1.
(c)
Metal Salt 'A'
White Solid 'B'
Brownish Black Substance 'C'
Type of Reaction
FeSO4.7H2O
FeSO4
Fe2O3
Thermal Decomposition
Explanation: Green coloured hydrated ferrous
sulphate crystals (FeSO4.7H2O) on heating,
first lose 7 molecules of water of crystallisation
and the colour changes to white and the salt
formed is anhydrous FeSO4.
Related Theory

Heat
FeSO4(s) + 7H2O
FeSO4.7H2O(s) →
'A'
'B'
On further heating, a black residue of ferric
oxide (Fe2O3) along with the characteristic
smell of burning sulphur is observed.
Heat
Fe2O3(s) + SO2(g) + SO3(g)
2FeSO4(s) →
'C'
The reactions in which a single compound
breaks down to give two or more simpler
substances are called decomposition reactions.
Decomposition reaction which takes place
by absorption of heat is called thermal
decompostion reaction.
Those reactions in which heat is absorbed
during the reaction are called endothermic
reaction. In this reaction, heating of FeSO4
crystals is an endothermic reaction. Lead
nitrate Pb(NO3)2 is not a hydrated salt, does
not have water molecules Pb(NO3)2 and is a
white coloured salt. Thus, option (A) is incorrect.
Copper sulphate is a hydrated salt i.e.,
CuSO4.5H2O. On heating, it changes to
anhydrous salt CuSO4. But it does not
decompose further. Moreover, CuSO4.5H2O
are blue coloured crystals, so option (B) does
not give the correct information. Pb(NO3)2 is a
white coloured salt. Thus, option (A) is incorrect.
Heat
PbO(s) + 4NO2(g) + O2(g)
2Pb(NO3)2(s) →
Heat
CuSO4 + 5H2O
CuSO4.5H2O →
...(i)
...(ii)
The colour of PbO formed on heating Pb(NO3)2
as shown in reaction (i) is yellow and the colour
of CuSO4 formed in reaction (ii) is white.
Decomposition reaction which takes place when
electric current is passed through the compound in
the molten state or in aqueous solutions is known as
electrolytic decomposition reaction or electrolysis.
The decomposition reaction which takes place on
absorption of light is called photodecomposition
reaction or photolysis.
Caution

Students must learn the colours of salts to identify
them. Sometimes, they also get confused with the
type of salts. Hydrated salts contain molecules of
water of crystallisation whereas anhydrous salts
have lost those molecules of water.
2. (d) Both (I) and (II)
Explanation: Zinc granules react with dilute
sulphuric acid with the evolution of gas and
heat.
Zn(s) + H2SO4(aq) ® ZnSO4(aq) + H2(g) + Heat
This reaction is also called simple displacement
reaction as zinc is more reactive and displaces
hydrogen from dilute sulphuric acid. The
solution formed is ZnSO4 which is colourless
so option (III) is incorrect. H2 gas formed is
colourless and odourless which can be tested
by bringing a lighted candle. You will observe
that it burns with a pop sound.
3. (a) Element
Explanation: In combination reaction, a single
product if formed from two or more reactants,
the product formed cannot be an element.
The reactant can be element, molecules or
compounds in a combination reaction.
2Mg(s) + O2(g) ® 2MgO(s)
...(i)
CaO(s) + H2O(l) ® Ca(OH)2(aq)
...(ii)
Mg is an element and O2 is a molecule.
CaO is compound.
Chemical Equations and Reactions
1
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In decomposition reaction, a single reactant
breaks down to give products. Reactant will
always be a compound as seen in reaction (ii)
whereas products can be elements, molecules
or compounds.
6. (d) (A) is false but (R) is true.
Explanation: Respiration is a process in which
glucose combines with oxygen in the cells of
our body and provides energy.
C6H12O6(aq) + 6O2(aq) ® 6CO2(aq) + 6H2O(l) energy.
Caution

Students get confused with the terms reactants and
products. The reactants are always written on the
Related Theory

left hand side (LHS) with a plus sign (+) between
them. Similarly, products are written on the right
hand side (RHS) with a plus sign (+) between them.
7. (A) Burning of a strip of magnesium ribbon
is a combination reaction
2Mg(s) + O2(g) ® 2MgO(s)
(B) (i) The colour of the flame is dazzling white
light.
(ii) The colour of the ash formed is white.
(C) (i) The ash formed on burning a strip of
magnesium ribbon is magnesium oxide
2Mg + O2 ® 2MgO
Dissolve the ash in water. On dissolving,
magnesium hydroxide is formed.
The solution of magnesium hydroxide is
basic i.e., MgO + H2O ® Mg(OH)2
Test the solution by using litmus paper.
There will be no colour change in blue
litmus paper whereas, red litmus
changes to blue showing, it is basic in
nature.
(ii) (1) Combination reaction between two
elements C(s) + O2(g) ® CO2(g)
(2) Combination reaction between two
compounds NH3(g) + HCl(g) ® NH4Cl(s)
The arrowhead points towards the products and
shows the direction of the reaction.
A
+
B 
→C
+D
Reactant
Products
4. (c) To balance a chemical reaction, coefficient
is always written infront of the formula.
Explanation: In option (c), coefficient is
written infront of the formula to balance a
chemical reaction but it does not provide
any information about the chemical reaction.
Physical state of the reactants and the
products is represented by using the symbols.
(s) for solids
(l) for liquids
(g) for gaseous
(aq) for aqueous solution
These symbols are written in brackets after
the symbols/formulas of the reactants and
products.
Zn(s) + H2SO4(aq) ® ZnSO4(aq) + H2(g)
The reaction conditions such as temperature,
pressure, catalyst etc., for the reaction are
indicated above and/or below the arrow in the
equation.
8. (A) Arrangement 'Y' is likely to form rust
after ten days. Rusting is the formation of
undesired layer on the surface of iron and
it is a surface phenomenon.
Arrangement of eight identical blocks in
figure Y has more surface area. Due to the
large surface area which is exposed, gets
more rust. The essential conditions required
for rusting are provided oxygen from air
and moisture by sprinkling water.
340atm
CO(g) + 2H2(g) → CH3OH(l)
Heat changes accompanying the chemical
reaction are written. The sign '+ Heat' is
written along with the products in exothermic
reactions and '+ Heat' is written alongside the
reactants in endothermic reactions.
C(s) + O2(g) ® CO2(g) + Heat
N2(g) + O2(g) + Heat ® 2NO(g)
(B) Iron metal Fe(s) does not react either with
cold or with hot water. It reacts with steam
to form iron oxide and hydrogen, so in the
given equation, water should be in the form
of steam, not liquid.
5. (a) Both (A) and (R) are true and (R) is the
correct explanation of (A).
Oxidation
Explanation:
CuO + H2
Heat
3Fe(s) + 4H2O(g) ® Fe2O3(s) + 4H2(g)
9. Sodium
Cu + H2O
Reduction
This is an example of redox reaction.
2
The decomposition of vegetable matter into compost
is also an exothermic reaction like burning of natural
gas and respiration.
sulphate (Na2SO4) and copper
chloride (CuCl2) are ionic compounds and
these are soluble in water. Aqueous solutions
of both sodium sulphate and copper chloride
dissociate completely in water. There is no
insoluble product formed on mixing the two
solutions that precipitates out of solution.
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Copper chloride and sodium sulphate
dissociates completely in aqueous solution and
exist as ions in the solution.
N2SO4  Na+(aq) + SO42–(aq)
CuCl2  Cu2+(aq) + Cl–(aq)
Therefore, no reaction takes place between
aqueous solution of sodium sulphate (Na2SO4)
and an aqueous solution of copper chloride
(CuCl2).
Caution

Students must remember that for finding out
oxidising agent, reducing agent, substance oxidised
and substance reduced, only reactants are to be
seen. The same reactant acts as reducing agent as
well as the substance oxidised and vice-versa.
12. (A) Tie two iron nails with a thread and immerse
them in the copper sulphate solution in a
10. (A) The type of the reaction shown in the given
test tube for about 20 minutes and keep
diagram is electrolytic decomposition.
(B) Energy in the form of electrical energy
is absorbed during the decomposition of
water.
other for reference.
Hence, it is considered as an endothermic
reaction.
(C) Balanced equation:
compare the odour of iron nail with the nail
which was kept for reference.
2H2O + energy ® 2H2 + O2
After 20 minutes, take out the iron nails
from the copper sulphate solution and
(B)
Test tube
Thread
11. (A) CH4 + 2O2 ® CO2 + 2H2O
6CO2 + 6H2O ® C6H12O6 + 6O2 (Any one)
Iron nail
(B) If a substance gains oxygen or loses
hydrogen during a reaction, it is said to be
oxidised and if a substance loses oxygen or
gains hydrogen during a reaction, it is said
to be reduced.
Copper sulphate
solution
A substance that supplies oxygen is an
oxidising agent.
Example of redox reaction
(C) Blue colour of the copper sulphate solution
fades and it changes into light green colour.
Heat
ZnO(s) + C(s) →
Zn(s) + CO(g)
ZnO is an oxidising agent as it has oxygen.
ZnO loses oxygen to form Zn. So, ZnO has
been reduced. C gains oxygen to form CO.
Hence, C is getting oxidised and C is also a
reducing agent as it has gained oxygen.
Gain of oxygen
oxidation
ZnO + C
Oxidising Reducing
agent
agent
Loss of oxygen
Reduction
Zn + CO
(D) Balanced chemical equation is as follows:
The iron nail that remained suspended in
the test tube has a brownish coating on its
surface.
Fe(s) + CuSO4(aq) ® FeSO4(aq) + Cu(s)
(E) In the above reaction, iron has displaced
copper from copper sulphate solution. It
means, iron is more reactive than copper
and this reaction is known as displacement
reaction.
Displacement reaction is a chemical
reaction in which an element takes the
place of another element in a compound.
Chemical Equations and Reactions
3
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1. (c) The pH of salt 'P' is less than 7.
Explanation: When milk changes into curd, the
pH will decrease due to the formation of lactic
acid in the curd. Curd is more acidic. Since,
more acidic is the substance, lesser is the pH
and vice-versa.
Explanation: Salt 'P' is NaHCO3.
NaCl + H2O + CO2 + NH3 ® NH4Cl + NaHCO3
Brine solution
Sodium hydrogen carbonate is basic in nature
as it is made of weak acid and strong base.
H2CO3 + NaOH ® NaHCO3 + H2O
It is basic in nature if its pH will be more than 7.
Related Theory

Related Theory

Sodium hydrogen carbonate is also known as
sodium bicarbonate. It is used as a constituent of
baking powder to aerate the dough. As on heating,
it gives out carbon dioxide.
Caution

Heat
2NaHCO3 → Na2CO3 + H2O+ CO2
2. (d) (II) only
Explanation: Due to acid rain, the soil has
become acidic. Coconut trees cannot tolerate
acidic soil. For optimum growth, a pH range
of 5.5-6.5 is ideal. So, I will suggest farmers to
use calcium oxide or calcium hydroxide which
are bases and they would neutralise the acidic
environment of the soil and make the soil
neutral for the growth of coconut trees.
Explanation: Nitric acid is a mineral acid and
it is prepared from minerals present in the
Earth's crust. Sulphuric acid is also a mineral
acid. The acid present in bee sting is methanoic
acid which is an organic acid.
6. (a) Both (A) and (R) are true and (R) is the
correct explanation of (A).
Explanation: Indicators have different colours
in acidic and basic medium.
Related Theory

Litmus, turmeric etc., are natural indicators whereas
cloves, vanilla, onion etc., are olfactory indicators.
7. (A) Preparation of turmeric indicator:
4. (a)
pH
Time
4
Students must remember that the solution having
lower pH will have more hydrogen ion concentration
while the solution having higher pH will have less
hydrogen ion concentration.
5. (c) (A) is true but (R) is false.
3. (b) Sodium hydroxide
Explanation: Adding excess of sodium
hydroxide to the acidic solution, would turn red
litmus solution blue.
An aqueous solution turns blue litmus solution
to red, it means it is an acidic solution. We
cannot add hydrochloric acid to the already
acidic soil. Sodium chloride and ammonium
chloride are salts, they would not be able to
reverse the direction. Hence, the option (c) is
correct.
The pH of fresh milk is 6, which is slightly acidic. In
rainy season, the milk man adds a small amount of
sodium hydrogen carbonate, which is basic in nature, so
as to shift the pH of fresh milk to make it slightly alkaline.
So, as to preserve the fresh milk for longer duration.
(1) Make a paste of a tablespoon full of
turmeric powder.
(2) Apply turmeric paste either on blotting
paper or filter paper and dry it.
(3) Cut thin strips of the yellow paper
obtained.
(B) (i) Turmeric is used as a natural indicator. It
is acidic in nature and yellow in colour.
Acidic solution remains yellow i.e.,
colour does not change when turmeric
indicator (paste) is added into it.
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(ii) Soap solution is basic in nature and
basic substances turn yellow turmeric
into brown colour. For example, a yellow
stain is formed as soon as the curry
falls on the shirt while eating. When
we apply soap solution on the shirt,
the yellow stain becomes brownish red
because soap solution is basic in nature.
On washing with excess water, it turns
yellow again because soap is washed
away.
(C) (i) The two indicators used are litmus
solution and phenolphthalein.
(1) Take acidic solution in the test tube
A and basic solution in the test tube
B.
(2) Add a few drops of blue litmus
solution in test tube A and a few
drops of red litmus solution in test
tube B.
(3) Note the change in colour.
(4) Repeat the same procedure but now
take a few drops of phenolphthalein
and add in both the test tubes and
see if there is any change in colour.
Dropper
Blue litmus
solution
Acidic
solution
Test tube A
Red
colour
Litmus solution itself is neither acidic nor basic and
it is purple in colour. The extracts of many other
naturally occurring substances can also be used
as an indicators. For example, red cabbage leaves,
colour petals of petunia, geranium etc.
8. (A) In a given mixture of an acid and base, the
colour of neither red nor blue litmus paper
changes, it shows that the amount of H+
is equal to the amount of OH– ions in the
solution.
H+(aq) = OH–(aq)
(B) A pH of 7 is considered as neutral i.e., 1.
From pH 7 to pH 8 is ten fold = 10. From
pH 7 to pH 4 is 3 time 10 fold i.e., 10 × 10
× 10 = 1000. Therefore, difference from pH
8 to pH 4 is 10 × 1000 = 10,000. Hence, a
solution of pH 4 would have 10,000 times
higher concentration of hydrogen ions
compared to a solution of pH 8.
9. (A) (1) The pH of an acid would increase.
(2) The pH of a base would decrease.
(B) Greater the pH than 7 means lower the
H+ ion concentration or greater the OH–
ion concentration and hence, more basic is
the solution. Whereas, lesser the pH than
7 means greater the H+ ion concentration
and more acidic is the solution.
10. (A) Solid baking soda (NaHCO3) on heating
decomposes to sodium carbonate (Na2CO3)
along with the evolution of carbon dioxide
and water vapour.
Test tube A
Dropper
Heat Na CO
2NaHCO3(s) →
2
3(s) + H2O(g)
Red litmus
solution
Basic
solution
Test tube B
Related Theory

Blue
colour
Test tube B
(ii) Observations
With litmus solution as an indicator:
(1) In test tube A, blue litmus solution
changes into red colour. This
indicates the substance is acidic.
(2) In test tube B, red litmus solution
changes into red colour, so the
solution in test tube B is basic in
nature.
With phenolphthalein as an indicator:
In test tube A, phenolphthalein indicator
remains colourless as it shows that
acidic solution is present in test tube A.
While in test tube B, it changes to red
indicating that it is a basic solution.
+ CO2(g)
(B) Gypsum
(CaSO4.2H2O)
on
heating
to a temperature of 373K loses two
water molecules of crystallisation and
becomes calcium sulphate hemihydrate
1
(CaSO4. H2O)
2
337K
CaSO4.2H2O(s) →
CaSO4.
1
H2O(s)
2
1
+ 1 H2O
2
(C) On passing electricity through brine
solution (an aqueous solution of sodium
chloride), it decomposes to form sodium
hydroxide, chlorine gas and hydrogen gas
are released. NaOH is formed near the
cathode, Cl2 gas is given off at the anode
and hydrogen gas (H2) at the cathode.
2NaCl(aq) + 2H2O(g) ® 2NaOH(aq) + Cl2(g)
+ H2(g)
Acids, Bases and Salts
5
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11. (A) Solutions P and R could possibly react with
zinc metal to produce hydrogen gas.
The acidity or alkalinity of a solution is
expressed in terms of pH. Solution P has pH
1 so it could be an acid. Acids react with
metals to form salt and hydrogen gas is
given off.
P + metal ® Salt of P + Hydrogen gas
Similarly, solution R having pH 14 could be
a base. Bases react with metals to form
salt and hydrogen gas.
R + metal ® Salt of R + Hydrogen gas
(B) Solution R could be formed by the reaction
of a metal oxide with water.
Metal oxide + water ® Metal hydroxide
We know solution R is metal hydroxide or
base having pH 14. Hence, R solution will
be formed when metal oxide react with
water.
(C) Solution Q could be the raw material for
the industrial manufacture of chlorine
solution. Q is neutral having pH 7.
Sodium chloride + Q ® Sodium hydroxide +
Chlorine gas + H2(g)
12. (A) Rajesh
was given sodium hydrogen
carbonate (NaHCO3). Heating NaHCO3
gives CO2, H2O and sodium salt.
Heat
2NaHCO3(s) →
Na2CO3(s) + CO2(g) + H2O(l)
(B) (1) Used in antacids
(2) Used in toothpaste
(3) Used as a first aid in acidic insect bites.
(Any one)
6
(C) The sodium salt formed in P gives another
basic salt on recrystallisation. The sodium
salt formed in P is sodium carbonate
Na2CO3. On recrystallisation of Na2CO3,
we get washing soda.
Na2CO3 + 10H2O ® Na2CO3.10H2O
(D)
6 volt
battery
Bulb
Switch
Beaker
Nail
Dilute solution of
sodium hydroxide
Rubber cork
(A)
The bulb will start glowing in the case
of beaker A containing dilute solution of
sodium hydroxide. But bulb will not glow in
beaker B having solution of ethanol.
Glowing of bulb indicates that there is a
flow of electric current through the solution.
The electric current is carried through the
solution by ions.
NaOH(aq) ® Na+(aq) + OH–(aq)
The OH–(aq) are anions present in the dilute
solution of sodium hydroxide, this suggests
that bases produce hydroxide ions OH–(aq) in
solution, which are responsible for the basic
properties. On the other hand, ethanol, an
alcohol, though do not ionise into OH–(aq)
ions so it does not conduct electricity.
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1. (a) All of these
Explanation: All the objects given in the list can
be made/manufactured using either metallic
or non-metallic body. For example for making
swings in the playground we need wood,
rope, screws, stainless steel, quick lime, swing
hangers, seat (may be even of polyvinyl) etc.
Calcium reacts with cold water whereas, magnesium
reacts with hot water. Metals like aluminium, iron
and zinc do not react either with cold or hot water.
But they react with steam to form the metal oxide
and hydrogen. Metals such as lead, copper, silver
and gold do not react with water at all.
5. (a) Both (A) and (R) are true and (R) is the
2. (b)
(b)
Related Theory

Anode
Cathode
Electrolyte
Impure
metal M
Pure
metal M
Water soluble
salt of metal
M
Explanation: The impure metal is taken in the
form of a thick block and made the anode in the
tank by connecting it to the positive terminal of
the battery. A thin plate of pure metal is made
the 'cathode' by connecting it to the negative
terminal of the battery. A suitable water
soluble salt of the metal is taken as electrolyte.
correct explanation of (A).
Explanation:
Strong
oxidising
agents
include nitric acid (HNO3). The hydrogen gas
created during the reaction with the metal
is converted to H2O, hence no hydrogen
gas is formed. Instead, it produces oxides of
nitrogen like NO2, NO, etc.
Related Theory

6. (b) Both (A) and (R) are true but (R) is not the
correct explanation of (A).
Explanation: The metal oxides which are
soluble in water form alkalis. Only a few metals
oxides form alkalis.
Na2O(s) + H2O(l) ® 2NaOH(aq)
K2O(s) + H2O(l) ® 2KOH(aq)
3. (c) X-Sulphur dioxide, Y-Oxygen
Explanation: When cinnabar is heated in air,
mercuric oxide and sulphur dioxide are formed.
On further heating of mercuric oxide, mercury
and oxygen are obtained.
Heat
2HgO(s) + 2SO2(g)
2HgS(s) + 3O2(g) →
Heat
2HgO(s) →
2Hg(l) + O2(g)
4. (d) (I) and (IV)
Explanation: Metals like potassium and
sodium react violently with cold water. The
reaction is so violent and exothermic that the
evolved hydrogen immediately catches fire.
The reaction of calcium and magnesium
in water is less violent. The heat evolved is
not sufficient for the hydrogen to catch fire
and the bubbles of hydrogen gas stick to
the surface of the metal. So, the metal start
floating.
Magnesium and manganese react with very dilute
nitric acid to evolve hydrogen gas.
Caution

Students should keep in mind that reactive metals
always form basic oxide whereas, non metals form
acidic oxides. Oxides of two metals form amphoteric
oxides. Some non-metals also form metal oxides.
7. (A) The ability of metals to be drawn into thin
wires is called ductility. Gold being highly
ductile is used in making jewellery.
(B) (i) Seema would have chosen copper
wires because copper is better electrical
conductor than aluminum.
(ii) Anodised articles of aluminum have
a thick coating of an oxide layer on
the surface. It protects the surface of
aluminum from corrosion.
Metals and Non-Metals
7
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(C) The reduction of metal oxide to metal
using aluminum as the reducing agent is
called thermite reaction. It is also called
aluminothermy. The materials used in the
reaction are iron (III) oxide (Fe2O3) and
aluminium powder (Al). When Fe2O3 is
heated with Al powder, the heat evolved
is so high that iron obtained is in molten
state. This reaction is therefore used for
welding the broken parts of iron machinery,
railway tracks, girders etc. This reaction is
a displacement reaction as more active
aluminium displaces the less active metal.
Heat
FeO3(s) + 2Al(s) →
2Fe(l) + Al2O3(s)
8. (A) A metal oxide on being heated with
carbon does not produce carbon dioxide
as the metal is more reactive than
carbon. For example, carbon cannot
reduce the oxides of sodium, magnesium,
calcium, aluminium etc., to the respective
metals as these metals have high affinity
for oxygen than carbon.
(B) Metal M forms an oxide MO. Valency of
oxygen is two, so the valency of metal is
also two. Therefore, metal M is divalent
metal. M forms a basic carbonate when
exposed to moisture and carbon dioxide,
therefore it must be copper.
(ii) When the current is started, copper will
continue to be deposited on the iron
plate.
(B) (i) There is no deposition of copper on the
silver plate before starting the current
even as silver is less reactive than
copper. So, no reaction takes place.
(ii) The concentration of copper sulphate in
the solution on passing electric current
through the solution in the set up with
the silver plate would remain the same
as silver is less reactive than copper so
there is no reaction.
(C) (i) The weight of the silver plate will
increase and that of the copper plate
will decrease.
(ii) Ag(s) + CuSO4(aq) ® AgSO4(aq) + Cu(s)
11. (A) The metal M is aluminium or zinc.
(B) Let metal 'M' is taken as Al.
Al2O3 + 2NaOH ® 2NaAlO2 + H2O
Al2O3 + 6HCl ® 2AlCl3 + 3H2O
If metal 'M' is taken as Zn
ZnO + 2HCl ® ZnCl2 + H2O
ZnO + 2NaOH ® Na2ZnO2 + H2O
(C) The metal 'M' aluminum or zinc, it would
displace iron from its oxide.
2Al + Fe2O3 ® 2Fe + Al2O3
3Zn + Fe2O3 ® 3ZnO + 2Fe
9. (A) Metal M can be obtained by electrolytic
reduction. Metal M is obtained by the
electrolysis of its molten chloride. The
metal is deposited at the cathode (the
negatively charged electrode) whereas
chlorine is liberated at the anode (the
positively charged electrode). The reactions
are:
At cathode: Na+ + e– ® Na
At anode: 2Cl– ® Cl2 + 2e–
(B) The major byproduct obtained in the
process is chlorine gas.
10. (A) (i) Copper was deposited on iron plate
even before the switch was turned on
because the displacement reaction
has taken place. Iron being reactive
displaces copper from its salt solution
(CuSO4 solution)
Fe(s) + CuSO4(aq) ® FeSO4(aq) + Cu(s)
8
12. (A) (i) Rust will be seen on the plastic coated
iron piece.
(ii) Rust will be seen on the painted iron
piece.
(iii) No rust will be seen on the zinc coated
iron piece.
(B) (i) The iron rod is in contact with air and
moisture.
(ii) Zinc is more reactive than iron and gets
oxidised in preference to the iron object.
(C) The process of applying a protective
zinc coating to steel or iron is called
galvanisation. Galvanisation is usually
done by displaying the iron articles in
molten zinc. The iron coated with zinc is
also called galvanised iron. After the zinc
coating on iron objects, they do not come
in contact with air and moisture and thus,
rusting of iron is prevented.
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1. (d) Only (P), (Q) and (R)
ethanoic acid (CH3COOH) reacts with baking
soda (NaHCO3) to form a salt sodium
ethanoate (CH3COONa) and water (H2O) with
the evolution of carbon dioxide gas (CO2).
Explanation: All alkanes, alcohols and
aldehydes
would
undergo
complete
combustion in an adequate supply of oxygen
producing carbon dioxide, water, heat and light
energy.
Combustion of alkanes (Methane and Ethane):
CH4 + 2O2 ® CO2 + 2H2O + Heat and light
7
C2H6 + O2 ® 2CO2 + 3H2O + Heat and light
2
Combustion of alcohols (Ethanol):
CH3CH2OH + 3O2 ® 2CO2 + 3H2O + Heat and
light
Combustion of aldehyde (Propanal):
CH3CH2CHO + 4O2 ® 3CO2 + 3H2O + Heat
and light
CH3COOH + NaHCO3 ® CH3COONa + CO2 +
H2O
The carbon dioxide gas thus evolved can be
easily identified by passing it through freshly
prepared lime water which turns milky due to
the formation of insoluble calcium carbonate
Ca(OH)2 + CO2 ® CaCO3 + H2O.
Related Theory

Related Theory

During combustion carbon is oxidised to carbon
dioxide and water by addition of oxygen, therefore,
combustion may also be regarded as an oxidation
reaction. Saturated hydrocarbon generally burn
in excess of air with a blue flame but unsaturated
hydrocarbon burn with a yellow flame with lots of
black smoke.
Caution

Students must learn the general formula for alkanes,
alkenes and alkynes which are CnH2n+2, CnH2n and
CnH2n–2respectively to avoid the mistakes. They
must also remember combustion is an oxidation
reaction but oxidation cannot be combustion. For
example rusting of iron is an oxidation reaction but
not combustion reaction.
2. (d)
O
— C — OH
Explanation: The functional groups present in
Compound P — Alcohol group
Compound Q — Aldehyde group
Compound R — Ketone group
Compound S — Carboxylic acid group
Only compounds containing carboxylic acid
group can cause decomposition of baking
soda to produce carbon dioxide. For example,
When baking soda is added to an aqueous solution
of ethanoic acid, a brisk effervescence is produced
due to the evolution of carbon dioxide gas and this
reaction is used as a test of carboxylic acids.
Caution
Students get confused with the formula of washing
soda and baking soda, similarly with the formula of
functional group so they are advised to learn them
properly.
The number of moles of saturated hydrocarbon
(C2H6) formed is same i.e., in both ethane and ethyne.

3. (b) Only (Q)
Explanation: Reactions which involve addition
of two reactants to form a single product
are called addition reaction. The unsaturated
hydrocarbons having the double and triple
bonds in alkenes and alkynes respectively are
more reactive. These unsaturated hydrocarbons
in the presence of catalyst such as palladium
or nickel give saturated hydrocarbon. Ethene
(C2H4) is an alkene having double bond
undergoes addition reaction to form saturated
hydrocarbon ethane (C2H6).
473K CH — CH ...(i)
CH2 = CH2 + H2 Nickel,
→

3
3
Ethyne (C2H2) is an alkyne having triple bond
that undergoes addition reaction to form
saturated hydrocarbon Ethane (C2H6)
CH º CH + 2H2 ® CH3 — CH3 Carbon and its Compounds
...(ii)
9
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in the reaction (i) the number of moles of
hydrogen consumed is only 1 whereas in the
reaction (ii), the number of moles of hydrogen
consumed is 2.
(B) Carboxylic acid: CH3 — C — OH
||
O
Alcohol: CH3CH2OH
(C) (i) When ethanol is heated at 443K with
excess concentrated sulphuric acid,
dehydration of ethanol takes place to
give ethene. Here concentrated sulphuric
acid acts as a dehydrating agent.
Related Theory

Hydrogenation is generally used to convert
vegetable oil to vegetable ghee in presence of
catalysts nickel or palladium
Nickel / Palladium
Vegetable oil + H2 
→ vegetable ghee
473k

Hot Conc.
→
CH3 — CH2OH 
H2 SO4
CH2 == CH2 + H2O
Catalysts are substances which can generally
increase the speed of a chemical reaction without
being used up in that reaction. Nickel or palladium
is catalyst used in hydrogenation of unsaturated
compounds to saturated compounds.
(ii) When ethanol reacts with sodium,
evolution of hydrogen along with the
formation of sodium ethoxide takes
place.
2CH3CH2OH + 2Na ® 2CH3CH2O–Na+
+ H2
4. (b) (Q) and (S)
Explanation: The functional group present in
these compounds are:
(P) CH3 — C — CH3 Ketone
||
O
8. (A) C3H4 is an unsaturated hydrocarbon and it
burns with a sooty or smokey flame as it
results in incomplete combustion.
(B) C3H4 is a propyne
(Q) CH3 — CH — CH3 — Alcohol
|
OH
H
X
(R) CH3 — CH2 — C — OH Carboxylic acid
||
O
H X
C
X
H
H
H
|
H—C—CºC—H
|
H
5. (a) Both (A) and (R) are true and (R) is the
correct explanation of (A).
9. (A) Out of the four compounds which are
6. (b) Both (A) and (R) are true but (R) is not the
correct explanation of (A).
the first members of their respective
homologous
series
given
here,
methanone has been written incorrectly
because the smallest ketone has three
carbon atoms moreover, there is no
compound named methanone.
Explanation: Carbon can neither gain nor lose
4 electrons to complete its octet to acquire the
nearest nobel gas configuration. It only shows
its 4 valance electrons either with carbon or
other atoms. The carbon compounds have low
melting and boiling points due to the forces
of attraction between the molecules of these
compound.
(B) She should have written propanone instead
of methanone.
H3C — C — CH3
||
O
7. (A) Ethanol is a good solvent and used in
Methanal is an aldehyde with formula
HCHO having —CHO (aldehyde) as
functional group. Methanoic acid is a
carboxylic acid with formula HCOOH.
medicines such as tincture iodine,
cough syrups and many tonic. It is also an
active ingredient of all alcoholic drinks.
10
C
X
(S) CH3 — OH Alcohol
(Q) and (S) compounds have alcohol as
functional group. So option (b) is correct.
Explanation: Vegetable ghee has saturated
carbon chains which increase the level of
bad cholesterol in blood. Animal fats like
ghee and butter contain saturated fatty acids
which are said to be bad for health. Therefore,
it is recommended to use oil containing
unsaturated fatty acids.
C
Methanol is the simplest alcohol with
formula CH3OH having —OH (alcohol) as
functional group.
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10. (A) Sodium and potassium salts of higher
C2H5OH
fatty acids are called soaps. Detergents
are sodium or potassium salts of long
chain sulphonic acids.
(B) A soap molecule has two parts, a long
hydrocarbon tail, this part is insoluble
in water and is called hydrophobic or
water repelling tail. The other one is a
negatively charged head. This part is ionic
part, soluble in water and hence it is called
hydrophilic or water attracting end.
(C) Soaps are not effective cleansing agent
in hard water because calcium and
magnesium ions present in hard water
react with soap to give curdy white
precipitate of calcium and magnesium
salts of fatty acids which attach to the
surface of the cloth. Due to formation
of precipitate, a lot of soap is wasted.
Therefore, hard water does not produce
any lather with soap. Hence, soaps are not
effective cleansing agents in hard water.
acid
CH3 — C — O — CH2 — CH3
||
O
'Y'
Therefore, 'Y' is an ester.
(ii) This type of compounds i.e., esters have
a sweet smell.
(iii) Esters are used in making perfumes and
used as flavouring agents.
(C)
Test tube
containing
reaction
mixture
the minimum number of carbon atoms
needed in a molecule for it to have a
structural isomer is 4. The hydrocarbon
containing less than 4 carbon atoms
cannot be arranged differently.
(B) The saturated hydrocarbon having the
minimum number of carbon atoms is
butane. Structural isomers of butane.
CH3 — CH2 — CH2 — CH3
(a)
CH3 — CH — CH3
|
CH3
(b)
(C) C3H7OH and C4H9OH constitute a
homologous series. The common difference
in the molecular formula and molecular
masses of these two consecutive members
of a homologous series are- CH2 unit and
14u (mass units).
atoms.
CH3COOH
'X'
CH3COOH + C2H5OH →
11. (A) In the case of a saturated hydrocarbon,
12. (A) 'X' compound will contain two carbon
4
Alkaline KMnO4 is known as oxidising agent
as it adds oxygen to the starting material
C2H5OH and changes alcohol to acid
(CH3COOH). The number of carbon atoms
remains same, only one atom of oxygen is
added. Acidified potassium dichromate can
also be used as an oxidising agent.
(B) (i) The type of compound formed in the
above reaction with respect to the
functional group it contains is ester.
Na+
Hydrophilic end
Hydrophobic end
alkaline
KMnO

→
+ Heat
Beaker
Water
Wire gauze
Tripod stand
Burner
(D) When ester ('Y') is treated with sodium
hydroxide solution, it gets converted back
to alcohol and sodium salt of carboxylic
acid. This reaction is also known as
saponification reaction because it is used in
the preparation of soap.
NaOH
CH3COOC2H5 → C2H5OH + CH3COONa
'Y'
Related Theory

Alkaline hydrolysis of an ester to give back the salt
of corresponding carboxylic acid and the alcohol is
called saponification. It is the reverse of esterification.
Carbon and its Compounds
11
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1. (c) Filtration: Q; Selective reabsorption: R
Explanation: Filtration takes place in
glomerulus (Q) and selective reabsorption
takes place in tubular part (R).
The first step in urine formation is the
filtration of blood which is carried out in the
glomerulus. The glomerulus is a network of
capillaries surrounded by a cup-like structure
called Bowman's capsule. (P) is a branch of
renal artery which brings blood having waste
materials in it and is filtered. The glomerulus
filtrate flows down the tubular structure where
reabsorption of useful substances like glucose,
amino acids, water etc, takes place. Finally, the
urine moves through the ureter and collects in
the urinary bladder till thrown out of the body
through urethra and urinary opening. Major
processes involved in the formation of urine are:
(1) Ultra-filtration of blood.
(2) Selective reabsorption of substances from
the filtrate
(3) Secretion of certain substances into the
filtrate.
Caution

3. (a) X is more than Y.
Explanation: During aerobic respiration,
glucose breaks down completely to produce
water and carbon dioxide. However, in
anaerobic respiration (fermentation), the
breakdown of glucose is incomplete. Therefore,
amount of X is more than that of Y.
Related Theory

Explanation: Photosynthesis is an example of
an anabolic reaction. During this process, green
plants make their food by using carbon dioxide
from air and water from soil in the presence
of sunlight. The process involves formation
of complex molecules from simple inorganic
molecules.
(b)
Yeast
Lactic
acid
Carbon
dioxide
Lactic
acid
Carbon
dioxide




Light
6CO2 + 12H2O Chlorophyll

→ C6H12O6 + 6H2O
+ 6O2
Digestion is a catabolic reaction as it involves
the breakdown of complex substances
into simple substances. Respiration is a
catabolic process as it involves breakdown of
glucose either aerobically or anaerobically.
Transpiration is the loss of water in the form
of vapour from the aerial parts of the plants.
Explanation: When there is a lack of oxygen
is our muscle cell, pyruvate is converted into
lactic acid. The build up of lactic acid in our
muscles during sudden activity causes cramps.
Lack of oxygen
Cytoplasm
→
Glucose In
→ Pyruvate in
muscle cells
Lactic acid + Energy
Is absence of oxygen, pyruvate is converted
into ethanol and carbon dioxide. This process
is also called fermentation which takes place
in yeast.
5. (a) Both (A) and (R) are true and (R) is the
Absence of
Cytoplasm
Glucose In
→
→ pyruvate 
oxygen
Ethanol + carbon dioxide + energy
12
During aerobic respiration energy is released in larger
amount as compared to energy released during
fermentation. Aerobic respiration takes place in
cytoplasm and mitochondria whereas, fermentation
takes place is cytoplasm and yeast.
4. (d) photosynthesis
2. (b)
Humans
Students must remember that the breakdown of
glucose to pyruvate always takes place in cytoplasm
which is common for both aerobic and anaerobic
respiration.
correct explanation of (A).
Explanation: The separation of the right side
and the left side of the heart is useful to keep
pure (oxygenated) and impure (deoxygenated)
blood from mixing which allows a highly
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efficient supply of oxygen to the body. This is
useful in animals that have high energy needs
such as birds and mammals.
Caution

Students should remember that the right chambers
of the heart contains deoxygenated blood and left
chambers of the heart always have oxygenated
blood.
6. (b) Both (A) and (R) are true but (R) is not the
correct explanation of (A).
Explanation: The rate of photosynthetic
absorption of carbon oxide is higher during day
times as compared to the rate of respiratory
release of CO2, which results in the production
of the greater amount of O2 by photosynthesis
than the amount needed for respiration.
7. (A) The digestive system converts the food
we eat into their simplest forms. Bile,
Pancreatic juices, intestinal juices act upon
different types of food. The action of these
enzymes convert protein into amino acids,
carbohydrates into glucose and fats into
fatty acid and glycerol. All these products
are soluble in water and easily absorbed
by the wall of the intestine which contains
blood capillaries. The brokendown food like
aminoacid, glucose etc, are then absorbed
into the bloodstream from the small
intestine and the nutrients are carried to
each cell in the body.
(B) Consequences of malfunctioning of pyloric
sphincter– food can get into the small
intestine too fast causing poor digestion or
poor absorption.
Consequence
of
malfunctioning
of
anal sphincters– It can lead to faecal
incontinence.
(C) (i) Partially digested food reaches the
stomach from the buccal cavity through
pharynx and Oesophagus. Gastric
glands present in the stomach release
hydrochloric acid, a protein digesting
enzyme called pepsin and mucus. The
hydrochloric acid creates an acidic
medium which facilitates the action
of the enzyme pepsin. Mucus covers
the inner lining of the stomach and
protects it from the corroding action of
hydrochloric acid.
(ii) The food coming from the stomach
is acidic in nature. The bicarbonate
ions secreted by pancreas makes the
medium alkaline. The alkaline medium
helps in activation of pancreatic enzmes
secreted by the acinar cells.
Related Theory

The pancreas is both an endocrine and exocrine
gland. The endocrine region of pancreas secretes
hormones, insulin and glucagon. The exocrine part
of pancreas secretes sodium bicarbonate and many
digestive enzymes.
8. (A) Amount of dissolved oxygen in water is
lower as compared to oxygen present in
the air. Hence, aquatic animals have to
breathe faster.
(B) Cartilaginous rings present in trachea
prevent the collapsing of trachea in
between breathing.
9. When different organs need the stored food for
growth, sugar from storage organs is moved to
phloem using ATP which is a form of energy.
This increases the osmotic pressure of the
tissue causing water to move into it.
Increased pressure inside the phloem cells
move sugar to cells with lower pressure to
reach other organs. This allows phloem to move
materials according to the plant's needs. The
transport of soluble products of photosynthesis
is called translocation and it occurs in the part
of the vascular tissue known as phloem.
10. (A) During the first circulation, oxygenated
blood from lungs is brought into the left
atrium by pulmonary vein, then pure blood
passes to the left ventricle, from where it is
distributed to the entire body by the largest
artery known as Aorta.
During the second circulation: deoxygenated
blood from body comes to right atrium and
then right ventricle to pass for oxygenation
to the lungs. The deoxygenated blood
from the body is collected by superior and
inferior vena cava which collect the impure
blood from upper and lower parts of the
body respectively. From right atrium, the
deoxygenated blood goes into the right
ventricle. On contraction of right ventricle, it
is passed to the lungs by pulmonary artery
for purification.
This type of double circulation allows for
separation of oxygenated and deoxygenated
blood in the body.
(B) The blood vessels that:
(i) Carry oxygenation blood from the lungs
to the heart is pulmonary vein.
(ii) Carry deoxygenated blood from the
heart to the lungs is pulmonary artery.
11. (A) The part of the body responsible for
excretion in:
(i) Amoeba: cell membrane and contractile
vacuole.
(ii) Human beings: A pair of kidneys.
Life Processes
13
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(B) (1) Excretion removes the unwanted and
toxic byproducts produced during
various metabolic processes.
(2) It regulates the water content of the
body fluids.
(3) It regulates the pH of the body fluids.
(C) The major waste substances produced by
various metabolic activities of plants are
oxygen, carbon dioxide and water.
(1) Respiratory waste such as carbon
dioxide and photosynthetic waste
i.e., oxygen are expelled out through
stomata.
(2) Excess of water is eliminated by
transpiration.
Detailed Answer:
(1) Some waste substances are excreted
through roots into the soil around them.
(2) In living cells, many plant waste
products are stored in cellular vacuoles.
(3) Waste products may be stored in the
form of resins, gums, tannins, alkaloids
etc.
12. (A) (i) The plants survive in dry conditions by
minimising the loss of water through
transpiration
by
photosynthesis
mechanism.
14
(ii) Since stored carbon dioxide can be
used, stomata need not be open for
photosynthesis to occur during the day.
Keeping the stomata closed during the
day helps to minimise water loss due to
transpiration.
(iii) Such plants are likely to take carbon
dioxide from the environment during the
day.
(B) (i) The
following
Mechanism/events
take place during the process of
photosynthesis:
(1) Absorption of
chlorophyll.
light
energy
by
(2) Conversion of light
chemical energy.
energy
to
(3) Photolysis of water i.e., splitting of
water molecules into hydrogen and
oxygen.
(4) Reduction of carbon dioxide to
carbohydrates.
Chlorophyll
6CO2 + 12H2O 
→ C6H12O6
Sunlight
+ 6O2 + 6H2O
(ii) The source of oxygen produced during
the process of photosynthesis are water
molecules.
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1. (c) I-Axon; II-Nerve ending,
III-Cell body; IV-Dendrite.
Explanation: The information is acquired at
the end of a dendrite tip of a nerve cell, sets off
a chemical reaction that creates an electrical
impulse. This impulse travels from the dendrite
to the cell body and then along the axon to
its end. At the end of the axon, the electrical
impulse sets off the release of some chemicals.
These chemicals cross the gap or synapse and
start a similar electrical impulse in a dendrite
of the next neuron.
Caution

Students
frequently
confuse
synapse
and
neuromuscular junction. Synapse is the gap between
two neurons. Neuromuscular junction allows deliver
of impulses from neurons to other cells like muscles.
2. (b) insufficient production of insulin in her body
Explanation: Sapna's blood sugar level
is high as compared to blood sugar level
in a healthy adult. It means there is
insufficient production of insulin in her body.
Pancreas secretes insulin which regulates the
metabolism of sugar. Excess of blood sugar
level in a person's body causes diabetes.
3. (b) Chemotropism
Explanation: Hydrotropism is when a plant
part moves in response to water. Roots of a
plant moves towards water, so they show
positive hydrotropism.
Chemotropism is when a plant part moves in
response to chemical stimulus.
Phototropism is the movement of shoot
towards light.
Geotropism is when a part of plant moves in
response to gravity.
4. (c) Both (a) and (b)
Explanation: In case of a spinal cord injury,
both involuntary actions and reflex actions
get disrupted.
Caution

Students must remember the difference between
voluntary, involuntary and reflex actions.
5. (b) Both (A) and (R) are true but (R) is not the
correct explanation of (A).
Explanation: Thyroxine is a hormone secreted
by thyroid gland and iodine is necessary for
the gland to make thyroxine hormone. In
case of iodine deficiency in our diet, there is a
possibility that we may suffer from goitre. One
of the symptoms in this disease is a swollen
neck.
6. (c) (A) is true but (R) is false.
Explanation: When the leaves of touch me not
plant are touched, the leaves of a plant move
very quickly in response to touch and there is
no growth involved in this movement. Whereas,
tropic movement happens as a result of growth
of plant part in a directional movement. These
tropic movements can be either towards the
stimulus or away from it.
7. (A) Stimulated cells release a chemical
compound which diffuse all around the
original cell. These hormones are usually
released into the blood. The blood carries
them to specific tissues or organs called
target tissues or target organs where
hormones trigger a physiological or
biological activity.
(B) Pea plants climb up other plants or fences
by means of tendrils. These tendrils are
sensitive to touch. When they come in
contact with any support, the part of the
tendril in contact with the object does not
grow as rapidly as the part of the tendril
away from the object does. This causes the
tendril to circle around the object and thus,
climb to it.
(C) The nervous system consists of nerves or
neurons which control and coordinate all
the functions in the body. Nervous system
consists of sensory receptors which collect
Control and Coordination
15
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information from the external environment
in the form of stimuli and then send them
to the brain in the form of electric impulse.
In the brain, the information is intercepted,
processed and the instructions to act are
sent to the effector organs i.e., muscles or
glands. Nerves alone cannot reach each
and every part of the body so they need
assistance from the hormones. Endocrine
glands secrete chemical substances called
hormones directly into the blood.
Reflex Action
Walking
It is inborn and It is not inherited
present
in
the and is acquired
individual
since through learning
birth.
It is automatic and It is under
occurs
without control
of
the will of the individual.
individual.
the
the
It cannot be changed. It can be changed.
Related Theory

Difference between reflex action and walking.
Chemical coordination is mainly based on feedback
mechanism and tells the body to either fasten up or
slow down as per the situation. Nervous control on
the other hand, is more of a direct control. Both of
them complement each other. Thus, it can be said
that the nervous and hormonal systems together
perform the function of control and coordination in
human beings.
Cerebrum (i)
(B)
8. (A) The mechanism of hormone action is
known as feedback mechanism.
(B) The sensor 'X' in the given flow diagram are
the cells of the pancreas.
If feedback mechanism is absent in
humans, the balance of life processes
would be disturbed.
9. (A) The
chemicals
that
control
the
developmental changes in the butterfly's
body structure are called hormones.
(B) The developmental change (other than the
external changes in the body structure) in
a human female during puberty brought
about by the action of type of hormones is
onset of menstrual cycle.
10. (A) The increase in heartbeat and his breathing
on a roller coaster ride is due to the
hormone adrenaline.
Adrenaline hormone is also known as fight
or flight hormone.
(B) (i) When some particles fall into our eyes,
our eyes start to water on their own
and we blink to get the particle out of
our eyes. This reaction is involuntary.
(ii) The pathway that brings this immediate
reaction to a stimulus is reflex arc.
(iii) (1) The organ that responds to a
stimulus is effector. The effectors
can be a muscle or a gland.
(2) The part of the brain that receives
sensory impulses is the forebrain.
11. (A) The instant jump on seeing a snake was an
involuntary quick reflex action.
Walking away from the snake was a
voluntary action.
16
Cerebellum (ii)
12. (A) Plant growth regulators do not always
promote growth. Abscissic acid (ABA) is
a plant hormone which promotes ageing,
wilting and inhibits growth.
(B) (i) As a first line of defence, abscissic acid
(ABA) is released in plants whereas
in animals, adrenaline is the stress
hormone which acts as first line of
defence.
(ii) It is reported that plant hormones are
found in animal bodies even though
they are not synthesized by the
animals. The most common pathway
entry of plant hormones in animals is
through food.
(C) (i) The plant hormone that controls
directional growth is auxin. When growing
plants detect light, auxin is synthesized
at the shoot tips that helps the cells to
grow longer. When light is coming from
one side of the plant, auxin diffuses
towards the shady side of the shoot. This
concentration of auxin stimulates the
cells to grow longer on the side of the
shoot which is away from light. Thus,
plants appear to bend towards light i.e.,
show directional growth.
(ii) Animal growth hormones cannot
promote growth under the influence
of external stimuli such as light, gravity
etc. While plant growth regulators do.
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1. (b) A - Ovary; B - Stigma; C - Style.
Explanation: Carpel is a female reproductive
part of an angiospermic flower. Carpel is also
known as pistil. It consists of stigma, style and
ovary.
Related Theory

Stamen is a male reproductive organ of an
angiospermic flower. It consists of anther and
filament. Outermost whorl of green leaves called
sepals are protective in function. Collection of petals,
coloured leaves from corolla attract insects for
pollination. Androecium is collection of stamens and
gynoecium is collection of carpels.
Caution

Students must know that plants which produce
seeds only can reproduce by sexual means where
as if we want faster and easier method, vegetative
propagation is practiced.
2. (d) S
Explanation: The various parts of male human
reproduction system are:
P – Urinary bladder. It collects and stores urine
Q – Prostrate gland. It secretes mucus and
slightly alkaline fluid which is released during
ejaculation. The secretion of prostrate gland
along with the secretion of seminal vesicle
makes the transport of sperms easier and this
fluid also provides nutrition.
R – Vas deferens. It carries sperms to urethra.
S – Testis. They are located outside the
abdominal cavity. They produce and form
sperms as well as secrete sex hormone
testosterone. So, the correct option is (d).
Related Theory

The hormone testosterone brings about the
development of secondary sexual characters.
(1) Enlargement of penis and scrotum
(2) Broadening of shoulders.
(3) Growth of pubic hair and hair on face, armpits
and on the chest.
(4) Deepening of voice.
(5) Increase in height.
(6) Day dreaming.
Related Theory

Students must not confuse the primary sexual
characters with the secondary sexual characters.
Primary sexual characters are present at birth
whereas secondary sexual characters develop at
puberty.
3. (a) (I), (III), (IV), (II)
Explanation: Internal fertilisation is an
essential part of reproduction in human beings.
During copulation, the human male ejaculates
the sperms in the vagina close to the cervix of
uterus. The mature egg enters the fallopian
tube where fertilisation takes place. The uterus
prepares itself every month to receive and
nurture the growing embryo. As a result of
fertilisation between sperm and ovum, zygote
formed is implanted in the uterus. The lining
of uterus thickens and is richly supplied with
blood to nourish the growing embryo.
4. (d) (C), (B)
Explanation: Brinjal flower is a bisexual flower.
It has both stamens and carpel it is one flower
which is seen only in option (C). Papaya flower is
unisexual flower and it contains either stamens
or carpel. In option (A) only stamens are shown
and in option (B) only carpel is present. So, both
options (A) and (B) have unisexual flowers of
papaya.
According to the question, brinjal flower (C) to
be kept before papaya, so only (d) gives the
correct option.
5. (a) Both (A) and (R) are true and (R) is the
correct explanation of (A).
Explanation: Oral pills are mainly hormonal
preparations and contain the hormones
estrogen and progesterone. They prevent
the development of egg and ovulation by
inhibiting the secretion of follicle stimulating
hormone (FSH). Copper T is a physical device
How do Organisms Reproduce?
17
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to prevent the implanation in the uterus of the
8. (A) Plants
produced through vegetative
propagation are genetically identical
to their parents but there are some
disadvantages of vegetative propagation
also. These are:
female reproductive system during copulation
Oral pills and copper T do not prevent sexually
transmitted diseases (STDs). Condom is a
physical barrier method used by males. It is a
(1) Both the parent plant and progeny will
be susceptible to same pathogen which
can wipe out the entire population.
covering for the penis and used during sex. It not
only prevents the chances of a female getting
pregnant but also prevents the transmission of
(2) There will be less genetic diversity as
the progeny is similar to parents and no
new variety will be produced.
many STDs infections.
6. (b) Both (A) and (R) are true but (R) is not the
(B) (i) The farmer should adopt vegetative
propagation or asexual method to
produce strawberries having the same
taste.
correct explanation of (A).
Explanation: The DNA (Deoxyribo nucleic acid)
molecule in the cell nucleus is the information
source for making proteins. If the information
(ii) The reasons for choosing vegetative
propagation to produce strawberries
having the same taste are.
• The characteristics of the parent
plant are conserved.
• The offspring produced by this method
can adopt the same environment
easily.
is changed, different proteins will be made.
These proteins will eventually lead to altered
body designs.
Related Theory

DNA copying is always accompanied by the creation
of an additional cellular apparatus and then DNA
copies separate each with its own cellular apparatus
and a cell divides to give two new cells.
9. (A) The living organisms reproduce:
(1) to increase the population of a particular
species.
(2) for perpetuation of species
(3) for evolution
7. (A) STDs are infectious diseases caused by
pathogens such as bacteria, viruses,
protozoans, fungi etc, and are transmitted
through sexual contact.
(B) Unicellular organisms reproduce only
through asexual reproduction because:
(1) They can produce a large number of
offsprings in a small period of time.
(2) The offsprings are adapted to survive in
the same environment.
(3) Character of parent plants are preserved.
The prime cause of transmission of STDs
is the sexual contact with the infected
partner. Sexually transmitted diseases can
also be transmitted by:
(1) transfusion of blood from an infected
person.
(2) sharing of injection needles
(B) Due to reckless female foeticides, child sex
ratio is declining at an alarming rate in
some sections of society.
10. (A) The characteristics of Planaria formed
The Government of India has prohibited sex
determination by law:
(1) to stop illegal sex-selective abortion of
female foetus.
(2) to maintain female-male sex ratio.
(C) Bacterial diseases:
(1)Gonorrhea
(2) Syphilis
Viral diseases:
(1) Warts
(2) AIDS
18
by regeneration will be the same as the
characteristics of the original Planarium as
regeneration does not involve the mixing of
gametes.
(B) Regeneration is not the choicest method of
reproduction in any organism.
If Planaria is cut into number of pieces,
each piece grow into a complete organism.
It is carried out by specialised cells. These
cells proliferate and make large number
of cells. From this mass of cells, different
cells undergo changes to become various
cell types and tissues. These changes take
place in an organised sequence referred to
as development.
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12. (A) (i)
Stigma
Anther
Filament
Style
Pistil
Petal
Ovary
Sepal
11. (A) Two structural designs of the placenta that
help the embryo to get nutrition are given
below.
(1) Placenta has villi on embryo side
(2) It has blood spaces on the mothers side.
(B) The placental tissue is not designed for one
way transport as the waste generated by
the developing embryo is transferred out
through the placental tissue.
(C) The placenta serves as the nutritive,
respiratory and excretory organ of the
foetus as the foetus gets nutrients, water,
oxygen, minerals, vitamins etc. from the
maternal blood and gives off wastes,
carbon dioxide etc.
(i) Longitudinal section of a flower.
(ii) (1) Male reproductive part Stamen – Anther, Filament
Female reproductive part
Carpel – Stisma, Style, Ovary
(2) Protective in function–Sepal Attract
the insect for pollination-petal.
(B) The changes that takes place after
fertilisation are:
(1) The zygote divides several times to form
an embryo within the ovule.
(2) The ovule develops a tough coat and is
gradually converted into a seed.
(3) The ovary grows rapidly and ripens to
form a fruit.
(4) The petals, sepals, stamens, style and
stigma shrivel and fall off.
How do Organisms Reproduce?
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1. (d) 100%
3. (a) Some amount of variation is produced even
2. (a) 75

Explanation: Attached earlobes is a recessive
traits. These traits express only in homozygous
condition. Since both the parents have attached
earlobes, the child might end up with attached
earlobes. Two parents with a recessive trait
can't have a child with a dominant one. So, two
parents with attached ear lobes should not be
able to have a child with unattached earlobes.
Explanation: Individuals carrying two identical
alleles are known as homozygous (TT or tt)
while individuals bearing different alleles are
known as heterozygous (Tt).
All tall heterozygous plants
Heterozygous tall plant × Heterozygous tall plant
Tt
Tt
T
t
T
during asexual reproduction due to
inaccuracy in cell division.
Explanation: There are only minor differences
or a few variations between the generations
during asexual reproduction. These variations
arise due to inaccuracy in DNA copying.
Related Theory
4. (c) gene
Explanation: The vehicle of heredity is
gene which is the unit of inheritance of
characters from one generation to another. A
chromosome is made up of proteins and DNA
and is found in the nucleus of a cell. It carries
genetic information in the form of genes. DNA
is deoxyribonucleic acid. The basic event in
reproduction is the creation of DNA copying.
The DNA in the cell is information source
for making proteins. The complex of DNA
and protein is called chromatin and found in
eukaryotic cell.
t
TT
Tt
Tt
tt
Phenotypic ratio
Tall : Short
3:1
Genotypic ratio
TT : Tt : tt
1:2:1
The percentage of total short homozygous
plants obtained after self pollination is 25%
Out of 300 plants, total number of short plants
obtained are 75.
Related Theory

Allele is a pair of genes that control the two
alternatives of the same phenotypic characteristics.
For example, TT or tt. Recessive is the gene which
is unable to express itself in presence of dominant
gene. Genotype is the genetic combination of an
organism which determines the characters and
phenotype is the appearance of an individual.
Students must remember chromosome DNA,
genes and chromatin material are present in the
nucleus of a cell Chromosomes contain information
for inheritance of features from parents to next
generation in the form of DNA. Functional segments
of DNA are called genes.
5. (a) Both (A) and (R) are true and (R) is the
Caution
 Students must remember that the genetic make up is
genotype while physical appearance is a phenotype.
Students should not get confused with genotypic and
phenotypic ratio otherwise they can get wrong answer.
20
When the cell is about to divide, chromatin material
arranges itself to be a chromosomes.
Caution

Related Theory

Greater diversity is seen in sexually reproducing
organisms.
correct explanation of (A).
Explanation: In females, there is a perfect
pair of sex chromosomes but males have
mismatched pair in which X is normal sized
while Y is a short one. Due to two number of
different sex chromosomes, males produce
two types of sperms.
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(6) Thus, the sex of a newborn child is a
matter of chance and depends on what
happens during fertilisation.
Related Theory

A child who inherits an X chromosome from
her father will be a girl and one who inherits Y
chromosome from her father will be a boy.
6. (b) Both (A) and (R) are true but (R) is not the
correct explanation of (A).
Explanation: When mendel crossed a tall pea
plant with a dwarf pea plant, he found that
in first generation (F1), all the plants produced
were tall.
tt
TT
T
F1 generation Tt
T
t
t
Tt
Tt
Related Theory

Some species rely entirely on environmental cues.
In some animals, the temperature at which the
fertilised eggs are kept determines whether the
animals developing in eggs will be male or female.
In snails, individuals can change sex, indicating that
sex is not genetically determined. In chrysema picta,
high incubation results in male progeny while a
temperature below 28°C produces only females.
8. (A) Genotype of parents
TT
Tt
T
Tt
Since, F1 plants are all tall and genotypically
are Tt, they have inherited 't' from one parent
which is not expressed, as it results in dwarf
plants.
7. (A) DNA copying is a biochemical reaction. No
biochemical reaction is absolutely reliable.
Therefore, it is expected that the process of
copying the DNA will have some variations
each time. As a result, the DNA copies
generated will be similar, but may not be
identical to the original.
(B) Chromosomes are special lineages of cells
in the sexually reproducing organisms.
These cells undergo a special type of cell
division, called meiosis. As a result, the germ
cells formed have only half the number of
chromosomes as the parent's cell. When
these germ cells from two individuals
combine sexual reproduction to form a new
individual and it results in re-establishment
of the number of chromosomes as the
parent organism.
(C) (1) The female gamete, ovum always
contains an X chromosome.
T
T
t
(F1 generation) TT
Tt
TT
Tt
When two pea plants are used to produce a
progeny of 20 pea plants having genotype
TT and Tt, in F1 generation all the plants
formed are tall and no short pea plants
were found in the progeny. 50% of the
plants produced in F1 generation are
homozygous tall having genotype TT and
50% are heterozygous tall with genotype
(Tt).
(B) Plants that reproduce through asexual
reproduction give rise to similar but not
identical offsprings because of inaccuracies
in copying of DNA from parent to offsprings
or mutations.
9. (A) The genotype of the parent plants to
give green and yellow seeds in equal
proportions will be:
1st parent – Gg
2nd parent – gg
This can be explained by monohybrid cross.
gg
(Genotype of
Gg
parents)
(Gametes)
G
g
g
g
Gg
gg
gg
(2) The male gamete, sperm is of either
having X chromosome or Y chromosome.
(3) Whether sperm will contribute the X
chromosome or Y chromosome is a
matter of chance and the male does not
have any control on it.
(4) If a sperm carrying X chromosome
fertilizes an egg, then the child born will
be a girl.
(5) But if a sperm carrying Y chromosome
fertilize an egg, the child born will be a
boy.
(F1 generation) Gg
The plants of green and yellow seeds are
in the ratio of 2 : 2 i.e., 1 : 1 and in equal
proportions.
(B) When a farmer crosses two heterozygous
green seeded plant, the number of green
and yellow seeds respectively in the F1
generation would be 75 and 25. This can
be explained by taking both the parents as
heterozygous green seeded plants.
Heredity
21
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Monohybrid cross
(Heterozygous Gg
green parents)
F1 generation
Gg
g
(Gametes) G
g
G
t
t
t
tt
tt
t
tt
tt
All offspring will be dwarf.
(F1 generation) GG
Gg
Gg
Green
3
:
:
gg
11. (A) In order to determine whether an accident
victim is male or female, any cell of the
body can be taken, as every cell has the sex
chromosomes as the 23rd pair.
(B) (i) New combinations of characters which
appear in F2 progeny are:
(1) Round green seeds (Rryy) or (RRyy)
(2) Wrinkled yellow seeds (rrYy) or (rrYY)
(ii) New combinations are produced
because of independent inheritance of
seed shape and seed colour trait.
Yellow
1
When a farmer crosses two heterozygous
green seeded plants and obtains 100 plants
in the F1 generation, the number of green
and yellow seeds obtained in F1 generation
is 75 and 25 respectively, as the phenotypic
ratio is 3 : 1. The yellow colour is present
in F1 generation but it does not express as
it is a recessive trait and green colour is a
dominant trait as the parent seeds taken
for the cross were heterozygous green.
10. (A) Using Mendel's laws of inheritance, the
genotypes of all the possible pairs that
could have dwarf offspring are:
(1) Tt × Tt
(2) Tt × tt
(3) tt × tt
The phenotypes for each of the above
genotypes are as follows:
(1) Tt (Tall) × Tt (Tall)
(2) Tt (Tall) × tt (dwarf )
(3) tt (Dwarf ) × tt (Dwarf )
(B) A cross (1) to show the genotype of the offsprings
that might arise in the next generation.
Tt
TT
(Parents)
(Gametes) T
(F1 generation)
T
T
T
t
T
TT
Tt
t
Tt
tt
Related Theory

The progeny formed in F1 generation is RrYy (Round,
yellow)
The progeny is F2 generation
Round Yellow 9
Round green 3
Wrinkled Yellow 3
Wrinkled green 1
12. (A) The most likely genetic factor for sex
t
75% will be tall and 25% dwarf.
Cross (2) to show the genotypes of offsprings
(Parents)
tt
Tt
(Gametes) T
t
t
t
(F1 generation)
t
T
t
Tt
tt
t
Tt
tt
50% will be tall and 50% dwarf.
Cross (3) to show the genotypes of offsprings
tt
tt
Parents
Gametes
22
t
t
t
t
determination in unisexual plants is sex
chromosomes.
(B) Temperature of the fertilised egg
determines sex of embryo in some reptiles.
For example,
In Agama agama (lizard), high incubation
temperature results in male progeny while
a temperature below 28°C produces only
females. Whereas, in Chrysema picta
(turtle), high incubation temperature
above 33°C results in the development
of a female progeny while a temperature
below 28°C produces only males. Snails
can also change sex indicating that sex is
not genetically determined.
(C) The law of segregation states that the
factors or alleles of a pair segregate from
each other during gamete formation such
that the offspring receives one allels from
each parent.
If sex determination in plants is governed
by genetic factors, the offsprings will get
one copy of a genes from each parents.
Sex determination violates the law of
segregation as the human female does not
have any copy of Y chromosomes.
(D) The father determines the sex of the
offspring in human beings. Because the
father can either pass X or Y chromosome
to the offspring.
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1. (c) nm is more than na.
Explanation: When an incident ray of light
enters in a medium from air, it bends towards
the normal.
Focal length of convex lens P, f ' = 0.50 m.
1
P' =
Power of P,
f'
Air
i
X
1
= 2.5 D
0.40
3. (a) Magnified and inverted.
\
sin i > sin r or i > r
As, angle of refraction is smaller than the angle
of incidence. We can say when light travels
from a rarer to a denser medium, it bends
towards the normal at the interface of two.
Related Theory
The basic cause of refraction is the change in the
speed of light, when it is going from one medium to
the other. Angle of bending of a ray depend upon
difference in the speeds of light in the two media.
When light passes from one medium to another
medium, the refractive index of second medium to
the first medium is written as 1n2 and called relative
refractive index.
Caution
Students must remember that the refractive index
is a characteristic property of the medium, whose
value depends only on nature of material of the
medium and the colour or the wavelength of the light.
2. (a) P is equal to 4.5 D.
P" =
Combined power of P and Q lenses
P = P' + P"
P = 2D + 2.5D = 4.5D
na is the refractive index of air.
nm is the refractive index of medium.
According to snell's law of refraction,
nm
sin i
>1
=
na
sin r

1
= 2D
0.5
Focal length of convex lens, Q, f " = 0.40 m,
1
P" =
f"
Y
Medium

P' =
Explanation: When two or more lenses are
placed in contact with each other, the power
of combined or equivalent lens is the sum of
powers of individual lenses.
Explanation: The distance between Q and
screen (As lens is placed at Q) is the approximate
focal length of the convex lens. When the object
is placed beyond double the focal length, a
real, inverted and diminished image is formed.
But when lens is moved towards object and is
placed at double the focal length from screen,
a magnified and inverted image is formed.
4. (c) –45 cm
Explanation: Linear magnification, m = –3
Object distance, u = –15 cm
Image distance, u = ?
−v
m=
u
–3 =
−v
or v = –45 cm
−15
The image is formed at 30 cm infront of the
mirror.
5. (a) Both (A) and (R) are true and (R) is the
correct explanation of (A).
Explanation: ABCD is a rectangular glass slab.
A ray of light travelling in air along PQ falls on
side AB at Q. As the ray is from side AB, from
a rarer medium to a denser medium, it bends
towards the normal.
Light: Reflection and Refraction
23
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M
A
i
Air
A
D
i
r
P
B
C
At
infinity
Q
F
B
r
N
(a)
Glass
slab
(C) (i) Concave mirrors are commonly used
in torches, search light and vehicle
headlights to get powerful parallel
beams of light.
r
R
D
C
e
(ii) Concave mirrors are commonly used as
shaving mirrors to see a larger image of
the face.
Air
X
S
(iii) Concave mirrors are commonly used by
dentist to see large images of teeth of
patients.
I
At R on the boundary of CD of glass slab,
second refraction occurs at R and the ray
emerges as RS. RS is the emergent ray after
suffering two refractions. The final emergent
ray RS is slightly shifted sideways from the
direction of original incident ray by a distance
X called lateral shift or lateral displacement.
(iv) Concave mirror are commonly used in
solar furnaces to concentrate sunlight
to produce heat in them.
Caution

at the sun directly or even into a mirror reflecting
sunlight as it may damage their eyes. They should
6. (b) Both (A) and (R) are true but (R) is not the
not get confused about spherical mirrors. Concave
correct explanation of (A).
Explanation: Convex mirror is a diverging
mirror and for it, magnification (m) is '+' and
less than one, and the image formed is virtual,
erect and shorter than the object.
mirror is a converging mirror whereas, convex mirror
is a diverging mirror.
8. As per Snell's law,
sin i
= Constant (n)
sin r
Related Theory
Since, the angle of incidence is minimum
in block X, the refractive index of block X is
minimum.
The refractive index of a material is given by,

For a concave mirror, m is '+', when image formed
is virtual and m is negative, when image formed is
real, m may be equal to one, less than one or even
greater than one.
Linear magnification produced by a spherical mirror:
m=
nm =
sizeof image( h ')
−v
=
u
sizeof object ( h )
Students must remember that magnification (m)
depends on signs of height of image (h') and height
of object (h).
7. (A) The term used for the distance between the
mirror and the paper, is focal length. Focal
length of a concave mirror is the distance of
Speed of light in air
c
=
Speed of light in medium
v
Since, refractive index of block 'X' is minimum,
speed of light is maximum in block 'X'.
We can also say that the material of block
'X' is least dense, hence the speed of light in
maximum is block 'X'.
The angle of incidence is maximum in block 'Z'.
So, the refractive index of block 'Z' is maximum.
Since, speed of light is minimum in block 'Z'.
Therefore, speed in X > speed in Y > speed in Z.
Caution

While doing this experiment, students should not look
9.
principal focus of the mirror from the pole P
of the mirror. It is represented by the letter
Liquid of
RI 1.5
F.
(B) He should place the object between pole
and principal focus.
24
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Since, the refractive index of the liquid is equal
to that of the material of the lens, the light rays
do not undergo refraction as they pass from the
liquid to the lens and back into the liquid.
Caution

Students must draw the rays through the lens and
further in the liquid in the same direction as the
incident ray without showing any bending at the
interface of the liquid and the lens.
10. (A) The
distance 10 cm signifies the
characteristic of lens P as focal length or
half the radius of curvature.
(B) The inversion of the image will happen at a
distance less than 10 cm.
A thicker lens has a smaller focal length.
The thicker the lens, the more light it
refracts which passes through it and the
focal length becomes smaller.
Using magnification formula
h'
−v
m=
=
h
u
−( −60 )
=
( −20 )
h' = –12 cm
Position of image is 60 cm in front of the
mirror.
Nature of image is real and inverted. Height
of image is 12 cm.
Ray diagram– The object lies between F
and C, image is formed beyond C.
M
E
A
B'
Related Theory

11. (A) (i) Convex mirror has larger field of view
as the image formed is diminished. It
is a diverging mirror and forms small
and erect image of a large number of
objects of the same area of vision.
(ii) The laws of reflection do not change
even when smriti uses a plane mirror,
instead of spherical mirror.
(B) Height of object h = 4 cm
Object distance u = –20 cm
Focal length of a concave mirror,
f = –15 cm
Using mirror formula
1
1 1
= +
v u
f
1
1 1
= −
v
f u
=
1
1
−
−15 ( −20 )
=
1
1
+
−15 20
−4 + 3
=
60
−1
=
60
v = –60 cm
D
P
C
B
The diameter of the reflecting surface of spherical
mirror is called its aperture. The distance between
the focal point and the middle of the lens is called
the focal length. The focal length changes depending
on how thick the lens is.
h'
4
=
F
A'
N
12. (A) Convex mirror can show a full length image
of a tall object in all its positions as the
image formed is virtual, erect and shorter
than the object.
Use of convex mirror: It is used as rear
view mirror and has a wider field of view
as it is curved outwards which enable the
driver to view much larger area.
(B) The entire image of an object can be seen
when the size of the plane mirror is half the
size of the object. In plane mirror, the size of
the image is always equal to the size of the
object.
Characteristics of image formed by a plane
mirror. Image formed by a plane mirror is:
(1) Virtual and erect
(2) Size of the image is equal to that of size
of the object.
(3) Laterally inverted.
(C) (i) The ability of a lens to converge or
diverge light rays depends on the focal
length. A concave lens of very short
focal length causes the light to diverge
more, so it appears that the light is
coming from a point closer to the lens.
The lesser the focal length, the more
is the divergence of the lens. This can
also be seen as the more the power, the
lesser the focal length.
1
P=
f
Light: Reflection and Refraction
25
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(ii) As object moves from infinity towards
optical center of the convex lens, image
is shifted away from its focal length and
towards infinity as the type of lens is a
converging lens.
(D)
Object distance h = –2m
h
2
Apply magnification formula
m=
h'
h
m=
h
2×h
1
=
2
26
m=
−v
u
v= 1 m
Image distance is 1 m.
Applying mirror formula
Let height of object h = h
\ height of image h' =
1
−v
=
2
−2
1
1 1
= +
f
v u
=
1 1
+
1 −2
1 1
= −
1 2
=
2 −1
2
1
=
2
\
f= 2 m
Focal length of the mirror is 2 m.
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4. (d) It is a colloid
1. (c)
Explanation: Rohan lit an incense stick in his
room and after an hour he observed a beam
of sunlight entered his room through a small
gap in the window. He was able to see the
path of the beam as the air present in the
room is colloid.
Sun
Black colour

Explanation: If the Earth did not have an
atmosphere and we looked at the sun, the
sky would have looked black. There is no
atmosphere, so there is no colour of sunlight
would be scattered and the sky would appear
black in the day time as it does at night.

Related Theory
5. (d) (A) is false but (R) is true.
Related Theory
Explanation: When we enter from bright light
to a room with dim light, after sometime, we
may be able to see things in the dim-lit room.
The pupil of an eye acts like a variable aperture
whose size can be varied with the help of iris. In
bright light, the iris contracts the pupil to allow
less light to enter the eye. But in dim light the
iris expands the pupil to allow more light to
enter the eye.
The sky appears dark to passengers flying at very
high altitudes as scattering is not prominent at such
heights.
Caution

Students must remember that scattering of light is
the phenomenon of change in direction of light on
striking an obstacle like an atom, molecule, dust
particle etc.
2. (c) bifocal
Explanation: A person's near point is at 45
cm and far point is at 2 m, it means that a
person is suffering from both hypermetropia
and myopia. For correction of both the defects,
the person would require bifocal lenses. Bifocal
lenses consist of both concave and convex lens.
The upper portion consists of a concave lens
which facilitates distant vision. The lower part
is a convex lens which facilitates near vision.
3. (d) Violet
Explanation: Violet colour of the white light
deviates the maximum during dispersion
of light by prism, as it has least wavelength
among all colours. White colour is dispersed
into its seven colour components by a prism.
Different colours of light bend through different
angles with respect to the incident ray as they
pass through a prism.
The phenomenon of Scattering of a beam of light by
the colloidal particles gives rise to Tyndall effect. The
colour of the scattered light depends on the size of
the scattering particles.
6. (a) Both (A) and (R) are true and (R) is the
correct explanation of (A).
Explanation: The least distance of distinct
vision of normal eye is 25 cm. At distance less
than 25 cm, we will see blurred image and
feel strain in the eyes and maximum power of
accomodation is 4D.
Related Theory

The range of a vision of a person is the distance
between near point and far point of his eyes. For a
normal eye, the far point lies at infinity while near
point lies at 25 cm. Therefore, for a person with
normal vision, the range of vision is infinite.
7. (A) The stars flicker due to atmospheric
refraction. When the amount of light
entering our eyes increases, the stars
look bright and when the amount of light
reaching our eyes decreases, the stars
look dim. Thus, the stars go on becoming
The Human Eye and the Colourful World
27
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bright and dim again and again. This is
called twinkling of stars at night. On 'no
moon night' the flickering or twinkling of
stars is clearly seen as there is no light
of the moon.
(B) (i) The length of the day increased by four
minutes on account of atmospheric
refraction. The sun is visible to us about
2 minutes before the actual sunrise
and about 2 minutes after the actual
sunset.
(ii) If the Earth had no atmosphere, this
effect as increasing the length of the
day would not occur.
(C) White colour of the clouds is not based
on atmospheric refraction. The clouds are
at much lower height. They are seen due
to scattering of light from lower parts of
Earth's atmosphere which contains dust
particles, water droplets etc. As the size of
the scattering particles is very large, all the
longer wavelength are scattered equally.
So, all equally scattered colours merge to
give us the sensation of white. Thus, clouds
generally appear white. All the other three
phenomena are based on atmospheric
refraction.
(ii) The curvature of eye lens can be
modified to some extent by ciliary
muscles. The change in the curvature of
the eye lens can thus change its focal
length. When the muscles are relaxed,
the lens becomes thin. Thus, its focal
length increases.
(B) When human eye changes its focus from
a distant object to the object closer to the
eye, various events take place in the eye.
The sequence of events are:
Ciliary muscles contract < Curvature of eye
lens increases > Focal length of eye lens
decreases.
When we are looking at objects closer
to the eye, the ciliary muscles contract.
This increases the curvature of the eye
lens. The eye lens then becomes thicker.
Consequently, the focal length of the eye
lens decreases which enables us to see the
nearby objects clearly.
11. (A) The distance between eye lens and retina
is the image distance inside the eye. The
image distance is fixed and it cannot
be changed at all. Therefore, when we
increase or decrease the distance of an
object from the eye, there is no change in
the image distance inside the eye.
8. (A) The phenomenon involved is Tyndall's
effect.
(B) (i) A glass slab has two parallel faces.
After refraction at two parallel faces of
a glass slab, a ray of light emerges in
a direction parallel to the direction of
incidence of white light. As rays of all
colours emerge in the same direction
i.e., the direction of the incidence of
white light, there is no dispersion.
However, there is lateral displacement.
(B) Nanda removed all the dust particles
from the air in the room by passing the
air through a very efficient filter. Filtering
the air removes the suspended dust
particles thus, preventing the scattering of
light which make the rays visible.
9. (A) Mars's atmosphere is composed mainly
of carbon dioxide, nitrogen, argon and
negligible amounts of oxygen, water
vapour and methane. There is no enough
water vapour in the atmosphere to cause
scattering of light.
(B)
Sunlight
Red
(ii) When a monochromatic light having
only one wavelength, passes through
a prism, it does not show dispersion
but only show deviation as prism
splits light because different colours
of light get refracted by different
amounts. Different colours of light
are characterised by their different
wavelength or frequencies. All these
colours travel in air with the same
speed, but their speeds in any other
refracting medium are different.
Violet
Related Theory

Sodium lamp gives monochromatic light of yellow
colour only. Light given by a mercury lamp is
10. (A) (i) The amount of light entering the eye
would be directly affected if the iris
does not function properly.
28
polychromatic, consisting of many colours or many
wavelengths. The sunlight is also polychromatic
consisting of all the seven colours.
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12. (A) If the eyeball of a person has become
slightly larger, the person should wear
concave lens to correct the defect in the
vision caused by this change in the size of
the eyeball.
(B) If a parallel white light beam passes
through a convex lens, the violet light will
converge at a point closest to the lens. This
happens because the violet light will bend
the most after refraction. Glass has the
highest refractive index for violet coloured
light.
(C) (i) A person who needs a lens of power
–5.0 D for correction of his vision, is
suffering from myopia.
(ii) The focal length (f) of corrective lens = ?
P = –5.0 D
P=
1
f
f=
1
= −0.2m
−5.0
f = –0.2m or –20 cm
(iii)
O
O
Myopic eye
The Human Eye and the Colourful World
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1. (c) Higher resistance, lower melting point.
Resistance of 2nd bulb
Explanation: A fuse wire should have high
resistance and low melting point, So that it
prevents current higher than the required value
to pass. Low melting point will help in breaking
the circuit when high current passes through
it as a lot of heat is generated so I would
recommend to have a fuse of high resistance
with low melting point.
2. (c) The voltage reading on V1 will be the same
as the reading on V2.
Explanation: In the given figure, voltmeter 1
(V1), voltmeter 2 (V2), bulb 1 and bulb 2 are
connected in parallel. In parallel circuit, the
potential difference across the resistance
(bulbs) remains the same, according to ohm's
law.
\ V = V1 = V 2
R2 =
Ratio between R2 and R1
R2
R1

When a number of resistances are connected in
parallel, the reciprocal of the equivalent resistance is
equal to the sum of the reciprocals of the individual
resistances and is smaller than any individual
resistance, connecting a number of resistors in
parallel is like providing an equal number of paths
for the electron flow which results in a decrease in
resistance. The main current divide and a different
current flows through each resistor.
4. (d) S
Explanation: The slope
represents
R = ρ
3. (b) 1 : 2
Explanation:
R=
30
R1 =
I
. Since, the graph shown above
R
l
, the resistivity of wire S will be the
A
5. (a) Both (A) and (R) are true and (R) is the
correct explanation of (A).
Explanation: The resistance of a conductor
is inversely proportional to its area of crosssection.
Rµ
l
A
Thus, a thick wire has less resistance and a thin
wire has more resistance. Therefore, current
will flow more easily through a thick wire.
6. (b) Both (A) and (R) are true but (R) is not the
V2
P
Resistance of 1st bulb
of the graph
highest as the length and diameter of two
wires is same.
Whereas in series combination, the equivalent
resistance is greater than the greatest resistance in
combination.
Students should remember that to obtain minimum
resistance and maximum resistances, resistors should
be connected in parallel and series combination
respectively.
I
V
shows the graph marked S has lesser slope, it
represents higher resistance. Using the relation,
Caution

50
= 220 × 220 ×
=2
25
220 × 220
R2 = 2R1
So, R1 : R2 = 1 : 2
Related Theory

220 × 220
25
220 × 220
50
correct explanation of (A).
Explanation: If an electric bulb is rated
100W-200V, it means an electrical energy of
100J is converted into heat and light by the
bulb in 1 second when operated at 200 V.
1W = 1 Js–1
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
Related Theory
An electric bulb is used to provide light by heating
its filament. The filament is made of a strong metal
Tungsten with high melting point.
7. (A) Meter 2 is the ammeter shown in the circuit
(B)
given. The meter 2 is connected in series
with the unknown resistor through which
the current needs to be measured.
A
A
OR
The extra resistor is connected in parallel
in the circuit. Potential difference for all the
resistors in a parallel circuit is the same and
is equal to the applied potential difference.
The current in a parallel circuit divides
in the inverse ratio of the resistances i.e.,
the current decreases as the resistance
increases and vice-versa.
(B) The electrical resistance of the two wires
can be the same if the area of cross-section
of the two wires is different. It means the
thickness of the two wires is not the same.
11. (A) All the resistors are arranged in parallel.
V
V
(C) Potential difference vs current graphs
(i) as expected by Amita
(ii) as based on actual observation she
would make
(ii)
Potential
difference
(i)
A number of resistors are said to be
connected in parallel if one end of each
resistor is connected to one point and the
other end is connected to another point.
(B) Let resistance of E = R1
Potential difference,
V = 6V, I = 0.3 A
Applying Ohm's law,
V = IR
V
R1 =
I
=
Current
8. (A) The resistance of the bulb filament
increases as the temperature increases
from t = 0 to t = t, as resistance is directly
proportional to the temperature.
(B) When the bulb is glowing at its full
brightness then
current (I) = 0.5 A
Potential difference,
(V) = 200V
P =V×I
P = 200 × 0.5 = 100W
The power consumed by the bulb when it is
glowing at its fall brightness is 100W.
6
= 20 W
0.3
(C) Current through resistance of E (IE) = 0.3A
Current through resistance of F (IF) = ?
Resistance (R) of F = 10 W
Potential difference (V) = 6V
Current through resistance of F
V
IF =
R
=
6
= 0.6 A
10
Resistance (R) of G = 5 W
Potential difference (V) = 6V
Current through resistance of G,
V
IG =
R
6
= 1.2A
5
9. (A) When an electrician touches the metallic
=
10. (A)
Total current through circuit,
I = IE + I F + I G
= 0.3 + 0.6 + 1.2
= 2.1 A
The total current 2.1 A is flowing in the
circuit.
touch screw, the lamp of the tester glows
but he does not get an electric shock as a
very low current flows through the tester.
(B) The resistor of the tester prevents the shock
when the metallic touch screw is touched.
A
12. (A) (i) All the LEDs are connected in series in
Extra resistor
Circuit
the circuit diagram.
(ii) If the LED marked 'LED 2' stops working,
all the other LEDs in the circuit will also
stop working as current cannot flow
across it.
Electricity
31
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(iii) 3V is printed on a label for 1 LED. He
connected all the lights to a 240 V
mains supply for the LEDs to work at
their power rating.
240
So, he would need
= 80 LEDs.
3
(iv) If Suresh connects all 100 LEDs, in a
parallel combination to the 240 V mains
supply, all will get damaged as each LED
will have a potential difference of 240 V.
As we know, the potential difference
for all the resistors in a parallel circuit
is same and is equal to the applied
potential difference. As all the LEDs are
getting the same potential difference
and current, so all of them will get
damaged.
(v) Power of each LED, (P) = 0.2W
Potential difference, for each LED (V) = 3V
P = VI
P
0.2
I=
=
= 0.067 A
V
3
According to the rating given in the
label, each LED is expected to draw
0.067 A current.
(B) The higher the resistance of a conductor,
the more heat will be generated as current
passes through it. The amount of heat (H)
produced in the wire is directly proportional
to the square of the current (I).
i.e.,
H µ I2
P = I2R or P =
V2
R
(i) If all the resistors are connected in series
RS = R1 + R2 + R3
= 10 + 10 + 10 = 30 W
(ii) If all the resistors are connected in
parallel,
1
1
1
1
+
+
=
RP
R1 R 2 R 3
1
1
1
+
+
=
10 10 10
3
=
10
32
RP =
10
W
3
(iii) If first two resistors are in series and the
series resistor in parallel with the third
resistor,
RS = (10 + 10)
= 20 W
Req =
1
1
+
20 10
1+2
=
20
=
3
20
20
W
3
Req =
(iv) If first two resistors are in parallel and
the parallel combination in series with
the third resistor,
1
1
1
=
+
RP
R1 R 2
=
1
1
+
10 10
=
2
10
1
=
5
RP = 5 W
Req = RP + R3
= 5 + 10 = 15 W
So, he should connect first two resistors
is parallel and the parallel combination
in series with the third resistor to get
15 W resistance
10 W
12 V
10 W
10 W
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1. (c) It will help to draw any current left out
in the body of appliances as soon as it is
connected to socket.
Explanation: Among the three pins namely
like, neutral and Earth. The earth pin is made
longer and thicker than the other two pins, so
that when we insert the plug into the socket,
the earth pin comes into contact with the
power supply before the other two pins so that
any unwanted changes which may be in the
circuit will be removed or grounded before the
other two pins go inside the terminals.

Related Theory

Caution

2. (a)
I
I
N
S
Explanation: In figures (a) and (c), current flows
in anticlockwise direction and in figures (b) and
(d), the poles are not shown correctly. If the
current is flowing in anti-clockwise direction,
then the face of the loop shows North pole,
which is seen in figure (a). So, figure (a) is the
correct option. On the other hand, if the current
is flowing in clockwise direction, then the face
of the loop shows South pole.
3. (d) North Poles: Q and S; South Poles: P and R
Explanation: The field lines emerge from
the north pole and merge at south pole. The
magnetic field lines emerge from the poles Q
and S so they are north poles. As in the figure,
the magnetic field lines merge at P and R
poles, so they are south poles. The direction of
the magnetic field is taken to be the direction
in which a pole of the compass needle moves
inside it.
Students must remember that the stronger the
magnetic field, closer are the field lines which are
seen at the poles of a magnet.
4. (d) Its magnitude was decreased.
Explanation: The strength of the magnetic
field produced by a straight conductor
depends on the current passing through the
conductor and is directly proportional to
the current. The magnetic field lines have
decreased as the magnitude of the current
is decreased.
Related Theory
Red insulation wire is called live wire or positive.
Black insulation wire is called neutral wire or
negative. Green insulation wire is earth wire which
is usually connected to a metal plate deep in the
Earth near the house. The metallic body is connected
to the earth wire, which provides a low-resistance
conducting path for the current.
The magnetic field lines are closed curves. The
relative strength of the magnetic field is shown by
the degree of relative strength of the magnetic field.
Related Theory

To find the direction of magnetic field due to a
current carrying conductor, Right Hand Thumb Rule
is used. Imagine the straight conductor in your right
hand such that the thumb points in the direction of
current. The direction of curling of fingers of the right
hand gives the direction of magnetic field lines.
Caution

Students should not get confused with Right Hand
Thumb Rule and Fleming's Left Hand Rule. In
the Right Hand Thumb Rule which is also called
Maxwell's Right Hand Thumb Rule, gives the direction
of magnetic field whereas the direction of motion of
conductor is given by Fleming's Left Hand Rule.
5. (b) Both (A) and (R) are true but (R) is not the
correct explanation of (A).
Explanation: The direction of force acting
on a current carrying conductor is given
by Fleming's Left Hand Rule. When current
carrying conductor is placed parallel to the
magnetic field, it does not experience any force.
6. (a) Both (A) and (R) are true and (R) is the
correct explanation of (A).
Explanation: In this experiment, if a compass
needle is put near a wire carrying electricity,
Magnetic Effects of Electric Current
33
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the needle is deflected because of the impact
of magnetism caused by the electric current
produced in the wire. It demonstrates the
connection between magnetism and electricity.
As a result, both assertion and reason are
right, and reason is the proper explanation for
assertion.
(B) Oersted had imagined the magnetic field
to be a straight line along the direction
of the wire. Based on the knowledge of
magnetic field around a wire is due to the
current that is perpendicular to the wire.
The needle shown in the figure is already
pointing in a direction perpendicular to the
wire, it will not get deflected.
7. (A)
N
10. (A)
B
A
S
K
(B) The field lines on the left side of X are
crowded as compared to the right side
indicating, a stronger field.
(C) (i) The wire experiences a force towards
the left.
(ii) Fleming's left hand rule. According to
this rule, if we stretch the thumb, the
forefinger and the middle finger of the
left hand, such that they are mutually
perpendicular to each other and the
forefinger points in the direction of
magnetic field and the second finger in
the direction of current, then the thumb
will point in the direction of motion or
the force acting on the conductor.
(B) As we move away from the centre of
the circular loop, the concentric circles
representing the magnetic field around it
would become larger and larger. By the
time, we reach at the centre of the circular
loop, the arcs of these big circles would
appear as straight lines. Every point on the
wire carrying current would give rise to
the magnetic field appearing as straight
lines at the centre of the loop. By applying
the right hand rule, it is easy to check that
every reaction of the wire contributes
to the magnetic field lines in the same
direction within the loop.
(C) The magnetic field produced by a currentcarrying wire at a given point depends
directly on the current passing through it,
so if there is circular coil having 'n' turns,
the field produced is 'n' times as large as
that produced by a single turn. The reason
is that current in each circular turn has the
same direction and the field due to each
turn then just adds up.
8. If magnet X is moved towards magnet Y, they
will repel each other. The right side of magnet
X and the left end of magnet Y are both north
poles as field lines are shown emerging from
there. The left side of magnet X and the right
end of magnet Y are both south poles as field
lines are shown merging there. This also shows
that magnetic field lines are closed curves. The
strength of the magnetic field is also shown by
the degree of closeness of the field lines, which
is at poles of a magnet.
11. (A) By right hand thumb rule, the magnetic
9. (A)
Bulb
34
N
(when current
is switched on)
S
(when current
is switched on)
field in the vicinity of wire is downward
and perpendicular to plane of paper. We
know, the conventional direction of electric
current is opposite to the direction of
motion of electron. By applying Fleming's
Left-Hand Rule, the force on electron is
a way from wire in the plane of paper,
therefore, the electron will be deflected
downward away from wire in the plane of
paper.
(B) The direction of magnetic field is from
north pole to the south pole as shown in
the figure. On applying Fleming's left hand
rule, the wire tends to move perpendicular
to plane of paper upward.
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(C) Diagram (i): Direct Current (DC)
Diagram (ii): Alternate Current (AC)
An advantage of AC over DC is that electric
power can be transmitted over long
distances without much loss of energy.
12. (A) (i) When the switch is closed in both
Madhu's and Rahul's circuit, the bulb
will glow. When the circuits are closed,
the current will flow in both the cases
and the bulb glows.
(ii) It will be safe to change the bulb in
Rahul's circuit. In this circuit, the bulb
point is no longer connected to the live
wire when the switch is in the open
position. It will be dangerous to change
the bulb in Madhu's circuit, as the bulb
point is still connected to live wire and
can give an electric shock even when
the switch is in the open position.
(B) (i) In case of overloading, the fuse will not
protect the electric oven from damage
because the fuse blows only after
current has passed through the oven
and damaged it. The Joule heating
that takes place in the fuse melts it to
break the electric circuit. Overloading
can occur due to an accidental hike in
the supply voltage. It is also caused by
connecting too many appliances to a
single socket.
(ii) If the oven has a rating of 13 A, the
minimum rating of the fuse should be a
little above 13 A. It could be 14 A or 15 A.
Magnetic Effects of Electric Current
35
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1. (b) Unidirectional and cyclic
Explanation: In a food chain, the energy moves
progressively through the various trophic levels
and is no longer available to the organisms of
previous trophic level. The energy captured
by the autotrophs does not revert back to the
solar input. So, we can say that the energy
flow in food chains is said to be unidirectional.
Flow of nutrients is cyclic as the decomposers
consume the dead remains of other organisms
into simpler inorganic substances that go into
the soil and are used up once more by the
plants.
10% energy
Plants
Inorganic matter
3. (b) Herbivores
Explanation: Plant matter comprises producers
as they are the autotrops and they synthesize
the food by the process of photosynthesis for
example, green plants and certain blue green
algae. Herbivores are primary consumers
and heterotrophs which consume the food
produced by plants directly.
Carnivores are flesh eaters and consume
primary consumers and becomes secondary
consumers. Decomposers like fungi and
bacteria help in decomposing the dead bodies
of plants and animals.
10% energy
Rabbit
Hawk
Decomposers
Related Theory
Related Theory

but faster than paper cups. So, Alisha would
see that after a few days, fruit peels have
been degraded fully and paper cups are in the
process of degradation.

Pesticides used for crop protection when washed
away go down into the soil. These pesticides are
absorbed by the plants which are producers. On
consumptions of these plants, the pesticides enter
the food chain and these pesticides are nonbiodegradable, get accumulated progressively and
enter our body. This is called biological magnification
which is also unidirectional.
4. (d) 10 : 1
Caution

Students often get confused between unidirectional
and bidirectional flow. Unidirectional means only in
one direction which is the case of flow of energy.
Bidirectional means cyclic i.e., reverts to the original
position. Flow of matter or nutrients is cyclic.
2. (b) Fruit peels
Explanation: Glass bowls and rubber slippers
are non-biodegradable and they cannot be
degraded naturally in our environment but
persists in the environment for a very long
time. Paper cups are of plant origin and are
degraded naturally, that's why they are said
to be biodegradable materials. Fruit peels are
also of plant origin and are degraded naturally
36
Decomposers help in cleaning the environment. The
various nutrients which are taken by plants from the
soil, air and water are returned to the soil, air and
water.
Explanation: Producers are autotrophs that
synthesize their own food whereas, primary
consumers are herbivores which depend on
producers for their food. The green plants
capture 1% of the energy from the sunlight
that falls on their leaves and convert it into
the food energy. When green plants are
eaten by primary consumers, a great deal
of energy is lost as heat to the environment,
some amount goes into digestion, and the
rest goes towards growth and reproduction.
An average of 10% of the food eaten is turned
into its own body and made available to the
next level as per ten percent law. Therefore,
we can say that if producers have 10 KJ
of energy, it will be passed on to primary
consumers as only 10%. Therefore, the ratio
of average amount of energy absorbed by
producers to the average amount of energy
absorbed by the primary consumers is 10%.
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5. (b) Both (A) and (R) are true, but (R) is not the
correct explanation of (A).
Explanation: The quantum of available energy
in a food chain successively gets decreased
at each trophic level due to 10% law. Loss of
energy at successive trophic level restricts the
size of food chain in an ecosystem to maximum
of 4 to 5 steps. The number of producers are
always maximum in any given food chain. The
number of individuals in subsequent trophic
levels goes on decreasing progressively.
6. (c) (A) is true but (R) is false
Explanation: Use of fertilizers in the fields
contribute to phosphate and nitrate nutrient
accumulation. Eutrophication is the process in
which a water body becomes enriched with
nutrients leading to overabundance of algae
and plants which results in-algal bloom and low
oxygen water that can kill fish and reduce fish
habitats. Oxygen depletion in water resulting
in the death of fish is due to eutrophication but
biological magnification is the accumulation of
a chemical by an organism from water and
food exposure in the tissues of organisms at
successively higher levels in food chain.
7. (A) Ozone is being continually destroyed due
to extreme low temperature. However,
ozone formation is also a continuous
process. But there is a depletion in the
ozone layer because the rate of destruction
is higher than the rate of formation.
(B) Depletion of ozone layer allows harmful UV
radiations to enter the Earth's atmosphere
and cause skin cancer, cataract in eyes and
damage to immune system and hence,
lowering the body's resistance to diseases.
UV radiations also results in the decline in
the rate of photosynthesis in plants.
(C) Ozone layer is present in the upper part of
atmosphere, called stratosphere.
Formation of ozone layer:
The higher energy UV radiations in the
higher levels of atmosphere split a part
some molecular oxygen (O2) into free
oxygen (O) atoms. These atoms then
combine with the molecular oxygen to
form ozone.
UV radiations
from sun
O + [O] Oxygen atom
O3 2
O2 + O ® O3
Ozone layer in the stratosphere acts as a
protective shield to protect all types of life
from the harmful effects of UV radiations.
Caution

Students must remember O3 is ozone, O2 is a
molecule of oxygen and [O] is an atom of oxygen.
8. (A) Plastic bottle and metal can are nonbiodegradable substances whereas bone
and paper sheet are biodegradable.
Biodegradable
substances
are
decomposed into simple substances by
the action of bacteria and fungi. The
least time will be taken by paper sheet to
decompose and the maximum time will
be taken to breakdown. Hence, the four
objects according to the time, they take to
get biodgraded is:
Paper sheet < Bone < Metal can < Plastic can
(B) Lions are generally found at tertiary or
quaternary levels in a food chain and
energy available after that trophic level is
not sufficient for sustenance. That is the
reason that lions do not have any natural
predator.
9. (A) Indiscriminate use of pesticides results in
the degradation of the environment. For
example, DDT is an organic pesticide which
is used to kill pests in crop field. When DDT
it used in large quantity, it can be passed
along the food chain from crops to a
human being or other animals and birds
and can harm them.
(B) Decomposers decompose complex organic
substances to inorganic substances
that enter into the soil and are used up
again by the plants. In case of absence of
decomposers, breakdown of complex or
dead bodies of organisms won't happen,
it means recycling of material, clearing
of the area in the biosphere will not take
place.
10. (A) The green plants in a terrestrial ecosystem
capture about 10% of the energy of
sunlight that falls on their leaves and
convert it into food energy only 10% of the
amount of organic matter that is present
at each step and available at any trophic
level of food chain reaches the next level of
consumers. When green plants are eaten
by primary consumers, energy is lost as:
Heat to the environment, Some amount
goes into digestion,
Some is used in doing work, the rest goes
towards growth and reproduction.
Our Environment
37
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(B) A lot of harmful chemicals eaten our
body through different sources like food.
Since human beings are at the top of the
food chain, maximum concentration of
such chemicals is found in human beings.
This phenomenon is known as biological
magnification. Harmful chemicals are
not degradable, these get accumulated
progressively at each trophic level. As
human beings occupy the top most
level in any food chain, the maximum
concentration of these chemicals get
accumulated in our bodies.
Caution

Biodegradable substances can be harmful if there
volume is too large. Their accumulation becomes a
breeding ground for germs.
12. (A) We know that vegetarians obtain food
directly from plants while non-vegetarians
Get the food from animals. Vegetarians eat
only plant products and they get 10% of
energy from the producers whereas nonvegetarians eat animal products along
with the plant products, so they get 10%
of energy from the producer. For example:
If producers have 1000J of energy. As per
10% law of energy, vegetarians would get
100J of energy whereas non-vegelatrians
would obtain only 10J of energy.
Related Theory

Our food grains such as wheat and rice, vegetables
and fruits and even meat contain varying amounts
of pesticide residues due to spraying of these nonbiodegradable chemicals. They cannot always
be removed by washing or other means. If we
consume food having such chemicals continuously,
the concentration of such substances increases in
our bodies and affect our health and also causes
diseases.
11. (A) We generate a lot of waste now a days due
to:
(1) Use of more and more disposable
substances.
(2) Changes in our attitude
(3) Improvements in our lifestyle due to
advanced technology.
(B) The factors that have contributed to the
deterioration of our environment are:
(1) Human population
(2) Advancement in technology
(C) A lot of waste is produced naturally
as well as by human beings. Biodegradable waste can be broken down
into harmless substances by the action of
microorganisms like bacteria and fungi, for
example, Vegetable and Fruit peels, used
tea leaves, egg shells etc. They do not
pollute the environment.
Non-Biodegradable waste cannot be acted
upon by microorganisms. They persist
in the environment for a long time and
pollute the atmosphere.
For example: Glass articles, plastic bags
and bottles.
38
10%
→ Herbivores 100J
Plants 1000J 
10% law
→ Herbivores 100J
Plants 1000J 
10% law

→ Carnivores 10J
(B)
Producer Herbivores Carnivores Decomposers
Tree
Grass
hopper
Lion
Bacteria
Grass
Rabbit
Eagle
Fungi
Deer
Vulture
Three step food chain:
Frog
(1) Grass ® Grass hopper ® Frog
(2) Grass ® Rabbit ® Lion
(3) Tree ® Deer ® Lion
(4) Tree ® Rabbit ® Vulture/Eagle
(B) (1) A food chain helps in understanding the
food relationship and interactions
among different organisms in an
ecosystem.
(2) It also helps to understand the
movement of toxic substances in
an ecosystem and the problem of their
biological magnification.
(3) It also helps to understand the flow
of energy as unidirectional because
food chain is always straight and
proceeds in a progressive straight line.
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