1.1 to 1.5 microscopy

Question 1

describe the purpose of the adjustment knobs (1)

Answer 1

they bring the sample into focus by moving the stage/ objective lenses up and down (1)

Question 2

the student wants to see the cells at a greater magnification. describe the steps that she should take. (2)

Answer 2

she should select the higher ( or given magnification of the lenses ) (1) and use the adjustment knobs to bring the sample back into focus (1)

Question 3

after she has viewed the cells, she wants to produce a scientific drawing of them. her teacher has advised her to use smooth lines to draw the structures she can see. give two other ways in which she can ensure she produces an accurate and useful drawing. (2)

Answer 3

she should use a sharp pencil./ she should draw outlines of the main features./ she should not colour or shade her drawing./ she should label her drawing with straight uncrossing lines./ she should include the magnification used and a scale./ her drawing should at least take up half of the space available./ she should keep the parts in proportion.

Question 4

the student compares the image that she sees with an image of onion cells viewed with an electron microscope. suggest how the two images would differ. explain your answer (3)

Answer 4

the image viewed with an electron microscope would be clearer and more detailed than the image viewed with the light microscope (1). this is because electron microscopes have a higher magnification (1) and a higher resolution than light microscopes (1)

Question 5

What is magnification?

Answer 5

The number of times bigger an image appears compared to the size of the specimen

Question 6

How can the total magnification of an image be calculated from lens powers?

Answer 6

total magnification = eyepiece lens magnification x objective lens magnification

Question 7

How can the magnification of an image be calculated?

Answer 7

magnification = size of image/ size of specimen

Question 8

What is resolution?

Answer 8

The smallest distance between two objects that can be distinguished

Question 9

How does a light microscope work?

Answer 9

Passes a beam of light through a specimen which travels through the eyepiece lens, allowing the specimen to be observed.

Question 10

What are the advantages of light microscopes? (4)

Answer 10

● Inexpensive
● Easy to use
● Portable
● Observe both dead and living specimens

Question 11

What is the disadvantage of light microscopes?

Answer 11

Limited resolution

Question 12

How does an electron microscope work?

Answer 12

t uses a beam of electrons which are focused using magnets. The electrons hit a fluorescent screen which emits visible light, producing an image.

Question 13

Name the two types of electron microscope

Answer 13

transmission electron microscope (TEM)
Scanning electron microscope (SEM)

Question 14

What is the advantage of electron microscopes?

Answer 14

Greater magnification and resolution

Question 15

Why do electron microscopes have a greater magnification and resolution?

Answer 15

They use a beam of electrons which has a shorter wavelength than photons of light

Question 16

How have electron microscopes enabled scientists to develop their understanding of cells?

Answer 16

● Allow small sub-cellular structures (e.g. mitochondria, ribosomes) to be observed in detail
● Enable scientists to develop more accurate explanations about how cell structure relates to function

Question 17

What are the disadvantages of electron microscopes? (4)

Answer 17

● Expensive
● Large so less portable
● Require training to use
● Only dead specimens can be observed

Question 18

How do you convert from m to mm?

Answer 18

× 1000 (× 10^3)

Question 19

How do you convert from m to μm?

Answer 19

× 1 000 000 (× 10^6)

Question 20

How do you convert from m to nm?

Answer 20

× 1 000 000 000 (× 10^9)

Question 21

How to you convert from nm to m?

Answer 21

÷ 1 000 000 000 (× 10^-9)

Question 22

How do you convert from m to pm?

Answer 22

× 1 000 000 000 000 (× 10^12)

Question 23

Write 0.005 in standard form (higher)

Answer 23

5 x 10 ^-3

Question 24

Write 10382 in standard form (higher)

Answer 24

1.0382 x 10 ^4

Question 25

Convert 1.527 m to μm. Write your answer in standard form (higher)

Answer 25

1.527 m × 1000000 = 1527000 μm
1527000 μm = 1.527 x 10^6 μm

Question 26

a student prepares a slide with a sample of onion cells and places it on the stage of a light microscope. describe the steps she should take to get a focused image of the cells (4)

Answer 26

select the lowest-powered objective lens (1) and move the stage up so the slide is just underneath the objective lens (1). looking through the lens, move the stage downwards until the specimen is nearly in focus (1). adjust the height of the stage with the fine adjustment knob until the image is in focus (1)

Question 27

calculate the length of a cell which has an image size of 7 x 10^-1 mm under a magnification of x400. write your answer in μm (3)

Answer 27

= 7 x 10^-1 (or 0.7 mm) / 400 (1)
= 0.00175 mm (1)
x 1000 = 1.75 μm (1)

Question 28

Total magnification?

Answer 28

The overall magnification in a light microscope due to the combined magnification of the eyepiece lens and the objective lens

Question 29

Eyepiece lens?

Answer 29

The lens that is closest to the eye when viewing a microscope

Question 30

Objective lenses?

Answer 30

A set of lenses above the stage that can be manually adjusted to provide a higher magnification

Question 31

Magnification scale?

Answer 31

A scale bar on an image that represents the actual size of an object

Question 32

Graticule?

Answer 32

A scale with many divisions that is printed on to the eyepiece lens to measure an object’s size

Question 33

Field of view?

Answer 33

The maximum diameter or area that is visible when looking through a microscope eyepiece

Question 34

Iodine solution?

Answer 34

An orange-brown dye that can be used to stain onion cells to make them easily observable

Question 35

Methylene blue?

Answer 35

A blue dye that can be used to stain cheek cells to make them easily observable