Concept:Biological membranes are composed of both lipids and proteins in specific proportions that differ based on species, cell type, and organelle.
Explanation:Biological membranes are semi-permeable barriers surrounding cells and organelles.
They consist of a phospholipid bilayer with embedded proteins.
Lipids provide fluidity and the basic structural framework.
Proteins function as channels, receptors, enzymes, and transporters.
The exact combination of lipids and proteins is unique to each species, cell type, and organelle.
Some membranes also contain carbohydrates attached to proteins and lipids (glycoproteins and glycolipids).
Option B (lipids only) is incorrect because proteins are essential components.
Option C (proteins only) is incorrect because lipids form the main structure.
Option D (none of the above) is wrong since the membrane has both lipids and proteins.
Answer:Option A: Lipids and proteins in varying combinations which are specific to each species, cell type and organelle.