Practical: Variation in Organisms (SQA National 5 Biology): Revision Note

Investigating variation in organisms

• Two species of snail from the same genus, Capaea, are found commonly in woodlands and grassland habitats in the UK

• The different variations in shell pattern across the two snail species show discrete variation

• We can investigate the frequency of the different patterns in the populations of snails in woodland and grassland areas to show the effect of habitat on variation

• There are four shell patterns:

Apparatus

• Quadrat (to select random sample areas)

• Camera or tablet (to photograph snails in their habitat)

• Identification key or species guide (to confirm snail species)

• Clipboard, field notebook or recording sheet (for tallying counts and habitat notes)

• Pencil and waterproof labels (for data recording outdoors)

• Ruler or measuring tape (to mark quadrat area if adjustable)

• Compass (to record sampling orientation if required)

• Gloves (for safe handling if needed)

• Calculator (for processing results)

Method

1. Select two different habitats where snails can be found, such as woodland and grassland

2. Place a quadrat at random positions within the first habitat to collect an unbiased sample

3. Take a clear photograph of all snails visible within the quadrat without touching or moving them

4. Repeat this process in different random quadrat positions until 50 snails have been photographed in total for that habitat

5. Repeat steps 2 to 4 in the second habitat to collect a comparable sample of 50 snails

6. Use the photographs to identify and categorise each snail into one of four variants: pink/brown plain, yellow plain, pink/brown striped, or yellow striped

7. Record the number of each snail type in a results table for each habitat

   • For each habitat, the snails are categorised into one of the four different variants: 

     • Pink/brown plain

     • Yellow plain

     • Pink/brown striped

     • Yellow striped

8. Present the results in a bar chart to compare the frequency of the four colour variants between habitats

• Keep the quadrat size, sampling method, and time of day the same in both habitats to ensure a fair test

• Leave all snails in their natural environment and avoid handling them to maintain ethical fieldwork practices

Expected results

• An efficient way to record the frequency of snails within each category is to use a tally chart:

• These results can then be presented in a bar chart:

Results analysis and conclusions

• Results analysis is about looking at the data to identify the key trends

• In the table above, we can see that:

  • all snails were recorded in both habitats

  • more pink/brown striped and pink/brown plain snails recorded in woodland compared to grassland

  • more yellow plain and yellow striped snails recorded in grassland compared to woodland

  • more than double the number of yellow plain snails recorded in grassland compared to woodland

  • more than double the number of pink/brown striped snails recorded in woodland compared to grassland