Bilateral symmetry

Definition

Bilateral symmetry is a type of symmetry where an organism can be divided into two identical halves along a single plane, typically through the middle. This form of symmetry is significant in the evolution of body plans, allowing for streamlined movement and more complex nervous systems, which became increasingly important during the Cambrian period as many new species emerged and diversified.

5 Must Know Facts For Your Next Test

1. Bilateral symmetry first became prominent during the Cambrian period, coinciding with the Cambrian Explosion, when many new animal forms appeared.
2. This type of symmetry allows for efficient movement and is commonly seen in animals that are active and have directional mobility, like vertebrates.
3. Organisms with bilateral symmetry often exhibit cephalization, where sensory organs are located at the front end, enhancing their ability to interact with the environment.
4. Many bilaterally symmetrical organisms have body structures organized into distinct regions, such as anterior (front), posterior (back), dorsal (top), and ventral (bottom) sides.
5. The development of bilateral symmetry has been linked to increased complexity in nervous systems, supporting more advanced behaviors and interactions with their environment.

Review Questions

• How does bilateral symmetry influence the movement and behavior of organisms that exhibit this trait?
  • Bilateral symmetry greatly enhances the movement and behavior of organisms by allowing them to move in a more streamlined fashion. This kind of symmetry facilitates directional movement, enabling animals to efficiently navigate their environment while searching for food or escaping predators. As a result, organisms with bilateral symmetry often exhibit more complex behaviors compared to those with other forms of symmetry.
• Discuss the role of cephalization in organisms with bilateral symmetry during the Cambrian period.
  • Cephalization plays a crucial role in the evolutionary success of bilaterally symmetrical organisms. During the Cambrian period, as new species emerged, cephalization allowed for the concentration of sensory organs and nervous tissue at one end of the body. This adaptation improved an organism's ability to respond to environmental stimuli and enhanced its survival prospects by facilitating more effective hunting and evasion strategies.
• Evaluate how bilateral symmetry contributed to the diversity of life forms observed in the Cambrian period and its impact on future evolutionary developments.
  • Bilateral symmetry significantly contributed to the remarkable diversity of life forms during the Cambrian period by providing a foundation for complex body plans and behaviors. This symmetrical arrangement allowed for specialized regions within an organism's body, leading to the development of advanced systems such as respiratory and circulatory systems. The advantages conferred by bilateral symmetry not only set the stage for further evolutionary innovations but also influenced subsequent animal lineages, ultimately shaping the biodiversity we observe today.

Related terms

Radial symmetry: A type of symmetry where body parts are arranged around a central axis, allowing for multiple planes of division.

Cephalization: The evolutionary trend where sensory organs and nerve tissues become concentrated at one end of an organism, often leading to the formation of a head.

Triploblastic: Describes organisms that develop from three embryonic germ layers: ectoderm, mesoderm, and endoderm, which allows for more complex body structures.