Irish Leaving Certificate Biology

## What scientific knowledge is Scientific knowledge is a body of explanations that have been tested against evidence. A fact is an observation that can be confirmed, such as the temperature at which a sample of liquid boils. A **hypothesis** is a proposed, testable explanation for an observation. A **theory** is a well-tested explanation that draws together many observations and has survived repeated attempts to disprove it. In everyday speech "theory" means a guess, but in science the theory of evolution by natural selection or the cell theory are among the best-supported ideas there are, because they explain a large amount of data and have made predictions that turned out to be correct. Scientific ideas are modified over time. When new evidence cannot be explained by an existing idea, the idea is adjusted or replaced. The classification of living things is a good example: organisms were once placed in two kingdoms, plants and animals, and later in five and six kingdoms as microscopes and then DNA sequencing revealed differences that the older scheme could not show. The change was not an error that embarrassed science; it was the process working, with better tools producing better models. Science is also a global activity. Scientists in different countries build on each other's results, which only works because they share conventions. SI units mean that a mass recorded in Dublin is read the same way in Tokyo. Binomial names mean that a species has one internationally…