Membrane Permeability

What is the main function of cell membranes?

• To allow all substances to enter and leave a cell freely

• To prevent any substances from entering or leaving a cell

• To allow certain substances to enter and leave a cell while blocking others

• To destroy harmful materials entering a cell

Plasma membranes are described as being selectively permeable. What does this mean?

• They allow all substances to pass through without restriction

• They prevent all substances from passing through

• They allow some substances to pass through but not others

• They change permeability based on the cell's energy levels

What is the simplest form of transport across a membrane called?

• Active transport

• Bulk transport

• Facilitated diffusion

• Passive transport

What are two main kinds of passive transport methods that don't use a protein for assistance?

• Osmosis and active transport

• Diffusion and facilitated diffusion

• Diffusion and osmosis

• Active transport and facilitated diffusion

What is equilibrium in the context of diffusion?

• When the movement of molecules stops completely

• When the concentration of materials is high throughout a space

• When the concentration of materials is low throughout a space

• When the concentration of materials is equal throughout a space

What is diffusion?

• Movement of solutes from areas of high concentration to low concentration.

• Movement of solutes from areas of low concentration to high concentration.

What is a concentration gradient?

• A method of transporting molecules across a membrane.

• A type of diffusion that requires energy.

• A difference of concentrations between two areas, usually a membrane separates the two areas.

• The same concentration across an area.

What is facilitated diffusion?

• The process where molecules move across a membrane without any assistance.

• The movement of molecules across a membrane through a concentration gradient.

• The transport of molecules across a membrane with the help of membrane proteins.

• The diffusion of molecules that does not involve a concentration gradient.

Which molecules typically require facilitated diffusion to cross the plasma membrane?

• Hydrophobic molecules that can easily pass through the membrane.

• Molecules that are small and nonpolar.

• Charged ions or polar molecules.

• Gases like oxygen and carbon dioxide.

What is the primary function of channel proteins in a cell membrane?

• To facilitate the diffusion of molecules by providing hydrophilic tunnels

• To produce energy for cellular activities

• To replicate DNA within the cell

• To communicate signals to other cells