B1 Microscopy (page 12)

Question 1

What is a Microcope?

Answer 1

They let us see things that we can’t see with the naked eye.

The microscopy techniques we can use have developed over the years as technology and knowledge have improved.

Question 2

What are Light Microscopes?

Answer 2

they use light and lenses to form an image of a specimen and magnify it (make it look bigger).

They let us see individual cells and large subcellular structures, like nuclei.

Question 3

What are Electron Microscopes?

Answer 3

they use electrons instead of light to form an image. They have a much higher magnification than light microscopes.

They also have high resolution (resolution is the ability to distinguish between two points, so a higher resolution gives a sharper image).

Question 4

What can Electron Microscopes let us see?

Answer 4

they let us see much smaller things in more detail, like the internal structure of mitochondria and chloroplasts. They even let us see tinier things like ribosomes and plasmids.

Question 5

How do you calculate the magnification of an image?

Answer 5

Image size
Magnification = ___________
real size

Image size and real size should have the same units. if they don’t you’ll need to convert them first (see page 8).

Question 6

If you want to work out the image size or the real size of the object, what can you do?

Answer 6

you can rearrange the equation using this formula:

                                Image size
                              \_\_\_\_\_\_\_\_\_\_\_\_\_\_
                         magni-              real
                       fication      x       size

Cover up the thing you’re trying to find. The parts you can still see are the formula you need to use.

see triangle diagram on page 12.

Question 7

A specimen is 50um wide. Calculate the width of the image of the specimine under a magnifcation of x 100. Give your answer in mm

Answer 7

1) Rearrange the formular
2) Fillin the values you know
3) Remember the units in your answer
4) Convert the units.

image size = magnification x real size

image size = 100 x 50
= 5000um
= 5mm

Remember to convert from micrometers (um) to millimeters (mm), you need to divide by 1000 (see page 8)

e.g. 5000um ÷ 1000 = 5mm

see page 12.

Question 8

You need to know how to work with numbers in standard form. What is standard form?

Answer 8

This is where you change very big or small numbers with lots of zeros into something more managable.

e.g. 0.017 can be written 1.7 x 10-²

you do this by moving the decimal point left or right.

Question 9

When you move the decimal point to write the numbers in standard form, how is this represented?

Answer 9

The number of places the decimal point moves is then represented by a power of 10

This is positve if the decimal point’s moved to the left, and negative if its moved to the right.

Question 10

A mitochrondrion is approximately 0.0025mm long.

Write this figure in standard form?

Answer 10

1) the first number needs to be between 1 and 10 so the decimal point needs to move after the ‘2’.
(0.00025)

2) Count how many places the decimal point has moved - this is the power of 10. Don’t forget the minus sign because the decimal point has moved right (2.5 x 10-³)

please see example on page 12

Question 11

A cheek cell is viewed under a microscope with x 40 magnification. The image of the cell is 2.4mm wide. Calculate the real width of the cheek cell. Give your answer in um. (2 marks)

Answer 11

real size = image size ÷ magnification

= 2.4mm ÷ 40
= 0.06 mm (1 mark)

0.06 x 1000 = 60 um (1 mark)

(um unit is micrometers)