45 WJEC Biology AS Level - Marianne Izen - 2nd Edition Flashcards
What are microscopes used for?
Microscopes are used to look at the detailed structure of cells and to measure structures inside them.
What is the simplest way to magnify?
The simplest way to magnify is to use a hand lens, which can give a 10- to 20-fold magnification.
What gives greater magnification than a hand lens?
Two or more lenses used together, creating a compound microscope, give greater magnification.
What is the maximum magnification achieved by modern light microscopes?
Some modern light microscopes can achieve an image magnified 2000 times
What is maximum magnification in microscopes in the school laboratories?
A maximum of x400 or x1000 is more common in microscopes in school laboratories.
When was the electron microscope developed?
The electron microscope was developed in the 1930s.
How do electron microscopes work?
It uses electrons instead of visible light to view material and can produce much greater magnification.
How much magnification can you get with electron microscopes?
Many magnify over a million times and some research instruments achieve over ten million.
Why does electron microscope have greater resolution than light microscopes?
Electron microscopes have greater resolution than light microscopes because electrons have a much shorter wavelength than visible light so they distinguish objects that are smaller and closer together.
What do you mean by the resolution of a microscope?
The resolution of a microscope tells you how close two points can be and still be separately distinguished, rather than being seen as a single image.
It tells you the detail which can be seen.
What you mean when you say that the light microscope has reached its limit of resolution?
For a light microscope, the resolution is about 0.2 μm.
When you use a light microscope, the higher the magnification of the image the more detail you can see in it, but magnifying to see distances smaller than 0.2 μm does not give any more detail.
The light microscope has then reached its limit of resolution.
What is the resolution of an electron microscope?
An electron microscope can resolve points 0.1 nm apart.
What can you see in a typical animal cell using a light microscope?
Using a light microscope, it is possible to see the nucleus and the nucleolus in a typical animal cell.
The cytoplasm appears granular and mitochondria may be visible.
What can you see in a typical animal cell using an electron microscope?
Using an electron microscope, it is possible to see far greater detail, including ribosomes on the rough endoplasmic reticulum.
Magnification (Key Term)
The number of times an image is bigger than the object from which it is derived.
Resolution (Key Term)
The smallest distance that can be distinguished as two separate points in a microscope.
How do you prepare an onion epidermis for microscopic examination?
Cut a white onion vertically and remove a leaf.
Insert fine forceps just below the epidermis on the adaxial surface, which is the upper surface on a piece of onion curving upwards.
Maintain the tension on the sheet of cells that lifts off, cut it off with scissors and place it on a microscope slide.
Use scissors to cut a square of unfolded epidermis, with each side about 5 mm.
Put two drops of methylene blue or iodine in potassium iodide solution on the specimen and cover with a cover slip.
How do you prepare an red onion and rhubarb epidermis for microscopic examination?
Insert fine forceps just beneath the epidermis of a rhubarb petiole or the adaxial epidermis of a red onion leaf and, maintaining the tension, pull the sheet of epidermis off.
Place over a microscope slide and use scissors to cut a square of unfolded epidermis, with each side about 5 mm.
Put two drops of water on to the specimen and cover with a cover slip.
What will you do as part of your laboratory work?
As part of your laboratory work, you will prepare slides and from them, draw live cells.
You will calculate their size and the magnification of
your drawing
