Micropyle
A pore in the membrane covering the ovum of some animals through which a spermatozoon
can enter.
Microspore
In plants, a haploid spore that develops into a male gametophyte; in seed plants, it becomes
a pollen grain.
Microtubules
A hollow rod of tubulin protein in the cytoplasm of all eukaryotic cells and in cilia, flagella,
and the cytoskeleton.
Microtubule Organizing Center
The microtubule-organizing center (MTOC) is a structure found in eukaryotic cells from
which microtubules emerge.
Microvillus
One of many fine, fingerlike projections of the epithelial cells in the lumen of the small
intestine that increase its surface area.
Middle lamella
A thin layer of adhesive extracellular material, primarily pectins, found between the primary
walls of adjacent young plant cells.
Midgut
The middle portion of the digestive tube in vertebrate embryos. Also known as mesenteron.
Mimicry
A phenomenon in which one species benefits by a superficial resemblance to an unrelated
species. A predator or species of prey may gain a significant advantage through mimicry.
Mineral
In nutrition, one of many chemical elements, other than carbon, hydrogen, oxygen, and
nitrogen, that an organism requires for proper body functioning.
Mineralocorticoid
A corticosteroid hormone secreted by the adrenal cortex that regulates salt and water
homeostasis.
Minimum dynamic area
The amount of suitable habitat needed to sustain a viable population.
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