Analysis of Cell Components

Question 1

Definition of magnification

Answer 1

The increase in apparent size of an object.

Question 2

What is resolution/resolving power?

Answer 2

The ability to show two objects as separate (shows how detailed the image is, if a microscope can’t separate two objects then increasing the magnification will not help)

Question 3

What is the equation for magnification?

Answer 3

I/AM - Image size = Magnification/Actual Size

Question 4

What unit do you always convert to?

Answer 4

Millimetres - mm

Question 5

What do you multiply by to convert between units?

Answer 5

Metre (m) x1000 Millimetre (mm) x1000 Micrometre (um) x1000 Nanometer (nm)
nm /1000 um /1000 nm /1000 m

Question 6

How would you draw a cell under a microscope?

Answer 6

Draw the cell within a circle, label each organelle and their function, add the magnification, label the cell type.

Question 7

What can you presume when looking at a magnified image of a cell.

Answer 7

The outer layer of the cell is the cell wall (depending on context - cell type), the eye piece is x10 magnification (times 10 by the magnification of the lenses), if you don’t know what an organelle is then ignore it.

Question 8

How would you measure the size of a cell from looking down a microscope?

Answer 8

Measure the field of view (diameter, circle) with a mm ruler by putting it directly on top of the specimen, count the number of cells and divide by this number, (calculate using I/AM?)

Question 9

How do scale bars work?

Answer 9

The length of the bar is the image size and the size the bar represents is the actual size.

Question 10

What dp/sgf do you leave your answer to?

Answer 10

Usually 3sgf but the same amount as in the question.

Question 11

Name the two types of microscope.

Answer 11

Optical (light) microscope, Electron Microscope (can be a Transmition Electron Microscope or a Scanning Electron Microscope).

Question 12

Differences in illumination between an Optical microscope, SEM’s and TEM’s?

Answer 12

Optical - Light, SEM + TEM - Electron beam

Question 13

Difference in what focuses the image in an Optical microscope, SEM’s and TEM’s?

Answer 13

Optical - Objective lenses, SEM + TEM - Condenser Electromagnets

Question 14

Differences in max magnification between an Optical microscope, SEM’s and TEM’s?

Answer 14

Optical - x1500, SEM - 500, 000 (or 1-2 mill), TEM - x50mill

Question 15

Differences in resolving power between an Optical microscope, SEM’s and TEM’s?

Answer 15

Optical - 200nm (worst), TEM - 1nm (best), SEM - 20nm (middle)

Question 16

Differences in specimens between an Optical microscope, SEM’s and TEM’s?

Answer 16

Optical - Living or Dead, SEM + TEM - Dead (specimens have to be placed in a chamber under vacuum so electrons aren’t absorbed by the air)

Question 17

Differences in specimen thickness between an Optical microscope, SEM’s and TEM’s?

Answer 17

Optical - thin, TEM - Extremily thin to allow electrons to penetrate, SEM - thicker than TEM (and optical - can view whole cells/tissues)

Question 18

Differences in ease of preparation between an Optical microscope, SEM’s and TEM’s?

Answer 18

Optical - Easiest, SEM - next easiest, TEM - slightly harder than SEM

Question 19

Differences in cost of equipment between an Optical microscope, SEM’s and TEM’s?

Answer 19

Optical - Cheaper, TEM + SEM - More expensive

Question 20

Differences in image colour between an Optical microscope, SEM’s and TEM’s?

Answer 20

Optical - Colour, TEM +SEM - Black and white but can be coloured using a computer

Question 21

Differences in image dimension between an Optical microscope, SEM’s and TEM’s?

Answer 21

Optical + TEM - 2D, SEM - 3D

Question 22

Disadvantages and advantages of a light (optical microscope)?

Answer 22

Poor resolution - light has a longer wavelength than electron beam.
Lower Magnification
However - Colour images
Can view LIVING samples

Question 23

How is the image produced on a light microscope?

Answer 23

A beam of light is condensed to produce the image.

Question 24

How does a transition electron microscope work?

Answer 24

Condenser electromagnets are used to focus a beam of electrons, which is then transmitted through a small section of the specimen. Denser parts of the specimen absorb more electrons which makes them look darker, lighter parts allow electrons to pass through making it look brighter.

Question 25

What can you see when looking through a transition electron microscope?

Answer 25

A 2D slice of the specimen, you can see ribosomes and the internal structures of larger organelles like chloroplasts because of its high resolution.

Question 26

What is the image produced from a transition electron microscope called?

Answer 26

The 2D image produced (a MICROGRAPH) can be photographed to produce an electronmicrograph/photomicrograph

Question 27

How does a scanning electron microscope work?

Answer 27

A beam of electrons from above is focused by condenser electromagnets and then passed through pairs of scanning coils which deflect the beam horizontally and vertically across a portion of the specimen in a regular pattern resulting in scattering of electrons and emission of secondary electrons from the surface of the specimen which are gathered in a cathode ray tube to produce an image. The pattern of scattering depends on the contours of the specimen's surface which creates the 3D image.

Question 28

What do the images produced by a scanning electron microscope show?

Answer 28

The surface of the specimen (are 3D), images a larger area of the specimen, images are often easier to interpret than TEM images

Question 29

What are the disadvantages of electron microscopes?

Answer 29

Vacuum used so only dead specimens can be used. Complex preparation and scanning of specimens required. Image only in black and white. Image (photomicrograph) may contain `artefacts` which result from the way the specimen's are prepared eg. dehydration of a specimen may result in distortion of key features.

Question 30

Advantages of an electron microscope?

Answer 30

Higher magnification and resolving power.

Question 31

When is a temporary mount used?

Answer 31

Also known as a wet mount, used to prepare a specimen when you want to look at it through a light microscope.

Question 32

What is the process to make a temporary/wet mount?

Answer 32

Pipette a drop of liquid (eg. water/oil) onto the centre of the slide. Use tweezers to place a thin (needs to let light through so can't be thick) slice of the specimen on top of the water droplet. Add a drop of stain. Add the cover slip (a square piece of glass that protects the specimen) by tilting and lowering it so it covers the specimen.

Question 33

What are stains used for when preparing a specimen to go under the microscope?

Answer 33

To highlight objects in a cell. (eg. eosin is used to make the cytoplasm show up and iodine in potassium iodide solution is used to stain starch grains in plant cell.

Question 34

What must you be careful not to do when preparing a slide for a light microscope?

Answer 34

Not get any air bubbles as they obstruct the view of the specimen.

Question 35

What are artefacts?

Answer 35

The things you can see down a microscope that aren't part of the cell or specimen you are looking at.

Question 36

Examples of artefacts?

Answer 36

Dust, air bubbles, finger prints, inaccuracies caused by squashing and staining your sample.

Question 37

Where are artefacts especially common?

Answer 37

Electron microscopes because slides need a lot of preparation.

Question 38

How did the first scientists distinguish between artefacts and organelles?

Answer 38

By repeatedly preparing specimens in different ways. If it showed up on one but not another it was an artefact.