Prebiotics and probiotics are different, but they have benefits in common. Both improve intestinal flora, vitamin absorption and the immune system.
Prebiotics are soluble fibers that stimulate intestinal flora. 
they increase the volume of the fecal cake, helping with constipation and decrease the absorption of cholesterol and glucose in the intestine. An example of prebiotics are fructooligosaccharides (FOS), which are made up of a sucrose molecule and some fructose. They can protect the intestine against cancer, help control blood glucose and restore the intestine after diarrhea, including reducing its incidence (depending on the cause). FOS are present in foods of plant origin, such as onions, garlic, tomatoes, bananas, barley, oats and wheat.
Probiotics are beneficial bacteria that improve microbial balance 
intestinal tract, prevent and treat diseases. They also increase vitamin B and amino acid levels and increase calcium and iron absorption. They can be found in fermented milk and yogurt. To obtain the positive effects of probiotics, intake of the food sources must be daily. Probiotics normally have a short shelf life and, therefore, must be kept well refrigerated.
Sources:
http://www.rgnutri.com.br/sqv/saude/pdm.php
http://www.dicasdenutricao.com/2010/08/fos-veja-os-beneficios.html