Symmetry in biology#Radial symmetry

The Radiärsymmetrie (also rotational symmetry ) is a form of symmetry, in which the rotation of an object takes to cover a certain angle to a straight line ( axis of rotation, axis of symmetry ) the object back to itself. This axis passes through the area or volume of the object - focus. This is called an n -fold radially or rotational symmetry when rotated by 360 ° / n, the object maps to itself. For example, equilateral triangles are triple radial symmetry and possess a symmetry axis perpendicular to the triangle plane to image when turned by 120 ° and 240 ° on itself.

Some radiärsymmetrische objects are displayed in rotation by an arbitrary angle back on itself, such as the circle, the sphere, the cylinder, or cone. This is called rotation symmetry. If the rotation is possible at any angle and any axis, so that the object is mapped to itself, then it is called radial symmetry.

In the two-dimensional projection (picture or drawing) the Radiärsymmetrie is retained when the symmetry axis is perpendicular to the projection plane, ie it depends only on the angle (see Figure jellyfish and coral skeleton ).

Examples of rotational symmetry can be found among others in the art ( Maltese cross, gear, armature laminations for electric motors ), art ( capitals ) and the morphology of living creatures.

Biology

In biology we mean by Radiärsymmetrie a three - or mehrzählige rotational symmetry.

Radial symmetry are many cnidarians and most echinoderms ( Penta symmetry; fünfzählig ). From the Radiärsymmetrie the Disymmetrie (2 planes of symmetry; Ctenophora ) and the bilateral symmetry ( a plane of symmetry; bilaterian ) distinguished.

In botany Radiärsymmetrie often occurs in the construction of the flowers; Here are some examples of different multiplicity:

• 3 planes of symmetry: Frog Bite
• 4 planes of symmetry: bloodroot
• 5 planes of symmetry: Bellflower
• 6 planes of symmetry: autumn crocus.

One also speaks of aktinomorphen flowers, unlike disymmetrischen flowers ( Bleeding Heart, cruciferous vegetables ) that have two planes of symmetry, and zygomorphic and dorsiventral flowers ( orchids, Lamiaceae ), which have only one plane of symmetry.

• Geometry
• Morphology