1 Regents Biology 2006-2007 Cell Membranes & Movement Across Them Regents Biology Vocab Words: lipid bilayer membrane semi-permeable membrane protein channel concentration simple diffusion facilitated diffusion Regents Biology Vocab Words (cont’d) active transport osmosis hyperosmotic hypertonic solution hypotonic solution isotonic Regents Biology Building a membrane How do you build a barrier that keeps the watery contents of the cell separate from the watery environment? What substance do you know that doesn’t mix with water? → FATS ← → LIPIDS ← Remember: oil & water don’t mix!! Regents Biology Lipids of cell membrane (review) Membrane is made of special kind of lipid phospholipids “split personality” Membrane is a double layer phospholipid bilayer inside cell outside cell lipid “repelled by water” “attracted to water” phosphate Regents Biology Semi-permeable membrane Cell membrane controls what gets in or out Need to allow some materials — but not all — to pass through the membrane semi-permeable only some material can get in or out aa H 2 O sugar lipids salt waste So what needs to get across the membrane? O 2 Regents Biology Crossing the cell membrane What molecules can get through the cell membrane directly? lipid soluble substances can pass directly through (fats and gases) inside cell outside cell lipid salt aa H 2 O sugar waste but… what about other stuff? Regents Biology Which of the following is a function of the cell membrane? A.breaks down lipids, carbohydrates, and proteins from foods B.stores water, salt, proteins, and carbohydrates C.keeps the cell wall in place D.regulates which materials enter and leave the cell Regents Biology What describes a membrane that allows certain materials to pass and others not? A.impermeable membrane B.semi-permeable membrane C.mucus membrane
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Keeping water balance § Cell survival depends on balancing
water uptake & water loss freshwater balanced saltwater
Regents Biology
Real life examples of osmosis § soaking lettuce leaves, beans, or rice in
water § soaking in water for a long time causes
“shriveling” of skin (which is actually swelling)
§ gargling with salt water when you have
sore throat
Regents Biology
Keeping right amount of water in cell § Freshwater
u a cell in fresh water u high concentration of water
around cell § cell gains water
§ example: Paramecium § problem: cells gain water,
swell & can burst w water continually enters
Paramecium cell
§ solution: contractile vacuole w pumps water out of cell
freshwater
No problem, here
KABOOM!
1
Regents Biology
Contractile vacuole in Paramecium § Controlling water in cell § In hyperosmotic environments less
water will be expelled and the contraction cycle will be longer
Regents Biology
Hyperosmotic vs Hypertonic Hyperosmotic: § A solution that has a higher solute
concentration than another solution.
Hypertonic: § A solution that contains more dissolved
particles (such as salt and other electrolytes) than is found in normal cells and blood. For example, hypertonic solutions are used for soaking wounds.
5
Regents Biology
A freshwater paramecium was placed in solution A and observed to expel water from contractile vacuoles (CV) at a rate of 11 cycles per minute. The same paramecium was then placed in solution B and observed to expel water from CV’s at a rate of 4 cycles per minute. Which of the following statements is correct?
A. Solution A is hyperosmotic to solution B. B. Solutions A and B are isosmotic. C. Solution B is hyperosmotic to solution A
Regents Biology
Keeping right amount of water in cell § Saltwater
u a cell in salt water u low concentration of water
around cell § cell loses water
u example: shellfish u problem: cell loses water
§ in plants: plasmolysis § in animals: shrinking cell
u solution: take up water
saltwater
I will survive!
I’m shrinking, I’m shrinking!
2
Regents Biology
Keeping right amount of water in cell § Balanced conditions
u no difference in concentration of water between cell & environment § cell in equilibrium § example: blood § problem: none
w water flows across membrane equally, in both directions
w volume of cell doesn’t change
balanced
I could be better…
That’s better!
3
Regents Biology
Hypertonic Solution § “Above strength” in concentration (of
solute outside of cell) compared to concentration of solute in cell
Vocab background § Solute is what is dissolved in solvent.
Together, they make a solution. § Solute is always the lesser quantity.
Regents Biology
Hypotonic Solution § “below strength” in concentration (of
solute outside of cell) compared to concentration of solute in cell
Regents Biology
Isotonic Solution § “same strength”, or when
concentrations of 2 solutions are equal, (or the concentration of solute inside and outside of cell are equal)
Regents Biology
Video on Tonicity and Osmosis https://www.youtube.com/watch?v=6MWl3DCa2uM
Regents Biology
What happens to the cell?
Regents Biology
Effects of changes in tonicity on RBC’s
6
Regents Biology
The diffusion of water across a selectively permeable membrane is called
A. osmotic pressure B. osmosis C. facilitated diffusion D. active transport
Regents Biology
An animal cell that is surrounded by fresh water will burst because the osmotic pressure causes
A. water to move into the cell B. water to move out of the cell C. solutes to move into the cell D. solutes to move out of the cell
Regents Biology
A hypertonic salt solution has a higher concentration of solutes than a blood cell. What happens when a blood cell is placed in a hypertonic salt solution?
A. the blood cell will shrink B. the blood cell will burst C. nothing will change about the blood
cell D. the salt will move into the blood cell
Regents Biology
Ice Fishing in Barrow
Regents Biology
Cell (plasma) membrane § Cells need an inside & an outside…
u separate cell from its environment u cell membrane is the boundary
IN food - sugars - proteins - fats salts O2 H2O
OUT waste - ammonia - salts - CO2 - H2O products - proteins