The question touches on a central problem of teaching Biology at IB.

We have to accept that there isn't time to teach students absolutely everything known about the human body. There are many things which would help our understanding that we never mention while teaching IB.

For example we don't teach;

• hormonal control of salt secretion/excretion,
• the role of aquaporins in membrane transport.

Both would give us a more complete understanding of the homeostasis of water and salt crutial in the functioning of the kidney.

In my experience there are some teachers (and some students) who feel more comfortable with a more full explanation so they can see why certain things happen (it helps them to remember the concepts) and there are others who prefer to keep the Biology content to the specific details mentioned within the guide.  The IB Biology guide is already a lot for some students to understand and learn. I think the same is true of text book writers too, perhaps with the exception of Andrew Allott who has written two books, an enormous complete guide and a thinner revision guide.

I love learning about all the details myself but I find the amount of content already quite a lot to cover in two years. So, I try to refrain from going over the top, and to help keep my students notes as simple as possible, while still enabling grade 7 achievement. However, when I get a chance, I try to show my students some "awe & wonder".  I still believe that living things are amazing and I try to share this with an occasional burst of over-enthusiasm, a superb 3D animation of some molecular mechanism or an awesome video of lyre bird capable of imitating a chainsaw or a mobile phone. 

I think the IB Guide tries to get a balance between an understanding of the amazing complexity of the human body, the living world and all the other aspects of the subject and the reality of 3.5 hours per week for 50 weeks of study.

So to answer Asli's first question, how much detail to give in an explation of the hormones of the menstrual cycle? I think you have to decide if the GnRH is really needed for your students to understand the menstrual cycle hormones.  Include it if you do, or leave it out if you don't. Personally I think I could tell students correctly that the hypothalamus controls the pituitary gland, and that estrogen causes an increase in FSH secretion which enhances production of estrogen without any mention of GnRH. This explanation would achieve high marks in an exam question, so I reason that it is enough.

If I had a keen student who liked understanding more I might point them to a text book or a medical school video which explains the fuller details very well.  This type of thing often forms part of an Activity 3 in the lesson plans on the Inthinking Biology site. However, I wouldn't want the whole of my mixed ability class to worry about these extra details.

There is one last consideration before abandoning GnRH completely, whether or not your class are going to study Option D.  The role of "releasing hormones" in the control of the anterior pituitary is covered in the HL section of Option D (see the summary  diagram at the top of this blog post). If you plan to do this option and all your class are HL students then it may be best to mention them here. But that's a question about planning a route through the IB Guide which will have to wait until another time.

If anyone can think of other examples of important details which are not mentioned in the IB Biology guide please mention them in the comments below.