1. Study Guide Answers

2. Draw and label the CM Fatty acid “tails” (lipids) Phospholipids
Integral protein
Peripheral protein
Fatty acid “tails” (lipids)
Phosphate Group

3. Cell Membrane
When the CM is said to be selectively permeable, it means that the CM regulates what enters and leaves the cell. It only allows some substances to enter freely.
When the CM is described to have the structure of the fluid mosaic model, it means that the phospholipids and proteins can move rapidly from side to side throughout the CM.

4. Passive Transport
high
low
In PT, molecules move down the concentration gradient; molecules from an area of high concentration to an area of low concentration.
Energy is not involved in PT because molecules are moving down the gradient, or with the gradient. Therefore, the gradient supplies enough force to move the molecules without extra energy input. If the molecules were moving in the opposite direction (against the gradient), then energy would be needed.

5. Simple Diffusion
When perfume is sprayed into the air in an enclosed space, the perfume particles will begin to spread out throughout the room. The perfume will move with the air particles, and continue to spread out until the entire container has been reached.
Solutes and solvents mix together to create a solution. In a solution, the solute is the substance that is being dissolved. The solvent is the substance that dissolves the solute. For example, in sugar water, sugar is the solute (being dissolved), and water is the solvent (doing the dissolving).
Sugar will dissolve in water just like perfume will spread through an enclosed room. When placed in the water, the solution wants to mix together so the container is in equilibrium. Therefore, the sugar cubes will dissolve in the water, and the sugar molecules will diffuse throughout the container (down the gradient from an area of high concentration to an area of low concentration) until the sugar is evenly distributed throughout the water.

6. Factors that affect diffusion
Steepness of gradient
The difference in concentrations across the membrane effects diffusion because the solution wants to reach equilibrium, therefore the larger the difference in the gradient, the longer the diffusion process will take to complete.
Temperature
The more thermal energy in a system, the faster the particles are moving. Therefore, increasing the temperature of a system would cause the molecules to diffuse faster across the membrane.
Size of diffusing molecules
Some molecules are too large or too small to diffuse across the membrane by themselves. Therefore, they may need a carrier protein, ion channel, etc. to help them get across the membrane.

7. Equilibrium
Equilibrium is when the concentration of the molecules is the same across a space/container.
Once equilibrium is reached, the molecules still move in both directions, but there is no longer a gradient.

8. Osmosis
Osmosis is the process by which water molecules diffuse across a membrane from high to low concentration. No energy is needed.
Practical examples: having to pee after sitting in a pool; watering plants

9. Hypotonic
The concentration of solute molecules outside the cell is lower than the concentration inside the cell.
Water molecules will diffuse into the cell until equilibrium is reached.
Water molecules move down the gradient.

10. Hypertonic
The concentration of solute molecules outside the cell is higher than the concentration inside the cell.
Water molecules will diffuse out of the cell until equilibrium is reached.
Water molecules move down the gradient.

11. Isotonic
The concentration of solutes outside and inside the cell are equal.
Water diffuses into and out of the cell at the same rate.
There is no net movement of water.

12. How do cells deal with osmosis?
osmoregulation in freshwater fish
keep body fluids from being too dilute or too concentrated
having to pee after swimming in a pool
contractile vacuoles: excess water out of the cell when the cell has gained too much water

13. Turgor Pressure
The pressure that water molecules exert against the cell wall in plant cells.
When plants are in a hypotonic environment, water will diffuse into the plant cells and will be stored in the central vacuole.

14. Plasmolysis Loss in pressure between the CW and CM in a plant cell.
When plants are in a hypertonic environment, the water will diffuse out of the cell, and the CM will pull away from the CW.

15. Cytolysis Cytolysis is cell bursting in animal cells.
When animal cells are in a hypotonic environment, the water will diffuse into the cell.

16. Crenation Crenation is cell shrinking in animal cells.
When animal cells are in a hypertonic environment, the water will diffuse out of the cell.

17. Facilitated Diffusion
FD is a type of passive transport where molecules move down the concentration gradient from an area of high concentration to an area of low concentration. In FD, molecules cannot easily diffuse across the CM, so they need a specific integral protein the “facilitate” their diffusion across the membrane.
Energy is not needed because the molecules are still moving with the concentration gradient, not against it.

18. Egg Lab Part I
After the egg was placed in the vinegar, the mass of the egg increased. This means that the vinegar must have diffused across the cell membrane and into the egg.
The vinegar was hypotonic compared to the egg.

19. Egg Lab Part II
When the egg was placed in maple syrup, water was pulled out of the egg and into the syrup solution.
The syrup was a hypertonic solution for the egg, Water was pulled out of the egg, and the cell appeared to be shriveled.

20. Egg Lab Part III
When placed in the water, water entered the cell (the egg). Therefore water was a hypotonic environment for the egg.
If left in the water longer, the egg and water solution would have eventually reached equilibrium, and be isotonic.