Download Introductory Biology

Movement Across
Membranes
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1. Diffusion
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Diffusion
Particles in liquids
and gases move in
random directions
with a certain
amount of kinetic
energy
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Diffusion
The overall effect of this is
that particles become evenly
distributed in their container
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Diffusion
Kinetic Energy can
be increased by
increasing the
temperature
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Examples:
• Diffusion of CO2 into stomata of leaves
during photosynthesis.
• Diffusion of O2 into the alveoli of the lungs
• Diffusion of O2 to respiring cells
• Diffusion of glucose, amino acids etc. into
the villi during digestion.
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2. Osmosis
The cell membrane is partially
permeable – it allows small,
particles to pass through by simple
diffusion
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The cell membrane is partially
permeable – it allows small,
uncharged or high energy particles
to pass through by simple diffusion
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• Osmosis is simply a special case of
diffusion…
• …that applies to WATER
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Water Potential
‘Water potential’ is a measure of
the amount of kinetic (movement)
energy water molecules have
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Water Potential
Water potential (y) is a measure of
the amount of kinetic energy water
molecules have
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Water Potential
In pure water at STP, the
molecules are given a water
potential of 0
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Osmosis
“Osmosis is the diffusion of water
molecules from areas of high water
potential to areas of lower water potential
through a partially permeable membrane”
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Osmosis
Osmosis is the diffusion of water
molecules from areas of high water
potential to areas of lower water potential
through a partially permeable membrane.
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Osmosis and Animal
Cells
Cells placed in
a solution of
higher water
potential
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Osmosis and Animal
Cells
Cells placed in
a solution of
higher water
potential
Cell
Water
bursts
enters by
(lysis)
osmosis
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Osmosis and Animal
Cells
Cells placed in
a solution of
lower water
potential
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Osmosis and Animal
Cells
Water leaves
by osmosis
Cells placed in
a solution of
lower water
potential Cell shrivels
(crenation)
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Osmosis and Plant
Cells
Cells placed in
a solution of
higher water
potential
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Osmosis and Plant
Cells
Cells placed in
a solution of
higher water
potential
Cell
Water becomes
enters by TURGID
osmosis
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Osmosis and Plant
Cells Cells placed in a
solution of lower
water potential
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Osmosis and Plant
Cells Cells placed in a
solution of lower
water potential
Cell shrivels
(PLASMOLYSED)
Water leaves
by osmosis
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Osmosis and Plant
Cells
These cells are placed in strong
sugar solution – would they
become turgid or plasmolysed?
plasmolysed
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• When plant cells lose water and
plasmolyse…
• …the plant is unable to support itself and
starts to WILT.
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Osmosis and Plant Cells
And when turgid the cell contents
exert outward pressure on the cell
wall
This helps to support plants and
keep them upright.
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Osmosis and Plant Cells
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Active Transport
Active transport moves
substances against a
concentration gradient.
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Active Transport
Movement involves the
hydrolysis of ATP to supply
energy
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Active Transport
Structural changes in the
carrier proteins result in the
movement of material
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What is active transport?
Movement of substances in and out of cells by diffusion involves molecules
moving down a concentration gradient from high to low concentration.
high concentration
diffusion
active transport
low concentration
Sometimes substances move into cells from low to high concentration. This is
called active transport.
Active transport needs energy to make it happen.
How do molecules move along the concentration gradient during active
transport?
Active transport and plants
Plants need mineral elements from the soil for healthy growth. Minerals enter a
plant though its roots.
The concentration of minerals in the soil is lower than that inside a root hair cell,
so how do minerals enter the root cell?
root hair
cell
mineral
element
soil
Active
transport
and
plants
The plant uses energy to move minerals up the concentration gradient from
Minerals enter a root cell by active transport.
the soil into its root cells.
Why is it important for plants to use energy in this way?
active transport
root hair
cell
mineral
element
soil
Summary:
• Active Transport is:
• “The movement of molecules AGAINST
their concentration gradient, using
ENERGY from respiration.”
• In mammals, nerves and brain cells carry
out Active Transport and use 1/3 of all the
energy in your body!
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So you could get fit just by thinking
about it!!
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Salt Glands
in marine
animals
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Why is Cyanide such an
effective poison?
• Murder:
• Gregor Rasputin
• Nazi gas Chambers (Zyklon B)
• Irwin Rommell
• Eva Braun
• Hermann Goering
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Why is Cyanide such an
effective poison?
• Suicide:
• Adolf Hitler
• Irwin Rommell
• Hermann Goering
• Heinrich Himmler
• Eva Braun
• Alan Turing
• Tamil Tigers
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What is Cyanide?
• Hydrogen Cyanide ( HCN)
• Found naturally in apple pips, apricot,
cherry and peach stones, clover leaves,
elderberrys
• Component of cigarette smoke
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How does it kill?
• Destroys the final enzyme in the
respiration chain ( in mitochondria)
• Without ATP energy, active transport
cannot occur
• Without aerobic respiration, brain and
heart cells die in 30 seconds.
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Jonestown Religious Cult – Mass
suicide. 900 dead.
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Concentrations of ions in a plant cell
Fresh water
• K+
0.1
120
75
• Cl-
1.3
65
106
• cell membrane
cytoplasm
cell wall
vacuole
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Compare the ways potassium and chloride ions
a) enter the cytoplasm from the water (2)
b) pass from the cytoplasm into the vacuole (2)
Fresh water
• K+
0.1
• Cl-
1.3
• cell membrane
120
75
65
106
cytoplasm
cell wall
vacuole
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