Every time you step into a forest or even look closely at a garden pond, you are witnessing a complex web where nothing survives entirely on its own. An is a biological community made up of interacting living organisms, known as components, and their physical, non-living environment, known as components.
The most crucial concept in an is . This means every component relies on the others to function, and a change in one will create a "knock-on" effect throughout the entire system.
When one part of an is altered, it triggers a . For example, if a primary consumer (such as a caterpillar) is removed from a woodland :
is the continuous movement of organic and inorganic matter between three main stores, often illustrated in a :
Decomposers like fungi and bacteria break down the store, releasing nutrients back into the soil as humus so plants can absorb them again. The relative sizes of these stores vary by :
Energy enters the via sunlight and moves through : Producers Primary Consumers Secondary Consumers Tertiary Consumers. At each stage, approximately 90% of the energy is lost through heat, respiration, and movement.
If the producers in a woodland generate 25,000 kJ of energy, how much energy will reach the secondary consumers? (Assume only 10% of energy is transferred to the next trophic level)
Step 1: Calculate the energy passed to primary consumers.
Step 2: Calculate the energy passed from primary to secondary consumers.
Answer: 250 kJ reaches the secondary consumers.
Large-scale global are known as , and their locations are primarily driven by latitude and .
For 'Interdependence' questions, you must provide a causal link. Don't just say species are connected; explain that if X decreases, Y will increase/decrease because of the specific relationship (e.g., loss of food source).
Common Exam Question: Compare nutrient cycling in two biomes. Use the Gersmehl diagram terms (Biomass, Litter, Soil) and state which store is largest and WHY (e.g., 'Biomass is largest in Rainforests due to high biodiversity').
Calculation Tip: In energy transfer questions, remember that energy is lost at each level. Ensure you apply the percentage reduction (usually 90% loss or 10% transfer) for every step between the producer and the target consumer.
When outlining biome distribution, always mention three things: latitude (e.g., 30° N/S), pressure belts (e.g., high pressure), and an example continent or region.
Ecosystem
A biological community of interacting living organisms (biotic) and their physical, non-living environment (abiotic).
Biotic
The living components of an ecosystem, such as plants, animals, fungi, and bacteria.
Abiotic
The non-living components of an ecosystem, such as climate, soil, water, light, and rock.
Interdependence
The reliance of every component within an ecosystem on the others, where a change in one triggers a knock-on effect elsewhere.
Trophic cascade
A process where a change at one trophic level of a food web results in a series of knock-on effects for other levels.
Nutrient cycling
The exchange of organic and inorganic matter back into the production of living matter via three stores: Biomass, Litter, and Soil.
Gersmehl diagram
A diagram representing the three main nutrient stores in an ecosystem and the flow of nutrients between them.
Biomass
The store of nutrients found in living plants and animals.
Litter
The store of nutrients found in dead organic matter on the soil surface.
Leaching
The process where heavy rainfall washes essential minerals and nutrients down through the soil profile.
Trophic levels
The hierarchical levels in an ecosystem comprising organisms that share the same nutritional relationship to the primary sources of energy.
Biome
A very large-scale global ecosystem characterized by its distinct climate, flora, and fauna.
Global Atmospheric Circulation
The large-scale movement of air that distributes heat and moisture across the Earth via cells (Hadley, Ferrel, Polar).
Continentality
The climatic effect of being far from the sea, resulting in more extreme seasonal temperatures and lower rainfall.
Latosols
Deep, red, nutrient-poor soils found in tropical rainforests.
Xerophytes
Plants that are specially adapted to survive in extremely dry, arid environments.
Salinisation
The accumulation of salts in the soil as water evaporates, common in arid environments.
Coral polyps
Tiny marine invertebrates that build coral reefs and live in symbiosis with algae.
Zooxanthellae
Microscopic algae that live inside coral polyps and provide energy via photosynthesis.
Put your knowledge into practice — try past paper questions for Geography B
Ecosystem
A biological community of interacting living organisms (biotic) and their physical, non-living environment (abiotic).
Biotic
The living components of an ecosystem, such as plants, animals, fungi, and bacteria.
Abiotic
The non-living components of an ecosystem, such as climate, soil, water, light, and rock.
Interdependence
The reliance of every component within an ecosystem on the others, where a change in one triggers a knock-on effect elsewhere.
Trophic cascade
A process where a change at one trophic level of a food web results in a series of knock-on effects for other levels.
Nutrient cycling
The exchange of organic and inorganic matter back into the production of living matter via three stores: Biomass, Litter, and Soil.
Gersmehl diagram
A diagram representing the three main nutrient stores in an ecosystem and the flow of nutrients between them.
Biomass
The store of nutrients found in living plants and animals.
Litter
The store of nutrients found in dead organic matter on the soil surface.
Leaching
The process where heavy rainfall washes essential minerals and nutrients down through the soil profile.
Trophic levels
The hierarchical levels in an ecosystem comprising organisms that share the same nutritional relationship to the primary sources of energy.
Biome
A very large-scale global ecosystem characterized by its distinct climate, flora, and fauna.
Global Atmospheric Circulation
The large-scale movement of air that distributes heat and moisture across the Earth via cells (Hadley, Ferrel, Polar).
Continentality
The climatic effect of being far from the sea, resulting in more extreme seasonal temperatures and lower rainfall.
Latosols
Deep, red, nutrient-poor soils found in tropical rainforests.
Xerophytes
Plants that are specially adapted to survive in extremely dry, arid environments.
Salinisation
The accumulation of salts in the soil as water evaporates, common in arid environments.
Coral polyps
Tiny marine invertebrates that build coral reefs and live in symbiosis with algae.
Zooxanthellae
Microscopic algae that live inside coral polyps and provide energy via photosynthesis.