Practical skills

• suggest why the area under the curve is used as a measure of infection instead of looking at visible area of infection

  • shows total/cumulative infection over time
  • on different days level of infection could be different
• what's the correct way of dealing with an anomalous result? (PPQ)

  • anomaly should be identified and excluded from processing
  • anomaly must be identified but could be included in calculations
  • repetition to obtain another reading
• why is it important to conduct repeats?

  • so a mean can be calculated
  • so anomalous results can be identified and excluded from results
  • so statistical test can be conducted
• why do we calculate % change in mass during osmosis experiments rather than change in mass?

  • different starting masses
  • allows for more accurate comparisons between changes in mass/readings
• what is the justification when using a t-test?

  making comparisons between means (relate it to experiment)
• what is a criticism of graphs displaying co-variables with a correlational relationship?

  cause and effect can't be identified
• how can you improve the validity of an investigation? state ways to do it and reasons

  increase sample size-

  • can identify and remove anomalies
  • improves repeatability

  conduct statistical test-

  • determines if there's a significant different between means

  calculate SD

  • add error bars
• true or false- method of random sampling must be stated in question to improve a procedure rather than just saying random sampling was used

  TRUE- improves repeatability and ensures procedures are standardised
• how can you improve accuracy of data?

  • increase sample sizes (specific examples)
  • repeat and calculate means
  • identify anomalies and exclude them
• what limits validity?

  • human interpretations of measurement can question accuracy
• state three ways of improving the quality of a mounted specimen to view under a light microscope.

  • use sharp blade- to obtain the thinnest section of the specimen- higher resolution
  • select thin slides/cover slips- so maximum light can penetrate through the sample
  • use a wet mount/squashed slides- prevents dehydration and makes cells easier to see
• discuss the benefits of using stains when making slides for light microscopy

  • contrast- to make structures stand out from others
  • gram staining- can identify gram positive and negative bacteria from crystal violet, so can identify treatments for killing bacteria
  • clearer image obtained
• during osmosis practicals of eg cells or visking tubing, what factor changes as the concentration of sucrose solution changes?

  water potential
• how should continuous data be represented?

  • in a line graph
  • state what each axis should be labelled as - y axis dependent variable, x axis independent variable
• what is an advantage of covering more in-between values when manipulating an independent variable (eg- temperatures as IVs of 5, 10, 15, and 20 degrees, cover more values inbetween like 7 degrees or 13 degrees)

  • clear trend can be identified
  • relate to question- can identify more clearly specific temperature/conc/etc something happens at
• state two important controls that is needed when conducting an osmosis experiment

  • wiping off excess sucrose solution/water/whatever- improves accuracy of mass measurement
  • use same size pieces- reduces surface area effect for osmosis
• what do range bars show? (NOT error bars, error bars use SD)

  less repeatability
• what is important to mention when planning a serial dilution?

  • volume of stock solution vs water to use for making up each concentration
  • the scale of measurement you're using and the vessel of measurement used (eg- 100cm cubed measuring cylinder- state resolution)
• what benefit is associated with making an experiment more repeatable?

  % error reduces
• describe the processes involved with TLC

  • silica gel applied to rigid surface like a sheet of glass
  • AAs are added to one end of the gel
  • this end is submerged in organic solvent
  • organic solvent moves through silica gel (mobile phase)
  • rate at which different AAs move through gel depends on H bonds they have with silica in stationary phase, and the solubility in mobile phase
  • this is how the AAs separate from each other
  • sprayed with ninhydrin and a purple/brown colour produced
  • centre of each spot marked with a pencil and the Rf value calculated