I'm currently preparing for the comprehensive exams for my PhD in horticulture. The comprehensive exam process involves taking a series of written exams (one for each of my committee members) followed by an oral exam (where all my committee members grill me on the details of horticulture all at the same time). The entire process can take several weeks to complete and is generally very stressful (no matter how prepared you are). Comprehensive exams are a right of passage for PhD students, so I'm looking forward to getting it over with!
This book isn't particularly enlightening for me (I've heard all this information before). However it has turned into a nice leisurely read that has helped me review some concepts and at least get me thinking about plant physiology in my free time (without it feeling like work). The author, Brian Capon, tends to leave out a lot of the specifics, which makes the book easier to read for non-scientists. These gaps in detail are great for me because I can read a section on a particular topic, fill in the details from memory, and get a little studying in at the same time.