Aleurone layer
The outermost cell layer of the endosperm of the grains (seeds) of wheat and other grasses;
when acted upon by gibberellin, the aleurone layer releases enzymes that digest the stored
food of the endosperm into small nutrient molecules that can be taken up by the embryo.
Algae
A photosynthetic, plantlike protist.
Alligator
Either of two large reptiles, Alligator mississipiensis of the southeast United States or A.
sinensis of China, having sharp teeth and powerful jaws. They differ from crocodiles in
having a broader, shorter snout.
Alimentary canal
The tube or passage of the digestive system through which food passes, nutrients are
absorbed, waste is eliminated.
Alkalinity
pH^ values above 7.^
Alkaline
Pertaining to substances that increase the relative number of hydroxide ions (OH –) in a
solution; having a pH greater than 7; basic; opposite of acidic.
Alkaloids
A type of chemical commonly found in plants and often having medical properties. e.g.:
atropine, caffeine, morphine, nicotine, quinine.
All-or-none event
An action that occurs either completely or not at all, such as the generation of an action
potential by a neuron.
Allantois
One of four extraembryonic membranes; serves as a repository for the embryo's
nitrogenous waste.
Allele
An alternative form of a gene.
Allele frequency
The proportion of a particular allele in a population.
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