Models of an axiomatic system are isomorphic if there is a one-to-one correspondence between their elements that preserves all relations. That is, the models are abstractly the same; only the notation is different. An axiomatic system is categorical if every two models of the system are isomorphic.
The Nucleus. The largest and most clearly visible of the cell's constituents is the nucleus. Within the nucleus, DNA molecules, the cell's genetic machinery, are stored, repaired, transcribed and eventually replicated. Around the outside of the nucleus is an envelope consisting of two layers of membrane.
These are the nucleus, the cytoplasm, and the cell membrane. The cell membrane is the outer-boundary of a cell, and it contains various channels to let materials into and out of a cell. The nucleus is at the center of the cell, and it is home to all of a cellâs chromosomes, or genetic material.The cytoplasm, then, is basically everything else.he cell membrane is the outer-boundary of a cell, and it contains various channels to let materials into and out of a cell. The nucleus is at the center of the cell, and it is home to all of a cellâs chromosomes, or genetic material.