Required practical - Field investigations (AQA GCSE Biology Combined Science): Revision Notes
Required practical - Field investigations
Field investigations help us study how organisms relate to their environment in real habitats. Scientists use special techniques called quadrats and transects to collect data about populations and environmental factors.
What are field investigations?
Field investigations let you study living things in their natural homes. You can find out how many organisms live in an area and what affects where they choose to live.
Field investigations are essential for understanding ecology because they allow scientists to observe real interactions between organisms and their environment, rather than studying them in artificial laboratory conditions.
There are two main methods you need to know:
- Quadrats - for counting populations
- Transects - for studying environmental effects
Method 1: Measuring population size using quadrats
Aim
To estimate how many plants of one species live in a habitat using random sampling.
What you need
- Tape measures
- Quadrats (usually 25cm × 25cm squares)
- Recording sheets
Method
- Mark your area - Use tape measures to mark out a large field area
- Place quadrats randomly - Put at least 10 quadrats in random positions within your marked area
- Count the organisms - Count how many of your chosen plant species are inside each quadrat
- Record results - Write your counts in a table
Tip for Species Selection: Dandelions are easy to spot and count, making them good for this investigation. Choose species that are clearly visible and distinguishable from other plants in the area.
Analysis
Use your quadrat results and the total field area to estimate the whole population size.
Critical for Accuracy: The more quadrats you use, the more accurate your estimate will be. Sharing results with other groups also improves accuracy. Always use at least 10 quadrats for reliable results.
Method 2: Investigating environmental factors using transects
Aim
To find out how environmental factors (like light intensity) affect where organisms live.
What you need
- Tape measure
- Quadrats
- Light metre
- Recording sheets
Method
- Lay your transect - Place a tape measure in a straight line (for example, from a tree base to open ground)
- Start at 0m - Place a quadrat at the start of your line
- Count and measure - Count organisms in the quadrat and measure light intensity with a light metre
- Move along the line - Repeat step 3 at regular intervals along your transect
- Record everything - Put all results in a table
Analysis
Plot a graph showing your results. This shows how the environmental factor affects organism numbers.
Worked Example: Light and Dandelion Distribution
Step 1: Set up transect from tree base (0m) to open ground (10m) Step 2: Count dandelions and measure light intensity every 1m Step 3: Plot results on a graph
Results might show:
- At 0m (tree base): 2 dandelions, 50 lux
- At 5m (partial shade): 8 dandelions, 200 lux
- At 10m (open ground): 15 dandelions, 500 lux
Conclusion: Dandelion numbers increase as light intensity increases when moving away from a tree.
Important safety and accuracy tips
Stay safe
Safety First:
- Don't place transects in dangerous areas (avoid cliffs, busy roads, or unstable ground)
- Choose safe intervals between measurements
- Always inform a teacher of your investigation location
- Work in pairs for safety
Get accurate results
Keys to Accurate Sampling:
- Use random sampling - This gives fair results that represent the whole area
- Take enough samples - More samples = more accurate results
- Count plants, not flowers - Plants are easier to identify accurately
- Choose appropriate intervals - Too small = lots of work, too large = miss important patterns
Improving your investigation
Enhancement Techniques:
- Work with other groups and combine results for larger sample sizes
- Use quadrats that are 0.25m × 0.25m (area = )
- You can investigate other abiotic factors like soil pH or temperature
- Consider using systematic sampling alongside random sampling for comparison
Understanding your results
When you plot a graph of your transect results, look for patterns in the data:
- Positive correlation - More organisms as the environmental factor increases
- Negative correlation - Fewer organisms as the environmental factor increases
- No correlation - The factor doesn't seem to affect organism numbers
Interpreting Your Graph: The graph in your results shows if there's a relationship between the environmental factor and where organisms choose to live. Look for clear trends rather than focusing on individual data points that might be outliers.
Remember!
Key Points to Remember:
- Quadrats help estimate population sizes in large areas by sampling small, random sections
- Transects investigate how environmental factors affect organism distribution along a line
- Random sampling is essential for fair, accurate results
- Safety first- always choose safe locations for your investigations
- More data = better accuracy - use at least 10 quadrats or measurement points
- Environmental factors like light, temperature, and pH all affect where organisms live
- Always plot your results on a graph to identify patterns and correlations