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
section 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 – in blue moves
from an area of
greater concentration
to lesser
concentration
Properties of Water – H2O
“universal” solvent
 polar covalent
 cohesion
 adhesion
 capillarity
 surface tension
 high heat capacity

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)
solution outside the cell is hypotonic
solution inside the cell
is hypertonic
Why does water move into
the cell?
Isotonic


describes a solution
whose solute
concentration is the
same both inside and
outside of the cell
water will move in both
directions to maintain
equilibrium
solution outside the cell is isotonic
to the solution inside 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 A – 20% starch, 80% water
cell B – 15% starch, 85% water
cell C – 10% starch, 90% water
cell 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.
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
requires energy (ATP) from the cell
 movement is against the gradient
 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