1. Study Guide
Answer Key

2. Cell Membrane Structure
1. Hydrophilic Head
Attracted to water
2. Phospholipid
Heads face exterior and tails interior, making up the structure of the cell membrane
3. Hydrophobic Tails
Repelled by water
4. Transmembrane Protein
Provide channels for large/polar molecules to pass; attachment points for cells
5. Cholesterol
Maintains fluidity of membrane
6. Carbohydrate
Marker for cell identification
7. Lipid Bilayer
Double layer of phospholipids describes the structure of the cell membrane

3. Cell Membrane Structure
Hydrophilic=attracted to water; hydrophobic=repelled by water. Should the cell membrane be damaged, these properties will always make the cell membrane return to it’s bilayer structure, with heads facing outside and tails in.
Lipid=fatty acids. Examples: Fats, waxes
Fluid mosaic model means the membrane is a dynamic, constantly moving structure.
Selectively permeable means some things can enter, while others cannot.

4. Station 2
The solute is the substance being dissolved. The solvent is the one doing the dissolving.
In the case of salt water, salt is the solute and water is the solvent.
Concentration is the amount dissolved in a container. A high concentration means there is a large amount of solute compared to solvent.

5. Passive Transport: Diffusion
High to low = Passive transport
In the picture, the concentration of molecules is higher in the top left corner. Therefore, diffusion of the molecules occurs until they reach equilibrium, or a balanced state.
Once equilibrium is reached, the molecules will continued moving, though remain balanced.
Facilitated Diffusion

6. Passive Transport: Osmosis
Osmosis is the diffusion of WATER across a selectively permeable membrane. It is a form of passive transport.
The water molecules move from where there is a high concentration to where there is a low concentration in order to reach equilibrium.
Plant prefer a hypotonic environment because this allows their vacuoles to remain full to maintain turgor pressure for structural support.
Solution 1
Solution 2
Solution 3
Cell shrinks; hypertonic
Cell swells, hypotonic
Cell remains the same; isotonic

7. Active Transport ATP = Energy Active Transport
Proteins work to actively transport molecules across the cell

8. Homeostasis
Homeostasis means maintaining a balance between your internal state and external changes.
Example: In heat, your body will sweat to cool down, while in cold, you will shiver to generate heat.
Buffers are chemicals that can raise or lower pH. They work constantly to maintain the correct pH in your cells.
The cell membrane contributes to homeostasis because it regulates what can and cannot enter the cell. It helps keep things balanced!