HSC Biology key terms

A thin, flexible barrier of lipids and proteins surrounding every cell. It controls which substances enter and leave, allowing the cell to keep a stable internal environment.

A specialised structure inside a cell that carries out a particular job, such as energy release, protein building or waste breakdown. Each type has its own structure suited to its function.

An organelle with folded inner membranes where aerobic respiration occurs. It releases usable energy from glucose, so cells with high energy demands contain many of them.

A green organelle found in plant cells that contains chlorophyll and carries out photosynthesis, capturing light energy to build glucose from carbon dioxide and water.

The net movement of particles from a region of higher concentration to a region of lower concentration, caused by random motion. It requires no energy input from the cell.

The diffusion of water across a partially permeable membrane from a dilute solution to a more concentrated one. It explains how cells gain or lose water in different surroundings.

The difference in concentration of a substance between two regions. A steeper gradient drives faster movement of particles and is maintained by transport and ventilation systems.

Movement of substances across a membrane against their concentration gradient, using carrier proteins and energy from ATP. It lets cells accumulate substances they need.

A protein that speeds up a specific chemical reaction by lowering the energy needed for it to proceed. Its shape determines which substrate it acts on.

The molecule an enzyme acts upon. It binds temporarily at the enzyme's active site, where it is converted into products before being released.

Loss of a protein's three-dimensional shape caused by heat, extreme pH or other factors, so the active site no longer fits its substrate and activity stops.

The breakdown of glucose using oxygen to release energy, producing carbon dioxide and water. It yields far more usable energy per glucose molecule than anaerobic pathways.

Release of energy from glucose without oxygen, producing lactic acid in animal cells or ethanol and carbon dioxide in yeast. It yields less energy but allows activity when oxygen is short.

The process in which plants, algae and some bacteria use light energy to convert carbon dioxide and water into glucose and oxygen inside chloroplasts.

The principle that all living things are made of cells, that cells are the basic unit of life, and that new cells arise only from existing cells.

A group of similar cells with a shared structure and function, such as muscle tissue or xylem. Tissues combine to form organs.

A structure made of two or more tissues working together to perform a specific function, such as a leaf, heart or kidney.

A group of organs that cooperate to carry out a major body function, such as the digestive, respiratory or circulatory system.

Vascular tissue in plants that transports water and dissolved minerals upward from the roots. Its dead, hollow cells also provide structural support.

Vascular tissue that transports sugars and other organic nutrients from leaves to other parts of a plant, including growing tips and storage organs.

Loss of water vapour from leaves through small openings called stomata. It pulls water up through the xylem and cools the plant.

Tiny pores in the leaf surface that open and close to control gas exchange and water loss. Guard cells change shape to regulate the size of each pore.

The movement of oxygen into an organism and carbon dioxide out of it, occurring across a moist, thin surface such as lungs, gills or leaf pores.

A group of organisms that can interbreed in natural conditions to produce fertile offspring, and are reproductively isolated from other such groups.

The variety of life, measured as the number of species, the genetic variation within them, and the range of ecosystems they form.

The two-part naming system for species, using genus and species names in Latin, such as Homo sapiens. It gives every species a universally recognised label.

A tool of paired, opposing statements that leads the user step by step to identify an unknown organism based on observable features.

A community of organisms interacting with each other and with the non-living parts of their environment, such as soil, water and climate.

A diagram showing the feeding relationships in a community, with arrows tracing energy flow from producers through herbivores to successive predators.

A feeding position in a food chain, such as producer, primary consumer or secondary consumer. Energy decreases at each higher level.

The total mass of living material in a given area or trophic level, usually measured as dry weight. It typically declines at higher trophic levels.

One of the alternative forms of a gene at a particular position on a chromosome. Different alleles produce variations in the trait the gene controls.

The combination of alleles an organism carries for a particular gene, such as homozygous dominant, heterozygous or homozygous recessive.

The observable characteristics of an organism, produced by the interaction between its genotype and its environment.

An allele that is expressed in the phenotype even when only one copy is present, masking the effect of a recessive allele for the same gene.

An allele whose effect appears only when two copies are present, because a dominant allele for the same gene overrides it.

A permanent change in the base sequence of DNA. It may be neutral, harmful or beneficial, and is the original source of new alleles in a population.

The process in which individuals with inherited traits better suited to their environment survive and reproduce more, so those alleles increase in frequency over generations.

A disease-causing organism or agent, such as a bacterium, virus, fungus or parasite. It must enter and multiply in a host to cause infection.

A substance that kills or inhibits bacteria without seriously harming human cells. It is ineffective against viruses and can lose effectiveness as resistance develops.

The ability of bacteria to survive and multiply in the presence of an antibiotic that once killed them, arising when resistant mutants are selected under drug exposure.

Introducing a weakened, inactivated or fragment form of a pathogen to trigger an immune response and memory cells, giving protection against future infection.

The body's ability to resist a particular infection, often through antibodies and memory cells produced after exposure or vaccination.

The maintenance of a relatively stable internal environment, such as constant temperature or blood glucose, despite changes outside the body.

A control mechanism in which a change from the normal level triggers a response that reverses the change, keeping a variable within a narrow range.

A chemical messenger produced by a gland and carried in the blood to target cells, where it alters their activity to regulate body processes.