Biology - Natural Defences (AQA Syllabus A)

In GCSE Science students will look at the requirements for keeping healthy. This is the fourth of six quizzes on that topic and it looks at the natural defences of the body against infection, such as white blood cells, antibodies, mucus, stomach acid and tears.

The human body is well defended against infection. Sometimes pathogens like bacteria and viruses do get through, making you ill. There are physical barriers like your skin and the cilia (tiny moving hairs) and mucus that line your respiratory system. The mucus is sticky and traps bacteria and viruses that enter your nose as you breathe in. There are chemical barriers too such as enzymes in tears and saliva that break down pathogens.

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When the pathogens do get past the first line of your body's defences, the second line is the white blood cells. There are several different types of these each working in a different way. Some of them engulf (surround) the pathogen and secrete enzymes that digest the bacteria, virus or single celled organism that has arrived in your body. Others neutralise any toxins that enter the bloodstream from the infection. Another type of white blood cell produces antibodies that react to a specific pathogen that enters your bloodstream. These antibodies then either damage the pathogen, making it harmless, or label it so that other cells can find and destroy it.

The white blood cells that produce the antibodies remain in your bloodstream so that the next time the pathogen gets into your body, it can immediately be tackled. They give you an immunity to disease. This natural defence can also be introduced artificially by vaccination. Some diseases are very harmful to the human body, for example, polio. This terrible disease left many children unable to walk properly until a vaccine was found. Nowadays children are vaccinated well before they can develop polio and it is virtually unknown in developed countries with a good health system.

But despite your natural defences, infections do get through. If you eat a properly balanced diet and exercise regularly, your immune system will work well against invading microorganisms.

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  1. Which of the following statements about white blood cells is incorrect?
    The surface of every cell is covered with molecules called antigens which are usually fragments of protein or carbohydrate molecule. The antigens on the surface of pathogenic cells are different from those on the surface of your own cells which means that your white blood cells can recognise pathogens
  2. Your body can develop a natural immunity to certain pathogens. What is the name of the cells responsible for this?
    Lymphocytes are one type of white blood cell
  3. What is produced by a lymphocyte that enables it to neutralise pathogens?
    Each lymphocyte produces a specific type of antibody that matches a specific antigen. Each pathogen has its own unique antigen. When a lymphocyte with the appropriate antibody meets the antigen, the lymphocyte is triggered to reproduce quickly which makes many copies of the antibody to neutralise the pathogen
  4. Which of the following statements is correct?
    Active immunity is where the white blood cells have 'learnt' how to defend agains a pathogen because you have been exposed to it before. Sometimes you may be treated for infection by receiving antibodies from someone else. That's passive immunity. Protection from passive immunity lasts only a few weeks or months. For example, antibodies passed from the mother to the baby before birth give passive immunity to the baby for the first 4-6 months after being born
  5. Which of the following also help your body defend itself against infection?
    As well as these examples, there is also the skin (which acts a physical barrier) and saliva (which contains enzymes)
  6. Which of the following is not one of the ways that white blood cells provide active immunity?
    This question tests if you know that you must use the word ingest and not 'eat' when describing how white blood cells work. Do remember not to be caught out by this please - it is a silly way to lose a mark in your exams
  7. Which of the following are the two main groups of white blood cells?
    Another word for phagocytes is macrophages
  8. The lymphocytes produce antibodies. How do antibodies work?
    Antibodies also exist that attach to the target pathogen and damage or destroy it
  9. Vaccination is used to immunise people against diseases. Pick the false statement:
    20 years before Jenner a Dorset Farmer, Benjamin Jesty, had carried out the same procedure to protect his family against smallpox but rarely gets any credit. A vaccine protects from a single disease but they can be combined, for example, the MMR vaccine against measles, mumps and rubella. Vaccines can be made from the pathogen itself - but either a weakened or inactivated version
  10. Why are antibiotics no good for treating colds and 'flu?
    This question is testing if you realise that colds and 'flu are caused by viruses and that antibiotics only work against bacteria

Author: Kev Woodward

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