Transport Mechanism

Cell Structure

Cell Membrane

  • Functions:

    • Outermost component of a cell

    • Encloses the cell and supports cell contents

    • Selective barrier (determines what enters/exits)

    • Role in communication between cells

Components of the Cell Membrane

  • Phospholipids: Main fabric of the membrane

  • Cholesterol: Tucked between phospholipid tails

  • Proteins:

    • Integral Proteins: Embedded in the bilayer

    • Peripheral Proteins: On the surface, not embedded

  • Carbohydrates: Attached to proteins/lipids on the extracellular side (glycoproteins and glycolipids)

Phospholipid Bilayer

  • Basic fabric of the plasma membrane. Amphipathic, with hydrophilic heads and hydrophobic tails.

    • Hydrophilic Head: Negatively charged phosphate group.

    • Hydrophobic Tails: Long, nonpolar fatty acid tails.

Transport Mechanisms in Cells

Overview

  • Cell Transport: Moving substances in/out of cells is vital.

    • Passive Transport: Requires no energy.

      • Substances move from higher to lower concentration.

    • Active Transport: Requires energy to move substances against their concentration gradient.

Types of Transport

  • Passive Transport:

    • Diffusion

    • Osmosis

  • Active Transport:

    • Pumps

    • Vesicular Transport: Exocytosis and Endocytosis.

Types of Osmosis Solutions

  • Isosmotic: Same concentration of solute particles.

  • Hyperosmotic: Higher concentration compared to another solution.

  • Hypoosmotic: Lower concentration compared to another solution.

Effects of Osmosis on Cells

  • Hypotonic Solution: Water moves into the cell (expansion)

  • Hypertonic Solution: Water moves out (shrinkage)

  • Isotonic Solution: No net movement of water.

Facilitated and Active Transport

  • Facilitated Diffusion:

    • Channel Proteins: Allow specific substances to cross the membrane.

    • Carrier Proteins: Change shape to transport substances.

  • Active Transport: ATP is used to move ions/molecules.

Example of Active Transport

  • Sodium-Potassium Pump: Moves sodium ions out and potassium ions into the cell using ATP.

Vesicle Transport

  • Endocytosis: Forming vesicles to bring substances into cells (phagocytosis and pinocytosis).

  • Exocytosis: Releasing substances from cells using vesicles.

Homeostasis and Cell Transport

  • Cells must maintain stable internal conditions.

    • Homeostasis is necessary for normal cell function.

  • Cell transport mechanisms play crucial roles in maintaining homeostasis.

Discussion Questions

  • What were the key concepts discussed in the lesson?

  • What insights did you gain?

  • Are there areas of confusion that need further exploration?

References

  • Campbell, N., et al. (2014). Campbell Biology, 10th Edition. Pearson Education, Inc.

  • Tate, P. (2012). Seeley’s Principles of Anatomy & Physiology, Second Edition. McGraw-Hill.

  • Khan Academy. (2023). Structure of the Plasma Membrane. Retrieved from https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/plasma-membranes/a/structure-of-the-plasma-membrane

  • LibreText. (2018). Fluid Mosaic Model.

  • LibreText. (2019). Cell Transport.

  • LibreText. (2018). Active Transport and Homeostasis.