Cells can interact with other cells?

Yes. Cells have 'cell receptors' that are used to receive messengers like hormones to communicate. Cell receptors have specific shapes that fit the shape of the messenger that they want to receive. Organs like the pancreas send our these messengers to the cells to order them to do different functions.

an adaptation is a change or process by which an organism takes to be better suited for its environment. for example; migration is a behavioral adaptation, this is needed because birds are not built to last extremely cold climates. there are different adaptations because there are different species needing to adjust to different things, bears don't migrate; they hibernate.

organ system-an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.