General terms and advice for exam papers Flashcards

1
Q

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

A
  • 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
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2
Q

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

A

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
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3
Q

Define the term ‘reliabilty’

A
  • 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
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4
Q

Define the term ‘validity’

A
  • 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
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5
Q

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

A

If pH is not maintained:

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

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6
Q

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

A

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
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7
Q

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

A

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
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8
Q

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

A

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
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9
Q

Define the term ‘accuracy’

A
  • 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
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10
Q

Define the term ‘precision’

A
  • 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
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11
Q

Define the term ‘fair test’

A
  • 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
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12
Q

Define the term ‘control test’

Hint: this is NOT the same as a fair test

A
  • 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
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13
Q

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

A

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

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14
Q

Define an anomalous result

A

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

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15
Q

Define the term ‘evidence’

A

Data which has been shown to be valid

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16
Q

Define the term ‘hypothesis’

A

A proposal intended to explain certain facts or observations

17
Q

Define the term ‘prediction’

A

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

18
Q

Define the term ‘limitation’

A
  • 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
19
Q

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

A
  • 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
20
Q

Define the term ‘resolution’ in microscopy

A

The ability to distinguish between 2 specific points

21
Q

Define an ‘error’

A
  • 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
22
Q

Define a ‘measurement error’

A

The difference between a measured value and the true value

23
Q

Define a ‘random error’

A
  • 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
24
Q

Define a ‘systematic error’

A
  • 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
25
Q

Define a ‘zero error’

A
  • 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
26
Q

Define the term ‘uncertainty’

A
  • 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%’
27
Q

Define a ‘categoric variable’

A

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

28
Q

Define a ‘continuous variable’

A
  • 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

29
Q

Define a ‘control variable’

A

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

30
Q

Define a ‘dependent variable’

A

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

31
Q

Define an ‘independent variable’

A

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

32
Q

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

A
  • 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
33
Q

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

A

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