Chapter 12: Ecosystem

Summary

• An ecosystem is a structural and functional unit of nature comprising abiotic (inorganic materials like air, water, soil) and biotic components (producers, consumers, decomposers).
• Ecosystems vary in size from small ponds to large forests and can be categorized into terrestrial (e.g., forests, grasslands, deserts) and aquatic (e.g., ponds, lakes, rivers).
• Key components of ecosystems include:
  • Productivity: Rate of biomass production by producers, divided into Gross Primary Productivity (GPP) and Net Primary Productivity (NPP).
  • Decomposition: Breakdown of complex organic matter into inorganic substances by decomposers, involving fragmentation, leaching, and catabolism.
  • Energy Flow: Unidirectional movement of energy from producers to consumers, with energy loss at each trophic level.
  • Nutrient Cycling: Movement of nutrients through ecosystems, categorized into gaseous and sedimentary cycles.
• Ecological pyramids illustrate the relationships between different trophic levels in terms of number, biomass, and energy.
• The productivity of ecosystems varies based on environmental factors, species composition, and nutrient availability.

Chapter 12: Ecosystem

12.1 Ecosystem - Structure and Function

• An ecosystem is a functional unit of nature where living organisms interact with each other and the physical environment.
• Ecosystems vary in size from small ponds to large forests or seas.
• Two basic categories of ecosystems:
  • Terrestrial: Forests, grasslands, deserts.
  • Aquatic: Ponds, lakes, wetlands, rivers, estuaries.
• Man-made ecosystems include crop fields and aquariums.

Key Components of Ecosystems

1. Productivity: Input of solar energy and biomass production.
2. Decomposition: Breakdown of organic matter.
3. Energy Flow: Transfer of energy through food chains/webs.
4. Nutrient Cycling: Movement of nutrients through the ecosystem.

12.2 Productivity

• Primary Production: Amount of biomass produced by plants during photosynthesis, expressed in gm⁻² or kcal m⁻².
• Gross Primary Productivity (GPP): Total production of organic matter.
• Net Primary Productivity (NPP): Biomass available after respiration losses (NPP = GPP - R).
• Secondary Productivity: Rate of formation of new organic matter by consumers.

12.3 Decomposition

• Decomposers break down complex organic matter into inorganic substances.
• Steps in Decomposition:
  1. Fragmentation: Breakdown of detritus into smaller particles.
  2. Leaching: Water-soluble nutrients leach into the soil.
  3. Catabolism: Degradation of detritus by bacterial and fungal enzymes.
  4. Humification: Formation of humus, a nutrient reservoir.
  5. Mineralisation: Release of inorganic nutrients.

12.4 Energy Flow

• Energy flow is unidirectional, moving from producers to higher trophic levels.
• Only 10% of energy is transferred to each successive trophic level.

12.5 Ecological Pyramids

• Types of Ecological Pyramids:
  • Pyramid of Numbers: Represents the number of individuals at each trophic level.
  • Pyramid of Biomass: Shows the dry weight of organisms at each level.
  • Pyramid of Energy: Illustrates energy flow through the food chain.

Example Data for Pyramid of Numbers

Example Data for Pyramid of Biomass

Common Mistakes and Exam Tips in Ecosystem Studies

Common Pitfalls

• Misunderstanding Trophic Levels: Students often confuse the roles of different trophic levels. Remember that producers are at the base, followed by primary consumers, secondary consumers, and tertiary consumers.
• Ignoring Energy Loss: Many forget that energy decreases at each trophic level due to the 10% law, where only about 10% of energy is transferred to the next level.
• Overlooking Decomposition Processes: Students may not fully describe the steps of decomposition, such as fragmentation, leaching, and catabolism.
• Confusing Gross and Net Primary Productivity: Be clear that GPP is the total production of organic matter, while NPP is what remains after respiration losses.
• Neglecting Nutrient Cycling: Failing to explain how nutrients are recycled in ecosystems can lead to incomplete answers.

Tips for Success

• Use Diagrams: Practice drawing and labeling ecological pyramids and energy flow diagrams to visualize concepts better.
• Understand Definitions: Make sure you can define key terms like primary productivity, decomposition, and ecological pyramids.
• Practice Exam Questions: Work through past exam questions related to ecosystems to familiarize yourself with the format and types of questions asked.
• Clarify Concepts: If unsure about concepts like food chains vs. food webs, seek clarification to avoid confusion in exams.
• Review Examples: Study examples of different ecosystems (terrestrial vs. aquatic) to understand their unique characteristics and functions.