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LESSON 17: DEFENCE AGAINST DISEASE STARTER ACTIVITY - 5,4,3,2,1: Name……… • 5 places a micro-organism can enter the body • 4 ways our body prevents the entry of micro-organisms • 3 types of micro-organism. • 2 diseases caused by a virus • 1 meaning of a pathogen LESSON 17: DEFENCE AGAINST DISEASE LEARNING OBJECTIVES: • Explain that bacteria and viruses spread rapidly and may produce toxins • Describe how viruses damage cells • Explain the different ways that white blood cells fight infection White blood cells If viruses and bacteria do get into the body, it is extremely likely that they will enter the blood stream. If this happens, the previous defence systems are useless and so the body brings in its next line of defence… How do white cells attack micro-organisms? White blood cells have 3 main methods of attacking microbes: 1. Chemicals called Antibodies produced by White Blood cells called Lymphocytes 2.Chemicals called Anti-toxins produced by White Blood cells called Lymphocytes 3. Phagocytosis (eating) by White Blood cells called Phagocytes 1. Releasing antibodies Invading pathogen has antigens on the surface White blood cell called LYMPHOCYTE release a chemical known as an antibody. Once attached, the antibodies can destroy the microbe….. Or make it more visible to be eaten by the other type of white blood cell Antibodies released to attack the Antigens Their shape is important because it fits exactly onto the antigen on the microbe. 2. Producing antitoxins bacterium white blood cell (Lymphocyte) antitoxins toxins The Anti-toxin links to the toxin and neutralises its effect. The toxin is now harmless. This happens on a large scale and reduces the effects of the infection. As each pathogen has a differently shaped antigens….. …..there are different white blood cells to produce different antibodies and anti-toxins. Antigens are different shapes For example…. In your body, there will be a specific lymphocyte responsible for dealing with virus that causes a sore throat….. 3. Phagocytosis Some white blood cells (PHAGOCYTES) 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. Digestive enzymes attack the ingested microbe and begin to break it down. The blood microbe is destroyed. Dead white cells chemicals that are and The pathogens collectreleased to form from PUS the digested microbe are used in other parts of the cell. Watch this animation Active Teach page 34, box C Engulfing microbes - what’s the order? 11 of 44 © Boardworks Ltd 2004 Engulfing microbes - what happens? 12 of 44 © Boardworks Ltd 2004 ACTIVITY 3: WRITE THESE STATEMENTS AS A FLOW DIAGRAM Your Task…. How WBC fights microbe Phagocytosis Antibodies Antitoxins Description Diagram ACTIVITY 4: NATURAL IMMUNITY “Once infected by a particular microbe, the body stores levels of that specific antibody/antitoxin”. Use the above statement to explain the following facts: 1. If that microbe infects again, there is no need for the body to spend time producing the specific white blood cells to make the relevant antibody. 2. Humans tend to only suffer from certain diseases once in their lifetimes. REVIEW YOUR LEARNING: Multiple choice questions 1) The outer body surface that acts as a barrier to the entry of microbes is... A B C D hair. skin. clothing. mucus. 2) A sticky substance is produced by the breathing organs and it can help trap microbes in the air you breathe in. It is called... A B C D gel. bile. mucus. glue. 3) An acid in the stomach can help to kill microbes that are accidentally eaten. This acid is called... A B C D hydrochloric acid. nitric acid. sulphuric acid. carbonic acid. 4) The blood cells that will attempt to destroy microbes that do gain entry to our body are the... A B C D red blood cells. platelets. white blood cells. glandular cells. 5) What is happening in the diagram? microbe blood cell A The white blood cell is about to bite the microbe. B The red blood cell is about to ingest the microbe and once the microbe has been ingested it will be digested. C The white blood cell is about to burst and release digestive enzymes onto the microbe. D The white blood cell is about to ingest the microbe and once the microbe has been ingested it will be digested. Homelearning Write a storyboard, describing how the body reacts to an invading pathogen….. Remember: use BBC bitesize to help…..