Question

Give the difference between the two types of symmetry that animals show.

(a) (i) Bilateral symmetry: Organisms having the same design on the left and right halves of the body are called bilateral symmetrical.

    (ii) Radial symmetry: Organisms with a body design such that it can be divided into two equal halves from any radius are known as radially symmetrical.

(b) (i) Bilateral symmetry: Organisms with a body design such that it can be divided into equal halves from any radius are known as bilateral symmetrical.

     (ii) Radial symmetry: Organisms having the same design on the left and right halves of the body are called as radially symmetrical.

(c) (i) Bilateral symmetry: Organisms having a different design on the left and right halves of the body are called as radially symmetrical.

    (ii) Radial symmetry: Organisms with a body design such that it can not be divided into two equal halves from any radius are known as radially symmetrical.

(d) None of these.

Answer 1

Hint: bilateral means something having or relating to two sides or affecting both sides. Radial in anatomy is something relating to the radius of the body. The image or body that cannot be divided into identical halves is asymmetrical.

Complete step by step answer:
Bilateral symmetry: Organisms having the same design on the left and right halves of the body are called bilateral symmetrical.
Radial symmetry: Organisms with a body design such that it can be divided into two halves from any radius are known as radially symmetrical.
- Some organisms in which radial symmetry is found are sea stars, sea anemones, jellyfish, etc.
- Some examples of bilateral symmetry are octopuses, crustaceans, insects, spiders, etc.
- A symmetrical organism (showing symmetry) would have a balanced distribution of the duplicate parts on each side of the axis.
- Special forms of radial symmetry are tetramerism (having four identical parts around the central axis) and pentamerism (with five identical parts around the central axis) .
- Biradial symmetry is the combination of radial and bilateral symmetries. Example: ctenophores (comb jellies) .
- The plane of symmetry that divides a bilateral animal into two symmetrical halves is called the median, longitudinal, or sagittal, plane.
- A flower is considered as symmetrical when each whorl consists of an equal number of parts or when the parts of anyone whorl are multiples of that preceding it. Example- a symmetrical flower will have five sepals, five petals, five stamens, and five carpels, or the number of any of these parts may be a multiple of five.

So, the correct answer is ‘(a) (i) Bilateral symmetry: Organisms having the same design on the left and right halves of the body are called as bilateral symmetrical, (ii) Radial symmetry: Organisms with a body design such that it can be divided into two equal halves from any radius are known as radially symmetrical.’

Note: In the case of radial symmetry, the sides exhibit correspondence or regularity of parts around a central axis. It lacks the left and right sides. Relatively fewer animals exhibit radial symmetry while the bilateral symmetry is the most common symmetry found in organisms.