3.2.1.3 Methods of studying cells

Question 1

What is magnification?

Answer 1

Magnification is how much bigger the image is than the specimen

Question 2

What is the formula for magnification?

Answer 2

Magnification equals size of image divided by size of real object

Question 3

What is resolution?

Answer 3

Resolution is how well a microscope distinguishes between two points that are close together

Question 4

Why is resolution important?

Answer 4

A microscope lens cannot separate two objects that are too close together so increasing magnification won’t help

Question 5

What are the two main types of microscopes?

Answer 5

Optical light microscopes and electron microscopes

Question 6

How do optical microscopes work?

Answer 6

They use light to form an image

Question 7

What is the maximum resolution of an optical microscope?

Answer 7

0.2 micrometres

Question 8

What structures cannot be viewed using an optical microscope?

Answer 8

Ribosomes endoplasmic reticulum and lysosomes

Question 9

What is the maximum useful magnification of an optical microscope?

Answer 9

About 1500 times

Question 10

How do electron microscopes work?

Answer 10

They use electrons to form an image

Question 11

What is the resolution of an electron microscope?

Answer 11

0.0002 micrometres

Question 12

What is the maximum useful magnification of an electron microscope?

Answer 12

About 1500000 times

Question 13

Why do electron microscopes give more detailed images?

Answer 13

They have a higher resolution and can show more organelles

Question 14

What are the two types of electron microscopes?

Answer 14

Transmission electron microscopes TEMs and scanning electron microscopes SEMs

Question 15

How do transmission electron microscopes work?

Answer 15

TEMs use electromagnets to focus a beam of electrons which is transmitted through the specimen

Question 16

Why do TEMs provide high resolution images?

Answer 16

Denser parts of the specimen absorb more electrons making them appear darker

Question 17

What are the limitations of TEMs?

Answer 17

They can only be used on thin specimens and the image must be in 2D

Question 18

How do scanning electron microscopes work?

Answer 18

SEMs scan a beam of electrons across the specimen and knock off electrons from the specimen which are gathered to form an image

Question 19

Why are SEMs useful for looking at thick specimens?

Answer 19

They can provide 3D images

Question 20

Why do SEMs give lower resolution images than TEMs?

Answer 20

Because the technique is less detailed than TEM

Question 21

How do you prepare a slide for an optical microscope?

Answer 21

Create a temporary mount by pipetting water on the slide adding the specimen and covering with a coverslip

Question 22

Why do you stain specimens on a microscope slide?

Answer 22

Stains are used to highlight objects in the cell by adding contrast

Question 23

What is iodine solution used for in microscope slides?

Answer 23

It is used to stain starch grains in plant cells

Question 24

What is cell fractionation used for?

Answer 24

To separate organelles from the rest of the cell

Question 25

What are the three steps of cell fractionation?

Answer 25

Homogenisation filtration and ultracentrifugation

Question 26

What happens during homogenisation?

Answer 26

The plasma membrane is broken up and organelles are released into solution

Question 27

Why must the solution be ice cold during homogenisation?

Answer 27

To reduce the activity of enzymes that break down organelles

Question 28

Why must the solution be isotonic during homogenisation?

Answer 28

To prevent damage to the organelles through osmosis

Question 29

What is the purpose of a buffer solution during homogenisation?

Answer 29

To maintain the pH of the solution

Question 30

What happens during filtration in cell fractionation?

Answer 30

The homogenised cell solution is filtered through a gauze to separate large debris from the organelles

Question 31

Why do organelles pass through the gauze during filtration?

Answer 31

They are much smaller than the debris

Question 32

What happens during ultracentrifugation?

Answer 32

The cell fragments are separated by spinning the solution in a centrifuge

Question 33

What forms at the bottom of the centrifuge tube during ultracentrifugation?

Answer 33

A thick sediment of heavier organelles called a pellet

Question 34

What happens to the supernatant during ultracentrifugation?

Answer 34

It is drained off and spun again at a higher speed to separate the next heaviest organelles

Question 35

What is the order in which organelles are separated during ultracentrifugation?

Answer 35

Heaviest organelles first such as nuclei followed by mitochondria lysosomes endoplasmic reticulum and finally ribosomes

Question 36

Why is cell fractionation repeated at higher speeds?

Answer 36

To separate the organelles in order of mass

Question 37

What is the unit of measurement for microscopy?

Answer 37

Micrometre which is equal to 0.001 mm

Question 38

How do you convert a millimetre to a micrometre?

Answer 38

Multiply by 1000

Question 39

What happens when the solution is spun faster during ultracentrifugation?

Answer 39

The heaviest organelles form a pellet while the rest remain suspended in the supernatant