If primers amplify a specific region of DNA, and the same DNA is present throughout the body, can a single primer be used across different cell lines and different organs from the same species?
As long as your DNA extraction protocol has removed any DNA binding proteins then the primers should work. Assuming all the cell lines and organs come from the same individual or there is not large heterogeneity at the primer binding sites.
Generally, the answer is yes, especially for model organisms that have been inbred for many generations. But you should talk with your research advisor about any known difficulties (e.g. polymorphisms, indels, etc).