Plasma Membranes
What does it mean that the plasma membrane is selectively permeable?
→ It controls what enters and exits the cell.
What is membrane potential?
→ The electrical charge difference across the plasma membrane. (Slide 3)
Which ion is more concentrated inside the cell?
→ Potassium (K⁺). (Slides 6–7)
What is diffusion?
→ Movement of substances from high to low concentration. (Slides 9–11)
What is active transport?
→ Movement of substances against their gradient, requiring energy. (Slides 8, 12)
Through which channels does K⁺ primarily leave the cell?
→ K⁺ leak channels. (Slide 13)
What does the Na⁺/K⁺ pump move in and out of the cell?
→ 3 Na⁺ out, 2 K⁺ in. (Slides 15–16)
Why is it important for all cells (not just nerve and muscle cells) to have a membrane potential?
→ It allows basic functions like transport and communication. (Slides 3–4)
What is homeostasis?
→ The state of balance within a biological system needed for proper function and survival. (Slide 18)
What are the two main macromolecule types that make up plasma membranes?
→ Lipids and proteins. (Slide 2)
What is the resting membrane potential (RMP)?
→ The electrical charge difference a cell maintains while at rest. (Slide 4)
Which ion is more concentrated outside the cell?
→ Sodium (Na⁺). (Slides 6–7)
What is osmosis?
→ Movement of water across a membrane. (Slides 9–11)
What molecule provides energy for primary active transport?
→ ATP. (Slide 12)
Why does Na⁺ enter the cell during resting conditions?
→ Both its chemical and electrical gradients favor entry. (Slide 14)
How many Na⁺ and K⁺ ions are exchanged per pump cycle?
→ 3 Na⁺ out, 2 K⁺ in. (Slides 15–16)
How does the Na⁺/K⁺ pump indirectly support secondary active transport?
→ By maintaining Na⁺ gradients used by cotransporters. (Slides 12, 15–16)
Why is homeostasis considered an active process?
→ Because the body is constantly in flux and must continuously adjust. (Slide 18)
How does the structure of the plasma membrane allow control over what enters and exits a cell?
→ Lipids form a barrier; proteins regulate transport. (Slide 2)
Which two gradients must be maintained for a resting membrane potential?
→ A chemical gradient and an electrical gradient, in opposite directions. (Slide 4)
What role do leak channels play in maintaining charge distribution?
→ They allow passive ion movement, shaping membrane potential. (Slides 6–7)
What is the difference between simple diffusion and facilitated diffusion?
→ Simple goes directly through the membrane; facilitated requires channels/carriers. (Slide 11)
How does secondary active transport differ from primary active transport?
→ Primary uses ATP directly; secondary couples one gradient to another. (Slide 12)
What does it mean that K⁺ movement is toward chemical equilibrium but against electrical equilibrium?
→ K⁺ moves out to balance concentration, but this increases electrical imbalance. (Slide 13)
Why does the Na⁺/K⁺ pump require ATP?
→ To move ions against their gradients. (Slides 15–16)
Why does a cell’s membrane potential represent “stored energy”?
→ Uneven ions create potential energy, like a battery. (Slides 3–4, 15)
What would happen if your body stopped being in flux (in states of change)?
→ You would die, since balance requires constant adjustment. (Slide 18)
Compare the roles of lipids and proteins in the plasma membrane.
→ Lipids create a hydrophobic barrier; proteins provide channels, carriers, and receptors. (Slide 2)
Why is RMP especially important in nerve and muscle cells?
→ It primes them to respond instantly with signals or contraction. (Slide 5)
Why do negatively charged molecules inside the cell contribute to the membrane potential?
→ They cannot leave, keeping the inside more negative. (Slide 6)
Why does passive transport not require energy?
→ Molecules move down their concentration gradient. (Slides 9–11)
Why does active transport require energy while passive transport does not?
→ Active goes up the gradient, passive goes down. (Slides 9, 12)
How does the balance of K⁺ leaving and Na⁺ entering set the resting membrane potential?
→ It keeps the inside negative while maintaining gradients. (Slides 13–14)
How does the Na⁺/K⁺ pump help maintain the resting membrane potential?
→ It restores Na⁺ and K⁺ gradients after leak movements. (Slides 15–16)
Apply the concept of gradients to explain how Gatorade (electrolytes) affects muscle cells.
→ It restores ion balance, helping muscles contract. (Supplemental, linked to Slides 5–7, 15–16)
What is the difference between negative and positive feedback loops?
→ Negative feedback slows as effects build; positive feedback increases as effects build. (Slides 19–21)
Why is selective permeability vital for maintaining a membrane potential?
→ It keeps ions unevenly distributed, creating electrical charge differences. (Slide 2)
Explain how RMP represents potential energy for a cell.
→ The uneven ion distribution creates stored energy. (Slide 3–4)
Explain how the unequal distribution of Na⁺ and K⁺ is maintained across the membrane.
→ By Na⁺/K⁺ pumps and leak channels. (Slides 6–7, 15–16)
Compare channel-mediated vs carrier-mediated diffusion.
→ Channel: always open; carrier: changes shape, sometimes closed. (Slide 11)
Explain how the Na⁺/K⁺ pump works as an example of active transport.
→ It uses ATP to move 3 Na⁺ out and 2 K⁺ in. (Slides 15–16)
Explain why the inside of the cell remains slightly negative even though Na⁺ enters.
→ More K⁺ leaves than Na⁺ enters, leaving negatives inside. (Slides 13–14)
Compare the Na⁺/K⁺ pump to passive leak channels in terms of function.
→ Pumps use ATP to restore gradients; leak channels allow passive flow. (Slides 6–7, 15–16)
Compare active vs passive transport in terms of efficiency and energy usage.
→ Passive: no energy, quick diffusion; Active: energy-dependent, maintains gradients. (Slides 8–12, 15–16)
Give an example of a negative feedback loop in the body.
→ Shivering when cold (Slide 20).
→ Sweating when hot (Supplemental: Textbook/Discussion).
→ Regulation of blood glucose by insulin (Supplemental: Textbook/Discussion).
Predict what would happen to a cell if its membrane became fully permeable to all substances.
→ The cell would lose ion gradients, membrane potential, and likely die. (Slide 2)
Apply the concept of RMP to explain how a neuron is “primed” for action.
→ The imbalance of ions allows rapid depolarization when channels open. (Slide 5)
Predict the effect on membrane potential if Na⁺ leak channels increased in number.
→ The cell would become less negative inside. (Slide 7)
Apply the concept of passive transport to explain how oxygen enters cells.
→ Oxygen diffuses directly through the membrane. (Slides 9–11)
Apply the concept of secondary active transport to explain how glucose may enter a cell.
→ Glucose moves in while Na⁺ moves down its gradient. (Slide 12)
Apply the concept of equilibrium to explain why K⁺ does not continue moving out indefinitely.
→ Electrical force balances chemical force at equilibrium. (Slide 13)
Apply the “compressed spring” analogy to explain potential energy in the Na⁺/K⁺ pump system.
→ Stored gradients are like a spring ready to release energy. (Slide 15)
Integrate diffusion, active transport, and pumps to explain how neurons reset after firing.
→ Diffusion moves ions, pumps restore gradients, reestablishing RMP. (Slides 12–16)
Give an example of a positive feedback loop in the body.
→ Platelet accumulation at a wound site (Slide 21).
→ Uterine contractions during childbirth (Supplemental: Textbook/Discussion).
→ Lactation (milk let-down reflex) (Supplemental: Textbook/Discussion).
How does selective permeability help a cell maintain a stable internal environment?
→ It regulates ion movement to keep balance and homeostasis. (Slide 2)
Why is the resting membrane potential important for nerve and muscle cells?
→ It enables rapid signaling and contraction. (Slide 5)
How does having more K⁺ leak channels than Na⁺ leak channels affect the inside of the cell?
→ More K⁺ leaves than Na⁺ enters, making the inside negative. (Slides 6–7)
What happens to a cell placed in a hypertonic solution?
→ Water leaves, and the cell shrinks. (Slides 9–11)
What would happen if a cell suddenly ran out of ATP?
→ Active transport would stop; gradients would collapse. (Slides 12, 15–16)
What would happen to the membrane potential if Na⁺ entered the cell more easily than normal?
→ The inside would become less negative. (Slide 14)
What would happen to ion gradients if the Na⁺/K⁺ pump stopped working?
→ Gradients would collapse, and RMP would be lost. (Slides 15–16)
How does drinking a sports drink with electrolytes help restore ion balance in muscle cells?
→ It replaces Na⁺ and K⁺ lost in sweat, restoring gradients. (Supplemental, linked to Slides 5–7, 15–16)
Why are most physiological processes controlled by negative feedback rather than positive feedback?
→ Because negative feedback stabilizes systems, while positive feedback amplifies changes. (Slides 20–21)
Explain how both lipids and proteins in the plasma membrane work together to control transport.
→ Lipids form the barrier, while proteins provide selective pathways for molecules. (Slide 2)
What would happen to a cell if it could not maintain a resting membrane potential?
→ It could not signal or contract properly. (Slides 3–5)
Why do cells use energy to keep Na⁺ and K⁺ unevenly distributed?
→ To maintain gradients needed for RMP and signaling. (Slides 6–7, 15–16)
How is facilitated diffusion different from simple diffusion?
→ Facilitated needs proteins; simple occurs through lipids. (Slide 11)
Why is active transport important even though it requires energy?
→ It maintains gradients for cell survival and signaling. (Slides 12, 15–16)
Why does the balance of Na⁺ and K⁺ leak channels keep the cell slightly negative inside?
→ More K⁺ leaks out than Na⁺ enters, leaving negatives inside. (Slides 13–14)
Why is the Na⁺/K⁺ pump essential for maintaining the resting membrane potential?
→ It actively restores gradients needed for stability and signaling. (Slides 15–16)
Why might changes in extracellular K⁺ levels (like too much K⁺ in the blood) affect muscle or nerve activity?
→ They reduce the normal gradient, making RMP unstable. (Slides 6–7, 13–14 + Supplemental)
How do feedback loops contribute to maintaining homeostasis?
→ They detect disturbances and trigger responses that restore balance, keeping body systems within operating parameters. (Slides 19–21)