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23 Dec 2025

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2 pages

AS Level Biology: Understanding Cell Membranes

Bethan Jones

@bethanjones_jdhy

Cell membranes are the crucial gatekeepers of our cells, controlling... Show more

Structure of the Cell Membrane

The cell membrane follows a fluid-mosaic model, where components are in constant motion. Picture a sea of phospholipids arranged in a bilayer with proteins floating within it like icebergs. These phospholipids aren't fixed in position—they move freely around each other, their tails flowing in continuous motion.

At its core, the membrane consists of a phospholipid bilayer with hydrophilic $water-loving$ heads facing outward toward watery environments and hydrophobic $water-fearing$ tails tucked safely inside. Cholesterol molecules weave through this structure, providing stability while maintaining flexibility.

Proteins embedded within the membrane come in two types: intrinsic proteins (which span the entire membrane) and extrinsic proteins (which attach to the surface). These proteins serve various functions including transport, communication, and identification.

Did you know? When phospholipids are placed in water, they naturally form structures called micelles or monofilms depending on conditions—this self-organizing property is fundamental to how cell membranes formed during evolution!

Cell Membrane Functions and Transport

Your cell's identity is established through unique combinations of glycoproteins and glycolipids on the membrane surface. These carbohydrate-attached molecules create a distinctive cellular "fingerprint" that helps your immune system distinguish between "self" and "foreign" cells—crucial for fighting infections.

Cell membranes serve six vital functions: controlling substance entry/exit, containing cellular contents, enabling communication, hosting chemical reactions, maintaining cell shape, and facilitating internal transport. Think of them as multifunctional barriers rather than simple walls.

The membrane regulates traffic of essential substances including water, respiratory gases, nutrients, ions and waste products. This selective permeability ensures your cells receive what they need while removing what they don't. Additionally, specialized cells can secrete important molecules like hormones and enzymes through their membranes.

Remember this: Every cell in your body contains approximately 10 billion membrane molecules, yet each cell type has a unique membrane composition tailored to its specific function!

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23 Dec 2025

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2 pages

AS Level Biology: Understanding Cell Membranes

Bethan Jones

@bethanjones_jdhy

Cell membranes are the crucial gatekeepers of our cells, controlling what enters and exits while maintaining cellular identity. This sophisticated boundary is not just a static wall, but a dynamic, fluid structure teeming with activity at the microscopic level.

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Structure of the Cell Membrane

Did you know? When phospholipids are placed in water, they naturally form structures called micelles or monofilms depending on conditions—this self-organizing property is fundamental to how cell membranes formed during evolution!

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Cell Membrane Functions and Transport

Remember this: Every cell in your body contains approximately 10 billion membrane molecules, yet each cell type has a unique membrane composition tailored to its specific function!