S.3 Bio. Excretion Notes Caltec S.3

1 CALTEC ACADEMY MAKERERE S3 BIOLOGY HOLIDAY PACKAGE EXCRETION AND OSMOREGULATION.. Excretion is the removal of waste products of metabolism from the body. Most of the waste products are toxic when allowed to accumulate in the body. Importance of excretion ™ To remove toxic waste products whose accumulation in the body poisons/ harms the organisms. ™ To remove excess materials in the body which when left to accumulate affects the body metabolism. Excretory products are divided into two groups i.e. 1. Nitrogenous excretory product s. These are excretory products, which contain the element nitrogen. They include ammonia, urea and uric acid. Ammonia: This is a highly toxic nitrogenous waste and it requires a lot of water for its elimination. It is very soluble in water and due to this it requires less energy to be excreted. Ammonia is excreted by organisms which live in fresh water and therefore have a lot of water in their bodies. Such organisms include bony fish, protozoans, and amphibians when in water, Urea: This is a less toxic nitrogenous waste. It requires less water for its excretion. It however requires a lot of energy for its excretion because of its low solubility in water compared to ammonia. Urea is excreted by terrestrial organisms, which have easy access to water, and marine organisms. Such organisms include terrestr ial mammals, amphibians when on land, cartilaginous fish, etc. Uric acid: This is less toxic than urea and requires no water for its elimination from the body. It is insoluble in water. The demerit of excreting uric acid is that it requir es a lot of energy for its excretion. Uric acid is excreted by birds, reptiles and insects and also common in desert animals. 2. Non nitrogenous excretory products. These are excretory substances that do not contain the …