AQA GCSE Biology B2.4 Respiration

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B2.4.1 Aerobic Respiration

  • This is one of the most important enzyme-controlled processes in living things.
  • The digestive system, lungs and circulation all work to provide cells with glucose and oxygen needed for respiration.
  • Glucose + oxygen --> carbon dioxide + water + energy.
  • You can test that it's occured with the limewater test; it turns cloudy when carbon dioxide bubbles through it.
  • Mitochondria-tiny rod-shaped organelles found in almost all plant/animal cells, and most aerobic respiration reactions take place here. They have a folded inner membrane, increasing surface area for enzymes.
  • The number of mitochondria in a cell shows how active the cell is.
  • Respiration releases energy from food we eat so our cells can use it.
  • Cells need energy to carry out basic functions of life-they build up larger molecules from smaller molecules to make new cell material. A lot of energy released in respiration is used for this. E.g.: In plants, sugars, nitrates, etc, build up to make amino acids, which build up to make proteins.
  • A lot of the energy released in animals is used to make muscles contract.
  • Energy is also used to maintain body temperature.
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B2.4.2 The Effect of Exercise

  • Muscles need more energy to contract. They are made up of protein fibres, which contain many mitchondria. Muscles also store gluose as the carbohydrate glycogen, which can be converted rapidly back to glucose to use during exercise.
  • When exercising, muscles contract faster and harder and need more glucose and oxygen and produce more carbon dioxide. The heart rate increases and arteries suppling blood to your muscles dilate-widen-, and these changes increases the supply of oxygen and glucose to muscles and the rate of carbon dioxide being removed.
  • Breathing rate also increases and you breathe deeper-more oxygen is brought into the body and eventually to exercising muscles.
  • Benifits of exercise-bother you heart and lungs become larger, developing a bigger and more efficient blood supply.
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B2.4.3 Anaerobic Respiration

  • This occurs when you exercise hard and your muscle cells become short of oxygen and your blood can't supply oxygen to the muscles fast enough, and so anareobic respiration is used, which doesn't need oxygen.
  • Glucose isn't broken down completely here, and produces lactic acid instead of carbon dioxide and water.
  • If you are fit, your heart and lungs will be able to keep a good supply of oxygen to your muscles while you exercise, and if you are unfit, your muscles run out of oxygen a lot sooner.
  • Glucose ---> lactic acid (+energy)
  • Build up of lactic acid causes muscle fatigue, which is when the muscle feels painful and stops contracting efficiently.
  • Anaerobic respiration isn't as efficient as aerobic respiration, as glucose isn't broken down properly and far less energy is released.
  • Oxygen debt: After exercising, you carry on panting for a while-the length of time this is depends on how fit you are.
  • Lactic acid is a problem as it can't be breathed out like carbon dioxide, so it has to be broken down with oxygen: Lactic acid + oxygen --> carbon dioxide + water.
  • The amount of oxygen needed to break down the lactic acid is the oxygen debt, which is why your heart and breathing rate stay high, to pay back this 'debt'.
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