Methods Of Studying Cells

Question 1

Microscopy

Answer 1

Microscopes instruments that produce a magnified image of an object.

A simple convex glass lens can act as a magnifying glass but such lenses work more effectively if they are used in pairs in a compound light microscope.

The relatively long wavelength of light rays means that a light microscope can only distinguish between two objects if they are 0.2 um, or further, apart.

This limitation can be overcome by using beams of electrons rather than beams of light.

Question 2

Magnification

Answer 2

Material put under microscope is an object

This appearance of the natural when view under the microscope is called an image

The magnification of an object is how many times bigger the image is compared to the object

Question 3

Unit scale

Answer 3

Kilometre-km-10 to the power of 3
Metre-m- 1
Millimetre-mm-10 to the power of minus 3
Micrometre-um-10 to the power of minus 6
Nanometre-nm-10 to the power of minus 9

Question 4

Resolution

Answer 4

The resolution or resolving power of a microscope is the minimum distance apart of 2 objects for them to be seen separate

Resolving power depends on radiation or wavelength used

Increasing magnification does increase the size of image but not the resolution

Question 5

Light microscopes

Answer 5

Poor resolution due to long wavelength of light due to being made in 1930

Question 6

Electron microscope and advantages

Answer 6

Uses beams of electrons
———————————-
Electron beam has very short wavelength and therefore can resolve objects well -high resolving power

Beams of electrons can be focused using electromagnets

Question 7

Conditions where electron microscopes work plus resolution.

Answer 7

Resolving power of 0.1nm

Due to electrons either getting absorbed or deflected by air a near vacuum has to be created in order if it working correctly

Question 8

2 types of electron microscopes

Answer 8

Transmittion electron microscope
Scanning electron microscope

Question 9

TEM

Answer 9

Consists of electron gun the produces a beam of electrons that’s focused on specimen

This beam passes through thin section of specimen

Some parts absorb and appear dark , some allow the electrons to go through and appear brighter

An image is then given and this can be photographed to form a photo micrograph

Question 10

What is resolving power of tem and why can it not always be achieved

Answer 10

Difficulties preparing the specimen limit the resolution

The higher energy electron beam could destroy the specimen

Question 11

What the limitations of TEM

Answer 11

Whole system is vacuumed so no living cells can be observed

A complex staining process is required

Specimen must be extremely thin

You can only see the image in 2 d, you can partly get over this but building up a 3D image from a series of photomicrographs but this is slow and complicated

Question 12

SEM limitations

Answer 12

Same limitations as TEM but the specimens don’t have to be as thin as electrons don’t penetrate

Question 13

How does an SEM work and advantages and disadvantages

Answer 13

Directs a beam of electrons onto the surface of specimen from above , this beam is then passed back and forth across a proportion of the specimen in a regular pattern

We can build up a 3D image from this by computer analysis of the pattern of scatters electrons and secondary electrons produced

Basic SEM has a lower resolution at 20nm