Tolerance Limits

Every organism survives best within a range of conditions — its tolerance limits. Key factors include body temperature, water availability, blood glucose, and blood CO₂. Push a factor outside the range and the organism is stressed; push it too far and it dies.

Performance peaks in the optimum range and falls away toward the limits of tolerance.

Organisms cope using three kinds of adaptation:

• Structural — physical features (e.g. insulating fur).
• Physiological — internal processes (e.g. sweating).
• Behavioural — actions (e.g. moving into shade).

To hold conditions steady, organs and systems communicate using nerves and hormones — the basis of homeostasis.