Estonian Basic-School Biology Exam key terms

A small structure inside a cell that carries out one specific job, such as energy release, protein building or storage. Each organelle type has its own task and is often separated from the rest of the cell by a membrane.

The thin outer layer of a cell that holds the contents together and controls which substances enter and leave. It lets some molecules pass and blocks others, so the cell's internal conditions stay stable.

An organelle where the cell releases usable energy from nutrients such as glucose, using oxygen in the process. Cells with high energy needs, like muscle cells, contain many of them.

A green organelle found in plant cells that captures light energy and uses it to make sugars from carbon dioxide and water. Its green pigment is chlorophyll, which absorbs the light.

The spontaneous spreading of particles from an area of higher concentration to one of lower concentration, caused by random motion. It needs no energy input from the cell and explains gas exchange in lungs and leaves.

The movement of water across a partially permeable membrane from a dilute solution towards a more concentrated one. It explains why plant cells take up water and why cells shrink in strong salt solutions.

The process in which green organisms use light energy to build sugars from carbon dioxide and water, releasing oxygen as a by-product. It stores energy in organic molecules that almost all food chains depend on.

The controlled breakdown of organic molecules such as glucose inside cells to release usable energy, typically using oxygen and producing carbon dioxide and water. It happens continuously in all living cells.

The firmness of a plant cell caused by water pressing the cell contents against the rigid cell wall. Loss of turgor makes leaves and stems wilt.

Plant tissue specialised for transporting substances over long distances. Xylem carries water and dissolved minerals upward from the roots, while phloem carries sugars made in leaves to other parts of the plant.

A small pore in the surface of a leaf, usually on the underside, bordered by two guard cells that open and close it. It lets carbon dioxide in and water vapour and oxygen out.

The loss of water vapour from a plant, mainly through leaf pores. It pulls water upward through the plant and cools the leaves, and its rate rises with warmth, wind and dry air.

The basic unit of biological classification: a group of organisms that resemble each other and can interbreed to produce fertile offspring in nature. Scientific names consist of the genus and the species name.

The science of naming, describing and grouping organisms into a hierarchy of ever broader categories, from species up through genus, family, order, class, phylum and kingdom. Groupings reflect evolutionary relationships.

A branching diagram showing how groups of organisms are thought to have descended from common ancestors. Branch points represent splitting events, and closer branches mean closer relatedness.

A single-celled organism without a nucleus or membrane-bound organelles, usually only a few micrometres long. Bacteria are extremely widespread and include decomposers, pathogens and organisms used in food production.

An organism with cells containing a nucleus but no chlorophyll, which feeds by absorbing nutrients from its surroundings. Fungi include moulds, yeasts and mushrooms, and many live in partnership with plants.

A mutually beneficial association between a fungus and plant roots, in which the fungus helps the plant obtain water and minerals while receiving sugars. Most land plants form such partnerships.

A close, long-lasting relationship between organisms of different species. It may benefit both partners, benefit one without harming the other, or benefit one at the other's expense.

An organism or virus that causes disease in a host. Pathogens spread between individuals by air, water, food, contact or vectors, and are countered by hygiene and by the immune system.

An organism, chiefly bacteria and fungi, that breaks down dead plant and animal material into simpler substances. Decomposers release nutrients back into the soil and keep ecosystems from piling up waste.

The ability of green plants and other photosynthetic organisms to capture light energy and store it in organic compounds. This stored energy enters nearly every food chain.

A sequence showing which organism eats which, starting with a producer and passing energy to herbivores and then to carnivores. Arrows point in the direction the energy flows.

A functioning unit formed by a community of organisms together with its non-living surroundings, such as soil, water and climate. Energy flows through it while matter is recycled within it.

All the individuals of one species living in the same area at the same time, which can interbreed with one another. Its size changes with births, deaths, immigration and emigration.

The particular place or type of environment where a species normally lives and finds the food, water, shelter and breeding conditions it needs. Destroying habitats is a leading cause of species loss.

An inherited feature or behaviour that improves an organism's chances of surviving and reproducing in its environment. Adaptations arise over generations through natural selection acting on variation.

The process by which individuals with inherited features better suited to their surroundings leave more offspring, so those features become more common in later generations. It is the main mechanism of evolution.

A change in the genetic material of a cell that can alter a trait and be passed on to offspring if it occurs in reproductive cells. Mutations are the original source of genetic variation.

The complete set of genes an organism carries, including which variants of each gene are present. It interacts with the environment to produce the observable characteristics of the organism.

The observable characteristics of an organism, such as height, flower colour or blood group, resulting from its genes interacting with environmental conditions during development.

A trait that appears in a hybrid individual even when only one copy of the responsible gene variant is present. The alternative, recessive trait shows only when both copies are of the recessive kind.

The body's ability to resist a particular infectious agent, either because it has met the agent before and formed defences or because it was vaccinated. It can be acquired actively or passed on passively.

The fluid tissue that circulates through the body, carrying oxygen, nutrients, hormones and heat to tissues and waste products away from them. It also transports defensive cells and helps clot wounds.

A muscular pump that drives blood around the body through a network of vessels. In humans it has four chambers, and its rhythmic contractions keep oxygen and nutrients reaching every tissue.

A protein that speeds up a specific chemical reaction in a living organism without being used up itself. Enzymes work best at particular temperatures and acidity levels and are central to digestion and metabolism.

The breaking down of food into small, soluble molecules that can be absorbed into the blood. It happens mechanically by chewing and churning and chemically by enzymes in the digestive tract.

In an experiment, the group that is treated exactly like the test group except for the one factor being investigated. Comparing the two groups shows whether that factor actually caused the observed effect.

Any factor in an experiment that can change or be changed, such as temperature, light or time. A well-planned investigation changes one variable deliberately while keeping the others constant.

A testable, reasoned proposal that offers a possible explanation for an observation or answers a research question. It must be stated so that evidence from an experiment or observation could support or refute it.