Symmetry In Biology

Biological symmetry refers to the symmetry found in organisms, including plants, animals, fungi, and bacteria. Specifically, symmetry refers to correspondence of body parts, in size, shape, and relative position, on opposite sides of differentiation or distributed around a central point or axis. External symmetry are often easily seen by just gazing at an organism. Most other organisms can generally be classified in three groups with relevance symmetry type.

Certain animals, particularly most sponges and therefore the ameboid protozoans, lack symmetry, having either an irregular shape different for every individual alternatively one undergoing constant changes of form. Internal features can even show symmetry, for instance, the tubes within the physical body (responsible for transporting gases, nutrients, and waste products) which are cylindrical and have several planes of symmetry. The overwhelming majority of animals, however, exhibit an exact symmetrical form; Four such patterns of symmetry occur among animals: spherical, radial, biradial, and bilateral.

Every straight cut through the center point of a sphere splits it into mirror-image sections in spherical, or point-symmetry. Point symmetry often referred to by biologists as universal symmetry and is seen in some floating animals with radiating parts, such as the Radiolaria order single-cell protozoans. The spherical form of symmetry is only possible in minute animals with simple internal construction, as in spheres the interior mass is high relative to the surface area and is too high for efficient functioning with size and complexity increase.

Radial, or line, symmetry, as exemplified by a cone or a disk that’s symmetrical a few central axis, is very suitable for sessile or floating animals. the most axis is heteropolar i.e., with unlike ends, one in all which bears the mouth and is termed the oral, or anterior, end, and also the other of which, called the aboral, or posterior, end, forms the bum of the animal and should bear the anus. Sessile organisms such as the sea anemone, floating organisms such as jellyfish, and slow-moving organisms such as sea stars, or starfish, show radial symmetry.

In addition to the anteroposterior axis, there are also two other axes or planes of symmetry at right angles to it and to each other in biradial symmetry: the sagittal, or median, vertical-longitudinal, and the transverse, or cross-axis. The biological group with the foremost obvious biradial symmetry is that the ctenophores; in ctenophores, the two planes of symmetry are (1) the plane of the tentacles and (2) the plane of the pharynx. Biradial symmetry occurs within the comb jellies.

In plane or bilateral symmetry, a particular plane, called the sagittal plane, divides the body into two equal halves, usually right and left halves which are each other’s mirror images. All bilaterians have some asymmetrical features, for instance, the human heart and liver are positioned asymmetrically despite the body having external correspondence. Bilateralism is characteristic of the overwhelming majority of animals, including insects, fishes, amphibians, reptiles, birds, mammals, and most crustaceans. Flowers like orchids and sweet peas are bilaterally symmetrical.

Actually, biological symmetry is thought of as a balanced distribution of duplicate body parts or shapes within the body of an organism. The concept of symmetry is additionally applied in botany. Importantly, unlike in mathematics, symmetry is always approximate in biology; it is one class of patterns in nature, whereby the pattern element is almost repeated, either by reflection or rotation. A flower is deemed to be symmetrical if each whorl consists of an equal number of parts or if the parts of anyone whorl are multiples of those that precede it.

While sponges and placozoans represent two groups of animals that show no symmetry (i.e. asymmetric), some form of symmetry exhibits, and is defined by, the body plans of most multicellular organisms. Thus, the asymmetrical flower may have five sepals, five petals, five stamens, and five carpels, or the quantity of any of those parts could also be a multiple of five. The importance of symmetry is illustrated by the very fact that groups of animals have traditionally been defined by this feature in taxonomic groupings.


Information Sources:

  3. wikipedia