Published by Australian Academy of Science
Glossary | Acid test for the seas

diatoms. A common type of phytoplankton which have cell walls made of silica.

logarithmic scale. A scale of measurement in which an increase or decrease of one unit represents a ten-fold change in the quantity measured.

parts per million (ppm). This is a way of expressing very dilute concentrations of substances. Just as per cent means out of a hundred, so parts per million or ppm means out of a million. Therefore 500,000 ppm is the same as 50 per cent, because 500,000 is half of a million.

pH. The pH scale is used to measure the strength of acids and bases (or alkalis). The acid strength in the human stomach is about pH 2. Alkalis such as caustic soda and basic household cleaners have a pH of about 12 to 14. Neutral is pH 7, (ie, neither acidic or alkaline). The scale is logarithmic, so pH 4 is ten times as acidic as pH 5 and pH 2 is ten times as acidic as pH 3, and so on.

photosynthesis. The biochemical process in which some microorganisms use energy from light to synthesise carbohydrates from carbon dioxide and water. Photosynthesis can be shown as:

phytoplankton. Plankton that possess plant-like characteristics.

zooplankton. Plankton that possess animal-like characteristics.