Not all groups of eubacteria have peptidoglycan, so all eubacteria may be classified as either Gram-positive (able to bind Gram's stain) or Gram-negative (unable to bind Gram's stain).
A portable DVD player is in the shape of a rectangular prism. A soccer ball is in the shape of a truncated icosahedron. These shapes are all examples of polyhedra. A three-dimensional shape whose faces are polygons is known as a polyhedron. This term comes from the Greek words poly, which means many, and hedron, which means face.. So, quite literally, a polyhedron is a three-dimensional object with many faces.
A polyhedron is said to be convex if its surface (comprising its faces, edges and vertices) does not intersect itself and the line segment joining any two points of the polyhedron is contained in the interior or surface. A polyhedron is a 3-dimensional example of the more general polytope in any number of dimensions.olyhedra with congruent regular faces of six or more sides are all non-convex, because the vertex of three regular hexagons defines a plane. The total number of convex polyhedra with equal regular faces is thus ten, comprising the five Platonic solids and the five non-uniform deltahedra.