Cell Structure Flashcards
What is magnification?
Tells you how many times bigger the image produced by the microscope is than the real-life object you’re viewing.
What is resolution?
The ability to distinguish between objects that are close together.
Features of light microscopes.
Maximum resolution of around 0.2 micrometers (200nm).
They can be used to view eukaryotic cells, their nuclei and possible mitochondria and chloroplasts.
They cannot view smaller organelles like ribosomes, endoplasmic reticulum and lysosomes.
Maximum magnification of around 1500x.
Features of electron microscopes.
Maximum resolution of around 0.2nm (1000 greater than light microscopes).
They can be used to view smaller organelles like ribosomes, the endoplasmic reticulum and lysosomes.
Maximum magnification of around 1,500,000x.
There are two types: transmission (TEMs) and scanning (SEMs).
Features of transmission electron microscopes (TEMs).
Uses electromagnets to focus a beam of electrons, which is transmitted through the specimen.
Give high-resolution images and allow internal structures within cells (or even organelles) to be seen.
Can only be used with very thin specimens.
Cannot observe live specimens.
Do not produce a colour image.
Features of scanning electron microscopes (SEMs).
They scan a beam of electrons across the specimen, which bounces off the surface of the specimen, and the electrons are detected, forming an image.
They can be used on thick, or 3D images.
They allow the 3D structure to be observed.
They do not produce a colour image.
They cannot be used on live specimens.
They give a lower resolution.
Features of laser scanning confocal microscopes.
Cells being viewed must be stained with fluorescent dyes, and a thick section of tissue or small living organisms are scanned with a laser beam, which is reflected by the dye.
They can be used on thick, 3D specimens.
They allow external, 3D structures to be observed.
It has a high resolution.
It is a slow process and takes a long time to obtain an image.
The laser has potential to cause photo damage to the cells.
How does a light (optical) microscope work?
Light is directed through the thin layer of biological material that is supported on a glass slide.
This light is focused through several lenses - so an image is visible through the eyepiece.
The magnifying power can be increased by rotating the higher power objective lens into place.
How do you prepare a liquid specimen on a light microscope?
Add a few drops of the sample to the slide using a pipette.
Cover the liquid with a coverslip and gently press down to remove air bubbles.
Wear gloves to ensure there is no cross-contamination of foreign cells.
How do you prepare a solid specimen on a microscope slide?
Take care when using sharp objects and wear gloves to prevent the stain from dying your skin.
Use scissors to cut a small sample of the tissue.
Peel away or cut a very this layer of cells from the tissue sample to be place on the slide.
Apply a stain.
Gently place a coverslip on top and press down to remove any air bubbles.
What are some guidelines for drawing microscopic images?
The drawing must have a title.
NO shading.
Lines should be clear, single lines.
Labelled lines should not cross or have arrowheads.
Well-defined structures should be drawn.
What is the equation for magnification?
magnification = image size / actual size of image
How do you calculate total magnification?
total magnification = magnification of eyepiece lens x magnification of objective lens
Differences between light microscopes and electron microscopes.
Light — used for specimens above 200nm, uses light, specimens can be living or dead, used for looking at whole cells, small organisms, or tissues within organs, up to 2000x magnification.
Electron — used for specimens above 0.5nm, fires beam of electrons, useful for looking at organelles, viruses and DNA, specimens have to be dead, over 500,000x magnification.
What is the cell wall?
Found in plant cells but not animal cells.
Formed outside of the cell membrane and offer structural support (provided by cellulose in plants, peptidoglycan in most bacterial cells).
Narrow threads of cytoplasm called plasmodesmata connect the cytoplasm of neighbouring plant cells.
