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9.2 Maintaining a balance: 2. A watery medium

Syllabus reference (October 2002 version)
2. Plants and animals transport dissolved nutrients and gases in a fluid medium

Students learn to:


Extract from Biology Stage 6 Syllabus (Amended October 2002) © Board of Studies, NSW

Prior learning: Science Stages 4 - 5 syllabus: Outcomes 4.8 (content 4.8.4 b, c, d and e: multicellular organisms).

Preliminary course module 8.3 (sub sections 4, 5 and 6)

Background: Blood is the transport medium of mammals. It maintains the internal environment of all organs as it supplies material to every cell in the body and removes the unwanted substances that cannot be allowed to accumulate in cells. From the Preliminary course, recall that blood consists of 55% plasma, a straw-coloured liquid of which 90% is water. The other components of the blood are red and white blood cells and platelets.

Red blood cells are unique in that they do not contain a nucleus and have a biconcave shape. They are much smaller than white blood cells and more numerous. They contain the protein haemoglobin, a complex protein molecule consisting of four polypeptides, each containing an iron atom. The iron atom has an affinity for oxygen molecules. When haemoglobin is combined with an oxygen molecule, it is called oxyhaemoglobin.

Plants carry dissolved mineral nutrients in the xylem vessels and carry food (mostly glucose) in phloem tubes.


identify the form(s) in which each of the following is carried in mammalian blood:

  • carbon dioxide
  • oxygen
  • water
  • salts
  • lipids
  • nitrogenous waste
  • other products of digestion

perform a first-hand investigation to demonstrate the effect of dissolved carbon dioxide on the pH of water

Basic procedure

Using a data logger with a pH probe, take readings of the change in pH of 100 mL of distilled water as exhaled air is bubbled through it over a two-minute period.

This experiment can also be performed using universal indicator paper and an indicator colour chart to estimate the pH at various stages of the experiment.

perform a first-hand investigation using the light microscope and prepared slides to gather information to estimate the size of red and white blood cells and draw scaled diagrams of each

explain the adaptive advantage of haemoglobin

analyse information from secondary sources to identify the products extracted from donated blood and discuss the uses of these products


When blood is donated, it can be used almost immediately as whole blood or it can be separated into its components. Whole blood is given to patients where major functions of the blood, such as oxygen carrying capacity, are impaired, or where more than 20% of blood has been lost and there is a decrease in blood pressure.

A good source of information on the components of blood is the Australian Red Cross, Blood Bank Service web site:

Different Donation Types (external website) Australia

Uses of blood can be found at Science clarified , USA 2007. Scroll down to Separation of blood components.
(These website were last accessed 2 June 2009).

Some blood products

Red blood cells (RBCs)

RBCs help patients who need to be able to carry more oxygen. RBCs may also be used to help replace cells lost following significant bleeding.

Platelet concentrate

Platelets are essential for the coagulation of blood and are used to treat bleeding caused by conditions or diseases where the platelets are not functioning properly.

Fresh frozen plasma (FFP)

FFP is used mainly to provide blood components that coagulate the blood. FFP contains all coagulation factors in normal amounts and is free of red cells, white blood cells and platelets. It is used for patients who require immediate clotting effects, such as those undergoing warfarin therapy (blood thinning) or when massive transfusions have taken place.

Cryoprecipitate anti-haemophilic factor

Cryoprecipitate AHF is a concentrate of clotting proteins and is used for the treatment of von Willebrand disease (similar to haemophilia), replacement of the clotting proteins, fibrinogen, Factor XIII and Factor VIII when no other option is successful.

analyse information from secondary sources to identify current technologies that allow measurement of oxygen saturation and carbon dioxide concentrations in blood and describe and explain the conditions under which these technologies are used.

The Internet is more likely to carry information about current technologies than reference books. Here is a place to begin.

Pulse oximetry (external website) Wikipedia

Assess the reliability by comparing with information from different sources. Information from an organisation, like the World Federation of Societies of Anaesthesiologists, is likely to be more reliable than information from an individual who is not affiliated to any organisation.

Monitoring oxygen and carbon dioxide concentration

One method used by hospitals to monitor blood oxygen and carbon dioxide levels in patient's blood is to use a pulse oximeter. A small clip with a sensor is attached to the person's finger, earlobe or toe. A cable connects the sensor to the pulse oximeter machine. The colour of the blood changes according to the amount of oxygen that is dissolved in the blood. Blood that is high in oxygen is bright red while blood low in oxygen is a darker colour. The sensor emits a light signal that passes through the skin. The sensor measures the amount of light absorbed as it passes through the tissue and blood, and transmits the information to the pulse oximeter. A reading is given in a percentage form.

Pulse oximetry is used to monitor the level of oxygen in a person's blood during heavy sedation or anesthesia. This device is also used when a person is on a ventilator, artificial breathing machine, during stress testing, in sleep laboratories, when checking the body's response to different medications or to monitor a person with asthma or who is having trouble breathing.

Another method of analysing blood gases is with arterial blood gas (ABG) analysis machines. These can measure the amount of oxygen and carbon dioxide in a sample of blood by monitoring the rate of diffusion of these gases through artificial membranes which are permeable to these gases. When moving through a membrane, oxygen in the blood produces an electrical current while carbon dioxide changes the pH of the solution.

analyse and present information from secondary sources to report on progress in the production of artificial blood and use available evidence to propose reasons why such research is needed


Blood transfusions have been the subject of medical research for centuries. In the early 1900s, successful transfusions were carried out as an understanding of blood components were understood. Up until the HIV crisis in the 1980s, there was little interest in artificial blood as there did not seem a great need. With the transmission of the virus during transfusions, there was nothing to replace donor blood, so artificial blood became a priority for research. Sensitive screening tests have now been developed for potential infective organisms, such as HIV and hepatitis, making donor blood much safer. There are now available safe and effective blood substitutes for certain applications, although they are still not ready for widespread use. Better blood substitutes are still needed. There is a continuing shortage of donor blood to help the victims of emergencies, civil and international conflicts and natural disasters. Furthermore, there is no guarantee that something similar to the HIV crisis will not occur in the future.

An Internet search on artificial blood will provide links, which include the history, current research and uses of artificial blood substitutes in blood transfusions. Some sites you could start with are:

Artificial blood (external website) Royal Society of Chemistry 2011

Perflurochemicals (external website) Wikipedia

Why research on artificial blood is needed

Some advantages of artificial blood could include the following:

  • Pasteurisation could be used to remove all pathogens.
  • There would be no need for cross-matching and typing as the artificial blood contains no blood-group antigens. This saves time and allows on-the-spot transfusion.
  • Artificial blood can be stored for more than one year, compared with about one month for donor blood using standard methods.

compare the structure of arteries, capillaries and veins in relation to their function

describe the main changes in the chemical composition of the blood as it moves around the body and identify tissues in which these changes occur

outline the need for oxygen in living cells and explain why removal of carbon dioxide from cells is essential

choose equipment or resources to perform a first-hand investigation to gather first-hand data to draw transverse and longitudinal sections of phloem and xylem tissue

describe current theories about processes responsible for the movement of materials through plants in xylem and phloem tissue


From your Preliminary course, you should recall that the transport system in plants involves phloem and xylem. Xylem transports water and mineral ions upward only, from roots toward leaves. Phloem transports organic materials, in particular sugars, up and down to where the material is needed or for storage.

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