In many scientific fields, but certainly in other types of writing as well, the conclusion indicates relevant questions for further study or exploration. While this might seem to contradict the idea of closure, in fact, the closure on the article or essay usually occurs just before this suggestion, and this suggestion of further research areas serves to provide a large sense of completeness. In many topics of public concern, this "further research" suggestion takes a different form - a call for further awareness of an issue or problem.
For some expository and argumentative essays, it’s appropriate to end with a call to action as your last sentence. For example, if you’re writing an informative essay about the sea creatures that live in the very deepest parts of the ocean, you may close with a sentence like this: “It’s clear that today’s scientists should continue to observe and document these mysterious creatures, so we may all learn more about life at the bottom of the ocean.” A call to action like this can make your reader feel inspired and informed after reading your essay.