Transcript Diffusion Iodine and Starch Reaction - OG

Diffusion
Iodine and Starch Reaction
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1. What caused the color change you
observed?
• Starch solution inside the
dialysis tubing
• Water outside the dialysis
tubing
• Iodine added to the water
• --- REACTION! Color
change!  How?
2. What was able to diffuse
across the membrane?
• Starch solution changed color
• Water in the beaker didn’t have a reaction
• What can you conclude:
– About the movement of starch molecules?
– About the movement of iodine molecules?
– About the movement of water molecules?
What molecules were able to
diffuse in/out the membrane?
• Water
• Iodine
• Why couldn’t
starch move across
the membrane?
3. Was the beaker of water hypertonic or
hypotonic compared to the starch solution in
the tubing?
• Hypertonic = more solute (high concentration)
• Hypotonic = less solute (low concentration)
• What’s a solute? – The substance you’re
dissolving (starch)
• What’s a solvent? – The substance you’re
dissolving the solute IN (water)
3. Where is the highest concentration
of solute? The lowest concentration?
4. Why was the weight of your tubing
different after adding iodine to the water?
• Water moves from high  low
concentration
• Water moved into the dialysis tubing due to
… OSMOSIS!
• Would water still move across the
membrane without using iodine?
How does the tubing represent a cell
membrane?
• Selectively (semi) permeable – only certain
molecules can cross the membrane
– Water, iodine, NOT starch
• Normally, cells exist in isotonic solution
– What’s isotonic? What’s the solution?
• Osmosis can cause cells to shrivel up, swell,
or even burst!
How can water cause a cell to burst?
• When cells are in a “freshwater” solution
• Water rushes in, bursting the cell
What about plant cells?
• What do plant cells have that animal cells
do not?
• Notice the cell wall does not collapse (or
burst), but the cell membrane can collapse
What allows water molecules in/out
of the cell?
• Aquaporins – water channel proteins
– Type of facilitated diffusion, because it requires
“help” from a specific channel protein
• Special protein channels are embedded in
the lipid bilayer – a double-layered sheet
that forms a strong, flexible barrier called
the …
• YOU GUESS IT! CELL MEMBRANE!
The Lipid Bilayer
2 sheets of lipids make the lipid bilayer
-- PHILIC = loving
-- PHOBIC = hating
Why is the hydrophilic portion on the outside
and the hydrophobic portion on the inside of
the two sheets?
Recap • Diffusion is…
movement of
molecules from high
to low concentration
• Osmosis is… movement
of WATER molecules
from high to low
concentration
– This creates osmotic
pressure - a force
produced by the net
movement of water
Types of Transport
• ACTIVE TRANSPORT
• Moves materials
against concentration
gradient
• Requires energy!
• Endocytosis - import
– Phagocytosis
• Exocytosis - export
PASSIVE TRANSPORT
• Occurs due to
concentration
gradient
• Requires no energy
• Diffusion
• Osmosis