Practicals

• Interval


  The quantity between readings, e.g. a set of 11 markings equally spaced over a distance of 1 metre would give an interval of 10 centimetres
• Precision


  Precise measurements are ones in which there is very little spread about the mean
• Prediction


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


  The maximum and minimum values of the independent or dependent variables important in ensuring that any pattern is detected
• Repeatable


  A measurement is repeatable if the original experimenter repeats the investigation using the same method and equipment and obtains the same results
• Reproducible


  A measurement is reproducible if the investigation is repeated by another person, or by using different equipment or techniques, and the same results are obtained
• Resolution


  The smallest change in the quantity being measured (input) of a measuring instrument that gives a perceptible change in the reading
• Sketch graph


  A line graph, not necessarily on a grid, that shows the general shape of the relationship between two variables. It will not have any points plotted and although the axes should be labeled they may not be scaled
• True value


  The value that would be obtained in an ideal measurement
• Uncertainty


  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%"
• Validity


  Suitability of the investigative procedure to answer the question being asked
• Valid conclusion


  A conclusion supported by valid data, obtained from an appropriate experimental design and based on sound reasoning
• Variables


  • Physical, chemical or biological quantities or characteristics
  • Categoric (values that are labels)
  • Continuous (values that can be given a magnitude)
  • Control (may affect the outcome and must be kept constant)
  • Dependent (value is measured for each change in the independent variable)
  • Independent (variable for which values are changed or selected by the investigator)
• Precision depends only on the extent of random errors - it gives no indication of how close results are to the true value
• A sketch graph will not have any points plotted and although the axes should be labeled they may not be scaled
• A valid conclusion is supported by valid data, obtained from an appropriate experimental design and based on sound reasoning
• Categoric variables have values that are labels, e.g. names of plants or types of material
• 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.)
• A control variable is one which may, in addition to the independent variable, affect the outcome of the investigation and therefore has to be kept constant or at least monitored
• The dependent variable is the variable of which the value is measured for each and every change in the independent variable
• The independent variable is the variable for which values are changed or selected by the investigator
• Accuracy


  A measurement result is considered accurate if it is judged to be close to the true value
• Calibration


  Marking a scale on a measuring instrument
• Data


  Information, either qualitative or quantitative, that has been collected
• Errors


  • Measurement error (difference between a measured value and the true value)
  • Anomalies (values in a set of results which are judged not to be part of the variation caused by random uncertainty)
  • Random error (cause readings to be spread about the true value, due to results varying in an unpredictable way from one measurement to the next)
  • Systematic error (cause readings to differ from the true value by a consistent amount each time a measurement is made)
  • Zero error (any indication that a measuring system gives a false reading when the true value of a measured quantity is zero)
• Evidence


  Data which has been shown to be valid
• Fair test


  A fair test is one in which only the independent variable has been allowed to affect the dependent variable
• Hypothesis


  A proposal intended to explain certain facts or observations
• Random errors are present when any measurement is made, and cannot be corrected. The fact of random errors can be reduced by making more measurements and calculating a new mean
• 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
• A zero error may result in a systematic uncertainty
• Why can the water, but not the sugar/salt move through the membrane?
• How will you measure the dependent variable (change in mass)?
• Change in mass


  Measured by initial mass - final mass
• Percentage change in mass

  (Initial mass - final mass) / initial mass
• GCSE Biology required practical activity 3: Food tests
• Food tests procedure


  1. Grind up food sample

  2. Dissolve in water

  3. Add reagents

  4. Observe colour changes
• Qualitative tests


  • Identify presence of substance, but not amount
• Quantitative tests


  • Identify amount of substance present
• GCSE Biology required practical activity 4: Enzymes