Bilateral symmetry

Definition

Bilateral symmetry is a body plan in which an organism can be divided into two identical halves along a single plane, typically creating a mirror image. This type of symmetry is essential for the development of complex structures and systems in animals, influencing their movement and coordination. It is a fundamental characteristic that has evolved over time, allowing organisms to adapt and thrive in various environments.

5 Must Know Facts For Your Next Test

1. Bilateral symmetry is closely linked to the evolution of more complex nervous systems and greater mobility in animals.
2. This symmetry type allows for directional movement, facilitating navigation through the environment and hunting or escaping from predators.
3. Many bilateral organisms exhibit cephalization, where sensory organs and a brain are located at the anterior end, enhancing their ability to interact with their surroundings.
4. The presence of bilateral symmetry has influenced the developmental processes of many animal phyla, including chordates and arthropods.
5. The emergence of bilateral symmetry is believed to have occurred during the Cambrian explosion, which led to increased diversity in body plans and ecological roles.

Review Questions

• How does bilateral symmetry influence the evolution of nervous systems in animals?
  • Bilateral symmetry significantly impacts the evolution of nervous systems by promoting cephalization, where nerve tissues and sensory organs cluster at one end of the body. This arrangement enhances an organism's ability to process information efficiently and respond to environmental stimuli more effectively. As a result, animals with bilateral symmetry tend to develop more complex behaviors and adaptive strategies for survival.
• Compare bilateral symmetry with radial symmetry, highlighting their advantages and disadvantages in evolutionary terms.
  • Bilateral symmetry offers advantages such as enhanced movement and directional navigation, crucial for predatory lifestyles or escaping threats. In contrast, radial symmetry provides advantages for sessile or planktonic organisms that benefit from equal access to their environment from all directions. While bilateral organisms can adapt to more dynamic habitats requiring mobility, radial organisms may be better suited for stable environments where mobility is less critical.
• Evaluate the impact of bilateral symmetry on morphological diversity among animal species during evolutionary history.
  • Bilateral symmetry has played a crucial role in driving morphological diversity among animal species since its emergence. This body plan allowed for specialization in form and function, leading to various adaptations like limbs for locomotion or appendages for sensory perception. The evolutionary success of bilateral organisms contributed to their dominance across many ecosystems, fostering diverse evolutionary pathways that shaped ecological interactions and species relationships throughout history.

Related terms

Cephalization: The concentration of sensory and neural organs at one end of the body, typically leading to the development of a head region.

Radial symmetry: A body plan where an organism can be divided into multiple identical sections around a central axis, commonly seen in organisms like jellyfish.

Morphogenesis: The biological process that causes an organism to develop its shape, which is influenced by its symmetry type.