Biology B6

Ocr, Gateway B6

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Bacteria cells compared to animal cells

  • Bacterial cells don't have a proper nucleus
    • they have bacterial DNA to control the cells activities and replication
  • Don't have mitochondria, chloroplasts or a vacuole
  • They have a cell wall to keep shape and stop bursting
    • not the same as plant cell though
  • sometimes have flagellum (tail) to help them move
  • come in 4 shapes: rods (bacilli), curved rods, spheres (cocci), spirals (spirilla)
  • can consume a huge range of organic nutrients from their surroundings- provides them with energy
  • means they can survive anywhere- in soil, water, air, in the house, human body and food
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Reproduction in Bacteria

Bacteria reproduce by Asexual reproduction

  • they are clones of each other
  • reproduce by binary fission
  • reproduce very quickly, if disease causing bacteria enter your body they can reproduce and cause disease before your body has a chance to respond
  • can reproduce faster in certain conditions
    • when its warm they have good source of nutrients
    • this is why its important to store food properly
    • food in the fridge means that it slows down the reproduction of bacteria as it is cold
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Making Yoghurt

  • Equipment is sterilised to kill off unwanted micro-organisms
  • The milk is pasteurised (heated up to 72'C for 15 seconds)- to kill off micro-organisms, the milk is cooled
  • A starter culture is added
  • The mixture is incubated (heated to about 40'c) in a vessel called a fermenter
    • the bacteria ferment the lactose sugar in the milk into lactic acid
    • lactic acid causes the milk to clot and solidify
  • A sample is taken to check its the right consistency
  • The flavours and colours are sometimes added
  • yoghurt is packaged
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Micro-organisms and disease

Micro-organisms that cause disease are called pathogens

Bacteria cause tuberculosis, septic wounds, cholera and food poisoning

  • food poisoning often caused by salmonelle or E.coli, get infected by eating the contaminated food
  • cholera is caused by vibrio cholerae, infected by drinking water contaminated with sewage

Viruses cause influenze (flu), chicken pox and smallpox

  • infected by inhaling airborne viruses, spread when people cough or sneeze

Fungi cause athlete's foot

Protozoa cause malaria and dysentery

  • dysentery is often caused by Entamoeba, infected by drinking water
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Stages of an infectious disease

1. micro-organism gets in to the body, 4 main ways:

  • nose- airborne micro-organisms
  • mouth- contaminated food and water
  • skin- cuts, insect bites, infected needles
  • sexual contact

2. when its in the body it reproduces rapidly

3. micro-organisms produce toxins which damage cells and tissues

4. toxins cause symptoms of infection

Exposure time to the micro-organism and the development of symptoms= incubation period

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  • good sanitation and public health measures are linked to a low incidence of disease:
    • clean water supply, good sewage works, public health education and clean hospitals to prevent spread of disease
  • poor sanitation: linked with high incidence of disease
    • e.g. a high incidence of food poisoning, dysentery and cholera might be caused by a lack of clean water or a broken sewage system
  • A high incidence of septicaemia might be caused by poor hygiene in hospitals and lack of education about cleaning cuts
  • developing countries are less likely to be able to afford good sanitation and public health measures
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Diseases and natural disasters

Disease often spread quicker after natural disasters

  • some disasters damage sewage systems and water supplies- contaminated drinking water supplies
  • transport systems can be damaged- difficult for medical services to reach
  • electricity supplies damaged- food goes off quickly because refrigerators can't work
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Antiseptics and Antibiotics

  • Antiseptics and Antibiotics are chemicals that destroy bacteria or stop them growing
  • antiseptics are used outside the body,
    • clean wounds and surfaces,
    • used to prevent infection
  • Antibiotics are drugs inside the body,
    • pill or injected, 
    • used to treat patients who are already infected
    • only kill bacteria
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Louis Paster (1822-1895)

came up with the germ theory of disease

He carried out experiments to prove the theory that there are microbes in the air which cause disease an decomposition, this experiments were:

  • heated broth in two flasks, both were left open to the air, one had a curved neck so the bacteria would settle in the loop and not get to the broth
  • the broth in the flask with the curved neck stayed fresh, proving it was air that made it go off
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Joseph Lister (1827-1912)

was the first doctor to use antiseptics in surgery

  • when he started hospital conditions were unhygienic
  • Lister's observation of wounds led him to think sepsis was a type of decomposition and he knew about paster's work on microbes in air, so he needed to kill the microbes that were getting into wounds
  • he began to treat and dress wounds using antiseptic carbolic acid, this killed bacteria and prevented sepsis
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Alexander Flemming(1881-1955)

discovered the antibiotic penicillin

  • flemming was clearing out some plates containing bacteria, he noticed that one of the plates also had mould on and the area around the mould was free of bacteria
  • he concluded that the mould must be producing a substance that killed the bacteria- penicillin
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Yeast is a type of fungus

It reproduces asexually by a process called budding

  • a bulge forms on part of the cell and it eventually becomes a daughter cell, identical to the parent
  • can be easily be stored in a dry condition

Yeast can respire aerobically or anaerobically

  • anaerobically- produces ethanol, carbon dioxide and energy- fermentation
  • glucose (C6H12O6)---->Ethanol (2C2H5OH) + carbon dioxide (2CO2)
  • aerobic- produces more energy (glucose+oxygen--->carbon dioxide + water)
  • whether yeast respires aerobically or anaerobically depends on whether there is oxygen present
    • oxygen present= aerobically
    • oxygen runs out- anaerobic respiration
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Yeasts growth rate

Depends on the conditions

  • reproduces faster when its warmer (growth rate doubles for every 10'c rise) but if its too hot the yeast dies
  • The more food there is the faster the yeast reproduces
  • Build-up of toxic waste products e.g. ethanol, slows down production
  • The pH has to be just right- too high or too low slows down reproduction

Waste water can be cleaned up with yeast

  • food processing factories need to get rid of sugary water (can't be released into waterways as would cause pollution, bacteria would overfeed, reproduce quickly use up all the oxygen and fish would die)
  • yeast is used to treat the contaminated water
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Yeast for brewing Beer and Wine- preperation

1. need to get sugar out the barley or grapes

  • beer- made from grain usually barley
  • barley grains are allowed to germinate for a few days, the starch grains are broken down into sugar by enzymes, grains dried in a kiln- malting
  • the malted grain is mashed up and water is added to produce sugary solution with lots of bits in- seived to remove bits
  • Hops are added to the mixture to give bitter flavour
  • wine- grapes are mashed and water is added
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The process

2. yeast is added and the mixture in incubated. the yeast ferments the sugar into alcohol, fermenting vessels are designed to stop unwanted micro-organisms and air getting in

  • rising concentration of alcohol in the fermentation is due to anaerobic respiration which eventually starts to kill the yeast, as yeast dies fermentation slows down
  • different species of yeast can tolerate different levels of alcohol

3, the beer and wine is drawn off through a tap, sometimes chemicals called clarifying agents are added to remove particles to make it clearer

4. the beer is pasteurised- heated to kill any yeast left in the beer and to stop fermentation, wine isn't pasteurised as it improves the taste, beer also tastes better if its unpasteurised and aged in the right conditions

the beer is the casked and the wine bottled

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Distillation increases the alcohol concentration:

  • This produces some spirits: cane sugar-> get rum, malted barley->whisky, fermented potatoes-> vodka
  • distillation is used to separate the alcohol out of the alcohol water solution thats produced by fermentation
  • fermentation products are heated to 78'C, the temperature at which alcohol boils and turns into vapour
  • the alcohol vapour rises and travels through a cooled tube which causes it to condense back into liquid alcohol and run down the tube into a collecting vessel
  • alcohol can only be distilled on licensed premises
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Biogas is made mainly of methane- 70% methane, 30% carbon dioxide

  • Biogas containing more than 50% methane burns easily but if it contains around 10% it is explosive
  • Biogas is made by bacteria in a digester, these bacteria are naturally found in marshes, septic tanks and animal digestive systems

Biogas can be used as a fuel:

  • can be burned to turn a turbine which can be used to generate electricity
  • biogas can be burned to heat water and produce steam to heat central heating systems
  • can also be used as fuel for cars and buses
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Production of Biogas- anaerobic fermentation

biogas is made from plant waste and animal waste in a digester

several types of bacteria are used to produce biogas,

  • some decompose the organic matter and this produces waste,
  • another type decompose that waste,
  • till you get biogas- type of fermentation

biogas digesters need to be kept at a constant warm temperature (30-40'C)

  • this is the optimum temperature for the bacteria's respiration,
  • any cooler the bacteria won't produce biogas as fast,
  • any hotter bacteria will be killed-
  • also need anaerobic conditions
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Types of digester

2 types:

  • batch digester's:
    • make biogas in smaller batches,
    • manually loaded up with waste which is left to digest and the digested material is cleared away at the end of each session
  • continuous digester-
    •  make biogas all the time,
    • waste is continually fed in,
    •  biogas and digested material is continuously removed at a steady rate.
    • continuous digester used on large scale

simple biogas generator:

  • an inlet for waste material to be put in
  • outlet for digested material to be removed through
  • and outlet so the biogas can be piped where its needed
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advantages of living in water


  • plentiful supply of water- no danger of water shortage or dehydration
  • in water there is less variation in temperature
  • water provides support for plants and animals with no skeletal system
  • waste disposal is easier
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Disadvantages of living in water


  • more resistant to movement than air,have to use more energy
  • have to control the amount of water in their bodies, because the water an animal lives in has different concentration of solutes from the animal cells
    • if animal lived in salt water probably has a lower solute concentration- if wasn't able to regulate water then water molecules would leave by osmosis and it would shrivel up and die
    • if animal lived in fresh water, cells would probably have a higher solute concentration than the surrounding water- if wasn't able to regulate would take in too much water by osmosis and swell and burst
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regulation of water content

  • kidneys of fish are specially adapted to either salt-water or freshwater to ensure that the concentration remains constant
    • some fish move from salt water to freshwater and need further adaptations like salmon live in the sea but move to freshwater to breed- adjust their hormones to fit environment
  • single-celled organisms like amoebas only have a cell membrane between them and surrounding water have different method:
    • regulate water with a contractile vacuole which collects the water that diffuses by osmosis, vacuole then moves to the cell membrane and contracts to empty the water outside
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plankton are microscopic organisms that live in fresh and salt water:

  • phytoplankton are microscopic plants
  • zooplankton are microscopic animals

phytoplankton photosynthesise and are the main producers in aquatic food webs

can't move far by themselves so rely on water currents

phytoplankton populations usually increase between late spring and summer- algal bloom- increase is due to longer, sunnier days;

  • more light is available for photosynthesis and the energy is used for growth
  • temperatures increase, causing both photosynthesis and growth rates to increase

population of zooplankton also increases as have more to feed on, an increase in nitrates and phosphates cause algal blooms because have more nutrients

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Causes of water pollution

Fertilisers and sewage- eutrophication

  • fertilisers and sewage enter water adding extra nutrients, algal bloom, algea die, bacteria feed on dead algae using up all the oxyg in the water, organisms that need water die
  • indicator species show how polluted water is- clean, mayfly nymph, high level- blood worm, water louse, red tailed maggot

industrial chemicals and pesticides

  • water polluted by chemicals which are taken up by organisms at the bottom of the food chains and can't be broken down so are taken up by the organisms in the food chaiins, the concentration increases as it is transferred and organism at top may die

oil- spills from tanker accidents and oil from boat engines damage water life

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Enzymes are used in biological washing powder

  • some stains are caused by soluble chemicals and so they wash out easily with water but  some contain insoluble chemicals like starch, protein and fats 
  • non-biological washing powders contain chemicals that break up stains
  • biological washing powders contain a mixture of enzymes which break down the stubborn stains
    • carbohydrates (jam, chocolate), enzyme-amylase, product simple sugars
    • Lipids (fats) (butter, oil), enzyme-lipases, product fatty acid and glycerol
    • protein (blood, grass) enzyme- proteases, product- amino acids
  • biological washing powders need cooler washes so the enzymes are not denatured
  • enzymes work best at pH 7 
  • can buy special stain removers which are special solvents but some certain specific enzymes that will break down the steam
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Enzymes in medical products

  • Diabetes is diagnosed by the presence of sugar in the urine-
  • nowadays reagent strips are used- change colour if sugar present
  • test is based on sequence of enzyme reactions
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Enzymes in food industry

low calorie food

  • table sugar (sucrose) - what sweeten food with
  • food industry enzyme- invertase is used to break down sucrose into glucose and fructose- much sweeter than sucrose
  • means get the same level of sweetness but using less sugar so its low calorie

cheese- rennet is used to clot milk in first stages of food production

Juice extraction- pectinase is used in fruit juice extraction, it breaks down pectin causing cell to reduce its juice

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Immobilising Enzymes

  • many industrial processes are immobilised enzymes, which don't need to be separated out from the mixture after the reaction has taken place
  • Immobilised enzymes are attached to an insoluble material e.g. fibres or silica gel. or they are encapsulated in alginate beads
  • the immobilised enzymes are still active and still help speed up reactions

advantages of immobilising enzymes:

  • the insoluble material with attached enzymes can be washed and reused
  • enzymes don't contaminate the product
  • immobilised enzymes are often more stable and less likely to denature at high temperatures or extremes of pH
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immobilised enzymes in Lactose-free milk

The sugar lactose is naturally found in milk and is broken down in the digestive system by enzyme lactase, produces glucose and galactose

  • some people lack the enzyme lactase, if they drink milk the lactose can't be broken down and gut bacteria feed on it causing diarrhoea and abdominal pain
  • cats are lactose intolerant
  • lactose-free milk can be produced using immobilised lactase
  • A method called continuous flow processing is used:
    • the substrate solution (milk) is run through a column of immobilised enzymes
    • the enzymes convert the substrate into the products but only the products emerge from the column. enzymes remain in the column
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Immobilised Enzymes are used in Reagent Strips

Diabetics use reagent *****s to measure their blood glucose concentration on a daily basis as they are quick and easy to use

there are immobilised enzymes on the reagent *****s

A drop of blood from a finger ***** is added to the *****, the enzymes in the ***** cause it to change different colours depending on the glucose concentration

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Transfer of Genes

Genes from one organism with often work with another one

Genetic engineering alters the genetic code of an organism. a gene giving a desirable characteristic is removed form one organism and inserted into another

The genetically modified organism is called a transgenic organism

The two main uses of genetic engineering are to produce medicines and to produce better crops

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Human Insulin

Put human insulin gene into bacteria so the bacteria can make human insulin

  • scientists identify the gene which controls the production of human insulin. They remove it from the DNA of the human cell by 'cutting it out with restriction enzymes
  • a loop of bacterial DNA (plasmid) is then prepared for the insulin gene to be inserted. Enzymes are used to cut open the plasmid
  • The insulin gene is inserted in the plasmid. Another enzyme called ligase is used to join inserted gene into bacterial DNA
  • The bacteria are checked using assaying techniques to make sure they contain the new gene
  • the bacteria are then cultivated to produce millions of identical bacteria, all making human insulin
  • This can be done on an industrial scale and the insulin can be separated out
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genetically modified crops

some plants are naturally resistant to disease and weedkillers.

  • the genes that cause resistance can be removed and inserted into commercial plants- creating new disease resistant plants

plants can be engineered to grow in poor conditions

production of crops can be increased by genetically engineering them to grow faster and bigger

plants can be genetically modified to be more nutritious as food e.g. GM rice contains a chemical which humans can turn into vitamin A

Genetically engineered strains of plants such as soya beans, maize and cotton are already grown in many countries

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Advantages and disadvantages


  • increase crop yield- cheaper food
  • places with poor farming conditions can grow crops
  • crops can be made more nutritious


  • unexpected harmful effects
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Thank you so much! All your Science revision cards have really helped me break down information, and understand it too! :-)

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