Transcript Transport Systems and Solutions

What is homeostasis?
Why is the ability to maintain
homeostasis important?
What are some things that the
human body must regulate?
How does the body
regulate these things?
What are some things that
cells must regulate?
water, salt, ions, glucose, temperature,
carbon dioxide, oxygen,…
How is a cell able to do
this?
nucleus monitors activities and the
cell membrane controls what enters
and exits the cell
Cells…
Homeostasis
and
Transport
Chapter 7.4

organisms, both simple and complex
must maintain homeostasis

individual cells must also maintain
homeostasis

cells maintain homeostasis by
regulating what gets into and out of
the cell

the cell part that is of great
importance in maintaining
homeostasis is …
THE CELL MEMBRANE
Cell Membrane Structure
1. two layers of (phospho-) lipids
◦
◦
called lipid bilayer
forms a barrier between external and
internal environment of the cell (both which
are watery)
2. scattered proteins
3. some carbohydrates
MOVEMENT OF MOLECULES

all molecules are in constant,
random motion – BROWNIAN
MOVEMENT

as a result of the random motion of
molecules, molecules tend to ….
move into areas where they
are less concentrated
TRANSPORT PROCESSES
(or Transport Mechanisms or
Transport Systems)
are ways in which substances
get into and out of cells

2 main categories:
PASSIVE TRANSPORT
ACTIVE TRANSPORT
Passive Transport Processes
movement of molecules from an area
of greater concentration to an area
of lesser concentration
 requires
no energy (ATP) from the
cell
 movement is with the gradient
 example: rolling a boulder down a hill
 types - diffusion; osmosis; facilitated
diffusion
Diffusion (type of passive transport)…
movement of a substance from area of
greater concentration to lesser concentration
Osmosis (type of passive transport)….
movement of water from greater concentration
to lesser concentration through a
semipermeable membrane
Water is essential to life
and to living things !!!!!
In living things water is
usually not pure, but is
found as part of a
solution.
a SOLUTION contains:
solute – substance being dissolved
solvent – substance doing the dissolving
(in living things the solvent is usually water)
solutions can be described as….
hypertonic, hypotonic, or isotonic
Hypertonic

describes a solution that contains a greater concentration
of solutes (than the solution it is compared to)
in this diagram,
colored dots = solute
white space = water
the solution outside the cell is
hypertonic as compared to the
solution inside
If osmosis occurs, what will
happen to the water?
If osmosis occurs, what will
happen to the cell?
Hypotonic

describes a solution that contains a lower
concentration of solutes (than the solution
it is compared to)
the solution outside the
cell is hypotonic as
compared to the
solution inside
If osmosis occurs, what
will happen to the water?
If osmosis occurs, what
will happen to the cell?
Isotonic

describes a solution whose solute
concentration is the same both inside and
outside of the cell
the solution outside the
cell is isotonic as
compared to the
solution inside
If osmosis occurs, what
will happen to the water?
If osmosis occurs, what
will happen to the cell?
Let’s Practice
cell A – 20% starch, 80% water
cell B – 15% starch, 85% water
cell C – 10% starch, 90% water
cell D – 25% starch, 75% water
What is the solute in these cells?
What is the solvent in these cells?
Which cell is hypotonic to the others?
Which cell is hypertonic to the others?
When comparing cells….
A and B, which is hypertonic?
A and D, which is hypertonic?
C and D, which is hypotonic?
Let’s Practice some more….
cell
cell
cell
cell
A – 20% starch, 80% water
B – 15% starch, 85% water
C – 10% starch, 90% water
D – 25% starch, 75% water
In which direction would water flow…
between cells A and B?
between cells A and D?
between cells B and C?
between cells C and A?
Which cell has the greatest solute
concentration?
Which cell has the greatest solvent
concentration?
Cytolysis
“cyte” = cell
“lyse” = burst
If a cell is placed in a hypotonic solution it
may burst or lyse. Why?
Some cells have evolved adaptations to
prevent cytolysis.
What type of solution is this
red blood cell in ?
before
during
after
Adaptations of Cells
Some unicellular
organisms have
contractile
vacuoles to collect
and pump out
excess water.
 Plant cells don’t
undergo cytolysis
because of the
rigid cell wall.

Turgor Pressure
(osmotic) pressure within a plant cell
due to the movement of water into
the cell
Plants rely on hypotonic environments to
get water into them and into their
vacuoles.
If plants are in a hypertonic environment
they will wilt (known as plasmolysis).
Facilitated Diffusion
(passive transport)

“assisted diffusion”

carrier proteins (in the cell membrane)
will assist the movement of some
molecules across the membrane
Active Transport Processes
movement of molecules from an area of lesser
concentration to greater concentration
movement is against the gradient
 requires energy (ATP) from the cell
 example: rolling a boulder up a hill
 types – pump mechanism; endocytosis; exocytosis

Pump Mechanism
(also known as a Cell Membrane
Pump)

active transport
process in which
small molecules are
moved from a region
of lower
concentration to
greater concentration
(against a gradient)
with the assistance of
proteins in the cell
membrane
Endocytosis (active transport)

process by which cells
ingest fluid,
macromolecules, or
large particles,
including other cells
(viruses and bacteria)
* the cell membrane
folds around the
particle and forms a
pouch (called a
vesicle)
Endocytosis (active transport)
2 types:
 Pinocytosis: transport of solutes or fluids
into the cell
 Phagocytosis: transport of large particles
or whole cells into the cell
 many unicellular organisms feed by phagocytosis
Exocytosis (active transport)

reverse of
endocytosis

a vesicle within
the cell fuses with
the cell membrane
and releases its
contents outside
the cell
Endocytosis & Exocytosis
Review Transport Mechanisms

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