The correct answer is: B. Unit membrane
A unit membrane is a biological membrane that consists of a lipid bilayer with embedded proteins. It is the basic structure found in all membranes such as those of mitochondria and chloroplasts.
The lipid bilayer is a two-layer sheet of phospholipids, with the hydrophobic tails of the phospholipids facing each other and the hydrophilic heads facing the water on either side of the membrane. The proteins are embedded in the lipid bilayer, and they perform a variety of functions, such as transporting molecules across the membrane, sensing changes in the environment, and catalyzing chemical reactions.
The unit membrane is a dynamic structure, and it can change its shape and composition in response to changes in the environment. This allows the membrane to carry out its many functions in a variety of conditions.
The other options are incorrect because:
- Option A, nuclear membrane, is a membrane that surrounds the nucleus of a cell. It is composed of two lipid bilayers with embedded proteins.
- Option C, plasma membrane, is a membrane that surrounds the cell. It is composed of a lipid bilayer with embedded proteins.
- Option D, cell wall, is a rigid structure that surrounds the cell wall of plant and fungal cells. It is composed of cellulose, a type of polysaccharide.