| root cap | <botany> A mass of parenchymtous cells which covers and protects the growing cells at the end of a root; a pileorhiza. The issue found at the apex of roots, overlying the root apical meristem and protecting it from friction as the root grows through the soil. Secretes a glycoprotein mucilage as a lubricant. (18 Nov 1997) |
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| phrygian cap | On cholecystography, an incomplete septum, or a fold in the gallbladder, whose shape suggests the liberty cap of the French Revolution. (05 Mar 2000) |
| plant root cap | A cone-shaped structure in plants made up of a mass of meristematic cells that covers and protects the tip of a growing root. It is the putative site of gravity sensing in plant roots. (12 Dec 1998) |
| polar | Describes a feature or phenomenon occuring at the end (pole) of an object (such as a planet) or organism (such as an amoeba). <chemistry> Describes a molecular that has a permanent electric dipole. See: polar group. Compare: nonpolar, nonpolar groups. (12 Mar 1998) |
| polar amino acid | An alpha-amino acid in which the functional group attached to the alpha-carbon (i.e., R in RCH(NH2)COOH) has hydrophilic properties; e.g., serine, cysteine, homocysteine. (05 Mar 2000) |
| polar anaemia | A form of anaemia sometimes observed in natives of temperate climates when they migrate to the Arctic or Antarctic regions. (05 Mar 2000) |
| polar body | <cell biology> In animals each meiotic division of the oocyte leads to the formation of one large cell (the egg) and a small polar body as the other cell. Polar body formation is a consequence of the very eccentric position of the nucleus and the spindle. (18 Nov 1997) |
| polar cataract | A capsular cataract limited to an area of the anterior or posterior pole of the lens. (05 Mar 2000) |
| polar cell | <cell biology> In animals each meiotic division of the oocyte leads to the formation of one large cell (the egg) and a small polar body as the other cell. Polar body formation is a consequence of the very eccentric position of the nucleus and the spindle. (18 Nov 1997) |
| polar compound | A compound in which the electric charge is not symmetrically distributed, so that there is a separation of charge or partial charge and formation of definite positive and negative poles; e.g., H2O. See also inorganic compound. (05 Mar 2000) |
| polar fibres | Those fibres of the mitotic spindle extending from the two poles of the spindle toward the equator. Compare: astral fibres, kinetochore fibres. (05 Mar 2000) |
| polar flagellation | <cell biology> Condition of having flagella attached at one end or both ends of the cell. (09 Oct 1997) |
| polar globule | <cell biology> In animals each meiotic division of the oocyte leads to the formation of one large cell (the egg) and a small polar body as the other cell. Polar body formation is a consequence of the very eccentric position of the nucleus and the spindle. (18 Nov 1997) |
| polar granule | <biology> Granules containing a basic protein found in insect eggs that induce the formation of and become incorporated into germ cells. (18 Nov 1997) |
| polar group | <chemistry> Any chemical grouping in which the distribution of electrons is uneven enabling it to take part in electrostatic interactions. (18 Nov 1997) |