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Practical 8Spec ref: B4aHigher Tier

Fieldwork — Quadrats and Transects

Linked to B7: Ecology

Aim

Use sampling techniques to investigate the distribution and abundance of organisms in a habitat.

PDF Resources

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Practical Guide

Method & analysis

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Exam Questions

Past-paper style

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Mark Scheme

Model answers

Equipment

  • •Quadrat frames (0.25 m² or 1 m²)
  • •Metre rules or tape measures
  • •Random number tables or app
  • •Data recording sheets
  • •Identification key
  • •Abiotic measuring equipment

Variables

Independent variable
Location along transect (m) or randomly selected quadrat position
Dependent variable
Number of organisms or percentage cover per quadrat
Controlled variables
Quadrat size, observer, time of day

Key Facts to Know

✓Quadrat: square frame used to sample a defined area
✓Random sampling prevents bias — every area has equal chance of being sampled
✓Transect: line across a habitat to show distribution along an environmental gradient
✓Population estimate = mean per quadrat × (total area ÷ quadrat area)
✓Abiotic factors (light, temperature, pH) affect species distribution

⚠️ Common Mistakes

  • ✗Using non-random sampling — students tend to avoid rough areas or choose 'good' spots
  • ✗Multiplying mean by total area without dividing by quadrat area first
  • ✗Not measuring abiotic factors — these are needed to explain distribution patterns

💡 Exam Tips

  • ★Explain WHY random sampling is used: to avoid bias / give every area equal chance
  • ★Population estimate calculation: mean per quadrat × total area ÷ quadrat area
  • ★For Higher: describe how abiotic factors explain the distribution pattern you observed

All Required Practicals

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