Cell Membrane Structure and Transport Mechanisms: Biology Flashcards

Why is a water molecule considered polar?

Because it has partial negative charges on the oxygen atom and partial positive charges on the hydrogen atoms.

Which region of a phospholipid molecule interacts favorably with water?

The polar, hydrophilic phosphate head.

Why are nonpolar molecules repelled by the interior of the phospholipid bilayer?

The interior consists of hydrophobic nonpolar fatty acid tails.

What type of molecules can easily pass directly through the nonpolar region of the lipid bilayer?

Small, nonpolar molecules.

Why do ions and large polar molecules require transport proteins to cross the plasma membrane?

They are repelled by the hydrophobic, nonpolar interior of the lipid bilayer.

What role do carbohydrate chains play on the outer surface of the plasma membrane?

They act as cell-surface markers or 'name tags' for cell recognition.

How do receptor proteins function in cell communication?

They recognize and bind to specific chemical signal molecules outside the cell, triggering changes inside.

What is the function of enzymes embedded directly within the plasma membrane?

They speed up chemical reactions occurring along the membrane.

How do cholesterol molecules affect the structure of the plasma membrane?

They stabilize the membrane by preventing phospholipid tails from sticking together.

What concept describes the plasma membrane as flexible with embedded proteins that can move?

The Fluid Mosaic Model.

What is the key difference between passive transport and active transport?

Passive transport moves substances down their concentration gradient without energy, while active transport requires energy (ATP) to move substances against their gradient.

In simple diffusion, in what direction do molecules move?

From an area of higher concentration to an area of lower concentration.

What condition is reached when molecules continue moving continuously in both directions at equal rates across a membrane?

Dynamic equilibrium.

How does facilitated diffusion differ from simple diffusion?

Facilitated diffusion requires transport proteins (channel or carrier proteins) to help molecules cross.

What type of transport protein forms open tunnels through the plasma membrane for specific molecules to pass?

Channel proteins.

How do carrier proteins transport specific molecules across the plasma membrane during facilitated diffusion?

They bind to the molecule, change shape, and release the molecule on the other side.

What is osmosis?

The diffusion of water molecules across a selectively permeable membrane from higher to lower water concentration.

What happens to a cell when it is placed in an isotonic solution?

Water enters and leaves the cell at equal rates, so the cell maintains its size and shape.

In a hypotonic solution, which direction does water net-flow relative to the cell?

Water moves into the cell because the solute concentration is lower outside than inside.

What is cytolysis, and in which type of cells does it occur?

The bursting of animal cells when placed in a hypotonic solution.

Why do plant cells not burst when placed in a hypotonic solution?

They have a rigid cell wall that exerts pressure against the expanding vacuole.

What state describes a plant cell that is firm and full of water in a hypotonic environment?

Turgid.

What happens to a cell's volume when it is placed in a hypertonic solution?

The cell loses water and shrinks.

What is plasmolysis?

The process where the cytoplasm and plasma membrane pull away from the cell wall in plant cells placed in a hypertonic solution.

What term describes the shriveling or spiky appearance of animal red blood cells in a hypertonic environment?

Crenation.

What form of cellular energy directly drives active transport pumps?

ATP.

What type of protein is utilized to pump substances against their concentration gradient in active transport?

Carrier proteins.

What process allows a cell to ingest large particles or fluids by engulfing them with its plasma membrane?

Endocytosis.

How do white blood cells engulf foreign bacteria or invaders?

Through endocytosis (specifically phagocytosis).

What bulk transport process allows cells to release or secrete materials outside the cell using vesicles?

Exocytosis.