Why do we usually use EC50 for cell-culture experiments (cells grown in a Petri dish) but use ED50 for animal studies or

[answerhappygod]

Why do we usually use EC50 for cell-culture
experiments (cells grown in a Petri dish) but use
ED50 for animal studies or use in
humans? (Hint: Both can be used to generate the same
graphs and the same data, the key is what the C and D stand
for.)
Please help me understand why one has the use in animals versus
the other in humans. The last person that tried to answer my
question gave me a very basic answer and I wasted a question.