Nucleotide
The building block of a nucleic acid, consisting of a five-carbon sugar covently bonded to a
nitrogenous base and a phosphate group.
Nucleus
(1) An atom's central core, containing protons and neutrons.
(2) The chromosome-containing organelle of a eukaryotic cell.
Null hypothesis
In statistical analysis, a hypothesis proposing that there is no statistically significant
difference between the observed results of an experiment and the expected results.
Neurotransmitter metabolism
Sum of chemical changes that occur with in the tissues of an organism consisting of
anabolism (biosynthesis) and catabolism of neurotransmitters; the buildup and breakdown
of neurotransmitters for utilization by the organism.
O
Obligate aerobe
An organism that requires oxygen for cellular respiration and cannot live without it.
Obligate anaerobe
An organism that cannot use oxygen and is poisoned by it.
Occipital condyle
An articular surface on the occipital bone which articulates with the atlas.
(invertebrate zoology) A projection on the posterior border of an insect head which
articulates with the lateral neck plates.
Oceanic zone
The region of water lying over deep areas beyond the continental shelf.
Ocelli
Simple eyes of insects.
Offset
A short runner in certain plants that produces roots and shoots at the tip.