The defender has admitted that his side face a tough task to make it to the final, but is refusing to throw in the towel just yet
The Catalan giants were unable to contain Bayern on Tuesday as they fell to a 4-0 defeat, with Thomas Muller (2), Mario Gomez and Arjen Robben helping the Bundesliga champions to a sensational victory.
But Bartra is still clinging on to the hope that Barca can draw upon the same spirit that saw them beat AC Milan 4-0 in the second-leg of their last 16 tie after losing the first leg 2-0.
"We are very disappointed after that defeat, it was not easy at all out there. We have to try to remain optimistic even though tonight's result makes things complicated," Bartra told Uefa.com.
"We will go into the second leg knowing what we managed to do against AC Milan [which was to win 4-0]. The fans will come to support us and for them and for the club we will give a huge effort in the return.
"We knew Bayern were good physically but we have to be self-critical now and learn from our mistakes. It was not our night but let us hope the next one is ours."
The return takes place at Camp Nou on May 1.