Sunday's home defeat by Wolves condemned the Gunners to their worst start to a season since 1981, losing five of their 10 Premier League games.
They are 14th in the table, with Mikel Arteta set to mark a year in charge.
"We have no excuse. We were really upset and we take responsibility," Bellerin told BBC Football Focus.
"We know what we want to do to win matches and if we don't do it we know it is our responsibility because maybe on that game our attitude wasn't right, or our positioning wasn't right. This is something we have all agreed and it is important we all step up."
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