Fertilization starts with a single undifferentiated cell. As our cells divide and multiply, they begin to group together with other cells similar in size, structure, and function, forming tissues. Let’s discuss our various bodily tissues, beginning with epithelial tissue.ts with a single undifferentiated cell. As our cells divide and multiply, they begin to group together with other cells similar in size, structure, and function, forming tissues. Let’s discuss our various bodily tissues, beginning with epithelial tissue.