AP Biology2005-2006
Cell (plasma) membrane Cells need an inside & an outside…
separate cell from its environment cell membrane is the boundary
INfoodcarbohydratessugars, proteinsamino acidslipidssalts, O2, H2O
OUTwasteammoniasaltsCO2
H2O products
cell needs materials in & products or waste out
IN
OUT
Can it be an impenetrable boundary? NO!
AP Biology
Lipids of cell membrane Membrane is made of phospholipids
phospholipid bilayer
phosphate
lipid
hydrophilic
hydrophobic
inside cell
outside cell
AP Biology
Phospholipid bilayer What molecules can get through directly?
inside cell
outside cell
fats & other lipidscan slip directly through the phospholipid cell membrane, but…
what about other stuff?
lipid
salt
aa H2Osugar
NH3
AP Biology2005-2006
A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer
AP Biology2005-2006
Membrane Proteins Proteins determine most of membrane’s
specific functions cell membrane & organelle membranes each
have unique collections of proteins
Membrane proteins: peripheral proteins = loosely
bound to surface of membrane integral proteins = penetrate into
lipid bilayer, often completely spanning the membrane =
transmembrane proteins
Many Functions of Membrane Proteins
Outside
Plasmamembrane
InsideTransporter Cell surface
receptorEnzymeactivity
Cell surface identity marker
Attachment to thecytoskeleton
Cell adhesion
AP Biology
The many functions of proteins…. Channel proteins – wide open passage Ion channels – gated Aquaporins – water only, kidney and
plant root only Carrier proteins – change shape Transport proteins – require ATP Recognition proteins - glycoproteins Adhesion proteins – anchors Receptor proteins - hormones
Membrane carbohydrates Play a key role in cell-cell recognition
ability of a cell to distinguish one cell from another antigens
important in organ & tissue development
basis for rejection of foreign cells by immune system
AP Biology
Cholesterol Provides stability in animal cells “temperature buffer” quality for membrane Replaced with sterols in plant cells
Membrane fat composition varies Fat composition affects flexibility
membrane must be fluid & flexible about as fluid as thick salad oil
% unsaturated fatty acids in phospholipids keep membrane less viscous cold-adapted organisms, like winter wheat
increase % in autumn
cholesterol in membrane
AP Biology
Getting through cell membrane Passive transport
No energy needed Movement down concentration gradient
Active transport Movement against concentration gradient
low high requires ATP
AP Biology
Diffusion 2nd Law of Thermodynamics
- Universe tends towards disorder
Diffusion movement from high low concentration
AP Biology2005-2006
Simple diffusion across membrane
inside cell
outside cell
Which way will lipid move?
low
high
lipid
lipid
lipid
lipid
lipid
lipid lipid
lipidlipid
lipid
lipid
lipid
lipid
lipid
AP Biology
Diffusion of 2 solutes Each substance diffuses down its own
concentration gradient, independent of concentration gradients of other substances
AP Biology2005-2006
Facilitated diffusion Move from HIGH to LOW concentration
through a protein channel passive transport no energy needed facilitated = with help
AP Biology2005-2006
Gated channels Proteins that open only in presence of stimulus
(signal) stimulus usually different from transported
molecule ex: ion-gated channels ex: voltage-gated channels
AP Biology
Active transport Cells may need molecules to move
against concentration situation need to pump against concentration protein pump requires energy
ATP
Na+/K+ pump in nerve cell membranes
AP Biology2005-2006
How about large molecules? Moving large molecules into & out of cell
requires ATP(energy)! through vesicles & vacuoles endocytosis
phagocytosis = “cellular eating” pinocytosis = “cellular drinking” receptor-mediated
endocytosis exocytosis
exocytosis
AP Biology2005-2006
Endocytosis
phagocytosis
pinocytosis
receptor-mediated endocytosis
fuse with lysosome for digestion
non-specificprocess
triggered byligand signal
AP Biology2005-2006
Osmosis is diffusion of water Diffusion of water from
high concentration of water to low concentration of water across a
semi-permeable membrane
AP Biology2005-2006
Concentration of water Direction of osmosis is determined by
comparing total solute concentrations Hypertonic - more solute, less water Hypotonic - less solute, more water Isotonic - equal solute, equal water
hypotonic hypertonic
water
net movement of water
AP Biology2005-2006
Managing water balance Cell survival depends on balancing
water uptake & loss
freshwater balanced saltwater
AP Biology
Hypotonicity animal cell in hypotonic
solution will gain water, swell & possibly burst (cytolysis)
Paramecium vs. pond water Paramecium is hypertonic H2O continually enters cell
contractile vacuole - pumps H2O out of cell = ATP
plant cell Turgid (turgor pressure) Cell wall
AP Biology2005-2006
Hypertonicity animal cell in hypertonic
solution will loose water, shrivel & probably die
salt water organisms are hypotonic compared to their environment
they have to take up water & pump out salt
plant cells plasmolysis = wilt
AP Biology2005-2006
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
Osmosis…
AP Biology
Water Potential Water moves from a place of greater water
potential to a place of lesser water potential (net).
As the concentration of a solute increases in a solution, the water potential will decrease accordingly. Which has the greater water potential:
.2M or .8M? Which has the greater water potential:
20% or 80% water?
AP Biology
intracellular waste
Animal systems evolved to support multicellular life
O2
CHO
CHO
aa
aa
CH
CO2
NH3aa
O2
CH
O2
aa
CO2
CO2
CO2
CO2
CO2
CO2 CO2
CO2
CO2
CO2
NH3
NH3 NH3
NH3
NH3
NH3
NH3NH3
O2
aa
CH
aa
CHO
O2
Diffusion too slow!
single cell
but whatif the
cells areclustered?
for nutrients in & waste out
extracellular waste
AP Biology
Overcoming limitations of diffusion Evolution of exchange systems for
distributing nutrients circulatory system
removing wastes excretory system
gas exchange respiratory system
systems to support multicellular organisms
systems to support multicellular organisms
aa
CO2
CO2
CO2
CO2
CO2
CO2 CO2
CO2
CO2
CO2
NH3
NH3 NH3
NH3
NH3
NH3
NH3NH3
O2
aa
CH
aa
CHO
O2
AP Biology
When is Diffusion Needed? Respiratory and Circulatory systems
Oxygen/CO2 transport into and out of bloodstream Skins, gills, alveoli, capillaries
Excretory systems Movement of wastes into or out of blood
Skin, nephridia, nephrons, gills
Q: What do these systems have in common for diffusion to occur? Large surface area
AP Biology
Gas exchange in many forms…
one-celled amphibians echinoderms
insects fish mammals
endotherm vs. ectothermsize
cilia
water vs. land ••
AP Biology
Counter current exchange system Water carrying gas flows in one direction,
blood flows in opposite direction
just keepswimming….
AP Biology
Blood & water flow in opposite directions maintains diffusion gradient over whole length
of gill capillary
maximizing O2 transfer from water to blood
water
blood
How counter current exchange worksfront back
blood
100%15%
5%90%
70% 40%
60% 30%
100%
5%
50%
50%
70%
30%
watercounter-current
concurrent
AP Biology
Gas Exchange on Land Advantages of terrestrial life
air has many advantages over water higher concentration of O2
O2 & CO2 diffuse much faster through air respiratory surfaces exposed to air do not have to
be ventilated as thoroughly as gills air is much lighter than water & therefore
much easier to pump expend less energy moving air in & out
Disadvantages keeping large respiratory surface moist
causes high water loss reduce water loss by keeping lungs internal
AP Biology
Intracellular Waste What waste products
are made inside of cells? what do we digest our food into…
carbohydrates = CHO lipids = CHO proteins = CHON nucleic acids = CHOPN
CO2 + H2O
NH2 =
ammonia
CO2 + H2O CO2 + H2O
CO2 + H2O + N
CO2 + H2O + P + N
|
| ||H
HN C–OH
O
R
H–C–
Animalspoison themselves
from the insideby digesting
proteins!
cellular digestion…cellular waste
AP Biology
Nitrogen waste Aquatic organisms
can afford to lose water ammonia
most toxic
Terrestrial need to conserve
water urea
less toxic
Terrestrial egglayers
need to conserve water need to protect
embryo in egg uric acid
least toxic
AP Biology
Land animals Nitrogen waste disposal on land
need to conserve water must process ammonia so less toxic
urea = larger molecule = less soluble = less toxic 2NH2 + CO2 = urea produced in liver
kidney filter solutes out of blood reabsorb H2O (+ any useful solutes) excrete waste
urine = urea, salts, excess sugar & H2O urine is very concentrated concentrated NH3 would be too toxic
OC
HNH
HNH
Ureacosts energyto synthesize,
but it’s worth it!
mammals
AP Biology
Animal Osmoregulation (blood solute levels)
Kidneys – generate urine by filtering wastes from blood Nephrons – basic unit of kidney
Water will move towards urine or blood as it becomes hypertonic via AQUAPORINS
Anti-Diuretic Hormone increases water movement back to blood….why?
Blood pressure is highly regulated by the kidney because without pressure, there is no filtration = toxic blood = death!!!
AP Biology
Osmotic control in nephron How is all this re-absorption achieved?
tight osmotic control to reduce the energy cost of excretion
use diffusion instead of active transportwherever possible
the value of acounter current exchange system
AP Biology
Osmoregulation
Why do all land animals have to conserve water?
always lose water (breathing & waste) may lose life while searching for water
Water balance vs. Habitat freshwater
hypotonic to body fluids water flow into cells & salt loss
saltwater hypertonic to body fluids water loss from cells
land dry environment need to conserve water may also need to conserve salt
hypotonic
hypertonic
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