Lecture Notes: Distribution of Organisms

Key Area 2: Distribution of Organisms

This lecture focuses on the factors influencing the distribution of organisms, including definitions, measurement techniques, and identification methods.

Definitions

• Abiotic Factors:
  • Non-living variables that influence where organisms live.
  • Examples: Light intensity, temperature, soil pH, moisture level.
  • Measurement considerations: Use correct terminology (e.g., light intensity, not just light).
• Biotic Factors:
  • Living factors affecting organisms.
  • Examples: Predation, disease, competition for resources.
  • Disease is a biotic factor, not abiotic.

Measuring Abiotic Factors

• Light Intensity:
  • Measured using a light meter.
  • Avoid casting shadows on the meter for accurate readings.
• Temperature:
  • Use a thermometer for air or a temperature probe for soil.
  • Clean probe between uses to avoid incorrect readings.
• Soil pH and Moisture:
  • Measured with specific soil pH and moisture probes.
  • Clean between uses to ensure accuracy.

Measuring Biotic Factors

• Quadrats:
  • Used for counting plant abundance.
  • Must be thrown randomly to avoid bias.
• Pitfall Traps:
  • Used for sampling small invertebrates.
  • Ensure traps are covered to prevent rain and predators from affecting results.

Identification Methods

• Identification Keys:
  • Branching Key: Uses binary questions to identify organisms.
  • Paired Statement Key: Similar structure without branching.
  • Example of use in exam settings provided.

Indicator Species

• Definition: Species that indicate environmental quality or pollution levels.
• Examples:
  • Air Pollution: Presence of various lichens indicates low pollution.
  • Water Pollution: Freshwater invertebrates, like sludge worms, indicate high pollution levels.

Summary Points

• Understand definitions and examples of abiotic and biotic factors.
• Know how to measure these factors accurately and avoid common mistakes.
• Practice using identification keys for organism identification.
• Recognize and remember indicator species for both air and water pollution.

Next Steps

• Next topic: Photosynthesis
• Prepare for upcoming prelims by reviewing these concepts.