Unit 2. Plant cell mitosis.

In cell biology, the centrosome is an organelle that serves as the main microtubule organizing center (MTOC) of the animal cell. It was discovered by Edouard Van Beneden in 1883 and was described and named in 1888 by Theodor Boveri.The centrosome is thought to have evolved only in the animal lineage of eukaryotic cells. Fungi and plants lack centrosomes and therefore use other MTOC structures to organize their microtubules. Although the centrosome has a key role in efficient mitosis in animal cells, it is not essential.
Centrosomes are composed of two orthogonally arranged centrioles.
http://en.wikipedia.org/wiki/Centrosome

Centrosomes are considered to be the major sites of microtubule nucleation in mitotic cells , yet mitotic spindles can still form after laser ablation or disruption of centrosome function . Scientists examined spindle formation in Drosophila cells after depletion of proteins involved in micotubule nuleation.
Adapted from http://www.cell.com/current-biology/abstract/S0960-9822%2806%2901062-1

Although the major cytoskeletal components are common to plant and animal cells, plants do not possess centrosome-like organelles. Nevertheless, they are able to build spindles and have developed their own specific cytoskeletal arrays: the cortical arrays, the preprophase band, and the phragmoplast.
http://www.sciencedirect.com/science/article/pii/S007476960220008X

1. What is the difference between centrosome and centriole?
   
2. Do plants have centrosomes?
   
3. Do plants build spindles during mitosis? How is that possible if they don't have centrosomes?
   
4. Is the centrosome essential for mitosis? How have scientists proved it?