Science 30 flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Homeostasis

Maintenance of a relatively stable internal environment within narrow limits despite external change, achieved by sensors, a control centre, and effectors acting through feedback loops.

Negative feedback

A control mechanism in which a detected deviation triggers a response that reduces that deviation, returning the variable toward its set point; for example, insulin lowering high blood glucose.

Positive feedback

A control mechanism in which a change triggers a response that amplifies the same change, driving the variable further from the starting state until an external event ends the cycle.

Receptor and effector

A receptor is a structure that detects a specific stimulus and generates a nerve impulse; an effector is a muscle or gland that carries out the response.

Action potential

A rapid reversal of membrane potential travelling along an axon, produced when depolarization reaches threshold and voltage-gated sodium channels open, followed by potassium-driven repolarization.

Synapse

The junction between a neuron and its target cell, where a neurotransmitter released from the presynaptic terminal diffuses across a gap and binds receptors on the postsynaptic membrane.

Thermoregulation

Control of body temperature by balancing heat gain and loss through sweating, vasodilation, shivering, vasoconstriction, and behavioural adjustments coordinated by the hypothalamus.

Osmoregulation

Control of water and solute balance, largely by the kidneys; ADH increases water reabsorption when blood becomes too concentrated, producing smaller volumes of more concentrated urine.

Adaptation versus acclimatization

Adaptation is a heritable, population-level change favoured by natural selection over generations; acclimatization is a reversible physiological adjustment made by an individual within its lifetime.

pH definition

pH equals the negative base-10 logarithm of hydronium ion concentration. Each one-unit decrease means a tenfold increase in acidity; neutral water at 25 degrees Celsius has pH 7.

Acid deposition

Sulfur dioxide and nitrogen oxides from combustion react with water and oxygen in the atmosphere to form sulfuric and nitric acids, which return to the surface as rain, snow, fog, or particles.

Liming

Addition of calcium carbonate or calcium oxide to neutralize acidic soil or water, raising pH and releasing calcium ions while producing water and carbon dioxide.

Eutrophication

Nutrient enrichment of water by nitrogen and phosphorus, causing algal blooms whose decomposition consumes dissolved oxygen and can suffocate fish and other aquatic organisms.

Biochemical oxygen demand

The amount of dissolved oxygen consumed by microorganisms decomposing organic matter in a water sample; a higher value indicates greater organic pollution.

Greenhouse effect

Atmospheric gases absorb outgoing infrared radiation from Earth's surface and re-emit it in all directions, warming the lower atmosphere and surface above the temperature they would otherwise have.

Photochemical smog

A brownish haze formed when nitrogen oxides and volatile organic compounds react in sunlight, producing ground-level ozone and other irritants harmful to lungs and plants.

Biomagnification

The increase in concentration of a persistent, fat-soluble substance such as methylmercury or PCBs at each successive trophic level, reaching highest levels in top predators.

Catalytic converter

An exhaust device using a catalyst to oxidize carbon monoxide and hydrocarbons and reduce nitrogen oxides, converting them mainly into carbon dioxide, water, and nitrogen.

Wave equation

For electromagnetic radiation, speed equals frequency multiplied by wavelength; in a vacuum the speed is 3.00 times 10 to the eighth metres per second.

Photon energy

Energy of a single photon equals Planck's constant (6.63 times 10 to the negative thirty-fourth joule-seconds) multiplied by frequency; shorter wavelengths therefore carry more energetic photons.

Electromagnetic spectrum order

Arranged by increasing frequency: radio, microwave, infrared, visible, ultraviolet, X-ray, gamma ray; wavelength decreases in the same order.

Visible light range

Wavelengths from roughly 400 nanometres (violet) to 700 nanometres (red); longer wavelengths appear red and shorter ones violet within this narrow band.

Refraction

Change in direction of light as it crosses a boundary between media of different optical density, caused by a change in speed; the index of refraction equals light speed in vacuum divided by speed in the medium.

Total internal reflection

Complete reflection of light back into a denser medium when it strikes a boundary beyond the critical angle, the principle behind optical fibres and certain prisms.

Real versus virtual image

A real image forms where light rays actually converge and can be projected on a screen; a virtual image forms where rays only appear to originate and cannot be projected.

Ionizing radiation

Radiation whose photons carry enough energy to remove electrons from atoms, including ultraviolet, X-rays, and gamma rays; it can damage DNA and living tissue.

Inverse-square law

Intensity of radiation from a point source equals power divided by four pi times distance squared, so tripling distance reduces intensity to one ninth.

Energy conservation

The first law of thermodynamics: energy cannot be created or destroyed, only converted between forms, so total energy in an isolated system remains constant.

Energy efficiency

The ratio of useful energy output to total energy input, usually expressed as a percentage; the remainder is lost mainly as low-quality waste heat.

EROI

Energy return on investment: the ratio of energy delivered by a source to the energy required to obtain it. A source is a net energy contributor only when the ratio exceeds one.

Carbon footprint

Total greenhouse gas emissions attributed to an activity or product, expressed as carbon dioxide equivalents using each gas's global warming potential over a stated time horizon.

Nuclear fission

Splitting of a heavy nucleus such as uranium-235 after neutron absorption, releasing energy from the mass defect along with additional neutrons and radioactive fission products.