Life Processes

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Organisms get rid of gaseous wastes generated during photosynthesis or respiration. Other metabolic activities generate nitrogenous materials which need to be removed. The biological process involved in the removal of these harmful metabolic wastes from the body is called excretion.

The excretory/urinary system consists of :

1. The kidneys: The excretory organ
2. The ureters: The ducts which drain out urine from the kidneys
3. The urinary bladder: The urinary reservoir
4. The urethra: The channel to the exterior

Plants have no special organs for removal of wastes. The waste products of respiration and photosynthesis are used as raw materials for each other. Oxygen gas produced as a by-product of photosynthesis is used up during respiration and carbon dioxide produced during respiration is used up during photosynthesis.

Excretion is carried out in the plants in the following ways:

1. The gaseous wastes, oxygen, carbon dioxide and water vapour are removed through stomata of leaves and lenticels of stems.
2. Some waste products collect in the leaves and bark of trees. When the leaves and bark are shed, the wastes are eliminated.
3. Some waste products are rendered harmless and then stored in the plant body as solid bodies. Raphides, tannins, resins, gum, rubber and essential oils are some such wastes.