Final answer:
Bilateral symmetry is when an organism can be divided into two equal right and left halves along a midsagittal plane. It includes a front (ventral) and back (dorsal) side, and is associated with cephalization for coordinated movement.
Step-by-step explanation:
Bilateral symmetry refers to a type of symmetry in biological organisms where the body can be divided into two equal right and left halves along a single plane, commonly known as a midsagittal plane. This symmetry is a characteristic feature of many animals, including humans, butterflies, and crabs.
The concept of bilateral symmetry suggests that these organisms have a distinct head (anterior) and tail (posterior), as well as clearly defined dorsal (back) and ventral (front) sides. Furthermore, this symmetry is associated with cephalization, where sensory structures and nerve tissues are concentrated at the anterior end of the organism, facilitating coordinated movements and behaviour. Bilateral symmetry is highly beneficial for active and directional motion, as opposed to radial symmetry, which is more common in stationary or sessile aquatic organisms.