Bio Test 2 Alternate

What is the plasma membrane?

The selectively permeable barrier surrounding a cell that controls what enters and leaves and helps maintain stable internal conditions.

What does selectively permeable mean?

A membrane allows certain substances to cross more easily than others based on their size, charge, polarity, and available transport proteins.

What is a phospholipid bilayer?

Two layers of phospholipids with hydrophilic heads facing water and hydrophobic tails facing inward.

What are hydrophilic heads?

The water-attracting, polar phosphate-containing parts of phospholipids that face the watery environments inside and outside the cell.

What are hydrophobic tails?

The nonpolar fatty acid chains that avoid water and point toward the center of the membrane.

Why do polar molecules and ions have difficulty crossing the membrane?

The membrane's hydrophobic interior prevents many charged or polar substances from passing through directly.

What is the fluid mosaic model?

A model describing the membrane as a flexible phospholipid bilayer containing different proteins and other molecules that can move laterally.

What does fluid mean in the fluid mosaic model?

Phospholipids and many membrane proteins can move sideways within the membrane.

What does mosaic mean in the fluid mosaic model?

The membrane contains a variety of proteins and other components with different functions.

What are peripheral proteins?

Proteins attached to the inner or outer membrane surface that do not penetrate the hydrophobic core.

What are integral proteins?

Proteins embedded in the membrane that penetrate its hydrophobic interior.

What are transmembrane proteins?

Integral proteins that extend completely across the phospholipid bilayer.

What are the six major functions of membrane proteins?

Transport, enzymatic activity, signal transduction, cell recognition, cell junctions, and attachment to structural components.

What is membrane fluidity?

How easily phospholipids and other components move within the membrane.

How do unsaturated fatty acids affect membrane fluidity?

Their double bonds create bends that prevent tight packing, increasing fluidity.

How do saturated fatty acids affect membrane fluidity?

Their straight tails pack tightly together, decreasing fluidity.

How does low temperature affect membrane fluidity?

It slows phospholipid movement and makes the membrane less fluid.

What does cholesterol do at moderate temperatures?

It restrains phospholipid movement and reduces membrane fluidity.

What does cholesterol do at low temperatures?

It prevents phospholipids from packing too tightly, helping prevent solidification.

What are glycolipids?

Membrane lipids with attached carbohydrate chains that help cells recognize one another.

What are glycoproteins?

Membrane proteins with attached carbohydrate chains that help with cell recognition and communication.

Where are the carbohydrate chains of glycolipids and glycoproteins located?

On the extracellular surface of the plasma membrane.

What is cell-to-cell recognition?

The ability of cells to identify and interact with other cells using surface molecules such as glycoproteins.

What is a receptor protein?

A protein that binds a specific signaling molecule and can initiate a response inside the cell.

What is signal transduction?

The process of converting an external signal received by a receptor into an intracellular response.

How can some HIV drugs prevent infection?

They interfere with viral interactions with cell receptors or other steps required for HIV to enter target cells.

What is passive transport?

Movement across a membrane without direct cellular energy input, down a concentration or electrochemical gradient.

What is a concentration gradient?

A difference in the concentration of a substance between two regions.

What is diffusion?

The net movement of particles from an area of higher concentration to an area of lower concentration.

What happens during diffusion at equilibrium?

Particles continue moving randomly in both directions, but there is no net movement.

What is simple diffusion?

Movement directly through the membrane without transport proteins or cellular energy input.

What is facilitated diffusion?

Passive movement down a gradient through a membrane channel or carrier protein.

What is osmosis?

The net diffusion of water across a selectively permeable membrane toward the side with a higher concentration of nonpenetrating solutes.

What happens to water during osmosis?

Water moves toward the side with more nonpenetrating solutes, making that side more dilute.

What is tonicity?

The ability of a surrounding solution to cause a cell to gain or lose water.

What is a hypotonic solution?

A solution with a lower effective concentration of nonpenetrating solutes than the cell, causing water to enter and the cell to swell.

What is an isotonic solution?

A solution with the same effective concentration of nonpenetrating solutes as the cell, causing no net water movement.

What is a hypertonic solution?

A solution with a higher effective concentration of nonpenetrating solutes than the cell, causing water to leave and the cell to shrink.

What happens to an animal cell in a hypotonic solution?

Water enters, causing the cell to swell and possibly burst.

What happens to an animal cell in an isotonic solution?

Water enters and leaves at equal rates, so the cell maintains approximately the same size.

What happens to an animal cell in a hypertonic solution?

Water leaves, causing the cell to shrink.

What is active transport?

Energy-dependent movement of substances across a membrane, often against their concentration or electrochemical gradient.

How does active transport differ from passive transport?

Active transport requires energy and can move substances against a gradient; passive transport moves down a gradient without direct energy input.

Why are transport proteins important?

They allow specific ions and polar molecules to cross the membrane when those substances cannot easily pass through the lipid bilayer.

How can ATP power active transport?

ATP hydrolysis supplies energy that changes a transport protein's shape and helps move substances against their gradient.