Skip to main content
eTopicals
O Levelbiology · Topic 19

Biology Paper 2 Topic 19: Relationships of Organisms With One Another and With the Environment

Master food webs, energy flow pyramids, carbon & nitrogen cycles, eutrophication, and conservation with Cambridge questions.

PDF Viewer - Relationships of Organisms With One Another and With the Environment

Loading PDF…

Download PDF

30

Download unlocks in 30s

Timer pauses if you switch tabs

Share:

About Relationships of Organisms With One Another and With the Environment

Relationships of Organisms With One Another and With the Environment covers ecological principles, nutrient biogeochemical cycles, population dynamics, and human environmental impacts. In Cambridge O Level Biology Paper 2 (5090), this comprehensive chapter evaluates students on trophic energy transfer, ecological pyramids (numbers and biomass), the carbon and nitrogen cycles, sigmoid population growth curves, aquatic eutrophication, and habitat conservation strategies.

Why Is Ecology and Environmental Biology Important?

Understanding how organisms interact with each other and their abiotic environments is critical for preserving global biodiversity and managing ecosystems sustainably. In Cambridge O Level examinations, ecology questions assess data analysis and environmental evaluation, requiring students to trace energy losses across trophic levels, predict food web disruptions, and explain chemical cycles.

Skills Tested In This Topic

Students are evaluated on constructing and interpreting food chains, food webs, and ecological pyramids; calculating energy transfer efficiencies between trophic levels; outlining the biological processes of the carbon and nitrogen cycles (including nitrogen fixation, nitrification, and denitrification); analyzing sigmoid population growth curves; explaining the step-by-step mechanism of eutrophication; and discussing conservation methods.

How This Topical Paper Helps

This topical past paper compiles authentic Cambridge Paper 2 questions dedicated to Ecology and Environmental Biology. Practising these curated questions enables students to master nitrogen cycle flowcharts, food web population shift predictions, eutrophication sequential essay prompts, and mark-scheme precision on human environmental impacts.

Exam Preparation Tips

Be precise with bacteria in the nitrogen cycle: nitrogen-fixing bacteria convert nitrogen gas to ammonia/ammonium, nitrifying bacteria convert ammonium into nitrites and nitrates, and denitrifying bacteria convert nitrates back to nitrogen gas under anaerobic conditions. For eutrophication, memorise the exact chronological sequence: fertilizer leaching, algal bloom, submerged plant death, bacterial decomposition, dissolved oxygen depletion, and fish death.

Why Practice Past Paper Questions?

Paper 2 frequently includes structured questions presenting inverted pyramids of numbers (e.g. one oak tree supporting thousands of caterpillars) or data tables on pesticide bioaccumulation. Solving past paper prompts sharpens graphical interpretation and ensures full credit on multi-step environmental questions.

Quick Answer

Relationships of Organisms With One Another and With the Environment in Cambridge O Level Biology (5090) covers food webs, trophic energy transfer, carbon and nitrogen cycles, population growth, and human impacts like eutrophication. Students should revise by diagramming pyramids of biomass, learning nitrogen cycle bacteria, tracing eutrophication stages, and practising structured Paper 2 topical past paper questions.

How To Revise Using This Paper

  • Review food web definitions and practice drawing pyramids of numbers, biomass, and energy.
  • Draw complete diagrams of the carbon and nitrogen cycles, labelling all bacterial types and chemical conversions.
  • Memorise the 6-step cause-and-effect sequence of aquatic eutrophication.
  • Analyze sigmoid population growth curves, identifying density-dependent and density-independent factors.
  • Answer the structured theory questions in this PDF under closed-book exam conditions.
  • Review your answers against official Cambridge mark schemes to refine ecological keywords.

Summary

Relationships of Organisms With One Another and With the Environment is the culminating chapter in O Level Biology Paper 2 that integrates ecological science with environmental stewardship. Excelling in this unit requires mastering energy flow calculations, nitrogen cycle bacteria, food web population shifts, eutrophication cascades, and conservation methods. Working through compiled topical past papers provides the targeted practice necessary to achieve top marks in Cambridge 5090 examinations.

Frequently Asked Questions

This topic covers energy flow through food chains and food webs, pyramids of numbers, biomass, and energy, the carbon and nitrogen biogeochemical cycles, sigmoid population growth curves, and human environmental impacts (such as deforestation, pollution, eutrophication, and conservation) in Cambridge O Level Biology 5090.

Ecology and Environmental Biology features heavily in Paper 2. Cambridge regularly evaluates students on trophic energy loss calculations, food web feeding relationships, nitrogen cycle bacteria identifications, sequential steps of eutrophication, and habitat conservation measures.

Only about 10% of energy is transferred from one trophic level to the next. The remaining 90% is lost as heat during cellular respiration, excreted as metabolic waste (urea), egested as undigested faeces, or locked in uneaten organism parts (bones, roots, wood).

A pyramid of numbers represents the total count of individual organisms at each trophic level and can be inverted (e.g. many caterpillars feeding on one oak tree). A pyramid of biomass represents the total dry mass of living material at each level and is almost always pyramid-shaped (narrowing toward the top).

Decomposers break down dead organic matter and urea into ammonium ions. Nitrifying bacteria convert ammonium to nitrites and then nitrates for plant uptake. Nitrogen-fixing bacteria convert atmospheric N2 gas into ammonia. Denitrifying bacteria convert nitrates back into N2 gas in anaerobic, waterlogged soils.

Eutrophication occurs when excess nitrate and phosphate fertilisers leach into waterways. This causes rapid algal growth (algal bloom) blocking sunlight. Submerged plants die due to lack of photosynthesis. Aerobic bacteria multiply rapidly decomposing dead plants, exhausting dissolved oxygen and causing fish to suffocate.

The four phases are: Lag phase (slow initial growth as organisms adapt), Exponential (log) phase (rapid reproduction where birth rate greatly exceeds death rate), Stationary phase (birth rate equals death rate as resources become limiting), and Death phase (death rate exceeds birth rate due to toxic buildup or starvation).

Deforestation leads to severe soil erosion and desertification, loss of habitat and biodiversity, disruption of rainfall patterns in the water cycle, and increased atmospheric carbon dioxide levels contributing to global warming.

Common errors include drawing food chain arrows backwards (arrows must point in the direction of energy transfer, from prey to predator), confusing nitrifying with nitrogen-fixing bacteria, omitting bacteria when explaining eutrophication, and confusing pyramids of numbers with pyramids of biomass.

Yes, this topical past paper PDF compiles official Cambridge O Level Biology Paper 2 (5090) questions from 2011 to 2024, providing structured theory practice and topic-focused revision for independent self-study.