Topic 2---A: Cell structure and division- 3.Analysis of cell components

Question 1

What is magnification?

Answer 1

It’s the number of times larger an image is than the speciman (sample your looking at).

Question 2

Magnification formula

Answer 2

Magnification=
Size of image
——————-
Size of real object

Question 3

What do you do if you want to convert a smaller unit into a bigger unit?

Answer 3

You divide by 1000

Question 4

What do you do if you want to convert a bigger unit into a smaller unit?

Answer 4

You multiply by 1000

Question 5

What is the order of the units from biggest to smallest?

Answer 5

• Millimetres
• Micro metres
• Nano metres

Question 6

What is resolution?

Answer 6

• It’s how detailed an image is.
• It is the minimum distance at which 2 points can be seen as separate.

Question 7

When will microscopes not be able to distinguish between objects?

Answer 7

Objects that are smaller than their maximum resolution.

Question 8

What are the two types of microscopes?

Answer 8

• Optical (light) microscope
• Electron microscope

Question 9

What is an optical (light) microscope?

Answer 9

• They use light rays to form an image.
• They have a maxium resolution of 0.2 micro metres.
• So this means you can’t use an optical micrscope to view organelles smaller than 0.2 micrometres e.g ribosomes, endoplasmic reticulum and lysosomes
• The maximum useful magnification of an optical microscope is x1500.

Question 10

What cellular structures will an optical microscope not be able to view?

Answer 10

• Ribosomes
• Endoplasmic reticulum
• Lysosomes

Question 11

What is an electron microscope?

Answer 11

• They use electrons to form an image
• They have a higher resolution than optical microscopes so give a more detailed image and can be used to look at more organelles.
• Maximum resolution of 0.0002 (1000 times higher than optical microscopes).
• Maximum useful magnification of an electron microscope is x 1 500 000
• They produce black and white images.

Question 12

What are the differences of an optical microscope and electron microscope?

Answer 12

• The maximum resolution of an optical microscope is 0.2 micro metres (lower) compared to 0.0002 micrometres for the electron microscope (higher).
• The maximum magnification for an optical microscope is x1500 (lower) compared to x 1 500 000 for an electron microscope (higher).

Question 13

What are the two types of electron microscopes?

Answer 13

• SEM (scanning electron microscopes).
• TEM (transmission electron microscopes).

Question 14

What is the transmission electron microscope?

Answer 14

• Electrons are passed through the microscope and focused onto the specimen by electromagnets.
• Denser parts of the specimen absorb more electrons making them look darker on the image

Question 15

What is the scanning electron microscope?

Answer 15

• They direct a beam of electrons onto a sample.
• Electrons don’t pass through the specimen but rather are scattered (bounce off) from the surface.
• Pattern of scattering depends on the contours of the specimen so a 3D image is formed.

Question 16

What are the advantages of a transmission electron microscope?

Answer 16

• Give high resolution images so small objects can be seen. (chloroplasts)

Question 17

What are the disadvantages of a transmission electron microscope?

Answer 17

• They can only be used on thin specimens
• Can only be used on non-living organisms because you can only view them in a vacuum.

Question 18

What are the advantages of a scanning electron microscope?

Answer 18

• Produce 3D images
• Can be used on thick specimens

Question 19

What are the disadvantages of a scanning electron microscope?

Answer 19

• Give lower resolution images compared to the transmission electron microscope.
• Can only be used on non-living organisms because you can only view them in a vacuum.

Question 20

What are the differences between SEM and TEM electron microscopes?

Answer 20

• TEM give higher resolution images compared to SEM.
• TEM can only be used on thin specimens but SEM can be used on thick specimens.
• SEM can be 3D images but TEM is only 2D.

Question 21

What is a similarity of the scanning electron microscope and the transmission electron microscope?

Answer 21

• They both can only be used on non-living organisms.

Question 22

What do you need to do if you want to look at a specimen with an optical microscope?

Answer 22

You will need to put it on a microscope slide which is often done using a temporary mount.

Question 23

What is a temporary mount?

Answer 23

This is where the specimen is suspended in a drop of liquid (e.g. water or oil) on the slide.

Question 24

How would you make a temporary mount?

Answer 24

1) Start by pipetting a small drop of water onto the centre of the slide.
2) Then use tweezers to place a thin section of your specimen on top of the water drop. It needs to be thin so light can get through it for you to be able to see it clearly under the microscope.
3) Add a drop of a stain which are used to highlight objects in a cell.
4) Finally, add the cover slip by standing it up right on the slide next to the water droplet then tilt and lower it until it covers the specimen.

Question 25

What is an example of a stain?

Answer 25

Iodine is used to stain starch grains in plant cells.

Question 26

What is an artefact?

Answer 26

They are things that you can see down a microscope that aren't part of the cell or specimen that you're looking at. Examples include, air bubbles and finger prints.

Question 27

How are artefacts made?

Answer 27

They are usually made during the preparation of your specimen

Question 28

How would you work out the magnification when you get given a scale bar?

Answer 28

You divide the real length of the scale bar by the stated length of it.

Question 29

What is cell fractionation used for?

Answer 29

It is used to separate organelles from a cell which you can look at under an electron microscope.

Question 30

What are the 3 steps in cell fractionation?

Answer 30

- Homogenisation - Filtration - Ultracentrifugation

Question 31

Homogenisation

Answer 31

- This is breaking up the cells and it can be done in several different ways. - It can be done by vibrating the cells or grinding the cells up in a blender. - This breaks up the plasma membrane and releases the organelles into a solution.

Question 32

How should the solution after homogenisation be kept?

Answer 32

- Ice-cold - Isotonic - A buffer solution

Question 33

Why should the solution be kept ice-cold?

Answer 33

To reduce the activity of enzymes that break down organelles.

Question 34

Why should the solution be isotonic?

Answer 34

- This means it should have the same concentration of chemicals as the cells being broken down. So it helps prevent damage to the organelles through osmosis (e.g. cell bursting)

Question 35

Filtration

Answer 35

- This is getting rid of the big bits - So this is when the homogenised cell solution is filtered through a gauze to separate any large cell debris or tissue debris like connective tissue from the organelles. - Your left with a solution containing a mixture of organelles.

Question 35

Ultracentrifugation

Answer 35

- This is separating the organelles - So the cell fragments are poured into a tube which is put into a centrifuge and is spun at a low speed at first. - The heaviest organelles (e.g. nuclei) get flung to the bottom of the tube by the centrifuge (pellet) and then the rest of the organelles stay suspended in the fluid above the sediment (supernatent). - The supernatent is drained off and poured into another tube and spun in the centrifuge at a higher speed . - This process is repeated at higher and higher speeds until all the organelles are separated out.

Question 35

Why should the solution be buffered?

Answer 35

Helps to maintain pH so enzymes don't denature

Question 36

What is a centrifuge?

Answer 36

A machine that separates material by spinning

Question 37

What is the pellet?

Answer 37

The thick sediment at the bottom

Question 38

What is the supernatent?

Answer 38

The fluid above the sediment

Question 39

What is the organelles order of mass from heaviest to lightest?

Answer 39

- Nuclei - Mitochondria - Lysomes - Endoplasmic reticulum - Ribosomes but in plant cells the chloroplasts come out after the nuclei but before the mitochondria.