Key Terms Flashcards
Dependent variable
The factor you measure in the experiments
Confounding variables
The factors you keep the same for the experiment
Eg temperature
Control experiment
To check that the difference in results is due solely to the independent variable
Sample size
Enough for a stats test?
Makes sample representative
Identify anomalous results
Time available for experiment
Mode
Most common value
Median
Middle value in range
Range
Give smallest and largest value
Don’t calculate difference
Standard deviation
Gives the variation around the mean
Designing an experiment
State IV and DV Identify confounding variables x2 Repeat Carry out stats test Identity if significant difference
Water bath use
To maintain constant temp
Monitor temp constantly, using thermometer
Control temp by adding hot/ cold water
Water has high specific heat capacity
Isotonic solutions
No net movement of water/ no osmosis
Due to equal water potentials
Prevents shrinking and bursting of cells
Why use cold solutions
Prevents enzyme activity
Preventing heat gain from lamp
Use glass/ plastic sheet between heat source and experiment
Use low energy light bulb
Increase water volume with tin experiment
Why control temp?
Enzyme activity increases as temp increases
Refer to no. of ES complexes formed
At high temp, may denature enzymes
Establishing anaerobic conditions
Layer of oil on top of solution
No oxygen diffuses to solution
Oxygen declines in solution
Will be initially aerobic
Why cover solutions?
Prevent evaporation of water
Changes to concentrations
Prevent contamination with bacteria
Features to control when choosing individuals for experiments
Age Sex Genes/ alleles Same body size Ethnic group
Repeat experiment with same animal
Individuals behave differently
Reduces variation
Data not comparable with other data
Repeat experiment with different animals
More representation of population
Prevent organisms learning
Reduced stress on organisms
Why wait a few minutes for equilibrium
To establish new conditions (temp, humidity…)
To allow rate of reaction to become constant
Ensure behaviour of organism is typical
Handling effect reduced
Reliability
Repeat to improve reliability Identify anomalies Calculate reliable mean Enough repeats for stats test Allows procedure to be checked (peer review)
Anomalous result/ variation
Biological organisms show huge variation
An anomalous result must fall outside normal/ expects range
Otherwise down to variation
Counting bubbles
Used for photosynthesis/ respiration Assume: Bubbles same size Proportion of gases same in each bubble No gas diverted into another process All bubbles rise, not trapped Can count bubbles accurately
Potassium hydroxide
Used to absorb carbon dioxide
Random sampling
Used to estimate population size Random number generator calculator Generate coordinates Tape measures perpendicular to represent axis Place quadrat at coordinate Count no. of organisms Repeat to calculate running mean Multiply to get no. of organisms considered
Transect
Used to identify change in organisms in habitat
Place tape on ground
Identify clearly direction placed towards
Systematic sampling (every 5 metres)
Count organisms
Repeat, 5 quadrats at each sampling point
Calculate mean
Dry mass
Heat sample to 100’c to evaporate water off
Weigh and heat until no further change in mass
Makes more accurate comparisons
Independent variable
The factor you change in the experiment
