Exam Techniques
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Two variables in the question
• Make comparative statements
Biotic and abiotic factors
• Always be specific e.g food, water, O2 concentration, soil concentration, sunlight,temperature e.t.c
How to describe comparisons
Valid comparison
Application question on quantity e.g. sample, volume (water, blood)
Number in sample varies
Explain
• Identify if its a knowledge/ application question • Underline key words • Write the definition of the keyword • Write down words associated with keyword topic e.g. • Plan your answer • Red blood cells: Oxygen transport • White blood cells: Immunity
Data
• Positive/ negative correlation e.g. for species • State what you see • Use variables in the question e.g. temperature • General trend: specific, range
Conclusion
• Fewer/ more (variable) • Comparison e.g higher% / lower % (variable)
keyword
Variation
concentration/diffusion/water potential gradient
maintains
Evaluate
• Other factor/ named variable might cause harm • Only one sample • No stats taken • Quote figures variables in the data
Safe
Harmful
Suggest one practical advantage of measuring the masses of frog eggs, tadpoles and adults, compared with measuring their volumes (4)
• More accurate/ less error in measuring mass • Causes less distress/ damage to animal to measure mass • Easier/ quicker to find mass because irregular shapes • Fewer measurements/ calculations
Trust your…
Gut
Key words to use when data would be similar
• Similar trends • Similar pattern • Similar peaks • Similar curve
Name two other variables the student should have kept constant during this investigation.
• Temperature; • Agitation/mixing/stirring; • Source/age/type of blueberries; • Crushing of the blueberries; • Rinsing of the blueberries prior to mixing; • Concentration of ethanol/acid;
How is standard deviation used to answer question?
• If the standard deviation does not overlap then the difference is statistically significant and the difference has not been due to chance • If the standard deviation does overlap then the difference is not statistically significant and the difference has been due to chance
• Large sample size so…. Long period of time (be specific and use the question in your answer) so… • Control used so…. • Chosen at random to…
• Large sample size so representative • Long period of time to allow… e.g. growth • Control used for comparison • Chosen at random to eliminate bias
Explain why a log scale is used to record the number of cells
• Large range/difference/increase in numbers; • Accept reference to exponential (increase)
Keywords for describing trends
• Less • Reduced • Slows
Some students investigated the effect of temperature on the rate of anaerobic respiration in yeast. The apparatus they used is shown in the diagram. The yeast suspension was mixed with glucose solution and the volume of gas collected in five minutes was recorded. Each student repeated the experiment and the results were pooled. Explain the advantages of collecting a large number of results (3)
• reduces the effect of anomalies on the mean • Increases reliability • More representative MEAN • Allows use of statistical test