The Organism in the EnvironmentEdexcel GCSE Biology: Revision notes
Section 1
Levels of Organisation
Organism → population → community → ecosystem.
Key termsorganismpopulationcommunityecosystem
Common mistake
Don't confuse population (one species) with community (many species).
Section 2
Abiotic and Biotic Factors
Abiotic: temperature, light, water, pollutants. Biotic: competition, predation.
Key termsabiotic factorbiotic factorcompetitionpredation
Section 3
Interdependence and Species Relationships
Interdependence: organisms rely on each other. Parasitism: parasite benefits, host harmed. Mutualism: both benefit.
Key termsinterdependenceparasitismmutualism
Section 4
Core Practical: Quadrats and Belt Transects
Quadrats: random placement, count/estimate cover. Belt transects: quadrats at intervals along a gradient.
Key termsquadratbelt transectrandom sampling
Section 5
Estimating Population Size
Estimated total = mean per quadrat × (total area ÷ quadrat area).
Key termspopulation estimate
Example
10 quadrats, mean=5/m², field=500m²: estimate=5×500=2500.
Must Know
- Organisation: organism→population→community→ecosystem.
- Abiotic: temp/light/water/pollutants; Biotic: competition/predation.
- Parasitism (one harmed) vs mutualism (both benefit).
- Quadrats/belt transects; population estimate = mean × (total area/quadrat area).
That's the notes covered.
Carry on to the next subtopic.