PSOW – Practical 2.1F Measuring Change Along a Transect with Teacher’s Notes

Description

IB ESS Practical 2.1F: Measuring Change Along a Transect

Give students hands-on experience of transect sampling and the trade-off between detail and effort in fieldwork methods.

In this practical activity, students find a location where the plant community is expected to change across space, such as from open ground into shade or from a path edge into undisturbed vegetation. They lay a transect of at least 20 m across the direction of change and record its compass bearing and end points. They then sample the same line using two methods:

• Interrupted belt transect: a quadrat placed at fixed intervals, usually every 2 m, recording every species and its percentage cover
• Continuous line transect: every species touching the tape recorded, along with the distances where each contact begins and ends

Students time each method, plot percentage cover against distance for at least three species, and compare the species lists produced by each method. Running both methods on the same line shows students exactly what each one gains and misses.

IB ESS Internal Assessment Skills

This activity is assessed using IB ESS Internal Assessment Criteria C: Method and E: Analysis and Conclusion, and the full rubrics are included. Students must:

• Describe both transect methods clearly enough to be repeated along the same line, including how they chose the interval spacing
• Analyze how species composition changes along the transect, identify where the change is sharpest, and consider the reliability limits of sampling a single line
• Conclude which method suits the study area best, using the species detected and the time taken as evidence

The activity teaches students to justify a sampling design rather than simply state it, which is a key difference between IA mark bands. The teacher’s notes also highlight how repeatedly walking the line can create the very disturbance the transect is meant to measure.

Ideal for

• Teaching transect sampling
• Comparing continuous and interrupted transects
• Introducing systematic sampling
• Measuring change in plant communities across space
• Graphing percentage cover against distance
• Preparing students for zonation fieldwork
• Preparing students for the IB ESS Internal Assessment

Digital download. No physical product will be shipped.