3.3 Cell Membrane KEY CONCEPT The cell membrane is a barrier that separates a cell from the external environment.

3.3 Cell Membrane Cell membranes are composed of two phospholipid layers. AKA the phospholipid bilayer

3.3 Cell Membrane Cell membranes are composed of two phospholipid layers. The cell membrane has two major functions. cell membrane

3.3 Cell Membrane Cell membranes are composed of two phospholipid layers. The cell membrane has two major functions. – –forms a boundary between inside and outside of the cell cell membrane outside cell inside cell

3.3 Cell Membrane Cell membranes are composed of two phospholipid layers. The cell membrane has two major functions. – –forms a boundary between inside and outside of the cell – –controls passage of materials cell membrane outside cell inside cell

3.3 Cell Membrane Cell membranes are composed of two phospholipid layers.

3.3 Cell Membrane cell membrane Cell membranes are composed of two phospholipid layers. The cell membrane is made of a phospholipid bilayer.

3.3 Cell Membrane cell membrane Cell membranes are composed of two phospholipid layers. The cell membrane is made of a phospholipid bilayer. There are other molecules embedded in the membrane. protein cholesterol protein carbohydrate chain protein channel

3.3 Cell Membrane cell membrane Cell membranes are composed of two phospholipid layers. The cell membrane is made of a phospholipid bilayer. There are other molecules embedded in the membrane. The fluid mosaic model describes the membrane. protein cholesterol protein carbohydrate chain protein channel

3.3 Cell Membrane Cell membranes are composed of two phospholipid layers.

3.3 Cell Membrane Cell membranes are composed of two phospholipid layers. The cell membrane is selectively permeable. Some molecules can cross the membrane while others cannot.

3.3 Cell Membrane Cell membranes are composed of two phospholipid layers. The cell membrane is selectively permeable. Some molecules can cross the membrane while others cannot.

3.3 Cell Membrane Chemical signals are transmitted across the cell membrane, allowing materials in or out Receptors bind with ligands and change shape. There are two types of receptors.

3.3 Cell Membrane Chemical signals are transmitted across the cell membrane. Receptors bind with ligands and change shape. There are two types of receptors. – –intracellular receptor

3.3 Cell Membrane Chemical signals are transmitted across the cell membrane. Receptors bind with ligands and change shape. There are two types of receptors. – –intracellular receptor – –membrane receptor

KEY CONCEPT Materials move across membranes because of concentration differences. 3.4 Diffusion and Osmosis Which side of the membrane has a high concentration of particles? Which side of the membrane has a lower concentration?

moleculesDiffusion: The movement of molecules from an area of high concentration to an area of low concentration (Does not require a semipermeable membrane) *What would stop this movement? Concentration gradient: the difference in concentration from one area to another Molecules diffuse down a concentration gradient. Why would a cell want to bring particles in and send particles out? 3.4 Diffusion and Osmosis

Before we take anymore notes..... Let’s talk about dinner……

water moleculesOsmosis is the diffusion of water molecules across a semipermeable membrane. highlowerThis is a special form of diffusion (molecules are still moving from a region of high concentration to lower concentration) 3.4 Diffusion and Osmosis

Osmosis is the movement of water however, water is usually never pure… There are three types of solutions. Isotonic: equal concentrations of solutes, _____ amount of H Diffusion and Osmosis Hypotonic: lower solute concentration,_____ amount of H 2 0 Hypertonic: higher solute concentration,_____ amount of H 2 0

Water will move to an area that has a higher SOLUTE concentration (typically the area with lower water concentration) Which direction will the water move? (Assume the dots represent a solute, like NaCl)

Water will move to an area that has a lower WATER concentration Why is this important? abs/LS03/LS03.htmlhttp:// abs/LS03/LS03.html 3.4 Diffusion and Osmosis

Ticket out the door Take out a sheet of paper and a pen and answer the following in your own words: 1. What is osmosis? 2. How is osmosis different that diffusion? 3. If a solution is hypotonic to a cell, in which direction will water move (in or out of the cell)? 4. If a solution is isotonic to a cell, is there movement of water? 5. What can happen to a cell if it is placed in a hypertonic solution? How does this apply to us?

KEY CONCEPT Materials move across membranes because of concentration differences. This happens two basic ways: Passive Verses Active Passive  Does not require energy  Molecules move from high concentration to low  Strive for balance between cell and outside  Examples:  Diffusion  Osmosis  Facilitated diffusion Active  Requires energy  Molecules move from low concentration to high  Examples:  Sodium potassium pump  Endocytosis  exocytosis

Passive transport does not require energy input from a cell. Molecules can move across the cell membrane through passive transport. There are two types of passive transport. Diffusion: movement of molecules from high concentration to low Osmosis: movement of water to an area of high solute content 3.4 Diffusion and Osmosis

Some molecules can only diffuse through transport proteins. Some molecules cannot easily diffuse across the cell membrane. Facilitated diffusion is diffusion through transport proteins. (like a tunnel) 3.4 Diffusion and Osmosis

KEY CONCEPT Cells use energy to transport materials that cannot diffuse across a membrane. 3.5 Active Transport, Endocytosis, and Exocytosis

Active transport requires energy input from a cell and enables a cell to move a substance against its concentration gradient. Passive transport requires no energy from the cell. Active transport is powered by chemical energy (ATP). 3.5 Active Transport, Endocytosis, and Exocytosis Cells use active transport to maintain homeostasis. Active transport occurs through transport protein pumps.

A cell can import and export large materials or large amounts of material in vesicles during the processes of endocytosis and exocytosis. Cells use energy to transport material in vesicles. Endocytosis is the process of taking material into the cell. 3.5 Active Transport, Endocytosis, and Exocytosis Phagocytosis is a type of endocytosis.

A cell can import and export large materials or large amounts of material in vesicles during the processes of endocytosis and exocytosis. Cells use energy to transport material in vesicles. Exocytosis is the process of expelling material from the cell. 3.5 Active Transport, Endocytosis, and Exocytosis