Diffusion Through a Membrane

Diffusion Through A Membrane Semi-permeable – some molecules are able to pass through while others can't WHY? Size and/or Shape 2

Diffusion Through A Membrane Glucose – small sugar molecule (simple sugar) Starch – several small sugar molecules bonded together Which is larger? 3

Diffusion Through A Membrane indicator – chemically indicates if a substance is present by changing color Iodine = starch indicator solution Benedict’s solution = glucose indicator solution – must be heated 4

Diffusion Through A Membrane Diffusion – movement of molecules from high concentration to low concentration – no energy needed (this is called passive transport) 5

Diffusion Through A Membrane we will use dialysis tubing to make a model of a cell. the tubing represents a semi-permeable cell membrane the dialysis tube is filled with a glucose solution and a starch solution, sealed and rinsed with water it will be placed in a beaker with water and iodine (an indicator) and allowed to sit 6

Diffusion Through A Membrane The initial set up The “Cell” filled with glucose and starch solutions Water & Iodine in the beaker cover the “cell”

Diffusion Through A Membrane –Pg 2 Question #9: Predict what you think will diffuse. Remember: There’s starch and glucose inside the “cell” and iodine outside the cell. Write which way you think the substances will move (into or out of the cell). NO WORRIES! You will not be marked wrong if your prediction (hypothesis) is incorrect!!! (So write what you think!) Make sure you list ALL three substances: STARCH, GLUCOSE and IODINE

Diffusion Through A Membrane – Pg 3 Chemical Test Results Amber-Colored Starch Indicator Solution (Iodine) Changes in presence of starch *If it changes from amber to dark purple/black, starch is present! (The result is positive).

Diffusion Through A Membrane – Pg 3 *Remember that you must HEAT the test tubes with the Benedict’s Solution for this INDICATOR to change color! *If it changes to orange/red when heated, glucose is present (the result is positive for glucose). Blue-colored Glucose Indicator Solution (Benedict's Solution)

Diffusion Through A Membrane – Pg 3 Table Two – Chemical Test Results Indicator Solution Used Distilled Water Starch Glucose Blue Colored BENEDICTS *HEATED! Amber Colored IODINE

Diffusion Through A Membrane – pg 4 Record any color changes observed in the “cell” and in the beaker Initial State

Diffusion Through A Membrane Final State: What Color is the Cell Now? What does that mean?

Diffusion Through A Membrane – pg 4 Record any color changes observed in the “cell” and in the beaker Final State

Diffusion Through A Membrane –Pg 4 Initial State Final State

Diffusion Through a Membrane 16

Initial and Final State I = Iodine S = Starch G = Glucose I I I I I I I I I S G S S S G G I I I I Use the letters I, S, and G to represent the substances used.

Diffusion Through A Membrane glucose molecule part of a starch molecule 18

Diffusion Through a Membrane Red Onion Cells Normal/Healthy Environment

Cell membrane is pressed against the inside of the cell wall Diffusion Through a Membrane cytoplasm red onion cells in tap water cell membrane cell wall Cell membrane is pressed against the inside of the cell wall 20

Diffusion Through a Membrane bathing the cells in 10% NaCl (salt water) NaCl 21

Cell membrane and cytoplasm have shrunk because water diffused out Diffusion Through a Membrane cytoplasm red onion cells in salt water cell membrane cell wall Cell membrane and cytoplasm have shrunk because water diffused out 22

Which is in distilled (pure) water and Diffusion Through A Membrane Which is in distilled (pure) water and which is in salt water? 23

Diffusion Through A Membrane Applications: salt on roads to melt snow intravenous saline solutions salty foods make you thirsty salt on slugs to kill them salty foods do not spoil as easily gargling with salt water 24

Isotonic "ISO" means the same 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.

When Placed in Hypertonic Solution Plant cells, the central vacuole loses water and the cells shrink, causing wilting. Animal cells, the cells also shrink, called crenation. In both cases, the cell may die.

Hypertonic The word "HYPER" means more… In this case there are more solute (salt) molecules outside the cell, which causes the water to leave the cell Moving from high water concentration inside the cell to a lower concentration outside the cell Solutes can be salt or sugar or nutrients….

When Placed in Hypertonic Solution Plant cells, the central vacuole loses water and the cells shrink, causing wilting. Animal cells, the cells also shrink, called crenation. In both cases, the cell may die.

Hypotonic "HYPO" means less There are less solute (salt) molecules outside the cell, which causes the water to enter the cell Remember: if there are less solute particles, then there are more water molecules. Water moves from high concentration outside the cell to low concentration inside the cell

When Placed in a Hypotonic Solution In plant cells, the central vacuoles (large storage areas) will fill and the plant becomes stiff and rigid (called turgor), the cell wall keeps the plant cell from bursting Animal cells are in danger of bursting because they don’t have a rigid cell wall When the cell bursts it is called hemolysis When it bursts, it dies