study guide ch 05 membrane transport

What does it mean that phospholipids are amphipathic?

Phospholipids have a hydrophilic (polar) head and hydrophobic (nonpolar) fatty acid tails.

How are phospholipids arranged in a membrane?

Phospholipids form a bilayer with heads facing water and tails facing inward away from water.

Why do phospholipids form a bilayer?

The bilayer forms because hydrophobic tails avoid water and hydrophilic heads interact with water.

What is one implication of the phospholipid bilayer?

It creates a selectively permeable barrier that controls what enters and leaves the cell.

What is the fluid mosaic model?

The membrane is a flexible layer of lipids with proteins embedded that move sideways.

What molecules make up a cell membrane?

Phospholipids, proteins, cholesterol, and carbohydrates make up the membrane.

How does temperature affect membrane fluidity?

High temperatures increase fluidity, while low temperatures decrease it.

How does membrane composition affect fluidity?

Unsaturated fats increase fluidity, while saturated fats decrease it.

What is the role of cholesterol in membranes?

Cholesterol stabilizes fluidity by preventing extremes in membrane movement.

What is the difference between integral and peripheral proteins?

Integral proteins are embedded in the membrane, while peripheral proteins sit on the surface.

What are six functions of membrane proteins?

Transport, enzymatic activity, signal transduction, cell recognition, intercellular joining, and cytoskeleton attachment.

What do glycoproteins and glycolipids have in common?

Both have carbohydrate chains used for cell recognition.

Where are carbohydrates located on the membrane?

They are found on the outer (extracellular) surface.

What is the role of membrane carbohydrates?

They help cells recognize and communicate with each other.

What does selectively permeable mean?

It allows some substances to pass while blocking others.

What is passive transport?

Movement of substances down their gradient without energy.

What is active transport?

Movement of substances against their gradient using ATP.

What is bulk transport?

Movement of large materials using vesicles.

How do hydrophobic molecules cross membranes?

They pass directly through the lipid bilayer.

How do hydrophilic molecules cross membranes?

They use transport proteins like channels or carriers.

What is diffusion?

Movement of molecules from high to low concentration.

What is osmosis?

Diffusion of water across a selectively permeable membrane.

What is a hypertonic solution?

Higher solute outside the cell, causing water to leave.

What is a hypotonic solution?

Lower solute outside the cell, causing water to enter.

What is an isotonic solution?

Equal solute concentrations, causing no net water movement.

What happens to animal cells in hypertonic, hypotonic, and isotonic solutions?

They shrink in hypertonic, swell or burst in hypotonic, and stay normal in isotonic.

What happens to plant cells in hypertonic, hypotonic, and isotonic solutions?

They plasmolyze in hypertonic, become turgid in hypotonic, and are flaccid in isotonic.

Why is a concentration gradient potential energy?

It stores energy that can drive movement down the gradient.

What adaptation does Paramecium use for water balance?

It uses a contractile vacuole to pump out excess water.

How can you predict movement across membranes?

Substances move from high to low concentration, and water moves toward higher solute concentration.

What is facilitated diffusion?

Passive transport using proteins to move substances down their gradient.

What is the difference between facilitated diffusion and active transport?

Facilitated diffusion needs no energy, while active transport requires ATP.

What is exocytosis?

Vesicles fuse with the membrane to release materials outside the cell.

What is endocytosis?

The membrane engulfs material to bring it into the cell.

When does a cell use exocytosis?

To secrete proteins, hormones, or wastes.

When does a cell use endocytosis?

To take in large particles or macromolecules.