Plant cells and animal cells share a common ancestor and thus many similarities. At the same time, they also exhibit fundamental differences. Unlike animal cells, for example, plant cells lack centrioles.
In animal cells, the centrosome serves to organize microtubules, major components of the cell's cytoskeleton, and plays an important role in cell division. The centrosome is composed of two centrioles, each of which contains nine bundles of microtubules. Microtubules are hollow cylindrical polymers of a protein called tubulin.
Plant cells do not contain centrioles. Their microtubules emanate from structures or regions called microtubule-organizing centers, or MTOCs, but do not have the centrioles found in animal cells.
During cell division, centrosomes in animals act as organizing centers for the microtubules that pull the chromosomes apart, ensuring that each daughter cell receives a copy of each chromosome. Plant cells must accomplish the same task during mitosis, but they do so without centriole-containing centromeres; the microtubules emanate from other MTOCs instead.