The standards are set by the kind of Academic Writing that appears in peer-reviewed Journals. This is an important way for scholars (academics) to set out their latest ideas and research. Their work always builds on a body of earlier research and authors are careful to show how their ideas have developed and to acknowledge the sources of their inspiration and evidence. In turn, this new writing enters "the public domain" and becomes available as a source of inspiration to more scholars (including you).
You need to see your work as part of this developing "web" of ideas - it does not exist in isolation but should link itself to what other writers and thinkers have said and written. Careful referencing allows you to do this and will earn you marks.
If you don't do your own research and don't express your own ideas and interpretations (because you have copied or bought an essay or part of an essay) or if you fail to reference your sources carefully, you may be accused of plagiarism. Universities prefer to trust their students to be honest about the work they are submitting but most UK Universities (including Exeter and Falmouth) now use software such as Turnitin to help them detect copied work.