Biology Revision

1. Biology Revision B6 Beyond the Microscope

2. 6a Understanding Bacteria • Bacteria – smaller than animal or plant cells, typically a few microns long (1000 of a mm) • Flagellum – for movement • Cell wall – for maintaining shape & stop it bursting • Bacterial DNA – for cell replication & control of cell • Bacteria lack: • A ‘true’ nucleus • Mitochondria • Chloroplasts • A vacuole Main shapes: Spherical Rod Spiral Curved rods

3. 6a Understanding Bacteria • Food sources – some consume organic nutrients like carbohydrates & proteins, some make their own using sunlight • Survival – extreme habitats e.g. hot springs, inside humans • Reproduction – by binary fission • Rapid reproduction causes fast spread of disease & food spoilage, but can be useful

4. 6a Understanding Bacteria • Making Yoghurt • In large steel fermenters • Equipment sterilised • Raw milk pasteurised – heated to 80°C, then cooled rapildy • Heated to 40°C • Live bacterial culture added & incubated • Bacteria feed on lactose & make lactic acid • Manufacturer samples yoghurt • Flavours & colours added

5. 6b Harmful Microorganisms • Pathogens – microbes that cause disease

6. 6b Harmful Microorganisms • Natural Disasters Rapid spread of disease because: • Sewage systems & water supplies damaged • Electrical supplies damaged -> food decay • Disrupted health services • Dysentery, cholera & food poisoning common

7. 6b Harmful Microorganisms • History of Disease Treatment • Pasteur – 1860’s – Germ Theory – microbes in the air cause food decay & passed from person to person causing disease • Lister – 1865 – development of antiseptics – use of carbolic acid during surgery • Fleming – 1928 – Penicillin – discovered accidentally that this mould killed bacteria

8. 6c Microorganisms – factories for the future? • Yeast – single celled fungus • Asexual reproduction – budding • Conditions for reproduction: • Lots of sugar • Optimum temperature (rate doubles for every 10°C rise, above 40°C?) & pH • Removal of waste products e.g. alcohol

9. 6c Microorganisms – factories for the future? • Fermentation – anaerobic respiration in yeast • Sugar -> Alcohol + Carbon Dioxide • Uses: • Cleaning sugar in water from food processing factories • Making alcohol e.g. beer from barley, wine from grapes, cider from apples

10. 6c Microorganisms – factories for the future? • Brewing Beer • Mashing – extraction of sugar from source material • Hops added for flavour • Yeast added to ferment (keep warm) • Tank sealed to cause anaerobic respiration & prevent unwanted microbes entering • Clarifying/clearing to leave a clear liquid • Pasteurising to kill harmful microbes • Bottling or casking

11. 6c Microorganisms – factories for the future? • Distilling spirits • Rum from cane sugar • Whisky form malted barley • Vodka from potatoes • Process: • Liquid heated to evaporate alcohol • Concentrated alcohol trapped and condensed into a liquid • Fermentation is limited by increasing levels of alcohol that eventually kill yeast

12. 6d Biofuels • Biogas – contains mainly methane (50% burns easily 10% is explosive), some carbon dioxide, traces of hydrogen, nitrogen & hydrogen sulphide • Biogas produced by decomposer bacteria in marshes, septic tanks, animal’s digestive systems • Uses: • Burned to generate electricity • Burned to produce hot water & steam for central heating • Fuel for buses (cleaner than diesel & petrol, but doesn’t produce as much energy)

13. 6d Biofuels • Large scale production of methane • Continuous flow method in a digester – organic material added daily & gas siphoned off • Optimum temperature – too low, little gas produced; above 45°c enzymes denatured, no gas produced • Advantages of biofuels: • Alternative source to fossil fuels – reduce greenhouse effect • No particulates produced • Cheap • Renewable/sustainable • Conservation of resources

14. 6e Life in Soil • Composition of soil: • Rock particles • Humus (dead organic matter) • Water • Living organisms e.g. fungi, microscopic protozoans, nematode works, earthworms, bacteria • Importance of worms: • Burying organic material for decomposition • Mixing soil layers • Aerating & draining soil • Neutralising acid soil

15. 6e Life in Soil • Soil Food Webs Detritivores e.g. earthworms Decomposers e.g. fungi

16. 6e Life in Soil Nitrogen fixing e.g. Azobacter, Rhizobium & Clostridium • Nitrogen Cycle Nitryfying e.g. Nitrosomonas & Nitrobacter convert ammonia to nitrates Saprophytic bacteria start decomposition & make ammonia

17. 6f Microscopic life in water Amoeba use active transport to pump water into small vacuoles which join into one contractile vacuole which empties out of the cell Salmon move from salt to fresh water – they alter their urine concentration to counteract osmosis in or out of cells

18. 6f Microscopic life in water • Plankton • Phytoplankton – microscopic plants capable of photosynthesis • Zooplankton – microscopic animals • Have limited movement/rely on currents • Seasonal variation in population due to changes in: • Light • Temperature • Nitrates Can cause algal blooms

19. 6f Microscopic life in water • Water Pollution • Sewage - cause eutrophication • Oil • Fertilisers – cause eutrophication • Pesticides e.g. DDT - bioaccumulate • Detergents • Acid rain • PCBs (chemical used to insulate electrical equipment) – bioaccumulate • Biological Indicators – of pollution/cleanliness

20. 6g Enzymes in action • Uses: • Biological washing powders – enzymes digest food stains • Cheese making – separate curds & whey • Fruit juice extraction • Alter food flavour • Reagent sticks e.g. glucose/urine test stick