Plasma Membrane Structure, Transport, and Cell Walls

Flashcards covering membrane structure (hydrophobic interior, polar heads), selective permeability, diffusion for gases, transport via channels, aquaporins, and differences between plasma membranes and cell walls, plus archaeal lineage.

What composes the hydrophobic interior of the plasma membrane?

Nonpolar lipid tails of phospholipids forming the interior and blocking polar molecules and ions.

Are the phosphate heads polar or nonpolar?

Polar.

What do the polar phosphate heads form on the membrane surface?

Hydrophilic exterior surfaces facing the aqueous environment.

Which molecules can freely diffuse through the membrane's hydrophobic interior?

Small nonpolar gases such as O2, N2, and CO2.

Which molecules are blocked by the hydrophobic interior of the membrane?

Polar molecules and ions.

How do large polar molecules and ions cross the membrane?

Through protein channels or transport proteins.

Give examples of ions that require channels to cross the membrane?

Na+, K+, H+, and Cl−.

What are aquaporins?

Protein channels that allow large amounts of water to move in or out of cells.

Where do small uncharged polar molecules like water and ammonia move, and how?

They can move through the membrane in small amounts; water and ammonia are examples.

How does carbon dioxide move across the membrane?

Diffuses freely because it is a small nonpolar molecule.

What are cell walls and where are they found?

Rigid structures outside the plasma membrane found in plants, some bacteria, archaea, and some fungi; animals lack cell walls.

How do plasma membranes differ from cell walls in terms of rigidity?

Plasma membranes are fluid and flexible; cell walls are rigid.