Ecosystems — Eduqas GCSE Combined Science

The study of ecosystems in the WJEC GCSE Combined Science specification explores the complex interactions between living organisms (biotic factors) and their non-living environment (abiotic factors). This topic bridges the gap between individual biological processes and the global environment, focusing on how energy flows from the sun through food chains and how essential nutrients like carbon and nitrogen are recycled to sustain life. Understanding these systems is crucial for grasping how human activity, such as pollution and deforestation, disrupts the delicate balance of nature.

Students will delve into the roles of producers, consumers, and decomposers, and learn to quantify these relationships using pyramids of number and biomass. A significant portion of the curriculum is dedicated to the efficiency of energy transfer, explaining why food chains rarely exceed five trophic levels due to energy loss through respiration, movement, and excretion. By mastering this topic, you will be able to predict the consequences of environmental changes and understand the scientific basis for conservation efforts and sustainable living.

• →Trophic Levels and Energy Transfer: Understanding that only approximately 10% of energy is passed from one level to the next, with the rest lost as heat, movement, or undigested material.
• →The Carbon Cycle: The processes of photosynthesis, respiration, combustion, and decomposition that move carbon between the atmosphere, living organisms, and fossil fuels.
• →The Nitrogen Cycle: The vital role of bacteria (nitrifying, nitrogen-fixing, and denitrifying) in converting atmospheric nitrogen into forms plants can absorb to make proteins.
• →Interdependence and Competition: How organisms rely on each other for food, shelter, and pollination, and how they compete for limited resources like light, water, and space.
• →Abiotic and Biotic Factors: Identifying non-living influences (pH, temperature, light intensity) and living influences (predation, disease, food availability) on a population.

• Distinction between individual, population, community, and ecosystem
• Identification of abiotic factors (pH, light, temperature, salinity) and biotic factors (predation, disease, food availability)
• Explanation of interdependence and competition
• Role of photosynthetic organisms as producers of biomass
• Trophic levels: producers, consumers (1st, 2nd, 3rd stage), herbivores, and carnivores
• Explanation of the carbon cycle (photosynthesis, respiration, decay, fossil fuels)
• Importance of the water cycle
• Use of quadrats for abundance and transects for distribution
• Principles of sampling and capture/recapture techniques
• Definition and importance of biodiversity and indicator species
• Impact of human interactions (positive and negative) on biodiversity
• Methods for protecting biodiversity and endangered species
• Issues surrounding biological control and alien species

• 💡Ensure you can define and provide examples for both abiotic and biotic factors
• 💡Be prepared to interpret food webs and explain the transfer of biomass
• 💡Understand the methodology for using quadrats and transects, including the need for representative sampling
• 💡Be able to explain the carbon cycle processes clearly
• 💡Practice evaluating the benefits and challenges of maintaining biodiversity
• 💡Use precise terminology when describing the Nitrogen Cycle. Do not just say 'bacteria'; specify 'nitrogen-fixing bacteria' or 'nitrifying bacteria' to secure high-tier marks.
• 💡When calculating energy transfer efficiency, always use the formula: (Energy transferred to next level / Total energy in) x 100. Double-check your units before completing the calculation.
• 💡In QER (Quality of Extended Response) questions about the Carbon Cycle, ensure you link each process to the specific form of carbon involved, such as 'carbon dioxide in the atmosphere' or 'glucose in plants'.

• Confusing abiotic and biotic factors
• Misinterpreting food chains/webs regarding biomass transfer
• Failing to explain the role of microorganisms in decay and carbon release
• Incorrectly applying sampling techniques (e.g., not collecting sufficient data)
• Confusing the roles of photosynthesis and respiration in the carbon cycle
• Energy is recycled in an ecosystem: In reality, energy flows in one direction and is eventually lost to the surroundings as heat. Only nutrients, such as carbon and nitrogen, are truly recycled.
• Pyramids of number always look like pyramids: While they often do, a single large producer (like an oak tree) can support thousands of insects, resulting in an inverted or 'top-heavy' pyramid of numbers. Pyramids of biomass, however, almost always retain the traditional pyramid shape.
• Plants only perform photosynthesis: Students often forget that plants also respire 24/7. While they take in CO2 for photosynthesis during the day, they constantly release CO2 as a byproduct of aerobic respiration.

1. 1Week 1, Day 1-2: Master the vocabulary. Create flashcards for biotic/abiotic factors, trophic levels, and the different types of bacteria in the nitrogen cycle.
2. 2Week 1, Day 3-5: Focus on cycles. Practice drawing the Carbon and Nitrogen cycles from memory, labeling every arrow with the correct biological process.
3. 3Week 2, Day 1-2: Quantitative skills. Practice drawing pyramids of biomass to scale and calculating the efficiency of energy transfers using past paper data.
4. 4Week 2, Day 3-5: Application and Exam Practice. Complete 6-mark QER questions on human impact (e.g., eutrophication or global warming) and use mark schemes to refine your technical language.

• 📋Data Interpretation: You may be given a food web and asked to predict the effect of removing one species. Advice: Always trace the 'flow' of the arrows and consider both direct and indirect effects on other populations.
• 📋Calculations: Calculating the percentage efficiency of biomass transfer between trophic levels. Advice: Ensure you are using the correct values from the provided table and show your working clearly.
• 📋QER (Quality of Extended Response): A 6-mark question asking you to describe the recycling of nutrients. Advice: Use a logical sequence (e.g., starting with atmospheric CO2) and include key terms like 'decomposition' and 'microorganisms'.
• 📋Short Answer: Identifying abiotic factors and how they are measured. Advice: Be specific—instead of 'weather', say 'temperature' or 'light intensity', and name the equipment used (e.g., a light meter).