Microscopes Flashcards
Define magnification?
how many times larger the image is compared to the object
define resolution?
Resolution is the ability to see two objects close together as separate objects
how does a optical [light] microscope work?
An optical microscope works by passing a beam of light through a specimen, magnifying and focusing the image using lenses.This means that the specimen needs to be quite thin.
what is the issue with the resolution of an optical microscope?
The resolution of an optical microscope is limited
by the wavelength of light To study very small structures, such as cell organelles, better
resolution is needed
how do electron microscopes work?
Electron microscopes use a beam of electrons, which has a much smaller wavelength than light, so they have much better resolution. This kind of microscope allows scientists to study the detailed structure of cells
why cant you study a live specimen when using a electron microscope?
Inside the microscope there must be a vacuum so that the electron beam can pass through without being scattered. Therefore you cannot study a living organism using an electron microscope.
Why cant you view the image of an electron microscope with human eyes?
Also, you cannot view the image directly, as our eyes are not sensitive to electron beams. The image can only be seen on a computer screen. Also, the image can only be seen in black and white, not colour.
what is one issue faced when using microscopes?
that the specimen has to be carefully prepared. This can mean adding chemicals to stabilise its structure, embedding it in wax or resin, adding stains and slicing it thinly before putting it onto a slide or grid to view under the microscope.
check your book for questions page 30
check actual book for equations
why do scientists use cell fractionation and ultracentrifugation?
because they find it useful to separate out the different organelles of a cell, so that they can study them.
describe processes in cell fractionation and ultracentrifugation?
■ Cells are broken open using a homogeniser.
■ The mixture produced is spun at high speed in a centrifuge. This forces the densest material to the bottom of the tube where it forms a pellet.
■ The liquid above the pellet is called the supernatant. This is spun again in a centrifuge at higher speed. This time the organelles that are next in density are present in the pellet.
what happens in stage 1 of cell fractionation and ultracentrifugation?
The buffer solution keeps the pH of the cell contents constant.
Any change in pH could denature the enzymes in the mixture, which means that any organelles isolated would not be very useful.
why is everything kept ice cold in stage 1 of cell fractionation and ultracentrifugation?
Everything is kept ice cold, so that the enzymes do not denature, but also so they are not active.
If the enzymes were active they might digest the organelles.
The buffer solution is isotonic so that the organelles do not take in water by osmosis and burst.
