1.6Cells, Organ Systems and Ecosystems
Ecosystems, Nutrient Cycles and Human Impact — WJEC GCSE Biology — WJEC GCSE Biology Revision Notes & Topical Questions
5 min read 2 parts Lesson 6 of 6
Section 1 of 2Energy flow and nutrient cycles
1Energy transfer
2The Carbon Cycle5 points
- Carbon dioxide is removed from the atmosphere exclusively by photosynthesis in green plants.
- Carbon dioxide is returned to the atmosphere by:
- Respiration in living plants, animals, and decomposers.
- Combustion of fossil fuels (coal, oil, gas) and biomass.
- Decomposition of dead organic matter by bacteria and fungi.
3The Nitrogen Cycle3 points
- Nitrogen-fixing bacteria(in root nodules of legumes or free in soil): convert atmospheric N2 gas into soluble nitrates.
- Decomposers & Nitrifying bacteriaconvert urea and protein wastes into ammonia, then nitrites, then nitrates absorbable by plant roots.
- Denitrifying bacteria(in waterlogged un-aerated soils): convert nitrates back into atmospheric N2 gas.
Section 2 of 2Human environmental impact
- EutrophicationLeaching of synthetic fertiliser nitrates into rivers causes rapid algal blooms, blocking light and killing submerged plants.
- Multiplying decomposer bacteria consume dissolved oxygen, suffocating fish.
- Acid RainSulfur dioxide and nitrogen oxides from burning fossil fuels dissolve in cloud rain, forming sulfuric and nitric acids that damage forests and acidify lakes.
- BioaccumulationNon-biodegradable toxins (e.g. heavy metals, DDT) build up in organism tissues and multiply in concentration at each successive trophic level, reaching lethal levels in apex predators.
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🌳 Student Search Tree & Frequently Asked Exam Questions: ecosystems, nutrient cycles and human impact
Step-by-step problem-solving guide, mark scheme criteria, and experimental error analysis curated by Dr. Khaled Dabour (DABOURHUB).
1. Identify all given values and convert non-standard units, 2. State the primary formula or physiological/chemical principle, 3. Calculate to 3 significant figures and clearly state units.
Avoid confusing independent vs dependent variables in practical questions. In calculation questions, double-check percentage change formula: (change / original) × 100.
Where can I find ecosystems, nutrient cycles and human impact past paper questions by topic with the mark scheme?
On DABOURHUB every ecosystems, nutrient cycles and human impact question is grouped by syllabus point and shown with the mark-scheme wording, so you can see exactly which sentence earns the mark instead of scrolling through whole year papers.
What is the most common ecosystems, nutrient cycles and human impact exam question and why do students lose marks on it?
The repeated pattern on IGCSE papers is a short stem that asks you to apply ecosystems, nutrient cycles and human impact and then justify it with a command word (explain, suggest, compare). Marks are lost by stating the fact without linking it back to the wording of the question, so each ecosystems, nutrient cycles and human impact item here is written as a full-mark answer.
Is there an alternative to Save My Exams or Physics and Maths Tutor for ecosystems, nutrient cycles and human impact?
Yes: the ecosystems, nutrient cycles and human impact notes, topical questions and MCQ quizzes on this site follow the same syllabus headings as the official specification, and they open straight from the search result with no download step.
How do I revise ecosystems, nutrient cycles and human impact in two weeks before the exam?
Three passes: read the ecosystems, nutrient cycles and human impact notes once, then do the topical questions and mark them against the mark scheme, then redo only the ones you missed. The quiz on the page gives instant feedback so the third pass takes minutes rather than an evening.