Question

an example should help you understand diffusion. picture yourself dropping a tea - bag into a cup of boiling water, but not stirring the cup. the bag itself represents the (1 ) cell membrane, which lets only some molecules leave the tea bag. as the tea molecules (2 ) in the hot water and collide repeatedly, they begin to “spread out” from the tea bag even though it was never stirred. eventually, as a result of their activity, the entire cup will have the same concentration of tea (3 ) and will appear uniform in color (a laboratory example that might be familiar to some students is illustrated figure 3.9). the hydrophobic core of the plasma membrane is a physical barrier to diffusion. however, molecules will (4 ) through the plasma membrane if any of the following are true. the molecules are small enough to pass through the membrane’s pores (channels formed by membrane proteins) the molecules are lipid - soluble. *the molecules are assisted by a membrane carrier. the unassisted diffusion of solutes through the plasma membrane (or any selectively permeable membrane) is called simple diffusion (figure 3.10a). solutes (5 ) this way are lipid - soluble (such as fats, fat - soluble vitamins, oxygen, carbon dioxide).
1 semipermeable 2 dissolve 3 molecules 4 diffuse 5 transported
1 diffuse 2 transported 3 semipermeable 4 dissolve 5 molecules
1 dissolve 2 molecules 3 diffuse 4 transported 5 semipermeable
1 transported 2 semipermeable 3 dissolve 4 molecules 5 diffuse
1 molecules 2 diffuse 3 transported 4 semipermeable 5 dissolve

Explanation:

1. A cell - membrane is semipermeable, allowing only some molecules to pass through, like the tea - bag.
2. Tea molecules dissolve in hot water.
3. Eventually, the tea molecules spread out evenly (diffuse) in the water.
4. Molecules can diffuse through the plasma membrane under certain conditions.
5. Solutes that can diffuse without assistance are lipid - soluble and are transported in this way.

Answer:

1. semipermeable
2. dissolve
3. molecules
4. diffuse
5. transported