Types of Transport

Passive Transport

• Definition: Movement of molecules without energy input, occurring down a concentration gradient.
• Observation: Commonly observed in daily life (e.g., odor spreading in a room, diffusion of food coloring in water).
• Types:
  • Simple Diffusion: Movement across the membrane without assistance (e.g., small, nonpolar molecules).
  • Facilitated Diffusion: Requires protein channels for movement across the membrane (e.g., ions needing specific channels).

Key Examples of Passive Transport

• Diffusion of Water (Osmosis):
  • Type of passive transport referring specifically to water movement across a semi-permeable membrane.
  • Key Definitions:
  • Requires: Movement of water down its concentration gradient.
  • Membrane: Must be semi-permeable (some things can move, others cannot).
  • Example: Adding food coloring to water showcases diffusion.

Active Transport

• Definition: Movement of molecules against their concentration gradient requiring energy input (e.g., ATP).
  • Process: Moves substances from low to high concentration.
• Examples:
  • Sodium-Potassium pump, which requires energy to maintain gradients across the membrane.
  • Example Analogy: Active transport is akin to a fan blowing air into a room to prevent it from escaping.

Endocytosis and Exocytosis

• Endocytosis: Process of taking large molecules into the cell via vesicles.
  • Types:
  • Phagocytosis: "Cell eating" for solid material.
  • Pinocytosis: "Cell drinking" for liquids.
• Exocytosis: Release of substances from vesicles to the outside of the cell.
  • Example: Cells secreting hormones or neurotransmitters.

Concentration Gradients and Tonicity

• Transmembrane Gradient: Difference in molecule concentrations across a membrane.
• Tonicity: Refers to how an external solution affects cell volume through osmosis.
  • Hypertonic: Higher solute concentration outside the cell; water leaves cell, causing it to shrink.
  • Hypotonic: Lower solute concentration outside the cell; water enters cell, causing it to swell/potentially burst (lysis).
  • Isotonic: Equal solute concentrations on both sides; no net movement of water.

Movement of Water: Osmosis Explained

• Osmosis is defined as:
  • A type of diffusion.
  • Movement of water across a semi-permeable membrane.
  • Does not require energy; moves down a concentration gradient.
• Factors Affecting Osmosis:
  • Concentration of osmotically active solutes (e.g., salt, sugars) impacts water movement.
  • Implications for medical treatment (e.g., IV solutions must be isotonic).

Thermodynamics Overview

• First Law: Energy is conserved; it cannot be created or destroyed, only transformed.
• Second Law: Entropy, or disorder, of the universe tends to increase; energy transfers increase randomness.

Energy Concepts

• Work: Defined as anything requiring energy (e.g., cellular processes).
• Types of Energy:
  • Kinetic Energy: Energy of movement (heat is a measure of kinetic energy at the molecular level).
  • Potential Energy: Stored energy due to position or chemical structure (food stores potential energy).

Chemical Reactions and Free Energy

• Spontaneous Reactions:
  • Exergonic: Release energy and are spontaneous; have a negative delta G (available energy decreases).
  • Endergonic: Require energy input, are non-spontaneous; have a positive delta G (available energy increases).