Transcript Slide 1

GCE BIOLOGY BY2
Transport of Respiratory Gases
GCE BIOLOGY BY2
Transport of Respiratory Gases
Fluid Mosaic Model of the Plasma Membrane
Carbohydrate
chain
Glycoprotein
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Transport of Respiratory Gases
Intrinsic
protein
Non-polar hydrophobic fatty
acid chain
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Phospholipids
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Transport of Respiratory Gases
One of the functions of the plasma
membrane is to control the movement of
substances in and out of cells.
Why does this plasma membrane need to
be semi-permeable?
What’s the connection?
What is the connection between the following structures?
GCE BIOLOGY BY2
Transport of Respiratory Gases
Hint: What do cells need to produce energy?
Alveolus
Red blood cells
Small intestine
Capillary
Lungs
Closed Circulatory System
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Transport of Respiratory Gases
Humans have a closed circulatory system consisting of the
heart, arteries, arterioles (narrow, thin walled arteries),
capillaries, venules (small veins) and veins.
The following diagram shows the relationship between these
vessels and illustrates the movement of blood within them.
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Transport of Respiratory Gases
The path of blood from an artery, to a capillary and a vein
Blood in the capillaries
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Once the blood reaches the capillaries, it is
in contact with the endothelium (the lining
of the capillary) which is one cell thick.
The plasma membrane of these cells are
adapted for controlling the exchange of
substances across them, as we will see in
the following slides.
Membrane Permeability
Plasma membranes are semi-permeable – this means that some substances can
pass through whilst others cannot.
What determines which substances pass through this membrane?
A substance has to be very soluble in the oily phospholipid bilayer. Steroid
hormones, oxygen and carbon dioxide are examples of such molecules.
Plasma membrane
SOLUBLE
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steroid hormone
oxygen
carbon dioxide
INSOLUBLE
glucose
protein
lipid
Click on the molecules to start their paths of motion
Exchange of gases across a capillary
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Transport of Respiratory Gases
In the following
animation, we
zoom into an
alveolus and enter
the capillary that
surrounds it.
Once inside the
capillary, we will
follow the
exchange of gases
that occurs in the
red blood cell.
Play Animation
Formation of hydrogen carbonate and the transport of carbon
dioxide in the blood
Tissue cells
CO2
Endothelium of capillary
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H2CO3
CO2
H2CO3
Diffusion
Red blood cell
First carbon dioxide (CO2) diffuses into the red blood cells where it
is converted into carbonic acid (H2CO3).
This reaction is catalysed by the enzyme carbonic anhydrase.
CO2
Tissue cells
Endothelium of capillary
H2CO3
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exchange
Gas
of Respiratory Gases
Transport
H+ +
CO2
_
HCO3
H2CO3
Red blood cell
H+ +
_
HCO3
Carbonic acid dissociates, forming protons (H+) and
hydrogencarbonate ions (HCO3-)
Tissue cells
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Transport of Respiratory Gases
Endothelium of capillary
H2CO3
Red blood cell
H+ +
_
HCO3
Diffusion into plasma
_
HCO3
The hydrogencarbonate ions diffuse out of the cell.
They are transported in solution in the plasma.
Tissue cells
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exchange
Gas
of Respiratory Gases
Transport
Endothelium of capillary
H2CO3
Red blood cell
H+ +
_
HCO3
Chloride shift
Diffusion into plasma
_
Cl
_
HCO3
_
Chloride ions (Cl ) diffuse inwards from the plasma to maintain
electrical neutrality.
This process is called the chloride shift.
Tissue cells
Diffusion
Endothelium of capillary
4O2
Oxygen unloaded
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exchange
Gas
of Respiratory Gases
Transport
HHb
Red blood cell
_
H+ + HCO3
HbO8
The proteins left inside the cell are mopped up by haemoglobin to
form haemoglobinic acid (HHb). This forces the haemoglobin to
release its oxygen load, hence the Bohr shift.
Tissue cells
Diffusion
Endothelium of capillary
4O2
Oxygen unloaded
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Transport of Respiratory Gases
HHb
Red blood cell
_
H+ + HCO3
HbO8
By taking up excess protons haemoglobin is acting as a buffer. This
is important in preventing the blood from becoming too acidic.
The Effect of CO2 on the Oxygen Dissociation Curve
How much oxygen is transported by a molecule of haemoglobin also
depends on partial pressure of carbon dioxide.
100
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Saturation of Haemoglobin / %
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80
CO2
60
From the graph we see that at high
partial pressures of carbon dioxide, the
oxygen dissociation curve shifts to the
right.
40
This is called Bohr’s shift.
20
Higher partial pressure of carbon
dioxide increases the dissociation of
oxyhaemoglobin
0
0
2
4
6
8
Partial Pressure of Oxygen/ kPa
10
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Haemoglobin
This diagram shows how a model of haemoglobin
reaches saturation with oxygen.
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haemoglobin
The molecule is now saturated.
Click on the numbered
sections on the graph for
an explanation of what
happens at each stage
Oxygen Dissociation Curve
100
5
4
80
3
Saturation of Haemoglobin / %
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60
40
Haemoglobin’s
The
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redconditions
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amount
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20
2
0
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Show/ hide line
1
0
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2
4
6
8
Partial Pressure of Oxygen/ kPa
10
12
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On the next slide we will see the path that the products of
digestion take as they diffuse from the small intestine into
the blood capillaries surrounding the gut.
The cells must rely on more than diffusion to get all
the glucose, amino acids and fatty acid and glycerol into
the blood.
What form of transport do you think is used?
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Absorption of digested food from the small intestine
Click on the box to magnify the view
Active Transport
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This is the movement of substances against a
concentration gradient (from a region of low
concentration to a region of higher concentration)
across a plasma membrane. This process requires
energy.
This energy is provided by mitochondria in the form of
ATP and cells performing active transport on a large
scale contains numerous mitochondria.
4.8
How does Active Transport work?
Active transport depends on proteins in the cell membrane to
transport specific molecules or ions. These can move. These carriers
can move:
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i)
ii)
iii)
one substance in one direction (uniport carriers)
two substances in one direction (symport carriers
two substances in opposite directions (antiport carriers)
The exact mechanism of active transport is unclear. Here are two
hypotheses:
4.8
Cotransport Hypotheses
Sucrose movement in glucose storing cells in a plant.
Show animation
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Sucrose
Proton pump
Symport carrier
H+
Sucrose
Here the process of pumping protons drives sucrose transport in a
plant cell. A pump using ATP as an energy source drives protons out of
the cell, as they diffuse back into the cell, sucrose in this case is
transported at the same time across a symport carrier.
4.8
Another Hypothesis
This hypothesis suggests that
one protein molecule
changes its shape in order to
transport solutes across a
membrane.
K+
K+
ATP
K+
Na+
K+
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Na+
K+
ATP
Na+
Na+
Na+
PP-
Na+
K+
Na+
Na+
K+
Na+ K+
Na+
Na+
Na+K+
Na+
K+
Na+
Na+
ADP P-
ADP
P-
K+
Na+
Na+
As ATP is hydrolysed to ADP
to release energy for the
process, ADP binds to the
protein and changes its
shape.
A sodium-potassium pump is
an example of this. These
pumps are vital in order to
generate impulses in nerve
cells.
4.8