CELL-TRANSPORT

Cell Transport Overview

  • Various types of transport processes occur across the cell membrane.

Simple Diffusion

  • Requires no energy.

  • Molecules move from an area of high concentration to an area of low concentration.

Diffusion

  • It is a passive process, meaning no external energy is used.

  • Molecules move spontaneously due to their natural kinetic energy.

Diffusion of Lipids

  • Process illustrated as:

    • (a) Dye is dropped into water.

    • (b) Diffusion begins, molecules start to distribute.

    • (c) Over time, dye molecules become evenly distributed among water molecules.

Diffusion Through a Membrane

  • High concentration on one side and low concentration on the other.

  • Solute moves down the concentration gradient (high to low).

Osmosis

  • Specifically refers to the diffusion of water across a membrane.

  • Water moves from areas of high water concentration to low water concentration.

  • Water is attracted to solutes; thus, it moves towards areas of higher solute concentration.

Direction of Water Movement

  • High Water Concentration: Water diffuses from higher to lower concentration.

  • Low Water Concentration: Water moves to areas with higher solute concentration.

Solutions and Cell Response

  • Isotonic Solution:

    • Solute concentration inside the cell is equal to that outside.

    • Water moves in and out at equal rates (equilibrium).

  • Hypotonic Solution:

    • Solute concentration outside the cell is lower than inside.

    • Water flows into the cell, causing it to swell.

  • Hypertonic Solution:

    • Solute concentration outside the cell is higher.

    • Water flows out, making the cell shrink.

Cellular Effects of Solutions

  • Cytolysis:

    • Occurs in hypotonic solutions; cells swell and burst.

  • Plasmolysis:

    • Occurs in hypertonic solutions; cells shrink and shrivel.

Osmosis in Red Blood Cells

  • Red blood cells exhibit different responses in isotonic, hypotonic, and hypertonic solutions.

Transport Mechanisms

Passive Transport

  • Simple Diffusion: Requires no energy; substances move from high to low concentration (e.g., oxygen, carbon dioxide).

  • Facilitated Diffusion: Uses transport proteins; molecules move from high to low concentration without energy (e.g., glucose).

Active Transport

  • Requires energy (ATP) to move substances against their concentration gradient (from low to high concentration).

  • Examples: Sodium-Potassium Pump; transports Na+ out and K+ in.

Types of Transport Proteins

  • Channel Proteins: Have pores for materials to cross.

  • Carrier Proteins: Change shape to transport materials across the membrane.

Endocytosis and Exocytosis

Exocytosis

  • A type of active transport moving substances out of the cell via vesicles that fuse with the plasma membrane.

  • Common in hormone secretion and cell communication.

Endocytosis

  • Divided into three forms:

    • Pinocytosis: Ingests extracellular fluid and dissolved substances.

    • Receptor-Mediated Endocytosis: Integral proteins recognize and take in specific molecules (e.g., hormones).

    • Phagocytosis: Engulfs large particles (e.g., bacteria) into vesicles.

Summary of Active Transport Types

  • Pinocytosis: Cell drinking (intake of fluids).

  • Phagocytosis: Cell eating (intake of larger particles).

  • Receptor-Mediated Endocytosis: Involves binding specific substances to receptors before uptake.