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OCR A-Level Biology > Chap 2 - Cell Structure > Flashcards

Chap 2 - Cell Structure Flashcards

1
Q

Define cell

A
  • smallest structural & functional unit of an organism.
  • every organism is made up of at least one cell
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2
Q

What is a eukaryotic cell?

A

cells that contain membrane-bound organelles (mitochondria, true nucleus, chloroplasts)

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3
Q

Define ultrastructure

A
  • structure of a cell in fine detail
  • ultrastructure images are usually from TEM
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4
Q

Outline the structure of the nucleus

A
  • DNA is surrounded by double membrane - nuclear envelope - encloses and protects the DNA
  • nuclear envelope contains nuclear pores - allows molecules to move in and out (mRNA move in/out carrying genetic info, not DNA as it is too big)
  • DNA is found in a complex - chromatin (DNA associated with histones - proteins) which coils and condenses to form chromosomes
  • nucleolus - responsible for ribosome production, composed of proteins and RNA
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5
Q

Outline the function of the nucleus

A
  • contains the DNA of the cell
  • directs protein synthesis of all proteins required by the cell
  • controls metabolic activity of the cell (many of the proteins are enzymes necessary for metabolism to take place)
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6
Q

Outline the function of the RER

A
  • responsible for synthesis and transport of proteins
  • has ribosomes bound to the surface
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7
Q

Outline the structure of the endoplasmic reticulum

A
  • network of membranes throughout the cytoplasm enclosing flattened sacs - cisternae.
  • connected to the outer membrane of the nucleus
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8
Q

Outline the function of the SER

A
  • responsible for lipid and carbohydrate synthesis and storage
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9
Q

Outline the structure and function of the Golgi apparatus.

A
  • stack of membrane bound cavities (cisternae)
  • modifies proteins and packages them into vesicles for transport (modifying could involve changing/rearranging the protein strcuture or attaching diff. molecules to protein)
  • does NOT contain ribosomes
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10
Q

Outline the structure and function of ribosomes

A

F: the site of protein synthesis

S: can be free floating in the cytoplasm or attached to endoplasmic reticulum forming RER (eukaryotic ribosomes)
- can also be in mitochondria, chloroplasts and prokaryotic cells (prokaryotic ribosomes)
- not surrounded by a membrane
- constructed of RNA made in the nucleolus

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11
Q

Outline the function of mitochondria

A

site of aerobic respiration, generate ATP

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12
Q

Outline the structure of mitochondria

A
  • surrounded by an envelope
  • inner membrane is folded to form structures - cristae
  • liquid inside of inner membrane - matrix
  • have their ‘own’ DNA (mitochondrial DNA) and their own 70S ribosomes
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13
Q

Outline the structure of vesicles

A

membrane bound containers with fluid inside found within cells. (generic term)

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14
Q

Outline the function of vesicles

A
  • involved in internal transport of substances within the cells
  • can also fuse with cell surface membrane to release its contents (excrete)
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15
Q

Outline the structure of lysosomes

A

types of vesicles that contain digestive (hydrolytic) enzymes

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16
Q

Outline the function of lysosomes

A
  • responsible for breaking down food/waste material in cells (incl old organelles) by fusing with a food vacuole or a vesicle containing old organelles
  • responsible for breaking down pathogens ingested by phagocytic cells
  • important role in programmed cell death
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17
Q

Outline the structure of vacuoles

A

larger vesicles, surrounded by a thin membrane and filled with fluid and any molecules they take in

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18
Q

Outline the function of vacuoles

A
  • membrane-bound (selectively permeable membrane around a permanent vacuole in a plant cell - tonoplast), carry a substance
  • permanent vacuoles (in plants - very large) - contain cell sap
  • food vacuoles - temporary - form from plasma membrane, engulf food and lysosome fuses with it to give it enzymes to digest the food
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19
Q

Outline the structure of chloroplasts

A
  • surrounded by an envelope
  • within the envelope - internal network of membranes which form flattened sacs - thylakoids
  • stacked thylakoids - granum (contain chlorophyll pigments) which are joined together by lamellae
  • internal liquid - stroma
  • have their own ribosomes (70S) and DNA to produce their own proteins.
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20
Q

Outline the function of chloroplasts

A

the site of photosynthesis

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21
Q

Outline the structure of plasma membrane

A

phospholipid bilayer with various proteins and cholesterol

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22
Q

Outline the function of plasma membrane

A

controls the entry and exit of substances into and out of the cell

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23
Q

Outline the structure of cell wall

A

made of fibrils of cellulose embedded in a matrix of other molecules

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24
Q

Outline the function of cell wall

A
  • protects the cell from pathogens, gives the cell its shape
  • high tensile strength allows plant cells to become turgid and press against the cell wall, making the cell rigid which supports both the cell and the plant as a whole
  • freely permeable - gaps for important molecules to get thru
  • plasmodesmata are connections of cytoplasm through cell walls and allow transport of substances between adjacent cells
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25
Q

Outline the structure of cytoskeleton

A

network of protein fibers throughout the cytoplasm

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26
Q

Outline the function of cytoskeleton

A
  • support the shape and position of the cell and the organelles within (provide mechanical strength to cells)
  • allow cells to move and the movement of structures within the cell
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27
Q

Outline the structure of centrioles

A
  • component of cytoskeleton in most eukaryotic cells
  • composed of microtubules (9 sets of 3 microtubules)
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28
Q

Outline the function of centrioles

A
  • found at the base of cilia and flagella, thought to play a role in the positioning of them
  • two associated centrioles form a centrosome which is involved in assembly and organisation of spindle fibers during cell div
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29
Q

State 3 similarities between plants and animal cells

A
  • both are eukaryotic (have a true nucleus and membrane-bound organelles)
  • both have a plasma membrane
  • both have mitochondria
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30
Q

State 3 differences between plants and animal cells

A
  • animal cells do not have a cell wall, plant cells do
  • animal cells do not have permanent vacuoles, plant cells do
  • animal cells do not have chloroplasts, plant cells do
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31
Q

Describe the interrelationship between the organelles involved in the production and secretion of proteins.

A
  1. proteins are synthesised on the ribosomes bound to the endoplasmic reticulum.
  2. proteins pass into the cisternae of RER and are packaged into transport vesicles.
  3. transport vesicles containing the proteins move towards the Golgi apparatus via the transport function of the cytoskeleton.
  4. vesicles fuse with the cis face of the Golgi and proteins enter it. Proteins are structurally modified while moving through Golgi’s cisternae before leaving the Golgi apparatus in secretory vesicles from its trans face.
  5. secretory vesicles with proteins move towards and fuse witht he cell surface membrane releasing their contents out of the cell by exocytosis.

(if lysosome enzymes are made, the vesicles turn into lysosomes and exocytosis does not happen)

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32
Q

Define prokaryotic cell

A

cells (unciellular organisms) that do not contain membrane-bound organelles.

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33
Q

List 4 examples of eukaryotic cells

A
  • erythrocyte
  • leucocyte
  • oocyte
  • hepatocyte
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34
Q

List 2 examples of eukaryotic cells

A
  • e. coli
  • streptococcus bacterium
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35
Q

Outline the structure and function of plant cell wall

A
  • found below the slime capsule
  • made out of peptidoglycan (murein)
  • provides protection and support
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36
Q

Outline the structure and function of slime capsule

A
  • outer layer of a prokaryote
  • provides protection from harmful things in the environment, helps bacteria be sticky (adhesive)
  • polysaccharide coating
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37
Q

Outline the structure and function of plant plasma membrane

A

same as an eukaryotic plasma membrane

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38
Q

Outline the structure and function of a prokaryotic flagellum.

A
  • thinner than the equivalent of eukaryotes, no 9+2 arrangement
  • it is attached to the cell membrane by a basal body and rotated by a molecular motor
  • molecular motor causes hook to rotate, creating true propeller motion
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39
Q

Outline the structure and function of the bacterial chromosome.

A
  • located in the cytoplasm, not in a membrane
  • acts as the ‘control center’ of the cell - controls metabolic activity
  • it is a single chromosome which is circular
    DNA is ‘naked’ - not wrapped around proteins
40
Q

Outline the structure and function of the plasmid.

A
  • small circular loops of DNA in addition to the chromosome
  • bacteria swap them with each other - form of sexual reproduction, transferring genes
41
Q

Outline the structure and function of pili.

A
  • hair like appendages found on surface of many bacteria/archaea
  • used for swapping plasmids and help them stick to cells and infect
42
Q

Outline the structure and function of prokaryotic ribosomes.

A
  • site of protein synthesis
  • 70S in prokaryotes (smaller than eukaryotic)
  • found in chloroplasts and mitochondria
43
Q

Compare the size of eukaryotic and prokaryotic cells

A

prokaryotic: 0.1 - 10 micrometers
eukaryotic: 10 - 100 micrometers

44
Q

Compare the nucleus of eukaryotic and prokaryotic cells

A

prokaryotic: no nucleus (nucleoid region)
eukaryotic: membrane-bound nucleus

45
Q

Compare the chromosomes of eukaryotic and prokaryotic cells

A

prokaryotic: single circular chromosome, DNA is not wrapped around histones
eukaryotic: multiple linear chromosomes, DNA is wrapped in histones

46
Q

Compare cell division between eukaryotic and prokaryotic cells

A

prokaryotic: binary fission
eukaryotic: sexual and asexual

47
Q

Compare the endoplasmic reticulum of eukaryotic and prokaryotic cells

A

prokaryotic: /
eukaryotic: involved in protein/lipid/carb synthesis

48
Q

Compare the ribosomes of eukaryotic and prokaryotic cells

A

prokaryotic: 70S type, smaller
eukaryotic: 80S type, larger

49
Q

Compare the mitochondria of eukaryotic and prokaryotic cells

A

prokaryotic: /
eukaryotic: site of aerobic respiration and ATP production

50
Q

Compare the lysosomes of eukaryotic and prokaryotic cells

A

prokaryotic: /
eukaryotic: vesicles that contain digestive enzymes

51
Q

Compare the golgi apparatus of eukaryotic and prokaryotic cells

A

prokaryotic: /
eukaryotic: involved in modifying proteins

52
Q

Compare the chloroplasts of eukaryotic and prokaryotic cells

A

prokaryotic: /
eukaryotic: plant cells have them - site of photosynthesis

53
Q

Compare the cell wall of eukaryotic and prokaryotic cells

A

prokaryotic: made of peptidoglycan
eukaryotic: in plants made of cellulose, in fungi made of chitin

54
Q

Compare the flagellae of eukaryotic and prokaryotic cells

A

prokaryotic: able to rotate (motor like motion)
eukaryotic: unable to rotate only whips back and forth

55
Q

Compare envelope-surrounded organelles of eukaryotic and prokaryotic cells

A

prokaryotic: /
eukaryotic: nucleus, mitochondria, chloroplasts

56
Q

State what SEM stands for

A

scanning electron microscope

57
Q

Outline how a SEM works

A
  • beam of electrons is sent across the surface of a specimen and the reflected electrons are collected
  • because electrons are reflected, you can see the specimen’s detailed surface features but not the interior
  • image produced will look 3D and it will not be in color because we are using electrons for imaging, not light
58
Q

State what TEM stands for

A

transmission electron microscope

59
Q

Outline how a TEM works

A
  • beam of electrons in transmitted through a specimen and focused to produce an image
  • because some electrons are able to pass through and some aren’t, we can generate an image of the internal features of the specimen
  • image will look 2D because we are passing electrons through a specimen and it will not be in color as we are using electrons and not light
  • darker = fewer electrons passed through, lighter bits = more electrons passed through
60
Q

Describe in principle what a microscope does

A

enables magnification of an object many times in order to observe structures/organisms which are impossible to see with a naked eye

61
Q

Name 4 different types of microscope.

A
  • light microscope
  • transmission electron microscope (TEM)
  • scanning electron microscope (SEM)
  • confocal laser scanning microscope (CLSM)
62
Q

What is the function of the eyepiece lens?

A
  • the lens the viewer looks through to see the specimen.
  • the eyepiece usually contains a 10X or 15X power lens.
63
Q

What is the function of the arm?

A
  • connects the body tube to the base of the microscope
  • used to safely carry the microscope
64
Q

What is the function of the coarse adjustment knob?

A

brings the specimen into general focus by moving stage up/down

65
Q

What is the function of the fine adjustment knob?

A

fine tunes the focus and increases the detail of the specimen.

66
Q

What is the function of the revolving nosepiece (turret)?

A
  • houses the objective lenses
  • the viewer spins the nosepiece to select different objective lenses
67
Q

What is the function of objective lenses? + give magnification of each

A

lenses closest to the specimen for magnification
- low power obj lens - 4x
- medium power obj lens - 10x
- high power obj lens - 40x

68
Q

What is the function of stage clips?

A

hold the slide in place

69
Q

What is the function of the stage?

A

the platform where the slide is placed

70
Q

What is the function of the iris/diaphragm?

A

adjusts amount of light that reaches the specimen

71
Q

What is the function of the condenser?

A
  • located above the light source
  • concentrate light into a cone of light that illuminates the specimen
72
Q

What is the function of the illuminator?

A
  • the light source for a microscope
  • older microscopes used to use mirrors to reflect light through the bottom of the stage
73
Q

What is the function of the base?

A
  • the base supports the microscope
  • where illuminator is located
74
Q

Outline how a laser scanning confocal microscope works.

A
  • specimen is treated with fluorescent chemical to illuminate/highlight specific structures
  • a single spot of focused light of a specific wavelength is moved across a specimen
  • fluorescence from the components labelled with dye is caused
  • emitted light is filtered through a pinhole apretrure
  • only light radiated from very close to the focal plane is detected
75
Q

Describe how to produce a temporary wet mount of living tissue.

A
  • put 1-2 drops of water/stain over the specimen
  • put coverslip down at 45deg angle and slowly lay it down (coverslip gets rid of air bubbles, slows drying out)
  • wick away any excess liquid
76
Q

Explain why slide preparations need to be thin.

A
  • so light can shine through it
  • details can only be seen if thin
  • if too many cell layers, can mistake structures for being in the transverse plane you are looking at when they are actually behind
77
Q

Explain how to use a stage micrometer to work out the real distance represented by small divisions in an eyepiece graticule under 3 different objective lenses.

A
  • work out how many micrometer divisions (10micrometers each) the graticule takes up
  • divide this length by number of divisions of graticule in order to calibrate it
  • then use the graticule to measure real microscopic lengths
  • when changing lens plug into magnification equation to re-calibrate the graticule without using the stage micrometer
78
Q

Explain how an adjustment to the ‘plane of focus’ can alter what is viewed within a cell.

A

we are able to distinguish which structures are above/below each other

79
Q

Explain why staining is useful for light microscopy & how it works.

A
  • enhances contrast of the image and highlights certain structures
  • different components of cell take up stains to different degrees
  • increase in contrast allows components to be visible clearly
  • without staining, hard to differentiate between different structures as they usually do not have a distinct color without staining
80
Q

Describe how to prepare a stained specimen for viewing under a light microscope.

A
  • place sample on slide and allow it to air dry
  • heat-fix it by passing it through a flame - cell will not break down & specimen adheres to slide
  • add the stain
81
Q

Name two common stains and the molecules they bind to.

A
  • iodine solution - binds to starch molecules stains them blue-black
  • fuschin - binds to collagen, smooth muscle or mitochondria stains magenta
82
Q

State the magnification formula

A

actual size x magnification = image size
image size / actual size = magnification
image size / magnification = actual size

83
Q

How do you convert measurements from one unit to another?

A

meters
x1000 millimeters /1000 ^
x1000micrometers /1000 ^
x1000 nanometers /1000 ^

84
Q

Define resolution

A

shortest distance between two objects that are still seen as separate objects

85
Q

Define magnification

A

degree of enlargement of an image compared to the object

86
Q

What is the diff between magnification and resolution?

A
  • high magnification makes small objects seem larger
  • high resolution allows us to see separate objects more clearly.
87
Q

State the resolution of light microscopes, SEM and TEM.

A

light microscopes: 200nm
SEM: 3nm
TEM: 0.2nm

88
Q

State the useful max magn of light microscopes, SEM and TEM.

A

light microscope: x2000
SEM: x500,000
TEM: x2,000,000

89
Q

What do flagella and cillia have in common?

A
  • both are extensions that protrude from some cell types.
  • both have a centriole at the base
  • both contain two central microtubules surrounded by nine pairs of microtubules arranged like a wheel (9+2 arrangement of microtubules)
90
Q

Describe the structure of cilia.

A

hair-like structures

91
Q

Outline the function of cilia

A
  • cells often have many of them, shorter than flagella
  • some cells use them for movement or to cause fluids or objects adjacent to the cell to move because they beat in a rhythmic manner
  • present in trachea to waft mucus up to be swallowed / vallopian tubes to move egg from ovary to uterus
  • pairs of parallel microtubules slide over each other causing it to move in a beating motion
92
Q

Outline the structure of flagella

A

whip-like structures

93
Q

Outline the function of flagella

A
  • cells usually have one or a few, they’re longer than cilia
  • used primarily to enable cells motility
  • sperm cells have them to move to the egg
  • generate propeller-like motion but DONT spin/rotate
94
Q

Outline structure and function of microfilaments

A
  • contractile fibers of actin
  • allow cells to move + cytokinesis (fibers can get shorter/longer which allows the cell to move)
95
Q

Outline the structure and function of microtubules

A
  • tubes made of chains of globular tubulin
  • form scaffold to maintain cell shape and form track ways along which organelles can move around within the cell
96
Q

Outline the function of independent filaments

A
  • provide additional strength to support the cell

OCR A-Level Biology (16 decks)

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