GCSE Biology (OCR A)

Topic Summaries

Hormone regulation and waste excretion

Water balance and protein removal

  • If body cells gain or lose too much water by osmosis, they do not function efficiently. If body fluids become too dilute, cells can swell and burst as they take up more water by osmosis. If body fluids are too concentrated, cells can shrink as more water leaves by osmosis.
  • Uncontrollable water loss can occur via the lungs during exhalation or as water, ions, and urea are lost from the skin in sweat.
  • The controlled removal of excess water (to maintain water balance), ions and urea takes place in the kidneys, which produce urine and maintain the water balance.
  • The digestion of proteins from the diet results in excess amino acids.
  • In the liver, excess amino acids are deaminated to form ammonia, which is toxic, so it is converted into urea which travels via plasma to the kidney for excretion

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