Body plan in which only a single imaginary line can divide the body into two equal halves.

• A. Radial symmetry
• B. Asymmetry
• C. Bilateral symmetry
• D. Spiral symmetry

Answer: (C)

Understanding symmetry in body plans helps explain how organisms are built and move. A body plan where only one imaginary plane can divide the body into two equal halves is bilateral symmetry. This means there is a single plane that splits the body into left and right sides that are mirror images, and the organism is usually organized forward-to-backward with a head region and a defined front. This arrangement supports directional movement and the development of paired structures and a distinct head, which many animals use for sensing the environment.

Radial symmetry, on the other hand, has many planes of division through a central point, so you could cut along several different lines and still get similar halves—think of a jellyfish or a starfish. Asymmetry describes bodies that don’t have a mirror-image division at all, like some sponges. Spiral symmetry isn’t a typical way to describe an overall body plan for most animals; it’s more about shapes that coil around an axis, such as certain shells, rather than how the body itself is divided into halves.

So the defining feature here is a single imaginary plane that creates two equal, mirror-image sides—bilateral symmetry.