Paper 2 Practicals

RP7: Chromatography

  • draw solvent line in pencil

  • dab the pigment on with a capillary tube, leave to dry and add more until spot is 5mm in diameter

  • place into solvent with solvent below origin, and with lid and place upright - at an angle would go off the plate

  • remove before solvent goes fully up

  • don’t touch plate directly → contamination

  • draw solvent line immediately, before it evaporates

  • measure from centre of spot

RP8: DCPIP and dehydrogenase

dehydrogenase is an enzyme in photosynthesis that catalyses electron transfer to NADPH

DCPIP is a redox indicator, it is reduced instead, blue → colourless reduced

faster turn colourless, faster dehydrogenase activity

dependent variable - absorbance of DCPIP

  • remove leaf stalks and grind with isolation medium, then filter (keep chilled) with muslin

  • place filtrate in ice bath, prevents enzyme denaturation

  • spin in centrifuge, spin supernatant again and suspend pellet with isolation medium

  • test tubes:

    • standard (chloroplast + water) - for comparison

    • chloroplast, water, DCPIP and foil - DCPIP will not decolorise without light

    • control - water + DCPIP - proves chloroplast is needed

    • varied colours of light → red, blue, green with chloroplast, DCPIP and water

  • place in front of lamp, time taken to decolourise compared to control

→ carry out in dark to limit exposure to light

→ red, blue then green order of decolourising. green light is reflected, same colour as chlorophyll

RP9: Respiration

  • add 10cm3 yeast to one tube, 10cm3 soda lime to other

  • add glucose to yeast, distilled water to soda lime

  • keep in water bath to control temp. at 30oC

  • soda lime absorbs CO2 → when respiring volume of oxygen will decrease, pressure decrease - measure distance coloured liquid moved

  • open three way tap and start stopwatch, noting position of coloured liquid

RP10: Choice Chambers

  • investigating taxis - directional response

  • damp dark, damp light, dry dark, dry light

  • place maggots in centre and leave for 5 mins

  • repeat several times to get reliable results + calculate mean, (observed value)

  • expected no. maggots/4 (no preference)

  • calculate degrees of freedom (no. of categories -1) = 3

  • look at critical value at 3 degrees of freedom

  • high calculated value than critical value → reject null

RP11: Glucose in Urine

  • produce dilution series of glucose

  • add 1cm3 of benedict’s to each solution, leave in water bath for 5 mins

  • filter solutions to remove precipitate

  • place solutions into cuvettes & measure absorbance with colorimeter

  • zero with distilled water, measure absorbance for all solutions for red light

  • plot calibration curve, measure absorbance of a ‘urine’ solution

  • follow absorbance on y to conc. of glucose on x

RP12: Sampling

  • gridded quadrat - used when too many organisms to count, measure percentage cover

  • create a gridded area by laying out two tape measures

  • generate random coordinates on calculator

  • count how many individual organisms are present

  • measure abiotic factor, e.g. light intensity

  • repeat and get a large number of samples

  • calculate % cover (give formula)

  • multiply by total area of field

  • place transect perpendicular to what is thought to cause change

  • place quadrat at appropriate intervals - how quickly is change seen in plant distribution

  • repeat with more transects parallel to previous one