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Y12 Practicals Flashcards

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1
Q

RP1: Investigation into the effect of a named variable on the rate of an enzyme-controlled reaction

Give examples of variables that could affect the rate of an enzyme-controlled reaction

A
  • enzyme concentration
  • substrate concentration
  • temperature of solution
  • pH of solution
  • inhibitor concentration
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2
Q

RP1: Investigation into the effect of a named variable on the rate of an enzyme-controlled reaction

Describe how temperature can be controlled

A
  • Use a thermostatically controlled water bath
  • Monitor using a thermometer at regular intervals and add hot/cold water if temperature fluctuates
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3
Q

RP1: Investigation into the effect of a named variable on the rate of an enzyme-controlled reaction

Describe how pH can be controlled

A
  • use a buffer solution
  • monitor using a pH meter at regular intervals
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4
Q

RP1: Investigation into the effect of a named variable on the rate of an enzyme-controlled reaction

Why were the enzyme and substrate solutions left in the water bath for 10 mins before mixing?

A

So solutions equilibrate/reach the temperature of the water bath

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5
Q

RP1: Investigation into the effect of a named variable on the rate of an enzyme-controlled reaction

Describe a control experiment

A
  • use denatured enzymes (e.g by boiling)
  • everything else same as experiment, same temp, conc/volume of substrate and enzyme, type/volume of buffer solution
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6
Q

RP1: Investigation into the effect of a named variable on the rate of an enzyme-controlled reaction

Describe how the rate of an enzyme-controlled reaction can be measured

A
  • measure time taken for reaction to reach a set point, e.g conc/volume/mass/colour of substrate/product
    > rate of reaction = 1/time
  • measure concentration/volume/mass/colour of substrate/product as regular intervals throughout reaction
    > plot on a graph with time on x axis and whatever is being measured on y axis
    > draw a tangent at t=0
    > initial rate of reaction = change in y / change in x
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7
Q

RP1: Investigation into the effect of a named variable on the rate of an enzyme-controlled reaction

Suggest a safety risk and explain how to reduce this risk

A
  • handling enzymes may cause an allergic reaction
  • avoid contact with skin by wearing gloves and eye protection
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8
Q

RP1: Investigation into the effect of a named variable on the rate of an enzyme-controlled reaction

Explain why using a colorimeter to measure colour change is better then comparison to colour standards

A
  • not subjective
  • more accurate
  • gives a quantitative measurement
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9
Q

RP1: Investigation into the effect of a named variable on the rate of an enzyme-controlled reaction

Explain a procedure that could be used to stop each reaction

A
  • boil/add strong acid/alkali —> denature enzyme
  • put in ice —> lower kinetic energy so no E/S complexes form
  • add high concentration of inhibitor —> so no E/S complexes form
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10
Q

RP1: Investigation into the effect of a named variable on the rate of an enzyme-controlled reaction

Explain why the rate of reaction decreases over time throughout each experiment

A
  • initial rate is highest as substrate concentration not limiting/many E/S complexes form
  • reaction slows as substrate used up and often stops as there is no substrate left
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11
Q

RP2: Preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify stages of mitosis in the stained squashes and calculation of a mitosis index

Describe how to prepare squashes of cells from plant root tips

A
  1. Cut a thin slice of root tip (about 5mm from end) using scalpel and mount onto a slide
  2. Soak root tip in hydrochloric acid then rinse
  3. Stain for DNA, e.g with toluiodine blue
  4. Lower coverslip using mounted needle at 45º angle without trapping air bubbles
  5. Squash by firmly pressing down on glass slip but do not push sideways
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12
Q

RP2: Preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify stages of mitosis in the stained squashes and calculation of a mitosis index

Why are root tips used?

A

Where dividing cells are found/mitosis occurs

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13
Q

RP2: Preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify stages of mitosis in the stained squashes and calculation of a mitosis index

Why is a stain used?

A
  • to distinguish chromosomes
  • chromosomes not visible without stain
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14
Q

RP2: Preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify stages of mitosis in the stained squashes and calculation of a mitosis index

Why squash/press down on cover slip?

A
  • spreads out cells to create a single layer of cells
  • so light passes though to make chromosomes visible
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15
Q

RP2: Preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify stages of mitosis in the stained squashes and calculation of a mitosis index

Why not push coverslip sideways?

A
  • avoid rolling cells together/breaking chromosomes
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16
Q

RP2: Preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify stages of mitosis in the stained squashes and calculation of a mitosis index

Why soak roots in acid?

A
  • seperate cells/cell walls
  • to allow stain to diffuse into cells
  • to allow cells to be more easily squashed
  • to stop mitosis
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17
Q

RP2: Preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify stages of mitosis in the stained squashes and calculation of a mitosis index

Describe how to set-up and use an optical microscope

A
  1. clip slide onto stage and turn on light
  2. select lowest power objective lens
  3. a) use coarse focusing dial to move stage close to lens
    b) turn coarse focusing dials to move stage away from lens until image comes into focus
  4. adjust fine focusing dial to get clear image
  5. swap to higher power objective lens, then refocus
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18
Q

RP2: Preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify stages of mitosis in the stained squashes and calculation of a mitosis index

What are the rules of a scientific drawing?

A
  • look similar to specimen/image
  • no sketching/shading —> only clear continuous lines
  • include a magnification scale
  • label with straight, uncrossed lines
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19
Q

RP2: Preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify stages of mitosis in the stained squashes and calculation of a mitosis index

Explain how the stages of mitosis can be identified

A

Interphase = chromosomes not visible but nuclei are
Prophase:
- chromosomes visible/distinct —> because condensing
- but randomly arranged —> because no spindle activity/not attached to spindle fibre
Metaphase:
- chromosomes lined up along equator —> because attaching to spindle
Anaphase:
- chromatids at poles of spindle
- chromatids V shapes —> because being pulled apart at their centromeres by spindle fibres
Telophase:
- chromosomes in 2 sets, one at each pole

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20
Q

RP2: Preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify stages of mitosis in the stained squashes and calculation of a mitosis index

What is a mitosis index?

A
  • proportion of cells undergoing mitosis (with visible chromosomes)
  • mitotic index = number of cells undergoing mitosis/total number of cells in sample
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21
Q

RP2: Preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify stages of mitosis in the stained squashes and calculation of a mitosis index

Explain how to determine a reliable MI from observed squashes

A
  • count cells in mitosis in FOV
  • count only whole cells —> standardise counting
  • divide this by total number of cells in field of view
  • repeat with many FOV selected randomly —> representative sample
  • calculate a reliable mean
22
Q

RP2: Preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify stages of mitosis in the stained squashes and calculation of a mitosis index

Suggest how to calculate the time cells are in a certain phase of mitosis

A
  1. identify proportion of cells in named phase at any time
    - number of cells in that phase/total number of cells observed
  2. Multiply by length of cell cycle
23
Q

RP3: Production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue

Describe how to calculate dilutions

A

C1 x V1 = C2 x V2
C1 = concentration of stock solution
V1 = volume of stock solution used to make new concentration
C2 = concentration of solution you are making
V2 = volume of new solution you are making
V2 = V1 + volume of distilled water to dilute with

24
Q

RP3: Production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue

Describe a method to produce of a calibration curve with which to identify the water potential of plant tissue (e.g potato)

A
  1. Create a series of dilutions using a 1moldm^-3 sucrose solution (0.0, 0.2, 0.4, 0.6, 0.8, 1.0) —> keep volume of solution the same
  2. Use scalpel/cork borer to cut potato into identical cylinders —> keep size, shape and SA of plant tissue the same, and the source of plant tissue e.g variety or age
  3. Blot dry with a paper towel and measure/record initial mass of each piece —> blot dry to remove excess water before weighing
  4. Immerse one chip in each solution and leave for a set time in a water bath at 30ºC —> keep same the length of time in solution, temperature and regularly stir/shake to ensure all surfaces exposed
  5. Blot dry with a paper towel and measure/record final mass of each piece —> blot dry to remove excess water before weighing
  6. Repeat (3 or more times at each concentration)
  7. Calculate % change in mass (final mass - intitial mass)/initial mass
  8. Plot a graph with concentration against percentage change in mass (calibration curve) (show positive and negative regions)
  9. Identify concentration where line of best fit intercepts x-axis (0% change) —> water potential of potato cells = water potential of sucrose solution
  10. Use table in textbook to find water potential of that solution
25
Q

RP3: Production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue

Why calculate % change in mass?

A
  • enables comparison/shows proportional change
  • as plant tissue samples had different initial masses
26
Q

RP3: Production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue

Why blot dry before weighing?

A
  • solution on surface will add to mass (only want to measure water taken up or lost)
  • amount of solution on cube varies (so ensure same amount of solution on outside)
27
Q

RP3: Production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue

Explain the changes in plant tissue mass when placed in different concentrations of solute

A
  • increase in mass = water moved into cells by osmosis, as water potential of solution higher than inside cells
  • decrease in mass = water moved out of cells by osmosis, as water potential of solution lower than inside cells
  • no change = no net gain/loss of water by osmosis, as water potential of solution = water potential of cells
28
Q

RP4: Investigation into the effect of a named variable on the permeability of cell-surface membranes

Describe a method to investigate the effect of a named variable (e.g temperature) on the permeability of cell-surface membranes

A
  1. Cut equal sized cubes of beetroot of same age/type using a scalpel
  2. Rinse to remove pigment released during cutting or blot on paper towel
  3. Add same number of cubes to 5 different test tubes containing same volume of water
  4. Place each test tube into a water bath at different temperatures
  5. Leave for same amount of time (e.g 20 mins)
  6. Remove beetroot and measure intensity of colour of surrounding solution:
    - semi-quantitatively
    > use a known concentration of extract and distilled water to prepare a dilution series (colour standards)
    > compare known results with colour standards to estimate concentration
    - quantitatively
    > measure absorbance of known concentrations using a colorimeter
    > draw a calibration curve —> plot graph of absorbance against concentration of extract and draw line of best fit
    > absorbance value for sample read off calibration curve to find associated concentration of extract
29
Q

RP4: Investigation into the effect of a named variable on the permeability of cell-surface membranes

What are the issues with comparing to a colour standard?

A
  • matching to colour standards is subjective
  • colour obtained may not match any of the colour standards
30
Q

RP4: Investigation into the effect of a named variable on the permeability of cell-surface membranes

Why wash the beetroot before placing it in water?

A
  • wash off any pigment on surface
  • to show that release is only due to named variable
31
Q

RP4: Investigation into the effect of a named variable on the permeability of cell-surface membranes

Why regularly shake each test tube containing cubes of plant tissue?

A
  • to ensure all surfaces of cubes remain in contact with liquid
  • to maintain a concentration gradient for diffusion
32
Q

RP4: Investigation into the effect of a named variable on the permeability of cell-surface membranes

Why control the volume of water?

A
  • too much water would dilute the pigment so solution will appear lighter (more light passes through in colorimeter)
  • so results are comparable
33
Q

RP4: Investigation into the effect of a named variable on the permeability of cell-surface membranes

How could you ensure beetroot cylinders were kept at the same temperature throughout the experiment?

A
  • take readings in intervals throughout experiment of temperature in tube using a digital thermometer/temperature sensor
  • use corrective measure if temperature fluctuates
34
Q

RP4: Investigation into the effect of a named variable on the permeability of cell-surface membranes

What does a high absorbance suggest about the cell-membrane?

A
  • more permeable/damaged
  • as more pigment leaks out making surrounding solution more concentrated (darker)
35
Q

RP4: Investigation into the effect of a named variable on the permeability of cell-surface membranes

Explain how temperature affects permeability of cell-surface membranes

A
  • as temperature increases, permeability increases
    > phospholipids gain kinetic energy and fluidity increases
    > transport proteins denature at high temperatures as H bonds break, changing tertiary structure
  • at very low temperatures, permeability increases
    > ice crystals can form which pierce the cell membrane and increase permeability
36
Q

RP4: Investigation into the effect of a named variable on the permeability of cell-surface membranes

Explain how pH affects permeability of cell-surface membranes

A
  • high or low pH increases permeability
    > transport proteins denature as H/ionic bonds break, changing tertiary structure
37
Q

RP4: Investigation into the effect of a named variable on the permeability of cell-surface membranes

Explain how lipid soluble solvents, e.g alcohol affect permeability of cell-surface membranes

A
  • as concentration increases, permeability increases
  • ethanol may dissolve phospholipid bilayer (gaps form)
38
Q

RP5: Dissection of animal or plant gas exchange system or mass transport system or of organ within such a system

Describe precautions that should be followed when performing a dissection

A
  • cover any cuts with a waterproof dressing
  • when using scalpel ,cut away from body onto hard surface
  • use a sharp blade
  • carry with blade pointing down
  • wear disposable gloves and disinfect hands/wash with soap
  • disinfect surfaces/equipment
  • safe disposal - put gloves/paper towels/organ in a seperate bag/bin to dispose
  • if poisonous chemicals/toxins involved, work in a well ventilated environment
39
Q

RP5: Dissection of animal or plant gas exchange system or mass transport system or of organ within such a system

Suggest an ethical consideration when dissecting animals

A
  • morally wrong to kill animals just for dissection
  • so use animals for dissection that have already been killed (humanely) for meat
40
Q

RP5: Dissection of animal or plant gas exchange system or mass transport system or of organ within such a system

Describe how you could prepare a temporary mount of a piece of plant tissue for observation with an optical microscope

A
  1. add a drop of water to glass slide
  2. obtain thin section of specimen and place on slide
  3. stain (e.g with iodine/potassium iodide to view starch)
  4. lower coverslip at an angle using a mounted needle without trapping air bubbles
41
Q

RP6: Use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth

Explain examples of aseptic techniques that could be used (5)

A
  • wash hands with soap/disinfect surfaces —> kill microbes/prevent contamination
  • sterilise pipette/spreader/boil agar growth medium —> kill microbes/prevent contamination
  • flame neck of bottle of bacteria —> kill microbes/prevent contamination
  • bunsen burner close —> upward current of air draws air-borne microbes away to prevent contamination
  • lift lid of petri dish slightly/minimise opening —> prevent entry of microbes/contamination
42
Q

RP6: Use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth

Describe a method to investigate the effect of antimicrobial substances on microbial growth

A
  1. prepare area using aseptic techniques
  2. use a sterile pipette to transfer bacteria from broth to agar plate using aseptic techniques
  3. use a sterile spreader to evenly spread bacteria over agar plate
  4. use sterile forceps to place same size discs that have been soaked in different types/concentrations of antimicrobials for same length of time, onto agar plate (at equal distances)
  5. lightly tape lid onto plate, invert and incubate at 25ºC for 48 hours
  6. measure diameter of inhibition zone around each disc and calculate area using pi x r (squared)
43
Q

RP6: Use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth

Why is it important to maintain a pure culture of bacteria?

A
  • bacteria may outcompete bacteria being investigated
  • or could be harmful to humans/pathogenic
44
Q

RP6: Use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth

Why hold lid with 2 pieces of tape instead of sealing it completely?

A
  • allows oxygen in preventing growth of anaerobic bacteria
  • which are more likely to be pathogenic/harmful to humans
45
Q

RP6: Use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth

Why use a paper disc with water/no antimicrobial agent?

A
  • acts as a control
  • ensuring antimicrobial prevented growth, not paper disc
46
Q

RP6: Use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth

Why incubate upside down?

A
  • condensation drips onto lid rather than surface of agar
47
Q

RP6: Use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth

What if inhibition zones are irregular?

A
  • repeat readings in different positions, calculate a mean
48
Q

Why not use higher antimicrobial concentrations?

A
  • more bacteria killed so clear zones may overlap
49
Q

RP6: Use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth

Why incubate at 25ºC or less?

A
  • below human body temp to prevent growth of pathogens
50
Q

RP6: Use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth

Describe how data about the effect of antimicrobial substances can be presented as a graph

A
  • categorical data —> bar chart (x = type of antimicrobial, y = area of inhibition zone)
  • continuous data —> line graph (x = concentration of antibiotic, y = area of inhibition zone)
51
Q

RP6: Use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth

Explain the presence and absence of clear zones

A
  1. Clear zones —> antimicrobial diffuses out of disc killing/inhibiting growth of bacteria
    > larger clear zones = more bacteria killed = more effective antimicrobial
  2. No clear zones —> if antibiotic used, bacteria may be resistant or antibiotic may not be effective against that specific bacteria

Biology Practicals (2 decks)

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