A bunch of cells make up tissue. A bunch of tissue makes up organs. A bunch of organs make up an organ system. And an organ system makes up a human. If cells are damaged, it would effect the tissue and the organ because cells make up tissues, which make up organs. Cells are the basic element of humans and everything in them. So when cells are damaged and can't function, then it affects what they make up as well. Just like if a permanent marker bleeds through one page, then it also bleeds through the rest of the pages, damaging them because the are all together.