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KS4 Biology Microbes 1 of 39 © Boardworks Ltd 2004 Contents Microbes What are microbes? Bacteria and viruses Microbes and disease How do microbes reproduce? Summary quiz 2 of 39 © Boardworks Ltd 2004 What causes disease? Why do people become ill? People who lead very unhealthy lifestyles sometimes become ill but it is also clear that people can become ill despite leading a healthy lifestyle. Why? Therefore, rather than something being wrong with that person, perhaps something else changes the normal state of the body and causes disease. These were eventually discovered to be… MICROBES 3 of 39 © Boardworks Ltd 2004 Microbes As the name suggests, they are microscopic organisms. They can only be seen using a microscope. 4 of 39 © Boardworks Ltd 2004 Microbes The two kinds of microbe that we will be dealing with are: BACTERIA VIRUSES Now it is important at this point to remember what it means to be living organism. A living organism must be able to demonstrate that it can perform the seven life processes. 5 of 39 © Boardworks Ltd 2004 The seven signs of life 6 of 39 © Boardworks Ltd 2004 Microbes The reason for looking back to these 7 characteristics is because although bacteria can perform all of these life processes, viruses cannot reproduce on their own. Does this mean that viruses are non-living? This question is still hotly debated! 7 of 39 © Boardworks Ltd 2004 Microbes Bacteria have a traditional cell structure, as with animals and plants. Viruses do not. Let us firstly consider what these microbes look like and how they compare to the structure of cells that we are familiar with. We will firstly deal with the general structure of a bacterium (singular of bacteria). Bacteria are amongst the smallest known to mankind. 8 of 39 © Boardworks Ltd 2004 Contents Microbes What are microbes? Bacteria and viruses Microbes and disease How do microbes reproduce? Summary quiz 9 of 39 © Boardworks Ltd 2004 A single bacterium Bacteria can be different shapes but this diagram can represent them. cell wall cell membrane cytoplasm loose genetic material present in animal cells absent from animal cells 10 of 39 © Boardworks Ltd 2004 Bacterium So, the bacterium shares some structural characteristics with an animal cell but shows important differences. The most obvious differences are: the absence of a distinct nucleus the presence of a cell wall The other major difference is the size of the cell. To get an idea of how small these cells are, remember that the human body consists of approximately 100 million animal cells. Bacteria cells are 10-1000 times smaller than animal cells. 11 of 39 © Boardworks Ltd 2004 Bacterium If we wanted to measure a single bacterium, its length would range from: 1 1 mm to 1000 mm 20 If a full stop is 1mm wide how many bacteria could you line up along it? Between 1000 and 20 bacteria would fit on a full stop! 12 of 39 © Boardworks Ltd 2004 Virus Now let’s consider the structure of the virus. injection tube protein coat loose genetic material tail plate Absent in animal cells 13 of 39 © Boardworks Ltd 2004 Viruses - how small? Viruses are very different to bacteria because they do not have a cellular structure and are much smaller. Bacteria are 100 times smaller than a human cell. Viruses are 1000 times smaller than a bacteria. So how small are viruses compared to a human cell? 100 000 times smaller! 14 of 39 © Boardworks Ltd 2004 Viruses and tennis balls! Here’s another way to think about the size of viruses... If a common cold virus was the size of a tennis ball, how big would a nose be? A. the size of a supermarket B. the size of Birmingham C. the size of Wales 15 of 39 © Boardworks Ltd 2004 Viruses – living or not? If viruses are such tiny microbes, how do they cause so much havoc? Viruses need to hijack a host cell, like a human body cell, in which to live and make more viruses. Viruses cannot function if they are outside of a host cell. Some scientists say that viruses are not ‘alive’ because of how they reproduce. Would you say a virus was living or not? 16 of 39 © Boardworks Ltd 2004 Bacterium – label the parts 17 of 39 © Boardworks Ltd 2004 Virus – label the parts 18 of 39 © Boardworks Ltd 2004 Virus and bacterium properties 19 of 39 © Boardworks Ltd 2004 Contents Microbes What are microbes? Bacteria and viruses Microbes and disease How do microbes reproduce? Summary quiz 20 of 39 © Boardworks Ltd 2004 Viruses and bacteria You probably know more about bacteria and viruses than you think. The following illnesses are all caused by microbes infecting the human body. How many do you recognise? 21 of 39 © Boardworks Ltd 2004 Common illnesses Most people have suffered from at least one of these illnesses: VIRUSES BACTERIA Influenza (flu) Food poisoning Mumps Sore throats Chickenpox Tuberculosis (TB) Smallpox Tetanus Polio Cholera Rabies Typhoid German measles Whooping cough So, how do these microscopic organisms actually cause illness in such a complex and relatively enormous organism like a human being? 22 of 39 © Boardworks Ltd 2004 Under attack! Firstly, as soon as a virus or bacterium enters the body, we are termed infected. This is not the same as being ill. Illness results from the effects these microbes have on our body. Bacteria and viruses have the ability to produce poisons known as... TOXINS 23 of 39 © Boardworks Ltd 2004 Under attack! When the microbe enters the body, it begins releasing these toxins which can damage body tissue and prevent body systems working properly. The body could probably cope with a small amount of poison, but microbes quickly reproduce themselves. If the microbes reproduce… We are said to be diseased. more microbes mean that more toxin produced… our normal state of well being is affected… 24 of 39 © Boardworks Ltd 2004 Diagram of a microbe attack These symbols and colours represent the process of becoming infected and then ill: 1 Person is well. The microbe levels are very low and the toxin levels are very low. 25 of 39 2 Person is infected. The microbe levels are low and the toxin levels are low. Toxin Levels Presence of microbes 3 Person is ill and diseased. The microbe levels are high and the toxin levels are high. © Boardworks Ltd 2004 Which microbe causes which disease? 26 of 39 © Boardworks Ltd 2004 The process of disease 27 of 39 © Boardworks Ltd 2004 Contents Microbes What are microbes? Bacteria and viruses Microbes and disease How do microbes reproduce? Summary quiz 28 of 39 © Boardworks Ltd 2004 Bacteria reproduction Bacteria can reproduce quickly and independently . One bacterium can divide into two new bacteria every 20 minutes! 29 of 39 © Boardworks Ltd 2004 Bacteria reproduction This means that if 1 bacterium enters your body at 8.00am, 4 hours later, you would have 4096 bacteria within your body! Do viruses reproduce in the same way as bacteria? No! 30 of 39 © Boardworks Ltd 2004 Virus reproduction Viruses need a host cell to reproduce within. This is a body cell, which will provide the machinery, and chemicals the virus requires to make copies of it. host cell e.g. a human body cell virus 31 of 39 © Boardworks Ltd 2004 The process of host cell infection Therefore the virus not only infects the body; it also infects the body cells. 1. Approach The virus approaches the host cell 32 of 39 2. Attachment The virus secures itself to the surface of the host cell. © Boardworks Ltd 2004 The process of host cell infection 3. Insertion The virus injects its genetic material through the injection tube and into the host cell. 4. Replication The genetic material makes multiple copies of itself. 33 of 39 © Boardworks Ltd 2004 The process of host cell infection 5. Assembly New viruses are assembled using chemicals from the host cell. The original virus dies and breaks down. It is at this stage that the viruses within the host cell can remain dormant. In other words, they sit within the cell without killing it or breaking out. With some viruses such as HIV, this period can last a number of years. This is why people can remain infected with HIV without realizing they are infected. 34 of 39 © Boardworks Ltd 2004 The process of host cell infection 6. Cell Lysis (cell breaks) - toxin The host cell splits open and dies. The viruses escape and release toxins. Each virus will then start another round of replication. 35 of 39 © Boardworks Ltd 2004 Virus reproduction - what’s the order? 36 of 39 © Boardworks Ltd 2004 Virus reproduction - explain it! 37 of 39 © Boardworks Ltd 2004 Contents Microbes What are microbes? Bacteria and viruses Microbes and disease How do microbes reproduce? Summary quiz 38 of 39 © Boardworks Ltd 2004 Microbes quiz 39 of 39 © Boardworks Ltd 2004