Plasma Membrane, Diffusion, and Tonicity Review

Flashcards covering plasma membrane structure and function, membrane dynamics (fluid mosaic), selective permeability, diffusion, and tonicity with plant-vs-animal cell considerations.

What is the primary function of the plasma membrane?

To regulate what enters and leaves the cell, providing selective permeability.

What is the phospholipid bilayer, and how are phospholipids arranged in it?

Two layers of phospholipids with hydrophilic heads facing outward toward water and hydrophobic tails facing inward; the tails of the two leaflets face each other in the middle.

What are hydrophilic heads and hydrophobic tails?

Hydrophilic heads are water-loving; hydrophobic tails are water-fearing (nonpolar).

Besides phospholipids, what other components are in the plasma membrane and what are their roles?

Proteins embedded in the membrane act as channels or carriers for passage; carbohydrates bound to the exterior (glycoproteins/glycolipids) play a role in immune response and cell recognition.

What does the Fluid Mosaic Model describe?

The plasma membrane is a dynamic, fluid mixture of lipids and proteins that can move laterally, not a rigid wall.

What does selective permeability mean for the plasma membrane?

The membrane allows some substances to pass while restricting others, based on properties like polarity and solubility.

Which types of molecules pass through the lipid bilayer most easily, and why?

Nonpolar, lipid-soluble molecules pass easily because of the hydrophobic interior of the membrane.

What is diffusion?

Spontaneous spreading of molecules from higher concentration to lower concentration, moving down a concentration gradient.

What factors affect the rate of diffusion?

Concentration gradient magnitude and temperature (and other factors); larger gradient and higher temperature increase the rate.

What is tonicity?

The relative solute concentration of two solutions around a cell, used to predict the direction of water movement.

How do isotonic, hypotonic, and hypertonic solutions affect cells?

Isotonic: no net water movement; hypotonic: water tends to move into the cell; hypertonic: water tends to move out of the cell, causing shrinkage.

What change occurs in plant cells in hypotonic conditions, and what structural feature helps resist this change?

Water enters the cell and the plant uses the cell wall to provide rigidity through turgor pressure.

What is turgor pressure?

The pressure from the cell contents against the plant cell wall that helps keep the cell rigid and supports the plant.

What happens if the plasma membrane is subjected to too much pressure?

The membrane can fail and the cell may burst (lyse).

What is the role of carbohydrates on the exterior of the membrane?

Carbohydrates bound to exterior components help with immune responses and cell recognition.