Helpful and Harmful Bacteria Helpful Bacteria Most bacteria
Helpful and Harmful Bacteria
Helpful Bacteria • Most bacteria are harmless to humans. • Many are useful: – Aid in digestion – Provide nutrients for plants by breaking down dead material by decomposition – Provide drugs and hormones – Provide some types of food.
Yoghurt • This is made by the action of a particular type of bacteria on milk. • Lactobacillus bulgaricus and Streptococcus thermophilus • These bacteria change milk sugar (lactose) into lactic acid. • The acid gives yoghurt its characteristic sour flavour and also causes the curd to separate from the milk.
Yoghurt • The resulting yoghurt is thick and creamy. • When it is eaten, the bacteria colonise the intestinal tract where it is thought that they aid the process of digestion.
Nutrient Cycles • Decomposers break down dead plant and animal material into simpler chemicals, releasing essential nutrients into the soil. • These nutrients can then be used for plant growth.
The Nitrogen Cycle • Atmospheric nitrogen can be fixed by lightning or certain nitrogen fixing bacteria called Rhizobium. • These Rhizobium live in a mutualistic relationship in the root nodules of leguminous plants such as lupins, gorse and clover. • Also some free-living soil bacteria “fix” nitrogen.
The Nitrogen Cycle • Denitrifying bacteria break down nitrates to nitrogen, thus returning it to the reservoir in the air. • This is known as Denitrification.
The Nitrogen Cycle
The Carbon Cycle
Harmful Bacteria
Harmful Bacteria • Micro-organisms that cause disease are called Pathogens. • An infectious disease is one that can be passed on from person to person.
Catching Diseases • Contaminated food and water. – Salmonella spp, Clostridium botulinum • Through the air – Sneezing or coughing Staphylococcus and Streptococcus • Skin contact – Particularly through broken skin – Staphylococcus spp
Catching Diseases • Contact with infected materials like towels and handkerchiefs • Contact with body fluids – E. g. blood, semen, saliva
Harmful Bacteria • Pathogenic bacteria make people feel sick by getting into the body and producing enzymes which break down body tissues or by excreting very strong poisons called toxins.
Bacterial Diseases • • Diptheria - Corynebacterium diphtheriae Syphillis - Treponema pallidum Tetanus - Clostridium tetani Typhoid - Salmonella typhi Tuberculosis - Mycobacterium tuberculosis Sore throat - Streptococcus Salmonella – Salmonella spp
Bacterial Diseases • • Meningitis - Neisseria meningitidis Whooping cough - Bordetella pertussis Cholera - Vibrio Cholerae Gonorrhoea – Neisseria Gonorrhoeae Chlamydia – Chlamydia trachomatis Plague - Yersinia pestis Pneumonia - Streptococcus pneumoniae
Harmful Bacteria • When people are sick, samples of their tissues, blood, or faeces may be taken and placed onto agar plates to see if the samples grow bacterial cultures. • This will determine if a particular type of bacteria is causing the illness and will help the doctor prescribe an antibiotic drug to kill the bacteria.
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