In GCSE Science, how organisms use nerves and hormones is one subject that is looked at. This is the third of five quizzes on that topic and it looks in particular at hormones, where they are produced, the effects that they have and their possible uses.
Hormones are chemical messengers in the form of protein molecules that are produced in endocrine glands. These enter the bloodstream and can therefore reach every cell in the body. Hormones cause effects to occur in certain cells, but not every cell reacts to every hormone.
In order for a hormone to have effects on cells, those cells must have the right receptor molecules on the surface of their cell membrane. The hormone (protein) molecules will only bind to those cells that have the correct receptor molecules. When this happens, the hormone affects enzymes within the cell, affecting its function.