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:
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
- nitrogenous waste
- other products of digestion
Perform your investigation, making sure you take readings of the initial pH of the distilled water.
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.
Red blood cells in a blood vessel Department of Biomedical Engineering and Computational Science (BECS) Centre of Excellence in Computational Complex Systems Research, Helsinki, Finland
Blood cells Wadsworth Center, New York State Department of Health
explain the adaptive advantage of haemoglobin
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 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.
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 Nuffield Department of Anaesthetists,
University of Oxford, UK (This site last accessed 12 June 2008)
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.
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 Royal Society of Chemistry 2011
Why research on artificial blood is needed
Some advantages of artificial blood could include the following:
compare the structure of arteries, capillaries and veins in relation to their function
Veins carry blood back toward the heart. They carry the same quantity of blood as the arteries but not at the same high pressures. Veins have the same three layers as the arteries: endothelium, smooth muscle and connective tissue. However, the layers are not as thick. The veins also contain valves that prevent the backflow of blood.
Capillaries have walls that are only one endothelium cell thick, as they have to allow diffusion of materials through their wall to reach the cells found in the tissues in which the capillary is located.
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.
The model has the following steps.
Step 1: Sugar is loaded into the phloem tube from the sugar source, e.g. the leaf (active transport)
Step 2: Water enters by osmosis due to a high solute concentration in the phloem tube. Water pressure is now raised at this end of the tube.
Step 3: At the sugar sink, where sugar is taken to be used or stored, it leaves the phloem tube. Water follows the sugar, leaving by osmosis and thus the water pressure in the tube drops.
The building up of pressure at the source end, and the reduction of pressure at the sink end, causes water to flow from source to sink. As sugar is dissolved in the water, it flows at the same rate as the water. Sieve tubes between phloem cells allow the movement of the phloem sap to continue relatively unimpeded.