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A Level Biology OCR A > cell structure > Flashcards

cell structure Flashcards

Chap 2

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1
Q

What is sample preparation?

A

When samples and specimens are prepared for examination through light microscopy

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2
Q

What are the 4 methods that can be used for sample preparation?

A

Dry mount
Wet mount
Squash slides
Smear slides

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3
Q

Dry mount dis/ad?

A

Quick & easy
Specimen is dried out so dies

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4
Q

Wet mount ad?

A

Prevents dehydration and distortion
Can view live specimen

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5
Q

Squash slides ad?

A

Can view all cell content at once

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6
Q

Dry mount method?

A

Solid specimen is cut into slices through ‘sectioning’
Once prepared, it is placed on a slide and covered with a cover slip

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7
Q

Wet mount method?

A

Specimens are suspended in liquid (water or immersion oil)
Then, the cover slip is placed at an angle

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8
Q

Squash slides method?

A

A wet mount is prepared
Then, a lens tissue is used to press down cover slip to slide

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9
Q

Smear slides method?

A

The edge of the slide is used to smear sample into a thin coat
Then the cover slip is placed on top

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10
Q

What are 4 steps to producing a slide? (Elaborate on first and last?)

A

Fixing (chemical preserves specimen)
Sectioning
Staining
Mounting (put on slide w/ coverslip)

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11
Q

How to stain a slide?

A

Air dry slide’s stain
Heat-fix by passing thru a flame
Specimen will adhere & absorb stain

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12
Q

What do stains do?

A

Increase contrast (of cell components)

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13
Q

How do gram negative stains work? Examples?

A

Repel neg material in cells and sit around cell, making components stand out
Nigrosin & Congo red

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14
Q

How do gram positive stains work? Examples?

A

Pos stain attracted to neg material in cytoplasm
Crystal violet & methylene blue

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15
Q

What is differential staining? 2 types?

A

Can identify 2 separate organisms and 2 separate organelles in 1 organism
Gram staining
Acid-fast staining

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16
Q

How do acid-fast stains work? (5 points)

A
  • red dye is added to all bacteria
  • bacteria washed w/ acid but bacteria w/ waxy cell walls like mycobacteria hold onto red dye
  • blue counterstain applied to all
  • other bacteria pick up blue
  • fast way of identifying diff bacteria
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17
Q

What is the diff between acid-fast and gram stain USES?

A

Gram stains separate bacteria into pos & neg groups whereas acid-fast separates mycobacteria from other bacteria

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18
Q

Light microscope’s vs electron microscope’s resolution

A

Light: 200nm
Electron: 0.1nm

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19
Q

Why do electron microscopes have a higher resolution?

A

Electrons have shorter wavelengths than light so there’s less diffraction (overlapping)

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20
Q

2 scales on the light microscope and where are they?

A

Stage micrometer (slide)
Eyepiece graticule (lens)

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21
Q

1 division on the stage micrometer=…

A

10 micrometres

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22
Q

Contrast

A

the difference in colour between 2 objects

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23
Q

Max mag of light microscope

A

x1500

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24
Q

What is the function of the eyepiece graticule?

A

To find calibration factor of specimen

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25
Q

Why is light mag capped?

A

At higher mags, res is too low and detail not seen

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26
Q

Artefacts? eg?

A

artificial structures introduced during prep eg air bubbles

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27
Q

Fluorescent tagging

A

Tagging a fluorescent dye to a molecule to increase its contrast and make it viewable

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28
Q

Why electron microscopy black and white?

A

Electron beams only have 1 wavelength so not all wavelengths of visible light

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29
Q

2 advantages of the 4 types of microscope

A

Light: coloured, live
Laser scanning confocal: coloured, live
TEM: highest res, inner cell
SEM: 3D

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30
Q

Which microscopy requires fluorescent tagging?

A

Laser scanning confocal

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31
Q

Limitation of TEM

A

Only works on thin and dead specimens

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32
Q

Limitations of SEM (2)

A

Lower res than TEM
Only scans surface

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33
Q

Limitation of Light

A

Low mag and res

34
Q

Limitation of laser scanning confocal (2)

A

Time consuming due to stacking layers
The laser can photo bleach and damage specimens

35
Q

Which microscope has the highest res?

A

TEM

36
Q

Principles of laser scanning confocal microscope (2)

A
  • laser scans dyed specimen (and so images may be COLOURED)
  • layers can be stacked to form 3D image
37
Q

Principles of TEM (2)

A
  • electrons transmitted thru specimen
  • denser parts absorb more e-
  • denser parts appear darker
  • electrons have a short wavelength so high res
38
Q

Principles of SEM (3)

A
  • electrons knock off electrons from specimen
  • electrons gathered in cathode ray tube
  • 3D image is only the surface
39
Q

3 functions/advantages of an organelle

A
  • creates distinct environment in cell
  • easier for structures to function
  • helps metabolism as metabolism requires enzymes that have different optimum conditions
40
Q

Nucleus function (2)

A
  • contains DNA which will direct protein synthesis
  • controls metabolism
41
Q

Nuclear envelope structure (2)

A
  • double membrane
  • nuclear pores
42
Q

Nuclear envelope function (2)

A
  • protects nucleus
  • exports RNA molecules
43
Q

Nucleolus function

A

produces ribosomes (by combining rRNA and proteins)

44
Q

Mitochondria structure (2)

A
  • inner membrane folds to make cristae
  • inner fluid called matrix
45
Q

Mitochondria function (2)

A
  • produces ATP molecules (energy)
  • produces own enzymes (eg for respiration) and reproduces using mitochondrial (mt)DNA
46
Q

Vesicle structure

A

Membranous sacs of fluid

47
Q

Vesicle function

A

store and transport cell material

48
Q

What are lysosomes and what does its structure allow?

A
  • specialised vesicles with hydrolytic enzymes THAT BREAK DOWN WASTE
  • spherical sacs surrounded by a single membrane, which prevents other structures being damaged from enzyme activity
49
Q

Lysosome function (2)

A
  • breaks down waste
  • breaks down engulfed pathogens
50
Q

Cytoskeleton structure (3 components)

A
  • microfilaments
  • microtubules
  • intermediate fibres
51
Q

Cytoskeleton function

A

controls organelle movement/holds them in place

52
Q

Microfilaments structure and what does it allow it do?

A

contractile fibres made from actin protein (which allow it to change length and move in the cell)

53
Q

Microtubules structure

A

tubules polymerised from globular tubulin proteins (which allow it to change length and move in the cell)

54
Q

Microfilaments function (2)

A
  • controls cell movement
  • controls cell contraction (in which the cell splits) in cytokinesis
55
Q

Microtubules function (2)

A

forms scaffold like structures which:
- controls cell movement
- form spindle fibres that segregate chromosomes in cell division

56
Q

Intermediate fibres function

A

gives cell mechanical strength

57
Q

Centriole structure

A
  • made from microtubules
  • centriole + centriole= centrosome
58
Q

Centriole/centrosome function

A

gathers and organises spindle fibres

59
Q

Flagella structure

A

whip like long extensions

60
Q

Flagella function (2)

A
  • enables cell motility
  • sensory organelle that detects chemical changes
61
Q

Cilia structure

A

hair like short extensions

62
Q

Mobile cilia function and eg?

A

beat in rhythmic manner to create a current that moves fluids/objects (eg in trachea w mucus)

63
Q

Stationary cilia function and eg?

A

sensory organelle (eg nose)

64
Q

Endoplasmic reticulum structure and what is it connected to?

A

Network of membranes enclosing flattened sacs of cisternae which are covered with ribosomes
Outer membrane of nucleus

65
Q

Smooth ER function

A

lipid and carb synthesis and storage

66
Q

Describe how DNA is
packaged in eukaryotes
(3)

A
  • DNA is coiled around proteins called histones
  • which form chromatins
  • which are supercoiled/condensed into chromosomes
67
Q

What are the 6 steps in protein synthesis?
(HINT transcription + translation are 3 points, movement is 3 points)

A
  • Gene for protein transcribed onto mRNA molecule in nucleus
  • mRNA molecule leaves thru pores
  • attaches to ribosomes in rough ER which read the instructions on mRNA to assemble the protein (translation)
  • rough ER process proteins into vesicles which will fuse with golgi apparatus
  • golgi apparatus modify and package proteins into (different) vesicles
  • vesicles fuse with cell surface membrane and release protein via exocytosis
68
Q

TEM res vs SEM range

A

TEM: 0.05-2nm
SEM: 5-50nm

69
Q

Compare the structures of prokaryotes and eukaryotes (6)

A

SIM
- Both have ribosomes
- Both have a cytoskeleton
- Both have a cell-surface membrane
DIFF
- Pro have 70S ribosomes whereas Euk have 80S ribosomes
- Pro lack membrane bound organelles whereas Euk do eg mitochondria
- Pro have 1 circular free chromosome whereas Euk have many linear chromosomes

70
Q

Compare DNA organisation in prokaryotes vs eukaryotes (6)

A

PRO
- 1 circular free chromosome
- plasmids (DNA circles)
- no nucleus
EUK
- many linear chromosomes
- associated with proteins called histones (to form chromatins)
- nucleus bound

71
Q

Which cells have a cell wall? What is each one made of? (3)

A

Bacteria- peptidoglycan
Fungi- chitin
Plants- cellulose

72
Q

What is the role of the plasmid? (2)

A

Plasmids are small
loops of DNA (1)
sometimes present in
prokaryotes. They often
contain antibiotic
resistance genes (1)
and are used in genetic
engineering.

73
Q

What is the role of:
pili
capsules
mesosomes

A
  • attachment to other cells (eg for sexual reproduction)
  • extra protection
  • helps form new cell walls
74
Q

Mag vs res definition

A

the number of times larger an image is compared to the object vs the ability to identify 2 separate objects

75
Q

Diameter of pro vs euk

A

pro: 0.1-10 micrometres
euk: 10-100 micrometres

76
Q

4 things that a plant cell has that an animal cell doesn’t? explain the new one?

A
  • amyloplast: small membrane bound organelle producing & storing starch
  • cell wall
  • chloroplast
  • vacuole
77
Q

4 structures of a chloroplast and explain? how does this contribute to overall function?

A
  • double membrane
  • stroma: fluid
  • grana: stacks of thylakoid membrane connected to lamellae membranes
  • thylakoid membrane: flattened sacs

Overall function: network of internal membranes have a large SA to contain more chlorophyll to increase rate of photosynthesis

78
Q

What are the 3 structures of the plant cell wall and how do they help its function?

A
  • cellulose= strength
  • cell contents push against wall= turgid/support
  • plasmodesmata (pores)= permeability + pathogen defence
79
Q

What is the evidence for the endosymbiotic theory?

A

Mitochondria and chloroplasts:
- have own DNA
- have ribosomes (like pro’s)
- double membrane (inner one like pro’s)
- same size as bacteria and susceptible to an antibiotic

80
Q

How did endosymbiosis occur? (3)

A

Ancestral prokaryote gains infolding of cell membrane
which aerobic bacterium enter via endocytosis
to form ancestral eukaryotes

A Level Biology OCR A (8 decks)

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