Biology RevisionB6 Beyond the Microscope

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 maintainingshape & stop it bursting Bacterial DNA – for cell replication & control of cell

Bacteria lack:1. A ‘true’ nucleus2. Mitochondria3. Chloroplasts4. A vacuole

Main shapes:SphericalRodSpiralCurved rods

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 reproductioncauses fast spread ofdisease & foodspoilage, but can be useful

6a Understanding Bacteria Making Yoghurt In large steel fermenters1. Equipment sterilised2. Raw milk pasteurised – heated to 80°C,

then cooled rapildy3. Heated to 40°C4. Live bacterial culture added & incubated5. Bacteria feed on lactose & make lactic

acid6. Manufacturer samples yoghurt7. Flavours & colours added

6b Harmful Microorganisms Pathogens – microbes that cause

diseasePathogen

Illness caused Transmission method

Bacteria

Cholera (Vibrio) Contaminated water

TB Airborne droplets

Food poisoning (salmonella & E. coli)

Contaminated food

Septic wound Contact with wound

Protozoa Dysentery (Entamoeba) Contaminated food/water

Malaria Mosquito bite

Viruses ‘Flu Airborne droplets

Chickenpox/smallpox Direct contact or airborne droplets

Fungi Athlete’s foot Direct contact

6b Harmful Microorganisms Natural DisastersRapid spread of disease because: Sewage systems & water supplies

damaged Electrical supplies damaged -> food decay Disrupted health services

Dysentery, cholera & food poisoning common

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

6c Microorganisms – factories for the future? Yeast – single celled fungus Asexual reproduction – budding Conditions for reproduction:1. Lots of sugar2. Optimum temperature (rate doubles for

every 10°C rise, above 40°C?) & pH3. Removal of waste products e.g. alcohol

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

6c Microorganisms – factories for the future? Brewing Beer1. Mashing – extraction of sugar from

source material2. Hops added for flavour3. Yeast added to ferment (keep warm)4. Tank sealed to cause anaerobic

respiration & prevent unwanted microbes entering

5. Clarifying/clearing to leave a clear liquid6. Pasteurising to kill harmful microbes7. Bottling or casking

6c Microorganisms – factories for the future? Distilling spirits Rum from cane sugar Whisky form malted barley Vodka from potatoes Process:1. Liquid heated to evaporate alcohol2. Concentrated alcohol trapped and

condensed into a liquid Fermentation is limited by increasing

levels of alcohol that eventually kill yeast

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)

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:1. Alternative source to fossil fuels – reduce

greenhouse effect2. No particulates produced3. Cheap4. Renewable/sustainable5. Conservation of resources

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:1. Burying organic material for decomposition2. Mixing soil layers3. Aerating & draining soil4. Neutralising acid soil

6e Life in Soil Soil Food Webs

Detritivores e.g. earthwormsDecomposers e.g. fungi

6e Life in Soil Nitrogen Cycle

Nitrogen fixing e.g. Azobacter, Rhizobium & Clostridium

Nitryfying e.g. Nitrosomonas & Nitrobacter convert ammonia to nitrates

Saprophytic bacteria start decomposition & make ammonia

6f Microscopic life in waterAdvantages of living in water

Disadvantages of living in water

No problem of water shortage or dehydration

Water is dense so resists movement

Less variation in temperature Difficult to control the absorption & release of water from living cells

Water gives more support so organisms grow bigger without increases in skeleton size

Waste is easily disposed

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

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

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

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