A minor detail -- the best bet is the X9 bus, which takes about 20 min to get from TXL to Bahnhof Zoo
You can work out ground travel itineraries on the Deutsche Bahn website (
www.db.de). Here's an example for your itinerary from Flughafen-Tegel, Berlin to Frankfurt(Oder):
Flughafen Tegel, Berlin 15:35 - 15:56 Bus X9 to Zoologischer Garten DB
Berlin Zoologischer Garten 16:11 - 17:28 RE 38085 (RegionalExpress train) to Frankfurt (Oder).
Best,
-jpm