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A level Biology > Studying cells > Flashcards

Studying cells Flashcards

1
Q

Methods of studying cells

A

Microscopy
Cell fractionation

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2
Q

What is cell fractionation?

A

A method of studying cell organelles by separating them from the cell

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3
Q

Step 1 of cell fractionation

A

Take a sample of cells and HOMOGENISE it in a blender with a buffer solution to break up cells (NOT ORGANELLES) and release organelles that are being studied

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4
Q

Properties of buffer solution

A

Cold
pH constant
Water potential in solution same as inside the cell (isotonic)

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5
Q

Why does the buffer solution have to be cold?

A

To keep enzyme activity low so destructive enzymes prevented from engulfing

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6
Q

Why does the buffer solution have to have a constant pH?

A

Because if pH changed, then the enzymes in organelles would denature and damage organelles

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7
Q

Why does the buffer solution have to have same water potential as inside cell

A

Prevents osmosis of water into and out of organelles causing them to swell or shrink respectively = damage

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8
Q

What is left after homogenisation?

A

The homogenate. Contains unbroken cells and different density organelles

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9
Q

What is done with the homogenate?

A

Put in a centrifuge to spin at relatively high speed
Balance out with same volume of sample in other tube

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10
Q

What is left after spinning at relatively high speed?

A

The larger organelles which experienced more force sunk to bottom (pellet)
But mid-small organelles remain in solution, not spun fast enough to sink (supernatant)

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11
Q

What is done with the supernatant and pellet?

A

Pour out supernatant so first tube is left with pellet of separated high density organelle

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12
Q

Why is the supernatant spun at increasingly high speeds?

A

So smaller density organelles are separated from solution and form a pellet to be separated

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13
Q

What should pellets be kept at?

A

Ice cold temperature to reduce enzyme activity

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14
Q

Will all organelles be separated perfectly?

A

No because pellets always contain traces of others

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15
Q

High density organelles

A

Nucleus
Golgi
Endoplasmic reticulum
Cell surface membranes

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16
Q

High- mid density organelles

A

Mitochondria

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17
Q

Mid- low density organelles

A

Lysosomes

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18
Q

Low density organelles

A

Ribosomes

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19
Q

Light microscopes

A

Using visible light to pass through specimens to view layers of cells with organelles

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20
Q

Eyepiece lens

A

View specimen here w eye piece graticule

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21
Q

Coarse lens

A

Moves stage up and down to focus it

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22
Q

Objective lens

A

Changes magnification by switching lens

23
Q

Fine focus

A

Fine tune focus without moving the stage

24
Q

Resolving power

A

Ability to distinguish between 2 separate objectives
Minimum distance between 2 objects where they are still seen as 2 separate objects

25
Q

Magnification on a scale bar

A

Measure length of scale bar
Find what actual size it represents
Mag = image size/actual size

26
Q

Actual size of an image

A

Find conversion of length of scale bar to actual size it represents
Measure image size of image
Use conversion to find its actual size

27
Q

Magnification =

A

Image size/actual size

28
Q

Why do we need to calibrate the stage micrometer?

A

Because we are unsure of the the scale on stage micrometer so can not be used to measure organelles/cells

29
Q

What item do you use to calibrate an eyepiece graticule?

A

A stage micrometer

30
Q

How to calibrate eyepiece graticule with stage micrometer

A

View stage micrometer under same magnification you will measure cell in
Ensure division of stage micrometer is known, eg each small division =1um
Find point where divisions line up to make conversion
Measure organelle with eyepiece graticule and use this scale

31
Q

What type of image does light microscope produce?

A

2D image
Able to view natural colour

32
Q

Magnification of a light microscope calculate by?

A

The eyepiece lens (always same in one microscope) x objective lens chosen

33
Q

Magnification of light microscope

A

Max of 1000x

34
Q

Is light microscope able to view living specimens?

A

Yes

35
Q

Resolution of light microscope

A

Low = around 200nm
So if objects less than 200nm they are not distinguished as 2 separate objects

36
Q

2 types of electron microscope

A

Transmission (TEM)
Scanning (SEM)

37
Q

How do electron microscopes work?

A

Using electron beams instead of light

38
Q

Transmission electron microscope works by?

A

Passing electron beams through a specimen then producing image on a screen

39
Q

Image produced by TEM

A

2D image
In black and white

40
Q

Can TEMs view living specimens?

A

No, because beams pass through species in a vacuum

41
Q

What must specimens be in TEMs?

A

Thinly sliced
Dead

42
Q

How do SEMs work?

A

Electrons don’t pass through specimen yet scattered on the surface of the specimen to produce an image once detected

43
Q

Image produced by SEMs

A

Produces 3D image
In black and white

44
Q

Magnification of TEMs

A

Very very high
High resolving power

45
Q

What is a temporary mount?

A

Placing a specimen on a slide with a drop of water then coverslip on top
Held by surface tension

46
Q

How are temporary mounts made?

A

Place a drop of water on a glass slide
Use forceps to place a THIN LAYER or specimen on it
Lower coverslip at an angle to reduce air bubbles

47
Q

When using a light microscope, how do you find the mean number of certain organelles in a cell?

A

Select a large number of cells at random
Count the number of organelles in each cell
Divide this total by number of cells selected

48
Q

Why do light microscopes have lower resolving power than electron microscopes?

A

Because light has a longer wavelength than electron beams

49
Q

Advantages of light microscope

A

Can see living specimens
Easier to prepare specimens
Variety of coloured stains

50
Q

Disadvantages of light microscope

A

Low resolution so less detailed and unable to view smaller components

51
Q

Advantages of TEM

A

Very high resolution at a higher magnification
Detail of organelles

52
Q

Disadvantages of TEM

A

dead specimens in a vacuum
difficult to prepare by creating very thin specimens
produces black and white image
artefacts spoil the image possibly

53
Q

Advantages of SEM

A

3D images can show structural formation of cells

54
Q

Disadvantages of SEM

A

Specimens dead
Hard to prepare
Black and white image

A level Biology (32 decks)

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