B6 - Beyond the microscope

Bacteria cells:

• have cell wall to help keep shape and stop them from bursting
• strand of DNA to control cell's activities and replication and flagellum to help them move
• 4 shapes: rods, curved rods, spheres and spirals

You can culture bacteria on a petri dish containing agar:

• important to use aseptic technique to protect from infection and contamination:
  • involves wearing gloves, sterilising equipment, sealing petri dish and dsiposing cultures safely by pressure sterilising in autoclave

Can use bacteria to make yoghurt:

• equipment sterilised and milk pasteurised (72 deg cel at 15 secs) to kill any unwanted microogranisms then milk is cooled
• lactobacillus bacteria added, mixture incubated in fermenter, bacteria breaks down lactose into lactic acid which causes milk to clot and solidify into yoghurt, sample taken, packaged

Viruses only reproduce in living cells:

• virus attaches itself to specific host cells and injects its genetic material in cell
• virus uses host cell to make components of new viruses
• eventually causes host cell to split open releasing new viruses

Diseases can be transmitted:

• in food e.g. food poisoning, prevented by good hygiene and cooking food properly
• in water e.g. cholera, prevented by good sanitation and waterborne diseases
• airborne droplets e.g. influenza, prevented by sneezing into tissue, washing hands properly
• through contact e.g. athlete's foot, prevented by disinfecting surfaces

Poor sanitation:

• poor sanitation is linked with a high incidence of disease
• developing countries are less likely to be able to afford good sanitation and public health measures

Four stages in an infectious disease:

• microorganism enters body and reproduces rapidly, producing more microogranisms
• microogranisms then produce toxins which damage cells and tissues
• toxins cause symptoms of infection
• time between exposure to microogranism and development of symptoms = incubation period

Antiseptics: used outside the body to help clean wounds and surfaces to prevent infection

Antibiotics: drugs used inside the body to treat patients already infected

Resistant bacteria:

• Random mutations can cause bacteria to have genes that allow them to survive and reproduce in a host who's being treated to get rid of infection
• leads to gene for antibiotic resistance being passed on = natural selection

Louis Pasteur:

• heated broths in two flasks, one has a curved neck so bacteria settled in loop and didnt get to broth
• flask with curved neck = broth stayed fresh, proving that microbes caused the broth to spoil

Joseph Lister:

• began to treat and dress wounds using antiseptic carbolic acid which killed bacteria and prevented sepsis
• lister's techniques were taken up by rest of medical profession

Alexander Fleming:

• cleared out plates containg bacteria and noticed one plate also had mould and area of mould was free of bacteria
• found that mould on plate was producing a substance that killed bacteria = penicillin

Respiration of yeast:

• anaerobic respiration = produces ethanol, carbon dixoide and energy  = fermentation:
  • glucose --> ethanol + carbon dixoide (+ energy)
  • C₆H₁₂O₆  --->  2C₂H₅OH  +  2CO₂ (+ energy)
• aerobic respiration = glucose + oxygen --> carbon dizoide + water (+more energy)
• growth rate depends on conditions:
  • yeast reproduces faster when it's warmer but dies when it's too hot
  • more food (glucose) there is = faster yeast production
  • build up of toxic waste products e.g. ethanol slows downs reproduction
  • too high or low pH slows down reproduction

Wastewater can be cleaned up with yeast:

• yeast is used to treat contaminated water as it uses up sugar in respiration

• first you get sugar out:
  • Beer - barley grains allowed to germinatewhere starch in grains broken down into sugar by enzymes then grains are dried in kiln = malting
    • malted grains mashed up and water added to produce sugary solution and sieved
    • hops are added to mixture to give beer bitter flavour
  • wine - grapes mashed and water added 
• yeast added and mixture incubated which ferments sugar into alcohol
• beer and wine produced drawn off through tap
• beer is pasteurised to kill any yeast left in beer and completely stop fermentation
• wine isn't pasteurised as any yeast left over carry on slowly fermenting sugar which improves taste of wine

Distillation increases alcohol concentration:

• fermentation products heated to 78 dc so alcohol boils and turns into vapour, not water
• alcohol vapour rises and travels thorugh cooled tube which causes it to condense into lquid alcohol and run down tube into collecting vessel

• Biomass = living / recently dead organic material + a store of energy
• biomass can be fermented by yeast and bacteria to create products such as biogas

Biogas:

• usually about 70% methane and 30% carbon dioxide
• biogas containing more than 50% methane burns easily but biogas containing around 10% methane can be explosive
• can be burned to power a turbine to generate electricity
• can be burned to heat water to produce steam to heat central heating systems

Made by anaerobic fermentation of waste material:

• needs a simple biogas generator:
  • inlet for waste material to be put in and an outlet for digested material to be removed 
  • biogas outlet so biogas can be piped to where it's needed

Advantages of biofuels:

• can be produced in a sustainable way using crops that can be replaced quickly
• plants grown to make biogas photosynthesis which removes carbon dioxide from atmosphere to balance out release of carbon dioxide
• biogas is cleaner than diesel or petrol - doesn't produce particulates

Disadvantages:

• doesn't contain as much energy as the same volume of natural gas because it's more dilute
• large areas of land are sometimes cleared of vegetation to create space to produce biofuels whcih can create habitat loss and extinction of species

Gasohol:

• 10% ethanol and 90% petrol
• less crude oil is used up, growth of crops means some carbon dioxide is absorbed by photosynthesis, most economically ciable in areas where there is plenty of sugar cane

Different types of soils:

• Sandy soils - large mineral particles so they have large pores, high air content,very permeable
• Clay soils - made up of tiny particles, pack tightly together, leave very small pores, have a low air content and low permeability, retain more water because water molecules cling to small particles
• Loam soils - mixture of sand and clay particles
• soils contain humus - decomposed, dead organic matter which helps support soil life

Measuring water content:

• take mass of small sample of soil, heat sample to 105 degrees until reaches constant mass
• take mass of soil sample again - difference between first and second reading = mass of water
• heat soil sample to 550 degrees for two hours to burn all humus from soil sample
• sample for third time - difference between second and thrid reading = mass of humus

Air content - fill a pipette and fill test tube - subtratct volume of water needed to fill up to soil

Soil contains herbivores, carnivores and detritivores

Soil needs the right conditions to support life:

• must contain water to carry out reactions and oxygen for respiration
• presence humus also helps to support life:
  • organic material is slowly broken down by decomposers which releases minerals and nutrients that can be used by other organisms
  • increases air content of soil making more oxygen available to organisms that live there

Earthworms keep soil healthy and fertile:

• charles darwin discovered why worms are good for soil structure and fertility:
  • earthworms bury leaves in soil where bacteria and fungi can decompose them
  • burrows allow air to enter soil and water to drain through it
  • mix up soil layers distributing nutrients equally
  • soil in earthworm poo is less acidic then the soil they eat which neutralises soil acidity

Advantages:

• isn't any danger of water shortages or dehydration
• less variation in temperature and waste disposal is easier
• provides support for plants and for animals that have no skeletal system

Disadvantages:

• more resistant to movement so it is much harder to move
• have to be able to control amount of water in their body

Amoebas regulate water content using contractile vauoles:

• vacuole collects water that diffuses in by osmosis, vacuole then moves to cell membrane and contracts to empty water outside the cell

Plankton:

• phytoplankton are microscopic plants and zooplankton are microscopic animals

Plankton populations vary according to season:

• during winter months and in deep water - light intensity and temperature are low which limit photosynthesis
• during summer and near water's surface - light intensity and temperature are higher but mineral concentration is lower which limits photosynthesis
• phytoplankton populations ususally increase between late spring and summer = algal bloom:
  • longer sunnier days, more light available for photosynthesis and energy is used for growth
  • temperatures increase which increases photosynthesis and growth rates
  • population of zooplankton also increases because there is more phytoplankton to feed on

Causes of water pollution:

• fertilisers and sewage which cause eutrophication
• clean water - sontefly nymph, low level - freshwater shrip, high level - bloodworm, very high level - rat-tailed maggot
• industrial chemicals and pesticides that can't be broken down which are eaten by organisms

Biological washing powders:

• contain enzymes which break down stubborn stains
  • carbohydrases digest starch and break it down into simple sugars
  • proteases digest proteins and break them down into amino acids
  • lipases digest lipids and break them down into fatty acids and glycerol

Medical products:

• reagent strips that are dipped in urine to see if sugar is present

Food Industry:

• low calorie food - enzyme called sucrase used to break down sucrose  into glucose and fructose which are much sweeter than sucrose
• cheese - enzyme rennet is used to clot milk in the first stages of cheese production
• juice extraction - pectinase breaks down pectin causing cell to release its juice

Immobilising enzymes:

• enzyme doesn't have to be seperated from the mixture after the reaction has taken place
• encapsulating enzyme in alginate beads then dropping it in calcium chloride solution
• advantages - enzymes don't contaminate product, can be used in continuous flow processing
• used to make lactose free milk by using immobilised lactase:
  • breaks down glucose and galactase which can be absorbed by someone who is lactose intolerant
  • milk is run through a column of immobilised lactase whcih converts lactose into glucose and galactose but only products emerge from column
• used in  reagent *****s:
  • drop of blood from a finger ***** is added and enzymes in ***** cause it to change different colours depending on glucose concentration which is then compared to a chart to find out level of blood sugar

Genetic engineering:

• alters genetic code of an organism
• gene giving desirable characteristic is removed from one organism and inserted into another
• able to transfer genes because the genetic code is universal - same four DNA bases
• genetically modified organism is called a transgenic organism

Main steps:

• identify gene that you want in an organsim and remove gene from organisms DNA
• cut open DNA of organism you want to put gene in using restriction enzymes and insert gene
• host is now a transgenic organism that you can clone to make more copies

Bacteria can be engineered to produce human insulin:

• scientists identify gene that controls production of insulin and remove it from DNA of human cell using restriction enzymes, restriction enzymes used to cut open plasmid so it has sticky ends, insulin gene inserted into plasmid which is taken up by bacteria.  

DNA fingerprinting:

• used in forensic science to compare DNA from crime scenes to DNA in suspects
• some people would like everyone's DNA fingerprints to be stores on a national genetic database as this would make it easier to solve crimes however some people think this is an invasion of privacy and data could be misinterpreted

How it works:

• first, extract DNA from cells in your sample, restriction enzymes used to cut DNA into fragments where they recognise a particular order of bases
• DNA fragments are seperated using a process called electrophoresis - fragments suspended in gel and electric current passed through gel, DNA negatively charged to it moves towards positive anode
• DNA tagged with radioactive probe then placed onto photographic film where it goes where the radioactivity revealing the positions of DNA fragments