Topic 4—C: Diversity and classification- 5. Investigating variation Flashcards
What is variation?
- the differences that exist between individuals
What can variation be caused by?
- genetic factors
What do different species have?
- different genes which causes variation between species
What do individuals of the same species have?
- the same genes but different alleles (versions of genes)- this causes variation within a species
How can variation within a species also be caused by?
- differences in the environment
E.g.
climate, food, lifestyle
What is most variation within a species caused by?
- a combination of genetic and environmental factors
E.g. genes determine how tall an organism can grow but nutrient availability affects how tall the organism actually grows
When studying variation within a species what do you usually look at?
- a sample of the population, not the whole thing
- samples are used for the whole population
- it would be too time consuming/ impossible to catch all the individuals in a group
What is important that the data gathered does?
It’s important that it accurately measures the whole population
- and any patterns observed are tested to make sure they’re not due to chance
To make sure the sample isn’t biased what should it be?
Random
How would you make it random?
- you could pick random sample sites by dividing the field into a grid and using a random number generator to select coordinates
To ensure any variation observed in the sample isn’t just due chance what is important to analyse?
The results statistically
What can you use mean and standard deviation to measure?
How much variation there is in a sample
Mean
- its an average of the values collected in a sample
Mean formula
Total of all the values in your data/ the number of values in your data
What can the mean be used to tell?
If there is variation between samples
Normal distribution
Symmetrical about the mean
Not a normal distrubution
Skewed
Standard deviation
- tells you how much the values in a single sample vary
- its a measure of the spread of values about the mean
Normal distribution curve (standard deviation)
- graph is steep as values are similar and close to the mean
- standard deviation is small
- graph is fatter as values vary a lot
- standard deviation is large
Formula for standard deviation
S= (Square root) sum of (x- ‘x’) squared / n-1
S= standard deviation
Square root sign
M symbol= sum of
X= value in the data set
‘X’= the mean
Squared= square the result
N= number of values
What is standard deviation a method of calculating?
The dispersion of data
What is another method of calculating dispersion?
By looking at the range (difference between the highest and lowest figures in the data)
Why is standard deviation more useful than the range?
- because it takes into account all the values in the data set whereas the range only uses two
- this makes the range more likely to be affected by an anomalous result (an unusually high or low value in the data set) than standard deviation
Using standard deviation to draw error bars
- they can be plotted on a graph/chart of mean values using error bars
- error bars extend one standard deviation above and one standard deviation below the mean (so the total length of an error bar is twice the standard deviation)
- the longer the bar, the larger the standard deviation and the more spread out the sample is from the mean
- the mean is in the middle of the error bar
- the smaller the error bars, the smaller the standard deviation and the less the data in the sample varies
