gen-define-the-structure-of-the-cell-membrane-and-give-one-short-925d

Define the structure of the cell membrane and give one short worked example.

# Structure of the Cell Membrane ## Basic Structure: Fluid Mosaic Model The cell membrane consists of: 1. **Phospholipid Bilayer** (foundation) - Hydrophilic (water-loving) phosphate heads face outward - Hydrophobic (water-fearing) fatty acid tails face inward - Arranged in two layers 2. **Proteins** (embedded or attached) - Integral proteins: span the entire membrane - Peripheral proteins: attached to surface 3. **Cholesterol** (in animal cells) - Maintains membrane fluidity and stability 4. **Carbohydrates** (attached to proteins/lipids) - Form glycoproteins and glycolipids - Important for cell recognition --- ## Worked Example: Oxygen Transport **Question:** Explain how oxygen (O₂) crosses the cell membrane to enter a muscle cell. **Answer:** - Oxygen is a **small, nonpolar molecule** - The hydrophobic interior of the phospholipid bilayer allows nonpolar substances to pass through - Oxygen diffuses **directly through the lipid bilayer** by simple diffusion - Movement occurs from **high concentration** (blood) to **low concentration** (inside muscle cell) - **No protein channels or energy required** for this process This demonstrates the membrane's **selective permeability** based on molecular properties.