1. Cell Membrane and Tonicity Worksheet

2. Composition of the Cell Membrane
The cell membrane is also called the plasma membrane and is made of a phospholipid bilayer.

3. Composition of the Cell Membrane

4. Composition of the Cell Membrane
The Phospholipids have a hydrophilic (water attracting) head and two hydrophobic (water repelling) tails.
The head of a phospholipid is made of an alcohol and phosphate group, while the tails are chains of fatty acids.
Phospholipids can move apart and allow water and other smaller molecules to pass through into or out of the cell.
This is known as simple diffusion or passive transport because it does not require ATP (energy) and the water or molecules are moving along the concentration gradient.

5. Composition of the Cell Membrane
Another type of lipid in the cell membrane is cholesterol that makes the membrane more fluid.
Embedded in the phospholipid bilayer are (transport) proteins that also aid in diffusion and in cell recognition.
Proteins called integral proteins go all the way through the bilayer, while peripheral proteins are only on one side.
Integral proteins are also called transport proteins. Large molecules like starches or carbohydrates use proteins to help move across cell membranes.
Some of the membrane proteins have carbohydrate receptors attached to help cells to recognize each other and certain molecules.

6. Composition of the Cell Membrane
List 4 functions of the cell or plasma membrane:
a. Regulate what may enter the cell
b. Regulate what may leave the cell
c. Maintain homeostasis within the cell
d. Allows the cell to remain flexible.

8. Osmosis Define osmosis. Define these 3 terms:
is the movement of water molecules through a selectively-permeable membrane up a concentration gradient.
Define these 3 terms:
a. isotonic- solutions that have equal osmotic pressure
b. hypertonic- a solution with a higher solute concentration outside of the cell compared to inside of the cell.
c. hypotonic- a solution with a lower solute concentration outside of the cell compared to the inside of the cell.

9. Hyper-, Hypo-, or Isotonic?
Use arrows to show the direction of water movement into or out of each cell. Color and label the cell in an isotonic environment light blue, the hypotonic environment yellow, and the hypertonic environment light green.

10. Matching _____ solution with a lower solute concentration
_____ solution in which the solute concentration is the same
_____ condition plant cells require
_____ condition that animal cells require
_____ red blood cell bursts (cytolysis)
_____ plant cell loses turgor pressure (Plasmolysis)
_____ solution with a higher solute concentration
_____ plant cell with good turgor pressure
_____ solution with a high water concentration
A. Isotonic
B. Hypertonic
C. Hypotonic

11. Label the Red Blood Cells
What type of solution are they in?
Hypotonic
Isotonic
Hypertonic

12. Label the Plant Cell What type of solution are they in? Hypotonic
Isotonic
Hypertonic

13. Transport Requiring Energy
What type of transport is represented by the picture below?
Hint the diagram shows that ATP is being used to transport the molecule inside the cell.
In what direction is the
movement occurring?
-against or along the concentration gradient?

14. Sodium-Potassium Pump

15. Sodium-Potassium Pump
One type of active transport is called the sodium potassium pump which helps muscle cells contract. This pump uses ATP to move ions against the concentration gradient. The protein that is used to pump the ions through is called a transport (carrier) protein and it changes its shape to move the ions across the cell membrane.
Label and color the carrier proteins red and the ions yellow.

16. Solutions
Definition- when one or more solutes are dissolved into a solvent.
Solvent- any substance that can dissolve.
Solute- any substance that can be dissolved by a solvent.