O

Oar: Instrument for propelling a rowing boat forward.

Observations: Information about objects and events, collected by using one or more of your senses.

Occupational Health and Safety: Safety issues related to the workplace, e.g. wearing a helmet.

Ocean currents: Movements of sea water caused by many factors including wind and the Earth's movement.

Oceanic: To do with the open ocean waters beyond the edge of the continental shelf.

Oceanic trench: Deep, steep-sided depression in the ocean floor, formed when one plate of the earth's crust is pushed beneath another plate.

Oceanography: The scientific study and exploration of the oceans and seas in all their aspects, including all processes in the oceans and interactions and relations with Earth.

Ochre star: A yellowish sea star that lives in the intertidal zone.

Octopus: A soft-bodied marine animal that has eight arms covered with suction discs. Octopuses are related to squid and cuttlefishes.

Omnivore: A plant and flesh eater.

On the plane: When a speed boat accelerates then levels out while travelling at speed.

Ooze: Fine-grained deep-sea sediments of biological origin, composed (in part) of the remains of small marine organisms.

Operculum: Bony covering over the gill slits of fish; or, in gastropod molluscs, the calcareous plate over the shell opening that protects the body when the animal withdraws into the shell.

Opportunist: An animal that eats almost any plant or animal that comes its way.

Oral-arm: Dangling structures a jelly uses to transfer food from its tentacles to its mouth; also called a palp.

Orange roughy: A bright orange fish that lives in the deep sea near Australia and New Zealand. Orange roughy grow very slowly—the orange roughy sold for people to eat may be 50 to 80 years old.

Orca: A black and white whale that hunts in packs; also called the killer whale. Orcas are actually the largest member of the dolphin family.

Order: In biology, a category that's part of the scientific system for grouping together related plants, animals and other organisms (kingdom, phylum, class, order, family, genus, species). Order is the category that ranks below a class and above a family.

Organism: A living thing--a plant, animal, bacterium or other life form.

Organic: From a living thing or organism; originating in nature rather than being made artificially.

Organophosphates: Chemicals used to fertilise plants.

Otoliths: Ear stones in fish.

Ovary: The female reproductive organ that makes eggs.

Overfishing: Catching too many fish; fishing so much that the fish cannot sustain their population. The fish get fewer and fewer, until finally there are none to catch.

Overflow current: Rough rapid-like water caused by tides running over submerged rocks.

Ovules: Small rounded bodies in the ovary of a flower, each ovule contains an ovum (egg cell).

Oxidation: Process by which oxygen is added to metals. Causes corrosion.

Oxygen: A colorless, odorless, tasteless gas. Most life on earth requires oxygen to live. Animals breathe oxygen out of the air or water. Plants also need oxygen, even though they produce oxygen by photosynthesis.

Oxygen minimum layer: A zone in the deep sea, usually around depths of 2,000 to 2,950 feet (600-900 meters) where oxygen reaches its lowest level. A special community of organisms is adapted to live in this habitat.

Ozone hole: Area where the thinning of the upper atmosphere each spring over Antarctica lets harmful ultraviolet rays through. Can have devastating effects on life on Earth.