Edexcel A Level (IAL) Biology -5.14 Core Practical 11: Quadrat & Transect Study- Study Notes- New Syllabus

CORE PRACTICAL 11: Studying the Ecology of a Habitat

(Quadrats, Transects, Distribution, Abundance, Abiotic Factors)

🌱 Introduction

When we study a habitat, we want to find out:

• Which organisms are present
• How many of them there are (abundance)
• Where they are found (distribution)
• What environmental factors affect them

To do this properly, we use simple ecological tools like quadrats, transects and instruments for abiotic factors.

🧭 Quadrat Study (To estimate abundance)

What is a Quadrat

A quadrat is a square frame (usually 0.5 m or 1 m). It helps us sample a small area and represent the whole habitat.

How to Use a Quadrat

• Choose the study area.
• Place the quadrat randomly (avoid bias).
• Identify the organisms inside the quadrat.
• Count each species carefully.
• Repeat many times for accuracy.
• Calculate the average number per quadrat.

Why Use Quadrats

• Impossible to count all organisms
• Gives a fair estimate of abundance
• Good for slow moving or stationary organisms (grass, plants, snails)

🌿 Example
If you place 10 quadrats and find an average of 6 dandelions per quadrat, you can estimate their density for the whole habitat.

🌲 Transect Study (To study distribution)

What is a Transect

A transect is a line across the habitat. Used when organisms change across a gradient (e.g., shade to sunlight, dry to wet area).

Types of Transects

• Line transect: record organisms touching the line.
• Belt transect: place quadrats along the line for more detail.

How to Use a Transect

• Stretch a measuring tape across the area.
• Place quadrats at regular intervals (every 1 m or 2 m).
• Record which species are present at each point.
• Note how distribution changes along the line.

🌿 Example
Grass may dominate in sunlight, while moss appears only in shady, moist areas along the transect.

🌤 Abiotic Factors to Measure

Abiotic factors influence where organisms live. Different habitats need different measurements.

Common Abiotic Factors and Instruments

• Light intensity → light meter
• Temperature → thermometer
• Soil pH → pH meter or indicator solution
• Soil moisture → moisture probe
• Wind speed → anemometer
• Water temperature / clarity (in aquatic habitats)

Why Measure Abiotic Factors

These help explain why organisms are abundant in some places and scarce in others.
Example: more moss found where light intensity is low.

📋 Summary Table