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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

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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

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What describes a membrane that allows certain materials to pass and others not?

A. impermeable membrane B. semi-permeable membrane C. mucus membrane

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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)

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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

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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)

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Diffusion (2 types) § Simple and Facilitated Diffusion

u passive transport u no energy needed

diffusion osmosis

diffusion of water

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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

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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

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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

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Facilitated diffusion animation §  http://highered.mcgraw-hill.com/sites/

0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html

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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

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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

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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

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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)

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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

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Transport summary

simple diffusion

facilitated diffusion

active transport

ATP

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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

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Osmosis Animation §  http://highered.mheducation.com/sites/

0072495855/student_view0/chapter2/animation__how_osmosis_works.html

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Keeping water balance § Cell survival depends on balancing

water uptake & water loss freshwater balanced saltwater

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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!

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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

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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.

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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

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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!

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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!

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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.

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Hypotonic Solution §  “below strength” in concentration (of

solute outside of cell) compared to concentration of solute in cell

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Isotonic Solution §  “same strength”, or when

concentrations of 2 solutions are equal, (or the concentration of solute inside and outside of cell are equal)

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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

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Regents Biology

The diffusion of water across a selectively permeable membrane is called

A.  osmotic pressure B.  osmosis C.  facilitated diffusion D.  active transport

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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