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Biology Practicals > Y13 Practicals > Flashcards

Y13 Practicals Flashcards

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1
Q

RP7: Use of chromatography to investigate the pigments isolated from leaves of different plants, e.g leaves from shade-tolerant and shade-intolerant plants or leaves of different colours

Describe how pigments from a leaf of a plant can be isolated with paper chromatography

A
  1. Crush leaves in pestle and mortar to extract pigments
  2. Draw a pencil line on filter/chromatography paper, 1cm above bottom
  3. Add a drop of extract to line (point of origin)
  4. Stand paper in boiling tube (organic) solvent below point of origin
  5. Add lid and leave to run (solvent moves up, carrying dissolved pigments)
  6. Remove before solvent reaches top and mark solvent front with pencil
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2
Q

RP7: Use of chromatography to investigate the pigments isolated from leaves of different plants, e.g leaves from shade-tolerant and shade-intolerant plants or leaves of different colours

Explain why the origin should be drawn in pencil rather than ink

A
  • ink is soluble in solvent
  • so ink would mix with pigments/line would move
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3
Q

RP7: Use of chromatography to investigate the pigments isolated from leaves of different plants, e.g leaves from shade-tolerant and shade-intolerant plants or leaves of different colours

Explain why the point of origin should be above the level of the solvent

A
  • pigments are soluble in solvent
  • so would run off paper/spots dissolve into solvent
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4
Q

RP7: Use of chromatography to investigate the pigments isolated from leaves of different plants, e.g leaves from shade-tolerant and shade-intolerant plants or leaves of different colours

Explain why a pigment may not move up the chromatography paper in one solvent

A
  • may be soluble in one solvent but insoluble in another
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5
Q

RP7: Use of chromatography to investigate the pigments isolated from leaves of different plants, e.g leaves from shade-tolerant and shade-intolerant plants or leaves of different colours

Describe how pigments can be identified

A
  • Rf value = distance moves by spot/distance moved by solvent front
  • compare Rf value to published value
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6
Q

RP7: Use of chromatography to investigate the pigments isolated from leaves of different plants, e.g leaves from shade-tolerant and shade-intolerant plants or leaves of different colours

Explain why the solvent front should be marked quickly once chromatography paper is removed

A
  • once solvent evaporates, solvent front not visible
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7
Q

RP7: Use of chromatography to investigate the pigments isolated from leaves of different plants, e.g leaves from shade-tolerant and shade-intolerant plants or leaves of different colours

Explain why the centre of each pigment spot should be measured

A
  • standardises readings as pigment is spread out
  • so allows comparisons to be made
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8
Q

RP7: Use of chromatography to investigate the pigments isolated from leaves of different plants, e.g leaves from shade-tolerant and shade-intolerant plants or leaves of different colours

Explain why the obtained Rf values were similar, but not identical, to the published value

A
  • different solvent/paper/running conditions may affect Rf value
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9
Q

RP7: Use of chromatography to investigate the pigments isolated from leaves of different plants, e.g leaves from shade-tolerant and shade-intolerant plants or leaves of different colours

Explain why Rf values are used and not the distances moved by pigment spots

A
  • solvent/pigment moves different distances
  • Rf value is constant for same pigment/can be compared
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10
Q

RP8: Investigation into the effect of a named factor on the rate of dehydrogenase activity in extracts of chloroplasts

Describe the role of the enzyme dehydrogenase in photosynthesis

A
  • catalyses the reduction of NADP in the LDR
    > NADP accepts electrons from photoionisation of chlorphyll/photolysis of water
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11
Q

RP8: Investigation into the effect of a named factor on the rate of dehydrogenase activity in extracts of chloroplasts

Describe how rate of dehydrogenase activity in extracts of chloroplasts can be measured

A
  1. Extract chloroplasts from a leaf sample using ultracentrifugation
  2. Set up test tubes as follows:
    A. control 1 - set volume of DCPIP, water and chloroplasts in isolation medium, covered in foil to block light
    B. control 2 - set volume of DCPIP, water and isolation medium without chloroplasts
    C. standard/reference - set volume of water and chloroplasts in solution without DCPIP
    D. experiment - set volume of DCPIP, water and chloroplasts in isolation medium
  3. Shine a light on test tubes and time how long it takes for DCPIP to turn blue (oxidised) to colourless (reduced) in tube D —> compare to tube C to identify end point
  4. Rate of dehydrogenase activity = 1/time taken
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12
Q

RP8: Investigation into the effect of a named factor on the rate of dehydrogenase activity in extracts of chloroplasts

Give examples of variables that could be controlled

A
  • source of chloroplasts
  • volume of chloroplast suspension
  • volume/concentration of DCPIP
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13
Q

RP8: Investigation into the effect of a named factor on the rate of dehydrogenase activity in extracts of chloroplasts

Explain the purpose of control 1 (tube A) - DCPIP, water and chloroplasts in isolation medium covered in foil

A
  • shows light is required for DCPIP to decolourise
  • shows that chloroplasts alone do not decolourise DCPIP
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14
Q

RP8: Investigation into the effect of a named factor on the rate of dehydrogenase activity in extracts of chloroplasts

Explain why DCPIP in control 1 stays blue (covered in foil)

A
  • no light so no photoionisation of chlorophyll
  • so no electrons released to reduce DCPIP
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15
Q

RP8: Investigation into the effect of a named factor on the rate of dehydrogenase activity in extracts of chloroplasts

Explain the purpose of control 2 (tube B) - DCPIP, water and isolation medium with no chloroplasts

A
  • shows chloroplasts are required for DCPIP to decolourise
  • shows that light alone does not cause DCPIP to decolourise
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16
Q

RP8: Investigation into the effect of a named factor on the rate of dehydrogenase activity in extracts of chloroplasts

Explain why DCPIP changes from blue to colourless

A
  • DCPIP is a redox indicator/gets reduced by electrons
  • From photoionisation of chlorophyll
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17
Q

RP8: Investigation into the effect of a named factor on the rate of dehydrogenase activity in extracts of chloroplasts

Suggest a limitation with the method and how the experiment could be modified to overcome this

A
  • end point (colour change) is subjective
  • use a colorimeter
  • measure light absorbance of sample at set time intervals
  • zero colorimeter using the colour standard
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18
Q

RP9: Investigation into the effect of a named variable in the rate of respiration of cultures of single-celled organisms

Describe how a respirometer can be used to measure the rate of aerobic respiration

A

Measures O2 uptake:
1. Add a set mass of single celled organism e.g yeast to a set volume/concentration of substrate e.g glucose
2. Add buffer to keep pH constant
3. Add a chemical that absorbs CO2 , e.g sodium hydroxide
4. Place in water bath at a set temperature and allow to equilibrate
5. Measure distance moved by coloured liquid in a set time

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19
Q

RP9: Investigation into the effect of a named variable in the rate of respiration of cultures of single-celled organisms

Explain why the liquid moves

A
  • organisms aerobically respire —> take in O2
  • CO2 given out but absorbed by NaOH solution
  • so volume of gas and pressure in container decreases
  • so fluid in capillary tube moves down a pressure gradient towards the organism
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20
Q

RP9: Investigation into the effect of a named variable in the rate of respiration of cultures of single-celled organisms

Explain why the respirometer apparatus is left open for 10 minutes

A
  • allows apparatus to equilibrate
  • allow for overall pressure expansion/change throughout
  • allow respiration rate of organisms to stabilise
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21
Q

RP9: Investigation into the effect of a named variable in the rate of respiration of cultures of single-celled organisms

Explain why the apparatus must be airtight

A
  • prevent air entering or leaving
  • would change volume and pressure, affecting movement of liquid
22
Q

RP9: Investigation into the effect of a named variable in the rate of respiration of cultures of single-celled organisms

Describe a more accurate way to measure volume of gas

A
  • use a gas syringe
23
Q

RP9: Investigation into the effect of a named variable in the rate of respiration of cultures of single-celled organisms

Describe how the rate of respiration can be calculated

A
  1. calculate the volume of O2 consumed/CO2 released (calculate area of cylinder)
    a. calculate cross sectional area of capillary tube using pi x r^2
    b. multiply by distance liquid has moved
  2. divide by mass of organism and time taken
  3. units - unit for volume per unit time per unit mass e.g cm^3 min^-1 g^-1
24
Q

RP9: Investigation into the effect of a named variable in the rate of respiration of cultures of single-celled organisms

Describe how a respirometer can be used to measure the rate of anaerobic respiration

A

Measures CO2 release:
- repeat experiment as normal but remove chemical substance that absorbs CO2
- make conditions anaerobic, for example:
> layer of oil/liquid paraffin above yeast = stops O2 diffusing in
> add a chemical that absorbs O2
> leave for an hour to allow O2 to be respired and used up

25
Q

RP9: Investigation into the effect of a named variable in the rate of respiration of cultures of single-celled organisms

In anaerobic respiration, explain why the liquid moves

A
  • yeast anaerobically respire —> release CO2
  • so volume of gas and pressure in container increases
  • so fluid in capillary tube moves down a pressure gradient away from organism
26
Q

RP9: Investigation into the effect of a named variable in the rate of respiration of cultures of single-celled organisms

In anaerobic respiration, explain why the apparatus is left for an hour after the culture has reached a constant temperature

A
  • allows time for oxygen to be used/respired
27
Q

RP9: Investigation into the effect of a named variable in the rate of respiration of cultures of single-celled organisms

Describe how redox indicator dyes such as methylene blue can be used to measure rate of respiration

A
  • redox indicators change colour when reduced (accept electrons instead of NAD/FAD)
    1. add a set volume of organism, e.g yeast and a set volume of respiratory substrate, e.g glucose to test tubes
    2. Add a buffer to keep pH constant
    3. Place in water bath at a set temperature and allow to equilibrate for 5 mins
    4. Add a set volume of methylene blue, shake for a set time (do not shake again)
    5. Record time taken for colour to disappear in tube
    Rate of respiration = 1/time taken
28
Q

RP9: Investigation into the effect of a named variable in the rate of respiration of cultures of single-celled organisms

Methylene blue: Give examples of variables that could be controlled

A
  • volume of single-celled organism
  • volume/conc/type of respiratory substrate
  • temperature (water bath)
  • pH (with a buffer)
  • volume of redox indicator (only control)
29
Q

RP9: Investigation into the effect of a named variable in the rate of respiration of cultures of single-celled organisms

Methylene blue: Why leave tubes in the water bath for 5 minutes?

A
  • allow for solution to equilibrate and reach the same temperature as water bath
30
Q

RP9: Investigation into the effect of a named variable in the rate of respiration of cultures of single-celled organisms

Methylene blue: Describe a control experiment and why it would be done

A
  • add methylene blue to boiled/inactive/dead yeast (boiling denatures enzymes)
  • all other conditions the same
  • to show change is due to respiration in organisms
31
Q

RP9: Investigation into the effect of a named variable in the rate of respiration of cultures of single-celled organisms

Methylene blue: Suggest and explain why you must not shake the tubes containing methylene blue

A
  • shaking would mix solution with oxygen
  • which would oxidise the methylene blue causing it to lose its electrons
  • so methylene blue would turn back to its original blue colour
32
Q

RP9: Investigation into the effect of a named variable in the rate of respiration of cultures of single-celled organisms

Methylene blue: Suggest one source of error in using methylene blue, explain how this can be reduced

A
  • subjective as to determination of colour change/end point
  • compare results to a colour standard (one that has already changed)
  • use a colorimeter for quantitative results
33
Q

RP10: Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or a maze

Describe how the effect of an environmental variable on the movement of an animal (e.g woodlice) can be investigated using a choice chamber

A
  1. set up a choice chamber to create different environmental conditions
    > e.g humidity - add a drying agent to one side and damp filter paper to another
    > e.g light - shine a light but cover one half with black card
  2. control other environmental conditions
    > e.g if investigating humidity, control light intensity with a dim even light above
  3. Use a teaspoon to place 12 animals on centre of mesh platform and cover with lid
  4. After a set amount of time, e.g 10 mins record the number of animals in each section
  5. Repeat after gently moving woodlice back to centre
34
Q

RP10: Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or a maze

The woodlice were left for 15 minutes before their movement was recorded when investigating the effect of humidity. Explain why

A
  • time to establish humidity/for substance to absorb water/water from paper to evaporate
  • woodlice no longer affected by handling
  • so that behaviour is typical of that humidity
35
Q

RP10: Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or a maze

Explain how you would ensure the safe and ethical handling of animals

A
  • safely = cover open wounds/wash hands with soap after
    > minimise risk of infection
  • ethical = handle carefully/return to habitat ASAP
36
Q

RP10: Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or a maze

Explain why a mesh platform is used when investigating humidity

A
  • to keep woodlice a safe distance from drying agent
37
Q

RP10: Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or a maze

Describe how the effect of an environmental variable on the movement of maggots can be investigated using a maze

A

Used to investigate turning behaviour in response to different environmental conditions
1. change environment at one end of T shape e.g add food source
2. place animal e.g maggot in stem of T
3. record whether animal turns towards or away from food source
4. repeat with large number of maggots
> wipe/clean maze between trials
5. repeat with food on other side of T

38
Q

RP10: Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or a maze

Explain why the same organism is not used more than once

A
  • reduces stress on maggots
  • prevents chance of learned behaviours
39
Q

RP10: Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or a maze

Explain why a clean petri dish/maze is used each time

A
  • animals may leave chemicals/scents
  • which influence behaviour of other animals
40
Q

RP10: Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or a maze

Explain why statistical test should be used to analyse results

A
  • chi squared
  • as data are categorical and comparing frequencies
  • to see if there is a significant difference between observed and expected frequencies
    > expected = equal numbers on each side
41
Q

RP11: Production of a dilution series of a glucose solution and use of colorimetric techniques to produce a calibration curve with which to identify the concentration of glucose in an unknown ‘urine’ sample

Describe how a calibration curve could be produced from glucose

A
  1. use distilled water and a glucose solution of known concentration to produce a dilution series
  2. heat a set volume of each solution with a set volume of benedict’s solution
  3. measure absorbance using a colorimeter
  4. plot a graph of absorbance against concentration of glucose solution and draw a line/curve of best fit
42
Q

RP11: Production of a dilution series of a glucose solution and use of colorimetric techniques to produce a calibration curve with which to identify the concentration of glucose in an unknown ‘urine’ sample

Describe how the concentration of glucose in an unknown ‘urine’ sample can be identified using a calibration curve

A
  1. perform benedict’s test on sample using same volumes of solutions used in producing calibration curve
  2. measure absorbance using a colorimeter
  3. absorbance value for ‘urine’ sample read off calibration curve to find associated glucose concentration
43
Q

RP11: Production of a dilution series of a glucose solution and use of colorimetric techniques to produce a calibration curve with which to identify the concentration of glucose in an unknown ‘urine’ sample

Give examples of variables that should be controlled

A
  • volume of benedict’s solution
  • volume of sample used
  • temperature of water bath
  • time samples heated in water bath for
44
Q

RP11: Production of a dilution series of a glucose solution and use of colorimetric techniques to produce a calibration curve with which to identify the concentration of glucose in an unknown ‘urine’ sample

Explain why a high blood glucose concentration can cause glucose to be present in the urine of a diabetic person

A
  • not all glucose reabsorbed at PCT
  • as glucose carrier proteins are saturated/working at maximum rate
45
Q

RP12: Investigation into the effect of a named environmental factor on the distribution of a species in a habitat

Describe how you could investigate the effect of an environmental factor on the distribution of a species in a habitat (random sampling in 2 areas)

A
  1. divide two areas into grids/squares, e.g place 2 tape measures at right angles
  2. generate a pair of coordinates using a random number generator
  3. place a quadrat here and count frequency of species
    > standardise this by one counting if more than half is in quadrat
  4. repeat a large number of times and calculate a mean per quadrat for both areas
  5. measure environmental factor in each area, e.g take soil moisture readings
46
Q

RP12: Investigation into the effect of a named environmental factor on the distribution of a species in a habitat

Suggest why percentage cover may be used rather than frequency

A
  • too difficult to count individual organisms/individual organisms are too small to count
47
Q

RP12: Investigation into the effect of a named environmental factor on the distribution of a species in a habitat

Explain why simple random sampling is used

A
  • to avoid sampling bias
48
Q

RP12: Investigation into the effect of a named environmental factor on the distribution of a species in a habitat

Explain the importance of a large sample size

A
  • minimises the effect of anomalies
  • ensures sample is representative of the population
49
Q

RP12: Investigation into the effect of a named environmental factor on the distribution of a species in a habitat

Describe how you could decide the number of quadrats that should be used in order to collect representative data

A
  • calculate a running mean
  • when enough quadrats, this shows little change
  • enough to carry out a statistical test
50
Q

RP12: Investigation into the effect of a named environmental factor on the distribution of a species in a habitat

Describe how you could investigate the effect of a factor on the distribution of a species in a habitat (systematic sampling)

A
  1. place a transect line across an area with an environmental gradient e.g tree to full sun
  2. place quadrats at regular intervals and record number of organisms of named species and factor e.g light intensity using a light meter
  3. repeat in other parallel areas and calculate mean number of plants at each point along the transect
51
Q

RP12: Investigation into the effect of a named environmental factor on the distribution of a species in a habitat

Explain the limitations of using systematic sampling to estimate the population of a species in a field

A
  • not appropriate unless there is an environmental gradient
  • transects run in one direction, but to cover the entire field, they would need placing in multiple directions
52
Q

RP12: Investigation into the effect of a named environmental factor on the distribution of a species in a habitat

Which statistical test should be used to determine the relationship between abundance and an environmental factor?

A
  • correlation coefficient

Biology Practicals (2 decks)

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