SACE Biology – Topic 3: Homeostasis (Vocabulary)

Vocabulary flashcards covering key terms and definitions from the lecture on Homeostasis and Tolerance Limits.

Homeostasis

The process of maintaining a relatively stable internal environment within narrow tolerance limits despite external changes.

Tolerance limits

Upper and lower boundaries of an environmental factor within which an organism can survive and function efficiently.

Law of the Minimum

Liebig’s principle stating that growth is controlled not by total resources available but by the scarcest resource (limiting factor).

Limiting factor

The single environmental condition in shortest supply that restricts the growth, survival or distribution of an organism.

Goyder’s Line

A boundary in South Australia marking areas that receive ≥ 250 mm annual rainfall; north of the line cropping and mallee growth are unreliable.

Set point

The normal or desired value of a physiological variable that a homeostatic system aims to maintain.

Temperature (as a limiting factor)

Environmental heat or cold that can restrict biological growth because enzyme activity is temperature-dependent.

Water availability

Amount of accessible water in an environment; critical for cellular processes and a common limiting factor in Australia.

Osmosis

Movement of water across a semi-permeable membrane from low to high solute concentration, causing cell swelling or shrinkage.

Isotonic (0.9 % NaCl)

A solution with the same solute concentration as blood plasma; cells neither gain nor lose water.

Blood glucose level

The concentration of glucose in the blood, normally about 75–95 mg dL⁻¹ in humans.

Hyperglycaemia

Condition in which blood glucose levels rise above the normal range.

Hypoglycaemia

Condition in which blood glucose levels fall below the normal range.

Diabetes

Disease characterised by chronic high blood glucose, usually due to lack of insulin or poor tissue response to insulin.

CO₂ concentration in blood

Normally 5–6 %; regulates breathing rate and depth and influences blood pH.

Acidosis

Lowering of blood pH caused by excess dissolved CO₂; severe cases impair body function.

Stimulus-response model

The sequence in which a stimulus is detected by receptors, processed by a control centre, and countered by effectors.

Receptor

A specialised structure that detects a specific stimulus and initiates a nerve impulse.

Control centre

Part of the nervous or endocrine system that analyses receptor input and determines an appropriate response.

Effector

A muscle or gland that carries out the response directed by the control centre.

Feedback

Information about a response that influences the original stimulus, forming a regulatory loop.

Negative feedback

Homeostatic mechanism in which the response reverses or diminishes the original stimulus.

Positive feedback

Regulatory mechanism in which the response amplifies or reinforces the original stimulus.

Sensory receptors

Groups of specialised cells that detect changes in the environment and convert them into nerve impulses.

Photoreceptor

Light-sensitive receptor found in eyes, enabling sight.

Chemoreceptor

Receptor sensitive to specific chemicals; found in nose and tongue for smell and taste.

Mechanoreceptor

Receptor that detects pressure, vibration or touch; located in skin and ears.

Thermoreceptor

Temperature-sensitive receptor present in skin and other tissues.

Pain receptor (nociceptor)

Receptor that responds to tissue damage and produces sensations of pain.

Nervous system

Rapid communication network using electrical impulses to coordinate body functions and contribute to homeostasis.

Endocrine system

Hormone-secreting glands that provide slower, longer-lasting regulation of body processes and assist in homeostasis.