Membrane models — According to the fluid mosaic model, what best describes the nature of biological membranes?

Introduction:
The fluid mosaic model is a cornerstone of membrane biology. This question assesses whether you can articulate the model's central idea: lateral fluidity of lipids and proteins forming a dynamic, heterogeneous mosaic.

Given Data / Assumptions:

• Typical eukaryotic plasma membrane.
• Key components: phospholipids and proteins; carbohydrates are present as glycoconjugates.

Concept / Approach:
In the model, a phospholipid bilayer provides a fluid matrix into which proteins are inserted. Proteins and many lipids diffuse laterally; composition varies by membrane domain and leaflet.

Step-by-Step Solution:

Verification / Alternative check:
Experiments such as FRAP (fluorescence recovery after photobleaching) demonstrate lateral diffusion of membrane proteins and lipids, validating the fluid aspect of the model.

Why Other Options Are Wrong:

• Proteins most common: by count and area, lipids dominate; proteins are abundant but not the majority by molecule number.
• Structure from protein–water interactions: the bilayer self-assembles from lipid amphipathic properties, not primarily protein–water interactions.
• Properties determined by phospholipids alone: protein composition strongly shapes function.
• Rigid lattices: contradicts extensive evidence for mobility.

Common Pitfalls:
Equating fluidity with randomness; membranes have microdomains and cytoskeletal fences that regulate diffusion without eliminating overall fluid behavior.

Final Answer:
the membrane is a highly mobile mixture of phospholipids and proteins.