1. What are the different modes of excretion in animals?
Modes of excretion include diffusion and specialised structures, so-called flame cells, nephridia, Malpighian tubules, and kidneys.
2. What are the chief excretory products in humans?
The chief excretory products in humans are urea, carbon dioxide, water, and salts.
3. What is the role of kidneys in the excretory system?
The kidneys filter blood and reabsorb the nutrients and water for further use in the body, excreting in the form of urine the waste products.
4. How does ammonia differ from urea and uric acid?
Ammonia is highly toxic and hence excreted by aquatic animals; urea is less toxic and excreted by mammals, and uric acid is least toxic and hence excreted by birds and reptiles.
5. Explain the regulation of excretion in human beings.
Excretion is under hormonal control, as ADH and aldosterone control the amount of water and salts reabsorbed in the kidneys.
6. What is the difference between excretion and egestion?
Excretion is the removal of metabolic waste products from the body, such as urea or carbon dioxide. Egestion, on the other hand, is the elimination of undigested food materials from the digestive tract through defecation. Excretion involves cellular waste, while egestion deals with unused food particles.
7. How do parasitic flatworms like tapeworms excrete waste without a dedicated excretory system?
Parasitic flatworms like tapeworms don't have a dedicated excretory system but use a network of tubules called protonephridia. These tubules are lined with flame cells that create currents to move waste products. The waste is collected and expelled through excretory pores on the body surface. Additionally, some waste products may be absorbed by the host organism.
8. How do kidney stones form, and what's their relationship to the excretory system?
Kidney stones form when there's an imbalance in the levels of stone-forming substances (like calcium, oxalate, or uric acid) and stone-inhibiting substances in the urine. They can develop when urine becomes too concentrated, allowing crystals to form and grow. Kidney stones can interfere with the normal function of the excretory system by blocking urine flow and causing pain and potential damage to the kidneys.
9. How do kidneys maintain blood pressure?
Kidneys help maintain blood pressure through several mechanisms. They regulate blood volume by controlling water excretion. They also produce hormones like renin, which activates the renin-angiotensin-aldosterone system, leading to increased sodium and water retention and vasoconstriction. These actions help maintain or increase blood pressure when needed.
10. What is the function of the urinary bladder?
The urinary bladder is a muscular sac that stores urine produced by the kidneys. It allows for the accumulation of urine over time, so an animal doesn't need to constantly urinate. When full, stretch receptors in the bladder wall signal the need to urinate. The bladder then contracts to expel urine through the urethra.
11. What is the function of antidiuretic hormone (ADH) in excretion?
Antidiuretic hormone (ADH), also known as vasopressin, regulates water reabsorption in the kidneys. When ADH levels are high, the collecting ducts in the nephrons become more permeable to water, leading to increased water reabsorption and production of more concentrated urine. This helps conserve water when the body is dehydrated.
12. What is the function of nephrons in the kidney?
Nephrons are the functional units of the kidney. They filter blood, reabsorb useful substances, and produce urine. Each nephron consists of a glomerulus (for filtration) and a series of tubules (for reabsorption and secretion). This structure allows for precise control of blood composition and waste elimination.
13. How do plants excrete waste products?
While plants don't have a dedicated excretory system like animals, they do have ways to eliminate waste. They can store waste products in vacuoles, incorporate them into cell walls, or release them through leaves as gases (like oxygen during photosynthesis). Some plants also excrete waste through their roots or by shedding leaves.
14. How do earthworms excrete waste?
Earthworms use specialized structures called nephridia for excretion. Each segment of an earthworm (except the first and last few) contains a pair of nephridia. These structures filter the coelomic fluid, reabsorb useful substances, and excrete waste products. The waste is then expelled through pores on the body surface or into the digestive tract for elimination.
15. How do aquatic mammals like whales and seals manage salt balance?
Aquatic mammals like whales and seals have specialized kidneys that can produce highly concentrated urine, allowing them to excrete excess salts while conserving water. They also have special glands near their eyes or in their mouths that can excrete excess salt. Additionally, they obtain most of their water from their food rather than drinking seawater, which helps maintain salt balance.
16. How does the countercurrent system in fish gills relate to excretion?
While primarily used for gas exchange, the countercurrent system in fish gills also plays a role in excretion and osmoregulation. In marine fish, specialized chloride cells in the gills actively excrete excess salts, helping maintain proper salt balance. In freshwater fish, the gills can absorb ions from the water, compensating for ions lost through dilute urine production.
17. How do marine invertebrates deal with excess salts in their environment?
Marine invertebrates have various adaptations to deal with excess salts. Some, like many crustaceans, have specialized glands (e.g., antennal glands) that actively excrete salts. Others maintain the same salt concentration as their environment (osmoconformers) or have low permeability to salts. Some also drink seawater and excrete concentrated urine to maintain salt balance.
18. How does the excretory system differ between simple and complex animals?
In simple animals like flatworms, excretion occurs through specialized cells called flame cells. As animals become more complex, they develop specialized organs like nephridia (in earthworms) or kidneys (in vertebrates) to handle excretion more efficiently.
19. How do single-celled organisms excrete waste?
Single-celled organisms, such as amoeba or paramecium, excrete waste through simple diffusion across their cell membrane or using specialized structures called contractile vacuoles. These vacuoles collect excess water and waste products, then contract to expel them from the cell.
20. How does the environment influence an animal's excretory system?
The environment greatly influences an animal's excretory system. Aquatic animals can afford to excrete ammonia due to abundant water availability. Terrestrial animals have adapted to conserve water by excreting less toxic forms of nitrogenous waste like urea or uric acid. Desert animals have highly efficient kidneys to conserve water.
21. How do the excretory organs of freshwater fish differ from those of marine fish?
Freshwater fish have to deal with water constantly entering their bodies due to osmosis, so they produce large volumes of dilute urine to expel excess water. Their kidneys are adapted to conserve salts. Marine fish, conversely, tend to lose water to their salty environment, so they produce small amounts of concentrated urine and have specialized cells in their gills to excrete excess salts.
22. How do insects excrete waste?
Insects have a unique excretory system called the Malpighian tubule system. These tubules extract nitrogenous wastes, salts, and other substances from the hemolymph (insect blood) and empty them into the hindgut. Water is then reabsorbed, leaving a semi-solid waste called frass, which is excreted through the anus.
23. What are the primary excretory organs in mammals?
The primary excretory organs in mammals are the kidneys. They filter blood, remove waste products, and regulate water and electrolyte balance. Other organs that play a role in excretion include the skin (through sweat), lungs (expelling CO2), and liver (processing toxins).
24. What is the role of the liver in excretion?
The liver plays a crucial role in excretion by detoxifying harmful substances in the blood. It converts ammonia, a toxic byproduct of protein metabolism, into urea, which is less toxic and can be excreted by the kidneys. The liver also produces bile, which helps eliminate certain waste products through the digestive system.
25. What is the main function of the excretory system in animals?
The main function of the excretory system is to remove metabolic waste products and excess water from the body, maintaining homeostasis and preventing toxin buildup. This system helps regulate the body's internal environment by balancing fluids, electrolytes, and other substances.
26. Why do animals need to excrete waste products?
Animals need to excrete waste products to maintain homeostasis and prevent the buildup of toxic substances in their bodies. Waste products are byproducts of metabolism and can be harmful if allowed to accumulate. Excretion helps maintain the proper balance of water, salts, and other substances in the body.
27. What is osmoregulation, and how is it related to excretion?
Osmoregulation is the process of maintaining proper water and solute balance in an organism's body. It's closely related to excretion because the excretory system plays a crucial role in regulating the body's water and salt content. For example, kidneys adjust urine concentration to maintain proper osmotic balance in the body.
28. What are the main types of nitrogenous waste excreted by animals?
The main types of nitrogenous waste excreted by animals are ammonia, urea, and uric acid. Ammonia is highly toxic and requires lots of water to dilute, so it's mainly excreted by aquatic animals. Urea is less toxic and is excreted by most terrestrial vertebrates. Uric acid is the least toxic and is excreted by birds and reptiles, requiring minimal water.
29. How do birds excrete nitrogenous waste differently from mammals?
Birds excrete nitrogenous waste primarily as uric acid, while mammals excrete urea. Uric acid is less soluble and forms a paste-like substance, allowing birds to conserve water. This adaptation is particularly useful for flying, as it reduces the weight of water needed for waste excretion and is beneficial for egg-laying, as uric acid can be safely stored in eggs.
30. How do amphibians manage excretion both on land and in water?
Amphibians have adaptable excretory systems to manage life both on land and in water. In water, they can excrete dilute urine and ammonia through their skin and kidneys. On land, they switch to producing and excreting urea, which is less toxic and requires less water. Their skin also plays a crucial role in osmoregulation and gas exchange.
31. What is the role of the skin in excretion?
The skin plays a role in excretion through sweat glands. Sweating helps regulate body temperature and also eliminates small amounts of waste products like urea, salts, and water. While not a primary excretory organ, the skin contributes to maintaining the body's overall balance of fluids and electrolytes.
32. How do desert animals adapt their excretory systems to conserve water?
Desert animals have several adaptations in their excretory systems to conserve water:
33. What is the difference between filtration and secretion in the kidney?
Filtration in the kidney occurs in the glomerulus, where blood pressure forces water and small molecules out of the blood into the nephron. Secretion, on the other hand, is an active process that occurs in the tubules, where certain substances are transported from the blood into the tubule lumen. Filtration is non-selective, while secretion is selective and helps eliminate specific substances.
34. What is the role of the loop of Henle in the kidney?
The loop of Henle is a U-shaped portion of the nephron that plays a crucial role in concentrating urine. It creates a concentration gradient in the medulla of the kidney through a countercurrent multiplication system. This allows the kidney to produce urine that's more concentrated than blood plasma, conserving water when needed.
35. What is the role of aldosterone in the excretory system?
Aldosterone is a hormone that plays a crucial role in regulating sodium and potassium balance in the body. It acts on the distal tubules and collecting ducts of the nephron, promoting sodium reabsorption and potassium excretion. This helps maintain proper blood pressure and electrolyte balance, which are key functions of the excretory system.
36. How do dialysis machines mimic the function of kidneys?
Dialysis machines mimic the filtration function of kidneys for people with kidney failure. They work by pumping the patient's blood through a semipermeable membrane. Waste products and excess water diffuse out of the blood into a dialysis fluid, while essential substances are retained in the blood. This process helps maintain fluid, electrolyte, and waste product balance in the body, similar to healthy kidneys.
37. What is the difference between obligate and facultative reabsorption in the kidney?
Obligate reabsorption refers to the automatic reabsorption of substances like glucose and amino acids in the proximal tubule, regardless of the body's needs. Facultative reabsorption, on the other hand, is regulated based on the body's current requirements. For example, water reabsorption in the collecting duct is facultative, controlled by antidiuretic hormone (ADH) levels.
38. What is the role of the juxtaglomerular apparatus in the kidney?
The juxtaglomerular apparatus is a structure in the kidney that plays a crucial role in regulating blood pressure and salt balance. It senses changes in blood pressure and salt concentration in the distal tubule. In response to low blood pressure or low salt, it releases renin, initiating the renin-angiotensin-aldosterone system, which increases blood pressure and promotes salt retention.
39. What is the function of podocytes in the kidney?
Podocytes are specialized cells in the Bowman's capsule of the nephron. They wrap around the capillaries of the glomerulus and form filtration slits. These slits act as a size-selective filter, allowing small molecules like water, ions, and glucose to pass through while retaining larger molecules like proteins in the blood. Podocytes are crucial for the initial step of urine formation.
40. What is the role of the vasa recta in urine concentration?
The vasa recta are specialized blood vessels that run parallel to the loop of Henle in the kidney. They play a crucial role in maintaining the concentration gradient in the medulla of the kidney. The vasa recta's countercurrent exchange system prevents the washout of the solute gradient created by the loop of Henle, allowing for the production of concentrated urine.
41. How do cnidarians (like jellyfish) excrete waste?
Cnidarians, such as jellyfish, have a simple body plan without specialized excretory organs. They primarily rely on diffusion across their body surface to eliminate waste products. Waste materials produced by cells diffuse into the gastrovascular cavity and are then expelled through the same opening used for feeding (the mouth/anus).
42. What is the function of aquaporins in the kidney?
Aquaporins are specialized protein channels in cell membranes that allow for the rapid movement of water molecules. In the kidney, aquaporins play a crucial role in water reabsorption, particularly in the collecting duct. The presence of aquaporins is regulated by antidiuretic hormone (ADH), allowing for precise control of water balance in the body.
43. What is the role of the glomerular filtration rate (GFR) in kidney function?
The glomerular filtration rate (GFR) is the volume of fluid filtered from the blood per unit time in the kidney's glomeruli. It's a key indicator of kidney function. A high GFR ensures efficient removal of waste products from the blood. The body carefully regulates GFR through various mechanisms to maintain proper blood filtering while preventing excessive loss of essential substances.
44. How do bony fish manage osmotic challenges in freshwater environments?
Bony fish in freshwater face the challenge of constant water influx due to osmosis. They manage this by:
45. What is the function of the macula densa in the kidney?
The macula densa is a group of specialized cells in the distal tubule of the nephron, located near the afferent arteriole. It acts as a sensor, detecting changes in the sodium chloride concentration in the tubular fluid. When it senses low sodium levels, it triggers the release of renin from nearby juxtaglomerular cells, initiating the renin-angiotensin-aldosterone system to increase blood pressure and sodium retention.
46. What is the role of the collecting duct in urine formation?
The collecting duct plays a crucial role in the final regulation of urine composition. It's responsible for:
