Transcript 7. Transport through membranes

SC: Compare passive with active transport.
Define osmosis, diffusion, facilitated diffusion,
active transport, concentration gradient
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Occurs in a fluid (liquid
or gas) where particles
are constantly moving
Is the movement of
particles from an area
of high concentration to
an area of low
concentration until the
concentrations are
equal.
(Note: Particles move in
both directions)
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Forms a barrier through which molecules
must pass to enter or exit the cell.
Recap: Phospholipid bilayer has hydrophilic
heads facing ___________ and hydrophobic
_________ facing ____________.
What particles will be able to pass through
this layer?
How do other particles get through?
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__________ diffusion - some molecules pass
through the lipid bilayer without assistance eg:
water, CO2, O2, lipids. http://highered.mcgraw-
hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.
html
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__________ diffusion – large molecules and
charged molecules require carrier proteins or
channel proteins to pass through the lipid
bilayer. http://highered.mcgraw-
hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_
diffusion_works.html
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O________ – diffusion of water molecules across a
selectively permeable membrane to an area of
lower concentration of water.
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html
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This is the movement of water molecules
from low concentration of water to high
concentration of water
Experiment Recap: How did you measure
concentration of water in yesterdays
experiment?
Experiment #
Concentration
of sucrose
solution in
beaker
Concentration
of sucrose
solution in
tubing
A
50%
5%
B
5%
5%
C
0%
5%
Mass change
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Water molecules are small so they easily
diffused through the membrane and moved
from the area where there are lots of water
molecules compared with solute molecules
(sugar).
Definitions: Hypotonic = low concentration of
water
Hypertonic = high concentration of water
Isotonic = balanced concentration of water on
each side of membrane
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Turgid:
Plasmolysed:
Flaccid:
Lysed:
These words are used to describe animal and
plant cells with different water potentials.
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What would happen if you drunk water only
during sport? Or very sugary drinks?
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Contain a similar concentration of ions as is
found inside the cells of your body.
Contain carbohydrates, water and essential ions
such as Na+ and K+
Hydrate the cells without bloating them or
removing excess water.
Sugary drinks can remove water from the cells
and cause excess sweating and urination.
Drinking water only can cause bloating and water
retention.
Isotonic drinks maintain the natural cell balance
during sustained exercise.
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Seawater has a lower concentration of water
than our cells (and a higher concentration of
ions).
Drinking it would cause water to diffuse from
our cells and be lost from the body by
urination.
Low water concentration in the cells would
cause a change in cell reactions.
The facts: Seawater has an average salinity of
35 g/L whereas our cells have a salinity of 9
g/L. Seawater is a hypertonic solution.
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Cells sometimes need to transport against a
concentration gradient (from low to high).
This can only be achieved by using energy in
the form of ATP and specific membrane
proteins.
This use of energy is about ¼ of all the
energy used by our bodies.
The sodium potassium pump is the most
common example of active transport.
http://highered.mcgrawhill.com/olc/dl/120068/bio03.swf
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What is the main difference between passive and
active transport?
Active uses energy to go up a gradient, passive –
diffusion down a concentrationgradient.
What molecules can diffuse though the
phospholipid layer?
CO2, H2O, O2, lipids
Does water travel towards or away from a high
concentration of sugar?
Towards because the molecules are actually
diffusing towards a low concentration of water
molecules.