Practical Skills in Biology

Question 1

What are precise results?

Answer 1

Precise results don’t vary much from the mean. Precision is reduced by random error.

Question 2

What is the difference between repeatable and reproducible?

Answer 2

Repeatable means that if the same person repeats the experiment using the same methods and equipment, they will get the same results.
Reproducible means that if someone different does the experiment, using a slightly different method or piece of equipment, the results will still be the same.

Question 3

What does valid mean?

Answer 3

Valid results answer the original question. To get valid results you need to control all the variables to make sure you’re only testing the things you want to.

Question 4

What does accurate mean?

Answer 4

Accurate results are really close to the true answer. Human interpretation of a measurement (e.g. determining a color change) can reduce the accuracy of results.

Question 5

What is the independent variable?

Answer 5

The variable that you change

Question 6

What is the dependent variable?

Answer 6

The variable that you measure

Question 7

Why should you control variables?

Answer 7

When you are investigating a variable you need to keep everything that could affect it constant. This means you can be sure that only your independent variable is affecting the dependent variable/your results

Question 8

What are negative controls, and why should they be used?

Answer 8

Negative controls are used to check that only the independent variable is affecting the dependent variable. Negative controls aren’t expected to have any effect on the experiment.

Question 9

Why should you repeat an experiment?

Answer 9

The experiment should be repeated at least three times and a mean should be calculated- this reduces the effect of random error on your experiment, which makes your results more precise. Doing repeats and getting similar results each time also shows that your data is repeatable and makes it more likely to be reproducible.

Question 10

What do you need to decide timewise during an experiment?

Answer 10

You need to decide what you are going to measure and how often you are going to take measurements/what intervals.

Question 11

How do you choose the most apparatus equipment and techniques for the experiment?

Answer 11

• use sensitive enough measuring equipment
• use appropriate equipment and apparatus
• use the correct technique

Question 12

How do you use a pipette?

Answer 12

Graduated pipettes have a scale so you can measure specific volumes- make sure you read the meniscus at eye level.

Question 13

How do you use a water bath?

Answer 13

Make sure you allow time for water baths to heat up before starting your experiment. Don’t forget that your solutions will need time to get to the same temperature as the water before you start the experiment too.

Question 14

How do you use a data logger?

Answer 14

Decide what you are measuring and what type of data logger you will need. Connect an external sensor to the data logger if you need to. Decide how often you want the data logger to take readings depending on the length of the process that you are measuring.

Question 15

What must be constant across all data collected?

Answer 15

Units

Question 16

What are risk assessments and why are they useful

Answer 16

They are needed to asses all the dangers in an experiment, who is at risk, and what can be done to reduce these risks
You also need to consider any ethical issues.

Question 17

How do you draw out a table to record your data?

Answer 17

• include enough rows and columns
• make sure each column has a heading and units
• this makes it easier to see anomalous results

Question 18

How do you calculate percentage change?

Answer 18

Percentage change = (final value- original value)/original value x100

Question 19

How do you calculate the mean and the range?

Answer 19

Mean= sum of values/number of values
Range= largest value- smallest value

Question 20

What does standard deviation tell you and how do you calculate it?

Answer 20

Standard deviation can be more useful than the range because it tells you how values are spread about the mean rather than just the total spread of data. A small standard deviation means the repeated results are all close to the mean- so the results are similar.

Question 21

What is the student’s t-test and what is it used for?

Answer 21

You can use the student’s t-test when you have two sets of data that you want to compare. It tests whether there is a significant difference in the means of the two data sets. The value obtained is compared to a critical value, which helps you decide how likely it is that the results or ‘differences in the mean’ were due to chance. If the value obtained is less than the critical value at a probability value of 5% or less then you can be 95% confident that the difference is significant and not due to chance. You can then reject the null hypothesis.

Question 22

What is the chi-squared test and what is it used for?

Answer 22

You can use the chi-squared test when you have categorical grouped data and you want to compare whether your observed results are statistically significant from your expected results. You compare your result to a critical value- if it is larger than the critical value at P=0.05 you can be 95% certain the difference is significant

Question 23

When will you use bar charts or pie charts?

Answer 23

When you have qualitative data or discrete data

Question 24

When will you use histograms or line graphs?

Answer 24

When you have continuous data

Question 25

When will you use a scatter graph?

Answer 25

When you want to plot one variable against the other.

Question 26

Why do you use logarithms when plotting graphs?

Answer 26

You use them when plotting graphs with very small or very large numbers on the same axis

Question 27

How do you find the rate from line graphs?

Answer 27

Calculating the gradient on a linear graph
Drawing a tangent and calculating a gradient on a curved non-linear graph

Question 28

What types of correlation can you have?

Answer 28

Positive, Negative, and no correlation

Question 29

What is the spearman’s rank correlation coefficient?

Answer 29

It is a statistical test that allows you to work out the degree to which two sets of data are correlated. It is given as a value between 1 and -1 . 1 means strong positive -1 means strong negative correlation. You can then compare your results to a critical value to find out whether or not the correlation is significant.
You have to be careful as a correlation could be due to change or there could be a third variable having an effect.

Question 30

What is a casual relationship in correlation?

Answer 30

If there is a relationship between two variables and a change in one variable does cause a change in the other it is called a casual relationship.

Question 31

How do you calculate percentage error?

Answer 31

Percentage error= uncertainty/reading x100

Question 32

How do you lower the uncertainty in an experiment?

Answer 32

You can plan your experiment so you measure a greater amount or use more sensitive equipment