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HSC – Biology – Maintaining a Balance
2) Plants and animals transport dissolved nutrients and gases in a fluid medium

Identify the forms in which each of the following is carried in mammalian blood:
i. Carbon Dioxide
ii. Oxygen
iii. Water
iv. Salts
v. Lipids
vi. Nitrogenous waste
vii. Other products of digestion
Blood is considered as a tissue and not a liquid as it is composed of cells in an extacellular fluid called
plasma. About 50 % of blood is made up of cells and the other 50 % plasma, although these figures vary.
The blood looks red due to the red blood cells it contains.
Blood volume for an average sized male is about five to six litres and for a female is 4-5 litres.
Plasma is a liquid containing various dissolved substances. One of these is the protein fibrinogen, the
substance that forms the clot when a you cut yourself. After the clot has formed, a yellow fluid is sometimes
seen near the clot – this is serum. This is plasma minus fibrinogen.
There are four main components of the blood:
1) Plasma – This suspends the blood cells and is the majority (55%) of the make up of blood. It also
contains substances that stabilize pH and osmotic pressure, promote clotting and contribute to
immune response.
2) White blood cells – These are about 0.1% of the blood and are used to destroy foreign cells and
debris, and also to act in immune response
3) Platelets – these are about 0.01% of the blood and aid in blood clotting and inflammation.
4) Red blood cells – About 45% of the blood and transport most oxygen and some carbon dioxide.
Each of the substances in the plasma is transported in a specific form:
Carbon Dioxide: Carbon dioxide is produced as a waste product of respiration in body cells.
Because its concentration is higher in the cell than in the blood, it diffuses into the blood. After
entering in the blood stream it may:
be dissolved in plasma
bind to haemoglobin forming carbaminohaemoglobin.
Be converted into carbonic acid and then hydrogen carbonate ions in red blood cells and
move into the plasma in which from it is transported.
Oxygen: Oxygen is transported attached to the haemoglobin in red blood cells
Water: Water is the solvent of plasma. Water as a plasma solution comprises 60 percent of the
volume of blood
Salts: Salts are transported dissolved in plasma. They are composed of positive and negative ions.
Positive ions include sodium, potassium, calcium and magnesium. Negative ions include chloride and
hydrogen carbonate.
Lipids: Digested lipids are re-synthesised into trigylcerides in the epithelial cells that line the small
intestine. The trigylcerides together with some phospholipids and cholesterol are wrapped in a coat
of protein to form a package called a chylomicron. These are released into the lymph vessels called
lacteals, which run parallel to the veins. They eventually pass from the lacteals into the veins and
are transported to the tissue cells for energy, or to the adipose tissue for storage.
Nitrogenous wastes: These are in the form urea, uric acid and creatinine and are transported
dissolved in the blood plasma.
Other products of digestion: They include aminoacids, nitrogenous bases, sugars, glycerol and
vitamins – these are mainly water soluble and are transported dissolved in the plasma.
White Blood cells
The general function of white blood cells is to combat infection.
They can move out of the bloodstream through connective and epithelial tissues. Many white blood cells are
phagocytotic which means that they ingest bacteria and other foreign material.
White blood cells survive for varying lengths of time. There is a limit to the amount of foreign material and
cell debris that white blood cells can ingest. If an individual is healthy, white blood cells may survive for
several days. If an individual has an infection of some kinds, then white blood cells may last for only a few
hours.
Platelets
If damage occurs to the vessels that transport blood, platelets initiate a chain of reactions that result in
blood clotting. Platelets clump together, which helps to plug the hole in the vessel and their membranes
rupture and clotting factors are released. Fibrin is this produced, in which red blood cells are caught, and
cannot move – thus forming a clot.
Platelets have short lives – usually lasting for about a week.

Compare the structure of arteries, capillaries and veins in relation to their function.
Blood travels in arteries, veins and capillaries. The vessels, with the heart and lungs, form the circulatory
system. Arteries are vessels that leave the heart. They branch into small arteries known as
arterioles. The arterioles continue to branch into thin-walled capillaries. Capillaries collect into small
veins called venules, which combine to form veins.
Arteries must withstand high blood pressure.
Nutrients, respiratory gases and wastes are exchanged between blood and body cells through the capillary
walls. Veins deliver blood back to the heart, sometimes against gravity
Because of these different functions, the arteries, veins and capillaries have different structures.
Blood vessels are composed of walls and a lumen (space between the walls).
The walls of the arteries and veins are composed of three layers – an outer layer of connective
tissue, a layer of elastic fibres and smooth muscle inside that, and an inner endothelial (lining)
layer.
The elastic fibre/smooth muscle layer is much thicker in arteries. This gives greater elasticity (ability to
return to their original shape when stretched by blood at high pressures) to the arteries.
Veins transport blood at lower pressures. Because of this and because of the blood flow in some veins
against gravity, the veins have valves. Valves are flaps that can close over to prevent the back flow of
blood. Blood is kept moving in the veins due to the contraction of surrounding muscles and this contraction
causes the opening and closing of the valves.
Note: The Lumen of arteries is smaller than that of veins.
Capillaries must have very thin walls for the rapid transport of substances between blood and cells. The
endothelial layer is just one cell thick and the lumen is small, just enough for red blood cells to move one
after the other.
No cell in the human body, is more than 130 micrometers from a capillary.
Arteries
Arteries are thick-walled vessels that carry blood away from the heart. Two arteries exit from the heart.
The pulmonary artery carried blood away from the heart towards the lungs. Another artery, the aorta,
carries blood away from the heart towards other body tissues.
The walls of the artery have three main layers.
-
-
The inner layer is an endothelium that is in direct contact with the blood and a very thin layer
of connective tissue
The second layer contains muscle controlled by sympathetic nerve fibres and elastic tissue.
This layer gives strength to the arteries. The amount of muscle tissue relative to elastic tissue
depends on the function of the artery. Large arteries such as the aorta and pulmonary artery
have a high proportion of elastic tissue and can be readily stretched. This allows them to stretch
and recoil as the heart beats.
The out layer is the non-elastic connective tissue that anchors the arteries place in the body.
The highly muscular arteries branch repeatedly into smaller and smaller arteries and give rise to arterioles.
These have the three layers found in small arteries but are much reduced in thickness. As arterioles enter
the tissues, they branch into microscopic vessels called capillaries. This muscle in the second layer allows
the arterioles to constrict/dilate and in this way they have control over blood flow into capillaries.
Capillaries
Although the blood flow into capillary networks is controlled by the arterioles, additional control occurs
through the contraction of smooth muscle cells that act as sphincters in the networks.
Capillaries are thin walled vessels. There walls are one cell thick and materials either pass through these
cells or pass between the cells as the leave or enter the blood.
Oxygen is able to diffuse through the endothelial lining cells to surrounding tissue fluid and cells. Carbon
dioxide makes the reverse journey. Water and small water soluble molecules such as glucose and inorganic
iions, diffuse through the gaps between the endothelial cells. Some proteins leave the capillaries through the
endothelial spaces of across the cells in vesicles. Most protein stays in the blood vessels.
Veins
Blood moves from the capillaries to the venules, which combine to form larger vessels called veins. The
walls of the veins have a basic structure similar to that of the arteries. However, veins have thinner walls.
The muscle and connective tissue layer of veins are thinner than the equivalent layers in the arteries. This
makes the veins much more flexible and distensible than arteries.
Blood flow slows as it moves from larger vessels into many branched smaller vessels. This leads to a
reduction in blood pressure as the blood circulated around the body. Although pressure increases as blood
flows from venules into veins, it is still significantly less than the pressure of the blood leaving the aorta.
Blood pressure in the veins is insufficient to return all the blood to the heart from extremities such as the
feet and legs. To counter this deficiency, veins have valves that prevent the backflow of blood. Contraction
of muscles near the veins also helps squeeze the wins and move the blood along.
Blood is not always distributed evenly throughout the body. Although all capillaries contain blood, and the
supply to the brain and heart is usually constant, the rate of movement of the blood may vary in other areas
from time to time. Blood flow can be controlled by the arterioles that relax or contract and by pre-capillary
sphincters.
Hypertension
The average blood pressure of a young male adult is about 16.0 kPa systolic and about 10.7 diastolic. The
systolic pressure is the pressure exerted in the arteries as the ventricles contract. The diastolic pressure is
the pressure remaining in the arteries as the ventricles relax. BP is generally expressed as systolic/diastolic.
If a person has persistent high blood pressure, the condition is called hypertension.
If high blood pressure continues, the energy required by the heart to pump blood around the body
increases. Heart muscle thickens and the heart enlarges, and has to develop more force by contracting
harder.
Damaged Valves
If thee valves become damaged, blood falls backwards and may accumulate in the veins causing them to
swell. Continual swelling results in stretched and flabby veins because the muscles in the veins lost their
elasticity. These damaged veins are called varicose veins.
The Heart
The heart is a pump that keeps the blood moving. The following is a brief overview of the heart to remind
you of its place in the total circulatory system.
It is continually on the move – collecting oxygen from the lungs, collecting nutrients from the intestines,
transporting the nutrients and oxygen to all the tissues of the body, and carrying carbon dioxide and other
wastes away from cells to those specialised regions where they are disposed of.
The heart can be thought of as two pumps joined together. The right side of the heart receives blood from
the head and other parts of the body and pumps it to the lungs. Because this blood has come from tissues,
it is relatively low in oxygen and high in carbon dioxide.
In the lungs, carbon dioxide is released from the blood. Oxygen is absorbed from the air in the lungs and
combines with the haemoglobin of the red blood cells.
The left side of the heart receives the blood from the lungs and pumps it to all other tissues of the body via
the main artery known as the aorta.
A force from behind is the main factor responsible for the continual movement of the blood. A beating heart
provides this force. If the heart stops beating, blood stops flowing.

Explain the adaptive advantage of haemoglobin
Structure of Haemoglobin
The red pigment haemoglobin is the main component of our red blood cells. Haemoglobin is composed of
four polypeptide chains (protein) known as globin. Towards the centre of each globin is a haem unit. Haem
is a ring structure with iron in the centre. It is the iron that binds the oxygen, in a weak interaction that can
be easily broken. There are two kinds of globins. Two are called alpha chains and the other two are
known as beta chains.
A red blood cell is packed with haemoglobin molecules. The cell has no nucleus so more haemoglobin
molecules can be included. The symbol for haemoglobin is Hb.
Function of Haemoglobin in Transporting Oxygen
The functions of haemoglobin include:
Transport of oxygen to body cells from the lungs
Transport of some carbon dioxide from body cells to the lungs
Conversion of some carbon dioxide to hydrogen carbonate ions by the action of the enzyme
carbonic anhydrase. Carbonic acid produces hydrogen ions
Buffering of the hydrogen ions.
The major role of haemoglobin is the transport of oxygen. Oxygen is not very soluble in water and most of it
is carried by the haemoglobin in red blood cells. The interaction of iron ions with oxygen binds oxygen to
haemoglobin, forming oxyhaemoglobin. This occurs when the pressure (concentration) of oxygen is very
high, for example in the lungs. Each haemoglobin molecule can bind four oxygen molecules (one molecule
per haem). The opposite occurs at the body cells where the oxygen pressure is low. This is a reversible
reaction that can be summarized:
There are approximately 280 million haemoglobin molecules in each red blood cell. If each haemoglobin can
bind 4 oxygen atoms, then each red blood cell can theoretically carry for than 1 billion molecules of oxygen.
Structure of Haemoglobin with oxygen
Haemoglobin Saturation is the percentage of haem units containing bound oxygen. For example if all the
haemoglobin molecules are fully loaded with oxygen, there is 100% saturation. Anything less than 100% is
known as partial saturation.
The saturation of haemoglobin with oxygen is dependant upon the pO2 (pressure of oxygen, which is directly
related to the concentration of oxygen) in the environment of the haemoglobin. At the lungs the pO2 is high
so the oxygen diffuses into the blood and binds to the haemoglobin. At the body cells the opposite occurs,
the pO2 is low so oxygen is released from the haemoglobin and diffuses to the body cells.
The reason for the sigmoidal curve is because the
shape of the haemoglobin molecule changes slightly
each time it binds to an oxygen molecule. The
attachment of the first makes it easier for the second
and so on.
The steep part of the curve(btw pO2 20 - 80 mm/Hg)
shows that a small rise in oxygen increases the
percentage binding by a large amount and vice
versa. The behaviour of haemoglobin gives an
adaptive advantage to the molecule. At pO2 values of
about 60 mm Hg (common at high altitudes)
haemoglobin is still 90% saturated so oxygen
transport can remain almost normal despite the
altitude and relatively low oxygen content of the air.
The relationship pO2 and haemoglobin saturation provides a mechanism for regulating the amount of oxygen
delivered to tissues. When tissues are relatively inactive the local pO2 is approximately 40 mm Hg. Not much
oxygen is released.
When the tissues become active they use more oxygen so the pO 2 in the tissues decreases to 15-20 mm Hg.
More oxygen is released from haemoglobin. So the release of oxygen depends on how much oxygen is being
used and the consequent oxygen demand of the tissues. Under normal resting conditions haemoglobin
returning to the lungs will still be 75% saturated with oxygen, (although it may be known as
deoxyhaemoglobin).
Other Factors affecting the saturation of haemoglobin with oxygen
pH and carbon dioxide concentration
A decrease in pH changes the shape of haemoglobin so that it releases oxygen more easily. The effect of
lowered pH decreasing the saturation of haemoglobin is known as a Bohr effect.
Carbon Dioxide concentration in blood has the greatest influence on lowering pH. When CO2 diffuses from
body cells into blood, an enzyme known as carbonic anhydrase, catalyses the reaction with water as
shown below:
The carbonic acid dissociates into hydrogen ions which lowers the pH.
So increased CO2 concentration leads to increased carbonic acid which leads to increased hydrogen ions,
leading to decreased pH which decreases the oxygen saturation of haemoglobin.
Temperature
Temperature changes also affect the haemoglobin saturation curve. As the temperature increases the
haemoglobin releases more oxygen and as the temp declines the haemoglobin becomes more saturated.
Temperature effects only become significant when tissues are producing large amounts of heat. In these
situations warm blood flows through the body and haemoglobin releases more energy than can be used by
cells.
Effect of PO2
The graph below is called the oxygen-haemoglobin dissociation (or saturation) curve. As expected, the
greater the vale of PO2 to which haemoglobin is exposed, the greater the percentage saturation of the
haemoglobin, which reaches a maximum of 97% saturation.
PO2 near tissues is low and oxygen readily leaves the blood so that haemoglobin drops to about 70%
saturated. If the person is very active, then body tissues at an increased rate use more oxygen. The
concentration gradient of oxygen from capillary to tissues will be greater than that in a person at rest and
more oxygen leaves the capillaries. The percentage saturation of haemoglobin as it leaves tissue capillaries
will be less than that in a person at rest.
Altitude
As altitude increases the air becomes ‘thinner’ that is the particles of gases in the air spread farther apart
and the partial pressure of gases, including oxygen, decrease. Thus the percentage saturation also
decreases.
As the percentage saturation of haemoglobin declines, there may not be sufficient oxygen available for
normal tissue metabolism. This condition is called hypoxia. As hypoxia develops, the body responds in
several ways to compensate for the deficiency of oxygen. This includes:
1) The initial response is to breathe more deeply and more often – this is called hyperventilation.
2) If the oxygen deficiency continues, longer-term changes occur. The body increases its
production of red blood cells and haemoglobin so that, even if the percentage saturation is
declining, the decline in oxygen availability is slowed down. People who live permanently at high
altitudes have much higher red blood cell count than those who live at sea level.
3) Initially, as cardiac output increases but, as more red blood cells and haemoglobin develop,
cardiac output and the increase in ventilation mentioned above return to normal.
4) Other long term changes include an increase in the efficiency of metabolism in tissues, blood
volume increases and capillaries increase in extent and diameter to accommodate the additional
blood.
Some of these physiological adaptations do not occur overnight – it takes two to three weeks. That is why
athletes travel to their competition sites and begin training in advance of the events.

Describe the main changes in the chemical composition of blood as it moves around the body and
identify the tissues in which these changes occur.
Simple Sugars
Simple sugars such as glucose cross the membranes of cells lining the gut and are absorbed into blood in
capillaries in the gut villi. From there, sugars are carried via the hepatic portal vein to capillaries in the liver.
The hepatic portal arrangement enables the liver to act on compounds absorbed from the gut before they
enter the general circulation. The liver may remove some compounds for storage or may alter other
compounds. Simple sugars are converted into glucose in the liver.
When glucose levels are high in the blood (say after a meal) some may be transported to the liver, where it
is converted into a high energy carbohydrate, glycogen. Some of this glycogen can also be stored at
skeletal muscle tissue.
Amino Acids
The digestion of proteins produces amino acids. Amino acids absorbed in the gut enter the hepatic portal
vein and are transported to the liver. From the liver, amino acids are carried by the blood to all parts of the
body where they are used.
Lipids
When fats are digested, fatty acids and glycerol are produced. Some of these diffuse through the cells lining
the intestine into nearby blood capillaries and are transported in blood, via the hepatic portal vein, to the
liver.
The majority of fatty acids are reassembled into chylomicrons. These small particles enter the lacteals of
the lymphatic system in the villi of the intestine. They are transported in the lymph and are released into
the venous circulation via the thoracic duct.
Cholesterol
Cholesterol is transported in the blood by two major kinds of proteins: low-density lipoproteins (LDL’s) and
high density lipoproteins (HDL’s). LDL’s are the main source of arterial blockage in people.
Foods that contain saturate fats, tend to raise the level of cholesterol in the blood. Replacing saturated fats
with polyunsaturated fats, such as safflower or sunflower oil, helps lower the blood cholesterol level.
Carbon Dioxide
Tissue cells produce carbon dioxide as a waste product during cellular respiration. The normal pH of tissue
cells is about 7.4. This is the pH at which nerve cells best operate and cellular enzymes act to control
cellular metabolism. If the carbon dioxide produced in cellular respiration accumulated within the cells, the
pH of the cells would fall, hence making them more acidic, eventually resulting in death.
Carbon dioxide diffuses down a concentration gradient in the same manner as oxygen. Blood entering the
tissue capillaries carries Carbon dioxide at low levels. Blood leaving the tissue capillaries has a higher level.
Carbon dioxide leaves the blood and diffuses down the concentration gradient across the capillary and
alveoli walls. Blood leaving the lung capillaries has low levels of CO2.
Low amounts of carbon dioxide can be carried in the blood due to its low solubility.
Carbon dioxide diffuses into blood in tissue capillaries from surrounding cells and most enters the red blood
cells. About seven per cent remains dissolved in the plasma and is transported back to the lungs in that
form. Within red blood cells the following reaction occurs:
A further reaction immediately follows:
The bicarbonate ions are very soluble and diffuse from the red blood cell into the blood plasma. The CO2 that
remains in the red blood cells combines with the haemoglobin. So blood carries carbon dioxide from body
tissues to lungs in three forms: bicarbonate ions, in the haemoglobin or dissolved in plasma.
In lung capillaries the processes that occur with relation to carbon dioxide are the reverse of what occur in
the blood.
Nitrogenous Wastes
Nitrogenous wastes can occur from two sources:
-
When excess amino acids are obtained by the body after digested of proteins
-
When cells metabolise proteins into constituent amino acids.
Amino acids cannot be stored. Excess is transported to the liver where they are deaminated.
Deamination is the removal of amino (NH3+) groups which are then converted to urea in mammals. Blood
transports nitrogenous wastes to the kidneys where it is excreted in urine formed by the kidneys.
Bilirubin
Red blood cells have limited lifetimes in the circulatory system. When they die, bilirubin is produced as a
waste product when the haemoglobin they contain is broken down. Bilirubin is removed from the blood by
the lever, then excreted into the gut with bile and moves out of the gut with faeces.
In ability to remove bilirubin results in Jaundice where the eyes take on a yellow colour.
Other Materials
Electrolytes
The electrolytes transported in plasma (such as bicarbonate, calcium, magnesium, sodium, potassium and H
ions) play a major role in osmotic distribution of fluid between extracellular and intracellular fluid as well as
buffering pH changes of the blood.
One particular area is at the skin. Sweat released from sweat glands is really a dilute solution of salts,
particularly sodium chloride, and includes low levels of some nitrogen containing compounds such as urea,
uric acid and amino acids.
Hormones
Hormones are secreted into the blood by endocrine glands and then transported to target tissues around the
body. Different hormones have different half-lives and so the time each remains in the blood also varies.
Extra: The Lymphatic System
Fluid, some protein and white blood cells escape from the capillaries and move into the tissue fluid.
Although some of the fluid that leaks out moves back into the capillaries. Most of the excess tissue fluid is
collected by the lymphatic system.
Lymph capillaries are blind-ending, thin walled and begin in spaces between tissue cells. Small lymph
capillaries combine to form larger and larger vessels. When tissue fluid enters a lymphatic, it is called
lymph.
The lymphatic system is a one-way system. It transports lymph from the tissues to the veins where the
lymph is returned back to the bloodstream.
The lymphatic system has no heart, but does have valves in the vessels that prevent backflow of the lymph.
In addition, breathing action, muscular movements and pressure from adjacent blood vessels help move
lymph through the lymphatic system.
The thicker areas in the lymphatic system are the lymph nodes. Lymph is strained through the nodes and
any micro-organisms or other foreign material are usually retained and destroyed there.

Outline the need for oxygen in living cells and explain why the removal of carbon dioxide is
essential
Breathing means life, and ensures that there this a supply of air close to the blood to provide oxygen and
remove carbon dioxide. The transport system and from tissues is the blood. The concentration of oxygen and
carbon dioxide in the blood varies depending on gas exchange in the lungs and in the tissues. Oxygen and
carbon dioxide diffuse across the membranes between the blood and lungs or body cells because of the
difference in concentrations of these gases between blood and lungs or blood and cells. (See Diagram on next
page)
The concentrations of other chemicals in the blood also change as it moves around the body.
For example urea, is a nitrogenous waste material produced by the liver and removed by the kidneys. The
concentration of urea in blood entering the kidneys is higher than the urea concentration leaving the kidneys.
Glucose levels in blood rise after a meal but as glucose is removed by the liver and muscle its concentrations
returns to normal.
Oxygen and carbon dioxide levels ion blood and cellular respiration
All living calls can respire, either with or without oxygen. Respiration is the breakdown of glucose using oxygen
to produce energy in the form of ATP. Respiration without oxygen is called fermentation. Carbon Dioxide and
water are by-products of respiration. All living cells that metabolise glucose require oxygen. It is supplied from
the red blood cells, which transport it from the lungs.
In producing energy from circulating energy, living cells also produce carbon dioxide. Carbon dioxide is of no
further use and must be removed from respiring cells and tissues. The accumulation of carbon dioxide can have
damaging effects in body chemistry. For example, increased carbon dioxide concentrations decrease pH
and change the ability of haemoglobin to bind with oxygen.
Carbon dioxide is removed from the blood in one of three ways – as a dissolved gas in the plasma, attached
to the haemoglobin, or as hydrogen carbonate ions in the plasma.
For cells to respire efficiently oxygen must be continually supplied and carbon dioxide removed. The transport
system for the supply and removal is the blood. The supply and removal sites for carbon dioxide are the
body cells (supply) and the alveoli in the lungs (removal)
The supply and delivery sites for oxygen are the alveoli in the lungs (supply) and the body cells and
tissues (removal).
Controlling the Concentration of Gases by Negative feedback and the Nervous System
Transportation of oxygen and carbon dioxide between lungs and tissues is a dynamic system capable of
responding to change. Some of the response are a direct result of the chemistry of these substances. Others are
coordinated by the nervous, circulatory and respiratory systems.
Control of the concentration of respiratory gases in the blood is achieved by the control of the breathing rate.
This is an involuntary action. We can exert some voluntary control over our breathing by using the
cerebral cortex of the brain. However this voluntary control can be overridden by the involuntary
system.
Regardless if the decision to hold your breath, respiration will still proceed in your body cells, carbon dioxide will
still be produced and pCO2 and H+ concentrations will increase in the blood. As well as a decrease in pO2.
The receptors that detect this are not in your blood however. The blood has proteins (such as
haemoglobin) to buffer the extra H+ so it is not easily detected there.
But CO2 diffuses readily from the blood into the cerebrospinal fluid where it forms carbonic acid and
so H+. There are no buffers here so the excess H+ are detected by the chemoreceptors in the brain
stem.
These receptors will detect the changes and relay them to the inspiration centre in the brain, which ensures
that breathing is again necessary, forcing you to inhale. This removed the excess CO2.
The maintenance of constant pO2 and pCO2
levels in the blood by the control of breathing
rate is a complex process. It involves a high
degree of
co-ordination
between
the
respiratory and circulatory systems which in
turn is influenced by the metabolism in cells.
Respiratory centers (both for inspiration and
expiration) in the brain stem establish both
the rate and depth of breathing by sending
out periodic nerve impulses that cause the
respiratory muscles to contract or relax.
The resulting breathing rate and consequent
pO2 and pCO2 levels in the blood are
detected
by
receptors,
and
negative
feedback to the respiratory centers adjusts
the breathing rate. Stretch receptors in the
bronchi and alveoli also detect overstretching of pulmonary tissues and influence
breathing rate, particularly expiration.
Research has shown that pCO2 levels exerts
the strongest negative feedback for the
control of breathing rate. This is because
when CO2 levels become too high, carbonic
acid levels rise. This releases H+ which lower
the pH and make the blood to acidic. The
effect of raised CO2 levels first in the blood
and then in cerebrospinal fluid is to provide
negative feedback to the inspiration centre to
increase inspiration, not so much as to
increase oxygen as to eliminate CO2 and
minimize pH changes.

identify current technologies that allow measurement of oxygen saturation and carbon dioxide
concentrations in blood and explain the conditions under which these technologies are used.
Arterial Blood Gas (ABG) Analysis
ABG analysis takes blood samples from an artery, usually the radial artery in the wrist and the sample is
tested in a Blood Gas Analyzer. The sample is tested for the concentration of oxygen, the concentration of
carbon dioxide and pH. The procedure is invasive and there can be a delay between sampling and the
availability of results. The results of ABG analysis provide vital information for critically ill patients who are
on ventilators, or undergoing respiratory therapy. Since many diseases show a range of similar conditions,
e.g. dizziness, chest pain and breathing difficulty, an ABG analysis can often reveal the cause of the
problem.
Pulse Oximetry
The pulse oximeter is a newer method and uses two wavelengths of light – red (660 nm) and infra-red (940
nm) to measure the amount of absorption of light as the light passes through the finger from the light
source to the photodetector. The amount of light absorbed by haemoglobin depends on whether the
haemoglobin is saturated with oxygen or reduced haemoglobin. Mathematical calculations work out the
proportion of oxygenated haemoglobin present. This method is used when a non-invasive approach is
needed or when rapid, continuous monitoring of arterial blood is needed eg. Through recovery phases.
Pulse oximeters are also used in intensive care units during mechanical ventilation and can quickly detect
problems with oxygenation.

Present information from secondary sources to report on the progress in the production of
artificial blood and use available evidence to propose reasons why such research is needed.
In the past
Attempts to treat massive bleeding in soldiers during World Wars I and II often failed and this spurred on
modern efforts to produce artificial blood.
Severe bleeding is a life-threatening condition thus the need for artificial blood was identified.
Additionally artificial blood was considered as an option to overcome setbacks with transfused blood:
■ cross-matching of blood types
■ the short storage life (only a few weeks) before donated blood and products must be discarded
■ the difficulty transporting blood into battle zones.
There was a resurgence in military-driven efforts in research for a blood substitute in the 1960s, in response
to difficulties in supplying blood to soldiers in the hot jungle conditions during the Vietnam war. The search
was on for an oxygen carrying solution that could expand the blood volume and also deliver (release) the
oxygen to tissues where it was required.
Research progresses slowly
It was during this era that a breakthrough was made by Dr Leland Clark, who began experimenting in the
mid-1960s with oxygen carrying compounds know as perfluorocarbons. Research into artificial blood
continued slowly and with poor results until the late 1980s, when active and urgent research began in
response to the sudden appearance of HIV in patients who had been given blood transfusions. This brought
with it concerns of the transmission of other infectious diseases (such as hepatitis C) that have a similar
‘window period’ during which they cannot be detected in donated blood—a further incentive for progress to
be made in research of artificial blood.
Characteristics expected in an artificial replacement for blood:
■ can be stored for long periods and easily transported
■ does not need to be cross-matched for different blood types
■ can be produced in large quantities at low cost
■ is completely safe (has no toxic effects on the body and is free from disease)
■ does not trigger an immune response
■ continues to circulate and, once the patient’s own blood is restored, may be safely excreted.
Areas of research
Perfluorocarbons carry oxygen in a dissolved form. They can carry up to 50 times more dissolved oxygen
than plasma, enough to supply sufficient oxygen to tissues in the absence of red blood cells. The main
difficulty with these products is in enabling them to mix with the bloodstream. They must be combined with
lipids to form an emulsion.
Haemoglobin-based oxygen carriers (HBOCs) involve extracting haemoglobin from outdated donated
human blood (or bovine blood) and modifying it to a form in which it can be used in artificial blood. Raw
haemoglobin cannot be used, as it exists in an unstable form that is potentially toxic and can damage
surrounding tissues and the kidneys in particular. It also has a greater affinity for oxygen than haemoglobin
found in blood, so it does not release oxygen as readily in tissues where it is needed. Current research for
the development and use of HBOCs in artificial blood involves the cross-linking of the haemoglobin to
enzymes found naturally in blood, to create a more stable ‘second generation’ HBOC that will not break
down.
Current research
The AIDS crisis in South Africa has been a driving force in it becoming one of the first countries in the world
to clear artificial blood for limited use in patients. Artificial blood is made from stabilized bovine haemoglobin
in a balanced salt solution; it has a shelf life of 36 months and can be stored at room temperature. The
Haemopure molecule is 1000 times smaller than a red blood cell, allowing it to flow through partially
blocked arteries and so it may be useful in heart surgery.
Polyheme is a brand of artificial blood that has been produced in laboratories in South Australia. It is made
from modified haemoglobin from human red blood cells. It can deliver oxygen up to three times more
efficiently than red blood cells. Both of these have a very short circulation time (12–24 hours) compared
with 50 days for donated red blood cells.
Advantages of artificial products
The main advantages of the current artificial bloods available is that they meet the following expectations:
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They can be sterilised.
They can be stored for long periods of time.
No cross-matching is needed (no cell membranes).
There is no risk of infection.
Perfluorocarbons are relatively cheap to produce.
Why research is needed:
An idea that arose as a result of ongoing shortages of blood and blood products, was to create ‘artificial
blood’—a suitable chemical blood substitute which could be transfused into patients to temporarily provide
some of the essential life-giving functions of blood until the patient’s bone marrow could make enough blood
to replenish their normal supply.

Describe current theories about processes responsible for the movement of materials through
the plants in xylem and phloem tissue
Processes involved in the transpiration stream
Transpiration is the loss of water from the leaves of plants. Water vapour is lost through the stomates. The
transpiration stream is the movement of water from the roots of plants up through the stems to the leaves.
Scientists reasoned that considerable force must be involved in this process since water and minerals move
up the plant against gravity.
Water and Ion movement into the plant roots
Water moves into plant roots by osmosis. It continues to move across the cells of the roots to the xylem
in the centre. There are two reasons for this:
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There is a continuous gradient of water potential from water in the soil to the cells in the
centre of the root. The cells on the outside have a higher water potential than those on the
inside so water continuously moves into the next cell towards the inside. This is because water is
continuously being removed from the inside cells up the xylem.
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The body of water moving across the root cells exerts a pressure on the water in front of it. This
is called root pressure.
Water potential is the tendency of a system to donate water to another system. In a system where
there is a large amount of water and less solutes (dilute solutions), the water potential is high.
Water tends to move from areas of high water potential to low water potential.
Movement of water up the Xylem
Water moves up the xylem because it is pulled from above. The pull from above is known as the
transpiration pull. The energy of sunlight gives water molecules at the surface of the leaf enough energy
to move out into the air. The loss of water through the stomata is called transpiration.
The walls of the mesophyll cells are moist and the air spaces around them contain water vapour. As the
sun shines, the stomata opens, and gases are able to diffuse in and out of the leaf. Water vapour moves
through the stomata into the air surrounding the leaf. Water evaporates from the wall of the mesophyll
cells to replace that lost from the air spaces.
As the water evaporates from the surface of the mesophyll cells, water moves out of the cells to ensure
that the walls are kept moist. In turn, water vapour moves from the small xylem vessels into the
mesophyll cells
When water moves out of the xylem of a leaf, it is replaced by water that is sucked in from the xylem
leading into the leaf. In effect water vapour moving out through the stomata sets up a chain reaction in
which water in xylem is moving through the vessels by pulling or sucking movement of water ahead of it.
Transpiration also creates a tension (a negative pressure or a pull) on the water further down the xylem
column.
Now two other forces come into play.
Cohesion (the attraction of water molecules for each other) causes water molecules further up to attract
water molecules below them to fill the space left by the water lost by transpiration.
Xylem tubes are relatively narrow and so some of the water in the xylem is in contact with the walls of the
xylem. The walls of the xylem contain both cellulose and lignin. There is a strong adhesion (attraction
between molecules of different types) between the cellulose in the xylem walls and the water in contact
with it. In narrow tubes, this is called capillarity and it also helps to drag the water up.
Remember C.A.T
This mechanism is sometimes called the evaporation (transpiration) – tension – cohesion
mechanism because evaporation of water (or transpiration) from the top of the plant leads to tension on
the water further down the xylem and cohesion then draws the water up.
Note that the mineral ions are carried up the xylem, dissolved in water.
They supply the leaves and may be redistributed to other parts of the plant later (in the phloem).
Hence the combined forces of the transpiration pull / tension, cohesion and adhesion / capillarity in the
leaves and stems, supplemented by water potential roots pressure in the root, transport water and
dissolved mineral ions from roots to leaves. It is a one way transport system – upwards only.
Evidence obtained by scientists for the C.A.T model
In 1893 E. Strasburger published the results of his experiments on plants that showed than no pumps
operated by cellular energy (ATP) were responsible for the transpiration stream. He has cut through tree
trunks about 20 m tall and place them into buckets of poison. The solution rose in the xylem and this only
stopped when the leaves were killed.
Although the tissue farther down in the trunks was already dad, the transpiration stream continued until
the leaves were destroyed. This indicated that:
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living cells pumping substances up the xylem were not responsible for the upward movement
since when they were dead, movement continued.
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The leaves play a crucial role in causing transport up the xylem
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Transport is not due to root pressure alone since the roots had been cut off.
The tension in xylem was measured by another scientist using a device known as a pressure bomb.
The evidence that exists today supports the C.A.T. model of the movement up xylem. No cellular energy is
involved. The energy source is the sun.
Processes involved in translocation
Translocation is the movement of sugars in the phloem of plants. Unlike the transpiration stream, it can
occur in any direction but it always moves from where the sugar is made or in abundance (called a
sugar source) to where the sugar is required (called a sugar sink)
Sugar is made in photosynthesising cells or it may be polymerized and stored as starch in any cells of the
plant. The sugar produced in photosynthesis is glucose. It is converted to the disaccharide sucrose before
being translocated to other parts of the plant
The starch is broken gown to glucose and then converted to sucrose. The transport of sucrose is an
economical method of transporting sugar – in units of two sugars, which is still a small enough molecule to
be transported across biological membranes.
Besides sugars, small amounts of amino acids, other nitrogenous compounds and other nutrients are
present in the sap (sugar solution) in the phloem vessels.
The use of radioactive tracers yielded valuable data to indicate that phloem is involved in translocation.
Plants were allowed to photosynthesise in air containing carbon dioxide that had been made from carbon-14
This is a radioactive substance and can be traced by placing the plant tissue in contact with autoradiographic
film. When the film is developed, dark areas show the compounds containing carbon-14.
These studies showed that the carbon-14 was present in the sugars that move through the phloem.
Based on this and other evidence, the pressure-flow mechanism theory was developed.
This process requires cellular energy (ATP). Consider the events at the sugar source.
Sucrose is loaded into the phloem (from nearby cells) against a concentration gradient, that is, by active
transport using ATP. This increases the solute concentration in the phloem and as a result water moves into
the phloem from the cells by osmosis.
Meanwhile at the sugar sink, sucrose is removed from the phloem into the plant cells that require it. This
occurs by active transport also. Water follows the sucrose from the phloem into the cells by osmosis.
Now consider the phloem vessel.
At one part of the phloem vessel (near the sugar source) there is a large amount of solute (sugar and other
nutrients) concentration and a high water content. This exerts a high water (turgor) pressure or hydrostatic
pressure (it is a situation of high water potential). Farther along the phloem vessel (near the sugar sink)
there is a low amount of solute, lower water content and a lower turgor pressure.
Water flows along the phloem from the area of high hydrostatic pressure to the area of low hydrostatic
pressure, that is from source so sink carrying the sucrose and other nutrients with it.
Pressure flow, therefore, drives the sugars in the phloem from photosynthetic or storage sites to other parts
of the plant for use or storage.
When sugar arrives at sinks it is used in different ways:
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It is stored as starch.
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It is used as subunits for building structural components of cells.
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It is used as an energy source in cellular respiration.
Evidence of the pressure-flow mechanism
Scientists observed that the phloem flow are could be as high as 1 m/h. This rate is too fast to be explained
by diffusion. If diffusion were the mechanism, it would take 8 years to travel 1m.
In searching for evidence, scientist needed to work with phloem vessels. They are quite difficult to work with
because, unlike xylem, they do not have strong walls and also their function can be easily disrupted by
probing instruments.
Scientists took advantage of a natural phloem probe – the aphid. This is a small insect that feeds on
phloem sap. It feeds by inserting its needle like mouth called a stylet into the phloem. The pressure within
the phloem can force sap into the aphids body so that it swells up.
Researchers froze the aphid, removed the body which left the stylet attached to the phloem. They could
then use the stylet as a tap that drips sap for analysis.
These techniques have provided the following data:
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The closer the stylet to a sugar source, the faster the sap drips out.
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The slower the stylet to a sugar source, the greater the sugar concentration.
This type of data has helped to support the pressure-flow model for translocation.
Comparing Plants With Mammals
The transport systems of plants and mammals have some similarities. They are both made up of a network
of fine tubes that penetrate all tissues and come close to every cell of the multicellular organism. They each
supply living tissues with the nutrients necessary to sustain life. However, there are some important
differences:
1) Mammals require the blood to provide a continuous supply of oxygen. The presence of a heart as a
pumping station in the blood circulatory system ensures a steady flow of blood. Plants on the other
hand, lack an equivalent organ in their system and rely on energy from the sun to facilitate
movement through the plant.
2) Mammals have special pigmented cells in the blood. Haemoglobin in red blood cells carries oxygen in
the blood close to tissues where the oxygen is required. The presence of haemoglobin results in
blood carrying much more oxygen that if the animal relied on oxygen in solution. The increase in
oxygen caters for the high energy needs of the cells. Plants have no such cells or pigment in the
transport systems, because they do not have the same needs for mass movement of oxygen. Most
of the plants oxygen needs are met by diffusion of by oxygen produced in cells during
photosynthesis.
3) The bulk intake of food and oxygen by mammals leads to large amounts of waste being produced
that must be transported to specialised organs where it can be removed from the body. In
particular, carbon dioxide is transported to lungs and nitrogenous wastes are transported to kidneys.
Plants produce their own food and have no bulk waste for disposal. Carbon dioxide produced in
respiration is used in photosynthesis and oxygen produced in photosynthesis is used in aerobic
respiration.
Extra:
Outside Syllabus but good to know.
Heart, Vein, Artery, Capillary – the works
The heart pumps blood out through one main artery called the dorsal aorta. The main artery then divides
and branches out into many smaller arteries so that each region of your body has its own system of arteries
supplying it with fresh, oxygen-rich blood.
Arteries are tough on the outside and smooth on the inside. An artery actually has three layers: an outer
layer of tissue, a muscular middle, and an inner layer of epithelial cells. The muscle in the middle is elastic
and very strong. The inner layer is very smooth so that the blood can flow easily with no obstacles in its
path.
The muscular wall of the artery helps the heart pump the blood. When the heart beats, the artery expands
as it fills with blood. When the heart relaxes, the artery contracts, exerting a force that is strong enough to
push the blood along. This rhythm between the heart and the artery results in an efficient circulation
system.
The arteries deliver the oxygen-rich blood to the capillaries where the actual exchange of oxygen and carbon
dioxide occurs. The capillaries then deliver the waste-rich blood to the veins for transport back to the lungs
and heart
Veins are similar to arteries but, because they transport blood at a lower pressure, they are not as strong as
arteries. Like arteries, veins have three layers: an outer layer of tissue, muscle in the middle, and a smooth
inner layer of epithelial cells. However, the layers are thinner, containing less tissue.
Veins receive blood from the capillaries after the exchange of oxygen and carbon dioxide has taken place.
Therefore, the veins transport waste-rich blood back to the lungs and heart. It is important that the wasterich blood keeps moving in the proper direction and not be allowed to flow backward. This is accomplished
by valves that are located inside the veins. The valves are like gates that only allow traffic to move in one
direction.
The vein valves are necessary to keep blood flowing toward the heart, but they are also necessary to allow
blood to flow against the force of gravity. For example, blood that is returning to the heart from the foot has
to be able to flow up the leg. Generally, the force of gravity would discourage that from happening. The vein
valves, however, provide footholds for the blood as it climbs its way up.
Blood that flows up to the brain faces the same problem. If the blood is having a hard time climbing up, you
will feel light-headed and possibly even faint. Fainting is your brain's natural request for more oxygen-rich
blood. When you faint, your head comes down to the same level as your heart, making it easy for the blood
to quickly reach the brain.
Because it lacks oxygen, the waste-rich blood that flows through the veins has a deep red color, almost like
maroon. Because the walls of the veins are rather thin, the waste-rich blood is visible through the skin on
some parts of the body. Look at your wrist, or hands, or ankles. You can probably see your veins carrying
your blood back to your heart. Your skin refracts light, though, so that deep red color actually appears a
little blue from outside the skin.
Unlike the arteries and veins, capillaries are very thin and fragile. The capillaries are actually only one
epithelial cell thick. They are so thin that blood cells can only pass through them in single file. The exchange
of oxygen and carbon dioxide takes place through the thin capillary wall. The red blood cells inside the
capillary release their oxygen which passes through the wall and into the surrounding tissue. The tissue
releases its waste products, like carbon dioxide, which passes through the wall and into the red blood cells.
Arteries and veins run parallel throughout the body with a web-like network of capillaries, embedded in
tissue, connecting them. The arteries pass their oxygen-rich blood to the capillaries which allow the
exchange of gases within the tissue. The capillaries then pass their waste-rich blood to the veins for
transport back to the heart.
Capillaries are also involved in the body's release of excess heat. During exercise, for example, your body
and blood temperature rises. To help release this excess heat, the blood delivers the heat to the capillaries
which then rapidly release it to the tissue. The result is that your skin takes on a flushed, red appearance. If
you hold your hand, for example, under hot water, your hand will quickly turn red for the same reason. Your
arm, however, is not likely to change color because it is not actually feeling an increase in temperature.
Artificial Blood.
Isolated Haemoglobin as a Substitute
Haemoglobin in red blood cells has a high oxygen carrying capacity, however, haemoglobin in solution,
isolated from red blood cells, cannot be used as a blood substitute. In isolation, toxic changes occur to
haemoglobin. Current work indicates attempts to stabalise isolated haemoglobin and make it safe to use as
a blood substitute.
Perfluorocarbon-based substitutes (PFC)
Oxygen and carbon dioxide are highly soluble in PFC, inert compounds that can carry much more dissolved
oxygen that plasma. PFC’s must be combined with lipids to form an emulsion that can mix with blood. One
product current under trial is Oxycyte , an emulsion of PFC micro-droplets that can carry at least five times
more oxygen than haemoglobin. A red blood cell is about 70 times larger, than this PFC so this means that
these are able to carry oxygen to areas that red blood cells cannot.
Advantages of PFC-based substitutes.
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Is inert and can be sterilized
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Can be stored at room temp – can be used in emergency vehicles.
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Shelf life of up to 12 months
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Can be used universally with all blood types
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Can be used temporarily during surgery.
Of course blood does much more than carry carbon dioxide and oxygen. Its vital functions must also be
upheld by the replacements – eg transport of nutrients, an ability to clot, and the initiation of immune
reactions. Thus there is still significant development needed for a substitute of blood to be manufactured.
Extra From Biology in Focus
Composition of the Blood
Red blood cells (erythrocytes)
There are approximately 4–6 million red blood cells per mL of blood and their main function is to transport
oxygen. Red blood cells form in bone marrow; at first each cell has a nucleus, but as the cell matures, the
nucleus disappears and a red pigment called haemoglobin develops inside the cell. As a result of the
absence of a nucleus, the mature red blood cells are small. Red blood cells are round, but they are
biconcave rather than spherical. Red blood cells have a lifespan of approximately 4 months and when they
die they are broken down and replaced by newly formed blood cells from the bone marrow. Red blood cells
are also able to transport a small amount of carbon dioxide in the blood and they help to maintain the pH
balance of the blood.
White blood cells (leucocytes)
White blood cells, also produced in bone marrow, function as part of the immune system. Their main role is
to protect the body against invading organisms. There are approximately 4000–11 000 white blood cells per
mL of human blood. White blood cells are larger than red blood cells and not as abundant. All white blood
cells have a nucleus.
Platelets (thrombocytes)
Platelets are fragments of special cells, also produced in the bone marrow. They are disc-shaped, about half
the size of red blood cells and there are about 400 000 per mL of blood. Platelets function in the clotting of
blood—they stick to each other and to blood fibres at the site of a wound. This contact causes them to break
open and they release an enzyme, thromboplastin, which sets in progress a sequence of steps to seal the
blood vessels and cause blood to clot, preventing excessive blood loss.
Plasma
Plasma, the yellow, watery fluid part of blood, consists of about 90% water and the other 10% consists
mainly of proteins. Plasma makes up most of the volume of blood and it carries many substances in either
dissolved or suspended form.
Haemoglobin
The fact that haemoglobin is enclosed in a red blood cell is also of advantage because if it were simply
dissolved in the plasma, oxygen would upset the osmotic balance of the plasma.
Comparison of Blood Vessels