Cell Membrane Structure and Function

Cell Membrane Structure and Function

• Cells are enclosed by a cell membrane, controlling substance entry and exit.
• The membrane is composed of a phospholipid bilayer and embedded proteins.
• Phospholipid molecules allow membrane flexibility due to their movement.
• Proteins are embedded within the phospholipid bilayer, acting as enzymes, receptors, and transport channels.
• The membrane is selectively permeable, allowing some substances to pass easily, others slowly, and some not at all, determined by size and lipid solubility.
• Small, lipid-soluble molecules (oxygen, water, carbon dioxide) pass through the phospholipid bilayer.
• Larger molecules (glucose) require protein channels for transport.
• Specific proteins facilitate transport of specific substances across the membrane.
• Very large molecules cannot cross the membrane.

Diffusion

• Diffusion is the net movement of molecules from an area of high concentration to an area of low concentration.
• It occurs down the concentration gradient (no energy required - passive transport).
• The larger the concentration difference, the faster the diffusion rate.
• Diffusion stops when the concentration of the substance is equal on both sides.
• Diffusion is crucial for transporting oxygen and glucose into cells and carbon dioxide and waste products out of cells.

Active Transport

• Movement against a concentration gradient requires energy (ATP) and involves protein channels (active transport).
• Substances like larger molecules and charged ions require active transport.

Osmosis

• Osmosis is the passive transport of water across a selectively permeable membrane from a high water concentration area to a low water concentration area.
• Solutions with high solute concentrations have low water concentrations (hypertonic).
• Solutions with low solute concentrations have high water concentrations (hypotonic).
• Solutions with equal solute concentrations are isotonic.
• Animal cells placed in a hypertonic solution will shrink, and in a hypotonic solution will burst. Plant cells in a hypotonic solution become turgid, and in a hypertonic solution become plasmolysed.

Diffusion vs. Osmosis

• Diffusion is the general movement of any substance down a concentration gradient.
• Osmosis is the specific movement of water across a selectively permeable membrane, following its own concentration gradient.

Explore the vital structure and mechanisms of cell membranes in this quiz. Understand how the phospholipid bilayer and embedded proteins contribute to the selective permeability of cells and the process of diffusion. Test your knowledge of how substances interact with the membrane.