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OCR Biology > Module 2: Cell Structure > Flashcards

Module 2: Cell Structure Flashcards

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1
Q

Magnification is determined by …

A

Type of lens, distance between lens and object, size of the eyepiece.

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2
Q

How to increase magnification?

A

Higher power objective lens that will decrease the distance between the lens and object.

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3
Q

Increasing magnification will …

A

Decrease resolution

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4
Q

Define resolution.

A

Minimum distance between 2 points where they’re seen as separate.

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5
Q

Resolution can be limited by …

A

Diffraction of light as it passes through samples and lenses.

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6
Q

What is diffraction?

A

Tendency of light waves to bend as they pass close to the edges of a specimen.

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7
Q

The light reflected from individual structures can …

A

Overlap, so they’re no longer seen as separate and detail is lost.

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8
Q

Resolution can be increased by …

A

Using a beam of electrons - x1000 shorter wavelength than light. Electron beams are still diffracted, but individual beams can come much closer before they overlap.

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9
Q

1000 micrometres

A

1 mm

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10
Q

Order of microscope discovery?

A

Light, electron (TEM/SEM), laser scanning confocal microscope.

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11
Q

Microscopes allow us to discover …

A

Function of cells/organs, chromosomes dividing, investigating diseases.

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12
Q

All microscopes require a …

A

Radiation wave (light/electrons/laser beam) to be directed to the sample.

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13
Q

Define cell theory.

A

How scientific theories change overtime as new evidence is gained and knowledge increases.

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14
Q

What does the cell theory state?

A

‘Both plant and animal tissues are composed of cells, cells are basic unit of all life, cells only develop from existing cells’

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15
Q

Cell theory wasn’t fully developed before 19th century because …

A

Magnification was too low to see and identify cells.

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16
Q

How does an optical light microscope work?

A

White light passes through the specimen from underneath through the objective and eyepiece lens and into the observers eye where the brain forms an image.

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17
Q

Each lens is magnified up to …

A

x2000

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18
Q

Objective lens …
Eyepiece lens …

A

Focuses the light and magnifies the image.
Magnifies the image.

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19
Q

What is the condenser lens?

A

Focuses light onto the specimen, doesn’t magnify it.

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20
Q

What is the diaphragm?

A

Controls amount of light reaching the specimen.

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21
Q

Why is magnification and resolution low for light microscope images?

A

Cells don’t absorb a lot of light and light has a longer wavelength so more diffraction as it passes through the sample.

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22
Q

Magnification and resolution of light microscope?

A

x1500, 0.2 micrometres.

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23
Q

Structures you can’t see under a light microscope?

A

ER, ribosomes, lysosomes, internal structures within cells.

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24
Q

Steps to using a light microscope?

A
  1. Clip slide onto stage, select lowest power objective lens.
  2. Use coarse adjustment knob to move OL to just above the slide.
  3. Look down at eyepiece and adjust focus using fine adjustment knob, until a clear image forms.
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25
Q

What does the fine adjustment knob do?

A

Moves lens away from the slide.

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25
Q

Pro’s and Con’s of light microscopes?

A

Pro - can be living or dead specimen, small and portable, sample in colour, cheaper.
Con - lower mag and resolution, only shows 2D shape.

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26
Q

Stains in light microscopes are …

A

Dyes

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26
Q

What is the purpose of stains?

A

Increase contrast as components take up stains at different degrees, so you can easily visualise different structures.

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27
Q

Iodine stains starch …
Eosin stains cytoplasm …

A

Blue/black
Pink

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27
Q

Differential staining is when …

A

Multiple stains are used together. Each stain is picked up by different structures so each part can be identified differently.

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28
Q

What to ensure before staining?

A

That the stain used isn’t toxic to the live specimen.

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29
Q

Gram+ bacteria …
Gram- bacteria …

A

Has a thick cell wall to retain a stain.
Has a thin murein cell wall that doesn’t retain the stain.

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30
Q

List the sample preparation techniques.

A

Fixation, sectioning/embedding in resins, dehydration, staining, mounting.

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31
Q

Fixation involves …

A

Using chemicals to preserve specimens and prevent decomposition. Could also freeze.

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32
Q

Sectioning involves …

A

Dehydrating specimens with alcohol and placed in a resin to form a hard block, which can then be sliced thinly with a knife.

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32
Q

Dehydration prevents …

A

Vaporisation of water in a vacuum.

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32
Q

Specimens are often treated with stains or …

A

Heavy metals to show different structures.

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33
Q

Mounting involves …

A

Securing the specimen to a microscopic slide and cover slip on top.

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33
Q

Scientific drawing rules.

A

Title, magnification, date. Smooth continuous lines, no shading, labels shouldn’t cross, no arrow head.

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34
Q

Define mount.

A

Where your specimen is placed on a microscopic slide.

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35
Q

Explain how a dry mount is prepared.

A

Specimen cut into a thin slice with a blade (sectioning). Place it in the middle of a clean slide using tweezers. Place a cover slip on top.

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36
Q

Purpose of a cover slip?

A

Holds the specimen in place and prevents damage.

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37
Q

What is dry mount often used with?

A

Hair, pollen, parts of insects, plants.

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38
Q

Why must specimens be thin?

A

So light can pass through and details can be seen.

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38
Q

Explain how to prepare a wet mount.

A

Put a drop of water in the middle of a clean slide using a pipette. Using tweezers to place specimen in water, and place a cover slip from one end at an angle, avoiding air bubbles. Put a drop of stain on one end of the cover slip then put a paper towel on the opposite edge, which draws the stain under and across the cover slip.

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39
Q

When do you use a wet mount?

A

Specimens in liquid such as water. It can be living like aquatic organisms.

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40
Q

Why do we need to avoid air bubbles?

A

Obstruct the view of the sample.

41
Q

What is a smear slide?

A

Type of wet mount used for blood samples.

42
Q

How to create a smear slide?

A

Place sample liquid at edge of microscopic slide. Use another slide to make a 45 degree angle, moving towards the sample and smearing it across the slide to create an even coating.

43
Q

How is a squash slide prepared?

A

Wet mount is prepared, then a lens tissue is used to greatly press down the cover slip.

44
Q

Define calibrate.

A

To find an unknown length.

45
Q

What is an eyepiece graticule?

A

Ruler with no units and remains unchanged with sample size, but increases as mag increases.

46
Q

Eyepiece graticule is slotted into the …

A

Eyepiece.

47
Q

What is a stage micrometer?

A

Microscopic slide with a tiny scale with units (micrometres) which is used to work out the no. divisions on the eyepiece at a particular magnification.

48
Q

1 division on stage micrometer =
1 whole divisions on stage micrometer =

A

0.1 mm
1 mm

49
Q

Steps to calibrate an eyepiece graticule?

A
  1. Select wanted mag and objective.
  2. Place stage micrometer on stage and line up the scales of the micrometer and eyepiece graticule.
  3. Count no. divisions on eyepiece equivalent to each division on the stage micrometer.
  4. Calculate the length of 1 division of the eyepiece in micrometres.
50
Q

To measure the size of the specimen …

A

Replace the stage micrometer with cell. You can then use the eyepiece graticule to measure the length of cells in micrometres.

51
Q

Actual size =

A

number of divisions x length of 1 division

52
Q

Define cell size.

A

Measure of volume/SA of a cell.

53
Q

Larger cells may indicate …
Smaller cells may indicate …

A

Mature, differentiated cell.
Younger, more actively dividing cell.

54
Q

Cell size may remain constant during …
Cell size would increase during …

A

Cell division.
Cell growth as it takes in more material and grows in volume.

55
Q

Explain how LSCM works.

A

Laser beams scan the specimen. Light is absorbed by fluorescent dyes and is re-radiated back from the specimen as a longer wavelength. The light is focused through a pinhole onto a detector to produce a magnified image.

56
Q

What happens in an electron microscope?

A

Electrons penetrate the sample and interact with the atoms in it.

57
Q

Why do electron microscopes have a better resolution than light?

A

Shorter wavelength than light waves.

58
Q

List the sample preparation techniques for an electron microscope.

A

Fixation, dehydration, embedding in resins, staining with heavy metals.

59
Q

What is staining with heavy metals?

A

With uranium or lead, unlike light microscopy which are dyes. Metal ions cause electrons in the specimen to scatter, causing some areas of the specimen to appear darker than others.

60
Q

Why is there a vacuum in an electron microscope?

A

Avoids electron scattering and ensures electron beams travel in straight lines.

60
Q

Pro’s and con’s of electron microscopes?

A

Pro - Higher mag and resolution, 3D structure so you can see internal structures.
Con - More expensive to buy/operate, specialist training, electron beam can damage samples so has to be non-living, needs a vacuum, sample preparation takes time.

61
Q

Define artefact.

A

Structural detail visible in the microscopic image that isn’t a natural part of the specimen.

62
Q

What are artefacts caused by?

A

Distortion during preparation like bubbles that get trapped under the cover slip. This can happen in both light and electron microscopes.

63
Q

Examples of artefacts?

A

Loss of continuity in cell membranes, empty spaces in cytoplasm.

64
Q

How does a TEM work?

A

Beam of electrons is transmitted THROUGH the sample and produces a 2D image. You can see stacked grana inside a chloroplast.

65
Q

TEM shows the …

A

Cross section of the sample.

65
Q

Preparation techniques for TEM?

A

Set in resin and may be stained.

66
Q

Denser parts of an image …

A

Absorb more electrons, making them look darker on micrographs.

67
Q

In less dense regions …

A

Electrons can easily pass through, making them look lighter on an electron micrograph.

68
Q

Pro’s and con’s of TEM?

A

Pro - higher resolution and mag than TEM.
Con - must be in a vacuum so dead specimens, thin tissue only as thick tissue easily absorbs electrons and don’t get good images.

69
Q

The angle at which specimens are cut …

A

Can affect appearance.

70
Q

How does an SEM work?

A

Directs a beam of electrons across the sample. Shows the surface of the sample.

71
Q

Sample preparation in SEM?

A

Coated in heavy metal.

72
Q

Pro’s and con’s of SEM?

A

Pro - 3D, can be used on thick sample.
Con - Lower resolution and mag than TEM.

73
Q

What is a cell?

A

Basic unit of life performing necessary functions.

74
Q

Some cells look structurally different under a microscope as …

A

Cells may be cut in different angles/shapes e.g. transverse/longitudinal. Or may have been sliced thinly.

75
Q

Define tissue.

A

Group of cells with the same function.

76
Q

Define organ.

A

Group of different tissues that have specific functions.

77
Q

Define ultrastructure.

A

Fine detail in a cell observed only with an electron microscope.

78
Q

Most organelles in eukaryotic cells are … except the …

A

Membrane bound, nucleolus.

79
Q

What does the nucleus contain?
Function of the nucleus?

A

Genetic info in the form of DNA.
Controls the cells activity and replication.

80
Q

Define gene expression.

A

Process where specific genes are activated to produce a required protein.

81
Q

Genetic info in the nucleus is in what 2 forms?

A

Chromatin and nucleolus.

82
Q

How is chromatin formed?

A

When DNA winds around histones to give a compact shape. This then coils and condenses to form chromosomes, so they fit in the cell nucleus.

83
Q

When this happens …

A

Length of DNA is reduced so can pack in a smaller space. Prevents DNA from damage.

84
Q

DNA stores instructions to make …

A

Proteins.

85
Q

The nucleolus is made up of …

A

Proteins and RNA.

86
Q

Function of the nucleolus?

A

Produces ribosomes - RNA is used to produce rRNA, which is combined with proteins to form ribosomes necessary for protein synthesis.

87
Q

What happens to the ribosomes after?

A

Move out of the nucleus to latch onto the RER where they produce proteins.

88
Q

Nucleus is surrounded by a …

A

Double membrane called a nuclear envelope - protects DNA from damage in the cytoplasm.

89
Q

Why is DNA transcribed to RNA in the nucleus?

A

DNA is too large to leave the nucleus to the site of protein synthesis in the cytoplasm. RNA can leave the nuclear pore.

90
Q

Where are plasma cells found?
What are they made of?

A

Blood and lymph.
Protein.

91
Q

What is the plasma membrane made of?

A

Proteins and lipids. Contain receptors that respond to chemicals like hormones.

92
Q

What does the cytoplasm store?

A

Water, salts and where metabolic reactions occur.

93
Q

Animal cells can be …
Animal cells are …

A

Unicellular or multicellular.
Heterotrophic, so they can’t generate their own food.

94
Q

Plant cells are only …
Plant cells are …

A

Multicellular.
Autotrophic, so they do make their own food by photosynthesis.

95
Q

Function of ribosomes?
Where are they found?

A

Create proteins from amino acids.
Cytoplasm or on the RER.

96
Q

What are ribosomes made up of?
Surrounded by a membrane?

A

rRna and proteins.
NO.

97
Q

Function of the cell wall?

A

Gives cell shape, prevent cell bursting due to pressure, allows turgidity, protects against pathogens.

98
Q

Cell wall is also …

A

Freely permeable, so soluble substances can easily pass through its pores. Unlike the plasma membrane that forms a phospholipid bilayer.

99
Q

Fungal cell walls made of …

A

Chitin.

100
Q

Function of mitochondria?

A

Produce ATP through aerobic respiration. Bound by a double membrane called an envelope.

101
Q

Function of amyloplasts?

A

Synthesise and store starch in plant cells only. MEMBRANE bound.

102
Q

Adaptations of mitochondria?

A

Large SA and inner membrane is folded into projections called cristae, which contain all enzymes needed to produce ATP. It’s filled with matrix fluid.

103
Q

Explain the structure of a chloroplast.
(check cell diagrams in notes)

A

Network of double membranes called a thylakoid which are stacked to form grana. Grana are joined by membranes called lamellae. Also have starch grains to store photosynthesis products.

104
Q

Where are the chlorophyll pigments?

A

In the grana.

105
Q

Where are chloroplasts found?

A

Stems and leaves, but not roots.

106
Q

Adaptation of chloroplast?

A

Thylakoid/internal membrane gives a large SA for enzymes and proteins needed for photosynthesis.

107
Q

Both mitochondria and chloroplasts have their own …

A

DNA and ribosomes, so can make their own proteins and reproduce themselves.

108
Q

What is the endosymbiosis theory?

A

OCR Biology (6 decks)

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