Question

which statements describe examples of facilitated diffusion? an epithelial cell releases calcium ions against their concentration gradient using a membrane pump and the energy of another concentration gradient. a plant cell loses water directly through its plasma membrane during plasmolysis in a hypertonic solution. a neuron allows potassium ions to leave the cell down their concentration gradient using a membrane channel. an erythrocyte low on glucose replenishes its supply using a membrane protein to transport glucose down its concentration gradient. an inner ear hair cell allows potassium ions to flow down their concentration gradient after sound waves stimulate a membrane protein. a neuron moves potassium ions into the cell against their concentration gradient using a membrane pump and cellular energy.

Explanation:

Facilitated diffusion is the passive transport of molecules or ions across a biological membrane via specific transport proteins (channels or carriers) down their concentration gradient.

1. The first option is active transport as it involves moving ions against the concentration - gradient using energy.
2. The second option is simple diffusion of water (osmosis) as water moves directly through the plasma membrane.
3. The third option is facilitated diffusion as potassium ions leave the neuron down their concentration gradient through a membrane channel.
4. The fourth option is facilitated diffusion as glucose is transported down its concentration gradient using a membrane protein.
5. The fifth option is facilitated diffusion as potassium ions flow down their concentration gradient through a membrane protein after sound - wave stimulation.
6. The sixth option is active transport as it involves moving potassium ions against the concentration gradient using cellular energy.

Answer:

• A neuron allows potassium ions to leave the cell down their concentration gradient using a membrane channel.
• An erythrocyte low on glucose replenishes its supply using a membrane protein to transport glucose down its concentration gradient.
• An inner ear hair cell allows potassium ions to flow down their concentration gradient after sound waves stimulate a membrane protein.