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Bacteria cells are smaller and simpler than animal cells

  • Bacteria cells have a cell wall to keep their shape ans stop them bursting, 
  • they have a strand of DNA in cytoplasm that controls activities and replication (some have loops of DNA called plasmids) and also some have a tail (Flagellum) to help them move
  • they come in 4 shapes: rods, curved rods, spheres and spirals
  • becteria can consume a huge range of organic nutrients from their surroundings which provide them with energy, some bacteria can produce their own nutrients meaning that bacteria can survive in almost any habitat (soil, water, air, human body and food)

Bacteria reproduce by asexual reproduction

  • they reproduce by asexual reproduction, they reproduce by a process called binary fission (split into two)
  • they produce very quickly
  • if a disease causing bacteria enters your body, they can reproduce and cause disease before your body can respond
  • bacteria produce faster when it's warm and with enough nutrients 
  • so storing food i coldplaces will reduce production of bacteria and make it more hygenic for longer
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Micro Organisms and Disease

Viruses can only produce inside living cells

  • viruses aren't cells, normally they consist of a protein coating around a strand of genetic material
  • they only produce inside living cells, so must infect other organisms in order to multiply 
  • viruses can infect plant, animal andd bacteria cells
  • a peticular type of virus will only attack specific cells, here's how they reproduce:
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For culturing bacteria, Aseptic technique is used

  • you can grow bacteria on a petri dish with agar jelly, and bacteria can be transferred using a wire inoculation loop
  • when culturing bacteria the aseptic technique will protect you and the sample from contamination, this involves:
  • wearing gloves, tying back long hair
  • sterilising equipment before and afterq use (with heat or radiation)
  • sealing the dish after transferring bacteria
  • safley disposing samples after use, usually done by pressure sterilising in an autoclave

Bacteria can be used for making Yoghurt.

  • the equipment is sterilised to kill off unwanted bacteria
  • milk is pasteurised (heated to 72'c for 15secs) to kill of unwanted microorganisms, then milk is cooled
  • a starter culture of lactoballicus bacteria is added, mixture is incubated to 40'c in a vessel called a fermenter
  • bacteria break down the lactose sugar in milk into lactic acid, causing the milk to clot and solidify into yoghurt
  • sample is taken to ensure correct consistency, then colours and flavours etc... are added.
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Micro Organisms and Disease

Different diseases can be transmitted in differnt ways:

  • FOOD - e.g foodm poisoning.  illness can come from eating food contaminated with bacteria. can be prevented through good hygiene and ensuring food is cooked fully before eating
  • WATER - e.g cholera. can come from drinking water contaminated with sewage, not an issue in developed world but in develpoing countries it can be an issue where sanitation is poor. it can be avoided by good sanitation
  • AIRBORN DROPLETS - e.g influenza can be transmitted nu airborn droplets through coughing and sneezing, this can be avoided by sneezing into a tissue, washing hands and disinfecting surfaces
  • CONTACT - athletes foot, fungus, is caused by bare feet on damp floors in showers, prevetned by washing feet and not walking around barefoot (also disinfecting surfaces)

Poor sanitation is linked to a high incidence of disease

incidence of a disease is the no. of new cases occuring in a population in a certain time. low incidence of disease comes from good sanitation (good sewage, health education, clean hospitals) and this can prevent spread of disease. poor sanitation is linked with high incidence of disease, from lack of clean water and bad sewage systems. developing countries are less likley to be able to afford the ways to prevent disease, making it more frequent

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Treating Infectious Disease

There are four stages to an inefctious disease

1) the microorganism enter the body, through the mouth or nose etc..

2) once the microorganisms enter the body, they rapidly reproduce

3)The microorganisms produce toxins which damage cells and tissue

4) The toxins cause symptoms (pain) and your healing can have syptoms (fever). the time between exposure and developemnt of symptoms is called the incubation period

Antiseptisc and Antibiotics can help control disease

these are chemicals that destroy bacteria or stop them growing. ANTISEPTICS are used outside the body to clean wounds & surfaces, they prevent disease rather than treat it. household products like bathroom cleaners contain these, they can prevent MRSA. Antibiotics are drugs inside the body taken as a pill or injection, they are used to treat already infected patients, but only kill bacteria and not viruses

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More on infectious diseases

Diseases spread more rapidly after natural disasters

  • natural disasters can damage sewage systems and water supplies, meaning contaminated drinking water (causing cholera)
  • people can become displaced when their homes are destroyed they might move into camps with large numbers of people with poor sanitation
  • this means diseases spread esially through close breathing air and contact

Scientists who have improved disease treatment:

Louis Pasteur

until the 19th century it was though disease spontaneously appeared, pasteur argued microbes in the air cuase disease. he heated two broths in seperate flasks, one with a straight neck and one with a curved neck so air wouldnt get to the broth. the broth wiith the curved neck stayed fresh and the straight neck was frementing from germs in the air

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Treating Infectious Disease

bacteria can evolve and become resistant to antibiotics

  • random mutations in bacterial DNA can lead to changed, which can sometimes mean the bacteria is less affected by a peticular antibiotic 
  • bacteria with these genes are better at surviving and reproducing in a host being treated for this infection
  • this leads to the gene for resistance being passed on through reproduction 
  • resistance to this can make it very hard to treat (like MRSA) so avoiding it is the best option

Finishing antibiotics is important

  • The more often antibiotics are used, the greater resistance the bacteria has
  • antibiotics dont cause resistance, but they create a situation where naturally resistant bacteria have an advtantage
  • only taking them when necessary is essential so that the bacteria immunity doesn't get passed on through generations
  • completing the dose is important becuase 1 bacteria can multiply again and again and the disease can become as extreme as it was to begin with
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More on infectious diseases

Joseph Lister

when working as a doctor, half of patients undergoing surgery died from infection, known as sepsis. listers observation of wounds led him to think sepsis was decomposition. he knew of pasteurs findings from air and realised he needed to kill microbes from getting to the wound. he began to treat wounds using the antiseptic carbolic acid. this killed bacteria in the wounds and prevented sepsis, his techniques were evetntually taken on by the medical industry

Alexander Fleming

fleming was clearing out some plated containing bacteria and he noticed one of the plates of bacteria also had mould on it and the area around the mould was free of bacteria. he found the mould (called penicillium notatum) on the plate was producing a substance that killed bacteria, this substance was penicillin

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When yeast respires anaerobically, without oxygen, it prudces ethanol, carbon dioxide and energy. this is called fermentation. Here is the equation

Glucose  Ethanol + Carbon Dioxide (+ energy)

 C6H12O6 → 2 C2H5OH + 2 CO2

the fermentation is used to make beer and wine. yeast can also respire aerobically which releases more energy. the type of respiration depends on wether there is oxygen present. yeast prefer to respire aerobically so fermentation only takes place in the absence of oxygen

Wastewater can be cleaned up with yeast

food processing factories need to get rid of sugary water, they can't just release into waterways as it would cause pollution. bacteria in water would feed on sugar and reproduce quicker, using up oxygen in water, so other organisms in water may die. yeast can be used to treat the contaminated water before it's released. it uses up sugar in respiration.

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Brewing beer and wine

  • with beer we need to get the sugar from barley grains. the grains germinate for a few days whilst the starch breaks down into sugar by enzymes. the grains are then dried (called malting) dried grains are mashed up and wateris added making a sugary soloution, which is sieved to remove btis of grain. hops are added to give flavour
  • with wine grapes are mashed, water is added.
  • after the sugar is taken, the yeast is added and the mixture is then incubated (kept warm) yeast ferments sugar into alcahol. feremting vessels are designed to stop microorganisms from air getting in. 
  • the beer and wine produced is drawn off through a tap, sometive clarifying agents are added to remove particles making it cleaner
  • beer is pasteurised (heated to kill yeast and stop fermentation)
  • in wine the yeast is left to slowly ferment the sugar, improving taste of wine. beer also tasted better if its unpasterised and aged in the right conditions, but bigger breweries pasteurise it becuase unpasteurised beer has a risk of spoiling if not stored in the right conditions after being sold. beer is casked and wine is bottled for sale
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Yeast's growth rate varies with changing conditions

the faster yeast respires the faster it reproduces. it's growth rate is controlled by temperature, availability of food, PH, and how quickly waste can be removed. yeast also produces faster with oxygen, one way of measuring how fast yeast is reproducing is to measure how much sugar (glucose) it breaks down, faster yeast production means more glucose being broken down

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Distillation increases alcohol concentration

if an alcohol is distilled it produces spirits, e.g if can sugar is distilled you get rum. distillation is used to seperate the alcohol out of the alcohol water soloution. heres the method:

  • fermentation products are heated to 78'c. this is the temperature where alcohol boils turning to vapour, but the soloution remains liquid
  • alcohol vapour rises and travels through a cooled tube which causes it to condense back into liquid alcohol and run down a tube into a collecting vessel 

this is a commercial process that can only be done with a liscenced premises, so it can't be done at home although brewing can

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energy can be transferred from biomass, this is living or recently dead organic material (e.g plants). their energy can be turned into more useful energy forms. fast growing trees can be burnt releasing heat. biomass can also be fermented by yeast and bacteria to create products like biogas which can be used as FUEL. 

biogas is usually 70% methane and 30% carbon dioxide. and also contains traces of hydrogen, nitrogen and hydrogen sulfide. biogas containing more than 50% methane burns esially, but can be explosive if containing 10%. biogas is made by bacteria in a digester, bacterias respiration produces methane. 

Biogas can be used as fuel

  • biogas can be burned to power a turbine which can generate electricity, especially useful for remote areas with no mains supply
  • it can also be burned to heat water and produce steam to heat central heating systems
  • it can be used as a fuel for cars and buses
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More biofuels


  • they are sustainable - crops which are decomposed are esialy replaced compared to fossil fuels which will run out
  • plants for biogas photosynthesise which removes CO2 (a greenhouse gas) making it CO2 neutral if plants are being planted at the same rate as being consumed. 
  • biogas is a cleaner fuel than diesel or petrol. butning fossil fuels produces particulates which can cause lung disease, which biogas doesn't produce


  • biogas doesn't release as much energy as the same volume of natural gas from underground becuase it's more dilute
  • large areas of land are sometimes cleared of vegetation to create space. this reduces the reduction of CO2 from plants, and also reduces habitat which can lead to the extinction of species.
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Biogas is made by Anaerobic fermentation of waste material

  • biogas can be made from plant and animal waste in a simple fermenter called a digester. sludge waste from sewage or sugar factories is used to make biogas on a larger scale
  • different types of bacteria are used, some decompose organic matter and produce waste, another decomposes that waste, ect.. until you get biomass. this is a type of fermentation - a breakdown of substances without oxygen
  • biogas digesters need to be kept at a constant warm temperature (30-40'c) which is the optimum for bacterias respiration. any cooler won't be as fast, and hotter and bacteria will die. 

Large-Scale biogas production uses a continuous flow method - organic waste is continuously fed into the digester and the biogas and solid digested material are continuously removed at a steady rate. 

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More biofuels

Ethanol can be used as a Biofuel!

  • ethanol can be burnt as  fuel, it's cleaner than fossil fuels as it makes less pollutants
  • it's renewable (produced by using yeast to ferment glucose in ethanol production (which somes from sugar cane or beet sugar)
  • cars can be adapted to run on a mixture of ethanol and petrol known as gasohol (10% ethanol 90% petrol)
  • using 10% othanol means using less crude oil, making it last longer
  • growth of crops for ethanol takes CO2 out of the enviroment
  • this balances the CO2 released when gasohol is burned
  • a disadvatnage is that it's only very useful in countries that can grow a lot of sugar canes (such as brazil) and not a lot of oil
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Different soils contain different particles.

SANDY SOILS - these are made up of large mineral particles, which are so large that they leave large gaps (pores) in the soil - so they have a high air content and are easily permeable so water passes through easily

CLAY SOILS - mainly consists of small particles which pack together tightly only leaving small pores in the soil so they have low air content and low permeability, they retian more water becuase water molecules can cling to small particles

LOAM SOILS - a mixture of sand and clay, their properties depend on the proportion of clay to sand molecules.

! most soils also contain humus - which is dead organic matter which has decomposed. it helps to support plant life

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Life in soil

Soil contains living organisms that need the right conditions

  • animals and plants use soil for food and oxygen
  • plants use soil for water, minerals and as an anchor for roots to hold onto (for support)
  • soil is an ecosystem containing herbivores, carnivores, detrivores
  • soil also contains microscopic protozoans, fungi, nematode worms and bacteria
  • in order to support life, soil must contain water and oxygen
  • this is becuase all organisms need water for reactions in cells and oxygen for respiraton
  • Humus also helps support life
  • as organic material is broken down by decomposers; minerals and nutrients are released into soil, other organisms can then use these compounds
  • humus increases air content of the soil making mroe oxygen avalable to organisms
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Measuring water and Humus content

 take a mass of the sample. heat it to 105'c until it reaches a constant mass - this will boil off all the water in the soil. take the mass of the sample again, the original amount of water in the first sample will be the difference between the two masses. then heat the soil sample to 550'c for two hours which will burn off all the humus from the sample, then take the mass for the third time, the difference between the third and the second sample is the amount of humus in the soil.

You can also measure air content 

loosley pack some of the sample soil into a beaker/test tube and measure the volume. Fill up a pipette with a known volume of water and gradually add it to the beaker letting it seep down into the soil sample. continue doing this until the water comes to the top of the soil sample. the amount of air in the sample is the total volume of original water minus the amount left in the pipette. 

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Life in soil

Earthworms keep soil healthy and fertile

charles darwin studied worms to see what food they consumed and their behaviour and in turn discovered why worms are good for soil;

  • earthworms bury leaves and other organic materials in soil where bacteria and fungi can decompose them
  • their burrows allow air to enter the soil (aeration) and water to drain through it
  • aeration provides life in soil with oxygen. however drainage is also important becuase if the soil is waterlogged there's less oxygen available
  • they mix up soil and layers, distributing the nutrients more equally
  • their extrement is less acidic than regular soil (important as acidic soils are less fertile than neurtal or alkali)
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Life in water

Advantages and disadvantages

  • plenty of water reduces chances of dehydration
  • less variation in temperature
  • gives physical support to animals with no framework (jellyfish)
  • easier to dispose of waste
  • more resistant than air, taking up more energy from movement
  • animals need to control the amount of water that they take in, if they take in all the water through osmosis then bodily soloutions could be weakened damaging chemical rections in the body
  • an animal living in salt water would have a lower solute concentration than the water so itwould diffuse out, and their cells would shrivel and die
  • an animal in fresh water would have cells with a higher concentration so they would take in too much water and the animal cell would burst.
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More life in water

Plankton population varies according to season

  • in winter and deep water there is low heat and light, but high levels of minerals, meaning light and heat limit rate of photosynthesis
  • in summer and near the surface there is high heat and light and low mineral levels, mineral concentration limits rate of photosynthesis. 
  • Phytoplankton populations increase between late spring and late summer, called a algal bloom due to more light and more heat. zooplankton also increase as there is more phytoplankton to feed on

There are different food webs in the oceans

  • ocean food webs are grazing food chains so they start with an organism that can produce it's own food (living producer)
  • if it's too cold or deep then the producer will be bacteria which rely on sulfur rather than phytoplankton which need sunlight
  • otherwise the bottom of the food chain feed on dead and dying material fallen from the surface (Marine snow) which is the main source of nutrients
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Life in water

Amoebas regulate water content using contractile vacuoles

single celled organisms like amoebas only have a cell membrane, and no organs to regulate anything, so amoebas regulate water with a contractile vacuole which collects the water that diffuses in by osmosis, the vacuole then moved to the cell membrane, contracts to empty water outside the cell. 

Plankton are microscopic organisms that live in water

plankton are microscopic organisms that live in fresh and salt water, one type is phytoplankton which are plants, and the other type is zooplankton which are microscopic animals, and they feed on phytoplankton, and phytoplankton photosynthesise and are the main producers in aquatic food chains, so they are important in the ecosystem of freshwater and saltwater enviroments.

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More life in water


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Enzymes in Action


Washing Powder - some stains are soluble so wash out with water. stubborn stains have insoluble chemicals like starch, protein and fats which can be broken down by enzymes in detergents. amylases break down carbohydrate stain from jam or chocolate into simple sugars. Lipases break down lipids from butter and oil into fatty acids and glycerol. Proteases break down protein stains from blood and grass into amino acids. they work best at lower temps. but some have been modified to work at higher temps. also work best at neutral PH. 

Medical Products - diabetes is diagnosed by the presence of sugar in urine,and is tested by benedict's soloution which turns from blue to orange is sugar is present but this involves chemicals. reagent strips are used nowadays which change colour using enzymes, which causes chemicals embedded in strips to change colour

Food industry - table sugar (sucrose) is used to sweeten food. sucrase is used to break down sucrose into glucose and fructose which is sweeter than glucose, meaning less sugar so less calories. the enzyme rennet is used to clot milk in the first stages of cheese production. the enzyme pectinase is used in fruit juice extraction, which breaks down prectin (part of the cell wall in apples and oranges) causing the cell to release its juice. 

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Genetic Engineering

genetic engineering alters the genetic code of an organism to give it desirable characteristics by taking that gene from another organism. this is done becuase all organisms have the same G-C-A-T DNA. a genetically modified organism is called a transgenic organism.

there are 5 main stages to genetic engineering. 1) identify the gene you're transferring. 2) remove the gene from the organisms DNA. 3) cut open the DNA of the new organism. 4) insert the gene into DNA of the new organism. 5) the host is now a transgenic organism, you can clone it to produce more copies. cutting and inserting is done using enzymes.

  • bacteria can be engineered to produce human insulin. 
  • scientists identify the gene which controls the production of human insulin
  • they remove it from DNA of a human cell by cutting it out with restriction enzymes, leaving the DNA with 'sticky ends'
  • a loop of bacterial DNA called a plasmid is prepared for insulin to be inserted. restriction enzymes are used to cut open the plasmid leaving it with sticky ends too
  • insulin gene is inserted in the plasmid, sticky ends allow another enzyme called ligase to join DNA strands together. the plasmid is then taken up by bacteria. 
  • the plasmid is known as a vector - something that carries a gene into another organism
  • the bacteria are now transgenic organs, theyre checked for the new gene using assaying techniques, then cloned ensuring large quantities of insulin are harvested
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More Enzymes in Action

Immobilising enzymes makes them easier to remove. a way to do this is encapsulate them in alginate beads (made by mixing the enzyme with alginate then dropping them into a calcium chloride soloution). Immobilised enzymes are still active and still speed up reactions. the advantages are that enzymes don't contaminate, and they can be used in continous flow processing

Immobilised enzymes can be used to make lactose-free milk. the sugar lactose is found in milk and yohgurt. the enzyme lactase breaks it down producing glucose and galactose which are then absorbed into the blood. people who dont have this enzyme in them can't break down milk and ferment it, causing abdominal pain, diarrhoea and wind. this is called lactose intolerant. immobilised lactase breaks down lactose into glucose and galactose and is put into lactose-free milk. this is made using the continous flow method, milk is run through a column of immobilised lactase, the enzymes then convert lactose into glucose and galactose but only the products come out, enzymes stay inside. 

Immobilised enzymes are also used in reagent *****s. a drop of blood from a finger ***** is added to the *****, the enzymes in the ***** cause it to change to different colours depending on the glucose concentration, the colour is then compared to a chart indicating blood sugar

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DNA fingerprinting

DNA is unique unless your an identical twin. DNA fingerprinting compared DNA samples, it's used in forensic science in crime scenes to find a suspect (using Hair, Fingerprints, skin flakes, Blood, Semen) and also for paternity tests. some people want everyones fingerprints to be stored on a database to find criminals easier, but other think it's an invasion of privacy. also data can be misinterpreted. How it works:

  • extract DNA from cells in the sample
  • restriciton enzymes cut DNA into fragments, they cut in every place where they recognise a peticular order of Bases, this is the area the everyones DNA will be different
  • if the DNA sample contains that little section of bases lots of times, then it will be cut into lots of little bits. if it only contains it a few times, it will be left in bigger bits
  • the DNA bits that have been cut are seperated out using a process called electrophoresis. fragments are suspended in a gel and an electrical current is passed through the gel, DNA is negativley chargedso moves towards the positive anode. small bits travel faster than big bits so will be further through the gel
  • The DNA is tagged with a radioactive probe then it's placed onto photographic film. the film goes dark where radioactivity is, revealing the positions of DNA fragments. 

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