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

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

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1
Q

What is magnification?

A

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

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2
Q

Magnification formula

A

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

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3
Q

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

A

You divide by 1000

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4
Q

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

A

You multiply by 1000

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5
Q

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

A
  • Millimetres
  • Micro metres
  • Nano metres
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6
Q

What is resolution?

A
  • It’s how detailed an image is.
  • It is the minimum distance at which 2 points can be seen as separate.
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7
Q

When will microscopes not be able to distinguish between objects?

A

Objects that are smaller than their maximum resolution.

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8
Q

What are the two types of microscopes?

A
  • Optical (light) microscope
  • Electron microscope
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9
Q

What is an optical (light) microscope?

A
  • 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.
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10
Q

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

A
  • Ribosomes
  • Endoplasmic reticulum
  • Lysosomes
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11
Q

What is an electron microscope?

A
  • 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.
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12
Q

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

A
  • 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).
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13
Q

What are the two types of electron microscopes?

A
  • SEM (scanning electron microscopes).
  • TEM (transmission electron microscopes).
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14
Q

What is the transmission electron microscope?

A
  • 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
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15
Q

What is the scanning electron microscope?

A
  • 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.
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16
Q

What are the advantages of a transmission electron microscope?

A
  • Give high resolution images so small objects can be seen. (chloroplasts)
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17
Q

What are the disadvantages of a transmission electron microscope?

A
  • 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.
18
Q

What are the advantages of a scanning electron microscope?

A
  • Produce 3D images
  • Can be used on thick specimens
19
Q

What are the disadvantages of a scanning electron microscope?

A
  • 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.
20
Q

What are the differences between SEM and TEM electron microscopes?

A
  • 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.
21
Q

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

A
  • They both can only be used on non-living organisms.
22
Q

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

A

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

23
Q

What is a temporary mount?

A

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

24
Q

How would you make a temporary mount?

A

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.

25
Q

What is an example of a stain?

A

Iodine is used to stain starch grains in plant cells.

26
Q

What is an artefact?

A

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.

27
Q

How are artefacts made?

A

They are usually made during the preparation of your specimen

28
Q

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

A

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

29
Q

What is cell fractionation used for?

A

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

30
Q

What are the 3 steps in cell fractionation?

A
  • Homogenisation
  • Filtration
  • Ultracentrifugation
31
Q

Homogenisation

A
  • 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.
32
Q

How should the solution after homogenisation be kept?

A
  • Ice-cold
  • Isotonic
  • A buffer solution
33
Q

Why should the solution be kept ice-cold?

A

To reduce the activity of enzymes that break down organelles.

34
Q

Why should the solution be isotonic?

A
  • 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)
35
Q

Filtration

A
  • 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.
35
Q

Ultracentrifugation

A
  • 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.
35
Q

Why should the solution be buffered?

A

Helps to maintain pH so enzymes don’t denature

36
Q

What is a centrifuge?

A

A machine that separates material by spinning

37
Q

What is the pellet?

A

The thick sediment at the bottom

38
Q

What is the supernatent?

A

The fluid above the sediment

39
Q

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

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

Biology (58 decks)

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