As both flagella and cilia are structural components of the cell, and are maintained by microtubules, they can be considered part of the cytoskeleton. Though eukaryotic flagella and motile cilia are structurally identical, the beating pattern of the two organelles can be different. The importance of cilia is evident from their involvement in many diseases, called ciliopathies. On the other hand, flagella are longer and there are fewer flagella per cell (usually one to eight). Cilia are short and more numerous than flagella. Some components, such as carbon monoxide (CO), hydrogen cyanide (HCN), and Each individual cilium has a microtubular backbone called a ciliary axoneme, and this is surrounded by a plasma membrane. Cilia (singular: cilium) are microscopic, hair-like structures that extend outwardfrom the surface of manyanimal cells. These components have specific functions and most of them are found on the apical surface of epithelial cells. Long hair- like projections of the plasma membrane with cores made up of microtubules are known as cilia. They are also the structural components of flagella and cilia. There are two types of cilia: motile and non-motile cilia. Cilia are smaller, grouped appendages found in micro-organisms and plants. The main purpose of these organelles is to aid in motility, or movement, of the organism they are attached to. Primary cilia contain a microtubular axoneme that is used as a railway for transport of both structural components and signaling proteins. For cells anchored in a tissue, like the epithelial cells lining our air passages, this moves liquid over the surface of the cell (e.g., driving particle-laden mucus toward the throat). Cilia Structure. This can include movement of the cell itself, or of other substances and objects past the cell. In cilia and flagella, the microtubules are organized as a circle of nine double microtubules on the outside and two microtubules in the center. The connecting cilium of the photoreceptor outer segment is a specialized type of cilium that shares many features and components with motile cilia and primary cilia , and many genes liked to retinopathy encode proteins that localize to the connecting cilium . Sometimes cilia help move along substances external to the cell. While motility are key functions, cilia and flagella possess many other functions. Primary cilia are highly conserved sensory organelles that extend from the surface of almost all vertebrate cells. Flagella are found in bacteria as well as in eukaryotes. They are made from the same basic components, but differ subtly in their construction and thus in their appearance.