Section 1 Passive Transport Chapter 5 Objectives Explain how an equilibrium is established as a result of diffusion. Distinguish between diffusion and osmosis. Explain how substances cross the cell membrane through facilitated diffusion. Explain how ion channels assist the diffusion of ions across the cell membrane.

Section 1 Passive Transport Chapter 5 Passive transport involves the movement of molecules across the cell membrane without an input of energy by the cell. Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration As a result of diffusion, the concentration of many types of substances eventually becomes balanced on both sides of a membrane

Diffusion Concentration gradient is the difference in the concentration of molecules across a distance Equilibrium is a state that exists when the concentration of a substance is the same throughout a space (homeostasis) Big Bang Theory MAKE YOUR OWN ANIMATION OF EQUILIBRIUM!!!!! High Conc. Water Low Conc. Water Low Conc. Solute High Conc. Solute

Diffusion What does this look like on the microscopic level? Animation http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html Sugar molecules, initially in a high concentration at the bottom of the beaker, will move about randomly through diffusion, and eventually reach equilibrium. At equilibrium the sugar concentration will be the same throughout the beaker. Diffusion occurs naturally because of the kinetic energy the molecules possess ***Another example of diffusion would be the dispersal of ink in a beaker of water

Chapter 5 Diffusion cont. Section 1 Passive Transport Remember that diffusion is movement from high concentrations to low concentrations,

Diffusion Diffusion Across Membranes Molecules can diffuse across a cell membrane by dissolving in the phospholipid bilayer or by passing through pores in the membrane Diffusion across a membrane is “simple diffusion” (only certain molecules pass through) NO energy is expended (used up) iodine baggy demo http://www.biologycorner.com/bio1/diffusion.html

Section 1 Passive Transport Chapter 5 Osmosis Osmosis is the diffusion (or passing) of water across a cell membrane. Since water is moving from a higher to lower concentration, osmosis does not require cells to expend energy. Therefore, osmosis is the passive transport of water

The Direction of Osmosis The NET direction of osmosis is determined by the relative concentrations of solute on either side of a membrane There are specific names for solutions depending on their solute concentrations: Hypotonic Hypertonic Isotonic Remember that CYTOSOL is the soluble portion of the cytoplasm – the fluid that water or solutes flow into or out of

Osmosis: Hypotonic Solutions Hypotonic (“Hypo-” is Greek for “under”) When the concentration of solute molecules outside the cell is lower than their concentration in the cytosol (cell), the solution outside is hypotonic to the cytosol (cell) What direction do you think water will diffuse? Water will diffuse INTO the cell until equilibrium is established

Osmosis: Hypertonic Solutions Hypertonic (“Hyper-” is Greek for “over”) When the concentration of solute molecules outside the cell is higher than their concentration in the cytosol(cell), the solution outside is hypertonic to the cytosol (cell). What direction do you think water will diffuse? Water will diffuse OUT OF the cell until equilibrium is established

Osmosis: Isotonic Solutions Isotonic (“Iso-” is Greek for “equal”) When the concentration of solute molecules inside and outside the cell are equal, the solution outside is isotonic to the cytosol(cell). What direction do you think water will diffuse? Water will diffuse IN AND OUT AT EQUAL RATES so there is no net movement of water (it’s in equilibrium!)

Hypertonic, Hypotonic, Isotonic Solutions Section 1 Passive Transport Chapter 5 Hypertonic, Hypotonic, Isotonic Solutions Table 5-1, pg 99

Chapter 5 Osmosis, continued Section 1 Passive Transport Chapter 5 Osmosis, continued The cell wall of plants are strong enough to resist the pressure (turgor pressure) exerted by water in the central vacuole. The condition of turgor pressure decreasing is called plasmolysis, and is the reason that plants wilt if they don’t receive enough water The bursting of cells due to the increase of turgor pressure is called cytolysis

Facilitated Diffusion Section 1 Passive Transport Chapter 5 Facilitated Diffusion Facilitated diffusion is the transport of substances through a cell membrane along a concentration gradient with the aid of carrier proteins Carrier protein is a protein that transports substances across a cell membrane In facilitated diffusion, a molecule binds to a carrier protein on one side of the cell membrane. The carrier protein then changes its shape and transports the molecule down its concentration gradient to the other side of the membrane.

Facilitated Diffusion Section 1 Passive Transport Chapter 5 Facilitated Diffusion Facilitated diffusion does not require additional energy, so it is considered passive transport Can work in two directions, both into and out of cell depending on concentration levels A good example of facilitated diffusion is the transport of glucose (sugar). Pg. 101, figure 5-5

Facilitated Diffusion Section 1 Passive Transport Chapter 5 Facilitated Diffusion

Diffusion Through Ion Channels Section 1 Passive Transport Chapter 5 Diffusion Through Ion Channels Ion channels are proteins, or groups of proteins, that provide small passageways across the cell membrane through which specific ions can diffuse. Each type of ion channel is usually specific for one type of ion Ex. A calcium ion channel will allow only calcium ions to pass through it Ions diffuse by moving through gates in cell membrane: these gates may open or close in response to three kinds of stimuli: stretching of the cell membrane, electrical signals, or chemicals in cytosol or external environment

Section 1 Passive Transport Chapter 5 Ion Channels

Section 2 Active Transport Chapter 5 Objectives Distinguish between passive transport and active transport. Explain how the sodium-potassium pump operates. Compare endocytosis and exocytosis.

Chapter 5 Active Transport Section 2 Active Transport Chapter 5 Active Transport Active transport moves molecules across the cell membrane from an area of lower concentration to an area of higher concentration. Unlike passive transport, active transport requires cells to expend energy (ATP).

Contractile vacuoles are found in paramecia and help them pump water into and out of their cell. These require energy are a type of ACTIVE transport.

Cell Membrane Pumps: Sodium-Potassium Pump Some types of active transport are performed by carrier proteins called cell membrane pumps. The sodium-potassium pump move three Na+ ions out of the cell for every two K+ ions it moves into the cytosol ATP supplies the energy that drives the pump Animation http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html

Sodium-Potassium Pump Section 2 Active Transport Chapter 5 Sodium-Potassium Pump

Chapter 5 Movement in Vesicles Section 2 Active Transport Chapter 5 Movement in Vesicles Some substances, such as macromolecules and nutrients, are too large to pass through the cell membrane by diffusion or osmosis In endocytosis, cells ingest external materials by folding around them and forming a pouch This is transferring molecules into the cell The pouch then pinches off and becomes a membrane-bound organelle called a vesicle.

Movement in Vesicles: Endocytosis There are two types of endocytosis: Pinocytosis (“cell drinking”) – vesicle contains solutes or fluids Phagocytosis (“cell eating”) – vesicle contains large particles or other cells http://bio1151.nicerweb.com/Locked/media/ch07/endocytosis.html

Movement in Vesicles, continued Section 2 Active Transport Chapter 5 Movement in Vesicles, continued Exocytosis In exocytosis, vesicles made by the cell fuse with the cell membrane, releasing their contents into the external environment (out of the cell). Cells may use exocytosis to release large molecules such as proteins, waste products, or toxins that would damage the cell if they were released within the cytosol Exocytosis involves ridding the cell of material by discharging it from sacs at the cell surface

Endocytosis and Exocytosis Section 2 Active Transport Chapter 5 Endocytosis and Exocytosis These two types of movement are exact opposites of each other, in and out