Mass Transport in Animals (AQA A Level Biology): Flashcards
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Define the term mass transport
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Define the term mass transport
Mass transport is the efficient movement of substances over large distances, usually via specialised transport systems.
Why do multicellular organisms need mass transport systems?
The distances between exchange surfaces and the cells are very large.
Diffusion alone would be too slow to supply the cells with everything they need.
Name the specialised transport systems found in animals and in plants
Animals use the circulatory system.
Plants use the vascular tissue.
How do mass transport systems move substances in the required direction?
They use pressure changes to force substances to move in the required direction.
Give one example of a substance moved from an exchange surface to the body cells by mass transport
Oxygen is transported from the alveoli to the body cells.
(Alternatively, glucose is transported from the intestinal epithelium to the body cells.)
Give one example of a waste substance transported back to an exchange surface by mass transport
Carbon dioxide travels from the cells back to the alveoli.
(Alternatively, urea moves from the cells to the kidneys.)
True or False?
In a large multicellular organism, diffusion alone is fast enough to supply cells with the substances they need
False.
The distances between exchange surfaces and cells are too large, so diffusion alone would be too slow; a mass transport system is required.
Mass transport allows the movement of materials from to the parts of an organism where they are needed.
Mass transport allows the movement of materials from exchange surfaces to the parts of an organism where they are needed.
The circulatory system uses changes to force substances to move in the required direction.
The circulatory system uses pressure changes to force substances to move in the required direction.
What type of molecule is haemoglobin, and what level of structure does it have?
Haemoglobin is a protein with a quaternary structure.
How many polypeptide chains make up a haemoglobin molecule, and what are they?
Four polypeptide chains.
Two α–globins and two β–globins.
What does it mean that haemoglobin has a quaternary structure?
It is made up of more than one polypeptide chain (four in haemoglobin), held together by interactions between their R groups.
What is the role of the hydrophobic R groups in haemoglobin?
They face inwards, helping to preserve the spherical tertiary structure.
What is the role of the hydrophilic R groups in haemoglobin?
They face outwards, helping to maintain solubility.
What does each haem group contain, and what can it bind?
Each haem group contains an iron(II) ion (Fe²⁺).
It can reversibly combine with one oxygen molecule (O₂).
How many oxygen molecules can one haemoglobin molecule transport?
Four oxygen molecules, as it has four haem groups.
True or False?
Haemoglobin is found only in humans
False.
Haemoglobin belongs to a group of chemically similar molecules found in many different organisms.
Haemoglobin has a quaternary structure made up of polypeptide chains.
Haemoglobin has a quaternary structure made up of four polypeptide chains.
The haem group of haemoglobin contains an ion, which binds oxygen.
The haem group of haemoglobin contains an iron(II) (Fe²⁺) ion, which binds oxygen.
What is the role of haemoglobin, and where is it found?
Haemoglobin transports oxygen around the body.
It is located within red blood cells.
Write the word equation for the reaction between oxygen and haemoglobin
oxygen + haemoglobin ⇌ oxyhaemoglobin
Why do red blood cells have no nucleus?
To maximise the space available for haemoglobin.
How does the biconcave shape of a red blood cell aid its function?
It maximises the surface area for the diffusion of oxygen.
Why are red blood cells highly flexible?
To allow them to pass through narrow capillaries.
How does the diameter of a red blood cell aid oxygen transport?
Its diameter is approximately the same as that of the capillaries.
This slows down the flow of blood, maximising the time for diffusion.
How many oxygen molecules and oxygen atoms can one haemoglobin molecule carry?
Four oxygen molecules.
This is equal to eight oxygen atoms.
True or False?
The binding of oxygen to haemoglobin is irreversible
False.
The haem groups combine reversibly with oxygen: oxygen + haemoglobin ⇌ oxyhaemoglobin.
Each haemoglobin molecule contains four groups, each of which binds one oxygen molecule.
Each haemoglobin molecule contains four haem groups, each of which binds one oxygen molecule.
Red blood cells have no in order to maximise the space available for haemoglobin.
Red blood cells have no nucleus in order to maximise the space available for haemoglobin.
What does the oxyhaemoglobin dissociation curve show?
It shows the percentage saturation of haemoglobin with oxygen at different partial pressures of oxygen (pO₂).
How is oxygen concentration expressed on the oxyhaemoglobin dissociation curve?
As the partial pressure of oxygen (pO₂).
When is haemoglobin described as saturated?
When all of its oxygen binding sites are taken up with oxygen, i.e. when it contains four oxygen molecules.
What gives the oxyhaemoglobin dissociation curve its distinctive S-shape (sigmoid) shape?
The cooperative binding of oxygen to haemoglobin.
Explain the shallow part of the curve at the bottom left
It is difficult for the first oxygen molecule to bind to haemoglobin, so binding of the first oxygen molecule is slow.
Explain the steep central region of the curve (cooperative binding)
After the first oxygen molecule binds, the haemoglobin protein changes conformation (shape).
This makes it easier for the next oxygen molecules to bind, speeding up their binding.
This is known as cooperative binding.
Explain why the curve levels off in the top right
As haemoglobin approaches saturation, there is a shortage of remaining binding sites.
So it takes longer for the fourth oxygen molecule to bind.
How does haemoglobin's affinity for oxygen compare at high and low pO₂?
At high pO₂, haemoglobin has a high affinity for oxygen.
At low pO₂, haemoglobin has a low affinity for oxygen.
Explain oxygen binding in the lungs compared with the respiring muscles
In the lungs, pO₂ is high, so haemoglobin binds (associates/loads) oxygen easily.
In the muscles, pO₂ is relatively low due to high rates of respiration, so oxygen dissociates (unloads) easily from haemoglobin.
In the steep, middle part of the curve, what is the effect of a small decrease in pO₂?
A small decrease in pO₂ causes a large decrease in the percentage saturation of haemoglobin.
This allows the easy release (unloading) of oxygen to the cells in respiring tissues.
True or False?
At a high partial pressure of oxygen, haemoglobin has a low affinity for oxygen
False.
At a high pO₂, haemoglobin has a high affinity for oxygen, so it binds (loads) oxygen easily.
The change in shape of haemoglobin that makes it easier for further oxygen molecules to bind is called binding.
The change in shape of haemoglobin that makes it easier for further oxygen molecules to bind is called cooperative binding.
What is the Bohr effect?
The Bohr effect is the way in which the concentration of carbon dioxide in the blood influences the dissociation of oxyhaemoglobin.
What is the effect of a high partial pressure of carbon dioxide (pCO₂) on haemoglobin's affinity for oxygen?
Haemoglobin's affinity for oxygen is reduced.
In which direction does the oxyhaemoglobin dissociation curve shift at a high pCO₂?
The curve shifts to the right.
Where in the body is the Bohr effect greatest, and why is this useful?
It is greatest in actively respiring tissues.
This means haemoglobin gives up (unloads) its oxygen more readily where it is needed.
Describe the sequence of the Bohr effect in actively respiring tissue
Respiration produces carbon dioxide as a waste product.
The partial pressure of carbon dioxide (pCO₂) in the blood is high.
Haemoglobin's affinity for oxygen is reduced.
Dissociation of oxyhaemoglobin increases.
The availability of oxygen to the tissues increases.
At a higher partial pressure of carbon dioxide, the oxyhaemoglobin dissociation curve shifts to the .
At a higher partial pressure of carbon dioxide, the oxyhaemoglobin dissociation curve shifts to the right.
True or False?
A high concentration of carbon dioxide increases haemoglobin's affinity for oxygen
False.
A high pCO₂ reduces haemoglobin's affinity for oxygen, causing more oxygen to be unloaded at respiring tissues (the Bohr effect).
At a higher CO₂ concentration, how does the percentage saturation of haemoglobin compare at any given pO₂?
At any given partial pressure of oxygen, the percentage saturation of haemoglobin is lower at higher levels of CO₂.
What is the benefit of the Bohr effect to respiring tissues?
More oxygen dissociates (unloads) from haemoglobin, increasing the availability of oxygen to the actively respiring tissues where it is needed.
Why do different organisms have different types of haemoglobin?
So that their haemoglobin can bind to and release oxygen in different environmental conditions.
These differences arise through natural selection.
What type of haemoglobin is needed by organisms living in low pO₂ environments, and why?
Haemoglobin with a higher affinity for oxygen.
It must pick up (load) oxygen at a pO₂ at which adult human haemoglobin would release it.
What type of haemoglobin is needed by highly metabolically active animals, and why?
Haemoglobin with a lower affinity for oxygen.
This allows it to release (unload) oxygen easily to the respiring tissues.
How does the affinity for oxygen of fetal haemoglobin compare with that of adult haemoglobin?
Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin.
Why does fetal haemoglobin need a higher affinity for oxygen?
So that it can obtain oxygen from the mother's blood at the placenta.
The mother's blood has a low pO₂ because it has already travelled around the body, so it is dissociating with oxygen there.
In which direction is the dissociation curve for haemoglobin with a higher affinity for oxygen shifted?
The curve shifts to the left.
Explain how the llama is adapted to living at high altitude
At high altitude the pO₂ in the air is low.
Llamas have haemoglobin with a high affinity for oxygen, which binds more readily to oxygen.
This allows them to reach a sufficient level of oxygen saturation in their blood when the pO₂ in the air is low.
Fetal haemoglobin has a affinity for oxygen than adult haemoglobin.
Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin.
True or False?
The oxyhaemoglobin dissociation curve for a species living at high altitude is shifted to the right of the human curve
False.
High-altitude haemoglobin has a higher affinity for oxygen, so its curve is shifted to the left.
What happens to fetal haemoglobin after birth?
The baby begins to produce adult haemoglobin, which gradually replaces the fetal haemoglobin.
This allows the easy release of oxygen in the respiring tissues of a more metabolically active individual.
On a graph, how can you identify which haemoglobin has the highest affinity for oxygen?
Choose any pO₂ on the x-axis and read upwards to the curves.
The curve showing the highest percentage saturation is the haemoglobin with the highest affinity for oxygen.
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