Cilia and flagella are hair-like outgrowths of the cell membrane. Clia are smaller structures while the flagella are longer. They are formed basal bodies which are centriole-like structures. Both help in movement of cell. The cilium and flagellum are covered with plasma membrane. They have a core called axoneme which has nine pairs of doublets of radially arranged peripheral microtubules and a pair of centrally located microtubules. This arrangemt of microtubules is calld 9+2 array. The central tubules are covered by a sheath and are connected to each other. The sheath is connected to one of the tubules of the peripheral doublet by a radial spoke. There ate nine radial spokes in total. The linkers connect the doublets to each other.
Receptor molecules are specific proteins in the cell's plasma membrane that receive chemical signals from outside the cell. When such chemical signals bind to a receptor, they cause some form of cellular response.