Question

cue questions for ap bio topic 2.6: facilitated diffusion

1. why cant charged ions like na⁺ and cl⁻ pass directly through the phospholipid bilayer?
2. what structural features of glucose prevent it from crossing the membrane without assistance?
3. how do aquaporins enhance water transport compared to simple diffusion?
4. what type of transport protein is used by amino acids to cross the membrane?
5. how does facilitated diffusion contribute to membrane polarization in nerve cells?

tonicity and osmoregulation: water potential and maintaining homeostasis | ap biology 2.8
here are 5 cue questions based on the ap biology 2.7 tonicity and osmoregulation study notes:
cue questions for ap bio topic 2.7: tonicity and osmoregulation

1. what determines the direction of water movement across a cell membrane?
2. how do hypotonic, isotonic, and hypertonic solutions affect animal and plant cells differently?
3. what role do contractile vacuoles play in freshwater protists like paramecium?
4. how does osmoregulation help organisms maintain homeostasis in different environments?

Explanation:

1. The phospholipid bilayer has a non - polar interior. Charged ions like Na⁺ and Cl⁻ are polar and are repelled by the non - polar region, so they cannot pass directly.
2. Glucose is a large, polar molecule. Its polarity and size prevent it from crossing the non - polar lipid bilayer without assistance.
3. Aquaporins are channel proteins that form a hydrophilic pore. They provide a specific pathway for water molecules, increasing the rate of water transport compared to simple diffusion through the lipid bilayer.
4. Amino acids use carrier proteins to cross the membrane. Carrier proteins bind to the amino acids, change shape, and transport them across the membrane.
5. In nerve cells, facilitated diffusion of ions (such as K⁺ and Na⁺) through ion channels contributes to the establishment and maintenance of the membrane potential, which is related to membrane polarization.

For the tonicity and osmoregulation questions:

1. The water potential gradient determines the direction of water movement across a cell membrane. Water moves from an area of higher water potential to an area of lower water potential.
2. Hypotonic solutions cause animal cells to swell and burst (lysis) while plant cells become turgid. Isotonic solutions result in no net water movement in both cell types. Hypertonic solutions cause animal cells to shrink and plant cells to plasmolyze.
3. Contractile vacuoles in freshwater protists like Paramecium collect and expel excess water that enters the cell due to the hypotonic environment outside, preventing the cell from bursting.
4. Osmoregulation helps organisms maintain a stable internal osmotic environment by regulating the movement of water and solutes, which is crucial for homeostasis in different environmental conditions.

Answer:

1. Charged ions are polar and repelled by non - polar interior of bilayer.
2. Glucose is large and polar.
3. Aquaporins provide specific hydrophilic pathway for water.
4. Carrier proteins.
5. Facilitated diffusion of ions affects membrane potential.

For tonicity and osmoregulation:

1. Water potential gradient.
2. Hypotonic: animal cells swell/lyse, plant cells turgid; Isotonic: no net movement; Hypertonic: animal cells shrink, plant cells plasmolyze.
3. Collect and expel excess water.
4. Regulates water and solute movement for homeostasis.