Class 11 Biology Chapter 16 Excretory Products And Their Elimination

Key Concept: Function Identification

d) Structural support and separation

[Solution Description] The Columns of Bertini provide structural support and separation for the renal pyramids by being extensions of the cortical tissue between them.

Key Concept: Vertebral Range

c) T12 to L3

[Solution Description] The human kidneys are located between the last thoracic vertebra and the third lumbar vertebra. This is a key anatomical feature.

Key Concept: Organ Function

c) Kidney

[Solution Description] Renal calculi form within the kidney, where the crystallisation of salts occurs.

Key Concept: pH Balance

b) By secreting hydrogen ions

[Solution Description] The PCT contributes to pH balance by selectively secreting hydrogen ions and ammonia into the filtrate, which helps control the acidity or alkalinity of the blood.

Key Concept: pH Regulation, Function of the Tubules

c) Distal Convoluted Tubule

[Solution Description] The Distal Convoluted Tubule (DCT) is responsible for conditional reabsorption of sodium ions under hormonal influence, often leading to water retention and affecting blood pressure. Additionally, it actively secretes hydrogen and potassium ions while reabsorbing bicarbonate ions, thereby regulating the pH of body fluids. These functions make it essential for both electrolyte balance and maintaining physiological pH levels.

Key Concept: Filtration Site

c) Glomerulus

[Solution Description] Glomerular filtration occurs in the glomerulus, which is a network of capillaries located at the beginning of the nephron. This is where blood plasma is filtered through the three layers to form the filtrate.

Key Concept: Comparative Toxicity, Evolutionary Adaptation

a) They conserve more energy by direct excretion.

[Solution Description]

Ammonia is more soluble and can be quickly diffused across gill surfaces or body membranes due to the concentration gradient in aquatic environments. This efficient diffusion mechanism allows aquatic organisms to eliminate ammonia rapidly without requiring complex metabolic conversion processes. While ureotelic organisms convert ammonia into less toxic urea, which conserves water, it involves additional energy expenditure. Therefore, the rapid elimination of ammonia by simple diffusion provides an ecological advantage in terms of reduced energy usage for ammonotelic organisms.

Key Concept: Terminology

c) Calyces

[Solution Description] The small cup-shaped structures that receive urine from the nephrons via the medullary pyramids are known as calyces.

Key Concept: Excretory Organ Functions

a) Osmoregulation

[Solution Description] Nephridia in annelids are responsible for osmoregulation and the filtration of bodily fluids to remove waste materials. They help maintain fluid balance and excrete metabolic wastes.

Key Concept: Clinical Diagnosis

b) Diabetes mellitus

[Solution Description] The simultaneous presence of glucose (glycosuria) and ketone bodies (ketonuria) in urine is a classic sign of uncontrolled diabetes mellitus. In this condition, due to insufficient insulin or insulin action, glucose cannot enter the cells for energy use, so it spills over into the urine. Ketones appear as fat metabolism increases because glucose is not available as an energy source.

Key Concept: Neural Mechanism

c) Autonomic nervous system

[Solution Description] The detrusor muscle, which forms a part of the bladder wall, is controlled by the autonomic nervous system. During micturition, the parasympathetic nervous system causes contraction of the detrusor muscle to facilitate urine expulsion.

Key Concept: Definition Recall

c) It is the rate of blood filtration in the kidneys.

[Solution Description] The Glomerular Filtration Rate (GFR) refers to the rate at which blood is filtered in the glomeruli of the kidney. It is an important indicator of kidney function and measures how much blood passes through the glomeruli each minute.

Key Concept: Renin-Angiotensin Pathway

c) Renin

[Solution Description] Angiotensinogen, a protein produced by the liver, is converted into angiotensin I by the action of renin. Renin is an enzyme released from the juxtaglomerular cells in the kidney when blood pressure is low.

Key Concept: Component Location

d) At the beginning of the renal tubule

[Solution Description] The Bowman’s capsule is part of the renal corpuscle and is positioned at the beginning of the nephron, specifically adjacent to the glomerulus. It marks the start of the process where blood filtration begins.

Key Concept: Advanced Permeability Dynamics, Detailed Counter Current Exchange

b) Without water reabsorption, the filtrate becomes more diluted as salts exit the tubule.

[Solution Description]

The ascending limb is impermeable to water but actively transports sodium and chloride ions into the interstitial space, creating an osmotic gradient. This results in the dilution of the filtrate as it ascends, as water remains in the tubule while salts move out. This process is crucial for establishing the hyperosmotic condition of the interstitial fluid necessary for water reabsorption from the collecting duct under the influence of antidiuretic hormone (ADH).

Key Concept: Comparative Analysis

c) Skin

[Solution Description] The skin has sweat glands that are responsible for excreting NaCl and small amounts of urea. Additionally, these sweat glands aid in regulating body temperature through the cooling effect of evaporation.

Key Concept: Blood Pressure Effect

d) It increases blood pressure

[Solution Description] ADH has constrictory effects on blood vessels, leading to an increase in blood pressure. It also increases glomerular blood flow, affecting the glomerular filtration rate (GFR).

Key Concept: Location Understanding

b) Inner concave surface

[Solution Description] The hilum is a notch located on the inner concave surface of the kidney.

Key Concept: Reflex Mechanism

d) Micturition reflex

[Solution Description] The neural mechanism responsible for the release of urine is known as the micturition reflex.

Key Concept: Urine Characteristics

d) Urea

[Solution Description] Urea is the primary nitrogenous waste excreted in human urine. It is produced from the breakdown of proteins and is filtered by the kidneys out of the blood to be eliminated in the urine.

Key Concept: Counter Current Exchange

d) NaCl

[Solution Description] The counter current mechanism involves the exchange of NaCl, which is transported by the ascending limb of Henle’s loop into the interstitium. It is then taken up by the descending limb of the vasa recta.

Key Concept: Urine Transport

c) Peristalsis

[Solution Description]

Ureters use a wave-like muscle contraction called peristalsis to move urine from the kidneys towards the bladder smoothly and effectively.

Key Concept: Cause and Effect

c) Bacterial infections

[Solution Description] Glomerulonephritis can be caused by various factors, including infections such as streptococcal infections that trigger an immune response. This immune response leads to inflammation of the glomeruli in the kidney.

Key Concept: Nephron Components

b) Glomerulus

[Solution Description] The nephron, which is the functional unit of the kidney, consists of the glomerulus and renal tubule as its main components.

Key Concept: Function Identification

a) Filtration

[Solution Description] The nephron’s primary function involves filtration, reabsorption, and secretion to form urine.

Key Concept: Nephron Parts

d) Proximal convoluted tubule

[Solution Description]

The proximal convoluted tubule (PCT) is the primary site for reabsorption of water, ions, and nutrients from the filtrate back into the bloodstream. This process significantly reduces the volume of filtrate and concentrates waste products.

Key Concept: Vasa Recta Role

c) By maintaining the osmolarity gradient through solute exchange

[Solution Description] The vasa recta maintains the osmolarity gradient by exchanging solutes with the tubular fluid in the nephron, ensuring that the gradient remains constant and effective for water reabsorption.

Key Concept: Comparative Analysis, Complex Process Understanding

d) To help conserve water by maintaining osmolarity

[Solution Description]

Ureotelic animals like mammals retain some urea within their kidney matrix primarily to maintain osmolarity balance. This retention helps in creating a gradient required for the reabsorption of water from the collecting ducts, which is crucial for conserving water, an essential adaptation for life on land.

The steps involved are:

– Urea is produced in the liver and released into the bloodstream.

– It reaches the kidneys where it is filtered out but part of it is retained.

– By retaining urea, the hyperosmotic environment is maintained, facilitating water reabsorption.

Therefore, the correct answer is that some urea is retained to help conserve water by maintaining osmolarity.

Key Concept: Comparative Analysis

c) Glycosuria involves high blood glucose levels, whereas Ketonuria indicates fat metabolism issues.

[Solution Description] Glycosuria is characterized by the presence of glucose in urine, often indicating diabetes mellitus due to high blood sugar levels. Ketonuria involves the presence of ketone bodies in urine, which indicates fat metabolism issues frequently associated with uncontrolled diabetes or starvation.

Key Concept: Basic Reabsorption

d) Proximal Convoluted Tubule

[Solution Description] The Proximal Convoluted Tubule (PCT) is known as the major site where around 70-80% of the electrolytes and water are reabsorbed.

Key Concept: JGA Function

c) Decreased blood pressure

[Solution Description] The Juxta Glomerular Apparatus (JGA) releases renin in response to a decrease in blood pressure or a decrease in sodium chloride concentration in the distal convoluted tubule, detected by macula densa cells. These conditions lead to decreased perfusion pressure at the afferent arterioles, triggering renin release.

Key Concept: Blood Pressure Effect

b) Decreases it

[Solution Description] ANF causes vasodilation, which results in decreased blood pressure by reducing vascular resistance.

Key Concept: Basic Concept

d) Henle’s Loop

[Solution Description] The Henle’s loop is responsible for generating an osmotic gradient in the medulla, which is crucial for water reabsorption. It uses the countercurrent mechanism to establish this gradient.

Key Concept: Substance Pathway

b) Along with bile into the intestines

[Solution Description] The liver processes cholesterol and secretes it into bile, which is then transported to the intestine. From there, it is eliminated along with feces.

Key Concept: Urine Characteristics

b) 6.0

[Solution Description] Human urine is slightly acidic with a typical pH around 6.0.

Key Concept: Osmolarity Role

d) Urea

[Solution Description] Small amounts of urea pass into the medullary interstitium through the collecting duct to help maintain osmolarity.

Key Concept: Structural Features

d) 120-170 g

[Solution Description] The average weight of a human kidney is given as 120-170 grams according to the syllabus. This falls within the options provided, and matches option d).

Key Concept: Basic Function

b) To act as a vasoconstrictor

[Solution Description] Angiotensin II primarily functions as a vasoconstrictor, which means it narrows blood vessels, leading to an increase in blood pressure and glomerular filtration rate (GFR).

Key Concept: Role in Ionic Balance

c) Selective secretion of H$\textsuperscript{+}$ and K$\textsuperscript{+}$ ions

[Solution Description] The collecting duct maintains ionic balance by selectively secreting ions like H$\textsuperscript{+}$ and K$\textsuperscript{+}$. This process adjusts the concentrations of these ions in the blood, ensuring proper electrolyte balance.

Key Concept: Basic Definition

c) Secretion of substances like H+, K+, and ammonia

[Solution Description] The primary role of tubular secretion in urine formation is to secrete specific substances into the filtrate. This process helps maintain the body’s ionic and acid-base balance by secreting ions such as H+, K+, and ammonia.

Key Concept: Electrolyte Transport, Acid-Base Homeostasis

c) Primarily via sodium chloride symporters and carbonic anhydrase activity for bicarbonate conservation.

[Solution Description] The DCT plays a crucial role by reabsorbing Na$^+$ ions through specific transporters, while concurrently handling HCO$_3^-$ reabsorption to maintain pH balance. Na$^+$ reabsorption primarily occurs via sodium chloride symporters, which ensure fine-tuning of sodium levels. Bicarbonate ion reabsorption involves carbonic anhydrase and exchange mechanisms that help conserve HCO$_3^-$ and excrete H$^+$ ions, thus aiding in acid-base homeostasis.

Key Concept: Process Understanding

b) It allows passage of molecules based on concentration gradient

[Solution Description] The cellophane tube acts as a semi-permeable membrane that allows smaller molecules such as urea and other waste products to pass through based on their concentration gradient, while larger molecules such as blood cells are retained.

Key Concept: Mechanism Analysis, Advanced Comparative Analysis

c) By increasing oxygen diffusion efficiency with minimal energy use.

[Solution Description] The countercurrent exchange mechanism in fish gills allows for a gradient where water entering the gill flows opposite to the blood flow, maximizing oxygen absorption as the concentration gradient is maintained over a larger surface area. This allows almost complete transfer of oxygen from water to blood. In contrast, the urea excretion mechanism in mammals is efficient in terms of conserving water, but it involves significant energy expenditure in converting ammonia to less toxic urea. Therefore, while both mechanisms are optimized for their specific needs (oxygen uptake vs. nitrogen waste removal), the countercurrent mechanism in fish gills is more direct and energetically favorable compared to the complex metabolic pathway required for urea production in mammals.

Key Concept: Excretion Rate

c) 200 mL

[Solution Description] The lungs are responsible for eliminating approximately 200 mL of CO$_2$ every minute. This is an essential function to help maintain the body’s acid-base balance.

Key Concept: Comparative Analysis, Physiological Impact

b) Major site of electrolyte and water reabsorption

[Solution Description]

The PCT primarily focuses on reabsorbing 70-80% of electrolytes and water, making it responsible for recovering most of the filtrate’s initial volume. In contrast, the Loop of Henle concentrates on creating a hyperosmotic medullary interstitium to enable further water reabsorption in the collecting ducts.

Solution Steps:

– PCT Reabsorption: Significant amounts of electrolytes (Na$\textsuperscript{+}$, Cl$\textsuperscript{-}$) and water are reabsorbed here.

– Loop of Henle Function: Establishes a concentration gradient that allows precise water retention later.

– Comparative Outcome: While both structures manage water/electrolyte balance, the PCT handles bulk reabsorption, whereas the Loop regulates osmolarity.

Primary Role Summary: PCT performs major reabsorption of water and electrolytes, while the Loop fine-tunes osmotic conditions.

Key Concept: Lungs CO2 Removal

c) 200 mL

[Solution Description] The amount of carbon dioxide removed by the lungs can be measured in milliliters. Typically, an average adult expels about 200 mL to 250 mL of CO$$_2$$ per minute under normal resting conditions.

Key Concept: Urine Formation Steps

c) Secretion

[Solution Description] Tubular secretion is the process where certain substances are moved from the peritubular capillaries into the renal tubule to be excreted in urine.

Key Concept: pH Balance

d) By secreting hydrogen ions

[Solution Description] The DCT contributes to acid-base balance by secreting hydrogen ions ($\text{H}^+$), which directly affect the acidity of blood. By excreting these ions, the DCT reduces the overall acidity, aiding in pH regulation.

Key Concept: Basic Definition

b) Filtration

[Solution Description] The glomerulus primarily functions as a site for blood filtration, filtering out waste and other substances from the blood to form urine.

Key Concept: Urine Characteristics

c) 6.0

[Solution Description] Normal human urine is slightly acidic and typically has a pH around 6.0, which helps maintain a proper acid-base balance in the body.

Key Concept: Comparative Analysis

d) Ketonuria

[Solution Description] Ketonuria refers to the presence of ketone bodies in the urine, which often occurs when the body breaks down fat for energy because it does not have enough insulin to use glucose or if there is not enough food intake. This is indicative of diabetes mellitus.