Microtubule are looks like minute tubules.
Discovery: Ledbetter and Porter in 1963 discovered microtubules.
Structure: They are long, unbranched, hollow tubular and usually, a diameter of 10 to 20 mμ.
(i) It gives mechanical support to cytoplasm.
(ii) It forms spindle fibres during cell division
(iii) It accelerates movement of water and different ions outside and inside the cell.
(iv) It plays a mentionable role in keeping the size of cell
(v) Cytoplasmic organelles are attached to microtubules.