Answer Key

Original Document: Chapter Review; Diffusion and Osmosis

What do you Know?

1. Label the three images below as isotonic/ hypertonic/ hypotonic (with regard to the solution the cell is placed in)

Hypertonic ...........................Isotonic...........................hypotonic


2. Movement across the cell membrane that does not require energy is called
[ active / passive ] transport.

3. The difference in the concentration of a substance across a space is called a concentration [ equilibrium / gradient ].

4. If there is a concentration gradient, substances will move from an area of high concentration to an area of [ equal / low ] concentration.

5. The cell membrane is [ selectively permeable / impermeable ].

6. [ Equilibrium / Diffusion ] is the simplest type of passive transport.

7. The diffusion of water through a selectively permeable membrane is called [ osmosis / diffusion ].

8. The direction of water movement across the cell membrane depends on the concentration of free water[ molecules / solutions ].

9. A solution that causes a cell to swell is called a [ hypertonic / hypotonic ] solution.

10. Organelles that collect excess water inside the cell and force water out are called
[ diffusion organelles / contractile vacuoles ]

11. The process of taking material into the cell by infolding the cell membrane is called [ endocytosis / exocytosis ]

12. In [ facilitated / molecular ] diffusion, membrane proteins help molecules across the membrane.

13. In diffusion, molecules [ spread out / condense ]

14. The lipid bilayer describes [ a type of transport / the cell membrane ]

15. Facilitated diffusion moves substances down their concentration gradient [ with / without ] using the cell's energy.


1. Know the parts of a solution (Solvent and solute) - the solute is the substance this is dissolved (sodium) and the solvent is the liquid it is dissolved in (often water)
2. Label a cell membrane (bilayer, proteins)


3. Explain what will happen to cells when placed in isotonic, hypertonic, and hypotonic solutions.


4. Know the definition of:

defintions are simplified

Diffusion - movement of substances from areas of high concentration to low
Equilibrium - when molecules are spread out evenly
Osmosis - diffusion of water
Isotonic - concentration of solution is equal to that of the cell
Hypertonic - concentration of solution is greater to that of the cell, water leaves cell, cell shrinks
Hypotonic -concentration of solution is less than that of the cell, water enters cell, cell swells
Facilitated diffusion - diffusion of substances across the membrane using a transport protein
Endocytosis - cell takes in large particles by engulfing them in its membrane
Phagocytosis - large solid particles engulfed
Pinocytosis -liquid engulfed
Exocytosis - pushing materials out of the cell, such as waste products

5. Explain what happens when you place a bag full of starch (solution) into a solution of iodine.

the iodine passes through the bag (because it is selectively permeable) and when it gets to the starch solution, it turns it from white to dark purple, because iodine is an indicator of starch.