If you ask them to turn their mind to something, chances are they'll readily recall all the information you're wanting on the subject at that one time. Put all the questions in one category on one area of the form, so that the layout reinforces the relationship between the questions. If possible, separate that area from the other areas. You can use, for example, a double line or a solid line - one that is thicker than the lines used within the categories. But don't mark it off too much, or the form will look disjointed.
White space is very important because it is where the eye rests.
The white space and the areas of text work together to create the overall look and the contrast between them can be used to reinforce the structure of the form. In general, therefore, there needs to be sufficient white space to serve this purpose. If you put each category of information into separate areas using one of these means, you will create a visual structure that will be immediately apparent to the reader. And, if you number the questions as well, the structure will be reinforced, you will be able to 'point' the reader to particular questions and readers will be alerted if they do inadvertently miss a question out. The logical sequence of the areas is also important.