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Human excretory system and products - class-X

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Which of the following is the most toxic excretory product?

  1. $CO _2$

  2. Ammonia

  3. Urea

  4. Amino acids


Correct Option: B
Explanation:

There are majorly the types of excretory product - Ammonia, Urea, and Uric acid. 

Among these Ammonia is most toxic because ammonia is basic in nature and  if ammonia is formed in more amount then it can hamper the acid base balance of our body. Increased cellular level of ammonia can result in hyperammonemia which leads to coma and death.
So, the correct option is (B).

Which of the following pairs is wrong? 

  1. Uricotelic - Birds

  2. Ureotelic - Insects

  3. Ammonotelic - Tadpole

  4. Ureotelic - Elephant


Correct Option: B
Explanation:

Insects are uricotelic i.e, they excrete uric acid. 

Which one of the following statements is incorrect? 

  1. Birds and land snails are uricotelic animals.

  2. Mammals and frogs are ureotelic animals.

  3. Aquatic amphibians and aquatic insects are ammonotelic animals.

  4. Birds and reptiles are urotelic


Correct Option: D
Explanation:

In Uricotelic organisms, the end product of nitrogen metabolism is uric acid.  include terrestrial arthropods (including insects), lizards, snakes, and birds. 

So, the correct option is 'Birds and reptiles are urotelic'. 

The following substances are the excretory products in animals. Choose the least toxic from among them.

  1. Urea

  2. Uric acid

  3. Ammonia

  4. Carbon dioxide


Correct Option: B
Explanation:

Nitrogenous waste substances such as ammonia, urea or uric acid are produced during protein metabolism according to the species. A small amount of nitrogenous waste substances are also produced during the metabolism of nucleic acids. Ammonia is the most toxic, followed by urea and then uric acid.

So the correct option is B.

The characteristic(s) common to urea, uric acid, and ammonia is/are 
(i) They are nitrogenous wastes. 
(ii) They all need a very large amount of water for excretion.
(iii) They are all equally toxic. 
(iv) They are produced in the kidneys.

  1. (i), (ii) and (iv)

  2. (i) only

  3. (i) and (iii)

  4. (i) and (iv)


Correct Option: B
Explanation:
Urea, uric acid, and ammonia are known as nitrogenous wastes as they are produced during protein metabolism. 
Ammonia needs very large amount of water for excretion, second in order comes urea and then uric acid. 
Ammonia is highly toxic, then comes urea and then uric acid. 
Ammonia and urea are produced in the liver and uric acid is formed mostly in the liver and to some extent in kidneys. 
So the correct option is 'B'.

Arrange the following in correct order based on increasing toxicity.

(a) Urea
(b) Uric acid
(c) Ammonia

  1. a-b-c

  2. b-a-c

  3. c-a-b

  4. c-b-a


Correct Option: B
Explanation:

Nitrogenous waste that is produced in the body needs to be excreted from the body as they are toxic to an organism. The waste is excreted in 3 forms, namely ammonia, uric acid, and urea. Ammonia is more water-soluble and most toxic. It requires less energy for excretion. Animals excreting nitrogenous waste in the form of ammonia are called as ammonotelic. Aquatic animals like protozoans, crustaceans, poriferans, fishes where water is not a constraint are ammonotelic. Urea requires comparatively more energy and is less toxic in nature. Animals excreting nitrogenous waste in the form of urea are called as ureotelic. Examples include cartilaginous fish, amphibians, mammals including humans. Uric acid is least soluble in water and is least toxic. However, it requires a large amount of energy. Examples include reptiles, birds.

Thus, the correct answer is 'b-a-c.'

Excretory products of mammals are useful to plants. Which of the following is not a part of such secretions?

  1. Carbon dioxide

  2. Mineral salts

  3. Bile pigments

  4. Urea


Correct Option: B
Explanation:

The major excretory products are carbon dioxide, excess water, and nitrogenous compounds like ammonia, urea, uric acid, etc. Carbon dioxide and water are produced in the process of tissue respiration. Nitrogenous compounds are formed from the breakdown of proteins and amino acids. So, the correct option is "B" (Mineral salt).

What is the first excretory substance in animal body?

  1. Urea

  2. Ammonia

  3. Amino acid

  4. Uric acid


Correct Option: B
Explanation:

Ammonia was the first and simplest excretory substance in the animal body and is excreted as it is toxic. It requires large amounts of water for its excretion and so it is seen in most aquatic vertebrates and invertebrates.

So, the correct answer is 'Ammonia'.

Which living organism is not a uricotelic?

  1. Insects

  2. Birds

  3. Crocodile

  4. Alsatian dog


Correct Option: D
Explanation:
A) Insects are uricotelic.
B) Birds are uricotelic.
C) Crocodiles and all reptiles are uricotelic.
D) The Alsatian dog is a mammal. Mammals are ureotelic (excrete urea).
So the correct answer is 'Alsheshan dog'.

Animals return water to the environment by
(i) Perspiring
(ii) Drinking
(iii) Urinating
(iv) Breathing

  1. (i), (iii) and (iv)

  2. (i) and (ii)

  3. (i) and (iii)

  4. (iii) and (iv)


Correct Option: A
Explanation:

A) Perspiration (sweating) is the loss of water and salts through the surface of the skin. This water evaporates. Urine is mostly water and is also composed of salts and is excreted by the animal into the environment. While breathing, minute molecules of water or water vapour are given out into the environment along with carbon dioxide.

B) While drinking water, the animal consumes it from the environment.
C) Perspiration and urination release water into the environment.
D) Breathing releases water in form of water vapour into the environment.
So, the correct answer is '(i), (iii) and (iv)'.

State whether the following statement is true or false.


Some organisms store wastes in body parts.

  1. True

  2. False


Correct Option: A
Explanation:

Organisms can store their wastes in different glands and organs such as the kidneys, sweat glands, lungs etc. All the nitrogenous and solid wastes are stored by different organisms for a certain period in certain body organs such as the kidneys and the intestines, after which they are eliminated from the body. So, the correct option is 'True'.

Assertion  :  Earthworms excrete both ammonia and urea



Reason    :    Excretion in earthworm depends on the
                       environment.




  1. If both the assertion and the reason are true and the reason

    is a correct explanation of the assertion

  2. If both the assertion and reason are true but the reason is

    not a correct explanation of the assertion

  3. If the assertion is true but the reason is false

  4. If both the assertion and reason are false

  5. If the assertion is false but reason is true


Correct Option: A
Explanation:

Earthworms excrete ammonia when sufficient water is available, because a large volume of water is needed by the animal to dissolve ammonia and eliminate it from, the body. Whereas in drier environment the animal eliminates urea as it requires only considerable amount of water for the excretion of urea because urea is very soluble in water.

Most abundant, harmful and universal waste product of metabolism is

  1. Uric acid

  2. $H _20$

  3. $CO _2$

  4. None of the above


Correct Option: C
Explanation:

The end products of aerobic metabolism of carbohydrates are carbon dioxide and water. Carbon dioxide remains dissolved in the blood and is carried by the veins to the lungs for oxygenation. If carbon dioxide is not removed from the metabolizing tissues, it will be toxic for that tissue and stop metabolism.

So, the correct option is 'Carbon dioxide'.

Which one is both osmoregulator as well as nitrogenous product?

  1. $NH _3$

  2. Urea

  3. Uric acid

  4. All of the above


Correct Option: B
Explanation:

Urea is both osmoregulator as well as nitrogenous waste. Urea is produced in the liver and excreted through urine. The urea helps in osmoregulation by participating in counter current system, small amounts of urea enter the thin segment of the ascending limb of Henle’s loop which is transported back to the interstitium by the collecting tubule.  

So, the correct answer is 'Urea'.

Excretory product of spider is

  1. Ammonia

  2. Uric acid

  3. Guanine

  4. All the above


Correct Option: C
Explanation:

The excretory product of spider is guanine. It is formed as a result of nucleotide metabolism. It does not require water for elimination because it is less soluble than uric acid and helps to conserve more water.

So, the correct answer is 'Guanine'.

A portion of uric acid is changed into urea and ammonia by intestinal

  1. Urogenolysis

  2. Ureolysis

  3. Uricolysis

  4. Ureotolysis


Correct Option: C
Explanation:
The bacteria present in intestinal tract break a portion of uric acid present in the food we eat into urea and ammonia. This phenomenon is called uricolysis. Hence a portion of uric acid is changed into urea and ammonia by intestinal bacteria is called as urinalysis.
So, the correct answer is 'Uricolysis'.

Characteristics shared by urea, uric acid and ammonia are
a. They are nitrogenous wastes
b. They need a large amount of water for excretion
c. They are equally toxic
d. They are produced in kidneys.

  1. a, c

  2. a, d

  3. a, c, d

  4. a only


Correct Option: D
Explanation:

The characteristic shared by urea, uric acid and ammonia are they are nitrogenous wastes. In comparison to Ammonia and Urea, uric acid is the least toxic and the least soluble in water. It can be stored in cells and body tissues without any toxic effects and hence needs less water for excretion when compared to Ammonia and urea.

So, the correct answer is 'a only'.

The first formed nitrogenous waste of vertebrates is

  1. $NH _2$

  2. Urea

  3. $NH _3$

  4. $NH _4$


Correct Option: C
Explanation:

For terrestrial vertebrates, nitrogenous wastes are removed from body fluids by the action of the kidneys, the same organ involved in maintaining water balance. Ammonia the direct waste produced as a byproduct of protein metabolism.  Produced by all animals.  Because of its toxicity, many animals convert ammonia into a less toxic form.  Any conversion of ammonia into other forms comes at a price, for animals must expend cellular energy (ATP) to convert ammonia to either form of nitrogenous waste listed below.


So, the correct option is 'Ammonia'.

Which is not a ketone body?

  1. Succinic acid

  2. Acetone

  3. Acetoacetic acid

  4. p-hydroxybutyric acid


Correct Option: A
Explanation:

Chemicals that the body makes when there is not enough insulin in the blood and it must break down fat instead of the sugar glucose for energy. The ketone bodies -- acetone,  acetoacetate, and beta-hydroxybutyrate -- are toxic acidic chemicals. They build up in the blood and then spill over into the urine. The body can also rid itself of acetone through the lungs. This gives the breath a fruity odor.

So, the correct option is 'Succinic acid'.

How many molecules of ammonia are required to form 8 molecules of urea?

  1. 24

  2. 8

  3. 16

  4. 4


Correct Option: C
Explanation:

Urea synthesis is a five-step cyclic process, with five distinctive enzymes. One turn of the cycle consumes 2 molecules of ammonia and  1 molecule of carbon dioxide and creates 1 molecule of urea ((NH2)2CO. Hence  16  molecules of ammonia are required to form 8 molecules of urea.

So, the correct answer is 'Option C'.

Which of the following statement, is false?

  1. Urea is more toxic than ammonia.

  2. Ammonia is converted to urea in liver.

  3. Ammonia is produced in the body cells by the metabolism of proteins.

  4. Fluid collected in Bowman's capsule is called glomerular fluid.


Correct Option: A
Explanation:

Ammonia is more water soluble and more toxic than Urea or uric acid. Ammonia is extremely toxic and its accumulation in the body can be lethal. So the liver converts toxic ammonia into less toxic urea through the urea cycle.

So, the correct answer is 'Option A'.

Ketone bodies consist of

  1. Nicotinic acid, folic acid and ascorbic acid

  2. Acetone, beta hydroxybutyryl CoA and if acetoacetic acid

  3. Acetoacetic acid acetone and beta hydroxybutyric acid

  4. Acetic acid, acetone and beta hydroxybutyric acid


Correct Option: C
Explanation:

Ketone bodies are byproducts in the metabolism of fat. During starvation or fasting conditions the liver synthesizes glucose through a process called gluconeogenesis. Gluconeogenesis is a metabolic pathway that results in the generation of glucose from fat. During gluconeogenesis, the ketone bodies are formed as byproducts where the product is glucose. The Kerone bodies consist of acetoacetic acid, acetone and beta-hydroxybutyric acid.

So, the correct answer is 'Acetoacetic acid, acetone and beta-hydroxybutyric acid'.

Which of the following sets of animals produce the same substances as their chief excretory product?

  1. Fish, pigeon and frog

  2. Camel, housefly and snake

  3. Frog, monkey and dog

  4. Amoeba, ant and antelope


Correct Option: A
Explanation:
  • Birds, reptiles, and fishes produce uric acid waste and they are called Uricothelic organisms.
  • They tend to excrete uric acid as its waste which is in the form of a white paste or powder.
  • Producing uric acid over urea is advantageous because it is less toxic and reduces water loss and the subsequent need for water.  in these organisms.
  • The correct answer is OPTION A.

Study the following.


(i) Uricase enzyme is not found in apes and man.
(ii) Purine metabolism leads to the formation of uric acid.
(iii) In ureotelic organisms, carbondioxideCO2 and ammonia converted into urea through the Cori cycle.
(iv) More energy consumed is for the production of uric acid.
(v) TMO (Trimethylamine oxide) protects the proteins from the effect of urea in Chondrichthyes fishes.

Which of the given statements are correct?

  1. All, except II

  2. All, except III

  3. All, except IV

  4. All, except V


Correct Option: B
Explanation:

When muscles work continuously enough, oxygen is not reached to muscles to burn glucose aerobically in such conditions glucose is converted into lactic acid i.e anaerobic glycolysis. The lactic acid produced in muscles is moved to the liver and converted to glucose. In ureotelic organisms, lactic acid is converted into Glucose through the Cori cycle. This metabolic cycle was discovered by Carl Ferdinand Cori and  Gerty Cori, hence named Cori cycle.

So, the correct answer is 'Option B'.

Some animals convert highly toxic $NH _3$ into least toxic trimethylamine oxide $(TMAO)$ and retain high concentration of $TMAO$ and urea to minimise $H _2O$ loss from body are

  1. Sharks and rays

  2. Fresh water bony fishes

  3. Myxine

  4. Marine bony fishes


Correct Option: A
Explanation:
  • Marine teleost fishes excrete a large proportion of their nitrogen as trimethylamine oxide (TMAO). Large amounts of this compound is also stored in their body for osmoregulation i.e. to minimize loss of water and entry of salts.

So, the correct option is 'Sharks and rays'
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