Plasma membrane Flashcards
plasma membrane (21 cards)
What is the primary function of the plasma membrane?
Separates the cell from its environment and controls the movement of substances in and out of the cell
The plasma membrane exhibits selective permeability.
What are phospholipids?
The most abundant membrane lipids that are amphipathic, containing hydrophilic heads and hydrophobic tails
They form a bilayer with hydrophobic tails shielded from water.
What is the Fluid Mosaic Model?
Describes the membrane as a fluid structure with proteins embedded like a mosaic
Proteins are not randomly distributed and often form specialized patches.
How does temperature affect membrane fluidity?
Higher temperatures increase fluidity, while lower temperatures may solidify the membrane
Solidification can lead to loss of function.
What role does cholesterol play in membrane fluidity?
Reduces fluidity at high temperatures and prevents solidification at low temperatures
Acts as a ‘fluidity buffer.’
What is diffusion?
The movement of molecules from high to low concentration until equilibrium is reached
It is a passive transport process.
Define osmosis.
The diffusion of free water molecules across a selectively permeable membrane
Water moves from areas of higher free water concentration to lower.
What happens to a cell in a hypertonic solution?
Water leaves the cell, causing it to shrink
In animal cells, this is called crenation; in plant cells, it leads to plasmolysis.
What is osmoregulation?
The regulation of water balance by organisms
Example: Paramecium uses a contractile vacuole to pump out excess water.
What are channel proteins?
Proteins that provide hydrophilic corridors for specific molecules or ions
Examples include aquaporins and ion channels.
What is the sodium-potassium pump?
An active transport mechanism that pumps 3 Na⁺ out and 2 K⁺ into the cell
Creates a net negative charge inside the cell.
Define membrane potential.
The voltage difference across a cell membrane, typically between -50 to -200 mV
The inside of the cell is negative relative to the outside.
What is cotransport?
A mechanism that uses an ion gradient created by active transport to drive the movement of another molecule against its concentration gradient
Example: H⁺/Sucrose cotransporter in plants.
What is exocytosis?
The process where transport vesicles fuse with the plasma membrane and release contents outside the cell
Examples include insulin secretion and neurotransmitter release.
What is phagocytosis?
A type of endocytosis that involves engulfing large particles or bacteria
Example: White blood cells attacking bacteria.
What is receptor-mediated endocytosis?
A process where specific molecules bind to membrane receptors before being internalized
Example: Cholesterol-bound LDLs.
Fill in the blank: The diffusion of free water molecules across a selectively permeable membrane is called _______.
[osmosis]
True or False: Active transport requires energy to move molecules against their concentration gradient.
True
List the two types of transport proteins.
- Channel Proteins
- Carrier Proteins
What happens to a cell in a hypotonic environment?
Water enters the cell, causing it to swell and possibly burst
In plant cells, it becomes turgid.
What are the effects of an isotonic solution on cells?
No net water movement; cells remain stable
In animal cells, they maintain normal shape.
