B3.3.1 (HL)—Movement adaptations

Movement is universal in living organisms, but locomotion is movement of the whole organism from one place to another. Motile organisms locomote; sessile organisms remain attached yet can still move parts or grow directionally.

A motile animal can change location using metabolic energy and structures such as legs, wings or fins. A sessile coral can move tentacles, and a rooted plant can grow or bend toward a stimulus without locomoting.

Locomotion can improve survival and reproduction: a blackbird forages for food, a hare escapes a predator, an orangutan searches for a mate, and a whale migrates between feeding and breeding areas.

A plant shoot curving toward light demonstrates movement through differential growth, whereas a bird flying to a feeding site demonstrates locomotion because its whole body changes location.

Sessile does not mean incapable of movement, and locomotion is not cost-free: it requires energy and often increases nutritional demand and exposure to risk.