Biology 5.2 Cell Membrane Physiology Quiz

Electrochemical Gradient

• The greater concentration of positively charged ions outside the cell is primarily due to the sodium-potassium pump actively transporting sodium ions out of the cell and potassium ions into the cell. This unequal distribution of charges creates an electrochemical gradient, where the inside of the cell is more negative than the outside.
• The voltage difference across the cell membrane is known as the membrane potential.
• The sodium-potassium pump maintains the concentration gradients of sodium and potassium ions across the cell membrane.
• The net negative charge inside the cell is due to the presence of negatively charged proteins and other molecules that cannot easily cross the membrane.

Sodium-Potassium Pump

• The sodium-potassium pump is responsible for maintaining the electrochemical gradient across the cell membrane.
• If the sodium-potassium pump stopped functioning, the concentration gradients of sodium and potassium ions would eventually dissipate, leading to loss of membrane potential and disruption of cell functions.
• One effect of the sodium-potassium pump on cellular activity is the establishment of a resting membrane potential, which is essential for nerve impulse transmission and muscle contraction.

Concentration and Osmosis

• The term "low concentration" signifies a solution with a lower number of solute molecules per unit volume, compared to a higher concentration.
• "High concentration" indicates a solution with a higher number of solute molecules per unit volume.
• Concentration levels are categorized based on the relative number of solute molecules per unit volume, which is related to osmotic pressure.
• The diagram represents that concentration levels can be categorized into high, low, and isotonic, where isotonic implies equal concentration inside and outside the cell.
• High concentration would most likely have the highest particle interaction due to greater solute molecules per unit volume.
• A common misconception regarding low concentration is assuming it always indicates a lower concentration of water. However, low concentration can signify a lower concentration of any solute molecule.
• The factor that does NOT influence concentration in the diagram is volume, as volume can be variable without altering the solute concentration.
• The gradient from low to high concentration indicates a potential for diffusion, where molecules tend to move from areas of high concentration to areas of low concentration to achieve equilibrium.

Osmosis and Solutions

• In an isotonic solution, the concentration of solutes is equal inside and outside the cell, so there is no net movement of water.
• A cell placed in a hypotonic solution (lower solute concentration) will gain water, as water moves from an area of high concentration (outside the cell) to lower concentration (inside the cell) to achieve equilibrium. This can cause the cell to swell and potentially burst.
• A hypertonic solution (higher solute concentration) will draw water out of the cell, causing it to shrink (crenation).
• An isotonic solution is characterized by having a solute concentration equal to that of the cell.
• A hypotonic solution is characterized by having a lower solute concentration than the cell.
• The primary effect of a hypertonic solution on red blood cells is causing crenation, where the cells shrink due to water loss.
• In an isotonic solution, water movement is equal in both directions, meaning there is no net water flow into or out of the cell.
• Placing a cell in a solution with a higher solute concentration than its interior leads to water moving out of the cell due to osmotic pressure, causing cell shrinkage.
• The term used to describe the ability of a solution to draw water through a semipermeable membrane is osmotic pressure.
• The primary function of the kidneys in the context of osmoregulation is to regulate the concentration of solutes and water in the blood.
• Organisms that typically do not experience cell lysis in a hypotonic environment are those with cell walls, such as bacteria, plants, and fungi.
• To maintain osmotic pressure and prevent excessive water gain, cells may have mechanisms to actively pump out excess water or have rigid cell walls to resist swelling.
• Active transport is necessary to move solutes across the cell membrane against their concentration gradient, such as when pumping solutes into a compartment where they are already highly concentrated.
• A consequence of poorly regulated osmotic pressure in animal cells can lead to cell lysis (bursting) or crenation (shrinking), both of which can be detrimental to cell function.
• Adaptations play a crucial role in osmoregulation for different organisms, enabling them to survive in diverse environments with varying salt concentrations.
• A semipermeable membrane contributes to osmotic pressure by allowing water to move freely across the membrane, while restricting the movement of certain solutes.
• The main source of energy for primary active transport is ATP, which is produced through cellular respiration.
• For each cycle of the sodium-potassium pump, three sodium ions are moved out of the cell.
• The binding of sodium ions to the pump triggers a conformational change in the protein.
• After the binding of potassium ions to the pump, the protein changes conformation again, releasing potassium ions into the cell and binding sodium ions for another cycle.
• The result of the sodium-potassium pump's activity is the establishment and maintenance of the electrochemical gradient across the cell membrane, crucial for nerve impulse transmission and muscle contraction.
• The protein has a higher affinity for potassium ions during the phase where it is releasing sodium ions and ready to bind potassium.
• The term "conformational change" refers to the change in shape of the sodium-potassium pump protein as it binds and releases ions.
• The maximum number of potassium ions translocated into the cell per cycle of sodium-potassium pump operation is two.