CELL TRANSPORT

Cell Transport Mechanisms

Types of Transport Across the Cell Membrane

  • Overview: Transport mechanisms enable substances to enter or leave cells through the cell membrane. There are two primary types: Passive and Active transport.

Cell Membrane Structure

  • Phospholipid Bilayer: Key structural component, consisting of two layers of phospholipids. This structure is crucial for maintaining cell integrity and regulating transport.

  • Proteins: Integral and peripheral proteins assist in various functions including transport and signaling.

  • Cytoplasm & Nucleus: Components involved in metabolic processes and genetic information storage.

Methods of Transport

Passive Transport (Requires No Energy)

  • Definition: Movement of molecules from high to low concentration without energy use.

    • Simple Diffusion: Molecules move freely across the membrane.

    • Facilitated Diffusion: Molecules require assistance from proteins (e.g., channel proteins).

    • Osmosis: Specific to water molecules moving through a semipermeable membrane.

Active Transport (Requires Energy)

  • Definition: Movement of molecules against their concentration gradient, requiring energy (ATP).

    • Includes the transport of ions and large molecules.

Simple Diffusion

  • Process: Molecules move from high concentration to low concentration spontaneously without energy.

  • Diffusion continues until molecules are evenly distributed.

Key Processes in Diffusion

  • Diffusion Through a Membrane: Solutes move from high to low concentration due to concentration gradients.

    • Movement is driven by natural kinetic energy of particles.

Examples of Diffusion

  • Gas Exchange: At alveoli in lungs and in photosynthesis.

  • Perfume Spread: Aroma diffuses through the air.

  • Food Coloring in Water: Color evenly distributes as it diffuses.

Factors Affecting Diffusion Rate

  • Temperature: Higher temperatures increase diffusion rates; larger molecules decrease diffusion speed.

Osmosis

  • Definition: Diffusion of water across a semipermeable membrane.

  • Water moves from high water concentration (low solute) to low water concentration (high solute).

Ingredients for Osmosis

  • Requires a semipermeable membrane and the presence of solvents with different concentrations.

  • A solvent dissolves solutes to form solutions.

Water Movement in Cells

Isotonic Solutions

  • Definition: Solute concentration is equal inside and outside the cell.

  • Water movement is balanced; no net movement occurs.

Hypotonic Solutions

  • Definition: Lower solute concentration outside the cell.

  • Water moves into the cell, potentially causing it to swell and burst.

Hypertonic Solutions

  • Definition: Higher solute concentration outside the cell.

  • Water moves out of the cell, leading to cell shrinkage.

Key Terms

  • Cytolysis: Cell bursting due to excessive water intake.

  • Plasmolysis: Cell shriveling due to excessive water loss.

Active Transport

General Mechanism

  • Definition: Movement of substances from low to high concentration using energy. Includes processes like the Sodium-Potassium Pump.

Transport Proteins

  • Types: Channel proteins for passive transport, carrier proteins change shape to move substances across membranes.

Endocytosis & Exocytosis

Exocytosis

  • Function: Molecules (such as hormones) exit the cell through vesicles that fuse with the plasma membrane.

Endocytosis Types

  • Phagocytosis: Ingesting large particles (cell eating).

  • Pinocytosis: Consuming dissolved molecules (cell drinking).

  • Receptor-Mediated Endocytosis: Specific uptake involving cellular receptors for selective transport.

Summary of Transport Mechanisms

  • Passive Transport is energy-efficient, utilizing diffusion principles.

  • Active Transport is energy-dependent, moving substances against concentration gradients.