GCSE AQA Biology 3(ii)

GCSE AQA Separate Science Biology 2011

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Food and Drink from Microorgansims

The theory of biogenesis has been developed over the years

  • People used to think that life could spontaneously generate from non-living material.
  • But then evidence showed that this couldn't be the case. The evidence supported the theory that living things are created from other living organisms; this is the theory of biogenesis.
  • The accepted theory was changed to fit teh available evidence.
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Lazzaro Spallanzani

Before 1765 it was believed that substances in food were changed into microbes, which caused the food to go off.

A scientist called Lazzaro Spallanzani boiled two sets of broth to kill the microbes, then sealed one flask and left the other open. Only the open one went off; although the broth in the sealed flask did go off when it was left open later.

This showed that microbes got into the food from the air, but oppenents just thought that it meant air from outside the flask was necessary to start the change.

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Theodor Schwann

The theory that 'fresh' air caused substances in food to change into microbes was disproved by Theodor Schwann in 1837. He showed that meat would not go off in air, provided that air was heated first to kill microorganisms.

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Louis Pasteur

A more conclusive experiment was carried out by the famous scientist Louis Pasteur in 1859.

He heated broth in two flasks, both of which were left in the open to the air. However, one of the flasks has a curved neck so that bacteria in the air would settle in the loop, and not get through to the broth.

The broth in the flask with the curved neck stayed fresh, proving that it was the microbes and not the air causing it to go off.

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Most Cheese is Made Using Bacteria...

1. A culture of bacteria is added to milk

2. The bacteria produce solid curds in the milk

3. The curds are separated from the liquid whey

4. More bacteria are sometimes added to the curds, and the whole lot is left to ripen for a while

5. Moulds are added to give blue cheese its colour and taste

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Yoghurt is Made Using Bacteria Too

Bacteria are used to clot milk during the manufacture of yoghurt.

1. The milk is often heat trated first to kill off any bacteria that may be in it, then cooled.

2. A starter culture of bacteria is then added. The bacteria ferment the lactose sugar, present in the milk, to lactic acid.

3. The acid causes the milk to clot and solidify into yoghurt

4. Sterilised flavours are sometimes then added

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Using Yeast

Yeast is a single-celled Fungus

Yeast is a microorgansim.

A yeast cell has a nucleus, cytoplasm, a vacuole, and a cell membrane surrounded by a cell wall.

Yeast can respire with or without oxygen

  • Anaerobic respiration, without oxygen, of glucose by yeast is a process called fermentation
  • Yeast can also respire aerobically, with oxygen. This produced much more energy, and is needed to grow and reproduce.
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Yeast is Used to Make Bread and Alcohol

Bread: 1. Yeast is used in dough to produce nice, light bread

2. The yeast converts sugars to carbon dioxide and some ethanol. It is the carbon dioxide that makes the bread rise

3. As the carbon dioxide expands, it gets trapped in the dough, making it lighter

Beer: 1.Beer is made from grain; usually barely

2. The barley grains are allowed to germinate for a few days, during which the starch in the grains is broken down into sugar by enzymes. then the grains are dried in a kiln. This process is called malting

3. The malted grain is mashed up and water is added to produce a sugary solution with lots of bits in it. this is then sieved to remove the bits.

4. Hops are added to the mixture to give the beer its bitter flavour

5. The sugary solution is then fermented by yeast, turning the sugar into alcohol.

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Microorganisms in Industry

Microorgansims are grown in fermenters on a large scale

A fermenter is a big container full of liquid culture medium which microorganisms can grow and reproduce in. The fermenter needs to give the microorgansims the conditions they need toi grow and produce their useful product.

1. Food is provided in the liquid culture meduim. More can be pumped if needed. Then air is piped in to supply oxygen to the microorganisms.

2. The microorganisms need to be kept at the right temperature. The microorganisms produce heat by respiration, so the fermenters must be cooled. This is usually done with water in a water-cooled jacket. The temperature is monitored by instruments.

3. The right pH is needed for the microorgansims to thrive. Instruments will monitor this.

4. Sterile conditions are needed to prevent contamination from other microorganisms.

5. The microorganisms need to be kept from sinking to the bottom. A motorised stirrer keeps them moving around and maintains an even temperature.

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Mycoprotein; Food From Fermenters

  • Mycroprotein means protein from fungi. it is a type of single-celled protein.
  • Mycroprotein is used to make meat substitures for vegetarian meals like Quorn.
  • A fungus called Fusarium is the main source of mycoprotein.
  • The fungus is grown in fermenters, using glucose syrup as food. The glucose syrup is obtained by digesting maize starch with enzymes.
  • The fungus respires areobicallty, so oxygen is supplied, together with nitrogen, as ammonia, and other minerals.
  • It's improtant to prevent other microorganisms growing in the fermenter. So the fermenter is initially sterilised using steam. The incoming nutrients are heat sterilised and the air supply is filtered.
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Penicillin is Made by Growing Mould in Fermenters

Penicillin is an antibiotic made by growing the mould Penicillium chrysogenum in a fermenter.

The mould is grown in a liquid culture medium containing sugar and other nutrients

The sugar is used up as the mould grows

the mould only starts to make penicillin after using up most of the nutrients for growth.

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Fuels from Microorganisms

Fuels cans be made by fermentation

  • Fuels can be made by fermentation of natural products; luckily enough, waste products can often be used.
  • Fermentation is when bacteria or yeast break sugars down by anaerobic respiration.

Ethanol is Made by Anaerobic Fermentation of Sugar

  • Yeast make ethanol when they break down glucose by anaerobic respiration
  • Sugar cane juices can be used, or glucose can be derived from maize starch by the action of carbohydrase
  • The ethanol is distilled to separate it from the yeast and remaining glucose before it's used
  • In some countries, cars are adapted to run on a mixture of ethanol and petrol; this is knwo as 'gasohol'.
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Biogas

  • Biogas is usually about 70% methane and 30% carbon dioxide
  • Lots of different microorganisms are used to produce biogas. They ferment plant and animal waste, which contains carbohydrates. Sludge waste from sewage works or sugar factories, is used to make biogas on a large scale
  • It's made in a simple fermenter called a digester or generator
  • Biogas generators need to be kept at a constant temperature to keep the microorganisms respiring away
  • There are two types of biogas generators - bath generators and continuous generators
  • Biogas can't be stored as a liquid, so it has to be used straight away.
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Fuel Production Can Happen on a Large or Small Sca

Large Scale biogas generators are now being set up in a number of countries. Also, in some countries, small biogas generators are used to make enough gas for a villiage or a family to use in their cooking toves and for heating and lighting.

Human waste, waste from keeping pigs, and food waste can be digested by bacteria to produce biogas

By-products are used to fertilise crops and gardens

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Not All Biogas Generators Are the Same

There are two main types of biogas generators - batch generators and continuous generators

Batch generators make biogas in small batches. They're manually loaded up with waste, which is left to digest, and the by-products are cleared away at the end of each session

Continuous generators make biogas all the time. Waste is continuously fed in, and biogas is produced at a steady rate. Continuous generators are more suited to large-scale biogas projects

Whether the generator is continuous or batch, it needs to have:

1. an inlet for waste material to be put in

2. an outlet for the digested material to be removed through

3. an outlet so that the biogas can be piped to where it is needed

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Four Factors to Consider

When biogas generators are being designed, some factors need to be considered:

COST: continuous generators are more expensive than batch ones, because waste has to be mechanically pumped in and digested material mechanically removed all the time.

CONVENIENCE: Batch generators are less convenient because they have to be continuously loaded, emptied and cleaned.

EFFICIENCY: Gas is produced most quickly at about 35degrees C. If the temperature falls below this the gas production will be slower. Generators in some areas will need to be insulated or kept warm. The generator shouldn't have any leaks or gas will be lost.

POSITION: The waste will smell during delivery, so generators should be sited away from homes. The generatore is also best located fairly close to the waste source

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Using Biofuels Has Economics and Environmental Eff

Biofuels are a 'greener' alternitive to fossil fuels. The carbon dioxide released into the atmosphere was taken in by plants which lived recently, so they're 'carbon neutral'.

The use of biofuels doesn't produce significant amounts of sulfur dioxide or nitrous oxides, which causes acid rain.

Methane is a greenhouse gas and is one of those responsible for global warming. It's given off from untreated waste, which may be kept in farmyards or spread on agricultural land as fertiliser. Burning it as biogas means it is not released into the atmosphere.

The raw material is cheap and readily available.

The digested material is a better fertiliser than undigested dung - so people can buy more crops

In some developing rural communities women have to spend hours each day collecting wood for fuel, biogas saves them this drudgery.

Biogas generators act as a waste disposal system, getting rid of human and animal waste that'd otherwise lie around, causing disease and polluting water supplies

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Using Microorgansims Safely

Microorganisms can be grown in a lab, but they need certain conditions to flourish. Also, precautions need to be take to stop unwanted microorganisms growing as well.

Microorganisms are grown on agar jelly in a petri dish.

They need carbohydrates as an energy source, plus mineral ions and sometimes supplementary proteins and vitamins.

These nutrients are usually added to the agar jelly.

Agar jelly can be poured when hot, and sets when cold. It's poured into shallow round plastic dishes called petri dishes.

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Equipment is Sterilised to Prevent Contamination

if equipment isn't sterilised, unwanted microorgansims in the growth medium will grow and contaminate the end product.

The unwanted microorgansims might make harmful substances, or cause disease.

Petri dishes and the growth medium must be sterilised before use.

Inoculating loops (used for transferring microorganisms to the growth medium) are sterilised by passing them through a flmae.

The petri dish must have a lid to stop any microorganisms in the air contaminating the culture. The lid should be taped on.

The temperature must be kept fairly low in school labs!

In the lab at school, cultures of microorgansims are kept at about 25degrees. Harmful pathogens (microogranisms that cause disease) aren't likely to grow at this temperature. In industrial conditions, cultures are incubated at higher temperatures so that they can grow a lot faster.

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