Daphnia CP Flashcards
which stats test is used in daphnia practical, what is it used for and what can it tell you?
spearmans rank correlation coefficient, used for continuous data of 2 variables. can tell you whether theres a statistically significant correlation between 2 measurements from the same sample when you have 5-30 pairs of data
what does correlation of below 0 mean
negative correlation, 2 variables dont correlate
what symbol represtents the correlation coefficient in spearmans rank? and what will the number be comapred to?
rs (will be a number between -1 and 1) will be compared to numbers in a table of critical values.
what does N represent?
the number of individuals in the sample
What does D represent?
The difference in rank (measure of the strength and direction of the association between two ranked variables) of the 2 measurements made on an individual
how can you find ∑D²
-rank each individuals measurement in the experiment from lowest to highest
-2 different rankings for each variable
-where 2 or more individuals have the same measurement the can get an average rank (e.g. if they were both the 4th lowest they would get the average rank 4.5 each or if 3 ranked 3rd they would all be given rank 4(3+4+5/3=4))
-find the square of the differences between each individuals rank for the 2 variables (e.g if an indvd ranked 2 for one variable and 5th for another it would be 3 (5-3) squared so 9)
- find the sum of the square differences for each indvd in the experiment (∑D²) - remember D=difference in rank
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explain how to use ∑D² and N to find the correlation coefficient
use equation:
rs= 1- (6 x ∑D² / N³ - N)
N= number of individuals in an experiment
D= difference in rank
number should be between -1 and 1- thats the correlation coefficient
How can you use the correlation coefficient to find if theres a statistically significant correlation between 2 variables and know whether to accept or reject our null hypothesis?
compare rs value to a table of critical values, is the rs value is above the critical value we can reject the null hypothesis- there is a statistically signif correlaysh
if it is below we accept null hypothesis, no signif correlaysh
describe the methods used in caffeine practical to lessen harm to daphnia
Returning the Daphnia to their natural habitat after use
Storing the Daphnia in conditions that replicate their natural environment
Working at a good pace to minimise time Daphnia are under any possible stress
Turning off the microscope lamp when not in use, as Daphnia are poikilotherms (cold-blooded)
Not using an excessive amount/concentration of caffeine
what is controlled in this experiment
Temperature – measure temperature with thermometer. Carry out in same place
Volume of solutions – use same number of drops on Daphnia each time
Stress of Daphnia – try to minimise stress of Daphnia (explained in Ethical Considerations section)
Size of Daphnia – try to pick Daphnia of around the same size for repeats
Time to acclimatise – leave Daphnia in caffeine solution for same amount of time to acclimatise (e.g. 5 minutes)
dependent variable
Heart rate of Daphnia (beats per minute)
independent variable
Caffeine concentration (M)
how to present results found in experiment
present your data in an appropriate table and graph. Work out any mean values from your repeats. The standard deviation can be displayed on the graph using error bars.
why use daphnia?
-reproduce asexually so no threat to reproduction
-less complex CNS so less awareness of pain
-very common, no threat of extinction
-transparent so can see heart and count heart beats
