Biology Chapter on Diffusion and Osmosis

Diffusion and Movement Across Membranes

• Diffusion refers to the movement of substances from areas of high concentration to low concentration.
• Ink dispersing in water illustrates diffusion in action.
• Channel proteins create tunnels within the lipid bilayer for specific substances to pass through.
• Sugar molecules utilize facilitated diffusion to cross cell membranes.

Transport Mechanisms

• Diffusion and osmosis do not require energy; they occur passively.
• Active transport requires energy to move substances against their concentration gradient.
• Ions move through ion channels via passive transport, enabling selective permeability.
• The movement of water into or out of cells is termed osmosis, a type of passive transport.

Water Passage through Membranes

• Water can pass through the cell membrane using specialized channel proteins designated for water transport.
• Isotonic solutions maintain equal solute concentrations with the cytoplasm, preventing net water movement into or out of the cell.

Active vs. Passive Transport

• Active transport, unlike passive transport, involves the use of energy (ATP) and typically involves carrier proteins.
• The sodium-potassium pump is a well-known example of active transport, moving sodium out and potassium into cells.

Sodium-Potassium Pump

• The pump moves two potassium ions into cells for every three sodium ions it ejects.
• The sodium-potassium pump is vital for maintaining cellular function and volume.

Transport of Large Molecules

• Proteins and polysaccharides too large for diffusion or active transport enter cells via endocytosis.
• Exocytosis allows cells to remove large molecules, utilizing vesicles to transport them out.

Hormones and Signal Molecules

• Hormones act as signal molecules that affect specific target cells rather than all cells indiscriminately.
• Signal molecules bind primarily to receptor proteins to enact cellular responses.
• Binding of signal molecules can lead to permeability changes due to activation of transport proteins.

Endocytosis Types

• Pinocytosis is the process where cells drink large dissolved molecules, while phagocytosis involves engulfing large particles (e.g., bacteria by white blood cells).
• Receptor-mediated endocytosis enables cells to specifically take in target substances, such as cholesterol from the blood, through receptor binding.

Epithelial Tissue Functions

• Epithelial tissue serves crucial roles in protection, absorption, secretion, and sensation.
• Different types, such as ciliated and columnar epithelium, have specialized functions; for instance, ciliated epithelium clears dust and bacteria from the respiratory tract.

Test your understanding of diffusion and osmosis in biological systems with this quiz. Explore key concepts such as movement through membranes and the behavior of substances in different concentrations. Perfect for biology students looking to reinforce their knowledge.