Studying Cells - How Microscopes Work (page 16 - 17)

Question 1

If Magnification is Size, what is Resolution?

Answer 1

Resolution is detail.

We all know that microscopes produce a magnified image of a sample, but resolution is just as important.

Question 2

Explain what Magnification is, and how it is calculated using what formula?

Answer 2

Magnification is how much bigger the image is than the specimen.

It is calculated using the formula:

Magnification = image size
____________
Object size

Question 3

Explain what Resolution is and how well do a microscope distinguish between two points that are close together?

Answer 3

Resolution is how detailed the image is.

How well a microscope distinguishes between two points that are close together, is if a microscope lens can’t separate two objects, then increasing the magnfication won’t help.

Question 4

In the exam, you might be told the actual and magnified size of an object and then be asked to calculate the magnification.

How can you do this? (what formula)?

Answer 4

Magnification = image size
____________
object size

Question 5

You have a magnified image that’s 5mm wide. Your specimen is 50 µm wide. how do you calculate this magnification?

Answer 5

first get everything ino the same units:

1 mm = 1000 µm

so 50 µm ÷ 1000 µm = 0.05 mm

Now calculate the magnification:

5 ÷ 0.05 = x 100

Please see diagram 2 on page 16

Question 6

If you need to rearrange the formular to work out the image size or object size of magnficatio, what can you to to the forula triangle to help you?

Answer 6

You can use the formula triangle to help you (see diagram of triangle on page 16). All you have to do is put your finger over what you want to kow and read off the formula.

e.g. if you want to know the object size, cover up the object size. That leaves image size ÷ magnification.

Question 7

How do you convert a micrometre µm to mm?

Answer 7

A micrometre (µm) is three orders of magnitude smaller than a millimetre (1 µm = 0.001 mm). To convert from µm to mm, divide by 1000

Question 8

What are the three types of Microscopes you need to learn for A level exams?

Answer 8

1) Light Microscopes
2) Laser scanning confocal Microscopes (a special type of light microscope)
3) Electron Microscopes

Question 9

Explain how a Light Microscope works? e.g. resolution, maximum useful magnification etc.

Answer 9

1) Light Microscopes use light
2) They have a lower resolution than electron microscopes - they have a maximum rosolution of about 0.2 micrometers (µm). So they’re usually used to look at whole cells or tissues.
3) The maximum useful magnification of a light microscope is about x 1500

Question 10

Explain how a Laser Scanning Confocal Microscopes work (e.g. laser beams, different depths, etc.

Answer 10

1) Laser Scanning Confocal Microscopes use laser beams (intense beams of light) to scan a specimen, which is usually tagged with a flourescent dye.

2) The laser causes the dye to floresce - giff off light. This light is then focused through a pinhole onto a detector. The detector is hooked up to a computer, which generates an image. The image can be 3D.

3) The pinhole means that any out of focus light is blocked, so these microscopes produce a much clearer image than a normal light microscope.

4) They can be used to look at objects at different depths in thick specimens.

Question 11

Explain what Electron Microscopes are?

Answer 11

Electron microscopes use electrons instead of light to form an image. they have a higher resolution than light microscopes to give more detailed images. There are two kinds of electron microscopes.

Transmission Electron Microscope (TEM)
Scanning Electron Microscope (SEM)

Question 12

Explain what a Transmission Electron Microscope (TEM) is used for?

Answer 12

TEM use electronmagnetics to focus a beam of electrons, which is then transmitted through the specimen. Denser parts of the specmen absorb more electrons, which makes them look darker on the image you end up with. TEMs are good because they provide high resolution images (so they can be used to look at a range of organelles), but they can only be used on thin specimens. Look at diagram 1 on page 17 of a mitochrondrion)

Question 13

What is Scanning Electron Microscope (SEM)?

Answer 13

It is when you scan a beam of electrons across the specimen. This knocks off electrons from the specmen, which are gathered in a cathode ray tube to form an image. The images produced show the surface of the specimen and can be 3D. But they give lower resolution images than TEMs. Look at SEM image of a mitochondrion on page 17 diagram 2.

Question 14

You need to be able to compare Magnfication and Resolution

What is the maximum Resolution and maximum magnificaion of:

a) light microscope
b) TEM
c) SEM

Answer 14

Maximum resolution
a) light microscope = 0.2 µm
b) TEM = 0.0002 µm
c) SEM = 0.002 µm

Maximum Magnification
a) light microscope = x1500
b) TEM = can be more than x 1 000 000
c) SEM = usually less than x 500 000

Question 15

Why do TEMs (Transmission Electro Microscopes) have the highest resolution?

Answer 15

because they can distinguish between the smallest objects (or objects that are only 0.0002 µm apart.

Question 16

An insect is 0.5 mm long. In a book, a picture of the insect is 8 cm long.

calculate the magnification of the image (2 marks)

Answer 16

Magnification = image size ÷ object size
= 80mm ÷ 0.5 mm (1 mark)
= x 160 (1 mark)

(always remember to convert everything to the sames units first - the insect is 0.5 mm long, so the length of the image needs to be changed from 8 cm to 80 mm).

Question 17

A light micrograph shows a human cheek cell at x 100 magnification. The actual diameter of the cell is 59 µm. What is the diameter of the cell in the image? (2 marks)

Answer 17

Image size = magnification x object size
= 100 x 0.059 mm (1 mark)
= 5.9 mm (1 mark)

(hint: To convert 59 µm into mm, divide by 1000)

Question 18

The table shows the dimentions of some different organelles found in animal cells.

Lysosome 0.1 (diameter/µm)
Mic
mochrondrion 2
nucleus 5
ribosome 0.02
vesicle 0.05

a) Name those organelles in the table that would be visible using a good quality light microscope. Explain your answer (3 marks)

b) Which organelles would be visible using an SEM? explain your answer (2 marks)

Answer 18

a) mitochrondrion (1 mark) and nucleus (1 mark)
the resolution of light microscopes is not good enough to show objects smaller than 0.2 µm (1 mark)

b) All of the organelles in the table would be visible (1 mark)

c) All of the organelles in the table would be visible (1 mark). The resolution of SEMs is good enough to resolve objects down to about 0.002 µm in size (1 mark).