We present the possibility to trap cells (mouse fibroblasts, bovine spermatozoa and diatoms), to manage their position and to induce rotation, by using optical tweezers. The aim is to place them in desired positions, in order to record holographic images in a microscope configuration. Then we are able to recover the 3D shape and to calculate the biovolume of the cells starting from the reconstructed quantitative phase maps (QPMs).