Cell Boundaries

Vocab Hypertonic Hypotonic Isotonic Protein channels Facilitated diffusion Active Transport Concentration gradient Endocytosis Phagocytosis Pinocytosis Exocytosis Cell membrane (phospho)lipid bilayer Cell wall Prokaryote Eukaryote High Concentration Low concentration Solute Solvent Equilibrium Diffusion Osmosis Selectively permeable

Objectives 1. What are the main functions of the cell membrane and the cell wall? 2. What happens during diffusion? 3. What is osmosis?

Cell Membrane All cells are surrounded by a thin, flexible barrier known as the cell membrane. The cell membrane regulates what enters and leaves the cell and also provides protection and support.

Cell Membrane

Cell Membrane The composition of nearly all cell membranes is a double-layered sheet called a lipid bilayer. It functions as a flexible barrier between the cell and its surroundings. Lipid bilayer

Cell Membrane Most cell membranes contain protein molecules embedded in the lipid bilayer. Carbohydrates are for recognition purposes. Protein channel

Cell Wall (plants) The main function of the cell wall is to provide support and protection for the cell.

Cell Wall Cell walls are found in plants, algae, fungi, and many prokaryotes. The cell wall lies outside the cell membrane. Most cell walls are porous enough to allow water, oxygen, carbon dioxide, and certain other substances to pass through easily.

Diffusion Through Cell Boundaries The cell membrane regulates movement of dissolved molecules from the liquid on one side of the membrane to the liquid on the other side.

Diffusion   Particles move from an area of more concentration to an area of less concentration. This process is called diffusion. When the concentration of the solute is the same throughout a system, the system has reached equilibrium.

High vs Low Concentration

Diffusion Substances diffuse across membranes without requiring the cell to use energy.

Diffusion A) There is a higher concentration of solute on one side of the membrane as compared to the other side of the membrane

Diffusion B) Particles move from the side of with a higher concentration to the side of the membrane with a lower concentration. The solute particles will continue to diffuse across the membrane until equilibrium is reached.

Diffusion C) When equilibrium is reached, solute particles continue to diffuse across the membrane in both directions.

Equilibrium is a balance of molecules on either side of the membrane.

Osmosis Osmosis is the diffusion of water through a selectively permeable membrane.

Selectively Permeable Cell membranes let some molecules enter a cell, but prevents other molecules from getting in. Can Enter Can Not Enter - Water - Small Molecules (O2 & CO2) - Non-polar lipids - Macromolecules - Ions (Na+,Cl-) - Hydrophilic molecules (glucose)

Osmosis Water tends to diffuse from a highly concentrated area of water to a less concentrated area of water.

Hypertonic hypertonic (“above strength”): the more concentrated solution SO, - Water leaves the cell - Animal cells shrink

c. Isotonic isotonic (”same strength”): When concentrations of solutions are the same on both sides of a membrane Water goes in and out at the same rate and pressure doesn’t change

Hypotonic hypotonic (“below strength”): the more dilute solution SO, Water enters the cell Animal cells expand and possibly burst

Types of Transport across a membrane

Simple Diffusion Molecules move from an area of high concentration to a low concentration. Does NOT require Energy. Happens naturally. (“Molecules move down its concentration gradient”)

Facilitated Diffusion Cell membranes have protein channels that act as carriers, allowing certain molecules to cross. The movement of specific molecules across cell membranes through protein channels is known as facilitated diffusion.

Facilitated Diffusion Only specific materials can enter or exit through each type channel.

Active Transport Sometimes cells move materials in the opposite direction from which the materials would normally move—that is against a concentration gradient. This process is known as active transport. Active transport requires ENERGY.

Active Transport Examples: Endocytosis is the process of taking material into the cell. Phagocytosis: Solids or large molecules moved Pinocytosis: “to drink,” Liquids moved Exocytosis removes materials from the cell.

Membrane Transport Summary Types of molecules transported Special channel required? Energy reguired? Diffusion Osmosis Facilitated diffusion Active transport no no Small molecules water no no yes no ions, sugars (glucose), salts yes yes ions (H+, K+, Na+, Ca2+)