Cells there are many different kinds of cells, some can be big and some can be very small. One of the first person to describe a cell is Hooke. All cells have cell membranes, organelles, cytoplasm and DNA. The smallest unit that can perform is a cell the basic cells are prokaryotic and eukaryotic.  Cells can also form tissues, tissues are a group of similar cells that perform a common function. Organs collection of tissues that carry out a specialized function of the body. A organ system is a group of organs that work together to perform a body function. The cells form tissues tissues form organs organs form organ system. A structure is the special normal or proper activity or an organ part.