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A Level Biology Flashcards - BB > Chapter 1: Cells and Microscopy > Flashcards

Chapter 1: Cells and Microscopy Flashcards

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1
Q

how is magnification calculated?

A

image size / actual size

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2
Q

how is total magnification calculated?

A

eye piece magnification x objective magnification

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3
Q

what are the differences between light and electron microscopes?

A

Radiation source = light v electrons

LM uses living specimen EM electron has vacuum ∴ dead samples

LM can distinguish colour EMelectron can’t

LM has has low mag. and res, EM electron has high mag. and res.

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4
Q

what does an electron microscope use to focus?

A

an electromagnet

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5
Q

what is the maximum resolution for a- light microscope- electron microscope?

A

LM 200nm

EM 0.1nm

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6
Q

what is the maximum magnification for a light microscope, scanning electron microscope (SEM), transmission electron microscope (TEM)?

A

LM 1500x

SEM 100,000x

TEM 500,000x

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7
Q

what is the definition of magnification?

A

the degree of enlargement of an image to reveal further detail

Remember: magnification is limited by reosolution of the microscope

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8
Q

what is the definition of resolution?

A

the ability to distinguish between two different points and to see detail

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9
Q

what is the use of a microtome?

A

to cut extremely thin non-living specimens so that the light rays or beam of electrons can pass through the specimen

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10
Q

how does a TEM produce an image?

A
  • e- passed through specimen
  • e- are scattered
  • magnetic lenses focus image on fluorescent screen / photographic plate
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11
Q

how does an SEM produce an image?

A

e- knock other e- from surface of specimen

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12
Q

what is added to TEM specimens?

A
  • heavy metal impregnation
  • used to stain specimen as atoms of heavy metals have large positivec nuclei that scatter e- beam
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13
Q

what is added to SEM specimens?

A

coated with carbon/gold

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14
Q

outline the process of preparing a temporary slide

A
  • fixation
  • staining
  • mounting
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15
Q

outline the process of prepaing a permanent slide

A
  1. fixation (immersion in gluteraldehyde)
  2. dehydration (incr. alcohol content)
  3. clearing (xylol removes alcohol)
  4. embedding (in epoxy/resin)
  5. sectioning
  6. staining
  7. mounting
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16
Q

what is cryosectioning?

A
  • tissue embedded in gel medium
  • then rapidly frozen to -20/-30oC
  • cut with cryostat into 5-10 um sections
  • then stained
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17
Q

what is the purpose of differential staining?

A

to improve contrast betwen diferent tissues and or strucrtures

i.e. to make certain structures appear darker or different in colour from other structures

to distinguish between

  • different types of cells
  • living and dead cells
  • different chemicals or metabolic processed
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18
Q

how is Leishman’s stain applied?

A
  • blood smear prepared
  • allow blood smear to air dry
  • fixed with methanol for 2 mins
  • dilute with distilled with water for 6 mins
  • slide washed until pink to naked eye
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19
Q

how is Wright’s stain applied?

A
  • blood smear prepared
  • allow blood to air dry
  • dipped in Wright’s stain for 3-4 minutes
  • dilute in distilled water
  • leave for 6-8 minutes
  • rinse in distilled fresh water for 25s (until pale pink edges are seen)
  • air dry vertically
  • oil applied
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20
Q

what is the purpose of a blood smear?

A
  • to observe the appearance of the blood:-
    • presence/absence of cells
    • cell morphology
    • cell health
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21
Q

how is a blood smear achieved?

A
  • place a small drop of blood at the end of a clean, sterile, dry slide
  • another slide used to spread blood at 30o angle
  • immediately labelled slide left to dry
  • fixative used to preserve cells
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22
Q

what are the functions of the blood?

A
  • delivery of oxygen to tissues
  • delivery of nutrients e.g. glc, fatty acids to tissues
  • removal of waste products e.g. carbon dioxide, urea from tissues
  • immunological protection e.g. circulation of antibodies, phagocytes and memory cells
  • clotting
  • transport cell signalling molecules e.g. hormones (insulin, glucagon, ADH etc)
  • acting as a buffer to regulate pH of plasma
  • distribution of heat to regulate core body temperature
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23
Q

what is the function of erythrocytes?

A

red blood cells, RBCs

  • Transport oxygen as oxyhaemoglobin from lungs to tissues
  • each Hb carries 4 oxygen moecules (i.e. 8 oxtgen atoms)
  • Transport carbon dioxide from tissues to lungs
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24
Q

how are erythrocytes produced?

A
  • produced from erythropoietic stem cells in bone marrow
  • following stimulation from erythropoietin
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25
Q

how is the structure of an erythrocyte related to its function?

A
  • no nucleus
  • few organelles (incl. no mitochondria, GA)
  • biconcave (incr. SA)
  • production of haemoglobin (for oxygen transportation)
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26
Q

how is the structure of a neutrophil related to its function?

A
  • lobed nucleus
  • granular cytoplasm
  • many lysosomes containing hydrolytic enzymes (phagocytosis)
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27
Q

what are the requirements of a haemocytometery sample?

A
  • mixed (representative)
  • known dilution (accurate counting)
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28
Q

how is a cell count performed using a haemocytometer?

A

count number of cells in 3-line square using NW rule

= ___find volume (0.2 x 0.2 x 0.1 = 0.004 mm3) in 1 mm3

= 1/0.004 x ___ = ~~~ cells account for dilution

= ~~~ x dilution factor = …….. cells

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29
Q

what is flow cytometery used for?

A

analysis of physical and chemical characteristics of cells in heterogenous cell populations

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30
Q

what are the components of flow cytometery?

A

flow cell (liquid stream carrying single file cells)

measuring system

detector

amplification system

computer + relevant analysis software

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31
Q

how can cell size and volume be analysed by flow cytometery?

A
  • specific antibodies can be tagged to different fluorochromes –> recognise and target specific antigens inside cells/on CSM
  • fluorochromes can be attached to a chemical that binds to a specific of DNA/cell membrane/cells structure
  • each fluorochrome has its own peak of excitation and emission wavelengthslaser causes tagged cell to fluoresce so it can be counted
  • scattering occurs based on size and density
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32
Q

what are the 6 principles of cell theory?

A
  1. cell = basic unit of all life forms
  2. organisms can be uni- or multi-cellular
  3. metabolic processes take place inside the cell
  4. new cells are derived from pre-existing cells
  5. cells process genetic material which is passed to daughter cells
  6. cell = smallest unit of an organism capable of surviving independently
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33
Q

what are the structural components of the cell surface membrane (CSM)?

A
  • phospholipid bilayer - selective permeabilitycholesterol - strength and consistency
  • proteins - integral (channels) and peripheral (recognition)
  • carbohydrates - glycoproteins (recognition)
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34
Q

what is the function of the CSM?

A
  1. maintains physical integrity
  2. maintains a chemical environment
  3. selective permeability
  4. marks and signals cell
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35
Q

what is the structure of the nucleus?

A
  • surrounded by double membrane called nuclear envelope
  • pores in nuclear envelope (allows exchange of molecules)
  • contains at least one nucleolus
  • large & spherical structure ~10-20um diameter
  • fluid within nucleus = nucleoplasm
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36
Q

what is the function of the nucleus?

A
  • contains genetic, hereditary material in form of DNA
  • control of hereditary characteristics
  • replication of DNA for mitosis in S stage of cell cycle
  • controls of expression
  • chromosomes carry genes for production of polypeptide chains → and hence proteins
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37
Q

what is the structure of the nucleolus?

A
  • granular and fibrillar
  • components ill-defined matrix
  • found within the nucleoplasm
  • small spherical structure
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38
Q

what is the function of the nucleolus?

A

Produces rRNA

Produces ribosomal subunits and assembles them into ribosomes

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39
Q

what is the structure of the mitochondria?

A
  • Rod shaped organelles
  • Capable of changing shape and replicating
  • ~1-10nm length
  • Possess their own small loop of DNA (code for production of enzymes used in aerobic respiration)
  • Surrounded by mitochondrial envelope (double membrane
  • Filled with liquid called matrix
  • Matrix contains 70s ribosomes & small plasmids (circular loops of DNA)
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40
Q

what is the function of the mitochondria?

A

ATP production through aerobic respiration

  • Main function = site of link reaction, Krebs cycle & oxidative phosphorylation (later stages of aerobic respiration)
  • Site of ATP production for the cell
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41
Q

what is the structure of the endoplasmic reticulum?

A
  • folding network of cisternae held together by cytoskeleton
  • RER also has attached ribosomes
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42
Q

what is the function of the endoplasmic reticulum?

A
  • RER: protein production
  • SER: production, metabolism and storage of fats and steroid hormones
  • sarcoplasmic reticulum: storage and release of Ca2+ ions for muscle contraction
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43
Q

what is the structure of a lysosome?

A
  • Small, fluid filled membrane bag organelle formed by GA
  • Contain different types of hydrolytic enzymes (proteases & lipases)
  • ~1.0mm diameter
  • Typical internal pH ~5
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44
Q

Outline the functions of a lysosome?

A
  • breaking down macromolecules in hydrolysis
  • remove unwanted cell structures & organelles and chemicals within cell
  • important role in phagocytosis & apoptosis
  • enzymes usually formed on RER and then enclosed in vesicles which bud off the Golgi body
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45
Q

what is the structure of the golgi apparatus?

A
  • Appear similar to SER but form convex shapes
  • Made from fluid-filled flattened sacs of cisternae held together by matrix proteins and cytoplasmic microtubules
  • Typically 40-100 stacks per GA & 3-6 cisternae per stack
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46
Q

what is the function of the golgi apparatus?

A
  • Assemble polypeptides into proteins
  • Package proteins and lipids made by RER and SER
  • Modify proteins and lipids
    • addition of glycocalyces (glycocalyx = singular) which are oligosaccharides → glycoproteins & glycolipids
    • addition of phosphate groups → phospholipids
  • Sort proteins into vesicles → ensures proteins/lipids are transported to correct place in cell
  • ost modification (glyco)proteins, (glyco)lipids and phospholipids packaged into golgi vesicles
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47
Q

what is the structure of a ribosome?

A
  • NOT membrane bound i.e. not true organelles
  • Actually cytoplasmic granules made from rRNA and protein
  • Found free in cytosol or bound to ER to form RER
  • Each ribosome contains 2 subunits: large & small subunit
  • Two types:
    • 80s
      • only found in eukaryotes (free or on RER)
      • 25-30 nm diameter
      • 1:1 ratio of rRNA:protein
      • Large subunit = 60s, small = 40s
    • 70s
      • found in cytosol of prokaryotes
      • 65%:35% ratio of rRNA:protein in prok.
      • also found in mitochondria & chloroplasts
      • Large subunit = 50s, small = 30s
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48
Q

what is the function of a ribosome?

A

synthesis of a polypeptide chain through translation of mRNA

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49
Q

what is the structure of a centriole?

A
  • Cylindrical structure found in membrane bound vesicle → centrosome
  • Membrane of centrosome is continuous with nuclear envelope during interphase
  • Found in pairs
  • Composed mainly of protein called tubulin in structures called microtubules (see later)
  • Short cylinders of 9+0 arrangement (i.e. 9 microtubules arranged in circle around the circumference but none in the centre)
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50
Q

what is the function of a centriole?

A
  • Organise spindle fibres in nuclear division (mitosis & meiosis)
  • Centriole within centrosome duplicates itself during G2 phase of cell cycle: they are arranged at right angles to each other
  • Centrosomes migrate to poles during prophase
  • Impotant in increasing effectiveness of mitosis
  • Involved in the movement of cilia and flagella
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51
Q

what is the structure of a vacuole?

A
  • membrane-bound sacs
  • surrounded by a sinlge membrane called a tonoplast (selectively permeable membrane)
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52
Q

what is the function of a vacuole?

A
  • Acts as reservoir for water (main content)
  • Also contain dissolved salts, sugars, organic acids
  • Provide support to the plant cell
  • Contributes to cell turgidity i.e. provides whole plant support
  • Surrounded by tonoplast
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53
Q

how do organelles work together to produce a protein?

A
  • nucleus contains gene for transcription of protein
  • nucleolus = site of ribosomal subunit production & assmebly
  • ribosomes = site of translation of mRNA to form ppc
  • RER is continuous with nuclear envelope
  • vesicles transport protein to golgi apparatus, which processes it (e.g. quaternary structure by adding prosthetic groups)
  • golgi vesicles transport protein to CSM
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54
Q

what are the features of a prokaryotic cell?

A
  • no nucleus
  • no embrane-bound organelles
  • 70 Svedberg ribosomes
  • peptidoglycan cell wall
  • flagella
  • polysaccharide capsule
  • plasmid DNA
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55
Q

what are the three main types of unicellular cells?

A
  • amoeba
  • chlamydomonas
  • paramecium
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56
Q

what is the role of the cytoskeleton?

A
  • cell stability
  • support
  • movement of cilia and flagella
  • changing shape of cell during cytokinesis
  • phagocytosis
  • exocytosis
  • movement of organelles/vesicles
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57
Q

what are the three components of the cytoskeleton?

A
  1. microfilaments
  2. intermediate filaments (10nm)
  3. microtubules (23nm)
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58
Q

outline the process by which motor proteins move along the cytoskeleton

A
  • binding conformational change
  • filament release
  • conformational relaxation
  • filament rebinding
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59
Q

what is the purpose of colourimetery?

A

quantitative analysis of a solution to determine its quantity/quality

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60
Q

what is simple diffusion?

A

passive movement of molecules down the concentration gradient (until an equilibrium is reached) across a partially permeable membrane

61
Q

what are the factors affecting the rate of diffusion?

A
  • Concentration gradient
  • Size of molecule
  • Amount of kinetic energy the molecules posses (i.e. directly related to temperature)
  • Polarity of the molecule
  • Surface area
  • Diffusion distance
62
Q

what is facilitated diffusion?

A

Passive movement of molecules down the concentration gradient through specialised proteins (until an equilibrium is reached) across a partially permeable membrane

63
Q

what is function of

  • channel proteins
  • carrier proteins?
A

Channel proteins

  • Form pores form aqueous channels which allows ions to cross
  • Can be gated which enables the channels to be open or closed depending on
    • A potential differences across the membrane
    • The presence of a specific molecule (a ligand)
  • Used to transport water soluble molecules and ions
  • Different channels are specific to specific ions i.e. some channels allow Na+ to cross whereas others allow Cl- ions to cross etc

Carrier proteins

  • each carrier protein has a complementary binding site to a specific molecule
  • carrier protein undergoes allostery i.e. a conformational change
  • The carrier protein changes between a ‘ping’ and ‘pong’ state
    • Ping state = binding site exposed to outside of the cell
    • Pong state = binding site exposed to inside of the cell
  • Used to transport larger molecules e.g. glucose, amino acids uptake in small intestine
64
Q

what is active transport?

A
  • the movement of molecules against their concentration gradient
  • requires ATP
  • requires a carrier protein:-
    • with a specific binding site
    • to undergo a conformational change
    • have a binding site for ATP- ∴ can carry out hydrolysis
65
Q

outline the process of active transport across a membrane

A
  • carrier protein takes up molecule from outside
  • molecule binds to carrier protein
  • ATP attaches to membrane protein on inside
  • molecule causes conformational change to structure –> access for molecule opened
  • molecules released to inside of membrane using E from hydrolysis of ATP
  • release of molecule causes carrier protein to revert to binding configuration
66
Q

what are the two forms of endocytosis?

A
  • intake of small quantitites of liquid by pinocytosis
  • intake of olid material by phagocytosis
67
Q

what is the function of endocytosis?

A
  • uptake of nutrients
  • engulfing bacteria
68
Q

State the function of exocytosis and give 2 exmpales

A
  • insoluble waste material excreted from cell
  • e.g.
    • the removal of waste products or secretion of useful products (e.g. secretion of pancreatic enzymes, secretion of insulin from -cells of the pancreas)
    • plant cells use it to develop the cell wall which is outside of the cell surface membrane
69
Q

Describe the how to test for lipids in

a) a liquid sample and
b) a solid sample

A

Testing liquid smaples:

  • add ethanol
  • add equal volume of distilled water
  • shake gently
  • mixture turns cloudy/milky

Testing solid samples

  • Place a small piece of each solid into test tube
  • Add 2 cm3 ethanol to test tube and shake thoroughly
  • Using the glass rod gently mash each sample: ensure rod is cleaned between samples to avoid cross-contamination
  • Shake each tube thoroughly
  • Allow the solid to settle to the bottom of the tube
  • Carefully pipette the ethanol from each sample into a fresh, labelled tube, leaving the solid sediment behind
  • Add 2 cm3 distilled water and shake gently to mix
  • Observe the appearance of each sample
70
Q

what are the similarities between a triglyceride and a phospholipid?

A

Both

  • contain glycerol
  • contain fatty acids
  • contain choline
  • contain ester bonds
  • contain C, H and O
  • formed by condensation reactions
71
Q

what are the differences between a triglyceride and a phospholipid?

A
  • T: 3 fatty acids; P: 2 fatty acids
  • T: 3 ester bonds; P: 2 ester bonds
  • T: absence of phosphate group; P: presence of phosphate group
72
Q

Whay do we preserve specimens?

A
  • To enable them to be cut into secrions to observe under a microscope
  • To enable them to be treated with different stains
73
Q

Describe how to prepare a temporary slide for observing under an LM

A
  1. Fixation: use 70% alcohol
  2. Staining: use few drops of appropriate differential stain
  3. Mounting: cover with coverslip to exclude dust and air
74
Q

State 2 advanatges of preparing temporary slides for use under an LM

A
  1. Rapid & simple procedure (no complex apparatus or skill required)
  2. Can mount specimen in glycerine to prolong examination period
75
Q

Explain why specimens need to be fixed before observing under a LM

A
  • specimen in life like condition
  • minimises distortion
  • chemicals such as or are added to make proteins and nucleic acids insoluble à fixing them in position
76
Q

Explain why specimens need to be dehydrated before observing under an LM

A
  • traces of water from fixed material
  • Achieved by placing the specimen in increasing e.g. up to 70% ethanol
77
Q

Explain why specimens need to be dehydrated before observing under an LM

A
  • Addition of xylol
  • Ensures material is made
78
Q

Explain why a specimen needs to be embedded as part of the preparation methd for preparin a temporary slide

A
  • material so it is firm enough for sectioning
  • can be resin, plastic or wax
79
Q

State 3 advantages of using differential stains

A
  1. General adv = most biological specimens are colourless & almost transparent → easier to observe tissues/cells/chemicals
  2. when observing animal tissue = allows observer to distinguish xylem vessels from other tissues etc
  3. when observing plant tissue = allows observer to distinguish between different types of WBC
80
Q

State 4 advanatages of using a LM

A
  1. Low skill set needed by user
  2. Can be transported to use in field work
  3. Can observe living organisms
  4. Relatively inexpensive so available for schools & colleges
81
Q

State 3 disadvantages of using a LM

A
  1. Low resolution
  2. Hence limited magnification
  3. Many internal cellular structures can’t be seen e.g. ribosomes, cristae,
82
Q

Discuss advanatges and disadvantages of using EM

A

Advantages of EM

  • greater resolution (~0.1nm)
  • higher magnifications can be used
  • finer detail seen e.g. ribosomes

Disadvantages of EM

  • specimen has to be placed in vacuum therefore must be dead (as essential specimen is completely dehydrated)
  • highly expensive so prohibits use in schools
  • high skill set required à need for training before use
  • must be used in specialist room due to electromagnets within the EM
  • more complex process to prepare specimen e.g. must be mounted on copper grid rather than glass slide
  • more prone to artefacts due to complex preparation procedure
83
Q

Compare TEM and SEM

A

Both

  • use e- beam
  • place specimen in vacuum
  • can only be used to observe dead specimens
  • produce images that can be colour enhanced
  • have higher resolution than LM
  • obtain higher magnifications than LM

Differences

  • TEM = 2D image, SEM = 3D image
  • TEM higher resolution than SEM
  • TEM max mag = 100 000x, SEM 10 000x
  • TEM shows internal detail, SEM shows surface detail and contours
    *
84
Q

State 6 advanatges of using Confocal Scanning Laser Microscope

A
  1. ability to eliminate or reduce background information away from the focal plane to reduce to image degradation
  2. capability to collect a series of optical sections from thick specimens ay various depths by optical sectioning
  3. ability to obtain high resolution images
  4. ability to obtain 3D reconstructions
  5. ability to image living cells and tissues
  6. any out-of-focus light is blocked à clearer image than standard LM
85
Q

Outline how CSLM works

A
  1. point source of light is detected on to the object plane
  2. point of emitted fluorescence light or reflected light from the specimen is directed through detector pinhole
  3. fluorescent/reflected light is enhanced using photomultiplier
  4. fluorescent/reflected light displayed on computer screen as a pixel
  5. specimen is scanned point by point & line by line à very thin, blur-free optical sections are recorded one pixel at a time
  6. series of images then combined à image stack → 3D image
86
Q

Outline how fluorescent markers can be used to detect biological chemicals/structures using a CLSM

A
  • fluorochromes attached to antibody that is specific for one antigen on or in the cell
  • fluorochromes can also be tagged to a chemical that binds specifically to a component of the csm, DNA or other structure
  • each fluorochrome has its own peak excitation & emission l
  • lasers with different l are used depending on which fluorochromes are used
  • laser excites the fluorochrome causing the tagged cells to fluoresce
  • this fluorescence is counted by the detector
  • the specific light scattering and fluorescent characteristics of each cell as they pass the laser beam is used for counting and sorting
87
Q

Describe how to calculate the field of view

A

Calculating field of view:

Field of view = area that can be seen when looking down through eyepiece

Hence FOV = area of circle i.e. π​r2 (units = mm2 assuming radius measured in mm)

88
Q

Describe the role of a thrombocyte

A
  • Role in blood clotting
  • Role in clot formation
89
Q

Describe the role of a neutrophil

A
  • Defend against bacterial and fungal infections
  • Engulf bacteria by phagocytosis
90
Q

State the main role of B-lymphoctyes

A

Produce immunoglobulins (antibodies)

91
Q

State the different types of T-lymphocytes and outline thier roles

A
  • Several types:
    • T helper cell – produces cytokines to coordinate the immune response
    • Cyotoxic T cell – binds to antigens on viral infected cells/tumour cells & destroys them
    • Natural killer cells – roles vary
92
Q

Outline the role of a monocyte

A
  • Carry out phagocytosis
  • Longer living than neutrophils
  • Can leave the blood stream by amoeboid movement & differentiate into macrophages in the liver, spleen & lungs
93
Q

State which cells can move out of the bloodstrem to become macrophages

A
  1. Neutrophils
  2. Monocytes
94
Q

State the 3 key points to the North-West rule when counting cells using a haemocytometer

A
  • count all cells that lie completely within the triple lined 5x5 grid
  • also include any cell that lies on the middle line of the north triple boundary and the middle line of the west triple boundary
  • if a cell lies on the middle triple line on the south or east boundary do not count them
95
Q

State 4 uses for flow cytometry

A
  • analysing the activity of molecules found in the cell surface membrane and within the cell
  • characterising and defining different cell types in heterogeneous (mixed) cell populations
  • assessing the purity of samples
  • analysing cell size and volume
96
Q

Describe how different cells can be identified using flow cytometry

A

Larger and more granular granulocyte cells produce a large population with high SS and FS

Monocytes are large cells, but not so granular, so these produce a separate population with high FS but lower SS

Smaller lymphocytes and lymphoblasts produce a separate population with less FS. They are agranular cells so also have low SS.

97
Q

describe the structure and role of the nuclear envelope

A
  • double membrane
  • that surrounds nucleus
  • outer membrane of NE is continuous with RER
98
Q

Describe the structure and role of the nuclear pore

A
  • Gaps within the NE (usually ~3000 pores)
  • Each pore~40-100nm diamete
  • Enables cell to control what enters and exits the nucleoplasm from cytosol e.g. allows exit of mRNA after transcription to enable translation to occur in cytosol
99
Q

Describe the structure of the SER

A
  • Series of flattened membrane sacks (cisternae) that form sheets in the cytosol
  • Tubular appearance
100
Q

Outline the functions of the SER

A
  • Site of lipid synthesis, storage and transport
  • Site of carbohydrate synthesis, storage and transport
  • Site of steroid hormone synthesis, storage and transport
101
Q

Describe the structure of the RER

A
  • Series of flattened membrane sacks (cisternae) that form sheets in the cytosol
  • Has ribosomes attached to outer surface of cisternae
  • Continuous with outer membrane of nuclear envelope
102
Q

Outline the function of the RER

A
  • Site of protein & glycoprotein synthesis
  • Site of folding of ppc into 20, 30 structure
  • Provides pathway to transport proteins & other materials through the cell
103
Q

Outline the functions of golgi vesicles

A
  • Used in various processes
    • secretion e.g. release of insulin from β-cell in pancreas, secretion of antibodies from B-lymphocyte by exocytosis
    • phagocytosis
    • endocytosis
    • transports phospholipids to csm for cell growth
  • Also used in cell metabolism and enzyme storage
104
Q

Outline the role of plasmodesmata

A
  • Cell to cell connections between adjacent plant cells
  • Enables materials and chemicals to be transferred between cells
105
Q

OUtline the structure and role of a plasmid

A

Structure:

  • Very small circular pieces of DNA
  • Separate from main DNA within cytosol
  • Capable of replicating independently of main DNA

Role:

  • Carry genes that increase survival chances of prokaryote e.g. genes to produce enzymes that breakdown antibiotics (i.e. antibiotic resistance genes)
106
Q

Explain how bacteria carry out respiration int he absnece of any mitochondria

A
  • Formed by invaginations of cell surface membrane (csm)
  • Site of aerobic respiration
107
Q

Outline the structure and role of pili

A
  • Hair-like structures
  • Extend through cell wall
  • Enable bacteria to adhere to each other (important in sexual reproduction in bacteria) or other surfaces
  • NB Not found in all species of bacteria
108
Q

Outline the structure and role of a flagellum

A

Structure

  • Specialist extension of csm and cytosol

Role

  • Enables motility and movement of bacteria
  • Rotation unit at base of flagellum (motor protein)
  • Some bacteria have multiple flagella
109
Q

Describe the structure of microfilaments

A
  • made from a specialised protein = actin
  • thinnest cytoskeletal filaments
  • consist of 2 intertwined strands
  • 7nm width
110
Q

Outline the role of microfilaments

A
  • maintain the cell shape
  • enable motility e.g. pseudopodia
  • enable muscle contraction e.g. skeletal muscle
  • enable cytokinesis of cell division
111
Q

Describe the structure of intermediate cytoskeleton filaments

A
  • ~10nm diameter
  • more stable than microfilaments
  • made specialised protein called keratin
  • consist of fibres wound together
112
Q

Outline the role of intermediate cytoskeleton filaments

A
  • maintain the cell shape
  • anchor the nucleus & organelles in the cytosol
113
Q

Describe the structure of microtubules

A
  • ~23 nm diameter
  • made of specialised protein called tubulin
  • arranged in hollow cylinders
114
Q

State 4 functions of microtubules

A
  • maintain the cell shape
  • enable motility e.g. cilia & flagella
  • enable movement of chromosomes
  • enable movement of organelles
115
Q

State 4 functions that all cell cytokeleton fibres have in common

A
  • help to maintain the cell’s shape & structure
  • enable the movement of organelles within the cytosol
  • enable the intracellular transport of molecules & materials
  • enable the movement of chromosomes to occur during mitosis & meiosis
116
Q

Outline how motor proteins can move cell structures within the cell

A
  1. Motor protein binds strongly to a cytoskeleton filament
  2. Motor protein undergoes a conformational change (allostery)
  3. Motor protein is released from the filament (unbound)
  4. Motor protein undergoes conformational relaxation (i.e. returns to original shape)
  5. Motor protein rebinds to the cytoskeletal filament i.e. process repeats
  6. This cyclical process à motor protein & associated organelle/molecule moves few nm at a time along filament
117
Q

State 8 roles of cell membranes

Hint: remember cell membranes include both the cell surface membrane (plamsa membrane) and internal cell membranes

A
  1. control entry & exist of molecules within organelles
  2. isolate organelles to enable specialisation of chemical reactions
  3. provide internal transport system
  4. concentrate enzymes & substrates to increase efficiency and productivity of organelle
  5. isolate enzymes to prevent cellular damage
  6. maintain internal specific conditions at optimal level
  7. can be moved within cell to where they are needed
  8. provide surfaces for chemical reactions
118
Q

State the 3 main components of cell membranes

A
  1. phospholipids
  2. proteins
  3. cholesterol
119
Q

State 5 key features/characteristics of cell membranes

A
  • 7nm wide
  • Allow lipid soluble molecules to cross bilayer
  • Prevent water soluble molecules from crossing bilayer
  • Allows membrane to be flexible
  • Allows membrane to be stable
120
Q

Define an integral/intrinsic protein

A
  • span across both monolayers
121
Q

State 6 functions of integral/intrinsic proteins

A
  1. Carrier proteins for specific molecules
  2. Channel proteins for water-soluble molecules & ions
  3. Electron carriers
  4. Structural role
  5. Receptor proteins
  6. Membrane-bound enzymes
122
Q

Define a extrinsic/peripheral protein

A

Proteins that only exist within one monolayer

123
Q

Describe the roles/functions on extrinsic proteins

A
  • Glycoproteins receptors
  • Membrane-bound organelles
  • Electron carriers
  • Structural role
  • Cell to cell recognition
  • Antigens that trigger an immune response
  • Cell to cell adhesion
124
Q

Describe the properties and arrangement of phospholipids in cell membranes

A
  • Have a polar head
    • Which consists of glycerol, choline & phosphate group
    • Is hydrophilic
  • And a non-polar tail
    • which consists of 2 fatty acid tails
    • is hydrophobic
  • PPL molecules are arranged as a bilayer (upper & lower monolayer)
  • PPL bilayer acts as a barrier to water-soluble molecules
125
Q

Describe the role of cholesterol in cell membranes

A
  • Provide mechanical strength to the cell membrane
  • Regulate fluidity of the membrane
  • Prevent water & water-soluble ions leaking out
  • Reduce lateral movement of PPL within the monolayer
126
Q

Describe the properties of cholesterol

A
  • It is a specialised lipid (steroid)
  • It is mostly hydrophobic but one part is hydrophilic (this area is attracted to the phosphate head of the PPL molecules)
  • The amount of cholesterol within different membranes varies
127
Q

State what a glycoclayx is and its function

A

State:

  • carbohydrate chain which can be added to a protein or a PPL

Function

  • Act as antigens
  • Act as recognition sites for the attachment of other molecules
128
Q

Outline the difference between glycolipids and glycoproteins and thier functions

A

Glycolipid = lipid + glycocalyx

  • Acts as recognition sites
  • E.g. cholera toxin

Glycoprotein = protein + glycocalyx

  • Acts as recognition site for molecules
  • E.g. Hormones & neurotransmitters
129
Q

Describe the properties of the phospholipid head

A
  • polar
  • hydrophilic
  • because it can form hydrogen bonds with water
  • this property stabilises the membrane
130
Q

Describe the propetries of the phosphlipid tails

A
  • non-polar
  • hydrophobic
  • unsaturated fatty acids contribute to fluidity of the membrane
  • fatty acid core forms barrier to hydrophilic substances and ions
  • fatty acid core allows movement of non-polar substances & fat-soluble molecules
131
Q

State the main components of a single phosphlipid

A

1 glycerol + 1 choline + 1 phosphate group + 2 fatty acids

132
Q

Outline how a triglyceride is formed

A
  • Requires 3 condensation reactions (one between each FA and glycerol)
  • 3 water molecules removed (and released as waste product)
  • 3 ester bonds formed (one between each FA & glycerol)
133
Q

OUtline how a phospholipid is formed

A
  • Formed by 2 condensation reactions
  • One condensation reaction between 1 FA and glycerol molecule
134
Q

Outline how cholesterol regulates the fluidty of cell membranes

A
  • at low*** temp it ***increases fluidity
  • at high*** temp it *****dec**_r_eases fluidity
135
Q

State 5 roles of glycoproteins in cell membranes

A
  1. Antigens and cell markers
  2. Cell adhesion
  3. Satabilises the membrane by interacting with water
  4. Acts as a receptor molecule for cell signalling
  5. Cell recognition
136
Q

Describe how carrier proteins involved in facilitated diffusion and active transport are similar

A

both

  • use intrinsic proteins
  • posses a binding site
  • have a binding site which is specific for a particular molecule
  • have a bindings site which is complementary to the molecule to be transported
  • undergo a conformational change (i.e. allostery) to move the molecules
137
Q

Describe how carrier proteins involved in facilitated diffusion and active transport are different

A

Carrier proteins involves in AT also

  • Have an additional binding site for ATP
  • Requires the hydrolysis of ATP to release the molecule form the binding site
  • Only work in one direction
  • Allow the accumulation of molecules within the cell (i.e. do not stop at the point of equilibrium)
  • Work against the concentration gradient
138
Q

Outline the process of phagocytosis

A
  • This is when cells take in solid material in large quantities
  • The cells are called phagocytes
  • They produce phagocytic vesicles
  • E.g. bacteria being engulfed by a phagocyte
139
Q

Outline the process of pinocytosis

A
  • This is when cells take in liquid material in large quantities
  • Very small vesicles are formed in a process called micropinocytosis
  • E.g. the uptake of nutrients by an ovum from follicle cells
140
Q

Explain the difference betwen a qualitative, semi-quantitiative and quantitative test

A

Qualitative test

  • Only tells of presence or absence of substance

Semi-quantitative test

  • Gives an indication of the relative amounts of a substance
  • Resulting positive result should be scaled low/medium/high

Quantitative test

  • provides information on absolute quantity of substance present
141
Q

Describe how testing for lipids can be produce qualitative, semi-quantitative or quantitative results depending on the method used

A

Qulaitative:

  • Emulsion test: cloudy /colurless = lipids present/absent

Semi-quantitative:

  • Emulsion test - degree of cloudines can indicate relative amounts of lipid present (more cloudy = mpre lipid present)

Quantitative :

  • Emulsion test: use colorimeter to measure transmission and then use a calibration curve to determine an absolute concentration of lipid
142
Q

Explain how temperature affactes membrane permeability

A
  • Higher temperatures (for example, from 55 °C) increased the permeability of the tonoplast and plasma membrane, which have the same structure.
  • Membrane (cell surface membrane and tonoplast) proteins become denatured.
  • Both these create spaces for pigment leakage by diffusion.
  • This occurs faster i.e. more pigment leaks out at higher temperatures.
  • Non linear trend
143
Q

Explain how alcohol affects membrane permeability

A
  • Ethanol will cause membrane disintegration as it forms temporary bonds with the phospholipid heads in the membrane.
  • Causes the phospholipids to move out of place so large gaps form in the membrane allowing pigment to leak out.
  • Ethanol also affects bonding in the membrane proteins leading to denaturation causing further gaps in the membrane.
  • Cholesterol, important in membrane structure, is soluble in ethanol, and so once it is removed, larger gaps allow increased permeability of molecules such as betalin.
144
Q

Suggest 3 limitations that can occur when investigating the effect of temperature/alcohol on membrane permeability

A
  • Cutting cylinders will damage some cell walls and tonoplasts → this will potentially vary between different cylinders
  • Differences between blotting techniques (more blotting → removes more pigment)
  • Cylinders sit on top of each other /next to each other in some tubes →decreases SA exposed to water (i.e. varies between tubes)
  • Degree of swirling will vary between tubes
  • Some beetroot loose tissue may be transferred to the cuvette
  • Fluctuations in waterbaths → temperature not fully stable & takes longer for cells in centre of cylinder to reach higher temperatures
  • Use of forceps to remove cylinder may squeeze tissue and damage cell walls & tonoplasts releasing more pigment
  • Insufficient intermediate temperatures → unable to see data between temperatures tested
  • No replicates → unable to determine if result is anomalous → can’t calculate SD to determine reliability
  • Lack of stirring of solution after removal of cylinder → more densely coloured liquid may not be poured into cuvette
145
Q

Suggest 2 errors that can occur when investigating the effect of temperature/alcohol on membrane permeability

A
  1. Accuracy of cutting cylinders → differences in SA
  2. Accuracy of timing period
146
Q

Suggest 3 improvements that could be carried out investigating the effect of temperature/alcohol on membrane permeability

A
  • Carry out at least 3 replicates at each temperature
  • Ensure all cylinders cut from same area of the same beetroot
  • Standardise blotting mechanism e.g. place on towel and roll once
  • Stir coloured liquid after removing cylinder before decanting
  • Decant coloured liquid through sieve into cuvette to remove any tissue debris
147
Q

Explain the effect of increasing temperature on the PPL molecules in a cell membrane

A
  • The kinetic energy of the PPL molecules increases
    • Causing the PPL molecules to move more within their monolayer
    • This causes the PPL molecules to become more spaced out
    • This causes spaces to occur between the PPL molecules within the cell membranes
    • This causes the cell surface membrane and the tonoplast to become disrupted
148
Q

Explain the effect of increasing temperature on the PPL molecules in a cell membrane

A
  • The kinetic energy of the protein molecules increases
    • Causing the protein molecules to move more within their monolayer
    • This causes the protein molecules to become denatured
    • This causes spaces to occur between the protein and PPL molecules within the cell membranes
    • This causes the cell surface membrane and the tonoplast to become more disrupted

A Level Biology Flashcards - BB (35 decks)

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