Bilateral symmetry

Definition

Bilateral symmetry is a body plan in which an organism can be divided into two mirror-image halves along a single plane, resulting in left and right sides that are roughly equal. This form of symmetry is commonly found in many animals, including humans, and is significant for the development of complex structures and organ systems, facilitating movement and interaction with the environment.

5 Must Know Facts For Your Next Test

1. Bilateral symmetry allows for greater mobility and streamlined movement, making it advantageous for predatory or fast-moving species.
2. In animals exhibiting bilateral symmetry, there is often a concentration of sensory organs at the anterior (front) end, which enhances their ability to interact with their environment.
3. Many bilateral organisms have specialized body regions: the head (cephalic), trunk (thorax), and tail (abdomen), allowing for efficient functioning of various organ systems.
4. During embryonic development, organisms that display bilateral symmetry typically undergo a process called gastrulation, leading to the formation of three germ layers: ectoderm, mesoderm, and endoderm.
5. Bilateral symmetry is contrasted with other forms of symmetry like radial symmetry and asymmetry, which reflect different evolutionary adaptations in animal life.

Review Questions

• How does bilateral symmetry contribute to an organism's ability to move and interact with its environment?
  • Bilateral symmetry enables organisms to have a streamlined body shape that enhances mobility. This symmetry allows for coordinated movements, as limbs or fins on either side can work together more efficiently. Additionally, having a centralized nervous system at the anterior end facilitates rapid responses to stimuli, improving the organism's ability to navigate its environment.
• Compare and contrast bilateral symmetry with radial symmetry in terms of their advantages for different types of organisms.
  • Bilateral symmetry is advantageous for animals that require directional movement and increased speed, such as fish or mammals. It allows for specialization of body regions and a more complex nervous system. In contrast, radial symmetry benefits organisms like jellyfish by allowing them to interact equally with their environment from all directions, which is ideal for sessile or free-floating life forms that do not move towards a specific direction.
• Evaluate how the concept of cephalization relates to bilateral symmetry and its evolutionary significance in complex organisms.
  • Cephalization is directly linked to bilateral symmetry as it involves the concentration of sensory organs and nervous tissue at the anterior end of bilaterally symmetrical animals. This evolutionary trend enhances an organism's ability to process information from its environment and respond effectively. As a result, cephalization has allowed for more complex behaviors and interactions within ecosystems, making it a key factor in the evolution of higher animals.

Related terms

Radial Symmetry: A body plan where an organism can be divided into multiple identical sections around a central axis, commonly seen in jellyfish and sea anemones.

Asymmetry: The lack of any symmetry in the body plan of an organism, which can be observed in certain organisms like sponges.

Cephalization: The evolutionary trend where sensory organs and nervous tissue become concentrated at one end of the body, often associated with bilateral symmetry.