Diffusion and Osmosis Worksheet
Name_____________________
The Main function of the cell membrane is to: _maintain homeostasis
What is the definition of homeostasis? (Look In the glossary)
the steady state physiological conditions of the body or cell
If no energy is used by the cell in transporting materials across the cell membrane it is called passive
transport.
1. Molecules are constantly in motion.
2. Define diffusion.
the movement of molecules from an area of higher concentration to an area of lower
concentration
3. The difference in concentrations of a substance across an area is called the
concentration gradient.
4. When does a space reach equilibrium?
When the concentration of the molecules is the same throughout the space (volume).
5. Define permeable.
A structure that allows substances to pass through the membrane .
6. Define semi-permeable.
A structure that allows only certain, specific substances to pass through and other substances
are blocked.
7. Define osmosis.
The process by which water molecules diffuse across a cell membrane from an area of higher
concentration to an area of lower concentration.
8. List one way osmosis is different from diffusion.
Osmosis is the diffusion of water only, or Osmosis requires the presence of a membrane.
9. List one way osmosis is the same as diffusion.
Both processes are descriptions of a method that allows substances to move from areas of
higher concentration to areas of lower concentrations.
10. What is a solution composed of?
A solute that is dissolved into a solvent.
11. The NET direction of osmosis depends on the relative concentrations of solutes
on the two sides of the membrane.
12. Define the word hypotonic.
When the concentration of solute molecules outside the cell is lower than the concentration of
solutes in the cell.
13. Define the word hypertonic.
When the concentration of solute molecules outside the cell is higher than the concentration of
solutes inside the cell.
14. Define the word isotonic.
When the concentration of solute molecules outside the cell and inside the cell are equal.
15. The prefixes hypo, hyper, and iso refer to the relative solute concentration of two solutions.
16. How do unicellular organisms rid themselves of excess water that enters them via osmosis?
Contractile vacuoles collect the excess water and then contract, pumping the water out of the
cell.
17. When water diffuses into a plant cell and builds up firm pressure, that is called
turgor pressure.
18. In a hypertonic environment, water leaves the cells through osmosis. What happens to the
cell, especially the cell membrane?
The cell membrane shrinks away from the cell wall (as water leaves the cell); Turgor pressure is
lost. In animal cells, the cells shrink and shrivel as they lose water.
19. Some cells can not compensate for changes in the solute concentration of their environment.
Give an example of a type of cell that cannot compensate for these changes and explain what
happens to the cell.
Red blood cells. In hypertonic solutions they shrink and shrivel (water is lost).
In hypotonic solutions they swell and burst (water is gained.)
20. Define cytolysis.
The bursting of cells caused by the intake of too much water.
21. Are osmosis and diffusion examples of active transport or passive transport? Explain your
answer.
Passive transport: Neither osmosis or diffusion requires the addition of energy,
only the presence of a concentration gradient.
22. Define facilitated diffusion.
The transport of substances through a cell membrane along a concentration gradient with the
aid of carrier proteins.
23. Is facilitated diffusion active or passive transport? Explain your answer.
Passive transport
Facilitated diffusion does not require the addition of energy in
order for it to proceed, only a concentration gradient and carrier proteins.
24. What assists the movement of molecules across the cell membrane in facilitated diffusion?
carrier proteins
25. Give an example of a molecule that enters the cell via facilitated diffusion.
Glucose
26. What are the two important properties of facilitated diffusion?
1. FD can help substances move either into or out of a cell, depending upon the concentration
gradient.
2. The carrier protein involved is FD are each specific for one type of molecule.
27. Cells must sometime move materials from an area of lower concentration to an area of higher
concentration or up the concentration gradient. What is this type of movement of materials
called? Does this method require energy?
Active transport. Yes it does.
28. What is another name for carrier proteins?
cell membrane pumps.
29. Summarize the steps that the carrier protein known as the sodium-potassium pump goes
through in order to perform its function. (Look at figure 5-6 on page 104)
1. Na+ ions located in the cytoplasm bind to the carrier protein.
2. A phosphate group is removed from ATP and is bound to the carrier protein.
3. The binding of the phosphate group from ATP changes the shape of the carrier protein,
allowing the Na+ ions to be released into the cell.
4. 2 K+ ions located outside the cell bind to the carrier protein.
5. The phosphate group is released, restoring the original shape of the carrier protein.
6. The 2 K+ ions are released into the cell.
7. Lather, rinse, repeat.lol
30. The three types of active transport that cells use are: cell membrane pumps, (carrier proteins),
Endocytosis, and Exocytosis.
31. Define Endocytosis. What does the prefix endo- mean?
The process by which cells ingest external fluids, macromolecules, large particles, and
sometimes entire cells .
Endo means inside.
32. List the similarities and differences between Pinocytosis and Phagocytosis.
Both processes involve the transport of particles inside the cell. Both are forms of active
transport. Pinocytosis involves the transport of solutes and fluids while Phagocytosis can involve
large particles and even entire cells.
33. Define Exocytosis. What does the prefix exo- mean?
The process by which a substance is released from a cell. Exo means outside.
34. Draw a picture showing both Endocytosis and Exocytosis. Label them so that you can tell the
difference later.
Endocytosis
Exocytosis