Diffusion Through a Membrane

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

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

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

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

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 2

Diffusion Through A Membrane – Pg 3 Chemical Test Results Amber-Colored Starch Indicator Solution (Iodine): *If it changes from amber to dark purple/black, starch is present (the result is positive for glucose).

Diffusion Through A Membrane – Pg 3 Blue-colored Glucose Indicator Solution (Benedict's Solution) *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).

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

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

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

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

Diffusion Through A Membrane – pg 4 Initial State Final State

Diffusion Through a Membrane

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

Diffusion Through A Membrane glucose molecule part of a starch molecule

Red Onion Cells  Normal/Healthy Environment Diffusion Through a Membrane

cell wall cytoplasm red onion cells in tap water cell membrane Cell membrane is pressed against the inside of the cell wall

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

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

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

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

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