rqp daphnia

Question 1

caffiene effects on humans

Answer 1

stimulant drug
raised stress and blood pressure.

Question 2

risk assessment

Answer 2

pond water may carry bacteria
wash hands before and after handling the daphnia or pond water

Question 3

independent variable

Answer 3

caffience concentration

Question 4

dependent variable

Answer 4

heart rate of daphnia (BPM)

Question 5

control variables

Answer 5

temperature- use thermometer
volume of solutions- same number of drops each time
stress of daphnia- try to minimise stress
size of daphnia- pick daphnia around same size for repeats
time to acclimatise- daphnia in solution for same amount of time to acclimatise

Question 6

how to minimise stress/suffering for daphnia

Answer 6

return daphnia to natural habitat after
store dapnia in replicated natural conditions
work in a fast pace to minimise time under stress
turn off microscope lamp whne not in use-daphnia are cold blooded
dont use an excessive amount of caffeine

Question 7

why are daphnia used?

Answer 7

common- not threat to species
no threat to reproduction- they reproduce asexually, so no loss of genetic variation
less developed nervous system- reduced pain awareness
transparent-heart is visible

Question 8

control experiment

Answer 8

count heart rate when caffiene conc is 0 in DISTILLED/POND water

Question 9

method

Answer 9

-Remove 1 Daphnia with a pipette and place it in a cavity slide under a microscope.
-Dab around the Daphnia with a tissue to remove the pond water and replace with drops of caffeine solution (e.g. 0.1M).
-Leave the Daphnia for 5 minutes to acclimatise and then observe & count (using a counter) the heart rate under the microscope for 30 seconds (multiply number by 2 to calculate beats per minute).
-Repeat this for measurements across 5 different caffeine concentrations (e.g. 0.2M, 0.3M, 0.4M and 0.5M).
-Repeats can then be carried out with two other Daphnia.

Question 10

evaluation points

Answer 10

left too long under microscpe- temp increase=faster heart rate (random error)
too high conc of caffeine-kills daphnia (systematic error)
water from daphnia extraction may have diluted caffeine conc (random error)
heart rate only counted for 30 seconds-missed beats, so count for 60 secs (systematic)