O

obligate

absolutely indispensable, essential.

optical radiation

The electromagnetic wavelength range between 100 nm and 1 mm is referred to as optical radiation. By definition, this includes ultraviolet radiation (UV), the visible light spectrum (VIS) and infrared radiation (IR). 

organic compound

Organic compounds are substances composed primarily of hydrogen (H) and carbon (C). Organic chemistry is concerned with the properties, composition and production of carbon compounds. 

organism

An organism is an individual life form - see living organism. 

oxidation

Oxidation generally refers to the chemical process in which an element reacts with oxygen or in which electrons are lost. 

Oxygen

Symbol O2 - Oxygen is the most common element on Earth. As molecular oxygen, it is an odourless, colourless gas. Oxygen occurs primarily in combination with other elements such as hydrogen (to form water); air is approx. 20% oxygen by volume. 

ozone

Represented as O3 - Ozone is a gas with strong oxidation properties that is toxic in high concentrations. The molecule consists of three oxygen atoms and is therefore unstable. Ozone arises naturally through the effect of solar radiation on the stratosphere.