AQA GCSE Biology Unit 3 Revision Cards

Topics covered:

  • anaerobic respiration
  • aerobic respiration
  • yeast
  • bread making
  • beer making (malting)
  • wine making (malting)
  • yoghurt making
  • cheese making

Anaerobic Respiration

·         when exercising for long periods of time, not even an increase in breathing and/or heart rate does not supply efficient oxygen

·         definition: respiration that does not involve oxygen/incomplete breakdown of glucose

·         releases a little bit of energy very quickly

·         glucose = lactic acid and energy

·         lactic acid has to be broken down into carbon dioxide and water, requires oxygen

·         oxygen debt- this is why heart rate is so high after exercise

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Aerobic Respiration

·         glucose combines with oxygen inside a living cell, releases energy

·         efficient method of creating energy

·         produces energy slower, but releases more

·         occurs for day-to-day activities

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·         single celled organisms with a nucleus, cytoplasm and membrane surrounded by a cell wall

·         reproduce asexually (budding)

·         aerobic respiration – water and carbon dioxide

·         anaerobic respiration (fermentation) – ethanol and carbon dioxide

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Making Bread

·         yeast grows and respires – produces carbon dioxide [causes bread to rise]

·         gas bubbles expand due to high temperature, giving bread light, wafery texture

·         all yeast cells are killed by the heat in the cooking process

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Making Beer

·         malting – barley grains soaked in water to keep them warm

·         germination begins – enzymes break down starch in grains into sugary solution

·         solution extracted then used as energy source for yeast

·         yeast + sugar mixture is fermented to give alcohol – hops often added to give drink a flavour

·         beer left to settle, clear and develop a flavour

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Making Wine

·         uses natural sugars, e.g. grapes, for yeast’s energy source

·         grapes pressed for their juices, then mixed with yeast and water

·         yeast left to respire anaerobically until all sugar is used

·         wine filtered to remove yeast then stored in bottles to mature

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Making Yoghurt

Old method

·         fermenting whole milk

New method

·         adding a culture of right type of bacteria to warm milk

·         keep mixture warm so bacteria can reproduce, grow and ferment

·         as bacteria break down lactose, lactic acid is produced [gives yoghurt sharp, tangy taste, lactic fermentation]

·         lactic acid causes milk to clot and solidify to create yoghurt

·         further bacterial action gives yoghurt creamy texture

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Making Cheese

·         same first three steps as yoghurt making

·         different type of bacteria is added, creates more lactic acid [extends solid parts (curds) that solidify almost completely]

·         enzymes added to help separate milk when completely curdled [whey also created]

·         curds used to make cheeses [whey used as animal feed]

·         curd mixed with other bacteria and moulds, left to dry out

·         bacteria and moulds added at this stage affect final texture and flavour [also on how much they ripen]

·         ripening may take months or years depending on cheese made

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