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Biology - Excretion and Homeostasis

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    Study Guide Biology – Excretion and Homeostasis 1. Excretory Systems All animals produce waste products as a result of normal life processes like digestion and respiration. The job of the excretory system is to remove these wastes from the body. This process is essential for keeping the internal environment stable — a condition known as homeostasis . What Is Homeostasis? Homeostasis means “staying the same.” It refers to the ability of an organism to maintain a stable internal balance , even when the external environment changes. By removing excess water, salts, and metabolic wastes, the excretory system plays a major role in maintaining this balance. 1.1 Excretion in Simple Organisms Single - Celled Organisms One - celled organisms live in direct contact with their environment. Because wastes can easily diffuse out of the cell, they do not need special excretory organs . 1.2 Excretory Systems in Multicellular Animals As organisms become larger and more complex, waste products must be transported away from cells and removed efficiently. Different animal groups have evolved different excretory structures to solve this problem. 1.3 Flatworms: Flame Cells Flatworms, such as planaria , have simple excretory structures called flame cells . • Flame cells contain cilia that beat constantly.

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    Study Guide • These cilia draw in water and metabolic wastes from surrounding tissues. • The wastes pass into excretory canals , which join together to form excretory tubules . • The fluid then exits the body through small pores . This system helps control water balance and removes waste products. 1.4 Earthworms: Nephridia In earthworms (phylum Annelida ), the excretory system is made up of repeating units called nephridia . Each nephridium includes: • A ciliated funnel that collects fluid from inside the body • A long, coiled tubule • A bladderlike sac that temporarily stores waste How It Works • Fluid enters the funnel from the body cavity. • As the fluid moves through the tubule, useful substances — such as glucose, amino acids, and salts — are reabsorbed into the body. • The remaining fluid contains metabolic wastes. • This waste collects in the bladderlike sac and later leaves the body through a pore in the skin . This process removes waste while conserving valuable materials. 1.5 Insects: Malpighian Tubules Insects use a different excretory system made of Malpighian tubules . • These tubules are long, thin structures that extend into the body cavity.

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    Study Guide • Fluid enters the tubules and moves along their length. • Cells lining the tubules carefully reabsorb water, salts, and other needed substances . • This precise reabsorption helps maintain internal balance. • The remaining waste passes into the intestine , where it is removed from the body along with solid waste. 2. Quiz Excretory Systems 1. Question Fill in the blank: Which of the following statements about the excretory system is FALSE ? Answer Choices • It focuses on the removal of metabolic waste products from the blood. • It involves the processing and removal of undigested food. • It plays a major role in homeostasis. Correct Answer It involves the processing and removal of undigested food. Why This Is Correct This statement is false because the excretory system removes metabolic wastes (such as urea, excess salts, and water) from the blood, primarily through the kidneys. The removal of undigested food is the function of the digestive system , not the excretory system. The other statements are true because: • The excretory system removes metabolic waste products from the blood. • It helps maintain homeostasis by regulating water balance, ion levels, and pH. Therefore, the false statement is that the excretory system processes and removes undigested food.

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    Study Guide 2. Question Fill in the blank: Which of the following excretory systems does a flatworm possess? Answer Choices • flame cells • Malpighian tubules • nephridia Correct Answer flame cells Why This Is Correct Flatworms use flame cells as their excretory and osmoregulatory system. Flame cells help remove excess water and metabolic wastes from the body through a network of tubules. The other options are incorrect because: • Malpighian tubules are found in insects. • Nephridia are excretory structures found in annelids, such as earthworms. Therefore, the correct answer is flame cells . 3. Question Fill in the blank: Which of the following excretory systems does an insect possess? Answer Choices • flame cells • Malpighian tubules • nephridia

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    Study Guide Correct Answer Malpighian tubules Why This Is Correct Insects use Malpighian tubules as their excretory system. These tubules remove nitrogenous wastes from the blood (hemolymph) and help regulate water and salt balance. The other options are incorrect because: • Flame cells are found in flatworms. • Nephridia are found in annelids, such as earthworms. Therefore, the correct answer is Malpighian tubules . 3. Human Excretory System The human excretory system helps keep the body clean and balanced by removing waste products from the blood. This system is essential for homeostasis , which means maintaining a stable internal environment even when conditions outside the body change. The main organs of the human excretory system are the kidneys . Inside each kidney are millions of tiny working units called nephrons . Together, these structures filter the blood, remove harmful substances, and carefully control how much water and salt the body keeps. Kidneys: The Main Excretory Organs The kidneys are bean - shaped organs located on either side of the backbone, roughly at the level of the stomach and liver . 3.1 Structure and Blood Flow • Blood enters each kidney through a renal artery . • Filtered blood leaves through a renal vein .

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