human waste

• EXCRETION

  • removal of the waste substances of metabolic reactions, toxic materials and substances in excess of requirements

  1. Carbon dioxide & water - aerobic respiration in cells
  2. Urea - breakdown of excess proteins (amino acids) in the liver
  3. Other substances in excess such as medical drugs (e.g.antibiotics) and dietary minerals (e.g. sodium)
• DANGER OF BUILD UP

  • Toxicity: in high concentrations eg CO2 dissolves in water -> acidic solution = lower the pH of cells -> reduce enzyme activity for metabolic reactions
  • Osmotic effect: body fluids can become more concentrated (hypertonic) due to higher amounts of waste products which can cause water to move out of cells, changing their water potential (crenation) and preventing them from carrying out essential reactions
  • storage: space within an organism is limited and is required for the storage of more useful molecules
• EXCRETORY ORGANS

  • kidneys: urea, water, mineral ions
  • lungs: CO2, water
  • skin: excess mineral ions (e.g. sodium), water
  • liver: breakdown of proteins (amino acids) into urea