Key Idea: Topic 2.1 explains how we **define and classify life**, how we **identify organisms**, and why populations are found where they are (because of **abiotic + biotic limiting factors** and **tolerance ranges**).
✅ Must-know definitions
🧬 Classification (why it matters)
🔍 Identification (field skills)
Evaluation question? Give **one strength + one limitation** of dichotomous keys, with a short example (e.g., damaged wing spots).
👥 Populations (exam favourite)
🌡️ Abiotic vs biotic limiting factors
Abiotic (non-living): Temperature (enzyme activity/metabolism). Light (photosynthesis). Water availability (all life processes). pH (enzyme function). Salinity (freshwater vs marine tolerance).
Biotic (living): Producers / consumers / decomposers. Predation. Competition. Disease / parasites.
The **most limiting factor** is the one that has the greatest effect on population size or distribution.
📈 Tolerance curves (range of tolerance)
Graph questions: read **optimum** from the peak x-value, then give the **tolerance range**, and identify **stress vs lethal zones**.
1) Define species (include fertile offspring). 2) Define population (same species/area/time). 3) Name 3 abiotic + 2 biotic factors. 4) Label a tolerance curve.