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MAKING SENSE OF THE BLOOD IGCSE Biology 2.3 Blood and Circulation Brought to you by MrExham.com Image © Depositphotos.com/[julos #4371007] 3cm 2cm 1cm • Its all to do with surface area to volume ratio. • Small organisms have a larger surface area to volume ratio then larger organisms. 1cm 3cm 2cm Width of cube (cm) Surface area (cm2) Volume (cm3) Surface area: volume 1 6 1 6 2 24 8 3 3 54 27 2 • Single celled organisms = large surface area to volume ratio • They can rely on diffusion to get what they need and remove wastes. Single celled organisms viewed down a microscope • Larger multicellular organisms = small surface are to volume ratio • therefore need a circulatory system to supply all the cells with what they need. – Provide oxygen – Remove carbon dioxide – Provide nutrients – Remove urea – Provide hormones – Provide antibodies • Can you recall the composition of blood? • What is the role of plasma in the transport of carbon dioxide, digested food, urea, hormones and heat energy? • How are red blood cells adapted for transporting oxygen? • How does the immune system respond to disease (pathogens) using phagocytes and lymphocytes? • Can you explain how vaccinations work? • How are platelets involved in blood clotting? • If you take a sample of blood and spin it in a centrifuge very quickly it will separate into two layers. • The blood cells will go to the bottom and a light straw coloured liquid called plasma comes to the top. • If you take a sample of blood and spin it in a centrifuge very quickly it will separate into two layers. • The blood cells will go to the bottom and a light straw coloured liquid called plasma comes to the top. 55% plasma Centrifuge 45% blood cells • Also known as . • They are made in the bone marrow. • Their function is to carry oxygen around the body. • These are the most numerous of all the blood cells, in every cubic millimetre of blood there are 5,000,000 cells. disc shape. • large surface area to volume ratio, – lots of oxygen can get to the centre of each cell by diffusion. • don’t have a nucleus. – carry more . • Haemoglobin is a carrier protein which picks up oxygen and forms . Oxygen + Haemoglobin oxyhaemoglobin • The oxygen is delivered to the respiring cells. Biconcave shape = increase SA for diffusion No nucleus = more space for haemoglobin • To protect our body against the invasion of disease causing organisms (pathogens). • This is done in two ways: – Phagocytosis (by phagocytes) – Antibody production (by lymphocytes) • 70% of our white blood cells are phagocytes. • These can engulf bacteria by the process of phagocytosis. Watch this video of phagocytosis. • 70% of our white blood cells are phagocytes. • These can engulf bacteria by the process of phagocytosis. Bacteria (Pathogen) Phagocyte • 70% of our white blood cells are phagocytes. • These can engulf bacteria by the process of phagocytosis. • 70% of our white blood cells are phagocytes. • These can engulf bacteria by the process of phagocytosis. • 70% of our white blood cells are phagocytes. • These can engulf bacteria by the process of phagocytosis. Digestive enzymes released by the cell to breakdown and destroy pathogen. • Approximately 25% of our white blood cells are lymphocytes. • Their function is to produce . • Pathogens have markers on their surface membranes called . • Antibodies stick to these and destroy the pathogen. Antibodies Pathogen Antigen • Antibodies stop pathogens in a number of ways: – Cause bacteria to burst. – Cause the bacteria to stick together making it easier for phagocytes to ingest them. – Neutralising toxins produced by the pathogens. • Some lymphocytes develop into memory cells. • Remain in blood for many years and provide immunity to that specific pathogen. • If it enters the blood again we will recognise it faster and mass produce the antibodies quicker. • This is called the . • Sometimes we can trick the body into thinking it’s been infected. • This will give us the immunological memory so that if we really get infected, the secondary immune response will occur. • The vaccination can be one of these things: – A dead pathogen – A weakened strain of the actual pathogen – Modified toxins of the bacteria – The antigens removed from a pathogen • Platelets are small fragments of cells that help your blood to clot when you cut yourself. • This stops bleeding and prevents infection of the wound. • They produce a chemical which causes a plasma protein called to change into . • Fibrin forms the clot. • Over 90% of plasma is water. • The plasma transports the following things: • Over 90% of plasma is water. • The plasma transports the following things: • Over 90% of plasma is water. • The plasma transports the following things: • Over 90% of plasma is water. • The plasma transports the following things: • Over 90% of plasma is water. • The plasma transports the following things: • Over 90% of plasma is water. • The plasma transports the following things: • Over 90% of plasma is water. • The plasma transports the following things: • Over 90% of plasma is water. • The plasma transports the following things: • Over 90% of plasma is water. • The plasma transports the following things: .