Animal and Plant Excretion: A Comprehensive Look
Excretion in Animals and Plants
Excretion in Animals
Excretion is the elimination of waste products resulting from cellular metabolism and is performed through urine, sweat, and breath. The excretory system carries out this process. Homeostasis consists of functions that enable organisms to balance their internal environment.
Waste Products in Animals
- Non-nitrogenous: CO2 and H2O. CO2 is eliminated through the respiratory surfaces, while water can be removed as a vapor by the same surfaces or in liquid form by the excretory system.
- Nitrogenous: Nitrogen can be eliminated as ammonia, urea, or uric acid. Animals are classified as:
- Aminiotelic: Excrete ammonia directly to the outside. Ammonia is very toxic, and only animals that have large amounts of water to dilute it can excrete nitrogenous waste in this way.
- Ureotelic: Excrete nitrogenous waste as urea, which is less toxic but also requires dilution. Ureotelic animals include sharks, reptiles, and humans.
- Uricotelic: Excrete nitrogen in the form of uric acid, which is formed from ammonia. This has two advantages: a) it represents a significant saving of water, and b) it is a compound of low toxicity. Uricotelic animals include insects and birds.
Excretion in Plants
Plants have their own characteristics. They do not have specialized structures for excretion. They produce less waste material, and some of it is used in anabolic processes. Not all waste products are eliminated to the outside.
Waste Products in Plants
- Gaseous substances: Carbon dioxide and ethylene.
- Liquid substances: The most common liquids produced by plants are:
- Essential oils: Can be expelled to the outside by nodal cilia or cells, or stored in oil-bearing bags.
- Resins: Lipids that, in some plants such as conifers, accumulate in the resin canals located in the parenchyma.
- Latex: Stored in the form of drops within the cell vacuoles.
- Solids: Some of these substances, such as calcium oxalate, accumulate as crystals of different types within the cell vacuoles.
Many of the waste products that plants form are useful for people, such as turpentine, natural rubber, and essential oils.
Excretory Systems in Invertebrates
The excretory system groups all organs that eliminate waste products from cell metabolism. Most animals have an excretory system. Less evolved animals, such as sponges, perform excretion by diffusion through the body wall.
Types of Excretory Systems in Invertebrates
- Protonephridia: Found in animals without a coelom, such as Platyhelminthes. They are highly branched tubes, ending in cells with cilia (flame cells) or flagella (solenocytes). Cilia and flagella are located in the lumen of the tube, and their continued movement causes the elimination of waste products to the outside.
- Metanephridia: Appear in coelomate animals, such as annelids and mollusks. They are composed of a coiled tube surrounded by a capillary network, with two openings: the external nephropore and the internal nephrostome, which opens to the coelomic cavity. Inside the metanephridium, compounds that are still useful are reabsorbed, while waste materials are expelled to the outside through the nephridiopore.
- Malpighian Tubules: An adaptation of insects that has contributed to their success in terrestrial environments. They are thin tubes, closed at one end and open at the other end to the digestive system. Waste, together with water and solutes, passes inside the tube. Waste is expelled through the anus, and water and solutes are recovered in the rear of the intestine.
- Green or Antennal Glands: Two glands located at the base of the antennae of crustaceans. Structurally, they consist of a blind sac (which collects waste material), a long tubule (which reabsorbs useful substances), and a bladder (from which waste substances are removed to the outside through a small hole).