VALID Science 8 key terms

The smallest unit of life that can carry out all the processes of living things. Some organisms are a single cell; others are built from many cells working together.

A thin, flexible layer that surrounds a cell and controls which materials enter and leave. It holds the cell together and separates its inside from the outside environment.

The control centre of a eukaryotic cell. It contains DNA, which carries the instructions that direct the cell's activities and are passed on when the cell divides.

A small structure inside a cell that performs a particular job, such as making energy or packaging proteins. Different organelles work together to keep the cell alive.

A green organelle found in plant cells that captures light energy and uses it to make food through photosynthesis. Its green colour comes from the pigment chlorophyll.

An organelle that releases energy from food through cellular respiration. Cells that need lots of energy, such as muscle cells, contain many mitochondria.

The process by which green plants and algae use light energy to combine carbon dioxide and water into glucose, releasing oxygen. It is the main way energy enters food chains.

The chemical process in cells that releases energy from glucose, usually using oxygen and producing carbon dioxide and water. It supplies the energy cells need to live and grow.

The movement of particles from an area where they are crowded to an area where they are less crowded, until they are spread evenly. It needs no added energy.

The movement of water across a partly permeable membrane from a region with more water to a region with less water. It is a special case of diffusion.

The process by which one cell divides to form two daughter cells that have the same genetic information as the parent. It is used for growth and for repairing damaged tissue.

The long molecule found in the nucleus that stores the instructions for building and running an organism. Sections of DNA called genes are passed from parents to offspring.

A tightly coiled package of DNA and protein found in the nucleus. Humans usually have 46 chromosomes in each body cell, arranged in 23 pairs.

A section of DNA that carries the instructions for one feature or for making one protein. Genes come in different versions, which is why individuals vary.

One of the different versions of a gene. An organism inherits one allele from each parent, and the combination of alleles helps determine a trait.

Describes an allele whose effect shows in an organism even when only one copy is present. A dominant allele masks the effect of a recessive allele paired with it.

Describes an allele whose effect appears only when two copies are present and no dominant allele is there to mask it. Recessive traits can skip generations.

The process by which individuals with helpful inherited features tend to survive and reproduce more, so those features become more common in later generations. It drives evolution.

A feature or behaviour that helps an organism survive and reproduce in its environment. Adaptations develop over many generations through natural selection.

A group of organisms that share similar features and can breed together to produce fertile offspring. Members of a species do not normally breed successfully with other species.

The slow change in the inherited features of populations over many generations. It can produce new species and explains the diversity of living things.

A community of living things together with the non-living parts of their environment, such as soil, water and air. The living and non-living parts interact and depend on each other.

An organism that makes its own food, usually by photosynthesis. Producers form the base of every food chain and supply energy to the other organisms in an ecosystem.

An organism that cannot make its own food and must eat other organisms to obtain energy. Consumers may eat producers or other consumers.

A diagram or description showing the order in which organisms eat one another, with arrows showing the direction energy flows. Each link depends on the one before it.

An organism such as a fungus or bacterium that breaks down dead plants and animals, returning nutrients to the soil. Decomposers recycle materials through the ecosystem.

The smallest particle of an element that still has the properties of that element. Atoms join together to form molecules and are made of protons, neutrons and electrons.

A pure substance made of only one kind of atom that cannot be split into simpler substances by chemical means. Elements are listed on the periodic table.

A pure substance formed when atoms of two or more different elements are chemically joined in fixed proportions. Its properties differ from those of the elements it contains.

The smallest particle of a substance that can exist on its own, made of two or more atoms held together by chemical bonds. Molecules may be of elements or compounds.

A process in which substances are changed into new substances with different properties. Atoms are rearranged, but no atoms are created or destroyed.

A starting substance in a chemical reaction that is used up as the reaction proceeds. Reactants are written on the left side of a word or symbol equation.

A new substance formed during a chemical reaction. Products are written on the right side of a word or symbol equation and have different properties from the reactants.

The principle that the total mass of the reactants equals the total mass of the products in a chemical reaction. Matter is rearranged but never lost or gained.

A push or a pull acting on an object that can change its speed, its direction or its shape. Force is measured in newtons and has both size and direction.

A force that opposes motion when two surfaces slide or rub against each other, converting some energy into heat. Rougher surfaces usually produce more friction.

The force of attraction between objects that have mass. On Earth it pulls objects toward the centre of the planet and gives falling objects an acceleration of about 9.8 m/s².

Two or more forces acting on an object that cancel each other out, so the object's motion does not change. An object at rest stays at rest when the forces are balanced.

The movement of energy from one object or store to another, for example when a moving ball heats the floor it hits. Energy is transferred, not created or destroyed.

The energy an object has because it is moving. It increases when the object's mass or speed increases and is measured in joules.