The material inside a cell membrane, excluding the nucleus, is called the cytoplasm.

Here's a breakdown:

* Cell membrane: The outer boundary of a cell that controls what enters and leaves.

* Nucleus: The control center of the cell, containing the genetic material (DNA).

* Cytoplasm: The gel-like substance that fills the cell, located between the cell membrane and the nucleus. It contains various organelles, including:

* Ribosomes: responsible for protein synthesis

* Endoplasmic reticulum: involved in protein and lipid synthesis

* Golgi apparatus: packages and modifies proteins

* Mitochondria: the powerhouse of the cell, generating energy

* Lysosomes: break down cellular waste

* Vacuoles: storage compartments for water, nutrients, and waste

So, the cytoplasm is essentially the "stuff" within a cell that does the work, excluding the nucleus which dictates that work.