Edexcel GCSE Combined Science glossary
87 key terms from the Edexcel GCSE Combined Science notes, A to Z. Each definition links to the note that teaches it.
A
- Active site
- The region of an enzyme where the substrate binds, with a shape complementary to the substrate.Revise it: How enzymes work
- Active transport
- Movement of substances against a concentration gradient, from dilute to concentrated, using energy from respiration.Revise it: Diffusion
- Allele
- A different version of the same gene.Revise it: Key genetic terms
- Alveoli
- Tiny air sacs in the lungs where gas exchange takes place.Revise it: Alveoli and gas exchange
- Antibody
- A protein made by white blood cells (lymphocytes) that binds to a specific antigen.Revise it: The specific immune system
- Antigen
- A molecule, usually on the surface of a pathogen, that the immune system recognises as foreign and that triggers an immune response.Revise it: The specific immune system
- Axon
- A long fibre that carries electrical impulses away from the cell body.Revise it: Neurone structure
B
- Belt transect
- A line (a tape measure) laid across a habitat, with quadrats placed along it at regular intervals, to show how organisms change along an environmental gradient.Revise it: Core practical: quadrats and belt transects
- Biomass
- The mass of living material, which in a plant is made from the glucose it produces by photosynthesis.Revise it: Photosynthetic organisms as producers
C
- Cancer
- The result of changes in cells that lead to uncontrolled cell division.Revise it: Cancer
- Cardiac output
- The volume of blood pumped out of the heart per minute, in cm³ per minute.Revise it: Heart rate, stroke volume and cardiac output
- Cell membrane
- Controls the movement of substances into and out of the cell.Revise it: Bacterial cells
- Cellular respiration
- An exothermic reaction which occurs continuously in living cells to release energy for metabolic processes.Revise it: Cellular respiration
- Chromosomal DNA
- A single loop of DNA found free in the cytoplasm, not enclosed in a nucleus.Revise it: Bacterial cells
- Chromosome
- A long molecule of DNA in the nucleus that carries many genes.Revise it: Key genetic terms
- Clomifene therapy Higher tier
- A drug for women who do not ovulate. It stimulates the release of FSH and LH.Revise it: Assisted reproductive technology
- CNS
- The central nervous system: the brain and spinal cord.Revise it: Receptors and the nervous pathway
- Communicable disease
- A disease caused by a pathogen that can be passed from one organism to another.Revise it: Communicable and non-communicable diseases
- Community
- All the populations of different species living in the same area.Revise it: Levels of organisation
- Competition
- Organisms needing the same limited resources, such as food, water, light or space.Revise it: Abiotic and biotic factors
- Cytokinesis
- The division of the cytoplasm and cell membrane to form two separate cells.Revise it: The cell cycle and mitosis
D
- Daughter cell
- One of the two new cells produced when a parent cell divides.Revise it: What mitosis produces
- Dendron
- A fibre that carries electrical impulses towards the cell body.Revise it: Neurone structure
- Differentiation
- The process by which a cell becomes specialised for a particular job by gaining the structures it needs.Revise it: Cell differentiation
- Diffusion
- The net movement of particles from a region of higher concentration to a region of lower concentration.Revise it: Diffusion
- Diploid
- A cell with two sets of chromosomes in its nucleus.Revise it: What mitosis produces
- Dominant
- An allele that is expressed in the phenotype even when only one copy is present.Revise it: Key genetic terms
- Double circulatory system
- One circuit takes blood from the heart to the lungs and back, the other from the heart to the body and back.Revise it: The heart and circulatory system
E
- Ecosystem
- A community together with the non-living (abiotic) parts of its environment, interacting with each other.Revise it: Levels of organisation
- Environmental variation
- Different characteristics caused by an organism's environment (acquired characteristics).Revise it: Causes of variation
- Enzyme
- A protein that acts as a biological catalyst, speeding up a reaction without being used up.Revise it: How enzymes work
- Eukaryotic cell
- A cell whose genetic material is enclosed in a nucleus. Animal and plant cells are eukaryotic.Revise it: Animal and plant cells
- Eutrophication
- Too many nutrients, such as nitrates, entering water, causing algal growth and then lack of oxygen.Revise it: Fish farming
- Evolution
- A change in the inherited characteristics of a population over many generations.Revise it: Evolution by natural selection
F
- Flagellum
- A long, whip-like structure that moves to make the bacterium swim. Some bacteria have one or more flagella.Revise it: Bacterial cells
G
- Gamete
- A sex cell (such as a sperm or egg) with half the number of chromosomes.Revise it: Key genetic terms
- Gene
- A section of a DNA molecule that codes for a specific protein.Revise it: The genome and genes
- Genetic engineering
- A process which involves modifying the genome of an organism to introduce desirable characteristics.Revise it: What is genetic engineering?
- Genetic variation
- Different characteristics as a result of mutation and sexual reproduction.Revise it: Causes of variation
- Genetically identical
- Having exactly the same genetic information (the same DNA).Revise it: What mitosis produces
- Genome
- The entire DNA of an organism.Revise it: The genome and genes
- Genotype
- The alleles an organism has for a gene (or genes).Revise it: Key genetic terms
H
- Haemoglobin
- The red substance in red blood cells that combines with oxygen to form oxyhaemoglobin.Revise it: The structure and function of blood
- Heart rate
- The number of times the heart beats per minute (bpm).Revise it: Heart rate, stroke volume and cardiac output
- Heterozygous
- Having two different alleles of a gene, for example Tt.Revise it: Key genetic terms
- Homeostasis
- Maintaining a constant internal environment in response to internal and external change.Revise it: Maintaining a constant internal environment
- Homozygous
- Having two identical alleles of a gene, for example TT or tt.Revise it: Key genetic terms
- Hormone
- A chemical messenger made by an endocrine gland and carried in the blood to its target organs.Revise it: The endocrine system
I
- Interdependence
- Species in a community depend on each other for food, shelter, pollination and seed dispersal, so a change in one affects others.Revise it: Interdependence
L
- Ligase Higher tier
- An enzyme that joins pieces of DNA together.Revise it: The main stages of genetic engineering
- Limiting factor
- A factor in short supply that stops the rate of a process from increasing.Revise it: Limiting factors
- Lysozymes
- Enzymes that break down bacterial cell walls. A chemical defence.Revise it: Physical barriers and chemical defences
M
- Memory lymphocyte
- A white blood cell that stays in the body after an infection and can respond quickly if the same antigen returns.Revise it: The specific immune system
- Myelin sheath
- A fatty layer around the neurone that insulates it and speeds up the transmission of impulses.Revise it: Neurone structure
N
- Natural selection
- The process by which organisms better adapted to their environment are more likely to survive, reproduce and pass on their alleles.Revise it: Evolution by natural selection
- Negative feedback Higher tier
- A change in a level causes a response that reverses the change and brings the level back to normal.Revise it: Thyroxine and negative feedback
- Non-communicable disease
- A disease that cannot be passed from one person to another and is not caused by a pathogen. Example: cardiovascular disease.Revise it: Communicable and non-communicable diseases
- Non-indigenous species
- A species that has been introduced to an area where it does not naturally live.Revise it: Fish farming
O
- Osmosis
- The diffusion of water from a dilute solution to a more concentrated solution through a partially permeable membrane.Revise it: Diffusion
P
- Parasitism
- A parasite lives on or in a host and takes food from it. The parasite benefits and the host is harmed.Revise it: Parasitism and mutualism
- Pathogen
- A disease-causing organism.Revise it: What is a pathogen?
- Percentage cover
- The percentage of a quadrat covered by a species. It is used when individuals are hard to count.Revise it: Estimating the number of organisms
- Phenotype
- The characteristics that are expressed and can be observed.Revise it: Key genetic terms
- Plasmid
- A small ring of extra DNA in a bacterial cell, separate from the chromosomal DNA.Revise it: Animal and plant cells
- Plasmid DNA
- Small rings of extra DNA, separate from the chromosomal DNA.Revise it: Bacterial cells
- Platelets
- Small fragments of cells with no nucleus that help the blood to clot.Revise it: The structure and function of blood
- Population
- All the organisms of one species living in the same area.Revise it: Levels of organisation
- Potable water
- Water that is safe to drink.Revise it: The water cycle and potable water
- Producer
- An organism that makes its own food. Photosynthetic organisms (plants and algae) are the main producers of food and biomass.Revise it: Photosynthetic organisms as producers
- Prokaryotic cell
- A cell with no nucleus. The genetic material is free in the cytoplasm. Bacteria are prokaryotic.Revise it: Animal and plant cells
Q
- Quadrat
- A square frame used to sample the organisms in a small, known area.Revise it: Core practical: quadrats and belt transects
R
- Recessive
- An allele that is only expressed in the phenotype when two copies are present (no dominant allele).Revise it: Key genetic terms
- Resolution
- How well a microscope can show two points that are close together as separate points.Revise it: Changes in microscope technology
- Restriction enzyme Higher tier
- An enzyme that cuts DNA at a specific base sequence.Revise it: The main stages of genetic engineering
- Ribosomes
- Where proteins are made.Revise it: Bacterial cells
S
- Selective breeding
- Humans choosing parents with desired characteristics to breed together, repeated over many generations.Revise it: Selective breeding
- Sensory receptor
- A cell that detects a stimulus and produces an electrical impulse.Revise it: Receptors and the nervous pathway
- Stem cell
- An undifferentiated cell that can divide and can differentiate into specialised cells.Revise it: Stem cells and meristems
- Sticky ends Higher tier
- Short, unpaired strands of DNA left at the ends of a cut, which can join with complementary sticky ends.Revise it: The main stages of genetic engineering
- Stomata
- Pores in the leaf surface, each surrounded by two guard cells, which let gases in and out.Revise it: Transpiration and stomata
- Stroke volume
- The volume of blood pumped out of the heart in each beat, in cm³.Revise it: Heart rate, stroke volume and cardiac output
- Synapse
- A gap between two neurones.Revise it: Receptors and the nervous pathway
T
- Translocation
- The transport of sucrose around the plant in the phloem.Revise it: Translocation
- Transpiration
- The loss of water vapour from the leaves, which pulls water and mineral ions up through the plant.Revise it: Transpiration and stomata
- Tumour
- A mass of cells formed when cells divide in an uncontrolled way.Revise it: Cancer
V
- Vector Higher tier
- A carrier, such as a plasmid or virus, used to insert a gene into another organism's cells.Revise it: The main stages of genetic engineering
Z
- Zygote
- The cell formed when two gametes fuse at fertilisation.Revise it: Key genetic terms
Test yourself on these terms with the Edexcel GCSE Combined Science flashcards, or tick them off on the specification checklist.