Transcript Homeostasis and Cell Transport

Homeostasis and
Cell Transport
Chapter 5
Homeostasis
The steady-state physiological condition of the
cell or body.
Cellular Transport
Passive Transport
Diffusion
The movement of particles
from an area of high
concentration to an area
of low concentration.
concentration gradient:
formed by the
concentration of
molecules at various
points between the high
and low areas.
Equilibrium: the
concentration of molecules
will be the same throughout
the space the molecules
occupy.
impermeable
Semi-permeable
permeable
Osmosis
The movement of water molecules across a
selectively permeable membrane. Water
moves from a region of high concentration to
one of low conc.
Hypotonic
When the concentration of solute molecules
outside the cell is lower than the concentration
in the cytosol.
Water diffuses into the cell until equilibrium is
established.
Hypertonic
When the concentration of solute molecules
outside the cell is higher than the
concentration in the cytosol.
Water diffuses out of the cell until equilibrium
is established.
Isotonic
When the concentration of solutes outside and
inside the cell are equal.
Water diffuses into and out of the cell at equal
rates, so there is no net movement of water.
Contractile Vacuole
Organelles in paramecia that collect excess
water and then contract, pumping the water
out of the cell.
Not a form of Passive
Transport. Why?
Turgor Pressure
The pressure that water molecules exert against the
cell wall.
Plasmolysis: the shrinking of the cell membrane of
a plant cell in a hypertonic solution in response to
the loss of water by osmosis.
Cytolysis
The bursting of cells.
Facilitated Diffusion
The transport of substances through a cell membrane
along a concentration gradient with the aid of carrier
proteins.
Carrier proteins: proteins that transport substances
across a membrane.
Ion Channels
• Transport ions such as:
Sodium (Na+)
Potassium (K+)
Calcium (Ca+)
Chloride (Cl-)
• Not soluble in lipids
• Each type of ion channel is usually specific for one
type of ion.
• Some ion channels are always open, some have
“gates.”
• Gates may open or close in response to 3 types of
stimuli: streching of the cell membrane, electrical
signals, or chemicals in the cytosol or external
environment.
Active Transport
Energy in the form of ATP
is used to move
substances through the
transport proteins.
Substances can move
across a membrane
against concentration
gradient.
The carrier proteins
involved are often
called cell membrane
“pumps.”
Sodium-Potassium Pump
• Transports Na+ and K+ ions up the concentration
gradient.
• At top speed, the pump can transport about 450 Na+
ions and 300 K+ ions per second.
• The exchange of 3 Na+ ions for 2 K+ ions creates a
positively charged environment outside the cell
membrane and negatively charged inside the
membrane.
• Important for the conduction of electrical impulses
along nerve cells.
Movement in Vesicles
Endocytosis: process by which cells ingest external fluid,
macromolecules, and large particles, including other
cells.
•External materials are enclosed by a portion of the cell’s
membrane, which folds itself and forms a pouch.
•The pouch pinches off from the cell membrane and
becomes a vesicle.
•Some vesicles fuse with lysosomes.
•2 types:
pinocytosis
phagocytosis
Pinocytosis
• Involves the transport of solutes or fluid.
Phagocytosis
Movement of large particles or whole cells.
Phagocytes: cells in animals that use phagocytosis to
ingest bacteria and viruses that invade the body.
They fuse with lysosomes and enzymes then destroy
the bacteria and viruses before they can harm the
animal.
leukocytes
Exocytosis
Process by which a substance is released from the cell
through a vesicle that transports the substance to the
cell membrane and then fuses with the membrane to let
the substance out of the cell.
Proteins
Waste
Toxins