AQA GCSE Further Biology: Microbiology

Simplified notes for the final unit of B3. I couldnt find any that covered it completely so I made my own ;')

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Single celled organism -  is a fungus!

Cell has:

  • nucleus
  • cytoplasm
  • vacuole
  • cell membrane
  • cell wall
  • nucleus containing DNA
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Aerobic and Anaerobic Respiration of Yeast

Yeast can respire with or without oxygen:

Aerobic Respiration

yeast + oxygen --> carbon dioxide + water

  • Necessary for yeast to grow and produce --> Produce more energy

Anaerobic Respiration (Known as Fermentation)

yeast --> carbon dioxide + ethanol (alcohol)

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Beer and Wine Making

Carbohydrates are used in the making of beer and wine = enerygy source for the yeast --> respiration

Beer Making:

  • Malting process - starch in barley grains broken down into sugar solution by enzymes (carbohydrase?) in germinating grains.
  • Sugar solution extracted and fermented.
  • Hops added to give flavour.


  • Use the natural sugars on the fruit as enerfy source for yeast.
  • Any fruit or vegetable can be used!

NB: The yeast will be poisoned if the concentration of ethanol exceeds 14%

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Yoghurt and Cheese Making

Yoghurt Making:

  • Starter bacteria added to warm milk
  • Bacteria ferments milk sugar -Lactose- to produce lactic acid.
  • Lactic acid causes the milk to clot and solidify to yoghurt.
  • Fruits and flavours can be added to give the yoghurt its taste.

Cheese Making:

  • Starter bacteria added to warm milk
  • Bacteria produces more lacic acid (than in yoghurt) and produces solid curds.
  • Curds are seperated from whey. (Whey can be used as animal feed)
  • Enzymes are added to speed up seperation process.
  • Mould and bacteria are added to give flavour.
  • The cheese is left to ripen. (The ripening time depends on the cheese being made)
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Growing Microorganisms on an Industrial Scale

Microorganisms are grown in large vessels called fermenters.

To control conditions, industrial fermenters have:

  • Air Supply -  sterilised air is provided for the microorganisms to respire aerobically.
  • Stirrer -  the content of the fermenter is stirred to provide an equal distribution of heat and nutrients for the microorganisms.
  • Water-Cooled Jacket - removes excess heat produced from the respiring microorganisms. Cold air is constantly pumped into the jacket.
  • Measuring instruments - moniter factors e.g pH, tempereture, so that changes are made accordingly.
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Phases of Bacterial Growth

(sorry couldn't insert the picture :( )

1) Lag Phase - the bacteria is starting to grow.

2) Exponential Phase - the bacteria is growing, doubling every twenty minutes.

3) Stationary Phase - growth slows and eventually stops.

4) Death Phase - the bacteria is dying faster than it is reproducing and doubling. 

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Conditions that may change the rate of growth

1) Food used up

2) Metabolism of bacteria causes rise in heat

3) Oxygen levels (respiration) falls

4) CO2 levels rise - change in pH

5) Waste products build up - poison bacteria

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  • Penicillin is grown from the mould Penicillim Notatum
  • Was discovered by Alexander Fleming
  • It was further developed and mass production method was developed by Howard Florey and Ernst Chain
  • A mould found on a melon was seen to have 200 times the yield of penicillin than that found by Fleming.
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Penicillin Process

  • The antibiotic is made by growing the mould (Penicillium) in a fermenter.
  • A sterilised medium of sugar, amino acids, mineral salts and other nutrients is added.
  • It is made by soaking corn in water.
  • The mould only starts producing the antibiotic after it had used up its nutrients (lag phase is about 40 hours).
  • The mould produces the antibiotic in aerobic respiration --> oxygen is needed.

To get the maximum yield of Penicillin:

  • In the first 40 hours, the mould is provided with enough food to grow.
  • Then, the supplies are limited so that the penicillin is produced.
  • Next 140 hours, the brith is removed regularly and small amounts of nutrients are added.
  • The is gives us the maximum yield of the antibiotic
  • It is then extracted and purified to be used as medicine
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The fungus Fusarium is ued to make mycoprotein.

Mycoprotein -  protein made from fungus

  • Grows and reproduces every 5 hours on cheep sugary syrup (made from waste carbohydrates)
  • Needs aerbic respiration
  • Fungal biomass is harvested, purified and flavours are added.

Can be used as a meat alternative:

  • High in protein, and low in fat.
  • High in fibre.
  • Low in calories
  • Versatile.
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  • Is a flammable gas made when bacteria breaks down plant and animal waste in anaerobic conditions
  • It is mainly methane but composition depends on waste added and bacteria present.
  • Plant and animal waste contain carbohydrates --> potentially enormous energy resources.

Bacteria in biogas works best at 30 degrees. Best suited to hot countries.

Reaction is exothermic. If heat is added at the beginning and generator is insulated --> can work anywhere.

Waste from the generator can be used as fertiliser.

On a small scale, biogas generators can supply enough energy to supply a family, a farm or even a small villiage.

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  • Main materials: waste vegetables, animal dung, human waste.
  • Excellent Fertiliser
  • Poor Quality biogas


  • Religious and culture taboos against using human waste
  • Cow and buffalo dung used
  • Less Fertiliser
  • Excellent Quality Biogas
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Ethanol as a fuel

Sugar Cane or Maize used.

  • If the sugar rich products of cane and maize fermented anaerobically --> broken down incompletely --> ethanol produced and extracted by distillation.

Sugar Cane -----------------> Ethanol


Maize ---------------------------.>Sugar--------------------> Ethanol

(Carbohydrase = starch --.> sugar)         (Fermentation)

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Advantages and Diadvantages of Ethanol as a Fuel


  • Effiecient
  • no toxic or greenhouse gases.
  • Can mix with conventional fuel -- reduces pollution a little
  • carbon neutral -- no overall increase in carbon dioxide levels in the atmosphere.


  • Takes a lot of plant material --> limited to countries with enough space and suitable climate to grow lots of plant material.
  • Methods of ethanol productions leaves large quantities of unused cellulose from plant material --> could find way of using it in the future.
  • When oil prices drop, can't subsidise with ethanol, still to expensive.
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Advantages and Disadvantages of Floating Drum biog

Used for small, medium family sized farms


  • Easy to construct
  • Easy to operate
  • Steady gas pressure produced
  • Reliable, well-tried tecnology


  • Metal gas holder relatively expensive.
  • Metal gas holder may rust.
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Advantages and Disadvantages of Fixed Drum biogas


  • Low initial cost
  • long useful life - no moving/rusting parts
  • well insulated


  • sealing of gas holder not always tight
  • gas pressure fluctuates
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Alshimaa A Elmasry

sorry, they say simplified...but they are really not!! Haha, my biology B3 exam is tomorrow!!

Star Pupils Tuition

Many thanks


this is really good, :)

Alshimaa A Elmasry

i have uploaded these onto my sister's account by accident!! I have no idea how to upload it onto mine, but my account is Miss_Jazz if anyone has queastions! :)

Alshimaa A Elmasry



A detailed set of revision cards that provide the right amount of technical detail needed for studying microbiology at GCSE. Team these up with a decent set of notes and some flashcards or a quiz for a  complete set of  revision resources.

هزل, يتبادل المزاح


هزل, يتبادل المزاح


هزل, يتبادل المزاح

It's strange how there are more cells in our brain than there are brains in our body


I'm well bad at bio, how do you get good?


Now, this is the story all about how
My life got flipped-turned upside down
And I'd like to take a minute, just sit right there
I'll tell you how I became the prince of a town called Bel Air

In West Philadelphia, born and raised
On the playground is where I spent most of my days
Chillin' out, maxin', relaxin' all cool
And all shootin' some B-ball outside of the school

When a couple of guys who were up to no good
Started makin' trouble in my neighborhood
I got in one little fight and my mom got scared
And said, "You're movin' with your aunty and uncle in Bel Air"

I begged and pleaded with her the other day
But she packed my suitcase and sent me on my way
She gave me a kiss and then she gave me my ticket
I put my Walkman on and said, "I might as well kick it!"

First class, yo this is bad
Drinkin' orange juice out of a champagne glass
Is this what the people of Bel Air are livin' like
Hmmm, this might be alright

But wait, I hear they're prissy, bourgeois and all that
Is this the type of place that they should send this cool cat?
I don't think so, I'll see when I get there
I hope they're prepared for the prince of Bel Air

Well, uh, the plane landed and when I came out
There was a dude look like a cop standin' wavin' my name out
I ain't tryin' to get arrested yet, I just got here
I sprang with the quickness like lightning, disappeared

I whistled for a cab and when it came near
The license plate said fresh and had a dice in the mirror
If anything I could say that this cab was rare
But I thought, nah forget it, yo home to Bel Air

I pulled up to the house about seven or eight
And I yelled to the cabby, "Yo homes, smell you later"
Looked at my kingdom, I was finally there
To sit on my throne as the prince of Bel Air


que the theme song d

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