AP Biology

AP Biology

The selectively permeable plasma membrane is composed of phospholipids and protein, which allow for its unique functions.A) DESCRIBE the structure and properties

of phospholipids and EXPLAIN the important roles of phospholipids in the plasma membrane.

B) EXPLAIN why proteins are an important component of the cell membrane, based on their structure and properties.

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Read lab packet Highlight all vocabulary in

background section Read procedures Complete #1 on page 15. TODAYTODAY: Part A

Procedures on page 6Table 1 on page 12

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Color Glucose

Time Bag Beaker Bag Beaker

Start clearclear amberamber ++ --

30 minutes

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CLASS DATA FOR % CHANGE IN MASS

Water

0.2 M

0.4 M

0.6 M

0.8 M

1.0 M

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#2: Iodine diffused into the bag (blue/black); Glucose diffused out of the bag into the environment; Osmosis was also occurring bc it went into the bag as glucose diffused out

#3: Yes, iodine and glucose diffused, but the starch could not diffuse bc it was too big

#4: Osmosis occurred which caused a net flow of water into the bag increasing its mass; More water because the environment was hypotonic (less solute). Equilibrium was reached.

#5: Hypotonic because it had less solute than the bags

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CLASS DATA FOR % CHANGE IN MASS OF POTATOES

Water

0.2 M

0.4 M

0.6 M

0.8 M

1.0 M

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https://www.youtube.com/watch?v=4JyT__Dea8Q

• Plant cells losing water in hypertonic solutions

• Shrinking• Cell membrane pulls away from outer

cell wall• Very rare• Opposite?

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Movement of a substance across a membrane with no energy investment

Direction depends on concentration High concentrations to low

concentrations DOWN or WITH its concentration

gradient Types: diffusion, osmosis, facilitated

diffusion

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Movement from high to low concentrations

2nd Law of Thermodynamics governs biological systemsuniverse tends towards disorder (entropy)

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diffusion

osmosis

movement of water

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Water is very important to life, so we talk about water separately

Diffusion of water from high concentration of water to low concentration of wateracross a

semi-permeable membrane

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Direction of osmosis is determined by comparing total solute concentrationsHypertonic - more solute, less waterHypotonic - less solute, more water Isotonic - equal solute, equal water

hypotonic hypertonic

water

net movement of water

AP Biologyfreshwater balanced saltwater

Cell survival depends on balancing water uptake andloss

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Cell (compared to beaker) hypertonic or hypotonic

Beaker (compared to cell) hypertonic or hypotonic

Which way does the water flow? in or out of cell

.05 M .03 M

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Isotonicanimal cell immersed in

mild salt solution example:

blood cells in blood plasma problem: none

no net movement of water flows across membrane equally,

in both directions

volume of cell is stable

balanced

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Hypotonica cell in fresh water

example: Paramecium problem: gains water,

swells & can burstwater continually enters

Paramecium cell solution: contractile vacuole

pumps water out of cell ATP

plant cells turgid

freshwater

ATP

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Contractile vacuole in Paramecium

ATP

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Hypertonica cell in salt water

example: shellfish problem: lose water & die solution: take up water or pump

out saltplant cells

plasmolysis = wilt

saltwater

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Water moves rapidly into & out of cellsevidence that there were water channels

1991 | 2003

Peter AgreJohn Hopkins

Roderick MacKinnonRockefeller

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Cell membrane is the boundary between inside & outside…separates cell from its environment

foodcarbohydrates,sugars, proteinsamino acids,lipids, salts, O2, H2O

wasteammoniasaltsCO2

H2O products

cell needs materials in & products or waste out

Can it be an impenetrable boundary?NO!

IN OUT

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What molecules can get through directly?fats & other lipids

inside cell

outside cell

lipid

salt

aa H2Osugar

NH3

What molecules can NOT get through directly?

polar molecules H2O

ions salts, ammonia

large molecules starches, proteins

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Membrane becomes semi-permeable with protein channels specific channels allow specific material across cell membrane

inside cell

outside cell

sugaraaH2O

saltNH3

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Diffusion through protein channelschannels move specific molecules across cell membrane

no energy needed

“The Bouncer”“The Bouncer”

open channel = fast transport

facilitated = with help

high

low

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Cells may need to move molecules against concentration gradientshape change transports solute from

one side of membrane to other protein “pump”“costs” energy = ATP

“The Doorman”“The Doorman”

conformational change

ATP

low

high

AP Biologysymportantiport

Many models & mechanisms

ATP ATP

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Passive TransportSimple diffusion

diffusion of nonpolar, hydrophobic molecules lipids high low concentration gradient

Facilitated transport diffusion of polar, hydrophilic molecules through a protein channel

high low concentration gradient

Active transportdiffusion against concentration gradient

low highuses a protein pumprequires ATP

ATP

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simplediffusion

facilitateddiffusion

activetransport

ATP

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Moving large molecules into & out of cell through vesicles & vacuolesendocytosis

phagocytosis = “cellular eating” pinocytosis = “cellular drinking”

exocytosis

exocytosis

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phagocytosis

pinocytosis

receptor-mediated endocytosis

fuse with lysosome for digestion

non-specificprocess

triggered bymolecular signal

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Any Questions??