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Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005. Ph.: 011-47623456
DATE : 04/03/2020
Class XScience
(CBSE 2020)
GENERAL INSTRUCTIONS :
Read the following instructions very carefully and strictly follow them :
(i) Question paper comprises three sections – A, B and C.
There are 30 questions in the question paper. All questions are compulsory.
(ii) Section A – question no. 1 to 14 – all questions or part thereof are of one mark each. These questions
comprises multiple choice questions (MCQ), very short answer (VSA) and Assertion-Reason type questions.
Answer to these questions should be given in one word or one sentence.
(iii) Section B – question no. 15 to 24 are short answer type questions, carrying 3 marks each. Answer to these
questions should not exceed 50 to 60 words.
(iv) Section C – question no. 25 to 30 are long answer type questions, carrying 5 marks each. Answer to these
questions should not exceed 80 to 90 words.
(v) Answer should be brief and to the point. Also the above mentioned word limit be adhered to as far as possible.
(vi) There is no overall choice in the question paper. However, an internal choice has been provided in some
questions in each Section. Only one of the choices in such questions have to be attempted.
(vii) In addition to this, separate instructions are given with each section and question, wherever necessary.
Time : 3 Hrs. Max. Marks : 80
Section-A
1 . Name the functional group present in propanone. [ 1 ]
Sol. The functional group present in propanone is ketone [ 1 ]
2 . The change in magnetic field lines in a coil is the cause of induced electric current in it. Name the
underlying phenomenon. [ 1 ]
Sol. Electromagnetic induction [ 1 ]
Set-2
Code No. 31/1/2
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2
Science (Class X)
Answer question numbers 3(a) to 3(d) and 4(a) to 4(d) on the basis of your understanding of
the following paragraphs and the related studied concepts.
3 . The growing size of the human population is a cause of concern for all people. The rate of birth and
death in a given population will determine its size. Reproduction is the process by which organisms
increase their population. The process of sexual maturation for reproduction is gradual and takes
place while general body growth is still going on. Some degree of sexual maturation does not
necessarily mean that the mind or body is ready for sexual acts or for having and bringing up children.
Various contraceptive devices are being used by human beings to control the size of population.
(a) List two common signs of sexual maturation in boys and girls. [ 1 ]
(b) What is the result of reckless female foeticide? [ 1 ]
(c) Which contraceptive method changes the hormonal balance of the body? [ 1 ]
(d) Write two factors that determine the size of a population. [ 1 ]
Sol. (a) Common signs of sexual maturation in boys and girls are :
(i) Thick hair growth in the pubic region and armpits.
(ii) Thin hair appears on legs and arms.
(iii) The skin frequently becomes oily and there might be occurrence of acne. (Any two) [2×½]
(b) Because of reckless female foeticide, child sex ratio is declining at an alarming rate in some
sections of our society. [ 1 ]
(c) The hormonal methods like oral pills change the hormonal balance of the body. [ 1 ]
(d) Birth and death rate in a given population determine the size of a population. [ 1 ]
4 . Human body is made up of five important components, of which water is the main component. Food
as well as potable water are essential for every human being. The food is obtained from plants through
agriculture. Pesticides are being used extensively for a high yield in the fields. These pesticides are
absorbed by the plants from the soil along with water and minerals and from the water bodies these
pesticides are taken up by the aquatic animals and plants. As these chemicals are not biodegradable,
they get accumulated progressively at each trophic level. The maximum concentration of these
chemicals gets accumulated in our bodies and greatly affects the health of our mind and body.
(a) Why is the maximum concentration of pesticides found in human beings? [ 1 ]
(b) Give one method which could be applied to reduce our intake of pesticides through food to someextent. [ 1 ]
(c) Various steps in a food chain represent: [ 1 ]
(a) Food web
(b) Trophic level
(c) Ecosystem
(d) Biomagnification
(d) With regard to various food chain operating in an ecosystem, man is a: [ 1 ]
(a) Consumer
(b) Producer
(c) Producer and consumer
(d) Producer and decomposer
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3
Science (Class X)
Sol. (a) As human beings occupy the top level in any food-chain, the maximum concentration of these
chemicals/pesticides get accumulated in the human body. [ 1 ]
(b) (i) Consume peeled and washed fruits and vegetables.
(ii) Ban the use of pesticides.
(iii) Consume the food produced by organic farming. (Any one) [1]
(c) Answer (b)
Trophic level [ 1 ]
(d) Answer (a)
Consumer [ 1 ]
5 . The compound obtained on reaction of iron with steam is/are : [ 1 ]
(a) Fe2O
3
(b) Fe3O
4
(c) FeO
(d) Fe2O
3 and Fe
3O
4
Answer (b)
Sol. 3Fe(s) + 4H2O(g) Fe
3O
4(s) + 4H
2(g)
OR
An element ‘X’ reacts with O2 to give a compound with a high melting point. This compound is also
soluble in water. The element ‘X’ is likely to be : [ 1 ]
(a) iron
(b) calcium
(c) carbon
(d) silicon
Answer (b)
Sol. 'Calcium' reacts with oxygen to give an ionic compound which has high melting point and is soluble
in water.
6 . The laws of reflection hold true for : [ 1 ]
(a) plane mirrors only
(b) concave mirrors only
(c) convex mirrors only
(d) all reflecting surfaces
Answer (d)
OR
When an object is kept within the focus of a concave mirror, an enlarged image is formed behind the
mirror. This image is : [ 1 ]
(a) real
(b) inverted
(c) virtual and inverted
(d) virtual and erect
Answer (d)
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Science (Class X)
7 . At the time of short circuit, the electric current in the circuit : [ 1 ]
(a) vary continuously
(b) does not change
(c) reduces substantially
(d) increases heavily
Answer (d)
OR
Two bulbs of 100 W and 40 W are connected in series. The current through the 100 W bulb is 1 A. The
current through the 40 W bulb will be : [ 1 ]
(a) 0.4 A
(b) 0.6 A
(c) 0.8 A
(d) 1 A
Answer (d)
8 . The chemical formula for plaster of Paris is : [ 1 ]
(a) CaSO4· 2H
2O (b) CaSO
4· H
2O
(c) 4 2
1CaSO H O
2(d) 2CaSO
4· H
2O
Answer (c)
Sol. The chemical formula of plaster of Paris is 4 2
1CaSO . H O
2
9 . In a double displacement reaction such as the reaction between sodium sulphate solution and barium
chloride solution : [ 1 ]
(A) exchange of atoms takes place (B) exchange of ions takes place
(C) a precipitate is produced (D) an insoluble salt is produced
The correct option is :
(a) (B) and (D) (b) (A) and (C)
(c) Only (B) (d) (B), (C) and (D)
Answer (d)
Sol. Na2SO
4(aq) + BaCl
2(aq) BaSO
4(s) + 2NaCl(aq)
10. Baking soda is a mixture of : [ 1 ]
(a) Sodium carbonate and acetic acid
(b) Sodium carbonate and tartaric acid
(c) Sodium hydrogen carbonate and tartaric acid
(d) Sodium hydrogen carbonate and acetic acid
Answer (*)
*In this question, it should be baking powder instead of baking soda as sodium hydrogen carbonate
itself is known as baking soda.
Had it been baking powder then the answer will be option (c)
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5
Science (Class X)
11. In an ecosystem, 10% of energy available for transfer from one trophic level to the next is in the form
of : [ 1 ]
(a) heat energy
(b) chemical energy
(c) mechanical energy
(d) light energy
Answer (b)
Sol. The transfer of energy from one trophic level to the next is in the form of chemical energy.
12. Soil fertility is determined by its ability to : [ 1 ]
(a) Decay organic matter
(b) Hold organic matter
(c) Hold water
(d) Support life
Answer (d)
Sol. Soil fertility refers to the ability of soil to sustain plant growth.
For question numbers 13 and 14, two statements are given – one labelled Assertion (A) and the other
labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as
given below.
(a) Both A and R are true and R is the correct explanation of the Assertion.
(b) Both A and R are true but R is not the correct explanation of the Assertion.
(c) A is true but R is false.
(d) A is false but R is true.
13. Assertion (A) : In a homologous series of alcohols, the formula for the second member is C2H
5OH
and the third member is C3H
7OH.
Reason (R) : The difference between the molecular masses of the two consecutive members of a
homologous series is 144. [ 1 ]
Answer (c)
Sol. The difference between the molecular masses of the two consecutive members of a homologous
series is 14 u.
14. Assertion (A) : In the process of nuclear fission, the amount of nuclear energy generated by the
fission of an atom of uranium is so tremendous that it produces 10 million times the energy produced
by the combustion of an atom of carbon from coal.
Reason (R) : The nucleus of a heavy atom such as uranium, when bombarded with low energy
neutrons, splits apart into lighter nuclei. The mass difference between the original nucleus and the
product nuclei gets converted to tremendous energy. [ 1 ]
Answer (b)
Section-B
15. What is ‘rusting’? Describe with a labelled diagram an activity to investigate the conditions under
which iron rusts. [ 3 ]
Sol. The slow eating up of iron articles by the action of air, moisture or a chemical on its surface
results into the formation of brown flaky substance on it, called rust. This phenomena is called
rusting. [ 1 ]
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Science (Class X)
In order to investigate rusting we take three test tubes and place clean iron nails in each of them as
shown below.
A B C
Air
Rustyiron nails
Water
Boiled distilled water(boiled to remove any dissolved air)
Anhydrous calciumchloride (drying agent)
Layer of oil(prevents airdissolving inthe water)
Air Dryair
[½]
(i) In test tube A, the nails are exposed to both air and water, therefore they get rusted. [½]
(ii) In test tube B, the nails are exposed only to water and there is no air dissolved in it. Therefore
they do not rust. [½]
(iii) In test tube C, the nails are exposed to dry air therefore they do not rust. [½]
16. What are homologous structures? Give an example. Is it necessary that homologous structures always
have a common ancestor. Justify your answer. [ 3 ]
Sol. Organs which are similar in origin and internal morphology but they differ in function and external
structure are called homologous structures. [ 1 ]
Example : The forelimbs of frog and lizard. [ 1 ]
Yes, it is necessary that homologous structures always have a common ancestor because these
structures are inherited from a common ancestor. The basic structure of the limbs of birds, reptiles
and amphibians are similar though it has been modified during the course of evolution to perform
different functions in various vertebrates, depending upon their habitats. [ 1 ]
17. Why is Tyndall effect shown by colloidal particles? State four instances of observing the Tyndall effect.
[ 3 ]
Sol. The phenomenon of scattering of light by the colloidal particles gives rise to tyndall effect. [ 1 ]
(i) Tyndall effect can be observed when sunlight passes through a canopy of a dense forest. [½]
(ii) Tyndall effect can be observed when a fine beam of light enters a smoke filled room through a
small hole. [½]
(iii) Blue colour of eye is due to scattering of light by translucent layer over the iris. [½]
(iv) Milk is a colloidal solution of globules of fat and protein. When a beam of light is directed at a
glass of milk, the light is scattered. [½]
OR
Differentiate between a glass slab and a glass prism. What happens when a narrow beam of (i) a
monochromatic light, and (ii) white light passes through (a) glass slab and (b) glass prism? [ 3 ]
Sol. A rectangular glass slab is a refracting medium with three parallel refracting surfaces while a glass
prism is a refracting medium with two or more non-parallel refracting surfaces. [ 1 ]
When a monochromatic light passes through a glass slab, then it displaces parallel to itself and when
it passes through a glass prism it gets deviate. [ 1 ]
When a white light passes through a glass slab, then it displaces parallel to itself only and when white
light passes through a glass prism get dispersed and deviated. [ 1 ]
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Science (Class X)
18. Draw a labelled diagram to show (i) reddish appearance of the sun at the sunrise or the sunset and(ii) white appearance of the sun at noon when it is overhead [ 3 ]
Sol. Answer (18)
(i) Reddish appearance of the sun at the sunrise or the sunset
Blue light scattered awaySun appears reddish
Sun nearhorizon Observer [1½]
(ii) White appearance of the sun at noon when it is overhead
Sun nearlyoverhead
Observer
Less bluescattered
[1½]
19. (a) List in tabular form two differences between binary fission and multiple fission. [ 3 ]
(b) What happens when a mature Spirogyra filament attains considerable length?
Sol. (a)
1. It gives rise to two daughter individuals.
2. It occurs during favourable conditions.
3. Nucleus of the parent cell divides only once to form two daughter cells.
4. Cytoplasm divides after nuclear division.
5. No part of the parent body is left unused.
Binary Fission Multiple Fission
1. It forms many (more than two) daughter individuals.
2. It can occur under favourable as well as unfavourable conditions.
3. Nucleus of the parent undergoes repeated divisions to form a number of daughter nuclei.
4. Cytoplasm does not divide after every nuclear division.
5. A part of the body, covering and residual cytoplasm, is left behind.
[Any two] [2×1]
(b) When a mature Spirogyra filament attains considerable length, its body breaks up into two or
more parts called fragments, each of which grows into a new individual. [ 1 ]
20. List the important products of the Chlor-alkali process. Write one important use of each. [ 3 ]
Sol.
Hydrogen (H )
Chlorine (Cl )
Sodium hydroxide (NaOH)
2
2
It is used as a fuel.
It is used for water treatment.
It is used for making soaps and detergents.
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Science (Class X)
OR
How is washing soda prepared from sodium carbonate? Give its chemical equation. State the type
of this salt. Name the type of hardness of water which can be removed by it [ 3 ]
Sol. Washing soda is prepared by recrystallisation of sodium carbonate. [ 1 ]
2 3 2 2 3 2Sodium Washing soda
carbonate
Na CO 10H O Na CO 10H O [ 1 ]
It is a basic salt. [½]
It can be used for removing permanent hardness of water. [½]
21. 3 mL of ethanol is taken in a test tube and warmed gently in a water bath. A 5% solution
of alkaline potassium permanganate is added first drop by drop to this solution, then in excess.
(i) How is 5% solution of KMnO4 prepared?
(ii) State the role of alkaline potassium permanganate in this reaction. What happens on adding it
in excess?
(iii) Write chemical equation of this reaction. [ 3 ]
Sol. (i) 5% solution of KMnO4 is prepared by dissolving 5 g of KMnO
4 crystals in 95 g of water. [ 1 ]
(ii) Alkaline KMnO4 acts as an oxidising agent. The colour of KMnO
4 will not disappear when added
in excess. [ 1 ]
(iii) 4Alkaline KMnO
3 2 3HeatCH CH OH CH COOH [ 1 ]
22. A squirrel is in a scary situation. Its body has to prepare for either fighting or running away. State theimmediate changes that take place in its body so that the squirrel is able to either fight or run [ 3 ]
Sol. The following immediate changes take place in the squirrel body which makes it able to either fight
or run:
(i) Adrenaline is secreted directly into the blood and carried to different parts of the body.
(ii) Heart beats faster resulting in supply of more oxygen to the muscles.
(iii) The blood to the digestive system and skin is reduced due to contraction of muscles around small
arteries in these organs.
(iv) Breathing rate increases because of contractions of the diaphragm and the rib muscles.
(Any Three) [3×1]
OR
Why is chemical communication better than electrical impulses as a means of communication betweencells in a multi-cellular organism? [ 3 ]
Sol.Chemical communication is better than electrical impulses as a means of communication between
cells in a multi-cellular organism because:
(i) The electrical impulses do not reach each and every cell rather, these reach only those cells that
are connected by nervous tissue. [ 1 ]
(ii) After the generation and transmission of an electrical impulse, the cell takes some time to reset
its mechanisms for the generation and transmission of a new impulse. [ 1 ]
(iii) Chemical communication is a steady and a persistent response. [ 1 ]
23. (a) State the relation correlating the electric current flowing in a conductor and the voltage applied
across it. Also draw a graph to show this relationship.
(b) Find the resistance of a conductor if the electric current flowing through it is 0.35 A when thepotential difference across it is 1.4 V. [ 3 ]
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Science (Class X)
Sol. (a) If the physical conditions remains unchanged (such as temperature), the potential difference
across the two ends of a conductor is directly proportional to the electric current flowing through
it.
V I [ 1 ]
V-I graph for a conductor
V
O I
[ 1 ]
(b) V = IR
1.4R = = 4
0.35[ 1 ]
24. (a) Write the mathematical expression for Joule’s law of heating.
(b) Compute the heat generated while transferring 96000 coulomb of charge in two hours through
a potential difference of 40 V. [ 3 ]
Sol. Answer (24)
(a) 2H I RT ...[1]
(b) H = VIT = VQ [ Q = IT] ...[1]
H = 40 × 96000
H = 3840000 J ...[1]
Section-C
25. (a) What is thermit process? Where is this process used? Write balanced chemical equation for the
reaction involved.
(b) Where does the metal aluminium, used in the process, occurs in the reactivity series of metals?
(c) Name the substances that are getting oxidised and reduced in the process. [ 5 ]
Sol. (a) Thermit process is a technique which is used to reduce metal oxide using more reactive metal
powder. [ 1 ]
The reaction of iron (III) oxide with aluminium is a thermit reaction which is used to join railway
tracks or cracked machine parts. [ 1 ]
Fe2O
3(s) + 2Al(s) 2Fe(l) + Al
2O
3(s) + Heat [ 1 ]
(b) Aluminium metal belongs to category of metals of high reactivity in the reactivity series. It is
more reactive than zinc and less reactive than magnesium. [ 1 ]
(c) Fe2O
3 is getting reduced and Al is getting oxidised in this process. [½+½]
26. (a) What is an electromagnet? List any two uses.
(b) Draw a labelled diagram to show how an electromagnet is made.
(c) State the purpose of soft iron core used in making an electromagnet.
(d) List two ways of increasing the strength of an electromagnet if the material of the electromagnet
is fixed. [ 5 ]
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Science (Class X)
Sol. (a) An electromagnet is a temporary magnet made from a piece of soft iron when current flows in
the coil wound around it. [ 1 ]
Uses of electromagnet :
(i) For removing pieces of iron from wounds [½]
(ii) For lifting and transporting the large masses of iron scrap, grinders, plates etc. [½]
(b)
Rh
SOFT
IRON
BAR
Q
A
P Q
B K
[ 1 ]
(c) If a core of soft iron is placed inside a solenoid, the magnetic field strength inside the solenoid
is greatly increased. [ 1 ]
(d) (i) By increasing the number of turns of winding [½]
(ii) By increasing the current [½]
27. Draw a ray diagram in each of the following cases to show the formation of image, when the object
is placed:
(i) Between optical centre and principal focus of a convex lens.
(ii) Anywhere in front of a concave lens.
(iii) At 2F of a convex lens.
State the signs and values of magnifications in the above mentioned cases (i) and (ii). [ 5 ]
Sol. (i) Between optical centre and principal focus of a convex lens
OF1
F2
A
B
A
B
[ 1 ]
m > 1 [½]
Sign of magnification - positive [½]
(ii) Anywhere in front of a concave lens.
F2
F1
O [ 1 ]
0 m < 1 [½]
Sign of magnification - positive [½]
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Science (Class X)
(iii) At 2F of a convex lens.
F1 2F
2F
22F
1 O
A
B B
A
[1]
OR
An object 4.0 cm in size, is placed 25.0 cm in front of a concave mirror of focal length 15.0 cm.
(i) At what distance from the mirror should a screen be placed in order to obtain a sharp image?
(ii) Find the size of the image.
(iii) Draw a ray diagram to show the formation of image in this case. [ 5 ]
Sol. (i) Given,
h = 4 cm
u = –25 cm
f = –15 cm
We have,
1 1 1
v u f
1 1 1
v f u[ 1 ]
1 1 1
v ( 15) ( 25)
1 1 1
v 25 15
1 2
v 75
75
v 37.5 cm2
[ 1 ]
(ii) Magnification (m) =
75
v 2
u 25
3m2
[ 1 ]
Now,
hm
h
h = m × h
3h 4
2
h = –6 cm [ 1 ]
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Science (Class X)
(iii)
A
B
C A F
B
M
P
M
AB ObjectA B Image
[ 1 ]
28. (a) What is genetics?
(b) What are genes? Where are the genes located?
(c) State and define three factors responsible for the rise of a new species. [ 5 ]
Sol. (a) Genetics is defined as the branch of biology which deals with the study of heredity and variations.
[ 1 ]
(b) Gene is the functional unit of heredity present at a specific point on a chromosome. [ 1 ]
(c) The following factors are responsible for the rise of a new species :
(i) Natural selection : It is a process in which heritable variations enabling better survival are
enabled to reproduce and leave greater number of progeny.
(ii) Genetic drift : It is the change in gene frequency by chance in a small population due to
random sampling.
(iii) Reproductive isolation : Over a period of time, a population may become so different from
the parent population that they are no longer able to interbreed with one another. It is called
reproductive isolation.
(iv) Geographical isolation : When a geographical barrier separates two populations of a
species, then these are no longer able to reproduce together. [Any three] [3×1]
29. The position of certain elements in the Modern Periodic Table are shown below.
1
1
Group
Period
2 3 to 12 13 14 15 16 17 18
G H
2 A C
3 D F
I B
E
Using the above table answer the following questions giving reasons in each case:
(i) Which element will form only covalent compounds?
(ii) Which element is a non-metal with valency 2 ?
(iii) Which element is a metal with valency 2 ?
(iv) Out of H, C and F which has largest atomic size?
(v) To which family does H, C and F belong? [ 5 ]
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Science (Class X)
Sol. (i) Element E [ 1 ]
Element 'E' is silicon and its valency is 4.
(ii) Element B [ 1 ]
Element 'B' is oxygen and it has 6 electrons in its outermost shell.
(iii) Element D [ 1 ]
Element 'D' is magnesium and it has 2 electrons in its outermost shell.
(iv) F has the largest atomic size. [ 1 ]
Atomic size increases down the group.
(v) H, C and F belong to noble gas family. [ 1 ]
Outermost shell of H, C and F is completely filled.
OR
Define atomic size. Give its unit of measurement. In the modern periodic table what trend is observed
in the atomic radius in a group and a period and why is it so? [ 5 ]
Sol. The atomic size may be defined as the distance between the centre of the nucleus and the outermost
shell of an isolated atom. [ 1 ]
It is measured in picometre [1 pm = 10–12 m] [ 1 ]
The atomic radius increases down the group in the Modern Periodic Table. This is because new shells
are being added as we move down the group. [½+1]
The atomic radius decreases on moving from left to right along a period in the Modern Periodic Table.
It is due to the increase in nuclear charge which tends to pull the electrons closer to the nucleus and
reduces the size. [½+1]
30. (a) Why is there a difference in the rate of breathing between aquatic organisms and terrestrial
organisms? Explain.
(b) Draw a diagram of human respiratory system and label – pharynx, trachea, lungs, diaphragm and
alveolar sac on it. [ 5 ]
Sol. (a) There is a difference between the rate of breathing between aquatic organisms and terrestrial
organisms because terrestrial animals can breathe the oxygen in the atmosphere but animals
living in water need to use the oxygen dissolved in water. Hence, the amount of dissolved oxygen
in water is fairly low compared to the amount of oxygen in the air, the rate of breathing in aquatic
organisms is much faster than that seen in terrestrial organisms. [1½]
(b)
Pharynx
Trachea
Lungs
Alveolar sac
Human Respiratory System
Diagram 1
Labelling 5 ½
OR
(a) Name the organs that form the excretory system in human beings.
(b) Describe in brief how urine is produced in human body. [ 5 ]
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14
Science (Class X)
Sol. (a) The organs that form the excretory system in human beings are :
(i) A pair of kidneys
(ii) A pair of ureters
(iii) A urinary bladder
(iv) A urethra [4×½]
(b) Each kidney consists of large numbers of filtration units called nephrons which filter out the waste
products from the blood. Urine is formed in the kidneys through filtration of blood. Some
substances such as glucose, amino acids, salts and a major amount of water are selectively
reabsorbed as the urine flows along the tube of nephron. Urine then enters into ureter and gets
stored in the urinary bladder until the pressure of the expanded bladder leads to the urge to pass
it out through the urethra. This is how urine is produced in human body. [ 3 ]
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