What is bilateral symmetry? Give an example.

Hint: A symmetry is all about shape and distribution of parts on the body. In the animal kingdom, animals are classified on the basis of symmetry. The multicellular organisms show some level of symmetry. They can be asymmetric, bilateral symmetrical or radially symmetrical.

Complete answer: The bilateral symmetry is present in most of the animals. In this kind of symmetry, the line divides the body into two equal halves. The right and left sides of the body are exactly the mirror image of each other. This is the characteristic of organisms that are free moving. An example of bilateral symmetry is seen in human beings. The line of symmetry running longitudinally (from head to tail) through the centre divides the body into two similar parts externally. The distribution of internal organs does not follow the symmetric pattern. The bilateral symmetry occurs due to the expression of genes. The advantage of bilateral symmetry is that it facilitates the formation of the head and tail region. The head is the centre of the nervous system. This kind of symmetry helps in movement which is more directional and helps the organism to move straight forward. The other organisms showing bilateral symmetry are butterfly, turtle, crab, etc.

Note: Asymmetric animals are animals like sponges which do not show any kind of symmetry. The radial symmetry is present in animals in which the plane along the vertical axis cuts the animal into two halves but with no definite left and right side. The radial symmetry is seen in jellyfish.