04/12 04 Membranes, Transport, and Cellular Communication Free Online FlashCards

How does the phospholipid bilayer create selective permeability?

A phospholipid bilayer has hydrophilic heads facing water and hydrophobic fatty-acid tails facing inward, creating a selectively permeable hydrophobic core.

Which molecules cross the lipid bilayer most readily by simple diffusion?

Small nonpolar molecules such as O₂ and CO₂ cross the lipid bilayer readily because they dissolve in its hydrophobic interior.

Why is facilitated diffusion still considered passive transport?

Facilitated diffusion is passive: a channel or carrier helps a substance move down its concentration or electrochemical gradient without direct ATP use.

What two forces make up an ion’s electrochemical gradient?

For ions, the electrochemical gradient combines the concentration gradient with the electrical difference across the membrane.

What happens to an animal cell in a hypotonic solution?

Water moves into an animal cell, causing it to swell and possibly lyse, because the outside contains fewer nonpenetrating solutes than the cell.

How is percent change in mass calculated in an osmosis investigation?

The percent mass change is (final mass − initial mass) ÷ initial mass × 100.

What is turgor pressure?

A plant cell in a hypotonic environment develops turgor pressure as water enters and presses the plasma membrane against the rigid cell wall.

What is the typical ion ratio of the Na⁺/K⁺ pump?

The Na⁺/K⁺-ATPase uses one ATP to move three Na⁺ ions out of the cell and two K⁺ ions into the cell.

How does secondary active transport obtain energy?

Secondary active transport uses the energy of an ion electrochemical gradient to move another substance uphill; it does not hydrolyze ATP directly at the cotransporter.

How do symport and antiport differ?

Symport moves two substances in the same direction, whereas antiport moves them in opposite directions.

What are the four main stages of a cell-signaling pathway?

The four stages are reception, transduction, response, and termination.

How does a ligand-gated ion channel produce a cellular response?

A ligand-gated ion channel opens or closes when a ligand binds, allowing ions to move down their electrochemical gradients and rapidly alter the cell’s state.