Topic 3 – Homeostasis & Tolerance Limits

Vocabulary flashcards covering key terms related to homeostasis, tolerance limits, and associated physiological concepts.

Homeostasis

The automatic maintenance of a stable internal environment despite external fluctuations.

Tolerance limits

The minimum and maximum values of an abiotic factor within which an organism can survive and function.

Zone of physiological stress

Range of an abiotic factor near the tolerance limits where only a few individuals of a species can survive.

Zone of intolerance

Range beyond an organism’s tolerance limits where it cannot survive; the species is absent.

Abiotic factor

A non-living environmental variable—e.g., temperature, water, light, mineral ions—that influences organisms.

Thermoregulation

The process by which organisms maintain internal body temperature within tolerance limits.

Optimum body temperature

Narrow temperature range that maximises enzyme-controlled metabolic reactions.

Osmoregulation

Control of water balance and solute concentrations inside organisms and their cells.

Water availability

Amount of water accessible to an organism; essential for transport, metabolism, thermoregulation, movement, reproduction, and support.

Blood glucose level (BGL)

Concentration of glucose in the blood (normal fasting range 3.9–5.5 mmol L⁻¹) that supplies cells with fuel for respiration.

Insulin

Pancreatic hormone that decreases blood glucose by promoting its uptake and storage as glycogen or fat.

Glucagon

Pancreatic hormone that raises blood glucose by stimulating glycogen breakdown and glucose release from the liver.

Hypoglycaemia

Condition of abnormally low BGL causing fatigue, shakiness, hunger, confusion, and potentially coma.

Hyperglycaemia

Condition of abnormally high BGL causing glucose in urine, dehydration, fatigue, vision problems, and diabetes.

Carbonic acid

Weak acid formed when CO₂ dissolves in blood; influences blood pH balance.

Respiratory alkalosis

Increase in blood pH due to low CO₂ levels (often from hyperventilation), leading to tingling, muscle spasms, and chest tightness.

Respiratory acidosis

Decrease in blood pH due to elevated CO₂ levels (often from hypoventilation), causing headache, confusion, and shortness of breath.

Physiological stress

State in which environmental conditions near tolerance limits impair normal biological function.

Liebig’s Law of the Minimum

Principle stating that growth or productivity is limited by the scarcest essential abiotic factor.