Question
Using simple wording and terms could you please explain why inter-relationships between living organisms are important in organic horticulture?

Answer
Hi Jen ... Sorry for the delay in answering.  I have been out of pocket for a while.  I like where Ike hit and it's been pretty crazy around here.
To answer your question:  The interrelationship of living organisms are important in organic gardening because all things working together correctly in that environment enables a balanced system and yields favorable results.  It's actually a pretty complex and long answer if you need more specific details.  A great book is "Trace Elements in Soil and Sand" by Alina Kabata-Pendias.  If you google this, you will be able to read excerpts that I think will help you understand the concept without having to purchase the book.