Cells (MICROSCOPES)

Question 1

What are the three types of microscopes

Answer 1

Light (optical) microscopes
Transmission Electron Microscopes (TEM)
Scanning Electron Microscope (SEM)

Question 2

What are the 2 types of electron microscope

Answer 2

TEM and SEM

Question 3

Which has a higher resolution, electron or light microscopes

Answer 3

Electron microscopes.
–> Light microscopes only have a resolution of 0.2 micrometres. Electron microscopes have a resolution about 1000 times higher than optical microscopes

Question 4

Compare electron microscopes to light microscopes

Answer 4

Light microscope:
* Beam of light is condensed to create an image
* Lower resolution than electron microscope as light has a longer wavelength
* Lower magnification than electron microscopes
* Samples can be living
* Sample is show in colour

Electron microscope:
*Beam of electrons are condensed using an electromagnet to create an image
* Higher resolution than light microscope as electrons have a shorter wavelength
* Higher magnification than light microscope
* Staining and preparation process is more complex and time consuming than light microscope
* Sample must be placed in a vacuum so cannot be living
* Sample is shown in black and white

Question 5

Compare Transmission Electron Microscopes to Scanning Electron Microscopes

Answer 5

TEM:
*Beam of electrons need to pass through specimen so sample must be very thin
* Higher resolution than SEM
* Able to observe ultra cellular structure in great detail
* Produces a 2D image

SEM:
* Beam of electrons scan the surface of specimen so reflected beam is observed
* Lower resolution
* Can only see the surface
* Produces a 3D image

Question 6

Which has a greater resolution TEM or SEM

Answer 6

TEM

Question 7

Why are some parts of the specimen darker when viewed under a TEM

Answer 7

Some parts of the specimen (the denser parts) absorb the electrons making them appear darker.
Parts that are lighter allow electrons to pass through

Question 8

What must you increase on a microscope to make the image less blurry

Answer 8

Magnification AND resolution

Question 9

Describe how to prepare a temporary slide

Answer 9

Place a drop of distilled water on a slide
Cut a very thin piece of potatoes and mush it using forceps and place on slide
Stain potato using iodine in potassium iodide solution
Using mounting needle , gently place cover slip on top of air bubbles

Question 10

Explain how you would calibrate a microscope and calculate an actual size of a specimen using microscope

Answer 10

Place the micrometer eyepiece into the eyepiece of the microscope
Place the stage micrometer slide on the stage of the microscope at the desired objective lens
Line up the epu and stage micrometer to calculate 1 epu at that objective lens
Remove the stage micrometer from the stage of microscope and add the specimen slide that you want to measure to the stage.
Measure epu of the specimen and calculate actual size by your multiplying the number of epu of the specimen by your calculated actual valve of 1 epu.

Question 11

Give the equation for magnification

Answer 11

I
AM

Magnification = image size/ actual size

Question 12

How do you convert mm to micrometres

Answer 12

x1000
( cm-mm is x10)