1. Helpful and Harmful Bacteria

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. The Nitrogen Cycle
Denitrifying bacteria break down nitrates to nitrogen, thus returning it to the reservoir in the air.
This is known as Denitrification.

8. The Nitrogen Cycle

9. The Carbon Cycle

10. Harmful Bacteria

11. Harmful Bacteria
Micro-organisms that cause disease are called Pathogens.
An infectious disease is one that can be passed on from person to person.

12. Catching Diseases Contaminated food and water. Through the air
Salmonella spp, Clostridium botulinum
Through the air
Sneezing or coughing Staphylococcus and Streptococcus
Skin contact
Particularly through broken skin
Staphylococcus spp

13. Catching Diseases
Contact with infected materials like towels and handkerchiefs
Contact with body fluids
E.g. blood, semen, saliva

14. 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.

15. Bacterial Diseases Diptheria - Corynebacterium diphtheriae
Syphillis - Treponema pallidum
Tetanus - Clostridium tetani
Typhoid - Salmonella typhi
Tuberculosis - Mycobacterium tuberculosis
Sore throat - Streptococcus
Salmonella – Salmonella spp

16. Bacterial Diseases Meningitis - Neisseria meningitidis
Whooping cough - Bordetella pertussis
Cholera - Vibrio Cholerae
Gonorrhoea – Neisseria Gonorrhoeae
Chlamydia – Chlamydia trachomatis
Plague - Yersinia pestis
Pneumonia - Streptococcus pneumoniae

17. 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.