IP Biology Upper Sec 11: Organisms and their Environment

These notes align with SEAB GCE O-Level Biology (6093) content used in IP programmes (exams from 2026).

Status: SEAB O-Level Biology 6093 syllabus (exams from 2026) checked 2025-11-30 - scope unchanged; remains the reference for this note.

What you must know

• Energy flow: sunlight → chemical energy in producers → consumers → decomposers; energy lost as heat/respiration, not recycled.
• Food chains/webs: producers, primary/secondary/tertiary consumers, decomposers; energy decreases up trophic levels; pyramids of biomass reflect energy content better than numbers.
• Carbon cycle: photosynthesis removes $\ce{CO2}$; respiration/combustion release it; decomposition returns carbon; oceans/forests as sinks.
• Human impacts: deforestation reduces carbon uptake, increases erosion; fossil fuel burning raises $\ce{CO2}$