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Brainlag

GCSE Science key terms

Biology (cells, digestion, infection, nerves, genetics, ecology), chemistry (atoms, bonding, reactions, crude oil, water, the atmosphere) and physics (energy, circuits, forces, waves, magnets, atoms, space), each card tagged by subject.

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Endothermic (reaction)
An endothermic reaction takes in energy from its surroundings; photosynthesis is endothermic.
Chlorophyll
Chlorophyll is the green pigment in chloroplasts; the light energy that photosynthesis takes in is absorbed by chlorophyll.
Respiration
Respiration is the reaction in every living cell, day and night, that releases energy from glucose; respiration is exothermic, the reverse reaction of photosynthesis.
Starch
Starch is the plant store made from glucose; starch is insoluble, so storage as starch does not upset the water balance of cells by osmosis.
Cellulose
Cellulose is made by a plant from its glucose to build and strengthen cell walls.
Amino acids
Amino acids are made by a plant from glucose and nitrate ions from the soil, then joined into proteins.
Independent variable
The independent variable is the variable that is changed, such as light intensity (changed by moving the lamp) when the rate of photosynthesis is followed.
Dependent variable
The dependent variable is the variable that is followed as the independent variable is changed, such as the oxygen made per minute by a water plant (counted as bubbles, or collected in a syringe) as light intensity is changed.
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Control variables
Control variables are variables that must be the same, such as temperature, carbon dioxide and the piece of pondweed when the rate of photosynthesis is followed.
Light (limiting factor)
Light is a limiting factor of the rate of photosynthesis: when light intensity is in shortest supply it limits the rate, so brighter light gives a faster rate.
Carbon dioxide (limiting factor)
Carbon dioxide is a limiting factor of the rate of photosynthesis: when carbon dioxide concentration is in shortest supply it limits the rate, so more light does nothing.
Eukaryotic cells
Eukaryotic cells are cells that keep their genetic material (DNA) inside a nucleus; animals, plants, fungi and protists are made of eukaryotic cells.
Prokaryotic cells
Prokaryotic cells are the cells of bacteria: much smaller than a typical animal cell, with no nucleus and DNA as one loop in the cytoplasm.
Plasmids
Plasmids are extra small rings of DNA often floating in the cytoplasm of prokaryotic cells, as well as the one loop.
Nucleus (cell)
The nucleus is the part of an animal or plant cell that holds the genetic material that controls the cell.
Cytoplasm
Cytoplasm is a jelly in animal and plant cells where most chemical reactions happen.
Cell membrane
The cell membrane is the part of a cell that controls what goes in and out.
Mitochondria
Mitochondria are the parts of a cell where aerobic respiration releases energy.
Ribosomes
Ribosomes are the parts of a cell where proteins are made.
Cell wall
The cell wall is a part of plant cells made of cellulose, for strength; bacteria have a cell wall too, but not made of cellulose.
Chloroplasts
Chloroplasts are parts of plant cells that absorb light for photosynthesis.
Permanent vacuole
The permanent vacuole is a part of plant cells full of cell sap, which keeps the cell firm.
Flagellum
A flagellum is a tail that many bacteria have, which turns to move the cell along.
Order of magnitude
An order of magnitude is one power of ten; to compare two sizes, put both in the same unit and divide the bigger by the smaller.
Magnification
Magnification is how many times bigger the image is than the real thing.
Resolution (microscope)
Resolution is how much detail you can see with a microscope: the smallest gap between two points that still look like two points.
Light microscope
A light microscope is a cheap, small microscope that works on living cells, magnifying up to about × 1500 and showing nuclei but not ribosomes.
Electron microscope
An electron microscope is an expensive, large microscope with far higher magnification and resolution, showing ribosomes, mitochondria and viruses.
Differentiate
Differentiate means a cell becomes specialised, gaining the structures that suit one job.
Sperm cell
A sperm cell is a cell with a tail to swim, many mitochondria to release energy, and an acrosome of enzymes to get into the egg.
Nerve cell
A nerve cell is a cell with a long axon that carries impulses a long way, and branched endings that connect to many cells.
Muscle cell
A muscle cell is a cell whose protein fibres slide to shorten the cell, with many mitochondria.
Root hair cell
A root hair cell is a cell with a long projection that gives a big surface area for water and mineral ions.
Xylem
Xylem is dead cells with no end walls that make hollow tubes, strengthened by lignin.
Phloem
Phloem is cells with sieve plates that let dissolved sugars flow, and companion cells that supply energy.
Meristems
Meristems are the tips of shoots and roots where a plant keeps making new cells that can become any kind of plant cell.
Meristem cells
Meristem cells are plant stem cells that can become any kind of plant cell and clone plants quickly and cheaply.
Stem cell
A stem cell is an undifferentiated cell that can divide to make more cells, which can differentiate.
Embryonic stem cells
Embryonic stem cells are stem cells that can become any human cell.
Adult stem cells
Adult stem cells are stem cells, such as those in bone marrow, that form a limited range of cells, such as blood cells.
Therapeutic cloning
Therapeutic cloning is when an embryo is made with the patient's own genes, so the cells the embryo gives are not rejected.
Chromosomes
Chromosomes are long molecules of DNA in the nucleus, each carrying many genes.
Mitosis
Mitosis is when a cell divides into two new cells that are genetically identical to each other and to the parent, with the same number of chromosomes.
Diffusion
Diffusion is the net movement of particles from where they are more concentrated to where they are less concentrated.
Osmosis
Osmosis is the movement of water through a partially permeable membrane from a dilute solution to a more concentrated one.
Active transport
Active transport is when substances move against the concentration gradient, from dilute to concentrated, using energy from respiration.
Surface area to volume ratio
Surface area to volume ratio is the ratio of an organism's surface area to its volume; small organisms have a big ratio, so diffusion through their surface is enough.
Binary fission
Binary fission is how bacteria reproduce: one cell splits into two.
Population
A population is all the organisms of one species in an area.
Community
A community is all the populations of different species in an area.
Habitat
A habitat is where an organism lives.
Ecosystem
An ecosystem is a community interacting with the non-living parts of its environment.
Interdependence
Interdependence is when species in a community depend on each other for food, shelter, pollination and seed dispersal.
Stable community
A stable community is one where the species and the environment are in balance, so population sizes stay about the same.
Parasitism
Parasitism is when a parasite lives in or on a host and takes food from the host, so the host is harmed.
Mutualism
Mutualism is when both species benefit, as when oxpeckers eat ticks from the skin of buffalo.
Abiotic factors
Abiotic factors are non-living factors, such as light intensity, temperature, moisture, soil pH and mineral content, and wind.
Biotic factors
Biotic factors are factors that come from living things: the food available, new predators, new pathogens, and competition.
Structural adaptations
Structural adaptations are body features that help an organism survive, such as small ears and thick fur on an Arctic fox.
Behavioural adaptations
Behavioural adaptations are what an organism does to survive where the organism lives, such as migrating, hibernating or feeding at night.
Functional adaptations
Functional adaptations are processes inside the body that help an organism survive, such as making very concentrated urine.
Extremophiles
Extremophiles are organisms that live in extreme conditions, such as very hot springs, high pressure on the sea floor or very salty lakes.
Belt transect
A belt transect is sampling with quadrats at regular distances along a tape, where conditions change steadily, such as up a beach.
Percentage cover
Percentage cover is how much of a quadrat plants cover, recorded for plants that are hard to count; in a quadrat of 25 squares each square is 4%.
Random sampling
Random sampling means quadrats are put at random coordinates, from random numbers for the two distances, so there is no bias.
Homeostasis
Homeostasis is keeping internal conditions within set limits automatically, such as body temperature, blood glucose concentration and water level.
Receptors
Receptors are the parts of a control system that detect a stimulus (a change inside or outside the body).
Coordination centre
The coordination centre is the part of a control system, such as the brain, spinal cord or pancreas, that processes the information and decides on a response.
Effectors
Effectors are muscles or glands, the parts of a control system that carry out the response.
Central nervous system
The central nervous system (CNS) is the brain and the spinal cord.
Sensory neurone
A sensory neurone is a neurone that carries electrical impulses from a receptor to the CNS.
Relay neurone
A relay neurone is a neurone that links neurones inside the CNS.
Motor neurone
A motor neurone is a neurone that carries electrical impulses from the CNS to an effector.
Synapse
A synapse is the tiny gap where two neurones meet; a chemical released by the first neurone diffuses across the gap to the next.
Reflex
A reflex is an automatic, rapid response that does not involve the conscious part of the brain.
Anomaly
An anomaly is a result that is clearly out of line with the rest; leave out any anomaly before taking the mean.
Pathogen
A pathogen is a microorganism that causes an infectious disease.
Communicable diseases
Communicable diseases are diseases caused by pathogens that pass from one person (or plant) to another.
Non-communicable diseases
Non-communicable diseases are diseases, such as heart disease or scurvy, that do not pass from one person to another: nothing is caught.
Bacteria
Bacteria are microorganisms, one of four kinds of pathogen, that reproduce quickly and may release toxins that damage tissues.
Viruses
Viruses are pathogens far smaller than bacteria that live and reproduce inside cells, damaging the cells.
Fungi (pathogen)
Fungi are one of four kinds of pathogen; fungi cause disease in plants and animals.
Protists (pathogen)
Protists are one of four kinds of pathogen; protists cause disease in plants and animals.
Toxins
Toxins are what bacteria may release, which damage tissues.
Vectors
Vectors, such as mosquitoes, are what pathogens spread through, as well as by air, water and direct contact.
Non-specific defences
Non-specific defences are defences that work against any pathogen, such as the skin, mucus in the nose and acid in the stomach.
Skin (defence)
The skin is a tough barrier, a non-specific defence that works against any pathogen.
Nose (defence)
The nose is a non-specific defence whose hairs and mucus trap particles.
Trachea and bronchi
The trachea and bronchi are a non-specific defence: mucus traps pathogens and cilia sweep the mucus up to the throat.
Cilia
Cilia are hairs in the trachea and bronchi that sweep mucus, which traps pathogens, up to the throat.
Stomach (defence)
The stomach is a non-specific defence because hydrochloric acid kills pathogens in food.
Eyes (defence)
The eyes are a non-specific defence because tears contain lysozyme, an enzyme that breaks down bacteria.
Phagocytosis
Phagocytosis is when a white blood cell called a phagocyte engulfs a pathogen and digests the pathogen.
Antibodies
Antibodies are proteins made by lymphocytes that bind to a pathogen's antigens; each antibody fits one antigen only.
Antigens
Antigens are the molecules on a pathogen's surface, which antibodies bind to.
Antitoxins
Antitoxins are made by white blood cells and neutralise the toxins that bacteria release; this is one of the three ways white blood cells attack a pathogen.
Memory cells
Memory cells are lymphocytes that make the right antibody fast and in large amounts the second time a pathogen appears.
Immune
Immune describes a person whose memory cells make the right antibody fast and in large amounts the second time a pathogen appears, so the pathogen is destroyed before symptoms appear.
Sexual reproduction
Sexual reproduction is reproduction that joins two gametes (sex cells), so the offspring get a mix of genetic information from two parents.
Asexual reproduction
Asexual reproduction is reproduction with one parent and no gametes, by mitosis, so the offspring are genetically identical clones.
Gametes
Gametes are sex cells, such as sperm and egg in animals or pollen and egg cells in flowering plants.
Clones
Clones are offspring that are genetically identical, made by mitosis in asexual reproduction from one parent.
Meiosis
Meiosis is how gametes are made: the cell divides twice, giving four genetically different gametes, each with half the normal number of chromosomes.
Fertilisation
Fertilisation is when two gametes join, so the full number of chromosomes is restored.
DNA
DNA is a polymer made of two strands twisted into a double helix.
Double helix
A double helix is what the two strands of the DNA polymer are twisted into.
Gene
A gene is a short section of DNA that codes for a particular sequence of amino acids, to make one protein.
Genome
The genome is all the genetic material of an organism.
Transcription
Transcription is when, in the nucleus, RNA polymerase moves along a gene making a strand of messenger RNA (mRNA).
RNA polymerase
RNA polymerase is the enzyme that binds to the non-coding DNA in front of a gene and moves along the gene making mRNA.
Messenger RNA (mRNA)
Messenger RNA (mRNA) is the strand RNA polymerase makes, complementary to the template strand of a gene; mRNA leaves the nucleus for a ribosome.
Uracil (U)
Uracil (U) is the base RNA has where DNA has thymine.
Translation
Translation is when, at the ribosome, mRNA is read in codons and amino acids are joined in the order of the codons into a protein.
Codon
A codon is a sequence of three bases on the mRNA that codes for one amino acid.
Transfer RNA (tRNA)
Transfer RNA (tRNA) is a molecule that carries one particular amino acid and has an anticodon of three bases that pair with a codon.
Anticodon
An anticodon is three bases on a tRNA molecule that pair with a codon on the mRNA.
Allele
Alleles are different versions of a gene; body cells have two alleles of each gene, one from each parent.
Dominant (allele)
A dominant allele (capital letter, B) is an allele that shows even if only one copy is present.
Recessive (allele)
A recessive allele (small letter, b) is an allele that shows only if there are two copies.
Homozygous
Homozygous describes a genotype with two identical alleles (BB or bb).
Heterozygous
Heterozygous describes a genotype with two different alleles (Bb).
Genotype
The genotype is the alleles for a characteristic, such as Bb.
Phenotype
The phenotype is the characteristic you see, such as black fur; the genotype is the alleles, such as Bb.
Carrier
A carrier (Tt) is a person who is heterozygous for a recessive condition: they have one recessive allele, so they are unaffected; an unaffected parent or child of an affected person must be a carrier.
Sex chromosomes
Sex chromosomes are one pair of the 23 pairs of chromosomes in human body cells: females are XX and males are XY.
XX (sex chromosomes)
XX is the pair of sex chromosomes in females; every egg carries an X.
XY (sex chromosomes)
XY is the pair of sex chromosomes in males; half the sperm carry X and half carry Y.
Cell (organisation)
A cell is the basic unit a large organism is built from, often specialised, such as a muscle cell or a red blood cell.
Tissue
A tissue is a group of cells with a similar structure and function, such as muscle tissue, glandular tissue or epithelial tissue.
Organ
An organ is different tissues working together on one job, such as the stomach.
Organ system
An organ system is organs working together, such as the digestive system.
Stomach (organ)
The stomach is an organ with muscle tissue to churn, glandular tissue to make juices and epithelial tissue to line the stomach.
Mouth
The mouth is the part of the digestive system where salivary glands release amylase.
Pancreas
The pancreas is an organ of the digestive system that makes amylase, protease and lipase and releases them into the small intestine.
Liver
The liver is an organ of the digestive system that makes bile, which the gall bladder stores.
Gall bladder
The gall bladder is an organ of the digestive system that stores bile made by the liver.
Small intestine
The small intestine is the part of the digestive system where digestion finishes and the products are absorbed into the blood through the villi.
Large intestine
The large intestine is the part of the digestive system where water is absorbed.
Active site
The active site is the part of an enzyme that the substrate fits, like a key in a lock, so each enzyme works on one substrate.
Bile
Bile, made by the liver and stored in the gall bladder, is alkaline: bile neutralises stomach acid and emulsifies fat into tiny droplets.
Emulsifies (fat)
To emulsify fat is to make fat into tiny droplets, giving lipase a much larger surface area to work on; bile does not break any bonds.
Denatured
Denatured describes an enzyme whose bonds holding its shape break, so the active site changes shape and the substrate no longer fits, a permanent change.
Optimum (enzyme)
The optimum is the temperature or pH at which an enzyme works best, such as near 37 °C and pH 7 for most human enzymes.
Sedimentary rocks
Sedimentary rocks are rocks, such as limestone from the calcium carbonate shells of sea creatures, that carbon was locked into, so carbon dioxide in the air fell.
Fossil fuels
Fossil fuels are coal from plant remains, and crude oil and natural gas from plankton buried in mud; carbon is locked into them.
Greenhouse gases
Greenhouse gases, such as carbon dioxide, methane and water vapour, absorb infrared and re-emit it in all directions, some back towards the surface.
Methane (greenhouse gas)
Methane is a greenhouse gas from cattle, rice paddies and rotting waste in landfill.
Carbon dioxide (greenhouse gas)
Carbon dioxide is a greenhouse gas from burning fossil fuels and from deforestation (burning, and fewer trees to absorb carbon dioxide).
Carbon footprint
A carbon footprint is the total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event.
Carbon capture and storage
Carbon capture and storage is catching carbon dioxide at power stations and storing it underground, to reduce a carbon footprint.
Carbon taxes and licences
Carbon taxes and licences make high-emission choices cost more, to reduce a carbon footprint.
Element
An element has only one type of atom, such as Fe, O2 or S8, and has a symbol in the periodic table.
Compound
A compound has two or more elements chemically combined in fixed proportions, such as H2O; only a chemical reaction can split it up.
Mixture
A mixture has two or more substances not chemically joined, such as air or sea water; physical methods separate it.
Filtration
Filtration is a method that separates an insoluble solid from a liquid, such as sand from water.
Crystallisation
Crystallisation is a method that separates a soluble solid from its solution: heat to evaporate some water, cool, filter off the crystals and dry them.
Simple distillation
Simple distillation is a method that separates a liquid from a solution, such as pure water from sea water.
Fractional distillation
Fractional distillation is a method that separates liquids with different boiling points; the liquid with the lowest boiling point reaches the top of the column first.
Paper chromatography
Paper chromatography is a method that separates the soluble substances in a mixture, such as the dyes in an ink.
Plum pudding (atomic model)
The plum pudding model is the model of the atom made after the electron was discovered: a ball of positive charge with electrons scattered through it.
Alpha scattering
Alpha scattering is the firing of positive alpha particles at thin gold foil: most go straight through, a few are deflected and a very few bounce back, so most of the atom is empty space, with the mass and positive charge in a tiny nucleus.
Nucleus (atom)
The nucleus is the tiny part of an atom that holds almost all the mass and the positive charge; it contains protons and neutrons, and most of the atom is empty space.
Protons
Protons are particles in the nucleus, where an atom's positive charge is; an atom has equal numbers of protons and electrons, so it has no overall charge.
Atomic number
The atomic number is the number of protons; it is the bottom number on a symbol.
Mass number
The mass number is the number of protons + neutrons; it is the top number on a symbol.
Isotopes
Isotopes are atoms of the same element with different numbers of neutrons, such as chlorine-35 and chlorine-37.
Ions
Ions are atoms that have gained or lost electrons: Na⁺ has 10 electrons and Cl⁻ has 18.
Period (periodic table)
A period is a row of the periodic table; the period number is the number of occupied electron shells.
Group (periodic table)
A group is a column of the periodic table; the group number is the number of electrons in the outer shell, and Group 0 has a full outer shell.
Group 0
Group 0 is the group of the noble gases, which have full outer shells, so they are unreactive; their boiling points rise down the group.
Group 1
Group 1 is the group of the alkali metals, which have one outer electron that they lose to form 1+ ions; with water they form a metal hydroxide and hydrogen.
Displaces (halogens)
A more reactive halogen displaces a less reactive one from a solution of its salt; iodine cannot displace bromine or chlorine.
Positive ion
A positive ion is an atom that has lost one or more of its outer electrons, as metal atoms do when they react with a non-metal.
Negative ion
A negative ion is an atom that has gained negative electrons, as non-metal atoms do when they react with a metal.
-ide (ending)
Non-metal ions take the ending -ide: chlorine becomes chloride and oxygen becomes oxide.
Giant ionic lattice
A giant ionic lattice is a regular three-dimensional pattern of huge numbers of positive and negative ions in a solid ionic compound.
Covalent bond
A covalent bond is a shared pair of electrons between two non-metal atoms, one electron from each atom; it is strong.
Pure substance
A pure substance is a single element or a single compound with nothing else mixed in, such as distilled water or copper wire.
Formulation
A formulation is a mixture designed as a useful product, with each component measured out carefully, such as paints, medicines and fuels.
Stationary phase (chromatography)
The stationary phase in chromatography is the paper; each substance is shared between the paper and the solvent.
Mobile phase (chromatography)
The mobile phase in chromatography is the solvent moving up the paper; a substance that dissolves well in the solvent moves further.
Locating agent (chromatography)
A locating agent is sprayed on the dry chromatography paper to make the spots of colourless substances, such as amino acids, show.
Reactivity series
The reactivity series lists metals from most to least reactive, with carbon and hydrogen put in for comparison.
Oxidation
Oxidation is gain of oxygen, and it happens together with reduction.
Reduction
Reduction is loss of oxygen, and it happens together with oxidation.
Ores
Ores are what most metals are found in, as oxides; how a metal is extracted from its ore depends on where it sits compared with carbon.
Redox
A redox reaction is a reaction in which one substance is oxidised and another is reduced.
Spectator ions
Spectator ions are ions that are there before and after a reaction unchanged, like sulfate ions in zinc + copper sulfate; an ionic equation leaves them out.
Salt (metals with acids)
A salt is made, with hydrogen, when metals above hydrogen react with dilute acids: hydrochloric acid makes chlorides and sulfuric acid makes sulfates.
Test for hydrogen
The test for hydrogen is to hold a lit splint at the mouth of the tube: hydrogen gives a squeaky pop.
Resolution (instrument)
The resolution of an instrument is the smallest change it shows: a burette reads to 0.05 cm³, a measuring cylinder to 1 cm³ or worse.
Random errors
Random errors are errors that scatter readings; repeats and means reduce them.
Systematic errors
Systematic errors are errors that shift every reading the same way, such as a balance that is not zeroed (a zero error).
Precise
Precise readings are repeats that are close together.
Accurate
Accurate readings are close to the true value.
Repeatable
Repeatable readings agree when the same person repeats them with the same method.
Reproducible
Reproducible readings are ones where others repeating the method get the same.
Exothermic
In an exothermic reaction, energy is transferred to the surroundings, so the temperature of the surroundings rises, as in combustion.
Endothermic
In an endothermic reaction, energy is taken in from the surroundings, so the temperature falls, as in thermal decomposition.
Crude oil
Crude oil is a mixture of a huge number of compounds, most of them hydrocarbons, made over millions of years from the remains of tiny sea creatures buried in mud; it is a finite resource.
Hydrocarbons
Hydrocarbons are compounds made of hydrogen and carbon atoms only.
Alkanes
Alkanes are a homologous series of hydrocarbons, and most of the hydrocarbons in crude oil are alkanes.
Homologous series
A homologous series is a family with the same general formula, where each member has one more CH2 than the last and all react in similar ways.
Methane (alkane)
Methane, CH4, is the alkane with 1 carbon.
Ethane
Ethane, C2H6, is the alkane with 2 carbons.
Propane
Propane, C3H8, is the alkane with 3 carbons.
Butane
Butane, C4H10, is the alkane with 4 carbons.
-ane (ending)
The ending -ane means an alkane; the start of the name counts the carbons: meth 1, eth 2, prop 3, but 4.
Saturated (hydrocarbon)
In a saturated hydrocarbon, such as an alkane, every carbon to carbon bond is a single bond.
Fractional distillation (crude oil)
Fractional distillation separates crude oil: molecules with different chain lengths have different boiling points, so they condense at different temperatures.
Complete combustion
Complete combustion is burning a hydrocarbon fuel in plenty of oxygen, which oxidises the carbon to carbon dioxide and the hydrogen to water.
Incomplete combustion
Incomplete combustion is burning with too little oxygen, which makes carbon monoxide (a toxic gas you cannot see or smell) and carbon (soot).
Cracking
Cracking is a thermal decomposition that breaks long alkanes into shorter, more useful alkanes and alkenes.
Catalytic cracking
Catalytic cracking is cracking (breaking long alkanes into shorter, more useful alkanes and alkenes) in which the alkane vapour is passed over a hot catalyst.
Steam cracking
Steam cracking is cracking (breaking long alkanes into shorter, more useful alkanes and alkenes) in which the alkane vapour is mixed with steam and heated to a very high temperature.
Alkenes
Alkenes are hydrocarbons with a C=C double bond, so they are unsaturated and more reactive than alkanes.
Unsaturated
An unsaturated hydrocarbon, such as an alkene, has a C=C double bond.
Bromine water
Orange bromine water tests for alkenes: an alkene changes it to colourless as bromine adds across the double bond, but with an alkane it stays orange.
Law of conservation of mass
The law of conservation of mass says that the total mass of the products equals the total mass of the reactants, as no atoms are made or destroyed.
g/s (rate unit)
A rate is in g/s when the quantity used up or made is a mass in g.
cm³/s (rate unit)
A rate is in cm³/s when the quantity used up or made is a volume of gas in cm³.
mol/s (rate unit)
A rate is in mol/s (Higher) when the quantity used up or made is an amount in mol.
Gradient (rate graph)
The gradient of the curve on a rate graph is the rate: steepest at the start, and flat when one reactant has run out.
Tangent
A tangent is a straight line that touches a curve at one point without cutting it; its gradient is the rate at that instant.
Pure (chemistry)
In chemistry, pure means one substance only, so potable water is not pure.
Potable (water)
Potable water is water that is safe to drink: it has low levels of dissolved salts and microbes, but it is not pure.
Fresh water
Fresh water is water that falls as rain and collects in the ground (in aquifers) and in lakes, rivers and reservoirs.
Aquifers
Aquifers are porous rock in the ground where fresh water collects.
Sea water
Sea water is water with far too much dissolved salt to drink, so dry countries with a coast may desalinate it.
Waste water
Waste water is sewage from homes, farms and factories, which must be cleaned before it goes back into rivers.
Filter beds
Filter beds are beds of sand and gravel that trap insoluble solids when treating water; dissolved substances pass straight through.
Sterilising (water)
Sterilising water is killing the microbes in it with chlorine, ozone or ultraviolet light; a trace of chlorine is left in so microbes cannot grow in the pipes.
Desalination
Desalination removes the dissolved salts from sea water, by distillation or by reverse osmosis; both need large amounts of energy.
Distillation (desalination)
Distillation removes the dissolved salts from sea water by boiling the water, then condensing the steam.
Reverse osmosis
Reverse osmosis removes the dissolved salts from sea water by pushing the water through membranes at high pressure.
Screening (sewage)
Screening removes large objects and grit when treating sewage.
Sedimentation (sewage)
Sedimentation is when sewage stands in tanks and separates into sludge at the bottom and liquid effluent at the top.
Sludge
Sludge is the sewage at the bottom of the tanks after sedimentation; anaerobic bacteria break it down to make biogas.
Effluent
Effluent is the liquid at the top of the tanks after sedimentation; air is bubbled through it so aerobic bacteria break down the organic matter.
Anaerobic (bacteria)
Anaerobic means with no oxygen: anaerobic bacteria break down the sludge from sewage, making biogas, mostly methane.
Aerobic (bacteria)
Aerobic bacteria are bacteria that break down the organic matter left in sewage effluent once air is bubbled through it; anaerobic bacteria (no oxygen) break down the sludge.
Biogas
Biogas is a gas, mostly methane, made when anaerobic bacteria break down the sludge from sewage.
Life cycle assessment (LCA)
A life cycle assessment (LCA) adds up the environmental impact of a product from start to finish, looking at energy, water, resources and waste.
Extracting and processing raw materials
Extracting and processing raw materials, such as mining ore, drilling for oil or growing cotton, is stage 1 of a life cycle assessment.
Manufacturing and packaging
Manufacturing and packaging is stage 2 of a life cycle assessment (LCA).
Use and operation
Use and operation, such as the fuel a car burns or the electricity a fridge uses, is stage 3 of a life cycle assessment.
Disposal
Disposal at the end of a product's life, by landfill, burning or recycling, is stage 4 of a life cycle assessment.
Reduce
To reduce is to use less in the first place, such as thinner cans or longer-lasting goods.
Reuse
To reuse is to use the object again as it is, such as washing and refilling glass bottles.
Recycle
To recycle is to break the material down and make something new, such as melting and recasting metals.
Carbon dioxide (early atmosphere)
Carbon dioxide in the early atmosphere was added by volcanoes; dissolving in oceans, photosynthesis and the formation of rocks and fossil fuels took it out.
Energy levels
Energy levels are the set distances at which electrons move around the nucleus of an atom.
Plum pudding (model of the atom)
In the plum pudding model, the atom was pictured as a ball of positive charge with electrons spread through the ball.
Nuclear model
In the nuclear model, from the alpha particle scattering experiment, the atom is mostly empty space, with the mass and positive charge packed into a tiny nucleus.
Bohr (model of the atom)
In the Bohr model of the atom, electrons orbit at fixed distances, in energy levels, and the calculations matched experiments.
Radioactive decay
Radioactive decay is when unstable nuclei give out radiation to become more stable; the decay is random.
Unstable (nucleus)
An unstable nucleus is a nucleus that will give out radiation to become more stable.
Activity
Activity is the rate at which nuclei in a source decay, measured in becquerels: 1 Bq is one decay per second.
Becquerels (Bq)
One becquerel (1 Bq) of activity is one decay per second.
Count rate
The count rate is the number of decays a Geiger-Muller tube and counter detects each second or minute.
Background (count)
The background count is radiation always around us from rocks, the air and space; subtract the background count before using a reading.
Ionising
Ionising means knocking electrons off atoms; each time radiation ionises an atom, the radiation loses some energy.
Battery
A battery is two or more cells joined together.
Ammeter
An ammeter measures current and goes in series, in the same loop as the component.
Voltmeter
A voltmeter measures potential difference and goes in parallel, across the component's two ends.
In series
In series means in the same loop as the component; an ammeter goes in series.
In parallel
In parallel means across the component's two ends; a voltmeter goes in parallel.
Closed circuit
A closed circuit is a closed loop with no gaps; for charge to flow you need a closed circuit and a source of potential difference.
Current
Current is the rate of flow of charge: how many coulombs pass a point each second.
Potential difference
The potential difference (p.d.) across a component is the push that drives charge through the component: the energy each coulomb transfers.
Resistance
Resistance is how much a component opposes the current; for the same p.d., a bigger resistance means a smaller current.
Ohmic conductor
An ohmic conductor, such as a fixed resistor at constant temperature, has a current directly proportional to the p.d. and a resistance that stays the same.
Directly proportional
Directly proportional means if one doubles, the other doubles too: for a fixed resistor at constant temperature, double the p.d. and you double the current.
Store (energy)
An energy store is where energy is, as physicists keep track of it: kinetic (anything moving), gravitational potential (anything raised up), elastic potential (anything stretched or squashed), thermal (anything warm) or chemical (fuels, food and batteries).
Kinetic (energy store)
The kinetic energy store is the energy store of anything moving.
Gravitational potential (energy store)
The gravitational potential energy store is the energy store of anything raised up.
Elastic potential (energy store)
The elastic potential energy store is the energy store of anything stretched or squashed.
Thermal (energy store)
The thermal energy store is the energy store of anything warm: the hotter, the more energy.
Chemical (energy store)
The chemical energy store is the energy store in fuels, food and batteries.
Mechanically (energy transfer)
Energy moves between stores mechanically when a force moves something.
Electrically (energy transfer)
Energy moves between stores electrically through a current.
By heating (energy transfer)
Energy moves between stores by heating, from something hot to something cold.
By radiation (energy transfer)
Energy moves between stores by radiation as light and infrared.
System
A system is the object or group of objects you choose to look at.
Specific heat capacity
Specific heat capacity: the energy needed to raise the temperature of 1 kg of a substance by 1 °C.
Power
Power is how fast energy transfers, in watts (W): one watt is one joule every second.
Work done
Work done is energy transferred by a force: force × distance, W = F s.
Wasted (energy)
Wasted energy is the rest of the input energy, which a machine does not turn into what you want.
Dissipated
Dissipated energy is energy that spreads out, usually into the thermal store of the surroundings, and is no longer useful.
Lubrication
Lubrication is using oil or grease to reduce friction in moving parts, so less energy is dissipated by heating.
Thermal insulation
Thermal insulation is a layer of material with a low thermal conductivity, such as foam in a wall cavity or fibre in the loft, that reduces the rate of energy transfer by heating.
Low thermal conductivity
A material with a low thermal conductivity lets energy through slowly by conduction.
Non-renewable (energy resource)
Non-renewable energy resources, such as fossil fuels and nuclear fuel, are being used up faster than the resources can be replaced.
Renewable (energy resource)
Renewable energy resources, such as wind, solar and tides, are resources that nature replaces as fast as we use them.
Reliable (energy resource)
A reliable energy resource can produce electricity whenever electricity is needed.
Distance
Distance is how far you travel; distance has a size only, so distance is a scalar.
Displacement
Displacement is how far you end up from the start, in a straight line, and in which direction; displacement is a vector.
Average (speed)
Average speed is how much distance you cover each second over the trip, since most real speeds change.
Speed
Speed is how much distance you cover each second, in metres per second (m/s).
Velocity
Velocity is speed in a given direction: a car going round a roundabout at a steady speed has a changing velocity, because its direction changes.
Stationary
Stationary means not moving: the distance is not changing, so on a distance-time graph the line is flat.
Vector
A vector is a quantity with a size and a direction, such as force, weight, velocity, displacement, acceleration or momentum.
Scalar
A scalar is a quantity with a size only, such as mass, speed, distance, time, energy or temperature.
Contact forces
Contact forces are forces that need the objects to touch, such as friction, air resistance, tension and upthrust.
Non-contact forces
Non-contact forces act across a gap: gravitational force (weight), magnetic force and electrostatic force.
Centre of mass
The centre of mass is the one point at which the weight of an object acts as if all the weight pulls there.
Resultant force
The resultant force is the single force that would have the same effect as the several forces that act on an object.
Scale drawing (forces)
A scale drawing is a drawing of forces to a scale, such as 1 cm = 10 N, used to add two forces at an angle: draw both from one point, complete the parallelogram and measure the diagonal.
Resolving (forces)
Resolving is splitting one force into two parts at right angles.
Normal (ray diagrams)
The normal is an imaginary line at 90° to a surface, drawn where the ray hits the surface; every angle is measured from the normal.
Specular reflection
Specular reflection is when a smooth surface, such as a mirror, reflects parallel rays in a single direction, so you see a clear image.
Diffuse reflection
Diffuse reflection is when a rough surface, such as paper, scatters parallel rays in many directions, so you see no image.
White (light)
White light is a mixture of all the colours, each colour a narrow band of wavelengths.
Opaque
Opaque objects transmit no light; the colour of an opaque object is the colour the object reflects.
White (objects)
White objects reflect all colours equally.
Black (objects)
Black objects absorb all colours.
Transparent
Transparent objects, such as clear glass, transmit light so you see clearly through the objects.
Translucent
Translucent objects, such as frosted glass, transmit light but scatter the light.
Filter
A filter transmits its own colour and absorbs the rest.
North pole
A north pole is one of the two poles of every magnet, where the magnetic effect is strongest; like poles repel.
South pole
A south pole is one of the two poles of every magnet, where the magnetic effect is strongest; a south pole and a north pole attract.
Repel
To repel is to push: like poles, N and N or S and S, repel.
Attract
To attract is to pull: unlike poles, N and S, attract.
Iron, steel, nickel and cobalt
Iron, steel, nickel and cobalt are the few materials attracted to a magnet; copper, aluminium and brass are not.
Permanent magnet
A permanent magnet makes its own magnetic field all the time.
Induced magnet
An induced magnet is a piece of magnetic material that becomes a magnet only while the material sits in a field.
Magnetic field
The magnetic field is the region round a magnet where a magnetic material or another magnet feels a force.
Right-hand grip rule
The right-hand grip rule says to grip the wire with your right hand, thumb along the current; your fingers curl the way the field lines go.
Solenoid
A solenoid is a long coil of wire, with a strong, uniform field inside and the same shape as a bar magnet's field outside.
Iron core
An iron core in a solenoid makes a stronger electromagnet; iron is magnetised easily and loses it as soon as the current stops.
Relay
A relay is an electromagnet switch: a small current in one circuit magnetises a coil, which pulls an iron contact and closes a second circuit carrying a large current.
Direct current (d.c.)
Direct current (d.c.) is current from a cell or battery that pushes charge round a circuit in one direction only.
Alternating current (a.c.)
Alternating current (a.c.) is current that flows one way, then the other, many times a second, as the potential difference keeps swapping direction.
Period (a.c.)
The period of an a.c. supply is the number of seconds for one complete cycle, from a peak to the next peak.
Frequency (a.c.)
The frequency of an a.c. supply is the number of cycles each second, in hertz (Hz).
Live wire (brown)
The live wire (brown) carries the alternating potential difference from the supply, at about 230 V; the fuse and the switch go in the live wire.
Neutral wire (blue)
The neutral wire (blue) completes the circuit and is at, or close to, 0 V.
Earth wire (green and yellow stripes)
The earth wire (green and yellow stripes) is a safety wire joined to any metal case; the earth wire carries a current only if something goes wrong.
Vector (momentum)
Momentum is a vector: on a straight line, pick one direction as positive, and momentum the other way is negative.
Closed system
A closed system has no outside forces, such as friction, acting; in a closed system the total momentum before an event equals the total after.
Solid (particle model)
In a solid the particles are touching, in a regular pattern, vibrating about fixed positions; the density is high.
Liquid (particle model)
In a liquid the particles are touching but jumbled, sliding past each other; the density is similar to the solid.
Gas (particle model)
In a gas the particles are far apart, moving fast in random directions; the density is about a thousand times lower.
Significant figures
Significant figures start at the first non-zero digit; give a calculated answer to the same number as the least precise data used.
Random error
A random error scatters readings both ways by different amounts; reduce the effect by repeating and taking a mean.
Systematic error
A systematic error shifts every reading the same way by the same amount; repeating does not help.
Zero error
A zero error is a systematic error where the instrument reads something when the instrument should read zero.
Solar system
The solar system is one star, the Sun, and everything that orbits the Sun.
Planets
The planets are the eight bodies from Mercury out to Neptune, all orbiting the Sun.
Dwarf planets
Dwarf planets are smaller bodies, such as Pluto and Ceres, that also orbit the Sun.
Moons
Moons: natural satellites that orbit planets.
Artificial satellites
Artificial satellites are satellites made and launched by people, such as weather and GPS satellites.
Satellite
A satellite is anything that orbits a larger body.
Nebula
A nebula is a cloud of dust and gas pulled together by gravity; the solar system formed from a nebula.
Galaxy
A galaxy is a huge group of billions of stars held together by gravity.
Light-year
A light-year is the distance light travels in one year; astronomers measure distances between stars in light-years.
Red giant
A red giant is what a star of about the Sun's mass swells into when the hydrogen in the core runs out.
White dwarf
A white dwarf is the small, hot, dense core that a red giant shrinks to; the white dwarf slowly cools.
Red supergiant
A red supergiant is what a star much more massive than the Sun swells into; the red supergiant then collapses and explodes as a supernova.
Supernova
A supernova is what happens when a red supergiant collapses and explodes.
Neutron star
A neutron star is the core left behind after a supernova.
Black hole
A black hole is the core left behind by the most massive stars, whose gravity is so strong that not even light escapes.
Energy (waves)
Every wave transfers energy (and often information) from one place to another without carrying the medium along.
Transverse (wave)
A transverse wave has vibrations at right angles to the direction the energy travels, such as ripples on water or light.
Longitudinal (wave)
A longitudinal wave has vibrations along the same direction the energy travels, such as sound.
Compressions (longitudinal waves)
Compressions are where the medium bunches up in a longitudinal wave such as sound.
Rarefactions (longitudinal waves)
Rarefactions are where the medium spreads out in a longitudinal wave such as sound.
Amplitude
Amplitude is the biggest displacement from the rest position, measured from the middle line to a crest.
Wavelength (λ)
Wavelength (λ) is the distance from a point on one wave to the same point on the next, such as crest to crest.
Frequency (f)
Frequency (f) is how many waves pass a point each second, in hertz (Hz).
Period (T)
The period (T) of a wave is the time for one complete wave to pass, in seconds.