ch. 5 homeostasis & cell transport - falcons life...
TRANSCRIPT
Ch. 5
Homeostasis
&
Cell Transport
5.1
Homeostasis & Permeability
Homeostasis – ability of cell to maintain balance
needed for life
To maintain balance:
cells must transport needed materials into cells
&
waste materials out of cells
Movement in or out of a cell depends on
permeability
Permeability
the ability of a molecule to move across a membrane
If molecule can move across, membrane is permeable to molecule.
If molecule cannot move across, membrane is impermeable to molecule.
most membranes are Selectively (semi) Permeable:
some molecules move across, others can't
Membrane is “Choosy”
Two Main Types of Cell Transport
1. Passive Transport
2. Active Transport
Passive Transport
Movement of substances across a membrane
without using energy
Molecules move down the Concentration
Gradient
Concentration gradient - difference in
concentration of molecules across a membrane
Molecules move HIGH TO LOW!
3 forms of Passive Transport:
a. Simple Diffusion
b. Osmosis
c. Facilitated Diffusion
a. Simple Diffusion:
Movement of SOLUTE across a membrane!
No energy needed!
HIGH TO LOW!
Which way will the purple molecules move?
To the right!
Molecules move back and forth until balance is
reached.
Balance = Equilibrium
When equilibrium is reached:
molecules still move but concentration does not
change.
ex: 2 molecules in = 2 molecules out
5.2
Osmosis
b. Osmosis
Diffusion of water across a membrane
Passive: no energy needed
Water is the solvent in cells BUT movement of
water depends on concentration of solute
To determine which way water will move, 1st
describe the solution:
3 types of solutions:
– a. Hypertonic: MORE solute outside cell
– b. Hypotonic: LESS solute outside cell
– c. Isotonic: solute is EQUAL inside & outside
Hypertonic Solutions & Osmosis
cell
Sugar molecule
Which way will
the water move?
Water will move
OUT of the cell
Cell will shrivel
Hypotonic Solutions & Osmosis
cell
Sugar molecule
Which way will
the water move?
Water will move
INTO cell
Cell will swell
Isotonic Solutions & Osmosis
cell
Sugar molecule
Which way will
the water move?
Water will move
IN & OUT of cell
Cell will stay the
same
Osmosis & Red Blood Cells
What Makes Water Move?
Osmotic Pressure:
Pressure created by water molecules
If water concentration is , osmotic pressure is
If water concentration is , osmotic pressure is
Water moves from an area of HIGH osmotic
pressure to an area of LOW osmotic pressure
HIGH TO LOW!
Osmosis in Plants
Osmosis affects Turgor Pressure - pressure of water that presses cell membrane against the cell wall
if soil is hypertonic (dry): water moves out of cell, turgor pressure , membrane pulls away from wall, plant wilts
if soil is hypotonic (wet): water moves into cell, turgor pressure , membrane pushes against from wall, plant is crisp
c. Facilitated Diffusion
•
passive transport
molecules insoluble in lipids or too large
molecules need help to cross
2 types:
1. Carrier proteins
2. Ion channels
Carrier Proteins
Proteins in membrane
Move substances from high to low
Proteins are specific: transport only
1molecule
Glucose moves this way
Ion Channels
Na+, Cl-, ions are important to cell function
Insoluble in lipid bilayer, can’t cross alone
Proteins form channels
Passive transport: high to low
Some channels always open, others have
“gates” that open in response to stimuli
5.3
Active Transport
Active Transport
Move substances up(or against)
concentration gradient: from low to high
concentration
Requires input of energy
2 types: cell membrane pumps, and
movement of vesicles
Membrane Pumps
Protein pumps that move substances from
low to high concentration
Require energy of ATP
ex: sodium-potassium pump: moves Na+
and K+ ions low to high
important to nerve function
Movement in Vesicles
move molecules too large to diffuse
move large quantities at one time
ex: nutrients & macromolecules
2 types:
Endocytosis
Exocytosis
Endocytosis
cells ingest large materials INTO cell
materials fill pouch in membrane
pouch forms vesicle
lysosomes attach & spill in enzymes
Pinocytosis: endocytosis of liquids
Phagocytosis: endocytosis of solids
Phagocyte: cell that ingests solid material
ex: white blood cells – ingest bacteria
Exocytosis
Material moved OUT of cell
Vesicle carries materials to membrane
Fuses w/ membrane & opens to outside
Proteins & wastes removed this way
Endo
Exo