Cell Membrane Structure and Function

Cell Membrane Structure

• Cell membranes are composed of lipids and proteins.
• They form a bilayer, with two layers of phospholipids arranged to face each other.
• Phospholipids have hydrophilic heads (water-loving) and hydrophobic tails (water-fearing).
• The heads face the watery environment inside and outside the cell.
• The tails face away from the water and towards each other.

Fluid Mosaic Model

• The fluid mosaic model describes the structure of the cell membrane more accurately.
• The membrane is fluid because the components (phospholipids and proteins) are not fixed in place but can move around.
• The membrane is a mosaic because of the diverse components embedded within it.
• The structure includes integral proteins, peripheral proteins, cholesterol, and glycoproteins/glycolipids.
• The bilayer of phospholipids is the main component.

Membrane Permeability

• Cell membranes are semipermeable, meaning that they only allow certain substances to pass through.

Passive Transport: Diffusion

• Diffusion is the movement of liquid or gas molecules from an area of high concentration to an area of low concentration across a semipermeable membrane.
• This is a passive process that does not require energy.

Passive Transport: Osmosis

• Osmosis is the diffusion of water across a semipermeable membrane.
• Water moves from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration).

Types of Solutions

• Hypertonic solution: Contains a higher concentration of solutes than the cell. Water moves out of the cell, causing it to shrink (plasmolyze).
• Hypotonic solution: Contains a lower concentration of solutes than the cell. Water moves into the cell, causing it to swell and potentially burst (lyse).
• Isotonic solution: Contains the same concentration of solutes as the cell. There is no net movement of water.

Active Transport

• Active transport moves molecules against their concentration gradient (low to high).
• This requires energy in the form of ATP.
• The sodium-potassium pump is an example of active transport in cells.

Bulk Transport

• Bulk transport moves large molecules across the membrane.
• Exocytosis: Releases large molecules out of the cell.
• Endocytosis: Takes large molecules into the cell.
• Types of Endocytosis includes Receptor-Mediated Endocytosis: takes specific molecules into the cell using receptors.

Facilitated Diffusion

• Facilitated diffusion moves molecules across the membrane using carrier proteins.
• This is a passive transport method that doesn't require energy.

This quiz explores the structure, composition, and function of cell membranes, including the fluid mosaic model and membrane permeability. Test your understanding of key concepts such as phospholipids, passive transport, and diffusion. Ideal for biology students to reinforce their knowledge of cellular structures.