Unlike when you were in high school or an undergraduate, people who read your scientific article will most likely actually read at least some of the articles cited in your bibliography. The quality of your research is no stronger than the quality of the articles you use to support it. If you are supporting a statement with a citation you found in Google Scholar, remember that Google Scholar searches through basically all "academic" journals. However academic journals are not created equally. Roughly 50% of journals defined as "academic" are actually predatory journals that contain essentially worthless articles. There is a lot of money to be made by publishing a predatory journal and those publishers do a great job of making their journal and their articles look legitimate.
If, however, you use a database that individually selects which journals' content it provides, you will greatly improve your chances of finding higher quality articles.
Therefore, if you choose to use Google Scholar, ensure that any article you choose to cite is from a reputable lab and a reputable journal (because, if you found it on Google Scholar, you've got an ~50/50 chance that the article you found is from a predatory or exceptionally low quality journal).
Plagiarism is common (both intentional and unintentional). Plagiarism.org indicates that all of the following are considered plagiarism:
For more information on plagiarism, visit OSU Libraries Plagiarism page.