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| Term | Definition |
|---|---|
| organic fertilizer | A natural fertilizer material that has undergone little or no processing. Can include plant, animal, or mineral materials. |
| organic matter | Any material originating from a living organism (peat moss, plant residue, compost, ground bark, manure, etc.). |
| organism | A living plant or animal. |
| ornamental plant | A plant grown for beautification, screening, accent, specimen, color, or other aesthetic reasons. |
| orthoptera | An insect family made up of species having a tough, leathery shell, membranous hindwings, and straight forewings. Includes locusts, crickets, grasshoppers, and katydids. |
| osmosis | Passage of materials through a membrane from an area of high concentration to an area of lower concentration. |
| ovary | The part of a flower containing ovules that will develop into seeds upon fertilization. Along with the style and stigma, it makes up the pistil (female sexual organ). |
| ovule | Within the ovary, a body that will develop into seeds after fertilization. |
| oxidation | The chemical process by which sugars and starches are converted into energy. In plants, this is also known as respiration. |