Summary and Exam Tips for Cycles within Ecosystems
Cycles within Ecosystems is a subtopic of Ecology and the Environment, which falls under the subject Biology in the Edexcel IGCSE curriculum. Nutrients like carbon and nitrogen are finite resources on Earth, necessitating their recycling for new organism growth. The Carbon Cycle involves carbon dioxide being absorbed by plants for photosynthesis, transferred to animals through feeding, and returned to the atmosphere via respiration. Decomposition in the absence of microorganisms can lead to fossil fuel formation, which releases carbon dioxide upon combustion. Human activities like increased fossil fuel use and deforestation elevate atmospheric carbon dioxide levels. The Water Cycle describes water's movement through evaporation, transpiration, condensation, and precipitation. The Nitrogen Cycle is crucial for protein synthesis, with nitrogen-fixing bacteria and lightning converting atmospheric nitrogen into absorbable forms. Plants absorb nitrates, while animals obtain nitrogen by consuming plants or other animals. Decomposers recycle nitrogen back into the soil, and nitrifying bacteria convert ammonium compounds into nitrates. Denitrifying bacteria can reverse this process, but farmers can mitigate their effects by aerating the soil.
Exam Tips
- Use precise terminology: Instead of "die out" or "grow," use "decrease" or "increase" when discussing food webs.
- Understand the cycles: Be clear on the processes of the Carbon, Water, and Nitrogen cycles, including key terms like photosynthesis, respiration, evaporation, and nitrification.
- Focus on human impact: Be prepared to discuss how human activities like deforestation and fossil fuel combustion affect these cycles.
- Read questions carefully: Tailor your answers to the specific organism or process mentioned in the question.
- Practice diagrams: Being able to draw and label the cycles can help reinforce your understanding and improve exam performance.
