Excretory waste products Questions in English

(B) Organisms are classified based on their nitrogenous waste products:
$1$. Ammonotelic: Excrete ammonia (e.g.,most aquatic invertebrates,bony fishes).
$2$. Ureotelic: Excrete urea (e.g.,mammals,terrestrial amphibians like frogs,and marine fishes).
$3$. Uricotelic: Excrete uric acid (e.g.,reptiles,birds,land snails,and insects like cockroaches).
Cockroaches are uricotelic organisms,meaning they excrete nitrogenous waste in the form of uric acid pellets to conserve water.

(D) In humans,the primary nitrogenous waste product is $Urea$.
$Urea$ is synthesized in the $Liver$ through the $Ornithine$ $cycle$ (also known as the $Urea$ $cycle$).
Once synthesized,$Urea$ is released into the blood and transported to the $Kidneys$.
The $Kidneys$ filter the blood and excrete the $Urea$ from the body in the form of $Urine$.
Therefore,it is synthesized in the liver but primarily eliminated by the kidneys.

(A) Organisms that excrete nitrogenous waste in the form of uric acid are called uricotelic organisms.
Uric acid is excreted in the form of a pellet or paste with a minimum loss of water,which is an adaptation for water conservation.
This mode of excretion is characteristic of reptiles,birds,land snails,and insects.
Therefore,among the given options,reptiles and birds exhibit the uricotelic mode of excretion.

(B) In plants,metabolic activities produce various substances that are not required for further physiological processes. These are known as waste products or excretory products.
Inulin is a polysaccharide stored in the roots of plants like Dahlia. However,in the context of plant physiology,raphides are needle-like crystals of calcium oxalate that act as waste products or defensive structures.
In many biological contexts,both are categorized under plant excretory or waste products that the plant stores or deposits in specific tissues.

(B) Urea is produced in the liver as a byproduct of the deamination of amino acids during the urea cycle.
Since the liver is the site of urea synthesis,the blood leaving the liver via the hepatic vein contains the highest concentration of urea compared to any other blood vessel in the body.
The hepatic portal vein carries blood from the digestive tract to the liver,while the renal vein carries blood away from the kidneys after filtration,and the dorsal aorta distributes oxygenated blood to the body tissues.

(B) In mammals,urea is produced in the liver through the ornithine cycle (urea cycle) as a byproduct of amino acid metabolism.
Since the liver is the site of urea synthesis,the blood leaving the liver via the hepatic vein contains the highest concentration of urea compared to any other blood vessel in the body.
The renal vein carries blood away from the kidneys,which have already filtered the urea out of the blood,so it contains the lowest concentration of urea.
The dorsal aorta carries oxygenated blood to various parts of the body,and the hepatic portal vein carries blood from the digestive tract to the liver,neither of which has as high a concentration of urea as the hepatic vein.

(D) Deamination is the process of removing an amino group $(-NH_2)$ from an amino acid,resulting in the formation of a keto acid and the release of ammonia $(NH_3)$.
This process primarily occurs in the liver,where the toxic ammonia is subsequently converted into urea via the urea cycle.
Therefore,the Assertion is incorrect because deamination does take place in the liver.
The Reason is correct as it accurately describes the biological purpose of deamination,which is to utilize excess amino acids that cannot be stored or incorporated into the protoplasm.

(D) The main nitrogenous waste product in human urine is $Urea$,not $Ammonia$.
Therefore,the Assertion is incorrect.
However,when urine is left to stand,bacteria decompose the $Urea$ present in the urine,leading to the production of $Ammonia$,which causes a strong pungent smell.
Thus,the Reason is correct.

(B) Osmoregulation is a homeostatic mechanism that regulates the optimum concentration of water and salts in the tissues and body fluids.
It maintains the internal environment of the body by balancing water and ionic concentrations.

(N/A) Terrestrial animals are either ureotelic or uricotelic,and not ammonotelic. This is because of the following two main reasons:
$(a)$ Ammonia is highly toxic in nature. Therefore,it needs to be converted into a less toxic form such as urea or uric acid.
$(b)$ Terrestrial animals need to conserve water. Since ammonia is soluble in water,it cannot be eliminated continuously. Hence,it is converted into urea or uric acid. These forms are less toxic and also require significantly less water for excretion. This helps terrestrial animals conserve water.

(B) healthy adult human excretes (on an average) $25-30$ $gm$ of urea per day.
Urea is the primary nitrogenous waste product in humans,produced in the liver via the urea cycle and excreted by the kidneys.

(N/A) Excretion is the biological process by which an organism eliminates metabolic waste products from its body to maintain homeostasis.
Animals accumulate various metabolic wastes such as ammonia,urea,uric acid,carbon dioxide $(CO_{2})$,water,and ions like $Na^{+}$,$Cl^{-}$,$K^{+}$,phosphates,and sulphates.
These substances are collectively known as excretory substances,and the process of their removal is termed excretion.

(N/A) The major forms of nitrogenous wastes are $Ammonia$, $Urea$, and $Uric \text{ } acid$.
$\Rightarrow$ $Ammonia$ is the most toxic form and requires a large amount of water for its elimination.
- $Uric \text{ } acid$ is the least toxic and can be removed with a minimum loss of water.
Based on the types of excretory substances, animals are categorized into three groups:
$(A)$ $Ammonotelic$ $(B)$ $Ureotelic$ $(C)$ $Uricotelic$
$(A)$ $Ammonotelic$: The deamination of amino acids produces $Ammonia$. It is a poisonous substance removed with the help of water.
- The method of excretion of $Ammonia$ is called the $Ammonotelic$ process.
- $Ammonia$, being readily soluble in water, is generally excreted by diffusion across body surfaces or through gill surfaces (in fish). Kidneys do not play any significant role in its removal.
- e.g., Aquatic insects, $Osteichthyes$, and tadpoles are $Ammonotelic$.
$(B)$ $Ureotelic$: $Ureotelic$ animals mainly excrete $Urea$.
- $Urea$ is a less poisonous nitrogenous substance. It is excreted mainly by terrestrial vertebrate animals.
- In such animals, $Ammonia$ produced by metabolism is converted into $Urea$ in the liver ($2$ molecules of $Ammonia + 1$ molecule of $CO_2 = Urea$) and released into the blood, which is filtered and excreted out by the kidneys.
$\Rightarrow$ Some amount of $Urea$ may be retained in the kidney matrix of some of these animals to maintain a desired osmolarity.
- The process in which excretion occurs in the form of $Urea$ is called $Ureotelism$. e.g., Mammals, $Chondrichthyes$, and adult amphibians.
$(C)$ $Uricotelic$: $Uric \text{ } acid$ is the least poisonous nitrogenous substance.
- In order to minimize the loss of water, these animals excrete $Uric \text{ } acid$ in the form of pellets or paste. $Uric \text{ } acid$ is formed in the liver from $Ammonia$ ($3$ molecules of $NH_3 + 2$ molecules of $CO_2 = Uric \text{ } acid$).
- e.g., Reptiles, birds, insects, and land snails.
- The process by which $Uric \text{ } acid$ is excreted is known as $Uricotelism$.

(N/A) $\Rightarrow$ Urine is a light yellow-coloured,watery fluid.
$\Rightarrow$ It is slightly acidic in nature with a $pH$ of approximately $6.0$ and possesses a characteristic odour.
$\Rightarrow$ On average,$25-30 \ gm$ of urea is excreted per day by a healthy adult.
$\Rightarrow$ The analysis of urine is crucial for the clinical diagnosis of various metabolic disorders and kidney malfunctions.
$\Rightarrow$ For instance,the presence of ketone bodies (Ketonuria) and glucose (Glycosuria) in the urine are strong indicators of $Diabetes \ Mellitus$.

(N/A) Uricotelism is the process of excreting nitrogenous waste in the form of uric acid.
Animals that exhibit uricotelism are known as uricotelic animals.
This mechanism is primarily an adaptation to minimize water loss,as uric acid is relatively non-toxic and can be excreted as a semi-solid pellet or paste.
Uric acid is synthesized in the liver from ammonia and carbon dioxide.
Examples of uricotelic organisms include reptiles,birds,insects,and land snails.

(N/A)

Ammonotelic	Ureotelic
$(1)$ Ammonia is dissolved in large amounts of water and eliminated.	$(1)$ Ammonia is converted into urea and then eliminated.
$(2)$ Energy is not utilized in the process.	$(2)$ Energy is utilized in the process.
$(3)$ Kidneys do not play a significant role in its elimination.	$(3)$ It is primarily removed by the kidneys.
$(4)$ Examples: Aquatic invertebrates,bony fishes (Osteichthyes),and tadpoles of amphibians.	$(4)$ Examples: Mammals,adult amphibians,and cartilaginous fishes (Chondrichthyes).

(A) Ammonia,produced as a result of the deamination of amino acids,is highly toxic.
Its elimination requires a large amount of water.
- Aquatic animals have access to sufficient water,so ammonia is excreted as a dilute solution.
- In aquatic insects,Osteichthyes (bony fishes),and tadpoles,ammonia is removed through the general body surface or gill surfaces.

(D) The body requires nutritive substances and $O_{2}$ for survival.
Similarly,substances formed as a result of metabolic activities,which are poisonous or unwanted,must be eliminated from the body to maintain homeostasis.
Specifically,nitrogenous poisonous substances and $CO_{2}$ must be removed.
If these excretory substances are not removed,their accumulation can severely affect health and disrupt physiological functions.
Therefore,the importance of excretion cannot be avoided.

(D) Osmoregulation is the process of maintaining the osmotic pressure of the fluids of an organism by the control of water and salt concentrations.
$1$. Our body consists of approximately $2/3$ water,and this proportion must be strictly maintained for physiological stability.
$2$. If the amount of $H_2O$ decreases,it leads to dehydration,which impairs cellular functions.
$3$. Excretory substances are removed via water; cellular waste enters the interstitial fluid,then the lymph,then the blood,and is finally transported to the excretory organs.
$4$. Excretory organs eliminate these wastes from the body. Therefore,a sufficient and regulated amount of water is essential for the effective removal of metabolic waste and the maintenance of homeostasis.

(C) Reptiles,birds,land snails,and insects excrete nitrogenous wastes as uric acid in the form of a pellet or paste with a minimum loss of water. This process is known as uricotelism,which is an adaptation to conserve water in terrestrial environments.

(D) Aquatic animals such as $Osteichthyes$ (bony fishes),aquatic amphibians,and aquatic insects excrete ammonia as their primary nitrogenous waste,hence they are known as ammonotelic.
Ammonia is highly soluble in water and requires a large volume of water to be dissolved and excreted through the body surface or gill surfaces.
Since aquatic animals live in water,the water required for the excretion of ammonia is easily available to them.
In contrast,terrestrial animals need to conserve water. Therefore,they excrete urea (ureotelic) or uric acid (uricotelic),which are less toxic than ammonia and require significantly less water for their removal. This is an essential evolutionary adaptation for water conservation in terrestrial environments.

(B) Terrestrial organisms have evolved specific excretory mechanisms to minimize water loss:
$1$. Terrestrial animals produce less toxic substances like urea or uric acid instead of highly toxic ammonia,which requires large amounts of water for dilution.
$2$. Mammals and many terrestrial amphibians are ureotelic,excreting urea,which requires significantly less $H_{2}O$ for elimination compared to ammonia.
$3$. Reptiles,birds,and insects are uricotelic,excreting uric acid in the form of a dry paste or pellet. This process requires negligible amounts of $H_{2}O$,making it an excellent adaptation for water conservation in arid environments.

(B) Animals accumulate metabolic waste products such as ammonia,urea,uric acid,carbon dioxide $(CO_{2})$,water,and ions like $Na^{+}$,$Cl^{-}$,$K^{+}$,phosphate,and sulphate through various metabolic activities. These substances are toxic or unnecessary for the body and are known as excretory substances,which must be eliminated to maintain homeostasis.

(N/A) No,the fresh water fish will not be able to survive in sea water.
Reasoning:
$1$. Sea water is hypertonic compared to the internal body fluids of a fresh water fish.
$2$. When placed in a hypertonic environment,the fish loses water from its body cells and tissues to the surrounding environment through the process of exosmosis.
$3$. This continuous loss of water leads to severe dehydration and physiological stress,ultimately resulting in the death of the fish.

(D) Animals are classified based on their primary nitrogenous waste product.
$1$. Ureotelic animals excrete urea,which includes humans and all other mammals,including aquatic mammals like whales.
$2$. Uricotelic animals excrete uric acid,which includes birds and lizards.
$3$. Ammonotelic animals excrete ammonia,which is typical of many bony fishes and aquatic amphibians.
Since whales are mammals,they are ureotelic,not ammonotelic. Therefore,option $D$ is incorrect.

(C) Bony fishes (osteichthyes) are ammonotelic,meaning they excrete nitrogenous waste primarily in the form of ammonia. Ammonia is highly toxic and requires a large amount of water for its elimination,which is readily available to aquatic bony fishes.

(B) The conversion of toxic ammonia into less toxic urea occurs via the $Ornithine$ cycle (also known as the $Krebs-Henseleit$ cycle),which takes place in the liver cells.
This process continuously removes highly toxic ammonia and $CO_{2}$ from the blood and releases urea into the bloodstream.
The kidneys then filter this urea from the blood to excrete it in the urine.

(D) Reptiles,birds,land snails,and insects excrete nitrogenous waste as uric acid in the form of a pellet or paste with a minimum loss of water. These organisms are called Uricotelic animals.

(C) The synthesis of urea occurs in the liver via the $Krebs-Henseleit$ cycle (also known as the urea cycle).
In this cycle,ammonia $(NH_3)$ and carbon dioxide $(CO_2)$ are converted into urea $(NH_2CONH_2)$ through a series of enzymatic reactions involving amino acids like ornithine,citrulline,and arginine.
The overall process can be summarized as:
$1$. Ornithine + $NH_3$ + $CO_2$ $\rightarrow$ Citrulline + $H_2O$
$2$. Citrulline + $NH_3$ $\rightarrow$ Arginine + $H_2O$
$3$. Arginine $\rightarrow$ Urea + Ornithine
Therefore,the liver is the primary site for urea synthesis,while the kidneys are responsible for the filtration and excretion of urea from the blood.

(A) The excretion of nitrogen in the form of uric acid as an excretory product is called Uricotelism,and the concerned animals are called Uricotelic,$e.g.,$ insects,birds,and reptiles.
Uric acid is the end product of purine metabolism and is excreted in a semi-solid form to conserve water.

(A) Proteins are composed of amino acids. When excess proteins are consumed,the amino acids undergo deamination in the liver,where the amino group $(-NH_2)$ is removed and converted into ammonia $(NH_3)$. Since ammonia is toxic,it is converted into urea $(CO(NH_2)_2)$ via the urea cycle and subsequently excreted by the kidneys. Therefore,a high-protein diet leads to an increased excretion of urea.

(C) The yellow colour of urine is due to the presence of the pigment Urochrome.
This pigment is a breakdown product of heme metabolism.
Bilirubin is processed in the liver and intestine to form urobilinogen,which is further oxidized to form Urochrome,the yellow pigment responsible for the characteristic colour of urine.

(D) In humans,the principal nitrogenous excretory compound,urea,is synthesised in the liver through the ornithine cycle (also known as the urea cycle).
Once synthesised,urea is transported via the blood to the kidneys.
The kidneys filter the blood and eliminate urea from the body as the primary component of urine.

(A) $(i)$ Ammonia $(NH_{3})$: It is the primary metabolic waste of protein metabolism. Ammonia is produced in the liver through the process of deamination. It is highly toxic and requires a large amount of water for its excretion.
$(ii)$ Urea: $A$ white crystalline solid product produced in the liver from $CO_{2}$ and $NH_{3}$. It is comparatively less toxic than ammonia. The normal level of urea in the blood is $18-38 \text{ mg}/100 \text{ mL}$.
$(iii)$ Uric Acid: It is the least toxic and is insoluble in water. It is produced in the liver by purine catabolism in birds and reptiles. It can be excreted in solid or semisolid form,which helps in water conservation. Therefore,the order of toxicity from lower to higher is: Uric acid < Urea < Ammonia.

(C) Nitrogenous compounds are produced by various metabolic processes,primarily through the process of deamination of amino acids.
In vertebrates,the first nitrogenous waste product formed during protein metabolism is ammonia $(NH_3)$.
Ammonia is highly toxic and requires a large amount of water for its elimination.
Since the earliest vertebrates were aquatic (fish),they could easily excrete ammonia directly into the surrounding water through their gills via diffusion.
Therefore,$NH_3$ is considered the primary and first-formed nitrogenous waste in the vertebrate lineage.

(C) Cockroach excretes uric acid as the chief nitrogenous excretory product,which is known as uricotelism.
Man excretes urea as the chief nitrogenous excretory product,making them ureotelic.
Earthworm is ureotelic in terrestrial conditions and ammonotelic in aquatic conditions,excreting $40\, \%$ urea,$20\, \%$ ammonia,and $40\, \%$ amino acids.
Frog excretes urea as the chief nitrogenous product in its adult stage,making it ureotelic.

(A) Urea is the primary nitrogenous waste product in many animals.
Animals that excrete urea as their main nitrogenous waste are known as ureotelic animals.
The process of excreting urea is called ureotelism.
Examples of ureotelic animals include mammals,adult amphibians,and marine fishes.

(C) Uricotelism is the process of excreting nitrogenous waste in the form of uric acid or urates.
This method is primarily found in animals that need to conserve water,such as birds,reptiles,and insects.
In these animals,nitrogenous waste is eliminated as a paste or in a semisolid state to minimize water loss.

(A) The urea cycle takes place in liver cells,where the hydrolytic enzyme $Arginase$ plays a crucial role. $Arginase$ catalyzes the hydrolysis of $Arginine$ into urea and ornithine,resulting in the production of urea as an excretory product.

(B) The liver is the primary site for the detoxification of ammonia into urea via the ornithine cycle (urea cycle).
Since the liver synthesizes urea,the blood that leaves the liver through the hepatic vein and travels towards the heart contains a significantly higher concentration of urea compared to the blood entering the liver.

(C) Ammonia is a highly toxic substance produced during the metabolism of amino acids. In the human body,ammonia is converted into urea through the $Urea$ cycle,also known as the $Krebs-Henseleit$ cycle. This process primarily takes place in the liver,where the liver cells (hepatocytes) utilize enzymes to combine ammonia with carbon dioxide to form urea,which is then transported to the kidneys for excretion.

(C) The urea cycle,also known as the Krebs-Henseleit cycle $(1932)$,is a series of biochemical reactions that occur in the liver to convert toxic ammonia into urea.
$1$. The cycle involves the formation and transformation of three key amino acids: ornithine,citrulline,and arginine.
$2$. Ornithine combines with carbamoyl phosphate to form citrulline.
$3$. Citrulline then reacts with aspartate to form argininosuccinate,which is subsequently converted into arginine.
$4$. Finally,arginine is hydrolyzed to release urea and regenerate ornithine,allowing the cycle to continue.
Therefore,the correct option containing the primary amino acids involved in the cycle is ornithine,citrulline,and arginine.

(B) Nucleotide metabolism,specifically the catabolism of purines (adenine and guanine),results in the formation of uric acid in humans.
Unlike many other vertebrates that possess the enzyme urate oxidase to further break down uric acid into allantoin,humans lack this enzyme.
Therefore,uric acid is excreted as the final waste product of purine nucleotide metabolism.
While urea is the primary nitrogenous waste product of protein metabolism in humans,uric acid is the specific end product of nucleotide (purine) metabolism.

(B) Most aquatic animals like aquatic arthropods,bony fishes,freshwater fishes,and amphibian tadpoles excrete nitrogenous waste in the form of ammonia. This phenomenon is known as ammonotelism,and the animals that exhibit this mode of excretion are called ammonotelic.

(B) Urea serves as both a nitrogenous waste product and an osmoregulator.
It is the primary excretory product in humans and other mammals,as well as in organisms like $Ascaris$,earthworms,and certain fishes such as sharks and stingrays.
In these organisms,urea is retained in the body fluids to maintain osmotic balance,making it a key molecule for osmoregulation.

(C) Spiders excrete guanine as their primary nitrogenous waste product,and therefore,they are classified as guanotelic organisms.
Guanine is a metabolic waste product derived from the breakdown of nucleotides (purine metabolism).

(A) Ammonia ($NH_4^+$ ions) is highly toxic to brain cells because it interferes with the normal functioning of the nervous system.
Specifically,these ions affect the brain cell functioning by altering the electrical polarity of the cell membrane.
This change in polarity disrupts the electrochemical gradients required for nerve impulse transmission and transport across the cell membrane,leading to neurological dysfunction.

(D) Urea,uric acid,and ammonia are all nitrogenous waste products produced during metabolism.
Therefore,statement $I$ is correct.
Ammonia is highly toxic and requires a large amount of water for excretion. Urea is less toxic than ammonia and requires less water. Uric acid is the least toxic and is excreted as a paste or pellet,requiring minimal water. Thus,statements $II$ and $III$ are incorrect.
Statement $IV$ is factually incorrect as they are processed differently in the body.
Hence,only statement $I$ is shared by all three.

(B) The $Hepatic$ $\text{vein}$ contains the highest concentration of urea in the body. This is because urea is synthesized in the liver through the ornithine cycle (urea cycle) and is then released into the blood via the hepatic vein.

(B) Marine teleost fishes are primarily ammonotelic,meaning they excrete ammonia as their main nitrogenous waste product.
Ammonia is highly toxic and requires a large amount of water for its elimination,which is readily available to these fishes in their aquatic environment.
Although some marine teleosts may excrete small amounts of urea,they are classified as ammonotelic because ammonia is the principal excretory product.