Biology Osmosis and Cell Transport

Osmosis and Solutions

• Water naturally moves to dilute more concentrated solutions, as per Van Hoff's Law.
• Normal osmolarity: 300 mOsm/L is isotonic, equivalent to 0.9% NaCl or 5% glucose.
• Hypotonic solutions have osmolarity below 0.9%, while hypertonic solutions exceed 0.9%.
• Red blood cells (RBCs) can experience osmotic fragility, leading to hemolysis when exposed to different osmotic conditions.

Active Membrane Transport

• Active transport enables molecule movement against concentration or electric gradients, requiring ATP energy.
• Primary active transport involves selective ion channels, such as the Na⁺-K⁺ pump, Ca²⁺-pump (in muscle cells), and H⁺ proton pump (in stomach cells).
• Secondary active transport uses a carrier mechanism where substances (like glucose) bind to ions (e.g., Na⁺) for membrane transport.
• Exocytosis releases molecules from cells, while endocytosis (including phagocytosis) allows uptake of larger molecules.

Na⁺-K⁺ Pump

• Na⁺-K⁺ pump (Na⁺-K⁺ ATP-ase) is located in the cell membrane and actively transports ions.
• It moves 3 Na⁺ ions out and 2 K⁺ ions into the cell, vital for maintaining electric charge renewal across body cells.
• The pump operates at a maximum capacity of 200 Na⁺ and 133 K⁺ ions per second and necessitates ATP for function.

Resting Membrane Potential (RMP)

• RMP measures the electrical difference between the positively charged extracellular space and the negatively charged intracellular space.
• The negative value results from selective permeability to K⁺, Na⁺, and Cl⁻ ions, influenced by their equilibrium potentials.

Overview of Medical Biophysics

• Medical biophysics integrates various medical sciences, addressing biological problems from atomic to organ levels.
• It provides insights into radiation effects, safety guidelines, and new diagnostic or treatment methods.

Human Cell Characteristics

• Cells are the fundamental units of the body, totaling approximately 60 trillion, varying in size from 4 to 120 µm.
• Key features include metabolism, excitability, and reproduction, organized into tissues forming organs.

Surface Membrane (SM)

• The surface membrane includes intracellular SM and plasmatic SM, providing functions such as semipermeability and protection.
• Composed of a phospholipid bilayer (45% hydrophilic heads, 45% hydrophobic tails) and proteins (50%), it facilitates ion transport and charge storage.

Membrane Transport Mechanisms

• Transport mechanisms are crucial for solute movement, impacting cell metabolism and membrane potentials.
• Passive transport includes diffusion (simple and facilitated) and osmosis, while active transport mechanisms require ATP.

Types of Diffusion

• Simple Diffusion: Passive transport of solutes from high to low concentration until equilibrium is reached. Influenced by concentration gradient, solubility, and temperature.
• Facilitated Diffusion: Involves transport proteins that assist larger molecules across the membrane, changing conformation during the process.
• Ion Channel Diffusion: Passive transport of ions like Na⁺ and K⁺ through selective protein channels, regulated by voltage or ligand binding.

Filtration

• Filtration is the passive movement of water and small particles driven by hydrostatic pressure gradients, distinct from concentration gradients, often seen in capillary actions.

Osmosis

• Osmosis is the passive movement of water through semipermeable membranes, moving from lower to higher osmotic pressure until equilibrium is established.

Explore the principles of osmosis, including the effects of hypotonic and hypertonic solutions on red blood cells. This quiz covers fundamental concepts such as Van Hoff's Law and active membrane transport mechanisms. Test your understanding of how these processes impact cellular environments.