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Plasma and cells in suspension If blood is separated it no longer looks like the red liquid that we recognise. centrifuge 55% 45% The blood sample separates into two parts. The top half is a straw coloured liquid called plasma. The bottom half is a dark collection of blood cells. 1 of 50 © Boardworks Ltd 2004 Products dissolved in plasma Blood has to rely on its plasma to transport some of these useful or waste products. For example, plasma carries CO2 from the cells to the lungs. blood flowing along a capillary plasma CO2 CO2 blood cell CO2 CO2 CO2 blood cell Dissolved digestive products The third and fourth roles are also centred around the moving of a substance from one place to another. Plasma is responsible for carrying dissolved food. Remember! Our digestive system breaks down the food we eat to release the useful nutrients. Leaving the plasma The soluble food dissolves into the plasma and is carried from the small intestine to the cells of the body. Here they diffuse into the cells and are used in various chemical reactions. glycerol sugars amino acids plasma body cell fatty acids Removing urea The final role of the plasma is to carry a particular waste product from the liver to the kidneys. The waste product is called urea. Urea is made in the liver by the breakdown of amino acids. As urea is toxic, it must be removed from the body as quickly as possible! The blood now has to help the body do this. The full load All this is being carried in just the plasma! white blood cell platelets fatty acids sugar red blood cell amino acids urea carbon dioxide Image of the 3 constituents red blood cells white blood cells platelets Inside the red blood cells Actually, although the red blood cell is a “cell”, it does not contain one of the 3 parts of a “normal” cell. Red blood cells have no nucleus. This may seem odd but, there is a reason for it. Red blood cells also contain a unique substance called haemoglobin. This is a special iron based pigment whose presence is essential if the red blood cell is to perform its job. Fe2+ Inside the alveoli Here is a close up showing the diffusion of oxygen gas. As the oxygen gas diffuses across the lining of the alveolus, it dissolves in the moist layer. This speeds up the diffusion process. moist layer O2 lining of alveolus lining of capillary red blood cell O2 Oxyhaemoglobin If we now concentrate on one red blood cell, we can see how important the haemoglobin molecule is to the process of transporting oxygen. The oxygen molecule diffuses into the red blood cell. each red blood cell contains the pigment... Haemoglobin + O2 Oxyhaemoglobin These two molecules bind together to produce this new substance. Oxygen diffusion at the capillary bed White blood cell Let’s now consider the white blood cell. The white blood cell is bigger than the red blood cell. It has a much more varied shape and there are different types of white blood cell within the blood. Role in defence White blood cells play a part in the defence system of the body. There are far fewer white blood cells within the blood compared with red blood cells. They are designed to fight microbes such as bacteria and viruses. Match the cells to the correct functions Methods of attacking microbes As we saw when we covered the blood system, white blood cells are found in blood. They have a nucleus, which can vary in shape from one sort of white blood cell to the next. They have 3 main methods of attacking microbes. 1. Producing antitoxins Remember that microbes can cause an infected person to feel ill by releasing toxins (poisons). The first way white blood cells defend the body is by releasing antitoxins. These chemicals are designed to neutralise the effects of the toxins and render them harmless. Methods of attacking microbes 2. Ingesting Microbes Some white blood cells actually ingest (eat) the microbes and then break them down once they are inside the cell. The microbe is destroyed by powerful digestive enzymes, which are released within the cytoplasm of the white blood cell. white blood cell microbe The white blood cell surrounds the microbe. Methods of attacking microbes 3. Releasing antibodies As well as releasing antitoxins, the white blood cell can release another chemical known as an antibody. Antibodies - you can think of them as target specific bombs. Their shape is important because it fits exactly onto a site on the microbe.