K

Karogamy: The fusion of nuclei of two cells, as part of syngamy.
Karyotype: A display of chromosome pairs of a cell arranged by size and shape.
Kerogen: A class of organic compounds found in some sedimentary rocks and thought to be derived from organic molecules from living organisms.
Keystone species: A species that is not necessarily abundant in a community yet exerts strong control in community structure by the nature of its ecological role or niche.
Kilocalorie (kcal): A thousand calories; the amount of heat energy required to raise the temperature of 1 kg of water by 1°C.
Kinase: An enzyme that adds phosphate groups onto other molecules.
Kin discrimination: The ability to distinguish between related and unrelated individuals.
Kin selection: A phenomenon of inclusive fitness, used to explain altruistic behavior between related individuals. A change in the frequency of an allele, caused by the effect of that allele on the fitness of other individuals who carry the allele.
Kinesis: A change in activity or turning rate in response to a stimulus.
Kinetic energy: The energy of motion, which is directly related to the speed of that motion.
Kinetochore: A specialized region on the centromere that links each sister chromatid to the mitotic spindle.
Kinetoplast: An independent replicating organelle lying near the base of the flagellum in kinetoplastids.
Kinetoplastid: Member of a phylum of eukaryotes in the Excavata kingdom characterized by the presence of a kinetoplast organelle.
Kingdom: A taxonomic category, the second broadest after domain.
Kinorhynch: Member of a phylum of tiny spiny animals. Phylum Kinorhyncha.