Excretion

• Excretion in plants (waste products)

  - Oxygen

  - Carbon dioxide

  - Water/ vapour
• Light intensity effect on waste products in plant

  Light (day) = rate of photosynthesis is greater than rate of respiration. This means that the waste product will be oxygen

  
  

  No light (night) = rate of respiration is greater than rate of photosynthesis (as energy required from sunlight). This means that carbon dioxide will be the waste product.

  
  

  NET EFFECT
• Where does excess gas diffuse out of plant? How?


  Leaf organ - stomata - via DIFFUSION
• Plants - chemical substances as waste

  - plant cells break down molecules into chemical substances no longer required by plant.

  - some substances cannot be converted into useful compounds = MUST be REMOVED from plant --> stored in dying tissues (wilting leaves)
• Excretion in humans - organs involved


  Kidney - excretion of urea (even though it is made by the breakdown of excess protein by the LIVER) + water + excess salts

  
  

  Lungs - excretion of carbon dioxide + water (during exhalation carbon dioxide leaves lungs as a waste product of respiration)

  
  

  Skin - excretion of excess mineral ions (sodium) + water via SWEATING
• Need of excretion in humans

  Metabolic reactions take place within cells of organisms = waste products
• Excretion definition


  Removal of waste substances of metabolic reactions, toxic materials, and substances in excess of requirement
• Dangers of waste products in humans


  Can become toxic if waste products allowed to reach high concentrations

  1. CO2 = dissolves in water making acidic solution which can lower the pH of cells = reduce enzyme activity that are essential in metabolic reactions

  2. Osmotic effect = body fluid become more concentrated (higher waste) = causes water to leave cells (high concentration to low), preventing them from carrying out essential reactions (as water potential is changed)