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Biology · Respiration

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Biology · Edexcel Paper 2

Respiration

Cellular Respiration and Aerobic Respiration

Respiration is the exothermic reaction in every living cell that releases the energy in glucose for metabolic processes.

  • Respiration A series of chemical reactions in living cells that releases energy from nutrient molecules such as glucose.
  • Aerobic respiration Respiration that uses oxygen to break glucose down completely into carbon dioxide and water, releasing energy.
  • Exothermic reaction A reaction that transfers energy to the surroundings, usually as heat.
A cell with a nucleus and mitochondria, with glucose and oxygen going in, carbon dioxide and water coming out and energy released from a mitochondrion.
Glucose and oxygen go in; carbon dioxide, water and energy come out.

Respiration and photosynthesis compared

  • Respiration An exothermic reaction that releases energy; Uses glucose and oxygen; Makes carbon dioxide and water
  • Photosynthesis An endothermic reaction that takes in light energy; Uses carbon dioxide and water; Makes glucose and oxygen

From the air to the energy in a cell

  • Breathing in Air containing oxygen is drawn into the lungs as you inhale.
  • Gas exchange Oxygen diffuses from the alveoli into the blood in the capillaries.
  • Transport Red blood cells carry the oxygen.
  • Respiration In the mitochondria, glucose and oxygen react to release energy…

Anaerobic Respiration

Aerobic respiration releases far more energy from glucose, but anaerobic respiration works without oxygen and gives a quick burst of energy.

  • Anaerobic respiration The release of energy from glucose without using oxygen, which releases much less energy than aerobic respiration.
  • Lactic acid The product of anaerobic respiration in muscle cells, which causes muscle fatigue.
  • Oxygen debt The extra oxygen needed after vigorous exercise to break down the lactic acid that has built up.
A graph of oxygen uptake that rises during exercise to less than the oxygen needed, then stays above the resting level during recovery as the oxygen debt is repaid.
The shaded area shows the extra oxygen taken in after exercise to repay the oxygen debt.

Aerobic and anaerobic respiration compared

  • Aerobic respiration Needs oxygen; Glucose is broken down completely to carbon dioxide and water; Releases a large amount of energy from each glucose molecule
  • Anaerobic respiration Does not need oxygen; Releases much less energy from each glucose molecule; Takes place in the cytoplasm

Core Practical: Investigating the Rate of Respiration

A respirometer measures the oxygen used by living organisms: soda lime removes the carbon dioxide, so the drop moves as the oxygen is used up.

  • Respirometer Apparatus that measures the rate of respiration of organisms by the oxygen they take in.
  • Soda lime A chemical that absorbs carbon dioxide, so that only the oxygen used changes the volume of gas.
  • Capillary tube A very thin glass tube in which a drop of coloured liquid moves as the volume of gas changes.
A respirometer with seeds, cotton wool and soda lime in a boiling tube in a water bath, and a capillary tube with a drop of coloured liquid beside a ruler.
As the seeds use oxygen, the drop moves towards the tube.

Germinating seeds or small invertebrates

  • Germinating seeds Easy to weigh and to keep still; Must be germinating, because dry seeds respire very slowly; No animals are harmed, so there are few ethical issues
  • Small invertebrates such as woodlice or maggots Respire quickly, so the drop moves a long way in a few minutes; Must be handled gently and kept in the tube only briefly; Must not be overheated and must be returned unharmed

Method: the effect of temperature on respiration

  • Set up the tubes Put a layer of soda lime in the bottom of a boiling tube, add a plug of cotton wool.
  • Set up a control Make an identical tube but replace the seeds with glass beads of…
  • Set the temperature Stand both tubes in a water bath at the first temperature.
  • Add the drop Put a drop of coloured liquid into the open end of the capillary tube.