Unit 3 : Homeostasis and Cell Transport
A. Maintaining Homeostasis
1. Homeostasis – process of regulating and maintaining a constant internal env.
2. Need to maintain homeostasis of water levels, glucose levels, temperature, and pH
3. pH control:
a. Buffers:used to regulate cell pH
b. How a buffer works: buffer added to an acidic or basicsolution to make it a neutral pH
4. Temperature Control:
a. if the organism is too hot :
1. dilation:blood vessels dilate (get bigger) and move closer to the skin’s surface to release
heat
2. sweating:evaporation of water from the skin to cool the body
b. if the organism is too cold :
1. constriction: blood vessels constrict (get smaller) and move away from the skin’s surface to
conserve (save) heat
2. shivering: body increases heat production by contracting muscles
5. Glucose level control:
a. if blood glucose levels are too high -
1. cells in pancreas produce insulinin response to high glucose levels
2.insulin convertsglucose (monosaccharide) to glycogen (polysaccharide) and stores the
glycogen in the liver
3. lowers the blood glucose concentration level
b. if blood glucose levels are too low -
1. cells in pancreas produce glucagon in response to low blood glucose levels
2. glucagon breaks down glycogen into glucose
3.hydrolysis increases the blood glucose concentration level
6. Water balance – occurs in the kidneys-
a. if there is too much water in the blood -
1. kidneys filter out & produce a large volume
of urine
2. urine will have a low solute concentration,
will be light yellow in color
b. if there is too little water in the blood -
1. kidneys produce a small volume of urine
2. urine will have a high concentration of
solutes, urine will be dark orange,
B.Plasma(Cell)Membrane
1.Functions of the plasma membrane:
a. maintains homeostasis by controlling what enters & leaves the cell
b.allows nutrients in & wastes out
c.acts as boundary between cell and ts environment
2. Selectively (Semi) Permeable: membrane only allowscertain molecules to come in and keeps
others out, membrane is selective
3. Membrane Structure:
a.PhospholipidBilayer – 2 layers of phospholipids
1. fatty acid tails – hydrophobic (“water fearing”)fatty acid
carbon chains
2. polar heads – hydrophyllic (“water loving”) phosphate
group attached to the lipid
3. proteins –located on the membrane surface or embedded
in the membrane to create channels for movement of
molecules through the membrane or receptors for
attachment of molecules
b. diagram:
c. Fluid Mosaic Model – flexibility of bilayer allows molecules in / out while maintaining membrane structure
4. Embedded Membrane Proteins: (help movement in/out)
a. hormone binding sites – holds hormones to cell
b. enzymes – facilitates reactions
c. protein channels for passive transport – allows solutes to flow from high concentration to low
concentration in/out of cell
d. protein pumps for active transport – using energy to move solutes from low concentration to high
concentration
5. Cell Recognition – lipids & proteins in the membrane help cells to identify each other
examples :
immune system & antibodies
rejection of transplanted tissues (organs)
blood type recognition of blood cells
C. Cellular Transport all cell transport (movement in/out) isbased on a concentration gradient
Concentration gradient:
Existence of high concentration of a
substance on one side of the membrane
and a low concentration of a substance
on the other side
1. Active TransportSubstances move from low concentration to high
concentration
a. ATP (energy in the cell) is required
b. equilibrium willnot be reached
2. Passive TransportSubstances move from high concentration to low concentration
a. No energy is required to move
b.Equilibrium will be reached
c.Threetypes of passive transport:
1. Diffusion– movement of solutes from high to low
concentration
(Solute: a substance that can be dissolved, ex. salt, sugar,
iodine, Ca++)
2. Facilitated diffusion – movement of large solute
molecules through the membrane with the
aid of transport proteins
3. Osmosis – movement of water molecules from high
to low concentration (a type of diffusion)
Active Transport / Passive TransportDirection / Move against concentration gradient / Move with the concentration gradient
Movement / From low to high concentration / From high to low concentration
Energy / ATP required / Not required
Equilibrium / Not reached / Reached
D. Osmotic Pressure: (osmosis)
1. hypOtonic:
a. Higher concentration of water outside the cell
b. Higher concentration of solute inside the cell
c. Water will move into the cell
d. Cell will swell (increase) in size
e. In plant cells, increase in turgor pressure - membrane willpush
against the cell wall making the cell appear very firm
(turgid).
f. In animal cells, increase can cause the cell to burst when water
pushes against the membrane.
2. Hypertonic:
a. Higher concentration of solutes outside the cell
b. Higher concentration of water inside the cell
c. Water will move out of the cell
d. Cell will shrink (decrease) in size
e. Freshwater plant in saltwater will cause cells to shrivel or
freshwater fish in saltwater will cause cells to shrivel (dehydration)
3. Isotonic:
a.Equal concentration of both solutes and water on inside and
outside of cell
b. Water will move in & out of cell through membrane at same rate
c.Dynamic equilibrium – shape of cell stays the same even though
water is moving through themembrane at an equal rate
% Solutes / Water flows? / Animal cell / Plant cell / Solution type3 / More solute in cell, so water moves in / Swells, could burst / Swells, but does not burst b/c of cell wall (firm fruit) / Hypotonic
7 / More solute out of cell, so water moves out / Cell shrinks, dehydration / Cell shrinks but wall keeps it from collapsing (plasmolysis) / Hypertonic
4 / Solute inside equals solute outside, water moves in & out at equal rate / Cell stays same size (homeostasis) / Cell stays same size (squishy fruit) / Isotonic