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Homeostasis & Transport
Section 1: Diffusion & Osmosis
Homeostasis
 Homeostasis: the
biological balance
between a cell or an
organism and its
environment
 Cells maintain
homeostasis by
controlling and regulating
what gets into and out of
the cell.
Passive Transport
 Passive Transport: the movement of any
substance across a cell membrane without
the use of cell energy




Diffusion
Osmosis
Facilitated Diffusion
Gated Channel
Diffusion
 Diffusion: the process by which
molecules move from an area of greater
concentration to an area of lower
concentration
Diffusion
Brownian
Motion
 Brownian Motion: molecules are in a
constant state of random motion
Brownian
Motion
Concentration Gradient
 Concentration Gradient: the
difference in concentration of a
substance across a space
Dynamic Equilibrium
 Dynamic Equilibrium: a state that exists
when the concentration of a substance is the
same throughout a space
Dynamic
Equilibrium
Review of Cell Membrane Structure
Diffusion Across Membranes
 Not all molecules can
diffuse through all
membranes.
 The ability of a molecule
to pass through a
membrane depends on
the size and type of
molecule and the
molecular structure of
the membrane.
Small nonpolar
molecules can diffuse
through the cell
membrane
Osmosis
 Osmosis: the diffusion of water
molecules through a selectively
permeable membrane from an area
of high water concentration to an
area of lower water concentration
Osmosis
Three Types of Solutions
90% H2O
10% solute
85% H2O
15% solute
95% H2O
5% solute
90% H2O
10% solute
90% H2O
10% solute
90% H2O
10% solute
Isotonic
(no net movement
of water)
Hypotonic
Hypertonic
Three Types of Solutions
Plant Cells
Three Types of Solutions
Animal Cells
Three Types of Solutions
Hypotonic solution
H2O
Isotonic solution
Hypertonic solution
H2O
H2O
H2O
(a) Animal
cell
Cytolysis
H2O
Normal
H2O
Shriveled
H2O
H2O
(b) Plant
cell
Turgid (normal)
Flaccid
Plasmolysis
Three Types
of Solutions
Contractile Vacuoles
 Contractile Vacuole: an organelle in
microorganisms that excretes water
 collect excess water → contract → squeeze
out water
Study the diagram below. It represents a container that is divided
by a semipermeable membrane. A different solution in its initial
state is shown on each side of the membrane.
1.
2.
3.
4.
Describe which molecule(s) will move through the
membrane and which molecule(s) will not.
Describe the relative rates at which the molecule(s) will
move across the membrane.
Describe in which direction the molecule(s) will move.
Describe how long the molecule(s) will continue to move.
Review of Cell Membrane Structure
Review of Cell Membrane Structure
Facilitated Diffusion
 Facilitated Diffusion: a process in
which substances move down their
concentration gradient across the cell
membrane with the assistance of a
membrane protein
 Examples: glucose, fructose, water & ions
Two
Types of
Membrane
Proteins:
Channels
&
Carrier
Proteins
Facilitated
Diffusion
Aquaporins = Water Channels
Gated Channel
 Gated Channel: a protein-lined gated
passage making cell membranes
permeable to certain large molecules as
needed
 Example: neuromuscular function
Gated Channel
Protein key
made by
nucleus
Review of Passive Transport
Review of Passive Transport
Section 2: Active Transport
Active Transport
 Active Transport: the movement of
any substance across a cell membrane
with the use of energy from ATP
 Sodium-Potassium Pump
 Endocytosis
 Exocytosis
Sodium-Potassium Pump
 SodiumPotassium
Pump: an active
transport
mechanism that
moves ions in
order to achieve
polarization
Proton Pump
 Proton Pump: an active transport
mechanism that consumes ATP
(energy) to force Hydrogen ions against
the concentration gradient
Proton Pump
Proton Pump & Cotransport
Endocytosis
 Endocytosis:
the process by
which a cell
engulfs and
surrounds large
substances
Phagocytosis
Pinocytosis
ReceptorMediated
Endocytosis
Exocytosis
 Exocytosis:
the process
by which
wastes are
packaged in
vesicles and
leave the cell
Exocytosis
Passive vs. Active Transport