Transcript Transport

Essential Question: How do materials get
in and out of a cell?
• You learned in section 1 that the membrane does
a lot to control what goes in & out of the cell.
• Today you will learn the specific ways materials
enter & exit the cell.
• You will see that the way a cell gets each material
it needs is unique and specialized.
• Also, that there are ways the cell gets its needed
materials in or out by both using and not using
energy.
Objectives: Passive & Active Transport
• Identify what determines the direction in which
passive transport occurs.
• Understand osmosis and why it’s important.
• Illustrate how substances move against a
concentration gradient in active transport.
Vocabulary
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Equilibrium
Concentration gradient
Diffusion
Carrier protein
Osmosis
Sodium-potassium pump
Before we get started…
• You’ll need to know these terms before we
begin. Define these in your notebooks.
• Solute: A solid particle
• Solvent: A liquid the dissolves solutes.
• Solution: Solute dissolved in a solvent
• Concentration: an amount of a substance within
a given volume
Passive Transport: Diffusion &
Equilibrium
• In a solution, randomly moving molecules tend
to fill up a space.
• Watch as I drop some food coloring into the
beaker.
• What happens?
• The process that causes this dispersion of polar
color molecules is diffusion.
• When the space is filled evenly with the
particles, a state called equilibrium is reached.
– A state that exists when the concentration of a
substance is the same through-out a space.
Temperature
Water temp
– As the ice
melts the
water
temperature
drops.
– The low
temperature of
the ice
equalizes with
the warmer
water temp.
Ice Temp
Equilibrium
http://highered.mc
grawhill.com/sites/0072
495855/student_vi
ew0/chapter2/anim
ation__how_diffusi
on_works.html
Passive Transport: Concentration
Gradient
• The amount of a particular substance in a given
volume is called the concentration of the
substance.
• When one area has a higher concentration than
another area does, a concentration gradient
exists.
– The difference in the concentration of a
substance across a distance.
Down
CONCENTRATION GRADIENT
Up
Visual Concept: Concentration Gradient
Area of High
Concentration
Area of Low
Concentration
Passive Transport: Diffusion
• The movement of particles from regions of
higher density to regions of lower density is
diffusion.
• Watch as I drop food coloring into the beaker.
• Would you all agree that the concentration of the
food coloring is highest right where it is
dropped?
• Over time, the particles of color naturally diffuse
through the water, without any need of physical
movement.
Diffusion
Visual Concept: Diffusion
Area of High
Concentration
Area of Low
Concentration
Diffusion or Simple Diffusion
• One of the main jobs of the cell membrane is to separate
the cytoplasm from the fluid outside the cell.
• But the cell still needs an abundance of materials that
comes from outside the cell.
• Some substances that the cell needs can enter and
leave the cell by diffusing across the cell membrane.
• The direction of movement depends on the
concentration gradient, meaning that the particles will
naturally flow where there is less of them, & usually
where more is needed.
• The greatest part of this is…
• DIFFUSION DOES NOT REQUIRE ENERGY!
Diffusion is Passive Transport
• In cells, diffusion through the
membrane is called passive
transport.
• In passive transport,
substances cross the cell
membrane down their
concentration gradient.
• Some substances diffuse
through the lipid bilayer.
• Other substances diffuse
through transport proteins.
Small & Non-Polar:
Diffuses directly
through membrane
Large & or Polar:
Cannot diffuse directly
through membrane
Small & Non-Polar:
Diffuses directly
through membrane
Passive Transport & Not So Simple
Diffusion
Facilitated Diffusion
• Facilitate means to help.
• Many ions, large, and polar molecules that are important
for cell function do not diffuse easily through the
nonpolar lipid bilayer.
• During facilitated diffusion, transmembrane proteins
help these substances (large &/or polar) diffuse through
the cell membrane.
• Two types of transport proteins:
– channel proteins
– carrier proteins.
Facilitated Diffusion: Passive Transport
Facilitated Diffusion through Channels
• Ions, sugars, and amino acids can diffuse through the
cell membrane through channel proteins.
• These proteins, sometimes called pores, serve as
tunnels through the lipid bilayer.
• Each channel allows the diffusion of specific substances
that have the right size and charge.
Passive Transport, Facilitated Diffusion
Facilitate Diffusion: Through Carrier Proteins.
• Carrier proteins transport substances that fit within their
binding site.
– A protein that transports substances across a membrane
• A carrier protein binds to a specific substance on one
side of the cell membrane. This binding causes the
protein to change shape.
• As the protein’s shape changes, the substance is moved
across the membrane and is released on the other side.
Visual Concept: Passive
Transport: Facilitated Diffusion
Link to McGrawHill online (a good textbook) for animations
and explanations of biology concepts.
Take the quizzes!
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animati
on__how_diffusion_works.html
Osmosis.
• Water is essential for our survival. It is a critical molecule
in the production of ATP.
– (without ATP we die)
• But water is polar & can’t go directly through the lipid
bilayer.
• Water gets into the cell via a form of facilitated diffusion,
called osmosis.
– Water has its own channel protein through which it can diffuse.
how_osmosis_works.html
Osmosis/ How the Environment Changes
•
When ions and polar substances
dissolve in water, they attract and
bind some water molecules. The
remaining water molecules are free
to move around.
•
If a concentration gradient exists
across a membrane for solutes, a
concentration gradient also exists
across the membrane for free water
molecules.
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Osmosis occurs as free water
molecules move down their
concentration gradient into the
solution that has the lower
concentration of free water
molecules.
Questions on Passive Transport?
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What is a concentration gradient?
What is diffusion?
What is passive transport?
What kinds of passive transport are there?
Does passive transport use energy?
Active Transport
Area of High
Concentration
Area of Low
Concentration
Active Transport
• The opposite of diffusion is active transport.
• In order to move substances against their
concentration gradients, cells must use energy.
• Active transport requires energy to move substances
against their concentration gradients.
• Most often, the energy needed for active transport is
supplied directly or indirectly by ATP.
Visual Concept: Comparing Active and
Passive Transport
Link on sodium potassium pump = NO
http--www.stolaf.edu-people-gianniniflashanimat-transportsecondary%20active%20transport.swf
Active Transport, continued
Pumps
• Pumps are carrier proteins that require energy to move
substances UP their concentration gradient.
• The sodium-potassium pump is a carrier protein that
actively transports three sodium ions out of the cell and
two potassium ions into the cell.
– This pump is one of the most important carrier proteins in animal
cells. It prevents sodium ions from building up in the cell,
resulting in osmosis into the cell… which could burst the cell.
– The concentration gradients of sodium ions and potassium ions
also help transport other substances, such as glucose, across
the cell membrane.
Sodium-Potassium Pump
Mass Transport Across
a Membrane
Vesicles
• Many substances, such as proteins, polysaccharides,
and even bacteria, are too large to be transported by
carrier proteins altogether.
• Instead, they cross the cell membrane in vesicles, which
are membrane-bound (lipid bi-layer) sacs.
• The vesicle membrane is a lipid bilayer, like the cell
membrane. Therefore, vesicles can bud off from the
membrane, fuse with it, or fuse with other vesicles.
Mass Transport Across a Membrane
Vesicles
• Vesicles help the movement of large
molecules two ways:
– Endocytosis
– Exocytosis
http://wps.aw.com/bc_goodenough_boh_4/
177/45510/11650562.cw/index.html
Endocytosis = “Into”
Cell ingests large macromolecules or other cells
Vesicle
Exocytosis = “Exits”
Opposite of Endocytosis
Release of contents in the cell to the external
environment
Vesicle
Summary Questions
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Does Passive Transport require Energy?
Does Active Transport require Energy?
What is the energy required for Active Transport?
What is the difference between active and passive transport?
Is diffusion Passive or Active?
Is Osmosis Passive or Active?
Is the Sodium-Potassium pump Passive or Active?
How would these substances get into the cell?
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Oxygen (non-polar)
Carbon dioxide (non-polar)
Glucose (a large non-polar substance)
Ions traveling down their concentration gradient (small polar)
Ions traveling up their concentration gradient (small polar)
Water (small polar molecule)
Amino acids (large molecules of varying polarity)
Concept Check
Summary
• In passive transport, substances cross the cell
membrane down their concentration gradient.
• Osmosis allows cells to maintain water balance as their
environment changes.
• Active transport requires energy to move substances
against their concentration gradients.
Group Practice
• Get into groups and complete the worksheet.
When completed, we will cover answers.
• Make sure to use the correct color for each
molecule.
• At the end of class, turn in
– Your completed Transport Practice Worksheet
• HW If not completed
– The HW from last night.
Take these Quizzes
• http://www.hbwbiology.net/quizzes/ch8-cellmembrane.htm