A stable, self-perpetuating community of organisms that has reached the final stage of ecological succession.

A gradual change in the characteristics of a species or population over a geographical area or environmental gradient.

A glandular region of the body in annelid worms, such as earthworms, that secretes mucus for egg formation.

A common opening for the digestive, excretory, and reproductive tracts in some animals, such as birds, reptiles, and amphibians.

A medication used to treat infertility in women by stimulating ovulation.

Hair-like structures on the surface of cells that beat in coordinated waves to move fluids or small particles over the cell surface.

A part of the eye located behind the iris that contains the ciliary muscle and is involved in the production of aqueous humor and accommodation.

A muscle in the eye that controls the shape of the lens, enabling focusing on near or distant objects (accommodation).

The physiological process that displays an endogenous, entrainable oscillation of about 24 hours, affecting sleep-wake cycles, hormone release, and other biological activities.

The movement of blood through the body, facilitated by the heart, arteries, veins, and capillaries to transport oxygen, nutrients, and waste products.