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1. title Humans and micro-organisms

2. content Humans and micro-organisms 24.1 What are micro-organisms? 24.2 How are micro-organisms useful to us? 24.3 How are micro-organisms harmful to us? 24.4 The importance of antibiotics 24.5 Food preservation

3. 24.1 What are micro-organisms? Micro-organisms (or microbes) • very small organisms that can only be seen with a microscope • can be useful or harmful to us there is an organism where ? where ?

4. 24.2 How are micro-organisms useful to us? • some micro-organisms are useful in Recycling of materials Producing useful nitrogen compounds for legumes Wine and bread making

5. Wine and bread making Yeast alcoholic fermentation anaerobic respiration CO2 alcohol for bread-making for wine-making • fruit juices are converted into wines • CO2 bubbles form holes in the dough through the process of fermentation • make the dough rise and spongy

6. Recycling of materials • important in maintaining the balance in ecosystems • example: saprophytic bacteria & fungi nitrite & nitrate bacteria inorganic nitrogen compounds organic matter nitrate ions absorbed by plants & recycled in ecosystem

7. Producing useful nitrogen compounds for legumes • legumes have nitrogen-fixing bacteria in the swollen parts of their roots (root nodules) nitrogen-fixing bacteria nitrogen gasin the air nitrogen compounds nutrients for plants Farmers take advantage of the plant/bacteria relationship by growing legumes in poor soil. Farmers take advantage of the plant/bacteria relationship by growing legumes in poor soil. Other plants grown in the field, after the legumes, will grow well, Other plants grown in the field, after the legumes, will grow well, because excess nutrients are left in the soil when the legumes are harvested. because excess nutrients are left in the soil when the legumes are harvested.

8. 24.3 How are micro-organisms harmful to us? Micro-organisms are harmful because they may be parasitic saprophytic • cause diseases • spoil our food and other useful materials

9. Micro-organisms which cause diseases • live in and obtain nutrients from host cells • may destroy host cells later • release toxins Micro-organisms which may cause diseases viruses bacteria protozoa fungi

10. viruses viruses bacteria protozoa fungi • live inside living cells • relying on the proteins of the cells, reproduce rapidly and destroy the cells to release new viruses e.g. influenza, rabies, measles and AIDS

11. bacteria viruses bacteria protozoa fungi • live inside cells  intracellular • live outside cells  extracellular • cause harm by • destroying body tissues e.g. tuberculosis • releasing toxins which affect normal functioning of body e.g. food poisoning

12. protozoa viruses bacteria protozoa fungi • feed on body tissues and produce harmful effects e.g. amoebic dysentery, malaria and sleeping sickness

13. fungi viruses bacteria protozoa fungi • infectious and parasitic on body tissues • cause inflammation and itching e.g. skin infections (ringworm & athlete’s foot), mouth infections and vaginal infections in women

14. Spoilage of food and other useful materials • some micro-organisms are saprophytic because they grow and feed on organic matter • change and spoil our food and other useful materials e.g. fruit, bread, leather, wood and camera lens Some people put their lenses in a special air-tight box with silica gel to prevent fungal growth

15. 24.4 The importance of antibiotics Antibiotics • chemicals produced by micro-organisms, usually fungi or bacteria • can kill other micro-organisms or inhibit their growth • important for curing diseases caused by bacteria • example: penicillin Remember: Do not stop taking antibiotics until the period given by the doctor ends !!

16. Demonstrating the effect of penicillin Demonstrating the effect of penicillin

17. 24.5 Food preservation • micro-organisms spoil our food  food preservation is needed • basic principles include : killing the micro-organisms inhibiting the growth of the micro-organisms

18. Methods of food preservation • Removing water • Killing bacteria with high temperature/chemicals natural drying adding preservatives UHT treatment smoking pickling freeze-drying pasteurization osmotic preservation sterilization • Preventing bacterial growth with low temperature refrigeration freezing

19. Natural drying • dehydration prevents micro-organisms from growing Dried food • the food may taste different from when it is fresh

20. Freeze-drying • the food is frozen very quickly at -196°C and then water inside is removed under low pressure • the food is very light in weight • the food substances are not changed • when water is added, the food returns to a form similar to the original

21. Smoking • smoke from the fire dries the food and coats it with substances which stop the growth of bacteria Smoked trout fillet • the flavour of food is changed

22. Osmotic preservation • the food is covered with salt or sugar • water will be drawn out due to osmosis • micro-organisms are either killed or inactivated Food preserved by osmotic effects

23. Pickling • the food is salted first and then stored in vinegar As a weak acid, vinegar can prevent the growth of bacteria. Pickled food • citric acid and alcohol are also used in pickling

24. Canning and bottling • the food is first heated to a high temperature under high pressure to kill the bacteria and destroy their toxins The process of killing bacteria is called sterilization. • the food is then sealed into sterilized tin cans or jars while the food is still hot prevents bacteria from getting into the food as it cools at lower pressure

25. Pasteurization • invented by Louis Pasteur • suitable for preservation ofmilk • 2 methods: The holding method The flash method Heat milk to 75°C for 15 seconds. Heat milk to 63-66 °C for 30 minutes. Cool it down quickly to about 10°C in sterilized bottles.

26. UHT treatment • UHT = ultra high temperature • another method for killing bacteria inmilk • milk is heated to 132°C for 1 second, then sealed into plastic-lined cardboard boxes • milk can be stored at room temperature for a longer time than pasteurized milk UHT milk

27. Refrigeration • the food is kept at a low temperature (2-7°C) to slow down bacterial and fungal growth Fish preserved by ice

28. Freezing • the food is frozen below -18°C to inhibit bacterial growth • once the food begins to thaw, the bacteria inside will start to grow again Food is preserved inside the food freezer

29. Adding preservatives • chemicals to kill bacteria • examples: SO2 in fruit juices & E211 in cakes • may be harmful to health Soft drink with preservatives Soy sauce with preservatives

30. include can be Concept diagram Micro-organisms viruses bacteria protozoa fungi useful harmful

31. in in can be prevented by works by Concept diagram useful harmful wine- and bread-making recycling of materials causing diseases spoilage of food producing nitrogen compounds in legumes food preservation dehydration killing micro-organisms preventing growth of micro-organisms

32. by means of Concept diagram dehydration natural drying freeze-drying smoking osmotic preservation pickling

33. with high temperature by with chemicals by Concept diagram killing micro-organisms sterilization (e.g. in canning and bottling) pasteurization UHT treatment adding preservatives

34. by Concept diagram preventing growth of micro-organisms refrigeration freezing