JCE General Science (Syllabus 43) key terms

A testable statement that predicts a possible explanation for an observation or a relationship between variables. A good hypothesis can be supported or rejected by evidence collected during an investigation.

The factor in an experiment that the investigator deliberately changes or selects, so that its effect on another factor can be observed. It is plotted on the horizontal axis of a graph.

The factor in an experiment that is measured or observed in response to changes in the independent variable. Its value depends on what the investigator chooses to alter.

A standard or comparison setup in which the factor being tested is kept constant or left out, allowing the investigator to judge whether the treatment actually caused the observed result.

How close a measured value is to the true or accepted value. Accuracy is improved by using well-calibrated instruments and careful technique, and it is not the same as precision.

How close repeated measurements of the same quantity are to one another, regardless of whether they lie near the true value. Precise results show very little scatter.

The arithmetic average of a set of values, found by adding all the measurements and dividing by the number of measurements. It gives a single summary figure for the data.

The smallest unit of living matter that can carry out all the basic processes of life. Some organisms consist of a single cell; others, such as plants and animals, are made of many.

The process by which green plants, algae and some bacteria use light energy to combine carbon dioxide and water into glucose, releasing oxygen as a by-product. Chlorophyll is needed to capture the light.

The chemical process in living cells that releases energy from glucose, usually using oxygen and producing carbon dioxide and water. It supplies energy for growth, movement and other life activities.

The movement of water molecules through a partially permeable membrane from a region of higher water concentration to a region of lower water concentration. It is important for water uptake by plant roots.

The net movement of particles from a region of higher concentration to a region of lower concentration, caused by their random motion. It needs no energy input and continues until the concentrations are even.

A protein that speeds up a specific chemical reaction in a living organism without being used up. Enzymes work best at particular temperatures and pH values and are destroyed by extremes.

A community of interacting living organisms together with the non-living parts of their environment, such as soil, water, air and sunlight. Energy and nutrients flow between these components.

An inherited feature or behaviour that helps an organism survive and reproduce in its particular habitat. Adaptations develop over many generations through the process of natural selection.

The smallest particle of an element that still has the chemical properties of that element. Atoms consist of a nucleus containing protons and neutrons, surrounded by moving electrons.

A pure substance made of only one kind of atom, which cannot be broken down into simpler substances by chemical means. Elements are arranged in the periodic table.

A pure substance formed when two or more different elements are chemically combined in fixed proportions. A compound has properties different from those of the elements that make it up.

A material containing two or more substances that are not chemically combined and can usually be separated by physical methods. The proportions of the components may vary.

A change in which new substances with different properties are formed, usually involving the breaking and making of chemical bonds. It is often difficult or impossible to reverse.

A change in the appearance, state or shape of a substance that forms no new substance. Melting, freezing and dissolving are examples, and such changes are usually reversible.

A substance that releases hydrogen ions when dissolved in water, turns blue litmus red, and reacts with bases to form a salt and water. Acids have a pH below 7.

A scale from 0 to 14 that measures how acidic or alkaline a solution is. Values below 7 are acidic, 7 is neutral, and values above 7 are alkaline.

A push or pull that can change the speed, direction or shape of an object. Force is measured in newtons and has both size and direction.

The force with which gravity pulls an object towards a planet or other large body. Weight is measured in newtons and changes when the strength of gravity changes.

The amount of matter in an object, measured in kilograms. Mass does not change when an object is taken to a different place, unlike its weight.

The capacity of a system to do work or cause change. Energy exists in many forms, including kinetic, potential, chemical, thermal and electrical, and is conserved during transformations.

The energy an object possesses because of its motion. It increases with the mass of the object and with the square of its speed.

A force that opposes the relative motion of two surfaces in contact. It converts some kinetic energy into heat and can be reduced by lubrication or by making surfaces smoother.

The distance travelled by an object per unit time, usually measured in metres per second. Average speed is the total distance travelled divided by the total time taken.

A closed path through which electric current can flow, containing a source of electrical energy and components such as lamps, switches and resistors joined by conductors.

A material that allows electric charge or heat to pass through it easily because it contains free electrons. Metals such as copper are good conductors.

The continuous movement of water between the oceans, atmosphere and land through evaporation, condensation, precipitation and run-off. It purifies water and distributes it around the planet.

The wearing away and removal of rock or soil by agents such as flowing water, wind, ice and gravity. Erosion shapes landscapes and can be made worse by human activities.

A natural resource that is replaced by natural processes at a rate at least as fast as it is used, such as sunlight, wind, flowing water and biomass. Such resources are not used up permanently.

The warming of a planet's surface caused by gases in the atmosphere that trap outgoing heat radiation. It keeps Earth warm enough for life but is strengthened by human emissions.

The variety of living species in a particular area or on Earth as a whole, including the genetic variation within species and the range of habitats and ecosystems present.

The collection and processing of used materials so that they can be made into new products, reducing the need for raw materials and the amount of waste sent to landfill.

A simple machine consisting of a rigid bar that turns about a fixed point called the pivot or fulcrum. A lever makes it easier to move a load by applying a smaller effort.