Bilateral symmetry

Definition

Bilateral symmetry is a body plan in which an organism can be divided into two equal halves along a single plane. This symmetry often results in distinct anterior (front) and posterior (back) ends, as well as dorsal (upper) and ventral (lower) surfaces.

5 Must Know Facts For Your Next Test

1. Bilateral symmetry is common in animals with a high level of mobility, allowing for streamlined movement.
2. Organisms with bilateral symmetry tend to exhibit cephalization, the concentration of sensory organs at the anterior end.
3. Bilateral symmetry is associated with the development of three embryonic germ layers: ectoderm, mesoderm, and endoderm.
4. It allows for greater specialization of body regions and structures compared to radial symmetry.
5. Examples of bilaterally symmetrical animals include humans, insects, and most vertebrates.

Review Questions

• What are the main advantages of bilateral symmetry for mobile organisms?
• How does bilateral symmetry relate to cephalization?
• Name three examples of bilaterally symmetrical animals.

Related terms

Radial Symmetry: A body plan in which any longitudinal cut through the central axis results in identical halves.

Cephalization:

The evolutionary trend toward concentrating sensory equipment at the anterior end of the body.

Germ Layers: The three primary layers formed during early embryonic development - ectoderm, mesoderm, and endoderm - that develop into various tissues and organs.