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In this topic of IBDP Biology, we will learn about what variation is and causes of variation.

Variation

- Variation means the differences in characteristics (phenotype) between organisms.
- There is variation within each species – intraspecific variation.
- Also, there are differences between different species – interspecific variation.

## Investigating Variation

- Take a representative sample:
- Measure the characteristic in a large number of different individuals
- Essential that sampling is random – this eliminates bias.
- Use random number tables or the button on a calculator

- The larger the sample size, the more representative the data.
- The smaller the sample, the higher the likelihood that chance can influence the data.
- Then plot a frequency histogram.
- This graph has the values of the characteristic on the X axis and the number of individuals showing that characteristic on the Y axis (frequency).
- The larger the number of samples

## Analyzing data

In IBDP Biology, **Mean**

- Commonly referred to as the average.
- Add up all measurements and divide by total number of measurements:
- Mean = Sum of all measurements/ Total number of measurements

**Standard Deviation**

- There are two kinds of numerical data acquired by biologists:

1. Counting; e.g. the number of females in a population The true value is obvious for this.

2. Measuring a continuous variable such as length or weight

- The measured values always reflect a range.
- The size of this is determined by such factors as:
- Precision of the measuring instrument
- Individual variability among the objects being measured.

- Biologists like to be confident that the data they achieve is within acceptable limits of variance from the mean.
- Standard deviation can be used to quantify the spread of the data around the mean.
- The data must show a normal distribution around the mean.
- I.E. when plotted as a graph it forms a bell shaped curve.
- Standard deviation actually measures the distance from the mean to the point where the graph goes from being convex to concave.
- This includes 68% of the measurements.
- Two times the standard deviation includes 95%.
- The larger the standard deviation, the greater the spread of data around the mean.
- This number can then be compared with the standard deviation of another set of data.
- So, the larger the difference between the two standard deviations, the more certain we are that the two seta of data are different.

## Causes of variation

When it comes to IBDP Biology, there are many causes of variation:

This is the end of part 1. You can go to part 2 now!