Excretion in Plants: Transpiration and Excretory Products

Did you know that like animals, plants also excrete waste? Isn't this surprising? Excretion is a catabolic process that eliminates toxic and waste products from an organism's body. Unlike animals, plants lack highly developed, advanced and specialized excretory systems.

Excretion is one of the important biological processes occurring regularly in both plants and animals, which is essential for healthy and disease free life. Plants have no excretory organs. As a result, excretion in plants occurs in a simpler and easier manner. In this article, we will discuss excretion in plants in more detail along with its types and the excretory products released during the process.

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Excretion in Plants

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Excretion in plants is the process by which metabolic waste from a plant is eliminated. Some plants store excretory products such as resins, gums, latex, oils, and so on in their stems, leaves, and bark. Energy is required for living organisms to perform cellular activities. The energy is derived from the breakdown of food during respiration.

• Carbon (IV) oxide is a by-product of respiration that must be removed because its accumulation in cells is harmful.
• Green plants use carbon (Iv) oxide as a raw material for photosynthesis and produce oxygen as a by-product.
• Plants are not generally thought to have special mechanism for eliminating wastes.
• In the presence of light, green plants produce oxygen, which diffuses out through stomata or through the cell walls of roots.
• Excess water exits through similar channels and is eliminated through guttation means droplet exudation and transpiration.
• As respiratory waste products, green plants kept in the dark room or plants lacking chlorophyll produce carbon dioxide and water.
• Resins, saps, and latex secreted by some plants are forced from the plant's interior by hydrostatic pressures and absorptive forces of plant cells.
• These are passive forces, and exudation necessitates no energy expenditure on the part of the plant.

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Types of Excretion in Plants

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Although excretion in plants is not as complex as that in animals, plants involve several mechanisms to eliminate waste. All the important forms of excretory plants are discussed below:

Excretion in plants occurs in the following ways:

1. Diffusion: Plants use photosynthesis to synthesise food, which involves the use of CO₂, water, sunlight, and chlorophyll. Oxygen is produced in the process of photosynthesis. This oxygen acts as an excretory product and is released through a process known as diffusion.
2. Photorespiration: Photorespiration is a process in which oxygen is taken in and CO₂ is expelled as a waste product by certain plants.
3. Storing: Sometimes organic waste also gets accumulated in the bark or leaves of plants.
4. Transpiration: Excess water in plants is expelled through the process called transpiration. Stomata, or small pores on the under surface of leaves, allow for transpiration.

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Excretory Products in Plants

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Plants generate waste, which accumulates in the vacuoles of ageing cells. These cells eventually die and detach from the plant. These structures can be tree stems, leaves, or bark.

• Tannins: Tannins are a type of plant waste that is commonly produced. Tannin is a plant product that is stored in the trunks of trees. They can be found in the bark of trees.
• Gums & Resins: Plants also produce gums, which are a by-product of cell decomposition. These are also useful to man in the production of a variety of products. Gums and resins are essentially stored in aged or old xylem. Few plants also expel waste into the soil via their roots.
• Latex: Latex is another waste product produced by plants. These are produced by lactified cells found in rubber plants. This plant waste latex is actually very useful to man in the manufacture of many rubber products.
• Excess Salt & Minerals: The plant tissue phloem is in charge of transporting water and minerals from the soil to the plant's aerial tissues. The leaves only use the minerals they need, and the rest are excreted. Excess salt and minerals are eliminated by plants in the form of crystals such as sodium oxalate crystals, calcium carbonate crystals, and so on.
• Alkaloids: Plants, like animals, eliminate ammonia products such as alkaloids. Plants commonly produce alkaloids such as morphine and quinone, which are used to treat a variety of human diseases.

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Transpiration in Plants

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Transpiration in plants is the process by which plants transport water from their roots to their aerial parts for elimination as water droplets or water vapour. It is required because it creates a water pull (the movement of water from the roots to the stem and leaves) in the leaf and stem. Transpiration is classified into three types based on where it occurs. These are outlined below:

• Stomata transpiration: Stomatal transpiration is the loss of water from plants through the stomata. The stomata are responsible for 90% of the water transpired from the leaves.
• Lenticular transpiration: Lenticular transpiration is the loss of water from plants via the lenticels.
• Cuticular transpiration: It is a type of transpiration that occurs from the surface of the leaves. The cuticle, a waxy layer covering the leaves, helps to reduce the amount of transpiration that occurs.

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Things to Remember

• Plants do not possess excretory organs for waste removal.
• Waste products from respiration and photosynthesis are used as natural resources for each other.
• The stomata of leaves and lenticels of stems remove gaseous wastes such as oxygen, carbon dioxide, and water vapour.
• Some waste products are stored in leaves and bark of plants.
• The wastes are eliminated when the leaves and bark are shed.
• Plant excretory products include gums, tannins, and resins.
• Lenticels are tiny openings that protrude from the barks of woody stems, twigs, and other plant organs.

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