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Homeostasis and Transport
Unit Notes
Cell Membrane
B. Function for the cell membrane
1. Forms a boundary between the inside and outside of
the cell.
2. Controls the passage of materials into and out from the
cell.
Membrane Review
Cell Transport and the Cell Membrane
A. Cell membranes are selectively permeable/semi-
permeable.
Cell Transport and the Cell Membrane
B. Selectively Permeable (Size and Concentration)
1. Some molecules can cross the membrane while others
can not.
2. A selectively permeable membrane allows for the cell
to maintain homeostasis.
3. Molecules can move across the membrane in a variety
of ways.
Some molecules can cross
the membrane while others
cannot.
Cell Transport
A. Key Concept
1. Materials move across the membranes because of
concentration differences.
Cell Transport
B. Two Forms of Transport
1. Passive Transport: does not require energy.
2. Active Transport: does require energy
Cell Transport
C. Passive Transport
1. Types of Passive Transport
a.
b.
c.
Diffusion
Osmosis
Facilitated diffusion
Cell Transport
C. Passive Transport
-
Diffusion
Molecules diffuse down a concentration
gradient.
2. Diffusion: the process whereby a molecule
will move from an area of a higher
concentration to an area of a lesser
concentration.
1.
Diffusion
Diffusion
Cell Transport
C. Passive Transport - Osmosis
1. Osmosis: the diffusion of water molecules across a
selectively permeable membrane.
a.
2.
Water will move from an area of a higher concentration of
water to an area of a lesser concentration of water, through a
selectively permeable membrane.
The net direction of osmosis is determined by the
relative solute concentration on the two sides of the
membrane.
Cell Transport
C. Passive Transport - Osmosis Cont..
3. A solution may be described as isotonic, hypertonic or
hypotonic relative to another solution.
• The solution outside of the cell
has the same amount of solutes
as inside the cell.
• Equal amounts of water will
enter and exit the cell.
• The term for this is “homeostasis”
Cell Transport
Hypertonic
• High solute outside of the cell than inside of the cell.
(More water inside the cell than
outside of the cell)
• Water will move out from the
cell.
• The cell will shrivel. Plasmolysis
is the term for the water loss.
Cell Transport
Hypotonic
• Fewer solutes out from the cell than
inside the cell. (More water outside
of the cell than inside the cell)
• Water will move into the cell.
• The cell could burst. This is called
cytolysis.
Cell Transport
Osmosis Practice
What will happen to a houseplant if you water it with salt
water?
2. What type of solution is this (from question #1)
(hypertonic, hypotonic or isotonic)
3. Which way will water flow in the following:
1.
Vegetables are sprinkled with water.
b. Salt is poured on a slug.
c. A cucumber slice is placed into salt water.
d. A potato slice is placed into pure water.
a.
Cell Transport
C. Passive Transport Facilitated Diffusion
1. Some molecules cannot easily diffuse across the
membrane.
2. Facilitated Diffusion: diffusion through the
membrane using transport proteins.
a.
b.
Typically carried out in the muscles, transporting glucose
through the membrane.
Facilitate means to “make
easier.” Transport proteins
make it easier for glucose
to enter or exit a cell.
Cell Transport
D. Active Transport
1. Types of Active Transport
a.
b.
c.
Protein pumps
Endocytosis
Exocytosis
Active transport requires energy (ATP) input from a
cell and enables a cell to move substances against its
concentration gradient.
3. Cells use active transport to maintain homeostasis
2.
Cell Transport
D. Active Transport - Protein Pumps
1. Sodium-Potassium Pump
a.
b.
Proton Pump
2.
a.
b.
3.
Used for nerve conduction in animals.
3 sodium ions are pumped out from the cell, while 2
potassium ions are pumped into the cell.
Used by the cell in order to pump hydrogen ions out from
the cell.
It is a form of stored energy that is used to power other active
transport gradients.
Protein Pumps in Plants
a. Used to transport sucrose into the cell.
Cell Transport
A cell can import and export large materials or large
amounts of material in vesicles during the process of
endocytosis and exocytosis.
Cells use energy when they transport materials in
vesicles.
Cell Transport
D. Active Transport - Endocytosis
Endocytosis: the process of taking materials into the
cell.
2. Two types
1.
a.
b.
Phagocytosis: large molecules move into the cell. “Cell
Eating”
Pinocytosis: small/liquids molecules move into the cell.
“Cell Drinking”
Cell Transport
D. Active Transport - Exocytosis
1. Exocytosis: the process of expelling materials from
the cell.