Heterochrony
Evolutionary changes in the timing or rate of development.
Heterocyst
A specialized cell that engages in nitrogen fixation on some filamentous cyanobacteria.
Hematopoietic system
The bodily system of organs and tissues, primarily the bone marrow, spleen, tonsils, and
lymph nodes, involved in the production of blood.
Hemocoel
A hemocoel is a series of spaces between the organs of organisms with open circulatory
systems, like most arthropods and mollusks
Heteromorphic
A condition in the life cycle of all modern plants in which the sporophyte and gametophyte
generations differ in morphology.
Heterosporous
Referring to plants in which the sporophyte produces two kinds of spores that develop into
unisexual gametophytes, either female or male.
Heterotroph
An organism that obtains organic food molecules by eating other organisms or their by-
products.
Heterozygote
A diploid organism that carries two different alleles at one or more genetic loci.
Heterozygote advantage
A mechanism that preserves variation in eukaryotic gene pools by conferring greater
reproductive success on heterozygotes over individuals homozygous for any one of the
associated alleles.
Heterozygous
Having two different alleles for a given genetic character.
Hibernation
A physiological state that allows survival during long periods of cold temperatures and
reduced food supplies, in which metabolism decreases, the heart and respiratory system
slow down, and body temperature is maintained at a lower level than normal.
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