Is It or Is It Not Plag iarism/cheating?

The following four incidents were brought to a college judicial-review board to determine if a student had After reading this case, would you share an honest opinion to the questions please. And please explain why so I can absorb and get the step by step full understanding of what is trying to be convey.

A student turned in an essay that included substantial material copied from a published source. The student admitted that he didn't cite the source properly, but argued that it was because he misunderstood the directions for the assignment, not because he was attempting to steal someone else's ideas.

Is this plag iarism/cheating?

How severe is it? (Rate it on a scale from 1 = low to 5 = high)

What should the consequence or penalty be?

How could this accusation of plag iarism/cheating been avoided?

2. A student turned in a paper that was identical to a paper submitted by another student for a different course.

Is this plag iarism/cheating?

How severe is it? (Rate it on a scale from 1 = low to 5 = high)

What should the consequence or penalty be?

3. A student submitted a paper he wrote in a previous course as an extra-credit paper for a course.

Is this plag iarism/cheating?

How severe is it? (Rate it on a scale from 1 = low to 5 = high)

What should the consequence or penalty be?

4. A student submitted a paper in an art history class that contained some ideas from art critics she read about and whose ideas she agreed with. The student didn't cite the critics as sources, but claimed it wasn't plag iarism/cheating because their ideas were merely their own subjective judgments or opinions, not facts or findings; furthermore, they were opinions she agreed with.

Is this plag iarism/cheating?

How severe is it? (Rate it on a scale from 1 = low to 5 = high)

What should the consequence or penalty be?

How could this accusation of plagiarism been avoided?

Looking back at these four cases. Which represents the most and least severe violation of academic integrity? Why?