Worksheet Key

Name ______________ ________________

Crossing the Membrane Worksheet Answer each question using a complete sentence. 1. What three methods of crossing the cell membrane require no work/energy? Diffusion

Osmosis

Facilitated Diffusion

2. What is a concentration gradient? A concentration gradient is a gradual change in the concentration of solutes in a solution between two areas. The gradient is a result of the unequal distribution of ions in a solution.

3. When does diffusion stop? Diffusion stops when there is an even distribution of solutes within the solution.

4. Sketch a red blood cell in a hypertonic solution, an isotonic solution, and a hypotonic solution. Use arrows to show the direction of water.

Isotonic

Hypertonic

Hypotonic

5. What is the difference between diffusion and osmosis? Diffusion is the movement of molecules (not water) from an area of higher concentration to an area of lower concentration. Osmosis is the movement of water molecules from a region of

higher concentration to an area of lower concentration through a semi permeable membrane. Osmosis involves water while diffusion involves any other solute. 6. Explain how the cell membrane is semipermeable. The cell membrane allows some molecules to flow through due to size and keeps larger molecules out of the cell. Channels are present within the membrane to allow access for these larger molecules. 7. Explain how a diffusion gradient allows a dog to follow a scent-trail to catch an animal. Scent particles released from what the dog is tracking are released and diffuse through the air from an area of high concentration to low. The dog can sense when the scent is stronger and goes that direction.