If you write some tips for prospective users, these will also appear on the Teacher's Guide. Cells carry on the many functions needed to sustain life. They grow and divide, thereby producing more cells. This requires that they take in nutrients, which they use to provide energy for the work that cells do and to make the materials that a cell or an organism needs. Disease is a breakdown in structures or functions of an organism.
Some diseases are the result of intrinsic failures of the system.
Variation in these structures are common and are passed to the next generation through reproduction. There is no intent to reflect in any way on any person or organization mentioned herein.