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Cellular Transport

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Lesson Focus



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You will explore diffusion by experimenting with laboratory supplies to create situations where certain molecules pass through selectively permeable membranes.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • Define diffusion as the net movement of particles from an area of higher concentration to an area of lower concentration.
  • Identify examples where diffusion has occurred.
  • Explain that a selectively permeable membrane allows specific molecules to pass but not others.
  • Describe dynamic equilibrium as the continuous movement of molecules.
  • Explain that facilitated diffusion is when a cell uses transport proteins to assist molecules that are too large or complex to pass through the cell membrane.

Everything You'll Have Covered

Molecules move constantly. During this continuous movement, the molecules collide with one another and eventually spread out randomly. Diffusion, or more scientifically known as molecular diffusion, is the movement of molecules from an area of higher concentration to an area of lower concentration. After a period of time where diffusion has had time to move all molecules to equal concentrations, the system is described as reaching equilibrium. Equilibrium is when the concentration of molecules is the same throughout a system.

Diffusion across a cell membrane requires zero energy from the cell. The movement of molecules that requires no energy is termed as passive transport. Osmosis, or the movement of water molecules from an area of higher concentration to an area of lower concentration, is another type of passive transport.

Another form of diffusion which does not require energy is termed as facilitated diffusion. Facilitated diffusion uses transport proteins, or simple channels, to carry larger, more complex molecules from one side of a plasma membrane with a high concentration to the other, lower concentrated side. Facilitated diffusion, as mentioned, does not require energy and is there considered a type of passive transport, just as diffusion is.

Tutorial Details

Approximate Time 20 Minutes
Pre-requisite Concepts Students should be familiar with cellular membrane, homeostasis, solubility, solvent, and solute.
Course Biology
Type of Tutorial Experiment
Key Vocabulary base, cell, chemicals