Y13 Practicals Flashcards
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
- Crush leaves in pestle and mortar to extract pigments
- Draw a pencil line on filter/chromatography paper, 1cm above bottom
- Add a drop of extract to line (point of origin)
- Stand paper in boiling tube (organic) solvent below point of origin
- Add lid and leave to run (solvent moves up, carrying dissolved pigments)
- Remove before solvent reaches top and mark solvent front with pencil
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
- ink is soluble in solvent
- so ink would mix with pigments/line would move
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
- pigments are soluble in solvent
- so would run off paper/spots dissolve into solvent
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
- may be soluble in one solvent but insoluble in another
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
- Rf value = distance moves by spot/distance moved by solvent front
- compare Rf value to published value
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
- once solvent evaporates, solvent front not visible
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
- standardises readings as pigment is spread out
- so allows comparisons to be made
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
- different solvent/paper/running conditions may affect Rf value
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
- solvent/pigment moves different distances
- Rf value is constant for same pigment/can be compared
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
- catalyses the reduction of NADP in the LDR
> NADP accepts electrons from photoionisation of chlorphyll/photolysis of water
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
- Extract chloroplasts from a leaf sample using ultracentrifugation
- 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 - 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
- Rate of dehydrogenase activity = 1/time taken
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
- source of chloroplasts
- volume of chloroplast suspension
- volume/concentration of DCPIP
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
- shows light is required for DCPIP to decolourise
- shows that chloroplasts alone do not decolourise DCPIP
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)
- no light so no photoionisation of chlorophyll
- so no electrons released to reduce DCPIP
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
- shows chloroplasts are required for DCPIP to decolourise
- shows that light alone does not cause DCPIP to decolourise
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
- DCPIP is a redox indicator/gets reduced by electrons
- From photoionisation of chlorophyll
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
- end point (colour change) is subjective
- use a colorimeter
- measure light absorbance of sample at set time intervals
- zero colorimeter using the colour standard
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
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
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
- 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
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
- allows apparatus to equilibrate
- allow for overall pressure expansion/change throughout
- allow respiration rate of organisms to stabilise
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
- prevent air entering or leaving
- would change volume and pressure, affecting movement of liquid
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
- use a gas syringe
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
- 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 - divide by mass of organism and time taken
- units - unit for volume per unit time per unit mass e.g cm^3 min^-1 g^-1
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
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
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
- 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
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
- allows time for oxygen to be used/respired
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
- 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
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
- volume of single-celled organism
- volume/conc/type of respiratory substrate
- temperature (water bath)
- pH (with a buffer)
- volume of redox indicator (only control)
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?
- allow for solution to equilibrate and reach the same temperature as water bath
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
- 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
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
- 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
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
- 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
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
- 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 - control other environmental conditions
> e.g if investigating humidity, control light intensity with a dim even light above - Use a teaspoon to place 12 animals on centre of mesh platform and cover with lid
- After a set amount of time, e.g 10 mins record the number of animals in each section
- Repeat after gently moving woodlice back to centre
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
- 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
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
- safely = cover open wounds/wash hands with soap after
> minimise risk of infection - ethical = handle carefully/return to habitat ASAP
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
- to keep woodlice a safe distance from drying agent
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
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
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
- reduces stress on maggots
- prevents chance of learned behaviours
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
- animals may leave chemicals/scents
- which influence behaviour of other animals
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
- 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
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
- use distilled water and a glucose solution of known concentration to produce a dilution series
- heat a set volume of each solution with a set volume of benedict’s solution
- measure absorbance using a colorimeter
- plot a graph of absorbance against concentration of glucose solution and draw a line/curve of best fit
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
- perform benedict’s test on sample using same volumes of solutions used in producing calibration curve
- measure absorbance using a colorimeter
- absorbance value for ‘urine’ sample read off calibration curve to find associated glucose concentration
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
- volume of benedict’s solution
- volume of sample used
- temperature of water bath
- time samples heated in water bath for
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
- not all glucose reabsorbed at PCT
- as glucose carrier proteins are saturated/working at maximum rate
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)
- divide two areas into grids/squares, e.g place 2 tape measures at right angles
- generate a pair of coordinates using a random number generator
- place a quadrat here and count frequency of species
> standardise this by one counting if more than half is in quadrat - repeat a large number of times and calculate a mean per quadrat for both areas
- measure environmental factor in each area, e.g take soil moisture readings
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
- too difficult to count individual organisms/individual organisms are too small to count
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
- to avoid sampling bias
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
- minimises the effect of anomalies
- ensures sample is representative of the population
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
- calculate a running mean
- when enough quadrats, this shows little change
- enough to carry out a statistical test
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)
- place a transect line across an area with an environmental gradient e.g tree to full sun
- place quadrats at regular intervals and record number of organisms of named species and factor e.g light intensity using a light meter
- repeat in other parallel areas and calculate mean number of plants at each point along the transect
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
- 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
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?
- correlation coefficient
