Excretion in Plants: Transpiration and Excretory Products

All living organisms sustain life, they undergo different processes to maintain and regulate their daily activities. Plants have a different mode of life. Green plants collect CO2 from the atmosphere and utilize it for the process of photosynthesis which is the metabolic waste product of respiration.

Elimination of toxic and harmful waste products from the body is called excretion. Plants produce a different type of waste they do not produce nitrogenous wastes like urea and uric acid because extra amino acids and nucleotides are not formed in the body of plants. They produce other types of waste products which are called secondary metabolites, e.g., alkaloids, tannins, aromatic oils.

Mechanism of Excretion in Plants

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Plants do not have any kind of process or mechanism to collect, transport and throw out their waste products. They have adopted varied strategies to protect their living cells from waste products and excrete waste and harmful substances from their body.

Simple, small plants excrete wastes over the surfaces of their cells mainly through leaves. Larger, vascular plants have developed different methods of excretion which involve the leaf as an excretory organ. In large vascular plants, the internal cells of the plant have no access to the outside environment so leaves play an important role in the process of Excretion. Like the cells of animals, they collect wastes at a particular part of the body and secrete their wastes into the intercellular spaces. Plants wastes are slightly different from the wastes produced by animals, plants produce oxygen as the main gaseous waste product.

Plant wastes are slightly different from animal wastes in that oxygen is the main gaseous waste product. To get rid of this oxygen, and bring in fresh carbon dioxide, plants rely on a series of openings of the small pores like structures present in the leaves, called a stoma. Through these stoma waste products can be eliminated from the plants. Also crucial in this process are the xylem and phloem, tissues within plants that allow water, sugar, and minerals to be transported around the plant. When the stomata are open, gas exchange into oxygen and excretion take place. The cells from all over the plant dump their wastes into the water travelling to the leaves, which is then cast out through the stoma.

Plants Organs involved in Excretion

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Old Leaves: Waste products are stored in the leaves which get older which soon fall off from the tree along with the waste products.

Old Xylem: Resins, gums, tannins and other waste products are deposited in the old xylem which soon becomes non-functional e.g., Hardwood.

Bark: Bark consists of dead cells which are peeled off periodically by the large trees. Tannins and other wastes are deposited in the bark of the trees. Incidentally, tannins are the raw material that is used for making dyes and inks.

Central Vacuole: Most plant waste products are stored in the central vacuole of their cells. They are unable to influence the working of cytoplasm due to the presence of a selectively permeable membrane called tonoplast.

Root Excretion: Some waste substances are excreted by the plants in the region of their roots.

Detoxification: The toxic oxalic acid is detoxified by the formation of calcium oxalate which gets crystallized into needles (raphides), prisms (prismatic crystals), stars (sphaeraphides) and crystal sand. When the calcium in plants gets excess is gets precipitated in crystals of calcium carbonate, e.g., cystolith.

Salt Glands: Plants excretes excess salts obtained from the habitat. 

Excretory Product

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The main products excreted by plants are:

1. Carbon dioxide and oxygen: Carbon dioxide is formed as a result of respiration. As a result of photosynthesis, oxygen is formed and secreted out with the help of leaves.
2. Excess water: It is excreted through stomata and the process is known as transpiration.
3. Excessive salts: When there is a high level of salts present in water or the soil and plants absorb these salts, then these usually excreted by plants which deposited in plants in the form of crystals.
4. Nitrogenous Waste Products: They are byproducts of general metabolism. There are some common nitrogenous waste products like alkaloids, e.g., quinine, morphine, atropine. This process is also known as Diffusion 
5. Organic Acids: They are metabolic intermediates. Some of them are without any other use. Rather some organic acids on accumulation, they may and become harmful and prove toxic, e.g., oxalic acid.
6. Tannins: They are complex aromatic compounds that are formed as secondary metabolites.
7. Latex: Latex is a milky white liquid or fluid produced by flowering plants such as rubber plants. It is an emulsion of various compositions and is excreted by special tubular cells which are known as laticifers
8. Resins: As a result of oxidation there are several products of aromatic oils are formed which are called Resins.
9. Gums: They are degradation products of cell walls.

Importance of Excretion in Plants 

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Excretion plays an important role to help and regulate the process of metabolism in plants. Excretion is an important part of osmoregulation or an organism’s attempts at controlling the environment within its cells. Osmoregulation is important for several reasons, mainly that the biochemical reactions needed for life to occur require precise conditions. Without the proper acidity and concentration of molecules, certain reactions like DNA synthesis and ATP production could not occur. Further, substances like ammonia (a by-product of the breakdown of amino acids), can be toxic to cells.