WACE ATAR Human Biology key terms

The maintenance of a relatively stable internal environment within narrow limits, despite changes outside the body. It relies on receptors, a control centre and effectors working through feedback loops.

A control mechanism in which a deviation from the normal value triggers a response that reduces that deviation, returning the body toward its set point. Most physiological regulation, such as temperature and blood glucose control, works this way.

A control mechanism in which a change is amplified rather than reversed, pushing the body further from the starting value. It is rare and usually short-lived, such as oxytocin-driven uterine contractions during childbirth or blood clotting.

The target value around which a regulated variable such as core temperature or blood glucose is held. Receptors detect deviation from this value and trigger corrective responses.

A specialised cell or sensory structure that detects a specific stimulus, such as temperature, stretch or a chemical, and sends signals to a control centre. Examples include thermoreceptors in the skin and chemoreceptors in the medulla.

A muscle or gland that carries out the response ordered by the control centre, producing the change that restores the regulated variable. Examples include sweat glands, skeletal muscle shivering and the pancreas.

The coordinated control of heat gain and heat loss to keep core body temperature near 37 degrees Celsius. It involves vasodilation, sweating, shivering, vasoconstriction and behavioural adjustments.

Widening of arterioles supplying the skin, which increases blood flow near the surface and so increases heat loss by radiation and convection. It is a key cooling response in thermoregulation.

Narrowing of skin arterioles, which reduces blood flow near the body surface and conserves heat in the core. It is a key warming response in thermoregulation.

A region of the brain that acts as the body's main control centre for temperature, water balance and other homeostatic variables. It compares incoming sensory information with set points and directs effectors.

The control of water and dissolved solute concentrations in body fluids so that cells neither swell nor shrink excessively. It depends mainly on the kidneys and on hormones such as ADH and aldosterone.

Antidiuretic hormone, released from the posterior pituitary when blood becomes too concentrated. It increases water reabsorption in the kidney collecting ducts, producing smaller volumes of more concentrated urine.

The functional filtering unit of the kidney, consisting of a glomerulus, Bowman's capsule, proximal tubule, loop of Henle, distal tubule and collecting duct. Each kidney contains about one million nephrons.

The pressure-driven movement of water and small solutes from blood in the glomerulus into Bowman's capsule, forming filtrate. Large proteins and blood cells are normally retained in the blood.

The movement of useful substances such as glucose, amino acids, water and ions from the filtrate back into the blood as it passes along the nephron tubules. Most reabsorption occurs in the proximal tubule.

The fluid formed in Bowman's capsule after blood plasma is filtered. It contains water, glucose, amino acids, urea and ions but normally lacks large proteins and blood cells.

A protein that speeds up a specific biochemical reaction by lowering its activation energy, without being consumed. Enzymes are usually specific to one substrate and are affected by temperature and pH.

The specific region of an enzyme where the substrate binds and the reaction takes place. Its shape is complementary to the substrate, which explains enzyme specificity.

The molecule on which an enzyme acts. It binds to the enzyme's active site to form an enzyme-substrate complex before being converted into products.

Loss of an enzyme's normal three-dimensional shape, and therefore its function, caused by excessive heat or extreme pH. The active site changes shape so the substrate can no longer bind.

The net movement of particles from a region of higher concentration to a region of lower concentration, driven by random molecular motion. It requires no energy input from the cell.

The diffusion of water molecules across a partially permeable membrane from a region of higher water potential to a region of lower water potential. It is passive and central to fluid balance in cells.

Passive movement of substances across a membrane through specific carrier or channel proteins, down a concentration gradient. It does not require ATP and is used for glucose entry into many cells.

Movement of substances across a membrane against their concentration gradient, using energy from ATP and carrier proteins. Examples include the sodium-potassium pump and glucose uptake in the kidney.

A barrier that allows some substances to pass through while blocking others, usually because of pore size or lipid solubility. Cell membranes are examples, freely passing water and small nonpolar molecules.

The double layer of phospholipid molecules that forms the core of cell membranes, with hydrophilic heads facing outward and hydrophobic tails inward. Proteins, cholesterol and carbohydrates are embedded within it.

A membrane protein that binds a specific substance and changes shape to move it across the membrane. It may work passively in facilitated diffusion or actively with ATP.

A molecule made of carbohydrate chains attached to a membrane protein. Glycoproteins act in cell recognition, immune identification and as receptor sites for hormones and other signalling molecules.

Adenosine triphosphate, the universal energy currency of cells. Breaking its terminal phosphate bond releases energy that powers active transport, muscle contraction and many synthesis reactions.

The oxygen-requiring breakdown of glucose to carbon dioxide and water, releasing a large amount of ATP. It occurs mainly in mitochondria and yields far more ATP than anaerobic pathways.

Breakdown of glucose without oxygen, producing a small amount of ATP plus lactate in human muscle. It allows short bursts of intense activity but leads to lactate accumulation and fatigue.

A membrane-bound organelle that is the main site of aerobic respiration. Its folded inner membrane increases surface area for the reactions that generate most cellular ATP.

A chemical messenger secreted by an endocrine gland into the blood, which travels to target cells bearing specific receptors and alters their activity. Examples include insulin, ADH and thyroxine.

A hormone released by the beta cells of the pancreas when blood glucose rises. It promotes glucose uptake into cells and glycogen formation in the liver, lowering blood glucose concentration.

A hormone released by the alpha cells of the pancreas when blood glucose falls. It stimulates the breakdown of liver glycogen into glucose, raising blood glucose concentration.

The homeostatic control of glucose concentration in the blood, mainly through the opposing actions of insulin and glucagon. Failure of this control leads to conditions such as diabetes mellitus.

A branched storage polysaccharide of glucose found mainly in liver and skeletal muscle. It is built up under the influence of insulin and broken down to glucose when blood levels fall.

A product of anaerobic respiration in human muscle, formed from pyruvate when oxygen is limited. It accumulates during intense exercise and is later converted back to glucose in the liver.