Excretory System - SS2 Biology Past Questions and Answers - page 2

Stomata

Excretion is the process by which organisms eliminate waste products generated through metabolic processes. Common waste products include carbon dioxide, urea, uric acid, and excess water. In organisms such as humans and mammals, excretion primarily occurs through the urinary system, which filters blood and eliminates waste in the form of urine. In insects, malpighian tubules remove metabolic waste and maintain water balance, while earthworms use nephridia for excretion. Plants excrete waste products through various mechanisms, such as the stomata on leaves for the release of gases and the shedding of leaves for the disposal of waste substances.

Earthworms possess a network of excretory organs called nephridia. Nephridia filter waste materials, excess water, and metabolic by-products from the coelomic fluid. These waste products are then transported through tubules and excreted through pores located on the surface of the body. Nephridia also play a role in maintaining osmotic balance within the earthworm's body.

Flatworms, such as planarians, utilize specialized excretory structures called flame cells or protonephridia. Flame cells contain cilia that beat to create water currents within the worm's body. These cells filter waste materials and excess water from the interstitial fluid, and the waste products are eliminated through excretory pores. Flame cells also assist in osmoregulation, ensuring the proper balance of ions and water within the flatworm's body.

Insects have a unique excretory system consisting of Malpighian tubules. Malpighian tubules remove nitrogenous waste, such as uric acid, from the hemolymph by actively transporting it into the tubules. These tubules also play a crucial role in regulating water balance. They actively transport potassium ions into the tubules, creating an osmotic gradient that drives the reabsorption of water from the hindgut back into the insect's body, effectively conserving water.

Mammals possess a complex excretory system centered around the kidneys. The kidneys filter waste products, excess water, and ions from the blood to produce urine. The urine is then transported through the urinary tract and eliminated from the body. The kidneys also play a vital role in maintaining homeostasis by regulating the balance of electrolytes, pH levels, and water reabsorption.

Flowering plants utilize various mechanisms for excretion. One significant process is transpiration, where excess water and certain waste substances are released as water vapor through the stomata on leaves. Plants also eliminate waste products through the shedding of leaves and bark. Additionally, some waste materials are stored in vacuoles within plant cells, isolated from the rest of the plant's tissues.