AP Biology Unit 2 FRQ

Question

Cells transport substances across their membranes.  

Choose THREE of the following four types of cellular transport.

        ·         Osmosis 

        ·         Active Transport                  

        ·         Facilitated diffusion         

        ·         Endocytosis/exocytosis

For each of the three transport types you choose

a.  describe the transport process and explain how the organization of cell membranes functions in the movement of specific molecules  across the membrane.

b. explain the significance of each type of transport to a specific cell (you may use different cell types as examples.)

Answer 1

Hi Wen!

For a word-heavy Bio problem like this one, I always begin by breaking down the question into my own simplified language. This is useful not just for understanding what is being asked of you, but will also help you begin to put a rough outline in place.

For example, your assignment states, "Cells transport substances across their membranes." This becomes a useful title or header, as shown below:

1. Transportation of Substances across Cell Membranes.

Next, your assignment instructs us to "Choose THREE of the following four types of cellular transport: (1) Osmosis; (2) Active Transport; (3) Facilitated diffusion; (4) Endo-/exocytosis." I went with the first three to begin outlining my answer, as shown below:

1. Transportation of Substances across Cell Membranes. (1) Osmosis; (2) Active Transport; (3) Facilitated diffusion.

Finally, "For each of the three transport types" we need to: "(a) describe the transport process and explain how the organization of cell membranes functions in the movement of specific molecules across the membrane;" and "(b) explain the significance of each type of transport to a specific cell (you may use different cell types as examples.)" Breaking down these two points into three smaller pieces (underlined above) helps build on your answer outline, as shown in the following example:

Transportation of Substances across Cell Membranes.

(1) Osmosis:

(i) Describe osmosis;

(ii) Explain how the membrane functions to move specific molecules during osmosis;

(iii) Explain the significance of osmosis to a specific type of cell.

(2) Active Transport:

(i) Describe active transport;

(ii) Explain how the membrane functions to move specific molecules in active transport;

(iii) Explain the significance of active transport to a specific type of cell

(3) Facilitated diffusion.

(i) Describe facilitated diffusion;

(ii) Explain how the membrane functions to move specific molecules in facilitated diffusion;

(iii) Explain the significance of facilitated diffusion to a specific type of cell.

Once you have a detailed outline in place, it becomes much easier to write your answer by essentially just filling in the blanks, as I did for osmosis in the example below:

Transportation of Substances across Cell Membranes.

1. Osmosis:
2. Describe osmosis: Whereby water molecules spontaneously move through the semi-permeable cell membrane in the direction of higher solute concentration, such that solute concentrations on either side of the membrane are equalized.
3. Explain how the membrane functions to move specific molecules during osmosis: The semipermeable nature of cell membranes plays an important role in osmosis. These membranes allow for water molecules to freely pass through them during osmosis, while solutes (molecules dissolved in water) remain stationary on either side of the membrane. Thanks to the semipermeable membrane, osmosis equalizes solute concentrations between the interior and exterior of the cell.
4. Explain the significance of osmosis to a specific type of cell: Osmosis is significant to the red blood cells of mammals. Healthy mammalian red blood cells contain a 0.3 M concentration of NaCl (salt) solutes and are doughnut-shaped. When placed in a solution that also contains a 0.3 M concentration of NaCl, these red blood cells maintain their normal size and shape.

I hope this helps! Please let me know if you have any further questions :)