Excretion in Plants | Excretion in Animals |

Excretion.

The elimination of wasteful metabolites, mainly the nitrogenous wastes from the body is called excretion. The carbohydrates and lipids are metabolized into CO₂ and H₂O. While the metabolism of proteins and nucleoproteins produces nitrogenous waste in different forms in different animals. The concentrated waste nitrogen is toxic in the cell. So it must be removed from the body by excretion. Excretion takes place in all the living things. It is one of the essential properties of the life.

Excretion in Plants

The plants have different mechanism of excretion. The plants produce following excretory products:

➤ Oxygen:

Oxygen is produced during photosynthesis.

➤ CO₂ and water

Carbon dioxide and water are produced during respiration as excretory products.

➤ Organic and inorganic compounds:

Plants also produce several organic and inorganic compounds. These compounds are stored for different purposes. They are removed when necessary. There different mechanism for the elimination of these wastes in plants likes stomata. Water is used for maintaining turgor in cell. The remaining water is lost through transpiration. Following structures are used for the removal of wastes in plants:

1. vacuoles:

Plants cells have large vacuoles. These vacuoles are used for storage of useful compounds and for the storage of waste substance.

2. Leaves:

Plants produces certain inorganic and organic wastes. These wastes are stored in different organs like leaves. These leaves fall off during autumn. In some cases, leaves die off, e. g. the leaves and stalk of certain bulb like blue bell. These leaves die and leave the bulb underground. This bulb grows next year. The falling leaves are good source of minerals. The gardeners use these rotten  autumn leaves as mineral source. The plants fall the yellow leaves in the autumn. It is a seasonal time for the plants to get rid of wastes. Thus leaves are also called excretophore. The colour of these falling leaves is not changed into yellow due to removal of chlorophyll. The microscopic examination of the autumn leaves show that these leaves have pigmented compounds and many toxic materials like heavy metals. These compounds give yellow colour to leaves. These compounds increase sharply with the yellowness of leaves.

3. Stems:

Some trees deposit strange chemicals in the structure like xylem in branches and trunks. These xylems are no longer used for water transport. This takes place in ebony. It produces very black wood in the centre. The plant physiologist considers that strange chemicals as waste materials.

4. Roots:

Some plants actively secrete waste compounds into the soil. Sometimes, they use these chemical as weapons against other competing plants e. g. conifers.

Excretion in Animals

The animals have several excretory products. These are:

1. Water:

Water is removed form the body in hypotonic environment. So it is a waste product in these conditions.

2. Salts:

Salts are removed from the body in hypertonic environment. So salts are excretory product for these animals.

3. Nitrogenous wastes:

The nitrogenous waste metabolites are chief excretory products. The catabolism of amino acid releases amino group (--NH₂) deamination. This amine group is not reused for the recycling of amino acid. Sometimes, this amine group may be reused by some other molecules. But mostly these amine compounds are removed from the body. The amine compounds are essentially dissolved in water and excreted from the body. Thus amine group does not make the plasma toxic. The rise of level of these compounds in the can cause convulsions coma or death. Mostly excess nitrogen are excreted in three forms:

➤ Ammonia

➤ Urea

➤ Uric acid

1. Ammonia:

Ammonia is kept as excretory product in those animals which live in hypotonic environment like fresh water. Ammonia is a very toxic substance. It dissolves quickly in the body fluid. Thus it must be kept in low concentration in the body. A large amount of water is required for . maintaining its low

concentration in the body. Water is also required to eliminate ammonia in the form of urine. This is possible only in a hypotonic environment. About 500 ml water is needed to excrete 1g of ammonia nitrogen. The animals secreting ammonia as excretory product are called ammonotelic.

2. Urea:

The animal living in low supply of water secrete urea. Ammonia cannot be kept as excretory product in low supply of water. So it is changed into less toxic substance like urea. Urea requires only 50 ml of water for its 1gram of nitrogen removal. Thus the excretory nitrogen is metalolically converted into urea by Urea cycle in the animals which live in low supply of water e. g. terrestrial animals. The animals secreting urea as their excretory products are called ureotelic.

3. Uric acid:

The animals living in acute  shortage of water produce uric acid. Uric acid is excreted with minimum amount of water. Only 1ml of water is required to eliminate 1gram of nitrogen in the form of uric acid. The reptiles and birds live in arid conditions. So they excrete ureic acid as excretory product. The animals secreting uric acid as their waste product are called uricotelic.

Ureotely and uricotely are evolutionary adaptations for nitrogenous wastes in their habitats. The animals have adapted themselves chemically to these habitats. They also show various adaptations and produce diversity in excretory structures.