Ara copies a paragraph directly from an article she found. She forgets to use quotation marks but she cites the source in her bibliography. Is this plagiarism?

Yes, it is.

Explanation:

In the strictest of terms, even if this was an unwilling omission, it would be considered plagiarism because an objective reader, even if he or she sees the cited reference in the bibliography, that reader will still be unable to figure out what exactly was cited from such source. Without quotation marks, there is no absolute way to differentiate between the source cited and the text around it.