Chapter+5+Notes

**Diffusion and Osmosis** **Diffusion** - the process by which molecules spread from areas of high concentratiion, to areas of low concentration. It is driven by kinetic energy already found in molecules. When the molecules are even throughout a space - it is called **EQUILIBRIUM** ~these molecules are still moving!!! **Concentration gradient** - a difference between concentrations in a space. What can affect diffusion? ~concentration gradient ~size of the molecule ~type of molecule ~chemical nature of the membrane (single layer or lipid bilayer) Selectively Permeable - membranes that allow some things through, the cell membrane is selectively permeable, **water and oxygen move freely across the cell's membrane, by diffusion** **Osmosis** - the diffusion of water (across a membrane) Water will move in the direction where there is a high concentration of solute (and hence a lower concentration of water.  A simple rule to remember is:   Salt is a solute, when it is concentrated inside or outside the cell, it will draw the water in its direction. This is also why you get thirsty after eating something salty.   Type of Solutions  "**ISO**" means the same
 * [[image:http://www.biologycorner.com/resources/isotonic.gif width="250" height="203"]] || If the concentration of solute (salt) is equal on both sides, the water **will move back in forth** but it won't have any result on the overall amount of water on either side.

Molecules are at even concentrations so... Equallibrium has been reached || The cell will gain water and grow larger. In plant cells, the central vacuoles will fill and the plant becomes stiff and rigid, the cell wall keeps the plant from bursting In animal cells, the cell may be in danger of bursting, organelles called **CONTRACTILE VACUOLES** will pump water out of the cell to prevent this.
 * [[image:http://www.biologycorner.com/resources/hypotonic.gif width="240" height="203"]] || The word "**HYPO**" means less, in this case there are less solute (salt) molecules outside the cell, since salt sucks, water will move into the cell.

Concentration is higher inside the cell so water moves in! || In plant cells, the central vacuole loses water and the cells shrink, causing wilting. In animal cells, the cells also shrink. <span style="FONT-FAMILY: Arial, Helvetica, sans-serif">In both cases, the cell may die. <span style="FONT-FAMILY: Arial, Helvetica, sans-serif">This is why it is dangerous to drink sea water - its a myth that drinking sea water will cause you to go insane, but people marooned at sea will speed up dehydration (and death) by drinking sea water. <span style="FONT-FAMILY: Arial, Helvetica, sans-serif">This is also why "salting fields" was a common tactic during war, it would kill the crops in the field, thus causing food shortages.
 * [[image:http://www.biologycorner.com/resources/hypertonic.gif width="240" height="203"]] || <span style="FONT-FAMILY: Arial, Helvetica, sans-serif">The word "**HYPER**" means more, in this case there are more solute (salt) molecules outside the cell, which causes the water to be sucked in that direction.

Concentration is higher outside the cell so water moves out! || <span style="FONT-FAMILY: Arial, Helvetica, sans-serif"> Osmotic Pressure in Red Blood Cells Turgor Pressure on Plant Cells

Diffusion and Osmosis are both types of **PASSIVE TRANSPORT** - that is, no energy is required for the molecules to move into or out of the cell.

<span style="FONT-FAMILY: Arial, Helvetica, sans-serif">Sometimes, large molecules cannot cross the plasma membrane, and are "helped" across by **carrier proteins** - this process is called **facilitated diffusion**. Diffusion through ion channels ~Ions are not soluble across the lipid membrane ~Ion channels are specific to thier ion, no other ion may pass through it ~Some factors affect the opening of the ion channel 1. stretching of the cell membrane = not open 2. electrical stimuli (+ and - charges) will open and close 3. chemicals in the cytosol ( muscle movement)

<span style="FONT-FAMILY: Arial, Helvetica, sans-serif">ACTIVE TRANSPORT
Active Transport - When cells must move materials in an opposite direction - against a concentration gradient. It requires Energy. Proteins or Pumps are found in the cell membrane transport molecules across the membrane. Molecular Transport - Proteins are used to move small molecules such as calcium, potassium, and sodium ions against the concentration gradient. Sodium potassium pump- protiens that are specific to sodium and potassium ions ~transports sodium and potassium ions against the gradient ~allows potassium concentrations and sodium concentrations to stay stable ~these two ions are important for neural impulses and muscular contractions [|View Animation of Active Transport] ATP splits and changes the shape of pump One complete cycle pumps three sodium outside of the cell and two potassium inside of the cell creating an electrical gradient like a battery <span style="FONT-FAMILY: Arial, Helvetica, sans-serif">**Endocytosis** - cell takes in large particles by engulfing them

<span style="FONT-FAMILY: Arial, Helvetica, sans-serif">Types of endocytosis:
 * Phagocytosis** - "cell eating" - extensions off cytoplasm surround a particle and package it within a food vacuole and then the cell engulfs it creating a **vessicle** (a pouch tha forms around the molecule being released) Ex. Amoebas use this process.
 * Pinocytosis** - the process of taking up liquid from the surrounding environment. Tiny pockets form along the membrane, fill with liquid, and pinch off.

<span style="FONT-FAMILY: Arial, Helvetica, sans-serif">**Exocytosis** - cell gets rid of particles that are waste or particles another cell needs, Exactly the opposite of endocytosis (turn the arrows around above)