Eduqas GCSE Biology 6 Ecosystems Exam Questions

About Eduqas GCSE Biology 6 Ecosystems

Ecosystems in Eduqas GCSE Biology has four parts: levels of organisation within an ecosystem, material cycling, biodiversity, and the biological challenges of increasing food yields using fewer resources. You study abiotic and biotic factors, food chains and webs, pyramids of numbers and biomass, and how much biomass passes between trophic levels. You then cover the carbon, water and nutrient cycles and decomposition, followed by sampling with quadrats, transects and capture-recapture, indicator species, alien species and food security. It links to photosynthesis and respiration. Examiners often ask for transfer efficiency calculations, capture-recapture estimates and explanations of the carbon cycle, and there are specified practicals on decomposition and species distribution.

What you need to know

• 6.1 Levels and factors Organism, population, community, ecosystem. Abiotic factors include light, temperature, pH and salinity; biotic factors include predation, disease, food availability and competition. Organisms are interdependent.
• 6.1 Biomass transfer Producers make biomass by photosynthesis; consumers are first, second and third stage. Pyramids of biomass show that biomass is lost at each level through respiration, waste (faeces and urine) and materials that are not eaten. Efficiency = (biomass transferred to next level / biomass at previous level) x 100.
• 6.2 Carbon and water cycles Carbon is removed from the air by photosynthesis and returned by respiration, decomposition and combustion of fossil fuels. The water cycle involves evaporation, transpiration, condensation and precipitation. Nitrates and phosphates are also cycled.
• 6.2 Decomposition Microorganisms break down dead material and waste, releasing carbon dioxide and mineral ions. The rate depends on temperature, water content and oxygen availability; anaerobic decay can release methane. SP6.2: factors affecting decomposition.
• 6.3 Sampling Use quadrats placed randomly to estimate abundance and a transect to study changes in distribution. Capture-recapture: population = (number in first sample x number in second sample) / number marked in second sample. SP6.3: factors affecting the abundance and distribution of a species.
• 6.3 Biodiversity Biodiversity is the variety of species in an area. Indicator species, such as lichens for air quality, show pollution levels. Humans reduce biodiversity through habitat loss and pollution; alien species and biological control agents can upset ecosystems; legislation and protecting endangered species help.
• 6.4 Food security Food security is threatened by population growth, changing diets, pests and pathogens, environmental change and the cost of inputs. Solutions include sustainable farming and genetically modified crops, balanced against protecting wildlife.

Common mistakes in 6 Ecosystems

• Saying energy or biomass is used up at each trophic level. It is lost from the food chain through respiration, waste and parts not eaten.
• Placing quadrats where the most interesting organisms are. Quadrats must be placed randomly, for example using random coordinates, to avoid bias.
• Writing that decomposers return energy to the soil. Decomposers return carbon dioxide to the air and mineral ions to the soil.
• Using the wrong number in capture-recapture. Divide by the number of marked individuals found in the second sample, not the first sample.
• Drawing food chain arrows from predator to prey. The arrow shows the direction of biomass transfer, from the organism eaten to the organism that eats it.

Try three 6 Ecosystems exam-style questions