SPA techniques:
Graph plotting
- Draw a line graph unless there is a good reason for doing otherwise(i.e. not bar charts, histograms)
- Identify the independent variable-the one that is changed or manipulated.
- Identify the dependant varaible-the one that is measured-on which the readings are made.
- use a sharp 2B or HB pencil
- Horizontal(X) axis should show the Independant variable
- Vertical(y) axis should show the dependant variable-the readings made
- use a simple scale
- Fill at least 2/3 or 1/2 the graph paper, but don't spill off the edges.
- label the graph(eg. The temperature on rate of reaction or Graph of rate of reaction(y-axis) against time(x-axis)
- label the axes and give the units(based on the table of data)
- Ringed dots or crosses to plot the points
- If the shape of the curve is not very clear, then draw a line of curve of best fit.
- if there is a relationship between the variables, draw a line of best fit/curve
- If you are not sure of the relationship between the variables and you do not need to extrapolate, then join the successive points with straight ruled lines.
- if you need to extrapolate or read the values from the graph, you should draw a line of best fit/curve
Otherwise, draw the dots accurately with ruled straight lines.
ERRORS
- Errors: Sampling error
- (Small sample size) use only one potato strip per salt concentration
- (Bias in sample selection against random selection) example, choosing seeds that are brightly-coloured in a seed pod for measurement in the study of genetic variation in seed length
- Experimental error
- Equipemnt, apparatus or materials that give inaccurate or unreliable results-failure to check for zero error.
- Sampling materials which are at different physiological stages
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