Biology Prefixes and Suffixes: end- or endo-

Echinodiscus tenuissimus - dorsal view of test (endoskeleton)
Test, or endoskeleton, of an Echinodiscus tenuissimus, an irregular sea urchin ("sand dollar"). By Didier Descouens (Own work) [ CC BY-SA 3.0], via Wikimedia Commons

Biology Prefixes and Suffixes: end- or endo-

Definition:

The prefix (end- or endo-) means within, inside or internal.

Examples:

Endobiotic (endo-biotic) - referring to a parasite or symbiotic organism that lives within the tissues of its host.

Endocardium (endo-cardium) - inner membrane lining of the heart that also covers heart valves and is continuous with the inner lining of blood vessels.

Endocarp (endo-carp) - hard inner layer of pericarp that forms the pit of ripened fruit.

Endocrine (endo-crine) - refers to the secretion of a substance internally. It also refers to glands of the endocrine system that secrete hormones directly into the blood.

Endocytosis (endo-cytosis) - transport of substances into a cell.

Endoderm (endo-derm) - inner germ layer of a developing embryo that forms the lining of the digestive and respiratory tracts.

Endoenzyme (endo-enzyme) - an enzyme that acts internally to a cell.

Endogamy (endo-gamy) - internal fertilization between flowers of the same plant.

Endogenous (endo-genous) - produced, synthesized or caused by factors within an organism.

Endolymph (endo-lymph) - fluid contained within the membranous labyrinth of the inner ear.

Endometrium (endo-metrium) - inner mucous membrane layer of the uterus.

Endomitosis (endo-mitosis) - a form of internal mitosis in which chromosomes replicate, however the division of the nucleus and cytokinesis do not occur.

It is a form of endoreduplication.

Endomixis (endo-mixis) - reorganization of the nucleus that occurs within the cell in some protozoans.

Endomorph (endo-morph) - individual with a heavy body type predominated by tissue derived from the endoderm.

Endophyte (endo-phyte) - a plant parasite or other organism that lives within a plant.

Endoplasm (endo-plasm) - the inner portion of the cytoplasm in some cells such as protozoans.

Endorphin (endo-dorphin) - a hormone produced within an organism that acts as a neurotransmitter to reduce the perception of pain.

Endoskeleton (endo-skeleton) - an organism's internal skeleton.

Endosperm (endo-sperm) - tissue within the seed of an angiosperm that nourishes the developing plant embryo.

Endospore (endo-spore) - inner wall of a plant spore or pollen grain. It also refers to a non-reproductive spore produced by some bacteria and algae.

Endothelium (endo-thelium) - thin layer of epithelial cells that form the inner lining of blood vessels, lymphatic vessels and heart cavities.

Endotherm (endo-therm) - organism that generates heat internally to maintain a constant body temperature.