Download Homeostasis and Cell Transport

Homeostasis and Cell
Transport
Chapter 5
Section 1
Movement of substances across the cell
membrane without any input of energy by
the cell.
Remember: The cell membrane’s function is
to help organisms maintain homeostasis
by controlling what substances enter or
leave the cell.
Passive Transport
Simplest type of passive transport.
 Movement of molecules from an area of
higher concentration to an area of lower
concentration.
 Concentration Gradient: the difference
in the concentration of molecules across a
distance.
 Equilibrium: the same throughout

Diffusion
Keep in mind that molecules are constantly
moving even if they appear to be still.
The many movements of all molecules in all
directions balances each other out so
equilibrium is maintained.
Why does sugar dissolve faster in hot tea
than in cold tea?
Important!!!
Diffusion of molecules across a
membrane.
 Depends on size, type, and chemical
charge. of molecule

◦ Small molecules, molecules that can dissolve in
lipids, and non-polar molecules may pass
through the membrane.
◦ Non soluble lipids may diffuse across the
membrane through pores in the membrane.
Simple Diffusion
Solution: composed of a solute dissolved
in a solvent.
 Solvent: Part of the solution that most
abundant: Water
 Solute: the “stuff” dissolved in the
solvent. Ex. Salt

Solution, solute, & solvent
The process by which water molecules
diffuse across an area of higher
concentration to an are of lower
concentration.
 No energy is used for this process
therefore it is still passive transport.

Osmosis
HIGH CONCENTRATION OF WATER TO
LOW CONCENTRATION OF WATER
 Hypotonic: external concentration has
lower concentration of solute (higher
water) than then internal concentration

Direction of Osmosis

Hypertonic: concentration of solute
molecules outside the cell is higher (water
lower) than inside the cell.
Direction of Osmosis
Isotonic: concentration of solutes on
inside and outside of the cell are equal.
 NO NET MOVEMENT!

Direction of Osmosis
Most cells are typically exposed to an
isotonic external environment.
 Freshwater fish are examples of an
organism in a hypotonic solution. Why?
 Contractile vacuoles: a structure in
some organisms that remove excess
water from the organism. NOT PASSIVE
TRANSPORT!!

Cells and Osmosis



Plant roots are typically always in a hypotonic
environment. This is important to the
survival of the organism.
Water moves into the roots by osmosis and
the cells swell (where is the water stored?)
When it fills with water, the cell membrane
swells and pushes up against the cell wall;
this pressure is called turgor pressure. The
condition when pressure is lost is called
Plasmolysis
Plant Cells
Another type of passive transport
 Used for the molecules that cannot readily
diffuse through cell membranes even if
there is a concentration gradient.
 Travel through proteins called carrier
proteins

◦ These molecules may not be soluble in lipids or
too large to pass through pores.
Facilitated Diffussion
Facilitate in movement down the
concentration across the membrane.
 Does not require energy!!!
 Molecules bind to carrier protein and once
bound, the protein changes shape to allow
molecule to enter the cell.
 Ex. Glucose transfer.

Carrier Proteins