Biology - Excretion and Homeostasis - Quick Guides | Biology

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Study GuideBiology–Excretion and Homeostasis1. Excretory SystemsAll animals producewaste productsas a result of normal life processes like digestion andrespiration. The job of theexcretory systemis to remove these wastes from the body. This processis essential for keeping the internal environment stable—a condition known ashomeostasis.What Is Homeostasis?Homeostasismeans “staying the same.”It refers to the ability of an organism to maintain astable internal balance, even when the externalenvironment changes. By removing excess water, salts, and metabolic wastes, the excretory systemplays a major role in maintaining this balance.1.1 Excretion in Simple OrganismsSingle-Celled OrganismsOne-celled organisms live in direct contact with their environment. Because wastes can easily diffuseout of the cell, theydo not need special excretory organs.1.2 Excretory Systems in Multicellular AnimalsAs organisms become larger and morecomplex, waste products must be transported away from cellsand removed efficiently. Different animal groups have evolved different excretory structures to solvethis problem.1.3 Flatworms: Flame CellsFlatworms, such asplanaria, have simple excretory structures calledflame cells.•Flame cells containciliathat beat constantly.

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Study Guide•These cilia draw inwater and metabolic wastesfrom surrounding tissues.•The wastes pass intoexcretory canals, which join together to formexcretory tubules.•The fluid then exits the body through smallpores.This system helps control water balance and removes waste products.1.4 Earthworms: NephridiaIn earthworms (phylumAnnelida), the excretory system is made up of repeating units callednephridia.Eachnephridiumincludes:•Aciliated funnelthat collects fluid from inside the body•A long,coiled tubule•Abladderlike sacthat temporarily stores wasteHow It Works•Fluid enters the funnel from the body cavity.•As the fluid moves through the tubule, useful substances—such asglucose, 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 apore in theskin.This process removes waste while conserving valuable materials.1.5 Insects: Malpighian TubulesInsects use a different excretory system made ofMalpighian tubules.•These tubules are long, thin structures that extend into the bodycavity.

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Study Guide•Fluid enters the tubules and moves along their length.•Cells lining the tubules carefullyreabsorb water, salts, and other needed substances.•This precise reabsorption helps maintain internal balance.•The remaining waste passes into theintestine, where it is removed from the body along withsolid waste.2. Quiz Excretory Systems1. QuestionFill in the blank:Which of the following statements about the excretory system isFALSE?Answer Choices•It focuses on the removal ofmetabolic waste products from the blood.•It involves the processing and removal of undigested food.•It plays a major role in homeostasis.Correct AnswerIt involves the processing and removal of undigested food.Why This Is CorrectThis statement is false because theexcretory systemremovesmetabolic wastes(such as urea,excess salts, and water) from the blood, primarily through the kidneys. The removal ofundigestedfoodis the function of thedigestive system, not theexcretory system.The other statements are true because:•The excretory system removes metabolic waste products from the blood.•It helps maintainhomeostasisby regulating water balance, ion levels, and pH.Therefore, the false statement is that the excretory system processes and removes undigestedfood.

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Study Guide2. QuestionFill in the blank:Which of the following excretory systems does a flatworm possess?Answer Choices•flame cells•Malpighian tubules•nephridiaCorrect Answerflame cellsWhy ThisIs CorrectFlatworms useflame cellsas their excretory and osmoregulatory system. Flame cells help removeexcess water and metabolic wastes from the body through a network of tubules.The other options are incorrect because:•Malpighian tubulesare found in insects.•Nephridiaare excretory structures found in annelids, such as earthworms.Therefore, thecorrect answerisflame cells.3. QuestionFill 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 GuideCorrect AnswerMalpighian tubulesWhy This Is CorrectInsects useMalpighian tubulesas their excretory system. These tubules remove nitrogenous wastesfrom the blood (hemolymph) and help regulate water and salt balance.The other options are incorrect because:•Flame cellsare found in flatworms.•Nephridiaare found in annelids, such as earthworms.Therefore, thecorrect answerisMalpighian tubules.3.Human Excretory SystemThehuman excretorysystemhelps keep the body clean and balanced by removingwasteproductsfrom the blood. This system is essential forhomeostasis, which means maintaining astable internal environment even when conditions outside the body change.The main organs of the human excretory system are thekidneys. Inside each kidney are millions oftiny working units callednephrons. Together, these structures filter the blood, remove harmfulsubstances, and carefully control how much water and salt the body keeps.Kidneys: The Main Excretory OrgansThekidneysare bean-shaped organs located on either side of the backbone, roughly at the level ofthestomach and liver.3.1Structure and Blood Flow•Blood enters each kidney through arenal artery.•Filtered blood leaves through arenal vein.

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