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Understanding Microbes – Revision Pack (B6) Bacteria: Bacterial cells have many features that allow them to survive: - They have a flagellum (tail) for movement They have a cell wall to maintain its shape and stop it bursting They have DNA (nucleoid) which controls the cells activities and replication of the cell NOTE – bacteria cells come in many different shapes and sizes; they can be spherical, rod-shaped, spiral or curved rods. Bacteria reproduce by splitting into two – this is a type of asexual reproduction which is known as binary fission. You can get bacteria to reproduce an agar plate but you MUST sterilise all the equipment beforehand to prevent contamination – this is called an aseptic technique. In terms of numbers, bacteria are very successful; this is because: - They can survive off of a lot of different energy sources They can survive in a great number of habitats Some survive by taking in organic nutrients BUT some can make their own food Bacteria reproduce at a very fast rate; this means they can very quickly spoil food or cause disease. This means that they must be handled carefully as to avoid contaminating food, people or animals. Yeast: Yeast is a single-celled fungus that is grown for many functions. You can alter the growth rate of yeast by: - Changing food availability Changing Temperature Changing pH Removing waste products The growth rate of yeast doubles for every 10oC rise until its optimum is reached; so if at 200C, it was growing at a rate of 40, at 30oC it would be growing at a rate of 80. Understanding Microbes – Revision Pack (B6) Viruses: Viruses are NOT living cells but very small structures made up of a protein coat surrounding a strand of genetic material. Viruses can only reproduce under certain conditions: - They only reproduce inside other living cells They only attack specific cells (e.g. plant, animal etc) A virus reproduces in a few simple steps: STEP 1 – it attaches itself to the host cell STEP 2 – it injects its genetic material into the cell STEP 3 – it uses the cell to make components of new viruses STEP 4 – it will then cause the host cell to die to release the new viruses Understanding Microbes – Revision Pack (B6) Past Papers: PPQ(1): PPQ(2): Understanding Microbes – Revision Pack (B6) PPQ(3): PPQ(4): Understanding Microbes – Revision Pack (B6) Mark Schemes: PPQ(1): PPQ(2): PPQ(3): PPQ(4):