Paper 5 Flashcards
When should a t-test be used?
To compare 2 means of continuous, normally distributed data
When is Pearson’s linear coefficient used?
To correlate two sets of continuous, linear and normally distributed data
When is chi squared test used?
To compare the observed against the expected frequencies
When is Spearman’s rank coefficient used?
To correlate ordinal data, which can be ranked and is not continuous
How are the degrees of freedom for t-test calculated
(n1-1)+(n2-1)
How are the degrees of freedom for Pearson’s linear coefficient calculated?
Number of pairs of data-2
How are the degrees of freedom for chi-squared test calculated
Number of categories -1
How are the degrees of freedom for Spearman’s rank coefficient calculated?
Number of pairs of data -2
Statistical conclusion phrasing
- State calculated value is smaller/larger than critical value at p=0.05
- There is less/more than 5% probability that the results are due to chance
- The results are/are not statistically significant
What does standard deviation measure
Spread of data
What does standard error measure
The reliability of the sample mean- how close the calculated mean is to the true mean
What is the range of error bars
+/- 2 x standard error
Why is percentage change calculated instead of actual change
May not have the same starting value, percentage change allows for a valid comparison to be made by showing the proportional change
Statistical test for biodiversity
Simpson’s index of biodiversity
What does the calculated value in Simpson’s index indicate
- It is between 0 and 1
- Closer to 1 indicates higher biodiversity
- Closer to 0 indicates lower biodiversity
Function of stage micrometer
Used to calibrate eyepiece graticules
Function of eyepiece graticule
Can be calibrate to make measurements, and can be used to draw structures proportionally
When are bar charts used
When the independent variable is qualitative
When are histograms used
For continuous data that is divided into classes
What is a systematic error
An error that is consistently repeated throughout the experiment
What is a random error
An unpredictable error with no patterns
How can the reliability of results be increased
By repeating the practical at least 3-5 times and taking a mean- identify and exclude anomalies
How can temperature be better standardised
By using a thermostatically controlled water bath
How can the accuracy of measurements be improved
By using apparatus with smaller divisions
5 components that should be in practical plan
- controlled variables
- independent variables
- dependent variables
- how to improve reliability
- safety
safety- what to write
- state the hazard and the level of risk
- state a safety precaution to take
dependent variable- what to write
- identify the dependent variable
- describe how it is measured and the apparatus needed
important procedures when setting up potometer
- male slanted cut of shoot underwater
- make sure apparatus if airtight
- use syringe to adjust gas bubble position to starting point
important procedures when setting up a respirometer
- make sure the apparatus is airtight
- air must be replaced between each set up
random sampling procedure
- make a grid using measuring tape
- use random number generator to obtain sets of coordinates
- place quadrats at coordinates
chromatography procedure
- draw pencil line at base of thin paper
- use a capillary tube to drop the extract onto the origin
- dry and repeat to concentrate spot
- dip in solvent
- cover solvent with bung to prevent evaporation
- after running the solvent, allow chromatography paper to dry
- calculate Rf
- compare Rf with known Rf values
preparing slide sample
- obtain required sample by cutting with scalpel/peeling with forceps
- Mount on a slide and add stain if necessary
- Squash by placing a cover slip on and pressing down gently
What is soda lime used for
To absorb carbon dioxide
How can light intensity be altered- photosynthesis prac
The distance of the light source from the plant
How can temperature be altered- for photosynthesis prac
changing the temperature of the water bath the test tube sits in
How can carbon dioxide be altered
The amount of sodium hydrogen carbonate dissolves in the water the pondweed is in
Why are 95% confidence intervals calculated?
95% probability that the actual mean population lies within the range
To test whether the means are significantly different
To get a measure of how close the calculated mean is likely to be to the true mean
What do the length of error bars indicate
Shorter error bars show that the true mean is likely to be closer to the calculated mean
Longer error bars show that the true mean is likely to be further away from the calculated mean
Outline how the population size of beetles can be estimated
- Mark release recapture technique
- Trap beetles and mark using a marker
- Re-trap the beetles
- Use lincoln index to estimate population size:
(number in first sample x number in second sample)/marked number in second sample
Why is standard deviation calculated
- Shows the spread about the mean
- Indicates the reliability of the data
- To put error bars on the graph, see if the standard deviations overlap
Why may a conclusion not be valid
Only 2 (concentrations) measured
no repeats
no statistical analysis
lab conditions may not be replicated in the field
Describe two ways the students can obtain the measurement needed to work out the results per unit area of leaf
- measure radius of area of leaf then use pi(r)2
- use transparent grid on the area, count squares
Advantages of finding standard deviation
- shows the spread of data about the mean
- allows calculation of confidence intervals
- allows determination of whether or not there is a significant difference between mean values 4. allows t test to be calculated
- to plot error bars on graphs
Why is conclusion not valid- pearson
- correlation does not mean causation
- fewer than the number of paired observations recommended
- no replicates, only done experiment once
- narrow range of (IV)
how to calculate volume of oxygen uptake in tube
- measure radius
- use pi(r)2 to find area
- multiply by distance in mm
RQ value of germinating seeds practical
- add fixed number of peas to respirometer
- a control containing glass beads of the same mass
- insert bung with tubing with clip and glass tubing with scale so that the apparatus is airtight
- dip the glass tube into coloured liquid
- place respirometer tube into a water bath at 15 degrees
- open clip and allow to equilibrate
- close the clip, mark position of dye and start stopwatch immediately
- measure the movement of dye on the scale for 5 minutes
- open clip and reset coloured liquid
- minimum of 3 measurements and take mean
- removing carbon dioxide absorbent
12.medium risk, carbon dioxide absorbent is an irritant, wear gloves
