1. Be able to explain why the plasma membrane is impermeable to most chemicals. 2.Be able to explain the relationship between osmosis and diffusion. 3. be able to use the words "hypotonic," and "isotonic" correctly in a sentence. 4. Be able to describe facilitated transport and the role of channel and carrier proteins. 5. Be able to contrast passive and active transport, and to explain how one can move molecules or atoms against the concentration gradient. 6. Be able to explain how passive transport can allow a single type of molecule to cross an otherwise impermeable membrane. 7. Be able to contrast simple diffusion and facilitated diffusion. 8. Be able to contrast primary and secondary active transport. 9. Be able to explain the function of the sodium potassium pump well enough to complete an incomplete diagram. 10. Be able to name to process by which a cell eats and the process by which it drinks. Both are examples of a more general process, be able to name that as well. 11. Be able to explain why cell walls and cell adhesion molecules are necessary, and what they do. 12. Be able to give three examples of cell: cell junctions commonly found in multicellular animals.

Expert Answers

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1. Receptors (protein molecules) recognize which substances can pass through. Thus, the membrane is called selectively permeable. 

2. Diffusion is the passing of objects across a semipermeable membrane due to concentration differences. Substances are said to move "down the concentration gradient" during diffusion. This means that the substances move from an area of higher concentration to an area of lower concentration. 

Diffusion of water molecules is called osmosis. 

3. Hypotonic substances have lower osmotic pressure than other substances. 

So, pure water is hypotonic to salt water. 

Isotonic means that two substances have the same osmotic pressure. Isotonic substances have reached equilibrium in which water is moving at equal rates in each direction across the membrane. 

4. Facilitated diffusion is a form of passive transport across the membrane. It does not require energy. However, it utilizes channel and carrier proteins to allow substances that are too big to fit between the gaps of the phospholipids that make up the cell membrane to pass through it. 

5. Passive transport does not require energy whereas active transport does. The energy used is in the form of ATP. Active transport requires energy because it pushes substances against the concentration gradient (from low to high concentrations). 

6. See answer number one.

7. Simple diffusion is a form of passive transport that does not require a carrier protein. Facilitated diffusion is a form of passive transport that does require a carrier protein. 

8. When the process uses ATP as the form of energy it is called primary active transport. When the process uses an electrochemical gradient the it is classified as secondary. 

9. It functions in the active transport of sodium and potassium against their concentration gradients. 

10. Phagocytosis is cell eating. Pinocytosis is cell drinking. Both are forms of endocytosis. The ions are pumped to opposite sides of the membrane. This builds an electrical gradient that can be used to drive other transport processes. 

11. Cell walls give the cell an extra layer of support and protection. Cell adhesion molecules are proteins found on the outside of a cell membrane that helps the cell stick to other cells (thus the term "adhesion"). 

12. Tight junctions, gap junctions, adherens 

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