Flashcards in Development Of Practical Skills :) Deck (66):
Precise results describe
Don't vary much from mean. Precision reduced by random error (unpredictable way in which all measurements vary)
Repeatable means if same person repeats the same experiment using same method and equipment they will get the same result
If someone different does the experiment using a slightly different method or piece of equipment the results will still be the same
Valid results describe
Answer original question
To get valid results you need to control all variables to make sure you're only testing the thing you want to
Accurate results describe
Really close to true answer
Human interpretation of a measurement e.g.determining a colour change can reduce accuracy of results
A good experiment gives results that are?
Repeatable and reproducible
How many variables should be changed at a time?
Variables are quantities that have the potential to change e.g. pH in an experiment that you can usually change one variable and measure its effect on another variable
What's the independent variable?
The variable you change
What's the dependent variable?
The variable you measure
What should happen to all the other variables?
They should be controlled when you're investigating a variable you need to keep everything else that could affect it constant meaning you can be sure that only your independent variable is affecting the thing you're measuring (dependent variable)
What else should be used?
Used to check only the independent variable is affecting the dependent variable. Negative controls aren't expected to have any effect in the experiment
What should happen to the experiment?
Repeated at least three times and a mean should be calculated
Reducing effect of random error on your experiment making your results more precise. Doing repeats and getting similar results each time also shows data is repeatable and makes it more likely to be reproducible
Example : investigating the effect of light intensity on rate of photosynthesis of Canadian pondweed?
Light intensity is the independent variable
Rate of photosynthesis is the dependent variable
pH, temperature and time pondered is left should stay the same (quantities recorded to allow someone else to reproduce experiment)
Repeated at least 3 times for each light intensity
Negative control of one in the dark so no photosynthesis should occur
When planning an experiment what do you need to decide?
What it is you're going to measure and how often you're going to take measurements.
E.g. If you are investigating the rate of respiration you could either measure the volume of oxygen used over time or the volume of carbon dioxide produced over time. You could rant measurements at e.g. 30 or 60 second intervals
What do you need to choose to use?
The most appropriate appartus, equipment and technique for the experiment
Why is it important to choose the right measuring appartus?
It has to be sensitive enough to measure changes you're looking for . E.g. Measure changes of 1cm3 you need a measuring cylinder that can measure in 1cm3 increments it wouldn't be any good trying to use into measuring 10cm3 increments it wouldn't be sensitive enough. If you need to measure a small change in pH a pH meter would be more sensitive than indicator paper
What does the equipment and appartus you choose have to be?
Appropriate for the function it needs to perform e.g. If you're trying to separate photosynthetic ligaments using thin layer chromatography you need to use the right solvent or it won't separate
What does the technique used have to be?
the most appropriate of for your experiment e.g. If you're growing a culture of microorganisms you need to use aseptic techniques to prevent contamination
Graduated pipettes have a scale so you can measure specific volumes-make sure you read the meniscus at eye level
What is the meniscus?
The curved upper surface of the liquid inside the pipette
Water baths describe
Make sure you allow time for water baths to heat up before starting your experiment. Don't forget that your solution will need time to get to the same temperature as the water before you start the experiment too
Decide what you are measuring and what type of data logger you will need e.g. Temperature, pH. Connect an external sensor to the data logger if you need to. Decide how often you want the data logger to take readings depending on the length of the process you are measuring
What do you need to make sure you're measuring things using?
Appropriate units e.g. If you're measuring time, it might be better to use seconds rather than minutes- when you come to processing your results it'll be easier to work with a result of 73 seconds than a result of 1.217 minutes. Also make sure you record your units properly e.g. If you're measuring the length of something and accidentally write cm instead if mm any calculations you do will be affected and your conclusion may be wrong
What should you make sure you perform?
All techniques carefully that any appartus is set up correctly this will help minimise errors which would affect your results
What do you need to carry out when planning an experiment?
A risk experiment
What do you need to identify in a risk assessment?
All the dangers in the experiment e.g. Any hazardous chemicals, microorganisms or naked flames
Who is at risk from these dangers
What can be done to reduce the risk wearing goggles or gloves or working in a fume cupboard
What else do you need to consider?
Ethical issues in your experiment e.g. For example if you're using living animals you must treat them with respect. This means handling then carefully and keeping them away from harmful chemicals, extreme heat sources and other things that might cause them physical discomfort
How should you display your results?
In a table
Make sure you draw enough rows and columns to record all data you need to. You might also need to include a column for processing your data e.g. Working out an average
Make sure each column has a heading
Units in column heading not in table
When you look at all the data in the table what may you notice?
Results that don't fit with the rest at all anomalous results. You should investigate anomalous results if you can work what happened (you measured badly) you ignore them when processing results. But you can't just ignore a result if you don't like it
What does calculating percentage change help?
Quantify how much something has changed
Percentage change formula
(Final volume- original value)/ original value * 100
What does a negative or positive result mean for percentage change?
Positive- means a percentage increase
Negative is a percentage decrease
Hoe do calculate the range
Largest value- smallest value
Why is standard deviation more useful than the range?
Because it tells you how values are spread about the mean rather than just the total spread of data
A small standard deviation means repeated results are all close to the mean so the results are all similar
When van you use the students t-test?
When you have two sets of data that you want to compare
Tests whether there is a significant difference in means of two data sets
Value obtained is compared to critical range which helps you decide how likely that the results or difference in mean were due to chance
If the value obtained is greater than the critical region of 5% or less
Then you can be 95% confident that the difference is significant and but due to chance
95% confidence limit which is good enough for biologists
If the result is greater than the critical region at a P value of less than 2% or 1%
you can be even more confident that the difference is significant
Can use chi-squared test when you have categorical (grouped) data and you want to compare whether observed results are statistical different from your expected results. Can compare results to a critical value of its larger the critical value at P=0.05 you can be 95% certain the difference is significant
Use most significant figures you typed into calculator to round to
If you end up with a very big or a very small number what do you use?
What graphs and charts?
A great way of presenting data- they can make results much easier to interpret
What do you do when you have qualitative data or discrete data?
Use bar charts or pie charts
What do you do when you have continuous data?
Use historians or line graphs
When can you use a scatter graph?
When you want to plot one variable against the other
What should do regardless what type of graph you choose?
Dependent variables on y-axis and independent on X-axis
Label axes using quantity and units and choose sensible scale
Make sure graph covers at least half of the graph paper
How do you draw the line of best fit?
Draw line through or as near to as many points as possible ignoring any anomalous results
What is rate?
A measure of change over time
Calculating rate can be useful when analysing your data.
Gradient= change in y/ change in X
How to find rate of change curve biology style?
By drawing tangent
Position ruler on graph at point where you want to know the rate
Angle the ruler so equal space between ruler and curve on either side of the point.
Draw line along ruler to make tangent
Calculate gradient of tengent to find rate
As one variable increases the other increases
As one variable increases the other decreases
No relationship between variables
What does spearman rank correlation coefficient allow you to do?
Work out the degree to which two sets of data are correlated. It is given as a value between 1 and -1. A value of 1 indicates a strong positive correlation. 0 means no correlation and -1 means a strong negative correlation. You can compare your result to a critical value to find out whether or not the correlation is significant.
Why do you have to be careful when drawing conclusions?
A correlation between two variables doesn't always mean that a change in one variable causes a change in the other
Correlation doesn't equal causation
What's a casual relationship?
Between two variables and a change in one variable does cause change in the other
When can it be concluded that a correlation is a casual link?
If every other variable that could possibly affect the result is controlled.
Correlations are generally accepted to be causal links when?
Lots of studies have been found the same thing
Scientists have figured out exactly how one factor causes the other
What can't you do when making a conclusion?
A broad generalisation from data you have to be very specific you can only conclude what results show and no more
Will your results from an experiment ever be completely perfect?
No there will always be a degree of uncertainty in your measurements due to limits in the sensitivity of the apparatus you're using
- Sign tells you the range in which the true value lies. The range is called the margin for error
Percentage error formula?
Uncertainty/ reading *100
What's one clear way to reduce errors in your measurement?
Buy the most sensitive equipment available
In reality there's not much you can do about this one you're stuck with whatever your school or college has but there are other ways to lower the uncertainty in experiment
Plan experiment so you weigh a greater amount of something
What do you need to assess about your experiment and data?
Make sure you evaluate your method
Decide how much confidence you have in your conclusion
Did you take enough repeat reading of the experiment?
Would you do more repeats if you were to do the experiment again?
Do you think you'd get similar results if you did the experiment again?
Have you compared your results with other people's results?
Were your results similar?
Could other scientists gain data showing the same relationship that are shown in your data?
Does your data answer the question you set out to investigate?
Make sure you evaluate your method?
Is there anything you could have done to make your results more precise or accurate?
Were there any limitations in your method e.g. Should you have taken measurements more frequently? We're they any sources of error in your experiment? Could you have used more sensitive apparatus or equipment? Think about how you could refine and improve your experiment if you did it again.