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Biology > TOPIC 2-Methods of studying cells > Flashcards

TOPIC 2-Methods of studying cells Flashcards

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1
Q

What is the equation for magnification?

A

size of image divided by size of real object.

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2
Q

What is the equation for image size?

A

magnification X size of a real object

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3
Q

What is the equation for size of real object?

A

size of image divided by magnification.

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4
Q

How do you convert a millimetre to a micrometre

A

x1000

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5
Q

How do you convert a Micrometer into a nanometer

A

x1000

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6
Q

How do you convert a nanometer into a micrometer?

A

divide by 1000

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7
Q

How do you convert a micrometer to a millimeter

A

divide by 1000

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8
Q

How do you convert cm to mm

A

divide by 10

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9
Q

What is resolution?

A

How well the microscope distinguishes between two points that are close together, if a microscope lens can’t separate two objects, then increasing the magnification will not help.

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10
Q

How do you work out the mean length?

A
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11
Q

What are the two types of microscopes?

A

Optical (light) microscopes
Electron microscope

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12
Q

What is the max resolution of a light microscope?

A

0.2 micrometers (you cannot view organisms that are smaller than 0.2 micrometers)

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13
Q

What organelles can you not see in a cell through an optical microscope?

A

ribosomes, endoplasmic reticulum and lysosomes (may or may not be able to view mitochondria)

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14
Q

What is the max magnification of a light microscope?

A

x1500

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15
Q

What is the maximum resolution of the electron microscope?

A

0.0002 micrometres

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16
Q

What is the maximum magnification of the electron microscope?

A

X1500000

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17
Q

What colour of image does an electron image make?

A

Black and white but are often coloured by a computer

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18
Q

What are the two types of electron microscopes?

A

-Transmission electron microscopes
-Scanning electron microscopes

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19
Q

How do TEMs focus?

A

They use electromagnets to focus a beam of electrons which are transmitted through the specimen

20
Q

Why do some parts of the images look darker than others?

A

Denser parts of the specimen absorb more electrons

21
Q

How do SEMs form an image

A

Scan a beam of electrons across the specimen knocks off electrons from the specimen which are gathered in a cathode ray tube to form an image

22
Q

What is the advantage of a TEM?

A

-Give high-resolution images so can show small images

23
Q

What is an advantage of SEMs?

A

-Can be used on thick specimens
-Can be 3D

24
Q

What is the disadvantage of TEMs?

A

-Can only be used on thin specimens
-Can only be used on non-living specimens as they need to be kept in a vacuum

25
Q

What is the disadvantage of SEMs?

A

-Give lower-resolution images than TEMs
-Can only be used on non-living organisms

26
Q

How do you prepare a temporary mount (a wet 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 (the specimen needs to let light through it for you to be able to see it clearly under the microscope-so if you have quite a thick specimen you need to take a thin slice)
  3. Add a drop of a stain, stains are used to highlight objects in a cell
  4. Add the coverslip (to protect the specimen) carefully tilt and lower it using a mounting needle so you do not get any air bubbles as they will obstruct your view of the specimen
27
Q

What are microscope artefacts?

A

Things that you can see down the microscope that aren’t part of the cell or specimen that you’re looking at…

28
Q

Give some examples of microscope artefacts?

A

-Dust
-Air bubbles
-Fingerprints
-Inaccuracies caused by squashing and staining the sample

29
Q

When are artefacts usually made?

A

During the preparation of the speciamn

30
Q

Where are artefacts usually common??

A

In electron micrograps because the specimans needs a lot of preparation before you can view them under the microscope

31
Q

How did the first scientists differentiate between artefacts and organelles?

A

By repeatedly preparing specimens in different ways (if an object could be seen in only one preparation technique, then it’s more likely to be an artefact)

32
Q

What are the stages in cell fractionation?

A

-Homogenization
-Filtration
-Ultracentrifugation

33
Q

What are two ways homogenization can be done?

A

-By vibrating the cells
-Grinding the cells up in a blender

34
Q

Why do the cells need to be broken up??

A

It breaks up the plasma membrane and releases the organelles into solution

35
Q

Why must the solution be kept ice cold?

A

To reduce the activity of enzymes that break down organelles and so the organelles do not start self-digesting

36
Q

Define isotonic

A

When a solution has the same concentration of chemicals as the cells being broken down

37
Q

Why does the solution need to be isotonic?

A

To prevent damage to the organelles through osmosis

38
Q

Why should a buffer solution be added?

A

To maintain the pH

39
Q

Why are the homogenized cell solution filtered?

A

To separate any large cell debris or tissue debris such as connective tissue from the organelles

40
Q

How is the solution filtered?

A

Through a gauze

41
Q

Why do the organelles pass through the gauze?

A

They are much smaller than the debris

42
Q

Why is ultracentrifugation used?

A

To separate a particular organelle from the others

43
Q

What order do the organelles separate out in?

A

1.Nuclei
2.Chloroplasts
3.Mitochondria
4.Lysosomes
5.Endoplasmic reticulum
6.Ribosomes

44
Q

What is the first step in Ultracentrifugation??

A

1.The cell fragments are poured into a tube.
2.The tube is put in the centrifuge and is spun at a low speed.
3. The heaviest organelles (nuclei) are flung to the bottom of the tube.
4.They form a thick sediment at the bottom of the pellet.
5.The rest of the organelles stay suspended in the fluid above the sediment which is known as the supernatant

45
Q

What is the second step in ultracentrifugation?

A

1.The supernatant is drained of a poured into another test tube
2.The new test tube is spun at a higher speed.
3.The heavier organelles form a pellet at the bottom of the tube.
4.The supernatant containing the rest of the organelles is drained off and spun in the centrifuge at an even higher speed.
5.The process is repeated at higher and higher speed until eventually all the organelles are separated out, each time the pellet at the bottom of the tube is made up of lighter and lighter organelles

46
Q

Why is cell fractionation used?

A

If you wanted to look at organelles under the microscope you would need to separate them out first

Biology (50 decks)

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