EMPA

Question 1

What are buffers used for?

Answer 1

Maintain constant pH

Question 2

You left … in a waterbath for 5 minutes first, why?

Answer 2

To equilibrate

Question 3

Did you use a water bath? Why?

Answer 3

Yes, temperature fluctuates more in air

Question 4

How did you make sure the temperature was reliable?

Answer 4

Measure temperature at the beginning and end, to show there was little variation

Question 5

Why did you do repeats?

Answer 5

Allows calculation of a mean

Allows anomalies to be identified

Question 6

Was your data reliable? Explain your answer.

Answer 6

Reliable - all values similar (or points close to best fit line)

Unreliable - give anomalous data (or points not close to best fit line)

Question 7

Why are control groups used?

Answer 7

To show the results were caused by the variable tested

Question 8

It was difficult to decide the endpoint when observing colour change, how could this be improved?

Answer 8

Use a colorimeter, record time taken to reach a set value

Question 9

Scientists found a correlation between x and y and suggested x caused y. Is this a valid conclusion?

Answer 9

No, correlation does not show a causal relationship

It may be due to another (named) factor

Question 10

Why did you shake the test tube?

Answer 10

To mix the solutions/ensure something was covered

Question 11

Why are were cold solutions used?

Answer 11

To slow down enzyme activity

Question 12

Why was an isotonic solution used?

Answer 12

Same water potential as the cells, so prevents bursting/shrinking

Question 13

How should the control group be treated?

Answer 13

Exactly the same as the experimental group, but not given the drug/given a placebo

Question 14

… was done randomly, why?

Answer 14

To avoid bias

Question 15

Why were a large number of … used?

Answer 15

To ensure the sample was representative

or

Minimise the effect of anomolies

Question 16

How could you place quadrats randomly?

Answer 16

Random number generation (e.g. using a calculator)

Using tape measures to form a grid of coordinates

Question 17

… was given as a percentage/per 1000 why?

Answer 17

To allow comparison between … with different sample sizes

Question 18

What information does standard deviation give about the data?

Answer 18

The spread of the data, about the mean

Question 19

What things affect the validity of conclusions?

Answer 19

• Animals being used, data being applied to humans
• Subjectivity of tests
• Number of species/types of … researched
• Sample size
• Overlap of data
• Suggesting a causal link from a correlation

Question 20

How is the test statistic interpreted?

Answer 20

Our value > critical value/bars do not overlap

⇒ reject null hypothesis

⇒ < 5% probability that the results are due to chance

Question 21

When investigating animals, why should the test area be cleaned between trials?

Answer 21

The animal may leave smell/substance/trail

Which could affect other animals

Question 22

In what ways should the organisms used be similar?

Answer 22

Same previous treatment

Same size/age

Same species

Question 23

Why did you do x number of trials?

Answer 23

Large enough for stastical test

The larger the sample, the more respresentative it is of the population

Not so many that insufficient time

Question 24

Did you repeat the experiment using the same organism? Why?

Answer 24

No:

Prevents learning

Reduces stress

Question 25

How can the data be used to see if there is a significant correlation/difference between x and y?

Answer 25

Construct null hypothesis

Use relevant statistical test to calculate the test statistic

Look up the critical value in the table (see if bars overlap for SE)

Use this to accept or reject the null hypothesis