MCQ (Practice) - Excretory System (Level 1) - Class 11 MCQ

Excretion involves the process of eliminating waste products from the body. The correct answer is option D: Substance of no further use or those present in excessive quantities are thrown out of the body. Let's break down the answer into detailed points:
1. Definition of excretion: Excretion is the process by which waste products, toxins, or substances that are no longer needed by the body are removed and eliminated.
2. Substance of no further use: Excretion involves getting rid of substances that have served their purpose in the body and are no longer needed. These substances include metabolic waste products, such as carbon dioxide, urea, and excess water.
3. Substances present in excessive quantities: Excretion also helps to eliminate substances that are present in excessive amounts in the body. For example, excess salts, excess water, and certain hormones can be excreted to maintain the body's balance and homeostasis.
4. Methods of excretion: Excretion occurs through various organs and systems in the body, including the kidneys (urine), the skin (sweat), the lungs (carbon dioxide), and the intestines (feces). Each organ/system plays a specific role in eliminating different types of waste.
5. Importance of excretion: Excretion is essential for maintaining the overall health and functioning of the body. If waste products are not effectively eliminated, they can accumulate and lead to various health issues, such as toxicity, organ damage, and imbalances in the body.
In conclusion, excretion is the process of eliminating waste products from the body, including substances of no further use or those present in excessive quantities. It is crucial for maintaining the body's balance and overall health.

Waste End Product of Nitrogen Metabolism in Aquatic Organisms:
Aquatic organisms have different mechanisms to eliminate waste products, including nitrogen waste. The waste end product of nitrogen metabolism in aquatic organisms is ammonia. Here is a detailed explanation:
1. Nitrogen Metabolism:
- Nitrogen is an essential element for living organisms and is required for the synthesis of proteins, nucleic acids, and other important biomolecules.
- Aquatic organisms, such as fishes, obtain nitrogen from their diet in the form of proteins and amino acids.
- Nitrogen-containing compounds, such as amino acids and nucleotides, are broken down during metabolism, releasing nitrogen waste.
2. Ammonia as the Waste Product:
- In aquatic organisms, the primary waste product of nitrogen metabolism is ammonia (NH3).
- Ammonia is highly toxic and needs to be eliminated from the body to maintain proper physiological functions.
- Aquatic organisms, such as fishes and amphibians, excrete ammonia directly into the surrounding water through their gills or skin.
3. Advantages of Ammonia Excretion:
- Ammonia excretion is energetically favorable compared to other nitrogenous waste products like urea or uric acid.
- Ammonia is highly soluble in water, allowing for easy elimination in aquatic environments.
- Aquatic organisms have evolved efficient mechanisms, such as specialized cells in the gills and skin, to excrete ammonia and maintain water and ion balance.
4. Other Nitrogenous Waste Products:
- While ammonia is the primary waste product in aquatic organisms, some species may also excrete other forms of nitrogenous waste, such as urea or uric acid.
- Urea is a less toxic form of nitrogenous waste produced through the conversion of ammonia in the liver of some fishes and marine mammals.
- Uric acid is the least toxic form of nitrogenous waste and is excreted by birds, reptiles, and insects.
In conclusion, the waste end product of nitrogen metabolism in aquatic organisms is ammonia. Aquatic organisms excrete ammonia directly into the water through their gills or skin to maintain proper physiological functions and water balance. However, some species may also excrete urea or uric acid as nitrogenous waste products.

Ammonotelic Animals: Predominantly Aquatic
Ammonotelic animals are organisms that excrete ammonia as their primary nitrogenous waste product. These animals are primarily found in aquatic environments, although some may also inhabit terrestrial habitats.
Reasoning:
- Ammonia is highly toxic and requires a large amount of water to be diluted and excreted effectively.
- Aquatic environments provide a readily available source of water for these animals to excrete ammonia.
- Terrestrial environments have limited access to water, making it more difficult for ammonotelic animals to excrete ammonia efficiently.
- Parasitic and volant animals do not necessarily correlate with ammonia excretion and are not the primary determining factors for ammonotelic animals.
Therefore, the correct answer is option D: Aquatic.

Explanation:
The kidney plays a crucial role in filtering waste products from the blood and maintaining the body's fluid and electrolyte balance. When the kidney is not functioning properly, certain substances can accumulate in the blood, leading to dangerous proportions. In this case, the likely substance to accumulate in dangerous proportion is urea.
Reason:
- Urea is a waste product that is produced when the body breaks down proteins. It is normally eliminated by the kidneys through urine.
- When the kidneys are not functioning properly, urea cannot be efficiently removed from the blood, leading to its accumulation.
- High levels of urea in the blood, known as uremia, can have toxic effects on various organs and systems in the body.
Other options:
- Sodium chloride (common salt) is a normal component of the blood and its levels are regulated by the kidneys. While high sodium levels can have negative health effects, it is less likely to accumulate in dangerous proportions solely due to kidney dysfunction.
- Ammonia is a waste product that is normally converted into urea in the liver and eliminated by the kidneys. While impaired kidney function can lead to increased ammonia levels, it is not typically the primary substance that accumulates in dangerous proportions.
- Lysine is an essential amino acid that is used by the body for protein synthesis. It is not a waste product and is unlikely to accumulate in dangerous proportions in the blood solely due to kidney dysfunction.
Therefore, the most likely substance to accumulate in dangerous proportions in the blood of a person with kidney dysfunction is urea (Option A).

Urea transportation in the body:
Urea, a waste product of protein metabolism, is transported in the body through various mechanisms. It is important to understand how urea is transported as it plays a crucial role in maintaining the body's nitrogen balance. Among the options given, the correct answer is A: Blood plasma.
Explanation:
- Blood plasma: Urea is primarily transported in the bloodstream through the plasma, which is the liquid component of the blood. The concentration of urea in the blood plasma is regulated by the kidneys, which filter and excrete urea as part of the urine production process.
- Leucocytes: Leucocytes, or white blood cells, are involved in the immune response and defense against infections. They are not directly involved in the transportation of urea.
- RBCs: Red blood cells (RBCs) are responsible for transporting oxygen to the tissues and carbon dioxide back to the lungs. They do not play a significant role in urea transportation.
- Haemoglobin: Hemoglobin is a protein found in red blood cells that binds and carries oxygen. It is not directly involved in the transportation of urea.
In summary, urea is primarily transported by blood plasma in the body. The concentration of urea in the blood plasma is regulated by the kidneys, and excess urea is excreted in the urine.

Explanation:
To determine which set of animals are uricotelic, we need to understand the concept of uricotelism.
Uricotelism:
Uricotelism is a type of excretion where animals excrete waste in the form of uric acid. This is different from ammonotelism, where animals excrete waste in the form of ammonia, and ureotelism, where waste is excreted as urea.
Identifying the uricotelic animals:
We need to analyze each set of animals and determine if they are uricotelic or not.
Set A: Fish, frog, lizard, and fowl
- Fish: Fish are ammonotelic, not uricotelic.
- Frog: Frogs are uricotelic.
- Lizard: Lizards are uricotelic.
- Fowl (bird): Birds are uricotelic.
Set B: Fish, snake, fowl, and man
- Same as Set A, fish and fowl are ammonotelic and uricotelic respectively.
- Snake: Snakes are uricotelic.
- Man (human): Humans are ureotelic, not uricotelic.
Set C: Camel, dog, monkey, and man
- Camel: Camels are uricotelic.
- Dog: Dogs are ureotelic, not uricotelic.
- Monkey: Monkeys are uricotelic.
- Man (human): Same as Set B, humans are ureotelic.
Set D: Crow, snake, cockroach, and lizard
- Same as Set A, lizard is uricotelic.
- Crow: Crows are uricotelic.
- Snake: Same as Set B, snakes are uricotelic.
- Cockroach: Cockroaches are ammonotelic, not uricotelic.
Conclusion:
From the analysis of all the sets, we can conclude that Set D (Crow, snake, cockroach, and lizard) consists of only uricotelic animals.

Major nitrogenous waste product in ureotelic animals like rabbit and other mammals is urea.
Explanation:
- Ureotelic animals are those that excrete nitrogenous waste primarily in the form of urea.
- Urea is a water-soluble compound that is produced in the liver through the metabolic breakdown of amino acids.
- It is less toxic than ammonia, which is the waste product excreted by ammoniotelic animals such as fish.
- Urea is transported to the kidneys via the bloodstream, where it is filtered out and excreted in urine.
- The ability to convert ammonia into urea is an important adaptation for terrestrial animals, as it allows for less water loss during waste excretion.
- Rabbits and other mammals are ureotelic animals, and therefore their major nitrogenous waste product is urea.
In summary, the major nitrogenous waste product in ureotelic animals like rabbits and other mammals is urea. This compound is less toxic than ammonia and is excreted in urine after being produced in the liver through the breakdown of amino acids.

To determine which set of animals produce the same substance as their chief excretory product, we need to consider the excretory products of each animal in the given sets.
Set A: Camel, housefly, and snake
- The chief excretory product of the camel is urine, which contains urea.
- The chief excretory product of the housefly is excreta, which contains uric acid.
- The chief excretory product of the snake is also excreta, which contains uric acid.
Since the excretory products of the camel, housefly, and snake are different, Set A does not fulfill the condition of producing the same substance as their chief excretory product.
Set B: Fish, pigeon, and frog
- The chief excretory product of fish is ammonia, which is excreted through their gills.
- The chief excretory product of pigeons is uric acid, which is excreted in the form of white paste.
- The chief excretory product of frogs is also ammonia, which is excreted through their skin.
Since the excretory products of fish, pigeon, and frog are different, Set B does not fulfill the condition of producing the same substance as their chief excretory product.
Set C: Amoeba, ant, and antelope
- Amoeba, being a unicellular organism, does not have a specific excretory product.
- The chief excretory product of ants is formic acid, which is excreted through their exocrine glands.
- The chief excretory product of antelopes is urea, which is excreted in their urine.
Since the excretory products of amoeba, ant, and antelope are different, Set C does not fulfill the condition of producing the same substance as their chief excretory product.
Set D: Frog, monkey, and dog
- As mentioned earlier, the chief excretory product of frogs is ammonia.
- The chief excretory product of monkeys is urea, which is excreted in their urine.
- The chief excretory product of dogs is also urea, which is excreted in their urine.
Since the excretory products of frog, monkey, and dog are the same (urea), Set D fulfills the condition of producing the same substance as their chief excretory product.
Therefore, the correct answer is Set D: Frog, monkey, and dog.

The blood which leaves the liver and moves to the heart has higher than the usual contents of Urea.
There are several reasons why the blood leaving the liver and moving to the heart has higher than usual contents of urea. Here is a detailed explanation:
Liver Function:
- The liver is an important organ responsible for various metabolic functions in the body, including the breakdown and excretion of waste products.
- One of the liver's primary functions is to remove toxins and nitrogenous waste from the bloodstream.
Urea Formation:
- Urea is a waste product formed in the liver as a result of the breakdown of proteins and amino acids.
- The liver converts ammonia, which is toxic, into urea through a process called the urea cycle.
- The urea is then transported through the bloodstream to the kidneys for excretion.
Urea in the Bloodstream:
- The blood leaving the liver contains higher concentrations of urea due to the liver's role in the formation and removal of this waste product.
- This is because the liver actively synthesizes and releases urea into the bloodstream as part of its metabolic processes.
- The concentration of urea in the blood leaving the liver is higher than in other parts of the circulatory system.
Transport to the Heart:
- The blood leaving the liver is transported to the heart via the hepatic vein.
- The hepatic vein carries blood from the liver back to the heart, specifically to the right atrium.
- From the right atrium, the blood is then pumped to the lungs for oxygenation and further circulation.
Conclusion:
In conclusion, the blood leaving the liver and moving to the heart has higher than usual contents of urea. This is because the liver plays a significant role in the formation and removal of urea, a waste product of protein metabolism. The concentration of urea in the blood leaving the liver is higher due to the liver's active synthesis and release of urea into the bloodstream.

Explanation:
Urea is a nitrogenous waste:
- Urea is a waste product that is produced in the liver as a result of protein metabolism.
- It is formed from the breakdown of amino acids in the body.
Substances that contribute to nitrogen:
- Nitrogen is an essential element for the synthesis of amino acids and proteins in the body.
- Amino acids are the building blocks of proteins and contain nitrogen.
- Therefore, substances that contain amino acids contribute to the nitrogen content in the body.
Options:
A. Mineral salts:
- Mineral salts do not directly contribute to the nitrogen content in the body.
- They are essential for various physiological processes but do not contain nitrogen.
B. Amino acids:
- Amino acids are the primary source of nitrogen in the body.
- They contribute to the nitrogen content by providing the nitrogen atoms necessary for protein synthesis.
C. Vitamins:
- Vitamins are organic compounds that are essential for various biochemical reactions in the body.
- While some vitamins may contain nitrogen, they do not directly contribute to the nitrogen content in the body.
D. Lipids:
- Lipids, also known as fats, do not contribute to the nitrogen content in the body.
- They are composed of carbon, hydrogen, and oxygen but do not contain nitrogen.
Conclusion:
- Among the given options, only amino acids contribute to the nitrogen content in the body.
- Therefore, the correct answer is B: Amino acids.

Explanation:

A man who has taken a large amount of protein in his diet will excrete more urea.

Reasoning:

• Protein is broken down into amino acids in the body.


• Amino acids are then converted into ammonia.


• The liver converts ammonia into urea, which is a less toxic substance.


• Urea is then excreted by the kidneys in urine.

Conclusion:

Therefore, when a person consumes a large amount of protein, their body breaks it down into amino acids, converts it into urea, and excretes it through urine.

Explanation:
Insects and Excretion:
- Insects are small invertebrate animals that have a specialized excretory system for removing waste products from their bodies.
- Excretion in insects primarily involves the removal of nitrogenous waste, which is a byproduct of protein metabolism.
Types of Nitrogenous Waste:
- There are three main types of nitrogenous waste: ammonia, urea, and uric acid.
- Ammonia is highly toxic and requires a large amount of water for dilution. It is the most primitive form of nitrogenous waste.
- Urea is less toxic and can be excreted in a more concentrated form, requiring less water. It is the main nitrogenous waste product in mammals.
- Uric acid is the least toxic and can be excreted as a solid, requiring very little water. It is the main nitrogenous waste product in birds, reptiles, and insects.
Excretory Types in Insects:
- Insects are uricotelic, which means they excrete nitrogenous waste mainly in the form of uric acid.
- Uric acid is insoluble in water and can be excreted as a dry, solid material, minimizing water loss.
- This adaptation is advantageous for insects as they often live in arid environments where water is scarce.
Conclusion:
- In summary, most insects are uricotelic, excreting nitrogenous waste primarily in the form of uric acid. This adaptation allows them to conserve water and thrive in arid environments.

Uric Acid as the Chief Excretory Product in Insects

Introduction:

Uric acid is a waste product that is formed from the breakdown of purines, which are nitrogenous compounds found in nucleic acids. It is excreted by various organisms as a means of eliminating excess nitrogen from their bodies. In insects, uric acid serves as the chief excretory product.

Insects:

• Uric acid production: Insects have a unique excretory system that involves the production of uric acid as the primary waste product.


• Advantages of uric acid: Uric acid has several advantages for insects:




• It is insoluble in water, which allows insects to conserve water in their bodies.


• It can be stored as a solid, which reduces the need for excessive water loss during excretion.


• It requires less energy for its synthesis compared to other nitrogenous waste products like ammonia or urea.




• Excretion: Insects excrete uric acid through specialized structures called Malpighian tubules. These tubules actively transport uric acid from the hemolymph (insect equivalent of blood) into the digestive system, where it is mixed with feces and eliminated from the body.

Comparison with other organisms:

• Earthworms: Earthworms excrete nitrogenous waste primarily in the form of ammonia, which is produced by their nephridia.


• Amphibians: Amphibians, such as frogs and salamanders, excrete nitrogenous waste in the form of urea through their kidneys.


• Mammals: Mammals, including humans, excrete nitrogenous waste mainly as urea through their kidneys.

Conclusion:

Insects have evolved a unique excretory system that utilizes uric acid as the chief waste product. This adaptation allows them to conserve water, store waste as a solid, and minimize energy expenditure. In contrast, other organisms like earthworms, amphibians, and mammals excrete different nitrogenous waste products such as ammonia or urea.

Snakes living in deserts are mainly Uricotelic.
Explanation:
- Uricotelic refers to the excretion of nitrogenous waste in the form of uric acid.
- Snakes living in deserts have adapted to conserve water due to the arid conditions.
- Uric acid is a relatively non-toxic and insoluble compound, allowing snakes to excrete waste without using excessive amounts of water.
- This is advantageous in desert environments where water is scarce and conservation is crucial for survival.
- Uricotelic animals, such as snakes, convert the toxic ammonia produced by protein metabolism into a less toxic form, uric acid.
- Uric acid requires less water for excretion compared to other nitrogenous waste products like ammonia or urea.
- By being uricotelic, snakes in deserts can minimize water loss and maintain their water balance more effectively.
- It is important for desert-dwelling snakes to have efficient water conservation mechanisms to survive in their harsh habitat.

The least toxic nitrogenous waste is Uric acid.
Explanation:
Uric acid is considered the least toxic nitrogenous waste among the options given. Here's why:
1. Ammonia:
- Ammonia is highly toxic to the body and requires a lot of water to dilute it.
- It is mainly excreted by aquatic organisms, such as fish, in the form of ammonia.
- High levels of ammonia in the body can lead to problems like ammonia poisoning.
2. Urea:
- Urea is the primary nitrogenous waste product in mammals, including humans.
- It is formed in the liver by the breakdown of amino acids and is less toxic than ammonia.
- Urea requires less water to dilute it, making it the main nitrogenous waste in terrestrial animals.
- Urea is excreted by the kidneys in urine.
3. Uric Acid:
- Uric acid is the least toxic nitrogenous waste among the given options.
- It is the primary nitrogenous waste in reptiles, birds, and insects.
- Uric acid is relatively insoluble in water, allowing it to be excreted as a paste or solid, reducing water loss.
- This is an advantage for organisms living in arid environments or those with limited access to water.
In summary, while urea is the primary nitrogenous waste product in mammals, including humans, uric acid is the least toxic nitrogenous waste among the options given. It is excreted by reptiles, birds, and insects, allowing for conservation of water in arid environments.

Reptiles: Storage of Uric Acid
Background Information:
- Reptiles are a class of cold-blooded vertebrates that include turtles, snakes, lizards, and crocodiles.
- They excrete waste in the form of uric acid, a nitrogenous waste product.
Storage of Uric Acid:
- Uric acid is stored in the cloaca of reptiles.
- The cloaca is a common chamber that serves as the exit for both the digestive and urinary systems in reptiles.
- It acts as a storage area for urine, feces, and reproductive products.
Reasoning:
- The anus is the opening at the end of the digestive tract through which waste materials are eliminated. It is not involved in the storage of uric acid.
- The liver is responsible for producing uric acid, but it does not store it.
- Fat bodies in reptiles primarily serve as energy reserves and insulation, not for the storage of uric acid.
Conclusion:
- In reptiles, uric acid is stored in the cloaca.
- The cloaca serves as a common chamber for waste elimination and reproductive functions in reptiles.

To determine the excretion form of benzoic acid in mammals, we need to analyze the different options provided and identify which compound is formed during the process.
Option A: Hippuric acid
- Hippuric acid is formed by the conjugation of benzoic acid with glycine in the liver.
- It is a major pathway for the excretion of benzoic acid in mammals, including humans.
- The formed hippuric acid is then excreted out in the urine.
Option B: Ornithinic acid
- Ornithinic acid is not involved in the excretion of benzoic acid in mammals.
- This option is not the correct answer.
Option C: Uric acid
- Uric acid is not formed during the metabolism or excretion of benzoic acid in mammals.
- This option is not the correct answer.
Option D: Aspartic acid
- Aspartic acid is not involved in the excretion of benzoic acid in mammals.
- This option is not the correct answer.
Therefore, the correct answer is Option A: Hippuric acid.

Excretory Product of Excess Metabolism of Creatine

Creatine is a naturally occurring compound found in the body that is involved in energy production, particularly during high-intensity exercise. When creatine is metabolized in excess, it is broken down into several byproducts, one of which is excreted as waste. The excretory product of excess metabolism of creatine is creatinine.

Key Points:

- Creatine is a compound involved in energy production.
- Excess metabolism of creatine results in the production of several byproducts.
- One of the byproducts, creatinine, is excreted as waste.

Other options mentioned in the question:

Oxalic acid:

- Oxalic acid is not a byproduct of creatine metabolism.

Uric acid:

- Uric acid is not a byproduct of creatine metabolism.

Urea:

- Urea is not a byproduct of creatine metabolism.

Therefore, the correct answer is creatinine.

Column of Bertini is found in the Kidney
The column of Bertini refers to the structures found within the kidney. Here is a detailed explanation:
What is the column of Bertini?
- The column of Bertini, also known as renal columns, are extensions of the renal cortex that project into the renal medulla.
- They are composed of connective tissue and contain blood vessels, nerves, and urine-collecting ducts.
Location of the column of Bertini:
- The column of Bertini is found within the kidney.
Function of the column of Bertini:
- The column of Bertini provides structural support to the kidney.
- It helps to separate and organize the renal pyramids, which are triangular-shaped structures in the renal medulla.
- The columns also contain blood vessels that supply oxygen and nutrients to the kidney tissues.
Other key points:
- The column of Bertini is not exclusive to any gender and is present in both males and females.
- It is an important anatomical feature of the kidney and plays a role in maintaining kidney structure and function.
Conclusion:
- The column of Bertini is found in the kidney and provides structural support to the organ.
- It is composed of connective tissue and contains blood vessels, nerves, and urine-collecting ducts.
- This anatomical feature helps separate and organize the renal pyramids in the renal medulla.

Man is Ureotelic
- Ureotelic refers to the excretion of nitrogenous waste in the form of urea.
- Man, along with many other mammals, excretes urea as a means of eliminating excess nitrogen from the body.
- Urea is produced in the liver through the breakdown of proteins and is then transported to the kidneys for excretion.
- The process of urea formation and excretion allows for the efficient removal of nitrogenous waste while conserving water.
- Ureotelism is a characteristic feature of mammals, including humans, as it allows for the disposal of toxic ammonia while minimizing water loss.
- Other animals, such as fish (ammonotelic) and reptiles (uricotelic), excrete nitrogenous waste in different forms.
- Therefore, the correct answer is B: Ureotelic.

The retroperitoneal kidney is:
- Kidney covered by peritoneum on the ventral side.
Explanation:
- The peritoneum is a membrane that lines the abdominal cavity and covers most of the organs within it.
- The retroperitoneal space is located behind the peritoneum.
- The retroperitoneal kidney is positioned in this space.
- It is covered by the peritoneum on the ventral (front) side, but not on the dorsal (back) side.
- This positioning helps protect the kidney and keep it in place within the abdominal cavity.
- The peritoneum acts as a protective covering for the kidney, providing support and preventing it from moving freely within the abdominal cavity.
- The retroperitoneal kidney is an anatomical term used to describe the specific location of the kidney within the body.
Therefore, the correct answer is A: Kidney covered by peritoneum on the ventral side.

Position of Kidney:
The position of the kidney is retroperitoneal, which means it is located behind the peritoneum. The peritoneum is a membrane that lines the abdominal cavity and covers most of the abdominal organs. The kidneys are situated on either side of the spine, just below the ribcage.
Explanation:
- The kidneys are retroperitoneal organs, meaning they are located behind the peritoneum.
- They are positioned on either side of the spine, in the back of the abdominal cavity.
- The kidneys are situated just below the ribcage, with the right kidney slightly lower than the left kidney due to the presence of the liver.
- The retroperitoneal position of the kidneys provides protection from external trauma and allows for easy access to the renal arteries and veins.
- The kidneys are responsible for filtering waste products and excess fluids from the blood, producing urine, and maintaining electrolyte balance in the body.
Summary:
The kidneys are retroperitoneal organs located behind the peritoneum. They are positioned on either side of the spine, just below the ribcage. The retroperitoneal position of the kidneys provides protection and easy access to the renal arteries and veins.

The Role of the Kidneys in Maintaining Blood Pressure Constant
The kidneys play a crucial role in maintaining the blood pressure of the body. Here's how they achieve this:
Filtration of Waste Products:
- The kidneys filter waste products, excess electrolytes, and toxins from the blood through tiny filtering units called nephrons.
- This filtration process helps maintain the composition of the blood by removing harmful substances.
Regulation of Fluid Balance:
- The kidneys help regulate the fluid balance in the body by adjusting the amount of water and electrolytes excreted in the urine.
- When blood pressure is too high, the kidneys remove excess fluid, reducing the volume and subsequently lowering the blood pressure.
- On the other hand, when blood pressure is too low, the kidneys retain more fluid, increasing the volume and raising the blood pressure.
Renin-Angiotensin-Aldosterone System:
- The kidneys produce a hormone called renin, which is involved in the regulation of blood pressure.
- Renin initiates a series of reactions known as the renin-angiotensin-aldosterone system (RAAS), which ultimately leads to the constriction of blood vessels and the retention of salt and water.
- These actions increase blood volume and subsequently raise blood pressure.
Control of Sodium and Potassium Levels:
- The kidneys play a crucial role in maintaining the balance of sodium and potassium ions in the body.
- Imbalances in these electrolytes can lead to changes in blood pressure.
- The kidneys adjust the reabsorption and excretion of these ions to maintain their optimal levels, thus contributing to blood pressure regulation.
In conclusion, the kidneys not only remove waste products from the blood but also play a vital role in maintaining blood pressure constant. Through filtration, fluid balance regulation, the renin-angiotensin-aldosterone system, and control of sodium and potassium levels, the kidneys help ensure that blood pressure remains within a normal range.

Answer:
The functional part of the kidney in adult reptiles, birds, and mammals is the Metanephros. Here is a detailed explanation:
1. Holonephros:
- Holonephros is the functional kidney found in adult fishes and amphibians.
- It is a primitive kidney structure that consists of a single tubule.
- This type of kidney is not found in reptiles, birds, and mammals.
2. Pronephros:
- Pronephros is the embryonic kidney that develops in vertebrate embryos.
- It is the first kidney structure to form in the developing embryo but degenerates before birth.
- Pronephros is not the functional kidney in adult reptiles, birds, and mammals.
3. Mesonephros:
- Mesonephros is an intermediate kidney structure found in vertebrate embryos.
- It develops after the degeneration of the pronephros and functions temporarily.
- In reptiles, birds, and mammals, mesonephros becomes non-functional during development and is replaced by the metanephros.
4. Metanephros:
- Metanephros is the final and functional kidney structure in adult reptiles, birds, and mammals.
- It develops from the intermediate mesonephros during embryonic development.
- Metanephros consists of nephrons, which are the functional units responsible for filtering and excreting waste products from the blood.
- This type of kidney is responsible for maintaining water and electrolyte balance in the body.
Therefore, the correct answer is D. Metanephros.

Kidney structure in different animals:
Frog:
- The kidney of a frog is not distinguished into cortex and renal medulla.
- It has a relatively simple structure compared to other animals.
Man:
- The human kidney is distinctly divided into two regions: the outer cortex and the inner medulla.
- The cortex is the outer layer and contains the glomeruli and the convoluted tubules.
- The medulla is the inner region and consists of renal pyramids.
Rabbit:
- Similar to humans, the kidney of a rabbit is also divided into cortex and medulla.
- The cortex contains the glomeruli and the convoluted tubules.
- The medulla consists of renal pyramids.
Camel:
- The kidney of a camel is also divided into cortex and medulla, similar to humans and rabbits.
- The cortex contains the glomeruli and the convoluted tubules.
- The medulla consists of renal pyramids.
Conclusion:
- Out of the given options, the kidney of a frog is the only one that is not distinguished into cortex and renal medulla.
- Therefore, the correct answer is A: Frog.

Main Function of Pyramids of Kidney:
The pyramids of the kidney, also known as renal pyramids, have several important functions in the urinary system. The main function of pyramids of the kidney is to contain the collecting tubules, which play a crucial role in the filtration and reabsorption processes of urine formation.
Explanation:
The detailed explanation of the main function of pyramids of the kidney is as follows:
1. Contain Collecting Tubules: The pyramids of the kidney house the collecting tubules, which are responsible for collecting the urine that has been filtered and processed by the nephrons. These tubules transport the urine towards the renal pelvis and eventually into the ureter.
2. Urine Flow: The pyramids of the kidney are shaped like cones, with the base facing towards the cortex and the apex pointing towards the renal pelvis. This arrangement allows for the urine to flow in a directed manner towards the renal pelvis and subsequently into the ureter for excretion from the body.
3. Support for Collecting Canals: The pyramids of the kidney also provide structural support for the openings of the collecting canals, which receive the urine from the collecting tubules. These canals merge to form larger ducts known as the papillary ducts, which transport the urine towards the renal pelvis.
In conclusion, the main function of pyramids of the kidney is to contain the collecting tubules, direct the flow of urine towards the renal pelvis, and provide support for the openings of the collecting canals. These functions are essential for the proper filtration and elimination of waste products from the body.

Factors influencing the activity of the kidney:
1. Vasopressin:
- Vasopressin, also known as antidiuretic hormone (ADH), plays a crucial role in regulating the activity of the kidney.
- It acts on the collecting ducts of the nephrons in the kidney, promoting water reabsorption and reducing urine output.
- When vasopressin levels are high, more water is reabsorbed by the kidney, leading to concentrated urine. Conversely, low levels of vasopressin result in increased urine production.
2. Adrenalin:
- Adrenalin, also known as epinephrine, is a hormone released by the adrenal glands in response to stress or excitement.
- It can influence the activity of the kidney by constricting the renal blood vessels, reducing blood flow to the kidneys.
- This constriction helps to divert blood to other vital organs during the fight-or-flight response, but it can also decrease urine production.
3. Gonadotrophins:
- Gonadotrophins are hormones released by the pituitary gland that stimulate the gonads (testes in males and ovaries in females).
- While gonadotrophins primarily influence reproductive functions, they can indirectly affect kidney activity by regulating the production of sex hormones.
- Sex hormones, such as estrogen and testosterone, can impact fluid balance and electrolyte regulation in the body, which can indirectly affect kidney function.
4. Thyroxine:
- Thyroxine, also known as T4, is a hormone produced by the thyroid gland that regulates metabolism and energy production in the body.
- It can influence the activity of the kidney by increasing blood flow to the kidneys, promoting filtration and urine production.
- Thyroxine also enhances the responsiveness of renal tubules to other hormones involved in fluid and electrolyte balance.
In conclusion, the factors that influence the activity of the kidney include vasopressin, adrenalin, gonadotrophins, and thyroxine. These hormones play essential roles in regulating water reabsorption, urine production, blood flow to the kidneys, and fluid and electrolyte balance.

Feature enabling the mammalian kidney to concentrate urine in the medullary region:
There are several features that enable the mammalian kidney to concentrate urine in the medullary region. Among them, maintaining a high osmotic pressure in the tissues between the tubules plays a crucial role. Here's a detailed explanation:
1. Maintaining a high osmotic pressure:
- The medulla of the kidney contains a concentration gradient, with the outer region having a lower osmotic pressure and the inner region having a higher osmotic pressure.
- This gradient is established through the countercurrent multiplication mechanism, which involves the reabsorption of water and solutes from the descending and ascending limbs of the loop of Henle.
- The reabsorption of water and solutes in the loop of Henle creates a hypertonic environment in the medulla, allowing for the concentration of urine.
2. Countercurrent exchange mechanism:
- The vasa recta, a network of blood vessels surrounding the loop of Henle, also plays a role in maintaining the concentration gradient in the medulla.
- The vasa recta acts as a countercurrent exchanger, allowing the exchange of water and solutes between the descending and ascending limbs of the loop of Henle.
- This countercurrent exchange mechanism helps to preserve the concentration gradient and prevent the dilution of the medullary interstitium.
3. Water reabsorption:
- The reabsorption of water in the collecting ducts is regulated by the hormone antidiuretic hormone (ADH).
- In the presence of ADH, the permeability of the collecting ducts to water increases, allowing for the reabsorption of water from the urine.
- This further concentrates the urine and contributes to the overall concentration of the medullary interstitium.
In conclusion, maintaining a high osmotic pressure in the tissues between the tubules is the key feature enabling the mammalian kidney to concentrate urine in the medullary region. This is achieved through the countercurrent multiplication mechanism, the countercurrent exchange mechanism, and the regulation of water reabsorption in the collecting ducts.

The Loop of Henle in the kidney of the rabbit is part of the Uriniferous tubule.
Explanation:
The kidney plays a crucial role in maintaining the body's water and electrolyte balance. The nephron is the functional unit of the kidney, and it consists of various components, including the glomerulus, Bowman's capsule, proximal convoluted tubule, Loop of Henle, and distal convoluted tubule.
The Loop of Henle is a U-shaped segment of the nephron that extends from the cortex to the medulla of the kidney. It is responsible for reabsorbing water and electrolytes from the filtrate, thereby concentrating the urine.
Here is a breakdown of the different parts mentioned in the question:
- Collecting duct: The collecting duct is responsible for further reabsorption of water and adjustment of urine concentration. It receives urine from multiple nephrons and plays a crucial role in maintaining the body's fluid balance.
- Glomerulus: The glomerulus is a network of tiny blood vessels located in the Bowman's capsule. It filters blood and forms the initial filtrate that enters the nephron.
- Uriniferous tubule: The uriniferous tubule is the entire structure of the nephron, including the glomerulus, Bowman's capsule, proximal convoluted tubule, Loop of Henle, and distal convoluted tubule. It is responsible for the formation of urine.
- Bowman's capsule: Bowman's capsule surrounds the glomerulus and collects the filtrate that is formed during the filtration process.
Therefore, the correct answer is C: Uriniferous tubule as the Loop of Henle is a part of it.

Trimethylamine oxide (TMAO) is excreted by marine teleosts.
Explanation:
- TMAO is a compound that helps marine teleosts, which are bony fishes that live in saltwater, to maintain osmotic balance in their bodies.
- Marine teleosts excrete TMAO through their gills and kidneys to regulate the concentration of solutes in their bodies.
- TMAO acts as a stabilizer of proteins and other macromolecules, protecting them from the denaturing effects of high salt concentrations in the marine environment.
- TMAO also helps to counteract the osmotic stress that marine teleosts experience in saltwater by balancing the concentration of solutes inside their cells.
- In contrast, fresh water fishes, such as freshwater teleosts, do not excrete TMAO because they live in a hypoosmotic environment where they need to conserve solutes.
- Molluscs and amphibians have different mechanisms for osmoregulation and do not rely on TMAO excretion.
Therefore, the correct answer is C: Marine teleosts.