Cell Boundaries 7.3

Cell Membrane

• Thin, flexible barrier around a cell; regulates what enters and leaves the cell.

Cell Wall

• Strong supporting layer around the cell membrane in plants, algae, and some bacteria.

Lipid Bilayer

• Double-layered sheet that forms the core of nearly all cell membranes.

Concentration

• The mass of solute in a given volume of solution, or the mass/volume.

Diffusion• Process by which molecules tend to

move from an area where they are more concentrated to an area where they less concentrated.

Equilibrium

• When the concentration of a solute is the same throughout a solution.

Osmosis• Diffusion of water through a selectively

permeable membrane.

Isotonic

• When the concentration of two solutions is the same.

Hypertonic • When comparing two solutions, the

solution with the greater concentrations of solutes.

Hypotonic• When comparing two solutions, the

solution with the lesser concentration of solutes.

Facilitated Diffusion • Movement of specific molecules across

cell membranes through protein channels.

Active Transport• Energy-requiring process that moves

material across a cell membrane against a concentration difference.

Endocytosis

• Process by which a cell takes material into the cell by infolding of the cell membrane.

Phagocytosis• Process in which extensions of cytoplasm

surround and engulf large particles and take them into the cell.

Pinocytosis • Process in which a cell takes in liquid

from the surrounding environment.

Exocytosis

• Process by which a cell releases large amounts of material.

Key Concept

• What are the main functions of the cell membrane and the cell wall?–The cell membrane regulates what

enters and leaves the cell and also provides protection and support. The main function of the cell wall is to provide support and protection for the cell.

Key Concept

• What happens during diffusion?–Because diffusion depends upon

random particle movements, substances diffuse across membranes without requiring the cell to use energy.

Key Concept

• What is osmosis?–It is the diffusion of water through a

selectively permeable membrane.