Field investigations (AQA GCSE Biology): Revision Notes
Field investigations
What are field investigations?
Field investigations help you study how living things interact with their surroundings in real habitats. These investigations are essential for understanding ecological relationships and collecting authentic data about populations and ecosystems in their natural environments.
Main Field Investigation Tools
You can use two main tools for field investigations:
- Quadrats - square frames for counting organisms in a set area
- Transects - lines or strips used to study how organisms change across an area
These tools help you collect data about populations and environmental factors in the wild.
Core practical: measuring population size
The aim
This investigation helps you estimate how many plants of one species live in a habitat. You use random sampling to get fair and unbiased results.
The method
Here's how to measure population size step by step:
- Mark out your area - Use two tape measures to create a large study area in the field
- Choose random spots - Pick at least 10 random locations to place your 25cm × 25cm quadrats
- Count carefully - Count the number of dandelion plants (not flowers!) inside each quadrat
- Record your data - Write all results in a clear table
Worked Example: Calculating Quadrat Area
A 25cm quadrat covers:
This standardised area allows you to calculate population density and estimate total population size across larger areas.
How to analyse your results
Use your quadrat counts and the total area you studied to estimate the whole population size. Sharing results with other groups makes your estimate more accurate by increasing your sample size and reducing the impact of random variation.
Core practical: investigating environmental factors
The aim
This investigation shows how environmental factors (like light intensity) affect where organisms live. You use a transect line to study changes in both organism distribution and environmental conditions.
The method
Follow these steps to investigate light intensity effects:
- Set up your transect - Lay a tape measure in a straight line from the base of a tree out to open ground
- Mark your sampling points - Place a quadrat at the 0m mark (start point)
- Collect data - Count dandelion plants in the quadrat and measure light intensity with a light metre
- Move along the line - Repeat steps 2-3 at regular intervals along your transect
- Record everything - Keep all measurements in a suitable table
Understanding your results
The data typically shows that dandelion numbers increase as light intensity increases. This correlation occurs because:
- Plants near trees get less light due to shade
- Plants in open areas get more light for photosynthesis
- Most plants grow better in higher light conditions
Why This Pattern Occurs
Light is a limiting factor for plant growth. As you move away from the tree canopy, light intensity increases, creating more favourable conditions for plant growth and survival. This demonstrates how abiotic factors directly influence the distribution of living organisms.
Important practical tips
Critical Considerations for Field Investigations
Choose your interval carefully:
- Small intervals = lots of samples but takes more time
- Large intervals = fewer samples but you might miss important patterns
Safety first: Be careful not to lay transects in dangerous places such as steep slopes or areas with hazardous vegetation.
Count plants, not flowers: This gives you the true number of individual organisms rather than reproductive structures.
Other factors to investigate: You could also study soil pH, temperature, moisture content, or other abiotic factors using similar methods.
Remember!
Key Points to Remember:
- Quadrats measure population size through random sampling in a set area
- Transects investigate factors by studying changes along a line
- Random sampling makes your results fair and reliable
- Environmental factors like light affect where organisms can survive and thrive
- Always count plants, not flowers for accurate population data
- Replication and sharing data improves the reliability of your estimates