Microscopes

Question 1

How do you convert from millimetres to micrometers ??

Answer 1

X1000

Question 2

How do you convert from micrometers to manometers ?

Answer 2

X1000

Question 3

What is the resolution of a light microscope ??

Answer 3

0.17 micrometers or around 200 manometers.

Question 4

What is he definition for magnification ?

Answer 4

How many times larger an image appears.

Question 5

What is the definition for resolution ?

Answer 5

The minimum distance between two objects before they appear as one.

Question 6

What are light microscopes often used to explore ?

Answer 6

Cell division or movement of cells.

Question 7

Name some issues with Light microscopes.

Answer 7

You often need stain to see the cells and this can kill the cells.

Question 8

How do lenses make an image visible in an optical/ light microscope ?

Answer 8

They converge the light rays to the specimen.

Question 9

Compare the different views of a SCanning electron microscope and a transmission electron microscope.

Answer 9

SEM -3D

TEM - 2D

Question 10

Compare how the SEM and TEM create images using electrons.

Answer 10

SEM - bounce off.
TEM- electron beam passes through a think sample. Passes through denser parts less easily creating contrasting black and white shades.

Question 11

Compare the thickness of specimens used in SEMs and TEMs.

Answer 11

TEM needs to be thin.

SEM can be thick or thin.

Question 12

Why is resolution often limited on an optical or light microscope ?

Answer 12

The wavelength of light is too long to resolve between close objects.

Question 13

Compare the resolution of all 3 microscopes.

Answer 13

Light - low

SEM & TEM - high

Question 14

Compare the types of specimens used in each microscope.

Answer 14

Light - living or dead

SEM & TEM - dead only

Question 15

How is magnification calculated ?

Answer 15

Magnification = image length / actual length.

Question 16

Explain how light microscopes and electron microscopes show a different image.

Answer 16

Electron microscopes only just a short beam of electrons which creates a high resolution.

Light microscopes use light - the wave length of light is often too long to distinguish between close together objects so a lower resolution image is shown.

Question 17

Explain the meaning of resolving power.

Answer 17

The ability to distinguish between points which are close together.

Question 18

Explain the reason for the difference in resolving power between light and electron microscopes.

Answer 18

Electrons have a shorter wave length. The wave length of light is too long to distinguish between close together points.

Question 19

Care must be taken in interpreting electron micrograph a. Some features visible in an electron micrograph may not be present in a living cell. Explain why.

Answer 19

Processes involved in preparation alter and distort the contents of the cell.

Question 20

Give one advantage of using a TEM rather than an SEM.

Answer 20

Higher resolution.

Question 21

Name two structures in a eukaryotic cell that cannot be identified using a light microscope.

Answer 21

Ribosomes , Centrioles, ER, lysosomes.

Question 22

Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cells when using an optical light microscope.

Answer 22

Place one drop of water on a clean slide.
Take a thin slice of epithelial tissue from the plant using tweezers and place this on the slide ensuring this is completely flat.
Cover the specimen with a solution of iodine in potassium iodide.
Cover the specimens with a thin glass cube and wipe away any excess liquid on the slide.
Place the slide on the microscope stage and adjust the view.

Question 23

Describe how you would use a microscope to find the mean diameter of triglyceride droplets on a cell.

Answer 23

Use an eyepiece graticule to accurately measure he radius of each triglyceride to 1 micrometer. Calibrate the graticule using a stage micrometer scale and repeat to calculate a mean.
Then divide the radius value for each triglyceride and divide this answer by the number of triglycerides investigated.