practical skills in biology
TRANSCRIPT
![Page 1: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/1.jpg)
Practical Skills in BiologyExperimental Design SkillsPractical SkillsPresentationInterpretation and EvaluationCommunication
![Page 2: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/2.jpg)
Experimental skills are examinable in the final examination
Consult the syllabus (handout given out)
![Page 3: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/3.jpg)
HYPOTHESISThe starting point of any experiment – want to find out something.An idea which experiments are designed to testA testable statement (cause and effect)A statement that connects the independent and dependent variable
e.g. 1. Light intensity will affect the growth of plants
2. An increase in temperature will affect the rate of enzyme action
![Page 4: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/4.jpg)
Independent VariableAlso referred to as the experimental variableThe variable which is deliberately changedShould be plotted on x-axis of a graph
e.g. light intensity, temperature
![Page 5: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/5.jpg)
Dependent VariableThe variable which may change as a result of changes to the independent variablePlotted on y-axis of the graph
e.g. growth rate, rate of enzyme action
![Page 6: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/6.jpg)
Fair TestingFactors to be held constantAll factors that are kept the same during an experimentAn experiment can only have one independent variable.All other variables must be kept the same, this ensures a fair testEnables fair comparisone.g. light, temperature, amount, source, pH, concentration of enzymes etc
![Page 7: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/7.jpg)
ControlA control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral "reference point" for comparison that allows you to see what changing a variable does by comparing it to not changing anything.
![Page 8: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/8.jpg)
ResolutionResolution is the smallest increment measurable by an instrumentResolution is a property of the measuring instrumentIt is determined by the number of digits from the measuring instrument (this should match the number of significant figures you use in your data)Resolution relates to individual measurements
e.g. high resolution = 0.001g (electronic balance)Low resolution = 1.0g (kitchen scale)
![Page 9: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/9.jpg)
Presentation of ResultsAll observations and measurements need to be recordedConstruct tables with headings and appropriate unitsDraw graphs with a title which clearly connects the independent and dependent variablese.g. “The effect of varying enzyme concentration on the rate of respiration”Describe the results, do not explain them.e.g as the enzyme concentration increased from 20 mM to 50 mM the rate of respiration increased. Concentrations above 55 mM resulted in a decreased rate of respiration”.
![Page 10: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/10.jpg)
TablesEnzyme Concentration (mM)
Rate of Respiration (mLs-1)
5
10
15
20
45
50
55
0
12
24
32.9
42
45
0
Note headings and units for the table
Which piece of data isinconsistent?Why?
![Page 11: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/11.jpg)
Drawing GraphsAxes labelled with units and appropriate title
An appropriate scale (uniform/use most of the axis
Accurate plot of points
Line of best fit
![Page 12: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/12.jpg)
GraphThe effect of varying enzyme concentration on the rate of
respiration
-10
0
10
20
30
40
50
60
5 10 15 20 45 50 55
Enzyme Concentration (mM)
Ra
te o
f R
es
pir
ati
on
(m
Ls
-1) Series1
Linear (Series1)
Log. (Series1)
Average results werePlotted
Note choice of axes,Scales, and units
Which is the most appropriate line?
10 20 30 40
![Page 13: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/13.jpg)
Random ErrorsRandom errors are caused by any factor that randomly affects the measurement variableThe amount of random error is indicated by the amount of scatter in the dataAn increase in sample size allows averages to be calculated- this reduces the effect of random errorsMeasurements are never perfect- therefore random errors are always presente.g. inconsistent reading of scales/use of timer
![Page 14: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/14.jpg)
Systematic ErrorsSystematic errors are present when measured values consistently differ from their true valueUsually due to faulty apparatus/equipment or experimental designTend to be consistent throughout practical so an average does not rectify the problem.However repeating experiment may identify a systematic error (need to use other equipment)Consistent results indicate the conclusion(s) drawn are likely to be validBalance not calibrated, contaminant in a solution
![Page 15: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/15.jpg)
Sample SizeThe number of samples in the experimental groupIncreasing the number of samples allows averages to be calculatedReduce the effect of random errorsData will be more consistent and reliablei.e. for each concentration of enzyme you may do replicates of 3.
![Page 16: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/16.jpg)
ReliabilityRefers to the extent which an experiment yields the same result on repeated trails under the same conditions Achieve reliability by minimising random errorsUse large number of samplesBe careful with measurements during the practical
![Page 17: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/17.jpg)
To repeat or not to repeat?Repeating the experiment with same procedure and apparatus at different times helps to identify systematic errorsRepeat experiment to validate the results, experimental design and be confident in our conclusionsUseful to repeat with different equipment, solutions etc… Are the results still the same?
![Page 18: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/18.jpg)
ValidityRefers to the degree to which an assessment method measures what it is supposed to measure.It is increased by:
1. appropriate experimental design (testing what it is meant to
test)2. repeating the experiment
![Page 19: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/19.jpg)
Precision and Accuracy
Low precision,high accuracy (fluke)
Low precision,low accuracy
Low precision,high accuracy (fluke)
Low precision,low accuracy
High precision,low accuracy
High precision, high accuracy
![Page 20: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/20.jpg)
PrecisionPrecision depends on how well random errors are minimisedRandom errors are present when there is scatter in the measured values
High scatter = low precisionLow scatter = high precision
![Page 21: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/21.jpg)
AccuracyRefers to how close the result of the experiment is to the true value
Systematic errors need to be detected if the result is to be accurate
Detected by repeating experiment
![Page 22: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/22.jpg)
Precise or Accurate? Student A Student B
4.3 4.55.0 4.64.9 4.64.4 4.54.7 4.5
Mean 4.6 4.5
![Page 23: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/23.jpg)
Resolution and Precision
The resolution of the stopwatch is 0.01s but the precision of the data does not match this.
Distance (cm)
time (s) mean (s) range(s)
40 0.9 0.98 0.93 0.95 0.94 0.08
80 1.25 1.29 1.27 1.21 1.26 0.08
119.5 1.54 1.54 1.44 1.41 1.48 0.13
![Page 24: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/24.jpg)
Resolution and Precision
The resolution of the stopwatch is now 0.1s
Distance (cm)
time (s) mean (s) range(s)
40 0.9 1 0.9 1 1 0.1
80 1.3 1.3 1.3 1.2 1.3 0.1
119.5 1.5 1.5 1.4 1.4 1.5 0.1
![Page 25: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/25.jpg)
Interpretation of Data (Discussion)Written in the third person (stated objectively)Inferences can be made when interpreting the dataAn inference is a reasoning based on observation and experience. To infer is to arrive at a decision or opinion by reasoning from known factse.g. “an increase in enzyme concentration influenced the rate of respiration as more enzyme was available for the reaction.”
![Page 26: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/26.jpg)
Analysis and Evaluation of the ExperimentIdentify sources and distinguish between random and systematic errorsList ways to improve procedures of the experiment (possibly give reasons why)Comment on suitability and importance of the sample sizeComment on the accuracy and precision of the experimentComment on the value of repeating the experiment
![Page 27: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/27.jpg)
ConclusionA brief statement that relates to the hypothesisShould be written at the end of each experimentSupports or refutes the hypothesisExperiments do not prove the hypothesisConfidence in the conclusions will depend on the validity (design) of your experiment and the care in execution.e.g. “this experiment indicates that enzyme concentration does have an affect on the rate of respiration” or “no conclusion can be drawn from tis experiment due to the large number of uncontrolled factors”
![Page 28: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/28.jpg)
Other things to consider..In the Materials and Methods, list the materials/equipment you actually used, and the method you used. It needs enough detail so that someone else could repeat exactly what you did. (Especially in a Design Practical)Write in Past Tense (Impersonal) Drawings may be used in the Results sectionIntroduction- a brief review of the theory, state the aim and hypothesis of experiment.
![Page 29: Practical skills in biology](https://reader033.vdocuments.net/reader033/viewer/2022052523/5565262bd8b42a08498b5199/html5/thumbnails/29.jpg)
HAPPY EXPERIMENTING AND WRITING