Diffusion and Osmosis Pre-Lab


1. What does it mean to describe the plasma membrane as a selectively permeable barrier?

The plasma membrane is called ‘selectively permeable’ because only certain molecules/substances can pass through the membrane, while the rest get blocked out.

2. Define simple diffusion and facilitated diffusion.

Simple Diffusion: a type of passive transport that transports non-polar nandad lip-soluble substances (gases, fat-soluble vitamins, some sex hormones, etc.) along the concentration gradient WITHOUT the use of proteins.

  • Simple diffusion does not require proteins because the substances they transport do not contain water. Since the phospholipid/fatty bilayer repels water, the substances are able to slip through easily

Facilitated Diffusion: a type of passive transport that transports molecules that are unable to cross the lipid bilayer; goes along concentration gradient WITH proteins.

  • F. Diffusion tackles substances that do contain water, meaning they are repelled by the phospolipid bilayer and cannot pass through without the help of protein channels

3. What is the difference between passive transport processes and active transport processes?

Passive Transport: is done naturally without the use of ATP/energy

Active Transport: must be activated by ATP

4. Define vesicular transport. Is vesicular transport an active or passive process?

Vesicular Transport: a type of active process that can…

  1. Engulf particles (endocytosis) and/or use receptors to sectively choose which particles to draw in (receptor-mediated endocytosis)

  2. Release particles as waste (exocytosis)

  3. English fluid w/ particles inside (pinocytosis)

To be more specific, endocytosis is a process where a cell’s plasma membrane engulfs a particle, drawing it in and pinching it off to form a vesicle. If the particle is larger, the process is known as phagocytosis.

Exocytosis is endocytosis’ counterpart, where vesicles destined for export fuse with the inner plasma membrane before its contents are released back to the outside of the cell.

5. Using your textbook, answer the following questions about osmosis.

a. Is osmosis an active or passive transport process?

Osmosis: a passive transport of water against the concentration gradient. It is a type of facilitated diffusion, meaning it cannot pass the lipid bilayer and must employ the use of protein channels to get across.

b. Is the plasma membrane permeable to water?

Because the cell membrane’s bilyaer is composed of phospholipids, it means water is repelled by its hydrophobic bipoles (the tails), so it cannot pass through without proteins.

c. Describe an isotonic solution, hypertonic solution, and hypotonic solution.

d. For each solution described below, explain what will happen to the cells in

the solution.

Isotonic: the ‘neutral’ state; the solubility of the inside of the cell and the outside is equivalent, so no concentration shifting is needed

Hypertonic: the ‘Dead Sea’ state: the solubility of the outside of the cell is greater than the inside, causing water to flow out of the cell (crenation).

Hypotonic: the ‘Pure Lake’ statel the solubility of the environment is lesser than the inside of the cell, causing water to flow into the cell (cell lysis)