core practicals

Question 1

daphnia variables

Answer 1

I- caffeine conc
D- heart rate of daphnia
C- age/ mass/ size/ species of daphnia (from same brood)
temperature, volume of solutions, activity of daphnia, time for acclimatisation

Question 2

daphnia method

Answer 2

place daphnia on cavity slide
use cotton wool to restrict movement
add distilled water and leave to acclimatise for 5 mins
count hr under microscope for 30s
repeat with 5 diff concentrations of caffeine
repeat each conc at least 3 times with different daphnia
ethical considerations

Question 3

limitations of daphnia

Answer 3

may not all be same size
microscope light could increase temp
high concentrations of caffeine/ high stress ma kill daphnia
counting/ calculation of hr may be inaccurate

Question 4

other contexts of daphnia practical

Answer 4

use of isolated hearts rather than whole organism
different sources of caffeine (eg tea vs coffee)
effect of caffeine conc on hr of zebra fish

Question 5

vitamin c practical variables

Answer 5

I- different types of fruit juice
D- volume of juice required to decolourise 1cm3 of DCPIP
volume of DCPIP required to discolour 1cm3 juice
control: temperature, conc of DCPIP, volume of DCPIP, shaking of test tube, end point (extent of decolourisation)

Question 6

vitamin c method

Answer 6

pipette 1cm3 blue DCPIP into a test tube
at 1% vitamin c solution drop by drop (titrate)
shake tube gently after each drop
continue until blue colour disappears
record volume needed to decolourise
repeat twice more and calculate a mean
repeat procedure with different juices

Question 7

vit c evaluation/ limitations

Answer 7

inconsistent shaking may add oxygen and restore DCPIP to blue
temperature may be difficult to control
end point may be difficult to judge
colorimeter may be used to make end point more accurate
volumes must be measured precisely

Question 8

other contexts of vit c practical

Answer 8

measuring vit c content of different foods
comparing fruit from different sources
comparing effect of storage time

Question 9

temp on permeability of membranes variables

Answer 9

independent- temp of water
dependent- absorbance of resulting solution (measured using a colorimeter)

Question 10

effect of alcohol on permeability of membranes variables

Answer 10

independent- concentration of alcohol
dependent- absorbance of light. by resulting solution