PDQ AP Biology

1. Why is the plasma membrane described as selectively permeable? Because it allows certain molecules through

2. Which types of molecules can passively cross a membrane? Some small molecules Hydrophobic molecules Molecules that are soluble in lipids The more lipid soluble the molecule is, the faster it can diffuse through the phospholipid bilayer

2. Which types of molecules can NOT cross a membrane freely? Electrically charged molecules Polar molecules Examples: amino acids, sugars, ions, water Two reasons why they can’t cross: 1.Not very soluble in the hydrophobic interior of the bilayer 2.They form hydrogen bonds with water and ions in the aqueous solutions on either side of the membrane

3. Diffusion Process of random movement toward a state of equilibrium Net movement of molecules from a high concentration to a lower concentration So concentration drives diffusion to take place

4. affects on rate of diffusion Molecular Size – smaller molecules diffuse faster Temperature – higher temperatures lead to faster diffusion (heat provides more energy for movement of molecules) Concentration Gradient – The greater the concentration gradient, the more rapidly a substance will diffuse

5. Osmosis and Osmotic Pressure Osmosis Diffusion process of water molecules passing through specialized channels in membranes Depends on the concentration of water on both sides of the membrane Osmotic Pressure Also called turgor pressure Pressure on a cell due to the build up of water Keeps plants upright If enough water leaves the cells, turgor pressure drops and the plant will wilt.

6. Let’s look at A Top picture is animal, bottom picture is plant cell Arrows are showing water movement What type of environment is this cell in? Isotonic, arrows are going in both directions, meaning there is no net change in water movement

6. Let’s look at B Top picture is animal, bottom picture is plant cell Water is moving INTO the cell What type of environment is this cell in? Hypotonic. There must be more water outside the cell than inside the cell. In terms of solute, there must be more solute inside the cell and a LOW amount of solute outside the cell Causes animal cells to explode and plant cells will get a lot of turgor pressure

6. Let’s look at C Top picture is animal, bottom picture is plant cell Water is moving OUT of the cell What type of environment is this cell in? Hypertonic. There must be more water inside the cell than outside the cell. In terms of solute, there must be less solute inside the cell and a HIGH amount of solute outside the cell Causes animal cells to shrivel and plant cells will have less turgor pressure and wilt (vacuole gets small and cell membrane moves away from cell wall)

6. Answers. A.C B.B (you have to examine what is being referenced in the question) C.A D.Animal cells shrunk and are going through crenation. Plant cells are losing water and are going through plasmolysis. E.Outside the cell – HIGH solute, low water Inside the cell – LOW solute, high water Water moves from high to low, therefore it moves out of the cell. F. Animal cells are exploding and going through cytolysis. Plant cells are getting more water, and experiencing turgor pressure.

7. How do substances that cannot readily diffuse through the cell membrane get transported across? Through integral proteins!

8. Facilitated diffusion Substances diffuse the plasma membrane using channel or carrier proteins. They are diffusing based on concentration gradients.

9. Channel vs. Carrier proteins Channel Integral proteins Form channels across the membrane through which certain substances can pass Example is an ion channel They are either open or closed and most of them open when there is a stimulus or chemical signal (ligand) Carrier Integral proteins Substances bind to them to allow them to diffuse through the phospholipid bilayer Example – this is done with sugars and amino acids

Channel proteins

Carrier Proteins

Saturation of a carrier protein There are so many carrier proteins per unit of plasma membrane So there is a maximum rate that facilitated diffusion can occur

10. Gated Channel Channel protein that opens when a stimulus is involved Ligand- gated channels – channels that are controlled by a chemical signal, called a ligand. Voltage – gated channel – channels that are stimulated to open or close by a change in the voltage (electrical charge) across the membrane

Ligand Gated Channel

Voltage Gated Channel

11. Water Channel Protein Aquaporin Water moves through these proteins and is still PASSIVE transport, no energy is required.

12. Facilitated Diffusion vs Active Transport Facilitated Diffusion Passive Transport No ATP needed Uses proteins to move molecules across membrane Moves molecules from high to low concentrations Active transport Active Transport ATP is required Uses proteins or vesicles to move molecules across the membrane Moves molecules from low to high concentrations

13. Why does the Na-K pump result in the formation of an electric gradient? The transfer of Na and K is not even 3 Na+ go out Only 2 K+ go in. There will more of a positive charge on the outside of the cell

Primary Active Transport Vs Secondary Primary Involves direct hydrolysis of ATP Example - Na-K Pump Secondary Does not use ATP directly Its energy is supplied by an ion concentration gradient or an electrical gradient, established by primary active transport Example – Glucose uptake when Na passively diffuses back into cell.

25. Three methods of Endocytosis MethodDescribeContrast PhagocytosisEngulfing of large particle of an entire cell Food vacuole (phagosome) fuses with lysosome for it to be digested FOOD/Cells Food vacuole is involved PinocytosisFluids/Proteins are being brought into the cell FLUIDS/DISSOLVED SUBSTANCES or PROTEINS Constantly is occurring in cells surrounding blood Receptor Mediated EndocytosisUptake of macromolecules, but it depends on protein receptors and a signal for it to occur MACROMOLECULES Involved signal

17. Transport Processes Type of TransportEnergy RequiredDirectionRequirementsExample DiffusionNoHigh to LowConcentration Gradient Oxygen through membrane OsmosisNoHigh to LowConcentration Gradient Water uptake in plant cells Facilitated TransportNoHigh to lowConcentration Gradient & Integral Proteins Channel Proteins; Carrier Proteins Active TransportYESLow to HighIntegral Proteins, ATP Sodium Potassium Pump ExocytosisYESOut of cellVesicleSecretion of Proteins EndocytosisYESInto cellVesiclePhagocytosis Receptor Mediated Pinocytosis