General terms and advice for exam papers

Question 1

Define the term ‘repeatable’ and explain how to make a procedure/method repeateable

Answer 1

• If the experiment is carried out by the same person using the same method and equipment the same results are obtained

Hint: don’t say if it is “repeated” by a person use the expression ‘carried out’

How to make the method repeatable

• To ensure the method is repeatable the steps within the procedure must clearly state:
  
  • Time periods: acclimatising, between readings etc
  • Volumes used
  • Concentrations of solutions
  • Temperature(s)
  • Sizes: lengths/masses etc
  • Use of any buffers

Question 2

Define the term ‘reproducible’ and explain how to make the procedure/method reproducible

Answer 2

Definition

• If the experiment is carried out by a different person and/or a using a different method and/or using different equipment the same results are obtained
• To ensure the method is reproducible the steps within the procedure must clearly state:

How to make the method reproducible

Include the following details in the method

• Specify exact time periods for acclimatising, between readings etc
• Specify exact volumes used
• Specify exact concentrations of solutions
• Specify exact temperature(s)
• Sepcify exact sizes: lengths/masses etc
• State that you will use buffers

Question 3

Define the term ‘reliabilty’

Answer 3

• reliability is used to describe the overall consistency of a measure.
• a data set has a high reliability if similar results were produced under consistent conditions
• i.e. if the SD is small then the data is described as reliable
• a small SD means there is a little spread of the data about the mean
• hence the larger the SD the less reliable the data is

Question 4

Define the term ‘validity’

Answer 4

• this assesses if the results answer the original question
• to ensure an investigation is valid all the key variables must be controlled
• e.g.
  
  • for any enzyme controlled process: pH, temp, [E], [S]
  • for any human physiology investigation: age, gender, BMI, smoking/non-smoking, PAL

Question 5

Explain why pH must be controlled when investigating any reaction that involves enzymes

Answer 5

If pH is not maintained:

the enzyme will denature therefore the rate of reaction will decrease (or fall to zero)

Question 6

Explain why temperature must be controlled when investigating any reaction that involves enzymes

Answer 6

If temperature increases:

• increase in temperature leads to increase in kinetic energy
• This will increase the number of successful collisions
• This will mean more enzyme substrate complexes will be formed
• Which will increase rate of reaction

If temperature decreases:

• decrease in temperature leads to decrease in kinetic energy
• This will decrease the number of successful collisions
• This will mean less enzyme substrate complexes will be formed
• Which will decrease rate of reaction

Question 7

Explain why the substrate concentration must be controlled when investigating any reaction that involves enzymes

Answer 7

If the substrate concentration increases:

• An increase substrate concentration will increase the number of molecules present
• This will increase the number of successful collisions
• This will mean more enzyme substrate complexes will be formed
• Which will increase rate of reaction

If the substrate concentration decreases:

• An decrease substrate concentration will decrese the number of molecules present
• This will decrease the number of successful collisions
• This will mean less enzyme substrate complexes will be formed
• Which will decrease rate of reaction

Question 8

Explain why the enzyme concentration must be controlled when investigating any reaction that involves enzymes

Answer 8

If the enzyme concentration increases:

• An increase senzyme concentration will increase the number of molecules present
• There will be an increased number of active sites available
• This will increase the number of successful collisions
• This will mean more enzyme substrate complexes will be formed
• Which will increase rate of reaction

If the enzyme concentration decreases:

• An decrease enzyme concentration will decrese the number of molecules present
• There will be a reduced number of active sites available
• This will decrease the number of successful collisions
• This will mean less enzyme substrate complexes will be formed
• Which will decrease rate of reaction

Question 9

Define the term ‘accuracy’

Answer 9

• If the data is accurate then it is close to the true value
• Some techniques are inherently less accurate:
  
  • counting bubbles (as bubble size can vary) → instead collect the volume of gas in a gas syringe or a upturned graduated measuring cylinder (or graduated pipette depending on the total volume of gas to be collected)
  • colour changes (as subjective) → instead use a colour standard comparator or a colorimeter which is zero referenced

Question 10

Define the term ‘precision’

Answer 10

• Precision is how close these data, measurements or results are to each other, working as a measure of the spread of data from the mean
• To increase precision the spread about the mean must be reduced
• i.e. reduce any random errors within the procedure

Question 11

Define the term ‘fair test’

Answer 11

• All variables other than the IV are kept constant
• A fair test is one in which only the independent variable has been allowed to affect the dependent variable

Question 12

Define the term ‘control test’

Hint: this is NOT the same as a fair test

Answer 12

• only the IV is changed
• all other factors remain constant
• acts as a negative control
• i.e. this “proves” that it is the changes in the IV that cause the changes in the DV
• run the experiment in the same conditions but replace the IV with an alternative that is not expected to generate results e.g.
  
  • respirometers: replace respiring organism with glass beads or dried seeds
  • enzyme controlled processes: replace enzyme with boiled enzyme or distilled water

Question 13

When carrying out any investigation, state and explain how many replicates you should consider

Answer 13

State:

• Always carry out at least 3 replicates at each value of the IV

Hint: state the actual number don’t just say “do repeats” or “repeat” – you must quantify it

Explanation:

• Replicates reduce the effect of random errors
• This increases precision of the data
• Also shows the data is repeatable
• And hence it is more likely to be reproducible
• Good practice is to use all 3 pieces of data when calculating a mean – this is because with only 3 pieces of data you can’t be certain that one piece of data is anomalous

Remember: replicates do not affect validity

Question 14

Define an anomalous result

Answer 14

These are values in a set of results which are judged not to be part of the variation caused by random uncertainty

Question 15

Define the term ‘evidence’

Answer 15

Data which has been shown to be valid

Question 16

Define the term ‘hypothesis’

Answer 16

A proposal intended to explain certain facts or observations

Question 17

Define the term ‘prediction’

Answer 17

A prediction is a statement suggesting what will happen in the future, based on observation, experience or a hypothesis

Question 18

Define the term ‘limitation’

Answer 18

• A design fault
• An action that affects every run of the entire investigation (i.e. equally affects every replicate)
• Do not list human errors here
• Consider resolution of the measuring apparatus
• Have all variables been appropriately controlled
• Have all solutions been acclimatised to the correct temperature before mixing etc

Question 19

Define the term ‘resolution’ when referring to a piece of apparatus’

Answer 19

• This is the smallest change in the quantity being measured (input) of a measuring instrument that gives a perceptible change in the reading.
• E.g. Ruler: resolution is 0.5mm

Question 20

Define the term ‘resolution’ in microscopy

Answer 20

The ability to distinguish between 2 specific points

Question 21

Define an ‘error’

Answer 21

• These are one off human mistakes!
• Only affect that one replicate and run e.g.
  
  • failure to start or stop timer appropriately
  • parallax error in reading the meniscus, using the incorrect named solution e.g. named enzyme/ inhibitor/ substrate solution
  • failing to tare the top pan balance between reading
  • using an incorrect volume of a named solution

Question 22

Define a ‘measurement error’

Answer 22

The difference between a measured value and the true value

Question 23

Define a ‘random error’

Answer 23

• These cause readings to be spread about the true value, due to results varying in an unpredictable way from one measurement to the next
• Random errors are present when any measurement is made, and cannot be corrected
• The effect of random errors can be reduced by making more measurements and calculating a new mean

Question 24

Define a ‘systematic error’

Answer 24

• These cause readings to differ from the true value by a consistent amount each time a measurement is made
• Sources of systematic error can include the environment, methods of observation or instruments used
• Systematic errors cannot be dealt with by simple repeats
• If a systematic error is suspected, the data collection should be repeated using a different technique or a different set of equipment, and the results compared

Question 25

Define a ‘zero error’

Answer 25

• Any indication that a measuring system gives a false reading when the true value of a measured quantity is zero, e.g. the needle on an ammeter failing to return to zero when no current flows
• A zero error may result in a systematic uncertainty

Question 26

Define the term ‘uncertainty’

Answer 26

• The interval within which the true value can be expected to lie, with a given level of confidence or probability
• E.g. ‘the temperature is 20 °C ± 2 °C, at a level of confidence of 95%’

Question 27

Define a ‘categoric variable’

Answer 27

Categoric variables have values that are labels, e.g. names of plants or types of material

Question 28

Define a ‘continuous variable’

Answer 28

• Continuous variables can have values (called a quantity) that can be given a magnitude either by counting (as in the case of the number of shrimp) or by measurement e.g. light intensity, flow rate etc)

Previously known as discrete variable

Question 29

Define a ‘control variable’

Answer 29

Control variable is one which may affect the outcome of the investigation and therefore has to be kept constant or at least monitored

Question 30

Define a ‘dependent variable’

Answer 30

Dependent variable is the variable of which the value is measured for each and every change in the independent variable

Question 31

Define an ‘independent variable’

Answer 31

Independent variable is the variable for which values are changed or selected by the investigator

Question 32

Make sure you remember the rules for how to draw a table

Answer 32

• IV in the first column (ascending or descending order) with correct unit symbols (see above)
• DV to the right of the IV with correct unit symbols (see above)
• Each category/value of the IV recorded in separate row
• Mean (NOT average) column to the right of the DV
• Informative column headings
• All cells surrounded by straight ruled lines with complete outer border
• All DV recorded to the appropriate level of precision
• Replicates recorded together for each IV category/value
• All mean values calculated correctly AND recorded to consistent number of decimal places AND all means recorded to one more decimal place than raw data (unless told otherwise)
• All lines must be drawn with a ruler
• The outer border must be complete around the entire table

Question 33

Make sure you remember the rules for how to draw a table

Answer 33

Hint: Think SPLATT

S = Scale - on each axis each gap must be of equal size

P = Plots - make sure these are accurate to +/- half a small square

L = Labels on axis - make sure your labels clearly state what the data is and include units

A = axis - make sure the independent variable is on the x-axis and the dependent variable is on the y-axis

T = title - it is good practice to always include an informative title

T = type of graph: make sure you have use a bar graph,, histogram or line graph