Science 30 key terms

The body's active maintenance of stable internal conditions, such as temperature, pH, and blood glucose, despite changes in the surrounding environment. It relies on continuous monitoring and corrective responses.

A control cycle in which a detected change triggers a response that counteracts the change and restores the original condition. It is the most common mechanism for keeping internal variables near a set point.

A control cycle in which a change triggers responses that amplify the same change, pushing a process to completion rather than restoring balance. Examples include childbirth contractions and certain immune responses.

A specialized cell, protein, or sensory structure that detects a specific stimulus, such as light, pressure, or a chemical, and sends that information toward a control centre for processing.

A muscle, gland, or organ that carries out the response commanded by a control centre, producing the change that adjusts a body condition. Effectors are the acting component of a feedback loop.

The target value that a control system works to maintain for a particular internal variable, such as 37 degrees Celsius for core body temperature. Deviations above or below it trigger corrective responses.

A chemical messenger released by an endocrine gland into the bloodstream, which travels to target cells bearing matching receptors and alters their activity. Insulin and adrenaline are examples.

A hormone released by the pancreas when blood glucose rises. It signals cells to take up glucose and the liver to store it, lowering blood glucose toward its normal range.

A nerve cell specialized to receive, conduct, and transmit electrical impulses. Its structure includes dendrites for input, a cell body, and an axon that carries signals toward other cells.

A chemical released at the end of a neuron that crosses a small gap and binds to receptors on the next cell, passing the signal onward or modifying its strength.

A rapid, involuntary nerve pathway that produces a protective response without waiting for conscious processing by the brain. A sensory neuron, interneuron, and motor neuron typically form the circuit.

The coordinated defence mounted by the body against pathogens and foreign substances. It includes barriers, inflammation, and targeted actions of white blood cells that recognize and destroy invaders.

A Y-shaped protein produced by certain white blood cells that binds specifically to a foreign marker, helping to neutralize or mark the invader for destruction.

A preparation that exposes the immune system to a harmless form or component of a pathogen, prompting memory cells to form so that later real exposure is fought off quickly.

An inherited feature or behaviour that improves an organism's chance of surviving and reproducing in its particular environment. Adaptations arise over generations through natural selection.

The process by which individuals with traits better suited to their environment tend to leave more offspring, so those traits become more common in later generations of a population.

The span of an environmental condition, such as temperature or salinity, within which an organism can survive and function. Conditions outside this range cause stress or death.

A living organism or community whose presence, absence, or condition reveals the health of an environment. Lichens, for example, are sensitive to air pollution and signal air quality.

A logarithmic scale from 0 to 14 expressing the concentration of hydrogen ions in a solution. Values below 7 are acidic, 7 is neutral, and above 7 is basic.

A substance that donates hydrogen ions when dissolved in water, producing a solution with a pH below 7. Acids react with bases to form salts and water.

A substance that accepts hydrogen ions or releases hydroxide ions in water, producing a solution with a pH above 7. Bases feel slippery and react with acids in neutralization reactions.

The reaction between an acid and a base that produces a salt and usually water, bringing the solution closer to neutral pH. It is used to treat spills and reduce environmental acidity.

A dissolved substance or mixture that resists large swings in pH when small amounts of acid or base are added, by absorbing or releasing hydrogen ions. Buffers help keep natural waters stable.

The falling of acidic pollutants, mainly sulfur dioxide and nitrogen oxides converted in the atmosphere, onto land and water as rain, snow, or dry particles. It can harm soils, lakes, and forests.

A rapid reaction between a fuel and oxygen that releases heat and light. Complete combustion yields carbon dioxide and water, while incomplete combustion can produce carbon monoxide and soot.

A colourless gas produced by respiration and combustion that absorbs infrared radiation. Rising atmospheric levels from human activity strengthen the greenhouse effect and influence ocean acidity.

The warming of a planet's surface because certain atmospheric gases absorb and re-emit outgoing infrared radiation. Without it Earth would be far colder, but intensification alters climate.

The complete arrangement of electromagnetic radiation by wavelength and frequency, from long radio waves through microwaves, infrared, visible light, ultraviolet, X-rays, and short gamma rays.

The distance between two consecutive matching points on a wave, such as crest to crest, usually measured in metres or nanometres. It determines colour for visible light.

The number of complete wave cycles passing a fixed point each second, measured in hertz. Higher frequency corresponds to shorter wavelength and greater energy per photon.

A discrete packet of electromagnetic energy. The energy carried by one photon increases with the frequency of the radiation and is released or absorbed when electrons change energy levels.

The narrow band of electromagnetic radiation that human eyes detect, roughly 400 to 700 nanometres. Different wavelengths within this band appear as different colours.

Electromagnetic radiation with wavelengths longer than visible red light, commonly felt as heat. Warm objects emit it, and it is used in remote sensing and thermal imaging.

Electromagnetic radiation with wavelengths shorter than visible violet light, carrying enough energy to damage biological molecules. It causes sunburn and can be limited by ozone in the atmosphere.

The ejection of electrons from a material when light of sufficient frequency strikes it. It demonstrates that light delivers energy in discrete packets called photons.

Energy derived from sources that are naturally replenished on a human timescale, such as sunlight, wind, flowing water, and biomass. Such sources produce little greenhouse gas while operating.

Energy from finite resources that are consumed far faster than they form, such as coal, oil, and natural gas. Burning them releases stored carbon into the atmosphere.

A carbon-rich fuel formed over millions of years from buried remains of organisms, including coal, petroleum, and natural gas. Its combustion supplies most global energy but adds carbon dioxide.

Energy captured from sunlight and converted into electricity by photovoltaic cells or into heat by collectors. It is renewable and produces no emissions during operation.

The ratio of useful energy output to total energy input for a device or process, often expressed as a percentage. The remainder is lost, frequently as waste heat.

A change of energy from one form to another, such as chemical energy in fuel becoming heat and then electricity. Each transformation conserves total energy but reduces usable quality.