Within Chapter Questions Class 11 Chapter 15 Biology Maharashtra Board

Excretion and Osmoregulation

Can you recall? Page No. 174

1. Why are various waste products produced in the body of an organism ?

Answer: Various waste products are produced in the body due to metabolism, which involves catabolic (breaking down) and anabolic (building up) processes. These processes generate by-products such as fluids (water), gaseous wastes (CO₂), nitrogenous wastes (ammonia, urea, uric acid), and other substances like creatinine, mineral salts, and pigments, some of which need to be eliminated to maintain homeostasis.

2. How are these wastes eliminated ?

Answer: Metabolic wastes are eliminated through various organs depending on their type: fluids and nitrogenous wastes (ammonia, urea, uric acid) are excreted via urine through kidneys; gaseous wastes like CO₂ are expelled through lungs; pigments like bilirubin are eliminated in feces, and urochrome in urine; sweat glands excrete water, salts, and urea; and volatile substances from spices are exhaled via lungs.

Have you ever observed ? Page No. 174

1. When does urine appear deeply coloured?

Answer: Urine appears deeply colored when the body is dehydrated or when there is a high concentration of urochrome (a pigment from hemoglobin breakdown) due to reduced water intake or increased metabolic waste, making the urine more concentrated.

2. If we consume onion and garlic, we get bad breath. Why?

Answer: Consuming onion and garlic causes bad breath because they contain volatile substances that are absorbed into the bloodstream and excreted through the lungs during respiration, releasing their odor in the breath.

Think about it Page No. 174

1. Do organisms differ in type of metabolic wastes they produce?

Answer: Yes, organisms differ in the type of metabolic wastes they produce, primarily based on their nitrogenous waste excretion: ammonotelic organisms (e.g., aquatic invertebrates) excrete ammonia, ureotelic organisms (e.g., mammals) excrete urea, and uricotelic organisms (e.g., birds, reptiles) excrete uric acid.

2. Do environment or evolution have any effect on type of waste produced by an organism?

Answer: Yes, the environment significantly affects the type of waste produced, as it is linked to water availability rather than phylogenetic relationships. For example, aquatic organisms like tadpoles excrete ammonia due to abundant water, while terrestrial organisms like adult frogs excrete urea or uric acid to conserve water, an adaptation shaped by evolutionary pressures.

3. How do thermoregulation and food habits affect waste production ?

Answer: Thermoregulation affects waste production as endotherms consume more food to meet energy demands, producing more nitrogenous wastes. Food habits also influence waste production; carnivorous diets, high in proteins, generate more nitrogenous wastes (e.g., urea, uric acid) compared to herbivorous diets, which produce less due to lower protein content.

Think about it Page No. 175

Endotherms consume more food in order to meet energy requirements. Also, carnivorous diet contains more proteins than herbivorous. Does it affect excretion of nitrogenous waste ?

Answer: Yes, a carnivorous diet and higher food consumption in endotherms significantly affect the excretion of nitrogenous waste. According to the document, endotherms consume more food to meet their energy requirements, and a carnivorous diet contains more proteins than a herbivorous one. Proteins are rich in amino acids, and the body cannot store excess amino acids. These are broken down through a process called deamination, which produces ammonia as a byproduct. Depending on the organism’s habitat and water availability, this ammonia is either excreted as is (in ammonotelic organisms) or converted into less toxic forms like urea (in ureotelic organisms) or uric acid (in uricotelic organisms).

Since carnivorous diets are high in proteins, they result in greater production of nitrogenous wastes due to increased deamination. This leads to a higher load on the excretory system, requiring efficient mechanisms to eliminate these wastes. For example, mammals (ureotelic) convert ammonia to urea in the liver, which requires less water for excretion compared to ammonia, while birds and reptiles (uricotelic) excrete uric acid, which requires minimal water, suitable for water conservation in their environments.

Use your brain power Page No. 175

Why is ammonia highly toxic?

Answer: Ammonia is highly toxic because it is a basic compound that can disrupt the pH balance of the body. The document explains that even a slight increase in pH due to ammonia retention can disturb enzyme-catalyzed reactions and make the plasma membrane unstable, potentially leading to cellular damage. Ammonia is readily soluble in water but requires a large quantity (300–500 ml of water per gram of ammonia) to dilute its toxicity for safe excretion. If not diluted or converted to less toxic forms like urea or uric acid, ammonia can accumulate in the body, causing severe physiological harm. This is why organisms with limited water access, such as terrestrial animals, have evolved mechanisms like ureotelism or uricotelism to convert ammonia into less toxic compounds before excretion.

Think about it Page No. 176

During summer, we tend to produce less urine, why is it so ?

Answer: During summer, the body tends to produce less urine due to increased water loss through sweating and the need to conserve water to maintain homeostasis. The document explains that when water intake is low or water loss is high (e.g., due to sweating in hot conditions), the body activates mechanisms to produce concentrated urine. The countercurrent mechanism in the kidneys, particularly in the loop of Henle and collecting ducts, facilitates this by reabsorbing water from the glomerular filtrate. Additionally, the release of Antidiuretic Hormone (ADH) from the posterior pituitary, triggered by osmoreceptors detecting increased blood osmolarity (e.g., due to water loss), enhances water reabsorption in the distal convoluted tubule (DCT) and collecting ducts. This reduces urine volume, making it more concentrated (up to 1200 mOsm/L compared to blood’s 300 mOsm/L), thus conserving water and resulting in less urine production.

Use your brain power Page No. 176

What would happen if human being has no option but to drink sea water ?

Answer: If a human being has no option but to drink sea water, it would disrupt osmoregulation and lead to severe physiological consequences. The document highlights that sea water is hypertonic (has a higher salt concentration) compared to human body fluids. Consuming sea water would increase the osmolarity of blood, causing dehydration as water moves out of cells into the bloodstream to balance the high salt concentration. The kidneys would attempt to excrete the excess salts, but this requires water, leading to further water loss through urine. The document notes that humans are osmoregulators, maintaining internal solute concentrations independent of the external environment, but they cannot handle the high salt load of sea water. This would result in hypernatremia (high blood sodium levels), cellular dehydration, and potential organ damage. Prolonged consumption could lead to kidney failure, as the kidneys struggle to filter the excess salts, and ultimately, it could be fatal due to the inability to maintain proper water and electrolyte balance.

Find out Page No. 176

How do freshwater fishes and marine fishes carry out osmoregulation ?

Answer: Freshwater Fishes: Freshwater fishes live in a hypotonic environment (water with lower salt concentration than their body fluids), causing water to enter their bodies by osmosis through their gills and skin, and salts to be lost. The document classifies them as osmoregulators, meaning they actively maintain their internal salt and water balance. To counteract water influx, freshwater fishes:

• Produce large amounts of dilute urine to excrete excess water, as their kidneys have numerous nephrons adapted for high glomerular filtration rates.
• Actively uptake salts (e.g., sodium and chloride) through specialized cells in their gills to compensate for salt loss.
• Minimize water intake by not drinking much water, relying on water absorbed through their skin and gills.

Marine Fishes: Marine fishes live in a hypertonic environment (sea water with higher salt concentration than their body fluids), causing water loss by osmosis and salt gain. The document notes that most marine organisms are osmoconformers, with body fluids isoosmotic to sea water, but marine bony fishes are osmoregulators. To maintain water and salt balance, they:

• Drink large amounts of sea water to replace water lost by osmosis.
• Excrete excess salts through specialized chloride cells in their gills via active transport, reducing salt accumulation in the body.
• Produce small amounts of concentrated urine to conserve water, as their kidneys have fewer nephrons and lower glomerular filtration rates compared to freshwater fishes.
• Some marine fishes, like sharks, retain urea in their blood to make it isotonic to sea water, preventing water loss by exosmosis, as mentioned in the document.

Internet my friend Page No. 179

Find out what is floating kidney?

Answer: A floating kidney, as referenced in the document under “Internet my friend,” is a condition where the kidney is not firmly anchored in its normal retroperitoneal position and can move or “float” within the abdominal cavity. This is also known as nephroptosis, often due to weak supporting tissues or loss of surrounding fat.

Can you recall? Page No. 179

Observe the figure carefully and label various regions of L.S. of kidney.

Answer: The document includes Figure 15.5: L.S. of Kidney and instructs to label its regions. The regions to be labeled, based on the description, are:

1. Renal cortex – Outer, red-colored, granular region containing Malpighian bodies, convoluted tubules, and blood vessels.
2. Renal medulla – Inner, pale red, striated region with loops of Henle and collecting ducts, arranged in renal pyramids.
3. Renal pyramid – Conical structures in the medulla.
4. Renal column (Columns of Bertini) – Extensions of cortex between pyramids.
5. Renal papilla – Narrow tip of the pyramid opening into the minor calyx.
6. Minor calyx – Structure collecting urine from renal papilla.
7. Major calyx – Formed by merging minor calyces.
8. Renal pelvis – Funnel-shaped area in the medulla, continuous with the ureter.
9. Ureter – Tube exiting the kidney through the hilus.

Can you tell? Page No. 182

1. Why are kidneys called ‘retroperitoneal’?

Answer: Kidneys are called retroperitoneal because they are located behind the peritoneum, the membrane lining the abdominal cavity, as stated in the document under “Kidney”.

2. Why urinary tract infections are more common in females than males?

Answer: Urinary tract infections are more common in females due to the shorter length of the urethra in females compared to males, making it easier for bacteria to enter the urinary bladder, as implied in the document’s context about urethra structure.

3. What is nephron? Which are it’s main parts? Why are they important?

Answer: A nephron is the structural and functional unit of the kidney, responsible for filtering blood and forming urine. Its main parts include:

• Bowman’s capsule
• Glomerulus
• Proximal convoluted tubule (PCT)
• Loop of Henle (LoH)
• Distal convoluted tubule (DCT)
• Collecting tubule (CT) They are important because nephrons perform ultrafiltration, selective reabsorption, and tubular secretion, maintaining homeostasis by regulating water, electrolytes, and removing metabolic wastes.

Think about it Page No. 182

How much blood is supplied to kidney?

Answer: About one-fourth of the cardiac output is supplied to the kidneys, equivalent to approximately 600 ml of blood per minute per kidney.

Can you tell? Page No. 185

1. Explain the process of urine formation in details.

Answer: Urine formation occurs in three steps, as detailed in section 15.3:

• Ultrafiltration/Glomerular Filtration: Blood enters the glomerulus via the afferent arteriole, creating high glomerular hydrostatic pressure (55 mm Hg) due to the narrower efferent arteriole. This pressure, minus osmotic (30 mm Hg) and capsular pressures (15 mm Hg), results in an effective filtration pressure (EFP) of 10 mm Hg. Plasma (except proteins) filters through capillary walls into Bowman’s capsule, forming glomerular filtrate (125 ml/min or 180 L/day), containing urea, glucose, amino acids, and ions.
• Selective Reabsorption: In the proximal convoluted tubule (PCT), 99% of filtrate is reabsorbed. High-threshold substances (e.g., glucose, amino acids, Na⁺, Cl⁻) are actively reabsorbed using ATP, while low-threshold substances (e.g., water, sulfates) are passively reabsorbed. The distal convoluted tubule (DCT) also reabsorbs water and ions, adjusting filtrate composition.
• Tubular Secretion/Augmentation: In the DCT and collecting tubule (CT), cells actively secrete wastes (e.g., creatinine, K⁺, H⁺) from peritubular capillaries into the filtrate, concentrating urine and adjusting its pH to acidic, aiding pH homeostasis.

2. How does counter current mechanism help concentration of urine?