cell membranes, diffusion, osmosis -...
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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
u phospholipids u “split personality”
§ Membrane is a double layer u 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 u semi-permeable
§ only some material can get in or out
aa H2O sugar lipids salt waste
So what needs to get across the membrane?
O2
Regents Biology
Crossing the cell membrane § What molecules can get through the cell
membrane directly? u lipid soluble substances can pass directly
through (fats and gases)
inside cell
outside cell
lipid salt
aa H2O 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
2
Regents Biology
What materials can pass directly through the lipid bilayer membrane?
A. water and sugars B. salts and waste C. amino acids D. gases and fats (lipids)
Regents Biology
Cell membrane channels § Need to make “doors” through membrane
u protein channels allow substances in & out § specific channels allow specific material in & out § H2O channel, salt channel, sugar channel, etc.
inside cell
outside cell
sugar aa H2O
salt waste Regents Biology
How do you build a semi-permeable cell membrane? § Channels are made of proteins
u proteins both “like” water & “like” lipids bi-lipid
membrane protein channels
in bi-lipid membrane
Regents Biology
Protein channels § Proteins act as doors in the membrane
u channels to move specific molecules through cell membrane
HIGH
LOW Regents Biology
Movement through the channel § Why do molecules move through
membrane if you give them a channel?
?
?
HIGH
LOW Regents Biology
Diffusion u molecules move from HIGH concentration
(of that substance) to LOW concentration (of that substance)
Regents Biology
Diffusion (2 types) § Simple and Facilitated Diffusion
u passive transport u no energy needed
diffusion osmosis
diffusion of water
Regents Biology
Simple Diffusion § Move from HIGH to LOW across membrane
inside cell
outside cell
Which way will fat move?
fat
fat
fat
fat
fat
fat fat
fat fat
fat
fat
fat
fat
fat
LOW
HIGH
Regents Biology
Facilitated Diffusion § Move from HIGH to LOW through a channel
inside cell
outside cell
sugar
sugar
sugar
sugar
sugar sugar
sugar sugar
sugar sugar sugar
Which way will sugar move?
sugar sugar
LOW
HIGH
3
Regents Biology
Diffusion u Simple Diffusion
§ no energy needed § directly through membrane
u Facilitated Diffusion (with help) § no energy needed § help through a protein channel
HIGH
LOW Regents Biology
Simple vs. facilitated diffusion
inside cell
outside cell
lipid inside cell
outside cell
H2O
simple diffusion facilitated diffusion
H2O
protein channel
Regents Biology
Facilitated diffusion animation § http://highered.mcgraw-hill.com/sites/
0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html
Regents Biology
Diffusion is the movement of particles from
A. an area of low concentration to an area of high concentration
B. an area of high concentration to an area of low concentration
C. an area of equilibrium to an area of high concentration
Regents Biology
Diffusion occurs because
A. molecules constantly move and collide with one another
B. the concentration of a solution is never the same throughout the solution
C. The concentration of a solution is always the same throughout a solution
D. molecules never move or collide with one another
Regents Biology
Simple and facilitated diffusion
A. both require energy B. both are passive and do not require
energy C. require special channels to move
molecules D. mean the same thing
Regents Biology
Substances transported by facilitated diffusion
A. move passively through specific channels from an area of greater concentration to one of lower concentration
B. move passively through specific channels from an area of lower concentration to one of greater concentration
C. may flow to a region of higher concentration by the expenditure of energy (ATP)
Regents Biology
Active transport § Cells may need molecules to move
against concentration “hill” u need to pump “uphill”
§ from LOW to HIGH using energy u protein pump u requires energy
§ ATP ATP
Regents Biology
Transport summary
simple diffusion
facilitated diffusion
active transport
ATP
4
Regents Biology
ATP is required in the transport of
A. water molecules B. all molecules across a membrane C. molecules to areas of lower
concentrations D. molecules to areas of higher
concentrations
Regents Biology 2006-2007
Osmosis Movement of Water Across Cell Membrane
Regents Biology
Osmosis § Water is very important, so we talk about
water separately § Osmosis
u diffusion of water from HIGH concentration of water to LOW concentration of water § across a semi-permeable membrane
Regents Biology
Osmosis Animation § http://highered.mheducation.com/sites/
0072495855/student_view0/chapter2/animation__how_osmosis_works.html
Regents Biology
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
cell needs materials in & products or waste out
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