Excretion

• Excretion is the removal of waste substances, toxic materials and substances in excess
• Waste products have toxic effects if allowed to reach high concentrations. For example, CO2 dissolves in water easily to form an acidic solution, this lowers pH of cells and therefore reduces activity of enzymes.
• Bodily fluids become more concentrated because of high amounts of waste products. Concentrated body fluids cause water to move out of cells by osmosis. Changes water potential and therefore preventing them from carrying out essential reactions
• Lungs - Excretion of CO2 and Water
• Skin - Excrete excess mineral ions and water
• Liver - Breakdown of proteins to urea
• Kidney - filters blood, removes waste products, controls water balance, controls blood pressure, controls pH
• Osmoregulation - Process of maintaining water and salt concentration
• Importance of Osmoregulation - Maintaining water levels is vital to prevent harmful water change to cells as a result of osmosis
• Cells have too much water - Swelling and lead to cell lysis
• Cells have too little water - Cells lose water, dehydrates, cell dies
• Two sources of water - Aerobic respiration and water in diet
• Water is lost - Lungs through exhalation, sweat and urine
• Waste substances - Urea, creatinine, ammonia, uric acid, excess salt/ions, excess water and excess hormones.