core practicals paper 1 Flashcards
topic 1 core prac 1 effect of caffeine concentration on Daphnia heart rate variables (5 control)
independent: caffeine concentration
dependent: heart rate of daphnia
control variables:
- temperature
- volume of solution
-stress of daphnia
- size of daphnia
- time of acclimatisation
topic 1
core prac 1
effect of caffeine concentration on Daphnia heart rate
method and outcomes
method
- remove 1 dapnia and place in cavity slide replace pond water with distilled, leave for 5 mins to acclimatise
- count heart rate under microscope for 30s then multiply by 2 to get beats per min. repeat with 2 more daphnia
- repeat again a 5 different caffeine concentrations
outcome
- as caffeine increases, heart rate increases
topic 1
core prac 1
effect of caffeine concentration on daphnia heart rate
possible evaluation issues
- ensuring daphnia are the same size
- left too long under microscope, temp increases due to lamp effecting heart rate
- ensuring enough data is collected
- too high conc. of caffeine kills daphnia
- counting heart beat inaccurate
topic 1 core prac 2 measuring the content of vitamin c in fruit juice variables (4 control)
independent: fruit juice
dependent: volume of juice required to decolourise 1 cm3 of DCPIP
control:
- temperature
- concentration of DCPIP solution (1%)
- shake each tube same number of times
- same end point colour. i.e until the blue colour of DCPIP just disappears.
topic 1
core prac 2
measuring the content of vitamin C in fruit juice
methods and calculations
method
- 1 cm3 blue DCPIP into test tube. using burette add 1% of vitamin C solution drop by drop. shake tube gently
- continue until blue colour just disappears. record volume needed to decolourise the DCPIP.
- repeat further 2 times and calculate mean result. repeat procedure with different fruit juices.
calculations:
1 cm3 of 1% vitamin C solution contains 10mg of vitamin C, therefore mass in 1cm3 = 10mg x volume of 1% vitamin C to decolourise 1cm3 of DCPIP
mass in sample = mass of vitamin C to decolourise 1cm3 of DCPIP + volume of sample required to decolourise 1cm3 of DCPIP
topic 1
core prac 2
measuring the content of vitamin C in fruit juice
evaluation points
- difficulty in controlling temperature
- amount of shacking (too much adds oxygen which slightly restore the DCPIP to blue)
- end point difficult to judge as needs to be just when blue colour disappears especially in highly coloured juices
- some loss of solution when transferring from one beaker to another
- accuracy of measuring equipment
topic 1
core prac 2
DCPIP and vitamin C
DCPIP is a redox dye
when oxidised it is blue
when reduced it is colourless
vitamin C is a reducing agent as it reduces DCPIP to colourless.
topic 2 core prac 3 the effect of temperature on cell membranes variables (3 control)
independent: temperature of water
dependent:% transmission of light through resulting solution
control
- volume of distilled water
- time left in water
- size of beetroot piece
topic 2
core prac 3
the effect of temperature on cell membranes
method, calculation and outcomes
method
- using a cork borer and knife cut pieces of beetroot into 1 cm length cylinders
- place in distilled water overnight to remove dye released on preparation. wash and blot dry
- place 8 boling tubes of distilled water into 8 water baths of different temperature. once at temperature add a piece of beetroot to each and leave for 30 mins.
- remove beetroot and shake tubes to disperse dye.
- set colourimeter to read % absorbance on blue/green filter calibrate using distilled water in a cuvette first
as temperature increased % transmission slightly increased to a point a which it greatly increased due to membrane molecules gaining more heat energy, vibrating more to a point where the vibrations caused large gaps in the membrane enabling the release of dye also protein in membrane denatured leaving large pores.
topic 2 practical 4 the effect of changing enzymes concentration on rate of reaction variables (5 control)
independent: concentration of enzyme
dependent: time taken for enzyme to break down substrate
control:
- temperature
- volume of enzyme
- volume of substrate
- concentration of substrate
- pH
T-2 prac 4
the effect of changing enzyme concentration on rate of reaction.
protease version. method, calculations, conclusions
method
- make up different conc. of enzymes using distilled water. set up water bath for temperature to keep constant
- place 1 test tube of 5cm3 casein solution into water bath alongside second test tube containing 2cm3 of 0.2% trypsin.
- allow to acclimatise for 3 min so that at same temperature then add trypsion to casesin.
- time how long it takes ofr casein solution to turn transparent. repeat a further 2 times then repeat for concentration
calculation: rate = 1 / time
as conc of enzyme increase rate of reaction increases until a plateau point where all enzyme has metabolised all substrate
T-2 prac4
the effect of changing enzyme concentration on rate of reaction
using catalase in yeast and hydrogen peroxide
method, calculations, outcomes
method
- using 1st conc. of yeast solution, acclimatise to temp along with hydrogen perioxide. set up gas syringe
- add perioxide to yeat and attach syringe. read of volume of oxygen produced every 10 mins until3 reading are the same. repeat 3 times for each concentration of yeast solution.
rate = initial rate of reaction = gradient at steepest point of volume against time for each concentration
T2 prac 4
the effect of changing enzyme concentration on rate of reaction
evaluation points
protease
- maintaining constant temperature
- accurately making up the different concentrations
- identifying end point consistently
- difficult to see the cross through the solution
catalase and hydrogen perioxide
- attaching syringe can be slower allowing loss of gas
- inaccurate reading of syringe
- inaccurate reading of syringes in making up dilutions
- reaction going too quickly to read
T3 prac 5
observing mitosis
methods, calculations, outcomes
chromosomes stained blue using orcein ethanoic stain
- place test tube of 2cm3 of 1M HCl into 60oc water bath
- cut of 1-2 cm of root tip. place in watch glass containing 2cm3 of acetic alcohol for 12 mins.
- remove then place into another watch glass containing 5 cm3 of ice cold distilled water. leave 4-5 min remove and dry
-place tips into heated HCl for 5 mins then repeat process.
transfer 1 tip to microscope slide gently macerate with mounted needle add 1 small drop of orcein ethanoic stain and leave for 2 mins. add cover slip and blot with filter paper.
- view under microscope to observe mitosis.
calculations: percentage of cells in each stage of mitosis
mitotic index. the number of cell containing visible chromosomes + total number of cells in the field of view.
T3 prac 5
observing mitosis
evaluation issues (3)
- resolution of microscope
- human error in counting number of cells
- enough time in the solution to enable successful maceration or staining
T4 prac 6
the strength of plant fibres
variables
(2 control)
independent. source and type of fibre
dependent. mass that can be held
control
length of fibre
- size of each individual mass