GCE O/L Science flashcards

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

Active transport

Movement of ions or molecules across a cell membrane from low to high concentration using energy from ATP and carrier proteins, e.g., mineral uptake by root hair cells.

Osmosis

Diffusion of water through a partially permeable membrane from a dilute solution (high water potential) to a concentrated solution (low water potential), without energy input.

Enzyme specificity

Each enzyme has an active site complementary to its substrate, so it catalyses only one reaction; the lock-and-key model explains this specificity.

Benedict's test

Test for reducing sugars: add Benedict's solution and heat in a water bath; a brick-red precipitate forms if a reducing sugar such as glucose is present.

Aerobic respiration equation

C6H12O6 + 6O2 → 6CO2 + 6H2O + energy (ATP). Occurs mainly in mitochondria and releases more energy per glucose molecule than anaerobic respiration.

Photosynthesis equation

6CO2 + 6H2O → C6H12O6 + 6O2, using light energy absorbed by chlorophyll in chloroplasts; produces glucose and oxygen.

Alveoli adaptations

Tiny air sacs in lungs with large surface area, thin one-cell walls, moist lining and rich blood supply, maximising gas exchange by diffusion.

Villi function

Finger-like projections in small intestine that increase surface area for absorption; have thin walls, rich blood supply and lacteals for fat absorption.

Transpiration

Loss of water vapour from plant leaves through stomata; rate increases with temperature, light, wind and low humidity; pulls water up xylem.

Homeostasis

Maintenance of a stable internal environment in the body, e.g., temperature, blood glucose and water balance, controlled by negative feedback mechanisms.

Nephron

Functional unit of the kidney; filters blood in the glomerulus and reabsorbs useful substances such as glucose, some ions and water to form urine.

Double circulation

Blood passes through the heart twice per circuit: right side to lungs (pulmonary), left side to body (systemic), maintaining high pressure to body.

Meiosis

Cell division producing four haploid gametes with genetic variation through crossing over and independent assortment; halves chromosome number.

Dominant allele

An allele that is expressed in the phenotype even when only one copy is present; represented by a capital letter in genetic diagrams.

Punnett square

Grid used to predict possible genotypes and phenotypes of offspring from parental gametes; shows ratios such as 3:1 for a monohybrid cross.

Natural selection

Process where organisms with advantageous inherited characteristics are more likely to survive and reproduce, passing those alleles to the next generation.

Food chain

Diagram showing feeding relationships, starting with a producer and arrows indicating direction of energy flow to consumers; energy is lost at each trophic level.

Eutrophication

Nutrient enrichment of water by fertiliser run-off, causing algal blooms that block light; decomposers use oxygen, killing aquatic organisms.

Greenhouse effect

Atmospheric gases such as carbon dioxide and methane absorb and re-emit infrared radiation, warming the Earth's surface; increased by human activity.

Isotope

Atoms of the same element with the same number of protons but different numbers of neutrons, e.g., carbon-12 and carbon-14.

Ionic bonding

Electrostatic attraction between oppositely charged ions formed by transfer of electrons from a metal atom to a non-metal atom, e.g., Na+Cl−.

Covalent bond

Bond formed by sharing one or more pairs of electrons between non-metal atoms, e.g., in water (H2O) and methane (CH4).

Mole

Amount of substance containing 6.02 × 10^23 particles (Avogadro constant); molar mass is the mass of one mole in grams.

Percentage yield

Actual yield divided by theoretical yield, multiplied by 100; measures efficiency of a chemical reaction and is always less than 100% in practice.

Exothermic reaction

Chemical reaction that transfers energy to the surroundings, usually shown by a temperature rise; e.g., combustion and neutralisation.

Neutralisation

Reaction between an acid and a base producing a salt and water; H+ ions from acid react with OH− ions from alkali.

Flame test

Qualitative test identifying metal ions by flame colour: lithium crimson, sodium yellow, potassium lilac, calcium orange-red, copper blue-green.

Reactivity series

Order of metals by reactivity: potassium, sodium, calcium, magnesium, aluminium, zinc, iron, tin, lead, copper, silver, gold; predicts displacement reactions.

Alkene

Unsaturated hydrocarbon with a carbon-carbon double bond, general formula CnH2n; decolourises bromine water; undergoes addition polymerisation.

Newton's second law

Resultant force on an object equals mass times acceleration (F = ma); acceleration is in the same direction as the resultant force.

Wave equation

Wave speed equals frequency multiplied by wavelength (v = fλ); frequency in hertz, wavelength in metres, speed in metres per second.

Ohm's law

Current through an ohmic conductor is directly proportional to potential difference across it, provided temperature remains constant (V = IR).