cell theory states that organisms contain at least one cell, that cells are the basic units of living things, and that new cells arise only from existing cells.

Cells from a nose lining, an onion and bacteria share basic cell features, although their structures differ. Visible light and glass lenses can produce enlarged views of nose and onion cells. A scanning electron microscope instead scans a specimen with electrons and can reveal bacterial surfaces.

Electron microscopy provides finer detail and greater useful magnification than light microscopy. The best choice depends on the structures you need to examine and whether the specimen must remain alive.

Length tells you how long something is from one end to the other, and it's how we describe height, width, and distance. The metric system measures length using millimetres, centimetres, metres, and kilometres. These units are all connected by powers of ten, so converting between them is really just moving a decimal point. For example, a door that is about 2 metres tall is the same as 200 centimetres, because there are 100 centimetres in a metre. The same idea works for even smaller units. There are 1000 micrometres in a millimetre, and 1000 nanometres in a micrometre. Every time you move to a smaller unit, you multiply by 1000, and every time you move to a bigger unit, you divide by 1000. Keeping track of that factor of a thousand is the whole trick to converting metric lengths correctly, whether you are measuring a doorway or the width of a cell under a microscope.