Key Terms

Question 1

Dependent variable

Answer 1

The factor you measure in the experiments

Question 2

Confounding variables

Answer 2

The factors you keep the same for the experiment

Eg temperature

Question 3

Control experiment

Answer 3

To check that the difference in results is due solely to the independent variable

Question 4

Sample size

Answer 4

Enough for a stats test?
Makes sample representative
Identify anomalous results
Time available for experiment

Question 5

Mode

Answer 5

Most common value

Question 6

Median

Answer 6

Middle value in range

Question 7

Range

Answer 7

Give smallest and largest value

Don’t calculate difference

Question 8

Standard deviation

Answer 8

Gives the variation around the mean

Question 9

Designing an experiment

Answer 9

State IV and DV
Identify confounding variables x2
Repeat
Carry out stats test
Identity if significant difference

Question 10

Water bath use

Answer 10

To maintain constant temp
Monitor temp constantly, using thermometer
Control temp by adding hot/ cold water
Water has high specific heat capacity

Question 11

Isotonic solutions

Answer 11

No net movement of water/ no osmosis
Due to equal water potentials
Prevents shrinking and bursting of cells

Question 12

Why use cold solutions

Answer 12

Prevents enzyme activity

Question 13

Preventing heat gain from lamp

Answer 13

Use glass/ plastic sheet between heat source and experiment
Use low energy light bulb
Increase water volume with tin experiment

Question 14

Why control temp?

Answer 14

Enzyme activity increases as temp increases
Refer to no. of ES complexes formed
At high temp, may denature enzymes

Question 15

Establishing anaerobic conditions

Answer 15

Layer of oil on top of solution
No oxygen diffuses to solution
Oxygen declines in solution
Will be initially aerobic

Question 16

Why cover solutions?

Answer 16

Prevent evaporation of water
Changes to concentrations
Prevent contamination with bacteria

Question 17

Features to control when choosing individuals for experiments

Answer 17

Age
Sex
Genes/ alleles
Same body size
Ethnic group

Question 18

Repeat experiment with same animal

Answer 18

Individuals behave differently
Reduces variation
Data not comparable with other data

Question 19

Repeat experiment with different animals

Answer 19

More representation of population
Prevent organisms learning
Reduced stress on organisms

Question 20

Why wait a few minutes for equilibrium

Answer 20

To establish new conditions (temp, humidity…)
To allow rate of reaction to become constant
Ensure behaviour of organism is typical
Handling effect reduced

Question 21

Reliability

Answer 21

Repeat to improve reliability
Identify anomalies
Calculate reliable mean
Enough repeats for stats test
Allows procedure to be checked (peer review)

Question 22

Anomalous result/ variation

Answer 22

Biological organisms show huge variation
An anomalous result must fall outside normal/ expects range
Otherwise down to variation

Question 23

Counting bubbles

Answer 23

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

Question 24

Potassium hydroxide

Answer 24

Used to absorb carbon dioxide

Question 25

Random sampling

Answer 25

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

Question 26

Transect

Answer 26

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

Question 27

Dry mass

Answer 27

Heat sample to 100’c to evaporate water off
Weigh and heat until no further change in mass
Makes more accurate comparisons

Question 28

Independent variable

Answer 28

The factor you change in the experiment