Unit 5- Cell Membrane & Cell Transport 5b- Cellular Transport.
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Transcript of Unit 5- Cell Membrane & Cell Transport 5b- Cellular Transport.
Unit 5- Cell Membrane & Cell Transport
5b- Cellular Transport
About Cell Membranes
• All cells have a cell membrane• Functions:
a. Maintains homeostasisb. Provides protection and
support for the cell
TEM picture of a real cell
membrane.• Animations of Active Transport & Passive Transport
What is the purpose of cellular transport?
• Homeostasis depends upon appropriate movement of materials across the cell membrane.– Required materials must pass into the cells so they can be
used.• Ex. Oxygen and glucose for cellular respiration
– Waste materials must pass out of the cells as they are produced• Ex. The CO2 produced as a waste product of cellular respiration
How?
• Each individual cell exists in a fluid environment, and the cytoplasm within the cell is a fluid environment. – The presence of a liquid makes it possible for substances (such as
nutrients, oxygen, and waste products) to move into and out of the cell.
• A cell membrane is semipermeable (selectively permeable).• Materials can enter or exit through the cell membrane by
passive transport or active transport.
Membrane movement animation
Passive Transport• Cell uses no energy • The movement of molecules
occurs along a concentration gradient
– meaning molecules move from an area of high concentration to an area of low concentration
• 3 types of passive transport
high
low
Weeee!!!
Passive Transport: 1. Diffusion: spreading out of molecules across a cell
membrane until they are equally concentrated (equilibrium) *molecules never stop moving, just stay spread out*
– results from the random motion of molecules– Occurs along a concentration gradient– Molecules can diffuse across a membrane by dissolving in the
phospholipid bilayer (ex O2, CO2) or by passing through pores in the membrane
Simple Diffusion Animation
2. Osmosis: diffusion of water across a membrane• Water moves from a high
concentration of water to a low concentration of water
• Net direction of osmosis is determined by the relative solute concentrations on the two sides of the membrane.
Osmosis animationPassive Transport:
Aquaporin
Solutions
• Solute- substance being dissolved
• Solvent- substance solute dissolves in
• Solution= solute+solvent
Passive Transport-OsmosisHypotonic Solution: The solute concentration outside the cell is lower than the solute concentration inside the cell.
(Low solute; High water)
Result: Water moves from the solution to inside the cell. Cell swells & may burst (cytolysis).Animation
Passive Transport-OsmosisHypertonic Solution: The solute concentration outside the cell is higher than the solute concentration inside the cell.
(High solute; Low water)
Result: Water moves out of the cell into the solution. Cell shrinks! Animation
shrinks
Plasmolysis
Passive Transport-OsmosisIsotonic Solution: The solute concentrations outside the
cell & inside the cell are equal.
Result: No net movement. Water moves equally in both directions & the cell remains same size. (Dynamic
Equilibrium)
Hypertonic, Hypotonic, Isotonic Solutions
In what type of solution are these cells?
A CB
Hypertonic
Isotonic
Hypotonic
How Cells Deal with Osmosis• Cells must compensate for the water that enters the cell in
hypotonic environments & leaves the cell in hypertonic environments.
• Protists, like paramecia, have contractile vacuoles that collect & pump out excess water.
• Plants & bacteria have cell walls that prevent them from over-expanding.– In plants the pressure exerted on the cell
wall is called turgor pressure. – Plasmolysis- in a hypertonic environment the
cells shrink away from the cell walls & turgor pressure is lost.
• Paramecium (protist) removing excess water video
How Cells Deal with Osmosis
• Animal cells are bathed in blood. Kidneys keep the blood isotonic by removing excess salt & water.
• Many multicellular organisms have outer surfaces that are waterproof to prevent water loss on land or water gain in freshwater.
3. Facilitated diffusion: diffusion of specific particles along a concentration gradient with the help of transport proteins • Transport Proteins are specific –
they “select” only certain molecules to cross the membranea. Transports larger or charged
molecules that cannot pass through the membrane on their own
b. Glucose is an example of a molecule that passes into the cell through facilitated diffusion
Facilitated diffusion (Channel Protein)
Diffusion (Lipid Bilayer)
Passive Transport:
Carrier Protein
A B
• http://bio.winona.edu/berg/Free.htm
High Concentration
Low Concentration
Cell Membrane
Glucosemolecules
Proteinchannel
Passive Transport: 3. Facilitated Diffusion
Transport Protein
Through a
Cellular Transport From a- Hig
h
Low
• Channel Proteins animations
Active Transport
• Requires the cell to use energy • Molecules move against the
concentration gradient – – from an area of low concentration to an
area of high concentration • Active transport is used to:
– move large molecules– concentrate molecules within the cell– remove waste from the cell
high
low
This is gonna
be hard
work!!
Types of Active Transport
1. Protein Pumps (aka cell membrane pumps) –transport proteins that require energy to do work
• Example: Sodium / Potassium Pumps are used in nerve cells to transmit messages.
Sodium Potassium Pumps
(Active Transport using
proteins)
Active Transport- Protein Pumps
• Sodium-Potassium Pump– ATP supplies the energy that drives the pump
Types of Active Transport
2. Endocytosis: • Cells take in large molecules by
folding around them & forming a pouch– Pouch then pinches off from
the membrane & becomes an organelle called a vesicle
• This is how white blood cells ingest bacteria
Types of Active Transport
3. Exocytosis: – vesicles made by the cell fuse
with the cell membrane, releasing their contents into the external environment
– Used to release large molecules, waste products, or toxins
– Used to release proteins after Golgi apparatus packages them into vesicles
Endocytosis & Exocytosis
animations
Endocytosis & Exocytosis