Review of Molecular Movement

Molecular Movement and the Cell Membrane

• Presenter: Dr. Paul Ulrich, Georgia State University

• Visual: African clawed frog, Brian Gratwicke (Flickr, CCA2G)

• Reference: Agre 2006, Proc Am Thorac Soc

Understanding Confidence Levels

• Survey on confidence regarding concepts of diffusion and osmosis:

  • Completely confident

  • Fairly confident

  • Somewhat confident

  • Slightly confident

  • Not confident at all

Passive Transport (Diffusion)

• Definition: Movement down a concentration gradient due to random molecular movement.

• Energy Requirement: Does not require energy input.

• Process Example:

  1. Solute is dropped into water.

  2. Solute molecules randomly collide with each other.

  3. Solute disperses into areas of lower concentration.

• Reference: Phelan, What is Life?

Membrane Functions

• Role: Cell membranes act as "gatekeepers" controlling the passage of substances in and out of the cell.

Types of Diffusion

• Simple Diffusion

• Facilitated Diffusion: Utilizes channel or carrier molecules for transport across membranes.

  • Components: Includes extracellular fluid and intracellular fluid.

Facilitated Diffusion

• Definition: A form of passive transport requiring a pathway or channel across the cell membrane.

• Energy Requirement: Does not require direct energy input.

• Reference: Belk, Biology: Science for Life

Osmosis

• Definition: Special case of diffusion focused on water movement across a selectively permeable membrane.

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

• Reference: Youtube.com, Organic Edible Garden

Selectively Permeable Membranes

• Description: Only certain molecules can pass, such as:

  • Water (H2O)

  • Proteins, Na+, and other ions

• Question: How can water move through a lipid membrane?

Role of Aquaporins

• Function: Special channels (aquaporins) facilitate water's diffusion through the membrane.

• Characteristic: Specifically allows water molecules to pass while restricting others.

• Source: ks.uiuc.edu/Research/aquaporins/

Water Movement in Osmosis

• Directional Movement: Identify in scenarios where water concentration differs across membranes.

• Example Question: Higher water concentration on the right than left; where does water move?

Effects of Osmosis on Cells

• Cell Types:

  • Plant Cell

  • Animal Cell

• Solution Types:

  • Isotonic Solution: Equal concentrations inside and outside.

  • Hypotonic Solution: Lower concentration outside, causes cell swelling.

  • Hypertonic Solution: Higher concentration outside, causes cell shrinkage.

• Reference: Belk, Biology: Science for Life

Active Transport

• Definition: Process of moving molecules across a membrane towards higher concentration areas.

• Energy Requirement: Requires energy, often in the form of ATP.

• Reference: Belk, Biology: Science for Life

Confidence in Explaining Osmosis

• Surveying confidence: “Water moves into plant roots by osmosis.”

  • Rate your understanding without using the words concentration or solute:

    • Completely confident

    • Fairly confident

    • Somewhat confident

    • Slightly confident

    • Not confident at all.