Most readers of English come to any piece of formal or academic writing with certain expectations about paragraphs:
Paragraphs will begin and end with important information.
The topic sentence will often let readers know what a paragraph is about.
A paragraph will make sense as a whole; its words and sentences will be clearly related.
A paragraph will relate to the paragraphs around it.
In academic writing, readers expect paragraphs to be unified, well developed, and coherent. A paragraph should focus on one main idea; the main idea should be developed fully and supported with specific details; and the paragraph’s parts must be clearly related.