The structure and functioning of ecosystems — Eduqas A-Level Geography

Ecosystems are dynamic systems where living organisms (biotic components) interact with each other and their non-living environment (abiotic components). This topic explores the structure of ecosystems, including trophic levels, food webs, and nutrient cycles, and how energy flows through them. Understanding these interactions is crucial for grasping how ecosystems function, maintain balance, and respond to changes like human impact or climate change.

In the WJEC A-Level Geography specification, this topic forms the foundation for understanding global ecosystems, biodiversity, and sustainability. You will examine key processes such as photosynthesis, respiration, decomposition, and the cycling of carbon and nitrogen. These concepts are not only central to physical geography but also link to human geography through topics like resource management and environmental degradation.

Mastering this topic enables you to analyse real-world issues such as deforestation, eutrophication, and climate change impacts on ecosystems. It also develops your ability to evaluate ecosystem services, conservation strategies, and the role of feedback loops. By the end, you should be able to explain how energy and matter move through ecosystems and why this matters for planetary health.

• →Trophic levels and energy flow: Energy enters ecosystems via photosynthesis (producers) and is transferred through consumers (primary, secondary, tertiary) and decomposers. Only about 10% of energy passes between levels due to respiration and heat loss (Lindemann's 10% law).
• →Nutrient cycles: Carbon and nitrogen cycles are essential. Carbon is stored in biomass, soils, oceans, and the atmosphere; processes include photosynthesis, respiration, combustion, and decomposition. Nitrogen fixation by bacteria converts atmospheric N₂ into usable forms for plants.
• →Food webs vs. food chains: Food chains show linear energy flow, but real ecosystems are complex webs with multiple interactions. Understanding food webs helps explain ecosystem stability and the impact of species removal.
• →Biotic and abiotic factors: Biotic factors include predation, competition, and disease; abiotic factors include temperature, light, water, and soil pH. These interact to determine species distribution and ecosystem dynamics.
• →Ecological succession: The process of change in species composition over time, from pioneer species to climax community. Primary succession occurs on bare rock; secondary succession on cleared soil. This links to ecosystem resilience and management.

• Explanation of the ecosystem concept including energy flows
• Comparison of nutrient cycling between two biomes (stores and rates of flow)
• Analysis of primary productivity levels linked to limiting factors (temperature, moisture, light, nutrient availability)

• 💡Ensure you can define and apply the concept of 'limiting factors' to different environments
• 💡Use specific examples of nutrient stores and flows when comparing biomes
• 💡Focus on the 'functioning' aspect—how energy and nutrients move through the system rather than just describing the plants and animals
• 💡Use specific terminology: In exam answers, always use correct terms like 'gross primary productivity (GPP)', 'net primary productivity (NPP)', and 'biomass'. This shows precision and gains marks.
• 💡Draw and label diagrams: For questions on energy flow or nutrient cycles, a clear, annotated diagram can earn you marks. Include arrows for energy flow and labels for processes like respiration and decomposition.
• 💡Link to case studies: When discussing human impacts, refer to specific examples like deforestation in the Amazon (affecting carbon cycle) or eutrophication in the Norfolk Broads (nutrient cycle). This demonstrates application of knowledge.

• Confusing the ecosystem concept with specific biome characteristics
• Failing to explicitly link primary productivity to the specific limiting factors mentioned in the specification
• Generalizing nutrient cycling without providing comparative detail between two distinct biomes
• Misconception: 'Energy is recycled in ecosystems.' Correction: Energy flows one-way through ecosystems and is lost as heat; it is not recycled. Only matter (nutrients) is cycled.
• Misconception: 'Food chains are simple and linear.' Correction: In reality, most organisms eat multiple prey and are eaten by multiple predators, forming complex food webs. Simple chains are models, not reality.
• Misconception: 'Decomposers are not important.' Correction: Decomposers (bacteria, fungi) are vital for breaking down dead matter and returning nutrients to the soil, enabling nutrient cycling. Without them, ecosystems would collapse.