The Basics of Cellular Biology

A cell is the smallest independently functioning unit of life. Cells are effectively made up of a number of different organelles, plus membrane, plus cytoplasm and a few other things. Tissues are an ensemble of cells, so a group of cells that act together to form a common function. Organs are collections of tissues joined together in a single structural unit to serve a commonfunction. The highest level within organisms is organismal; this is the most familiar with biology but it's also the hardest to define.