Modern Concept Science and Environment – 8 193
Properties of bases or alkalis
a) Physical properties of bases or alkalis
i) Bases are soapy in touch and bitter in taste.
ii) Bases turn red litmus paper into blue, methyl orange into yellow and
phenolphthalein into pink.
iii) Strong bases or alkalis like NaOH, KOH , etc. dissolve in oil and grease.
iv) Strong bases or alkalis burn our skin.
b) Chemical properties of bases or alkalis
i) Bases or alkalis react with acids to form salt and water.
Base + Acid Salt + Water
2KOH + H2SO4 K2SO4 + H2O
NaOH + HCl NaCl + H2O
Mg(OH)2 + H2SO4 MgSO4 + 2H2O
ii) Bases or alkalis react with carbon dioxide and form corresponding carbonate and
water.
Alkali + Carbon dioxide Carbonate + Water
2NaOH + CO2 Na2CO3 + H2O
2KOH + CO2 K2CO3 + H2O
Ca(OH)2 + CO2 CaCO3 + H2O
iii) Alkalis react with ammonium salts and form salt, water and ammonia gas.
Alkali + Ammonium salt Salt + Water + Ammonia
NaOH + NH4Cl NaCl + H2O + NH3↑
Ca(OH)2 + 2NH4Cl CaCl2 + 2H2O + 2NH3↑
Mg(OH)2 + (NH4)2CO3 MgCO3 + 2H2O + 2NH3↑
Uses of Bases
a) Sodium hydroxide (NaOH) is used to make soaps, detergents, papers, etc. and
purification of petroleum products.
b) Calcium hydroxide [Ca(OH)2] or slaked lime is used for making mortar and bleaching
powder, to reduce hardness of water and to neutralize acidity of soil.
c) Potassium hydroxide (KOH) is used in alkaline batteries and to make soft soap.
d) Aluminium hydroxide [Al(OH)3] and magnesium hydroxide [Mg(OH)2] are used to
reduce hyperacidity of stomach.
e) Ammonium hydroxide (NH4OH) is used to remove grease and stains from clothes and
to make fertilizers.
f) Calcium oxide (CaO) or quick lime is used for softening hard water, purification of
sugar and production of cement.
194 Acid, Base and Salt
14.6 Salt
Salt is a chemical substance which is formed by partial or complete replacement of hydrogen
ion of an acid molecule by a metal or ammonium radical. In general, salts are neutral
compounds but some may be acidic or basic in nature. The process by which acid and base
react together to give salt and water is called neutralization reaction. In this reaction, H+ -ions
of the acid are completely replaced by a metal.
Acid + Base Salt + Water
HCl + NaOH NaCl + H2O
H2SO4 + 2KOH K2SO4 + 2H2O
In acid-base reaction, there may be a complete or partial replacement of hydrogen ion(s) of an
acid by a metal or ammonium radical. For example,
NaOH + H2SO4 NaHSO4 + H2O
In this example, only one hydrogen ion (H+ ) from sulphuric acid is replaced by sodium ion.
2NaOH + H2SO4 Na2SO4 + 2H2O
Here, both the hydrogen ions (H+) from sulphuric acid are replaced by sodium ion.
Properties of salts
a) Generally, salts are neutral but some may be acidic or basic in nature.
b) Most of the salts are water soluble but chloride salts of silver and lead and sulphate salts
of lead and barium are insoluble.
c) Salts of metals like Na, K, Mg, Ca, Al and Ba are white or colourless whereas salts of Cu,
Co, Mn, Ni, Fe and Cr are colourful.
d) Some salts are salty in taste but most salts are bitter.
e) Salts conduct electricity in molten or solution state.
f) Some salts are amorphous whereas some are crystalline.
Uses of salts
a) Table salt (NaCl) is used in our foods and also as a preservative.
b) Sodium carbonate is used for manufacture of soaps, detergents and glasses. It is also
used to reduce hardness of water.
c) Calcium sulphate is used in medical field for plastering of fractured bones and for
mixing in cement.
d) Sodium bicarbonate is used as baking powder, for reducing hyperacidity and in fire
extinguisher.
e) Copper sulphate is used for making fungicides and in copper plating.
f) Ammonium chloride is used in dry cells as an electrolyte.
g) Ammonium sulphate is used as chemical fertilizer.
h) Ferrous sulphate is used as a medicine to treat iron deficiency in anaemia patients.
Modern Concept Science and Environment – 8 195
14.7 Indicators
Indicators are those chemical substances which are used to indicate whether the given
substance is acidic or basic or neutral in nature. Indicators, when treated with acidic or basic
solution, change their own colour. They remain chemically unchanged but indicate the end
point of the reaction. Litmus paper, methyl orange and phenolphthalein are some common
indicators. They are obtained from different parts of plants like roots, flowers, leaves, etc.
These are collected, crushed and mixed with organic solvent to obtain indicators. The colour
change of different indicators with acidic, basic and salt solution is given in the table:
S.N. Indicators Colour in acid Colour in basic Colour in neutral salt
1) Red litmus paper solution solution solution
No change in colour Changes into blue No change in colour
2) Blue litmus paper Changes into red No change in colour No change in colour
3) Methyl orange Changes into red Changes into yellow No change in colour
4) Phenolphthalein No change in colour Changes into pink No change in colour
5) Red cabbage juice Changes into red Changes into green Changes into rose red
14.8 Universal Indicator
A universal indicator is a special kind of indicator which is used to
measure the strength of acidity or alkalinity. It is prepared by mixing
several ordinary indicators of different colour. A universal indicator
changes its colour when kept in an acidic, basic or neutral solution. The
change in colour is matched with pH chart to determine the strength of
the given solution.
Differences between ordinary indicators and universal indicators
SN Ordinary indicator SN Universal indicator
1 Ordinary indicators indicate only 1 Universal indicators indicate whether
whether the substance is acid, base or the substance is acid, base or salt along
salt. with their strength.
2 They are obtained from the parts of 2 They are obtained by mixing different
plants like leaves, flowers, roots, etc. types of ordinary indicators.
14.9 pH and pH Scale
The measure of hydrogen ion concentration present in a Memory Tips
solution is called pH (potential of Hydrogen). In an acidic The pH concept was
solution, there is high concentration of hydrogen ions and introduced by the Danish bio-
in basic solution, there is less concentration of hydrogen chemist, Soren Peter Lauritz
Sorensen in 1909 AD.
ions. It is measured by using pH paper and pH meter.
196 Acid, Base and Salt
The standard scale which is used to measure the strength of acidic and basic solutions is called
pH scale. This scale shows the degree of acidity and alkalinity. pH scale consists of numbers
from 1 to 14 with their corresponding colours on the scale.
←Acidity increases Neutral Alkalinity increases→
7 8 9 10 11 12 13 14
pH 1 23 4 56 Greenish blue Blue Deep blue
Red Light green Green
Rose Yellow
The process of identification of acid, base or a neutral Memory Tips
substance with the help of pH scale is given below: Human blood has pH between
First of all, pH paper is dipped into the given solution and 7.35 to 7.45. It is slightly alkaline in
the change in colour is observed. Then the colour in the pH nature.
paper is matched with the pH scale to know the value. The
pH value below 7, i.e. 1 to 6 represents acidity and above 7, i.e. 8 to 14 represents alkalinity
whereas pH value 7 represents neutrality. The substance having pH value 1 is the strongest
acid and that having pH value 14 is the strongest alkali.
Increasing Acidity (Neutral) Increasing Alkalinity
pH scale
14.10 pH Meter
pH meter is a scientific instrument which is used to measure the pH pH meter
value of a given solution directly in a number. It has a box with different
readings and a rod. The rod is dipped into a solution whose pH value is to pH
be measured. The rod has a connection with box and it directly indicates 1
the pH value with the help of a pointer or by displaying a value on its 1.2
screen. 2.5
3
pH value of some substances 6
7
S. N. Compounds 7.3
1. Hydrochloric acid (HCl) 8.5
2. Sulphuric acid (H2SO4)
3. Lemon juice
4. Apple, vinegar, carbonic acid
5. Butter
6. Water, salt solution, sugar solution, ethanol
7. Human blood
8. Baking soda
Modern Concept Science and Environment – 8 197
9. Ammonium hydroxide (NH4OH) 10
10. Washing soda (Na2CO3) 11.5
11. Sodium hydroxide (NaOH) 13
ACTIVITY 1
OBJECTIVE : To identify the given solutions as an acidic, a basic and a salt solution.
1. Take three different test tubes and mark A, B and C.
2. Keep table salt solution in one test tube, lemon juice in another test tube and a solution of ash in
another test tube.
3. Take blue and red litmus papers and dip one in each of the three solutions.
4. What effect do you observe? Fill the table shown below.
Substances With red litmus paper With blue litmus paper
Salt solution ? ?
Lemon solution ? ?
Ash solution ? ?
ANSWER WRITING SKILL
1. Define acid, base and salt.
Ans: Acids are those chemical substances which give hydrogen ions when dissolved in water. Metallic
oxides and hydroxides are called bases. Similarly, salt is a chemical substance which is formed by a
partial or complete replacement of hydrogen ion of an acid molecule by a metal or ammonium radical.
2. Write down any three examples each of acid and base which are used in a laboratory.
Ans: Three acids used in a laboratory are hydrochloric acid (HCl), sulphuric acid (H2SO4) and nitric
acid (HNO3). Similarly the three bases used in a laboratory are sodium hydroxide (NaOH), calcium
hydroxide [Ca(OH)2] and ammonium hydroxide (NH4OH).
3. Write any two differences between acid and base.
Ans: Differences between acid and base are:
S.N. Acid S.N. Base
1 Acids are those chemical substances 1 Metallic oxides and hydroxides are
which give hydrogen ions when called bases.
dissolved in water.
2 Acids have pH value less than seven. 2 Bases have pH value more than seven.
4. Why are citrus and amala sour in taste?
Ans: Citrus contains citric acid and amala contains ascorbic acid. So, they have a sour taste.
5. We should handle acids very carefully. Why?
Ans: Strong acids are corrosive in nature. They can burn skin, clothes, etc. So, it is necessary to handle
them carefully.
198 Acid, Base and Salt
6. Nettle stings and ant bite is painful. Why?
Ans: Stinging hairs of a Nettle and saliva of an ant contain formic acid. As this acid enters into our skin,
we have a burning sensation which is painful.
7. We use aluminium hydroxide and magnesium hydroxide to reduce acidity in our stomach, why?
Ans: Aluminium hydroxide and magnesium hydroxide are alkalis. They neutralize the excess amount
of hydrochloric acid present in our stomach. So, acidity can be controlled by using these alkalis.
8. How can we prepare indicator from flowers?
Ans: We collect petals of flowers and crush them along with sand to get a fine paste. This
paste is mixed with alcohol and filtered to get a clear solution. This solution works like
a simple indicator. Immerge the strips of papers in the solution and let them to become dry.
Now, the paper strip becomes a simple litmus paper.
STEPS EXERCISE
STEP 1
1. Fill in the blanks with appropriate words.
a) Acid give …………. ions in a solution.
b) Alkalis are ………… soluble bases.
c) pH is the measure of …………… concentration.
d) The pH value of acids is less than ……………
e) The colour of phenolphthalein in basic medium is……………
2. Write True for the correct and False for the incorrect statements.
a) Citric acid is an organic acid.
b) A strong acid has pH value of 14.
c) Sodium hydroxide is a weak base.
d) Potassium nitrate is used in fertilizers.
e) Distilled water is neutral with a pH value of 7.
STEP 2
1. Answer the following questions in one word.
a) Which chemical species are called proton donor?
b) What is the taste of acid and base?
c) What is the range of pH scale?
d) What is the pH value of the strongest acid and strongest base?
e) What is the pH value of distilled water?
2. Write any two differences between: b) Organic and inorganic acids
a) Acid and base
Modern Concept Science and Environment – 8 199
c) Strong and weak acids d) Base and alkali
e) NaOH and HCl f) Universal and simple indicator
3. Give reasons.
a) Hydrogen sulphate is an acid.
b) NaOH is an alkali.
c) Ferrous oxide is a base but not an alkali.
d) HCl is a strong acid but CH3COOH is a weak acid.
e) All alkalis are bases but all bases are not alkalis.
4. “A” denotes a salt solution, “B” demotes an acid solution and “C” denotes an alkali
solution. On the basis of this information, complete the table given below:
Indicators Substance A Substance B Substance C
Blue litmus paper
Red litmus paper
Phenolphthalein
Methyl orange
STEP 3
1. Answer the following questions
a) List three physical properties of acids and bases each.
b) Mention three important chemical properties of acids and bases each.
c) What is an acid? Name three organic acids and three inorganic acids with their
molecular formula.
d) Write five uses of acids.
e) What is a bases? Name three bases and three alkalis with their molecular formula.
f) Define alkali. List five uses of bases.
g) Name a strong acid present in human stomach.
h) What is salt? List the names of any five salts with chemical reaction.
i) Write down five major uses of salts.
j) Define indicator. What is the instrument used to measure the pH value of a
solution directly?
k) Define pH and pH scale.
2. Complete the following chemical equations.
a) ............. + Zn ZnSO4 + .......
b) HCl + ………. NaCl + H2O
c) NaOH (aq)
Na+ + ……….
d) 2KOH + CO2 ........... + .............
200 Some useEfsutilmcahteedmtieaccahlinsg periods Theory Practical
5 1
UNIT
15 Some useful chemicals
Syllabus issued by CDC Glycerol
Introduction to water
Physical and chemical properties of water
Hard and soft water
Types of hardness of water (temporary and permanent)
Removal of hardness of water
Introduction to sodium carbonate, sodium bicarbonate and glycerol with their uses
LEARNING OBJECTIVES
At the end of this unit, students will be able to:
explain the properties of water and define hard water and soft water.
describe the types of hard water and explain the methods of removing hardness of water.
introduce sodium carbonate, sodium bicarbonate and glycerol.
Key terms and terminologies of the unit
1. Soft water : The water which has very less or no minerals and readily produces lather
with soap is called soft water.
2. Hard water : The water which has high mineral content and generally produces less
lather with soap is called hard water.
3. Temporary hardness of water : The hardness of water which is caused by mixing magnesium bicarbonate
and calcium bicarbonate is called a temporary hardness of water.
4. Permanent hardness of water : The hardness of water which is caused by mixing of calcium chloride
(CaCl2), magnesium chloride (MgCl2), calcium sulphate (CaSO4) and
magnesium sulphate (MgSO4) is called permanent hardness of water.
5. Permutit : Permutit is a process of removing permanent hardness of water by
exchanging calcium and magnesium ions with sodium ions of the sodium
zeolite.
6. Sodium carbonate : Sodium carbonate is also known as washing soda. It is a sodium salt of
7. Sodium bicarbonate carbonic acid with molecular formula Na2CO3.
8. Glycerol : Sodium bicarbonate is also known as baking soda or edible soda. It is a
white crystalline solid with molecular formula NaHCO3.
: Glycerol is an organic compound made up of carbon, hydrogen and
oxygen. Its molecular formula is C3H5(OH)3. It is normally called glycerine.
Modern Concept Science and Environment – 8 201
15.1 Introduction
We use different kinds of chemical compounds in our daily life. For example, water, soap,
detergents, toothpaste, plastics, baking soda, table salt, sugar, glycerine, petrol, diesel,
insecticides, pesticides, fertilizers, medicines, dettol, etc. Among them some are regularly
used in our daily life and some are used occasionally. All these chemicals make a part in our
life. Water is a universal solvent. It is used for cooking, washing, drinking, transportation, etc.
Baking soda is used in bakery industries and reducing the acidity in our stomach. Similarly,
washing soda is used for making soap and detergent. Glycerol is used for making medicines,
print ink, stamp pad, etc. In this unit, we will discuss about water, sodium carbonate, sodium
bicarbonate and glycerol.
15.2 Water Memory Tips
After air, water is the most important substance for living 1. 97.4%ofthewaterontheearthis
in the form of salt water. Only 2.6
beings. Living beings cannot live without water. More than % is fresh, and 2/3 of that is ice.
65% of the human body is composed of water. Other living 2. Water constitutes the major
part of the protoplasm in
organisms also contain significant amount of water in their animal cell and plant cell.
body. It is the most abundant substance on the earth’s 3. Pure water does not conduct
electricity.
surface. About /2 rd of the earth’s surface is covered with
3
water.
Water occurs naturally in three states: solid (ice), liquid
(water) and gas (water vapour). Snow caps, rainfall, river,
lakes, springs, wells and streams are the major sources of freshwater. Apart from drinking, we
need water for domestic works, industrial purposes, irrigation, power production, etc.
Well River Lake Ocean
Properties of water
a) Physical properties of water
i) Pure water is odourless, colourless and tasteless liquid.
ii) It is clean and transparent.
iii) Naturally, water exists in three states: solid (ice), liquid (water) and gas (water
vapour).
iv) Pure water is a poor conductor of electricity.
v) Water attains its maximum density at a temperature of 4°C.
vi) Water boils at 100°C temperature and freezes at 0°C temperature at normal pressure.
vii) Water is called a universal solvent as it dissolves large number of substances in it.
viii) Pure water is neutral to indicators as it has a pH value of 7.
202 Some useful chemicals
b) Chemical properties of water
i) Water is one of the best known ionizing agents.
ii) It combines with certain salts to form hydrates. For example, copper sulphate
pentahydrate (CuSO4.5H2O), sodium carbonate decahydrate, Na2CO3∙10H2O, etc.
iii) It reacts with non-metal oxides to form acids.
iv) It acts as a catalyst in many important chemical reactions.
v) It is made up of two parts of hydrogen and one part of oxygen.
vi) It is a neutral substance. It means that water is neither acidic nor basic in nature.
Hard water Memory Tips
The water which has high mineral content and generally The water that contains chloride,
produces less lather with soap is called hard water. Due to its sulphate and bicarbonate salts of
less lather producing capacity, hard water is not considered calcium and magnesium is called
good for washing and cleansing purposes. Hard water with a hard water.
a desired concentration of minerals is used as a drinking
water. Mineral water is an example of hard water. Hard water makes our teeth and bones
strong and healthy. Water of well, river, sea, ocean, etc. are some examples of hard water.
Soft water Memory Tips
The water which has very less or no mineral content and The water that does not contain
readily produces lather with soap is called soft water. Due chloride, sulphate and bicarbonate
to its high lather producing capacity, soft water is good for salts of calcium and magnesium is
washing and cleansing purposes. It is also used for making called soft water.
carbonated drinks and beverages. Distilled water, boiled
water, rain water, etc. are some examples of soft water.
Differences between hard water and soft water
SN Hard water SN Soft water
1 The water that contains chloride, 1 The water that does not contain chloride,
sulphate and bicarbonate salts of calcium sulphate and bicarbonate salts of calcium
and magnesium is called hard water. and magnesium is called soft water.
2 Hard water generally produces less 2 Soft water readily produces lather with
lather with soap. soap.
15.3 Hardness of Water
Comparative to other solvents, water can dissolve large number of substances at normal
temperature and pressure. The solute dissolved in water determines the hardness and softness
of water. Among different solutes, salts of calcium and magnesium cause hardness in water.
Chloride, sulphate and bicarbonates of calcium and magnesium are responsible for hardness
in water.
Modern Concept Science and Environment – 8 203
ACTIVITY 1
OBJECTIVE : To test soft water and hard water.
REQUIREMENT: Three test tubes, surf or cleansing powder, different sample
of water
METHODS :
1. Take samples of water from different sources like tap, well, river Tap Well River
water water water
and rain water (if available) and keep them in different test tubes.
2. Add a pinch of surf or cleansing powder or a drop of liquid soap in each of the test tube.
3. Shake the test tube well for about two minute.
4. Can you differentiate them into soft and hard water?
OBSERVATION: Some water samples produce more lather and some other produce less lather.
CONCLUSION: The water that produces more lather than other water samples is called the softest
water and the water that produces very less lather than other samples is called the hardest water. For
your convenience you can differentiate other samples into softer and harder.
Types of Hardness in water
Based on the presence or absence of calcium and magnesium salts, hardness of water is
divided into two types. They are temporary hardness and permanent hardness.
a) Temporary hardness
The hardness of water which is caused due to mixing of magnesium bicarbonate and calcium
bicarbonate is called temporary hardness of water. Hard water is tasty while drinking and
makes our bones healthy.
Removal of temporary hardness of water
Temporary hardness of water can be removed by boiling or treating it with lime-water.
FACT WITH REASON
Boiled water is not as tasty as cold water from tap, why?
Cold water from the tap is full of minerals. So, it is tasty. But when it is boiled, salts are broken down
into metal carbonates. So, hard water changes into soft water and does not give a good taste.
i) By boiling : After boiling, the soluble salts of magnesium bicarbonate and calcium
bicarbonate are converted into insoluble magnesium carbonate and calcium carbonate.
These insoluble salts settle down on the bottom of the boiler or container. Now, the water
is filtered to remove these insoluble salts. In this way we can remove temporary hardness
of water by boiling. The chemical reactions involved in this process are given below:
Magnesium bicarbonate Magnesium carbonate + Water + Carbon dioxide
Mg(HCO3)2 ∆ MgCO3 + H2O + CO2
Calcium bicarbonate Calcium carbonate + Water + Carbon dioxide
Ca(HCO3)2 ∆ CaCO3 + H2O + CO2
204 Some useful chemicals
FACT WITH REASON
Bicarbonates of magnesium and calcium are called thermally unstable salts, why?
Bicarbonates of magnesium and calcium are called thermally unstable salts because they break down
into water soluble salts after heating.
ACTIVITY 2
OBJECTIVE : To remove temporary hardness of water by boiling.
METHODS :
1. Take two beakers each of 250 ml and add 100 ml distilled water in
each beaker.
2. Add one spoon of calcium bicarbonate in one beaker and stir it.
3. Add another spoon of magnesium bicarbonate in another beaker and stir it.
4. Take two test tubes and pour about 5 ml of solution in each test tube from each beaker.
5. Add 2 drops of liquid soap or a pinch of surf powder in each test tube. Shake the solution well.
Observe lather in each test tube. You will not see enough lather in the solution.
6. Now heat the above beakers, one containing calcium bicarbonate solution and another
containing magnesium bicarbonate solution. After heating, solutions are allowed to cool down.
7. Pour the solution in each test tube and add 2 drops of liquid soap or a pinch of surf powder in
each test tube. Shake these solutions well.
8. You will see enough lather in the solution in this case. It means that water became soft after heating.
CONCLUSION: In this way, by boiling, we can remove temporary hardness of water.
ii) By treating with lime water: Adding lime water or slaked lime (calcium hydroxide)
in water can remove its temporary hardness. Lime water reacts with bicarbonates of
magnesium and calcium and converts them into insoluble carbonates. These insoluble
carbonates can be filtered to get soft water.
Magnesium bicarbonate + Calcium hydroxide Calcium carbonate + Water +
Magnesium hydroxide
Mg(HCO3)2+ 2Ca(OH)2 2CaCO3+ 2H2O + Mg(OH)2
Calcium bicarbonate + Calcium hydroxide Calcium carbonate + Water
Ca(HCO3)2 + Ca(OH)2 2CaCO3 + 2H2O
b) Permanent hardness
The hardness of water which is caused due to soluble salts like calcium chloride (CaCl2),
magnesium chloride (MgCl2), calcium sulphate (CaSO4) and magnesium sulphate (MgSO4) is
called permanent hardness of water. Permanent hardness of water can be removed by using
chemical processes.
Removal of permanent hardness of water
Permanent hardness of water can be removed by using washing soda (sodium carbonate) and
by permutit process using zeolite.
Modern Concept Science and Environment – 8 205
i) By treating with washing soda : Sodium carbonate is popularly known as washing
soda. It reacts with chloride and sulphate of calcium and magnesium and converts these
salts into their insoluble carbonates. These insoluble carbonate salts are removed by
filtration. The chemical reaction is shown below:
Magnesium chloride + Sodium carbonate Magnesium carbonates + Sodium chloride
MgCl2 + Na2CO3 MgCO3 + 2NaCl
Calcium chloride + Sodium carbonate Calcium carbonate + Sodium chloride
CaCl2 + Na2CO3 CaCO3 + 2NaCl
Magnesium sulphate + Sodium carbonate Magnesium carbonate + Sodium sulphate
MgSO4 + Na2CO3 MgCO3 + Na2SO4
Calcium sulphate + Sodium carbonate Calcium carbonate + Sodium sulphate
CaSO4 + Na2CO3 CaCO3 + Na2SO4
FACT WITH REASON
Sodium carbonate is used to remove permanent harness of water, why?
Sodium carbonate is used to remove permanent hardness of water because sodium carbonate changes
soluble chlorides and sulphates of magnesium and calcium into water insoluble carbonates.
Differences between hardness caused by calcium bicarbonate and hardness caused by calcium sulphate.
SN Hardness caused by calcium SN Hardness caused by calcium sulphate
bicarbonate
1 Calcium bicarbonate causes temporary 1 Calcium sulphate causes permanent
hardness in water. hardness in water.
2 The hardness caused by calcium 2 The hardness caused by calcium sulphate
bicarbonate can be removed by boiling. can be removed by using detergent.
ii) Permutit process : Sodium zeolite (Na2-Z) or
sodium aluminosilicate (Na2Al2SiO8) is the major
chemical constituent of the permutit process. When
hard water is passed through permutit, the calcium
and magnesium ions are exchanged by the sodium
ions of the zeolite. This process results the formation
of calcium and magnesium zeolites. Exchange of
calcium and magnesium makes the water soft. The
chemical processes involved in permutit process are: Permutit process
Magnesium chloride + Sodium zeolite Magnesium zeolite + Sodium chloride
MgCl2 + Na2-Z Mg-Z + 2NaCl
Calcium zeolite + Sodium chloride
Calcium chloride + Sodium zeolite
CaCl2 + Na2-Z Ca-Z + 2NaCl
Magnesium sulphate + Sodium zeolite Magnesium zeolite + Sodium sulphate
206 Some useful chemicals
MgSO4 + Na2-Z Mg-Z + Na2SO4
Calcium sulphate + Sodium zeolite Calcium zeolite + Sodium sulphate
CaSO4 + Na2-Z Ca-Z + Na2SO4
Differences between temporary hardness of water and permanent hardness of water.
SN Temporary hardness of water SN Permanent hardness of water
1 Bicarbonate salts of calcium and 1 Chloride and sulphate salts of calcium
magnesium are responsible for and magnesium are responsible for
temporary hardness in water. permanent hardness in water.
2 Temporary hardness of water can be 2 Permanent hardness of water can be
removed by boiling and by using lime removed by using washing soda and
water. permutit process.
ACTIVITY 3
OBJECTIVE : To remove permanent hardness of water by using sodium carbonate.
METHODS :
1. Take a beaker containing 50ml of distilled water.
2. Add some amount of magnesium chloride and calcium chloride in it and stir the solution.
Now, the water becomes permanently hard in nature.
4. Take some amount of solution in a test tube and add two drops of a liquid soap or a pinch of surf
powder in the test tube and shake for a while. Observe lather in it. We do not get lather in it.
5. Add about half spoon of washing soda (sodium carbonate) in the beaker and stir the solution.
6. Take some amount of solution in the test tube and add about two drops of liquid soap or a
pinch of surf powder in the test tube and shake for a while. You will see the formation of
lather in water.
CONCLUSION : In fact calcium and magnesium ions present in hard water react with sodium carbonate
to produce insoluble carbonates. These insoluble carbonates precipitate in the beaker making water
soft. In this way, permanent hardness of water can be removed by using sodium carbonate.
15.4 Sodium Carbonate (Na2CO3)
Sodium carbonate is a sodium salt of carbonic acid. Its molecular formula is Na2CO3. It is also
known as washing soda or soda ash. It is a water soluble salt. Pure sodium carbonate is a
white, odourless powder that absorbs moisture from the air. It has an alkaline taste and forms
strongly alkaline solution.
Uses of sodium carbonate
i) Sodium carbonate is used for making soap and washing
powder.
ii) It is used in manufacturing of glass and paper. Sodium carbonate
iii) It is used for softening of hard water.
iv) It is used for making caustic soda in a laboratory.
v) It is used as a wetting agent in the brick industry to reduce the amount of water.
Modern Concept Science and Environment – 8 207
vi) It is used in toothpastes, where it acts as a foaming agent.
15.5 Sodium bicarbonate (NaHCO3)
Sodium bicarbonate is an alkaline salt of carbonic acid with molecular formula NaHCO3. It is
made up of sodium, hydrogen, carbon and oxygen atoms. It is a water soluble salt. It is a white
crystalline solid but often appears as a fine powder. It is found dissolved in many mineral
springs. It is also known as baking soda, bread soda, cooking soda
or bicarbonate of soda. It is naturally present in our blood stream to
regulate pH.
Uses of sodium bicarbonate
i) Sodium bicarbonate is used for making baking powder. Sodium bicarbonate
ii) It is used for reducing hyperacidity in our stomach.
iii) It is used for making soft drinks like soda water, coke, pepsi, etc.
iv) It is used in fire extinguishers as a source of carbon dioxide.
v) It can be used as a medicine to control the fungal growth.
vii) Use of sodium bicarbonate as a pesticide has no adverse health effects. So, it can be used
as an effective biopesticide.
FACT WITH REASON
Sodium bicarbonate in our blood is critical to life, why?
Sodium bicarbonate in our blood is critical to life because it is naturally present in our blood stream to
regulate pH which is critical to life.
Sodium bicarbonate is called a baking soda, why?
Sodium bicarbonate is mixed with potassium hydrogen tartrate ( KC4H5O6) to produce baking powder.
In bakeries, baking powder is used to increase the volume of cakes, biscuits, breads, etc. So, dodium
bicarbonate is called a baking soda.
15.6 Glycerol {C3H5(OH)3} Structure of Glycerol Glycerol
Glycerol is a colourless, odourless, non-toxic, viscous
thick liquid having a sweet taste. Its molecular formula
is C3H5(OH)3. It is commonly called glycerine. It is an
organic compound also called trihydric alcohol. It is made
up of carbon, hydrogen and oxygen atoms. It is widely
used in pharmaceutical products. Glycerol is soluble in
water and hygroscopic in nature.
208 Some useful chemicals
FACT WITH REASON
Why is glycerol extensively used in glues and adhesives?
Glycerine is hygroscopic in nature. That is, it absorbs moisture from air. Therefore, it is extensively
used in glues and adhesives to prevent them from drying too fast.
Why do people use glycerol mostly during winter?
Glycerine is colourless, odourless, non-toxic, viscous thick liquid which keeps our skin moist and
prevents loss of water. So, people use glycerol mostly during winter for protection of their skin.
Uses of glycerol
i) Glycerol is used for making medicines like cough syrup, mouthwash, skin care product
etc., toothpaste, printing ink and ink for stamp pads.
ii) It is used as a sweetening agent in confectionary foods and beverage.
iii) It is used to make different kinds of cosmetic products.
iv) It is used for manufacturing high quality soap.
v) It is used to preserve tobacco, fruits, etc.
vi) It is used as a smoothening and lubricating agent in various purposes.
vii) It is used as a solvent to preserve different kinds of materials.
viii) It is used to make explosives like dynamite, gelignite, etc.
ANSWER WRITING SKILL
1. Write down the name with molecular formula of the salts which are responsible for permanent
hardness in water.
Ans: The salts which are responsible for permanent hardness in water are:
i. Calcium sulphate- CaSO4 ii. Calcium chloride- CaCl2
iii. Magnesium sulphate - MgSO4 iv. Magnesium chloride - MgCl2
2. How do villagers wash cloth if soap does not produce lather in cold water?
Ans: Villagers boil water for washing cloth if soap is not producing lather in cold water.
3. Which chemicals are used for making high quality cosmetics,baking powder,and washing powder?
Ans: Cosmetics are made from glycerine, baking powder is made from sodium bicarbonate and washing
powder is made from sodium carbonate.
4. What is Permutit process? Which chemical is used in it? Write down its molecular formula.
Ans: The process in which hard water is made soft by exchanging magnesium and calcium ions with
sodium ions is called permumit process. In Permutit process we use sodium zeolite (Na2-Z). Its
molecular formula is sodium aluminosilicate(Na2Al2SiO8).
5. If we try to wash hands with soap and rain water, it is too difficult to get rid of lather. Why?
Ans: If we wash hand with soap and rain water, it is very difficult to get rid of lather because rain water
is very soft water. So, it produces more lather in rain water.
Modern Concept Science and Environment – 8 209
6. Write any two differences between rain water and sea water.
Ans: The two differences between rain water and sea water are:
S.N. Rain water S.N. Sea water
1 Rain water is a soft water. 1 Sea water is a hard water.
2 It produces lather with soap easily. 2 It does not produce lather with soap easily.
7. Write down any three uses of hard water?
Ans: The three uses of hard water are given below:
i. Bathing in Luke warm hard water cures skin diseases.
ii. Hard water supplies minerals in our body if we drink it.
iii. Hard water supplies various minerals in soil. So it is good for plants.
8. Write down any three properties of glycerol.
Ans: Three properties of glycerol are:
i. Glycerol is a colourless, odourless, non-toxic and transparent liquid.
ii. It has a sweet taste.
iii. It is soluble in water.
STEPS EXERCISE
STEP 1
1. Fill in the blanks with appropriate words.
a) Salts of ……..and……..are responsible for permanent hardness in water.
b) Permutit process is used to remove ………… hardness of water.
c) The molecular formula of the sodium zeolite is…………..
d) NaHCO3 is called …………
e) ……………… is also known as washing soda.
2. Write True for the correct and False for the incorrect statements.
a) Water is a universal solvent.
b) Pure water is basic in nature.
c) Calcium and magnesium salts in water cause hardness in water.
d) Boiling removes temporary hardness of water.
e) Sodium bicarbonate is used as a sweetening agent.
f) Glycerol is also known as glycerine.
STEP 2
3. Answer the following questions in one word.
a) Which salts are responsible for permanent hardness in water?
b) Which salts are responsible for temporary hardness in water?
210 Some useful chemicals
c) How is the temporary hardness of water removed?
d) Which chemical is used to make high quality cosmetics and toilet soap?
e) Which chemical is used in detergent?
4. Write any two differences between:
a) Hard water and soft water
b) Temporary hardness in water and permanent hardness in water
c) Hardness caused by calcium bicarbonate and hardness caused by calcium sulphate
d) Sodium carbonate and sodium bicarbonate
5. Give reasons.
a) Sodium carbonate is used to remove permanent harness of water.
b) People use glycerol mostly during winter.
c) Sodium bicarbonate is critical to life.
d) Bicarbonates of magnesium and calcium are called thermally unstable salts.
e) Sodium bicarbonate is called a baking soda.
6. Write down the molecular formula of the following chemical substances:
a) Chemicals causing permanent hardness in water
b) Chemicals causing temporary hardness in water
c) Washing soda
d) Baking soda
e) Glycerol
STEP 3
7. Answer the following questions
a) Define hard water. How can we identify hardness and softness of water?
b) What is temporary hardness of water? Name the salts that causes temporary
hardness in water.
c) What is permanent hardness of water? Name the chemicals which are responsible
for permanent hardness in water? Write their molecular formula.
d) What is soft water? Write two uses of each hard water and soft water.
e) Write two ways to remove temporary hardness of water.
f) Write two ways to remove permanent hardness of water.
g) What are washing soda and baking soda?
h) What is glycerol? Write down its molecular formula and three properties.
i) List any three important uses of each of the following compounds:
i) Sodium carbonate ii) Sodium bicarbonate
iii) Glycerol
8. Explain the process with chemical equations and diagram to remove permanent
hardness in water by using permutit process.
UNIT Estimated teaching periods Theory MPordaecrtnicCaolncept Science and Environment – 8 211
12 2
16
Living Beings
Syllabus issued by CDC Anton Van
Introduction to some microscopic organisms ( bacteria, virus and fungi) Leeuwenhoek
Modification of different parts of the plants (root, stem and leaf)
Structure and function of seed.
Dispersal of seed.
Lifecycle of a flowering plant.
LEARNING OBJECTIVES
At the end of this unit, students will be able to:
Introduce some microscopic organisms (Bacteria, Viruses and Fungi)
Explain the structure and functions of the modified parts of plants (root, stem and leaf)
Explain the structure and function of the different parts of a seed.
Describe structure and methods of dispersal of seeds.
Describe and demonstrate the germination of seed and the conditions (air, water and heat)
required for the germination of seed.
Explain and demonstrate the life cycle of a flowering plant.
Key terms and terminologies of the unit
1. Microorganisms : Those tiny organisms which cannot be seen by our naked eyes are called
microorganisms.
2. Bacteria : Bacteria are the smallest, single-cellular, prokaryotic organisms.
3. Viruses : Viruses are the smallest microscopic, acellular, non-protoplasmic bodies that
are considered to be the connecting link between living and non-living things.
4. Bacteriophage : The virus that attacks and replicates within a bacterium is called a
bacteriophage.
5. Fungi : Fungi are unicellular or multicellular eukaryotic organisms without chlorophyll.
6. Modification of parts of plants : The change in structure of leaves, stem and roots of plants to perform
various functions and to adopt according to the changing environment is
called modification of parts of plants.
7. Seed : A seed is a ripened ovule of a flowering plant.
8. Dicotyledonous plants : The plants having two cotyledons in their seeds are called dicotyledonous plants.
9. Monocotyledonous plants : The plants having one cotyledon in their seeds are called
monocotyledonous plants.
10. Endospermic seeds : The seeds in which food is stored in endosperm are called endospermic seeds.
11. Non-endospermic seeds : The seeds in which food is stored in cotyledons are called non-
endospermic seeds.
212 Living Beings
12. Dispersal of seeds : Dispersal of seeds means distribution or scattering of seeds away from the position of
their origin.
13. Germination : Germination is a process by which the embryo in the seed becomes active and begins
14. Pollination to grow into a new seedling.
: The process of transfer of pollen grains (male gametes) from anther to stigma of a
flower is called pollination.
15. Self-pollination : The process of transfer of pollen grains (male gametes) from the anther to the stigma
of the same flower or different flower of the same plant is called self-pollination.
16. Cross-pollination : The process of transfer of pollen grains (male gametes) from the anther to the stigma
of the different flower of the different plants is called cross-pollination.
17. Fertilization : Fertilization is a process of fusion of a male gamete and a female gamete to form a
zygote.
18. Endosperm : Endosperm is a structure filled with reserve food materials which is a source of
19. Life cycle nutrients for an embryo.
: Life cycle of an organism is a series of changes that an organism spends to develop
from its embryonic stage to its maturity.
16.1 Introduction
The earth is a home for various living beings. Millions of living beings are inhibited here.
Scientists are still busy to discover new living beings. It is very difficult to study these living
organisms one by one. So, the living beings are broadly divided into two groups. They are
plants and animals. Plants are kept in the kingdom plantae and animals are kept in the
kingdom animalia. Some plants on the earth are very big and some other plants are very small.
Similarly, some animals are very big like a whale, elephant, rhinoceros, horse, buffalo, etc.
and some other animals like amoeba, plasmodium, etc. are very small. The organisms whose
body is made up of only one cell are called unicellular organisms. For example, bacteria,
amoeba, paramecium, etc. Similarly, those organisms whose body is made up of many cells
are called multicellular organisms. All unicellular and some multicellular organisms are very
small to see. So, they are studied under microscope. These organisms are called microscopic
organisms. In this unit, we will discuss briefly about bacteria, virus, fungi, etc. We will also
discuss about the modification of different parts of plants like roots, stems, leaves, etc.
16.2 Microorganisms
A large variety of organisms are present on the earth surface.
Among them some are very small and some are very big. To make
our study easy, all these organisms are broadly classified into
two groups. They are microorganisms and macro-organisms. Bacteria Fungi
Those organisms which cannot be seen by our naked eyes are Protozoa
called microorganisms. Microscope is used to observe these Virus
microorganisms. So, microorganisms are also called microscopic
organisms. The body of microorganism may be unicellular or multicellular. The group of
microorganisms is very diverse. It includes all virus, bacteria and some algae and fungi.
Modern Concept Science and Environment – 8 213
16.3 Bacteria
Bacteria are the smallest, single-cellular, prokaryotic organisms. They were
the first life forms to appear on the earth. Bacteria are universal organisms.
Therefore, they can be found in wide range of habitats including air, water,
soil, body of animals and plants, food, oceans, hot springs, etc. They were
first discovered by Antonie Van Leeuwenhoek in 1676 AD and the term
bacteria was coined by Christian Gottfried Ehrenberg in 1828 AD. Bacteria
Structure of bacteria
DNA
Bactria has very simple structure. A bacterial cell contains Cytoplasm 2µm (microns)
living substance called protoplast which is bounded by Cell membrane
a thin membrane called plasma membrane. The plasma
membrane in bacterial cell is protected by an outer rigid Flagella
thin cell wall called capsule. Its protoplasm contains
cytoplasmic fluid, circular DNA (Deoxyribonucleic
acid) , ribosomes and flagella like cellular components.
Flagella are very thin hair like outgrowth projected out Structure of bacteria
from the capsule. They are the organs for locomotion in
bacteria. The bacterial cell does not contain membrane bound cell organelles like nucleus,
mitochondria, chloroplasts, etc. They are very small organisms. In average a bacterial cell has
about 2 micrometres (μm) length and 0.5 μm diameter.
Characteristics of bacteria Memory Tips
i) Bacteria have prokaryotic cell. 1. Earwax has antimicrobial
ii) They do not have membrane bound nucleus and properties. It reduces the
other cell organelles. growth of bacteria and fungi in
iii) They have a rigid cell wall outside the cell membrane. the human ear.
iv) They occur alone or make a colony. 2. Honey is a natural reservoir for
v) Except bacilli and spirilla, most of the bacteria are the Botulism bacteria. Adults
immotile, i.e. cannot move. can normally digest it and
infants cannot. This is why we
vi) They reproduce asexually by means of fission.
should not give honey to the
vii) They are found everywhere in air, water, soil, food, babies.
inside the living beings, etc.
viii) They show autotrophic as well as heterotrophic nutrition.
Types of bacteria (on the basis of shape)
On the basis of shape, there are four types of bacteria. They are:
a) Coccus or spherical shaped bacteria
Cocci (singular- coccus) have spherical shape. They are found in a cluster or chain
structure. Examples: Streptococci, Staphylococci, Diplococci, etc.
214 Living Beings
b) Bacillus or rod-shaped bacteria
Bacilli (singular- bacillus) have rod-shaped structure.They may be present individually
or in a chain. Examples: Escherichia coli, Bacillus anthracis, etc.
c) Spirillum or filamentous or spiral shaped bacteria
Spirilla (singular-spirullum) have spiral-shaped or filamentous structure. They may
have one or more flagella at the end of each cell. Examples: Laptospira, Spirillum, etc.
d) Vibrio or Comma shaped bacteria
These bacteria have comma-shaped body. Some of them also have curve shaped body.
For example: vibrio chlolera
Cocci bacteria Bacilli bacteria Spirillum Vibrio cholera
Types of bacteria
Types of bacteria (on the basis of mode of nutrition)
On the basis of mode of nutrition, bacteria are divided into following types:
a) Chemosynthetic bacteria
Those bacteria which obtain energy from the oxidation of inorganic substances like
sulphur, iron, etc. are called chemosynthetic bacteria. Examples: sulphur bacteria, iron
bacteria, etc.
b) Photosynthetic bacteria
Those bacteria which use photosynthetic pigments to synthesize their own food are
called photosynthesis bacteria. Example: Cyanobacteria, chlorobium limicola, etc.
c) Saprophytic bacteria
Saprophytic bacteria get their nutrition from dead organic matter. Examples: Zygomonas,
acetobacter, etc.
d) Parasitic Bacteria
Parasitic bacteria derive their nutrition from the plants and animals on which they grow.
They are also known as pathogenic bacteria. Salmonella typhi, Mycobacterium tuberculosis,
Vibrio cholerae, Triponema pallidum, etc. are some examples of parasitic bacteria. They
cause diseases in animals and plants. Plant parasitic bacteria are responsible for various
plant diseases like citrus canker, yellow rot of wheat, ring rot of potato, etc.
e) Symbiotic bacteria atmosphere
Symbiotic bacteria live in close association with other organisms
with mutual benefit.They derive their nutrition without hampering
the host organism. Rhizobium, Azotobactor, Clostridium, etc. are some N2
examples of symbiotic bacteria. Rhizobium is present in the root nodules
of leguminous plants. They help in nitrogen fixation and increase the Soil
nitrogenous compounds in the soil. It is an important process to grow
the leguminous plants. In return, Rhizobium bacteria get their shelter and
nutrition from the leguminous plants.
Modern Concept Science and Environment – 8 215
Economic importance of bacteria
Bacteria have both harmful as well as useful effects. Some of the harmful and useful effects of
bacteria are mentioned below:
a) Useful effects of bacteria
i) Bacteria are used to produce antibiotics which are used to cure or prevent diseases.
ii) They are used as a source of enzymes in laboratories and industrial processes.
iii) They are widely used in biotechnology like production of foods, genetically
modified animals, etc.
iv) They help in digestion of food in humans and other animals.
v) They degrade and decompose the dead bodies of animals and plants and recycle
the nutrients back in the environment.
vi) The nitrifying bacteria maintain the concentration of nitrogen in the soil. So, they
help in production of crops.
vii) Bacteria are used for manufacturing alcohols, leathers, cheese, etc.
b) Harmful effects of bacteria
i) Pathogenic bacteria cause different kinds of diseases to human beings, animals
and plants.
ii) Some bacteria produce toxins which are fatal to human beings, animals and plants.
iii) Some bacteria spoil foods and food products like cooked food, fish, meat, dairy
products, etc.
iv) Denitrifying bacteria decrease the productivity of land by decreasing the nitrogen
content in the soil.
v) Bacteria produce bad smell as a result of decomposition.
16.4 Virus
The word virus has been derived from the Greek word venom which means poison or
poisonous fluid. Viruses are the smallest microscopic, acellular, non-protoplasmic bodies that
are considered to be the connecting link between living and non-living things. Virus is a small
infectious agent that shows living characteristics only inside Memory Tips
the living cell. So, it is also known as obligatory parasite. It
was first discovered by Dmitri Ivanovsky in 1892 AD. Virus The first discovered virus was
is too small to observe under the light microscope. So, we Tobacco Mosaic Virus (TMV).
need an electron microscope to observe them. The size of It was discovered by a Russian
Microbiologist, Dmitry Ivanovsky
virus ranges from 25 nanometers to 250 namometers.
in 1892 AD.
FACT WITH REASON
Viruses are called obligatory parasites, why?
Viruses show living characteristics and multiply inside the living host only. Outside of a living cell,
viruses show non-living characteristics. So, viruses are called obligatory parasites.
Viruses are called the connecting link between living and non-living things, why?
All viruses are completely parasite. They behave like living organisms inside the living host cell. They
are inactive and like a dust particle outside the living cell. Therefore, they are kept on the boundary of
living and non-living things.
216 Living Beings
Structure of a virus Capsid
Head
Viruses have different shapes and sizes. They may be spherical, DNA
cylindrical, helical, polyhedral, hexagonal or complex. Most viruses Tail
are smaller than bacteria. A complete virus particle is known as a
virion. It consists of nucleic acid (DNA-Deoxyribonucleic acid or RNA- Tail
Ribonucleic acid) surrounded by a protective coat of protein called fibres
capsid. Viruses can have a lipid “envelope” derived from the host cell
membrane. It contains a tail which ends at a tail plate having tail fibres. Structure of virus
Occurrence of viruses
Viruses are present in different habitats like food, water, air, soil and even in rocks. They can
infect all types of life forms, from animals and plants to microorganisms, including bacteria.
In humans, viruses cause different diseases like rabies, HIV/AIDS, polio (or poliomyelitis),
measles, common cold, etc. Viruses enter into the human body through air, water, food, soil,
wounds, pores, openings, etc.
Living properties of virus
i) Viruses contain genetic materials like DNA or RNA.
ii) They are capable of rapid multiplication (reproduction) in a host cell.
iii) They are capable of transferring generic materials from parent cells to their offspring.
iv) They eat and digest living cells of bacteria, infect them and cause diseases to plants and animals.
Non-living properties of virus
i) Viruses do not have definite cellular structures.
ii) They remain inert and inactive outside the living cell.
iii) They do not perform metabolic activities.
iv) They can be crystallized in laboratory like crystalline solids.
Classification of virus (On the basis of genetic material)
On the basis of genetic material, viruses are divided into two types. They are DNA virus
and RNA virus.
a) DNA virus: The virus containing DNA (Deoxyribonucleic acid) as a genetic material
is called DNA virus. Examples: Bacteriophages, Memory Tips
Adenoviruses, Small pox virus, etc. Coliphage is a bacteriophage. It is
b) RNA virus: The virus containing RNA (Ribonucleic a DNA virus. It infects Escherichia
acid) as a genetic material is called RNA virus. coli which is a bacterium present
Examples: Polio virus, Retro virus, Paramyxo virus, in human intestine.
Rhino virus, Rhabdo virus, etc.
Modern Concept Science and Environment – 8 217
Classification of virus (On the basis of host)
On the basis of host cell, viruses are divided into three types. They are: Capsid
Head
a) Bacteriophage virus DNA
Tail
The virus that attacks and replicates within a bacterium is called
a bacteriophage. T2 phage, T4 phage, etc. are some examples of Tail
bacteriophage. The body of a bacteriophage has a head and a tail. fibres
Head is protected by an outer sheath called capsid. Inside the capsid
there is DNA as a genetic material. The tail contains a tail plate with Bacteriophage
one or more fibres called tail fibres.
b) Plant virus
The virus that infects and replicates within a plant cell is Plant virus
called a plant virus or phytophage. Plant virus contains
RNA as a genetic material. In the structure of a plant virus,
capsid makes only external boundary. Tobacco mosaic
virus (TMV), Dahlia mosaic virus (DMV), Wild potato
mosaic virus (WPMV), Cauliflower mosaic virus (CaMV),
Wound tumour virus (WTV), etc. are some examples of
plant virus.
c) Animal virus
The virus that infects and replicates within animal cell is called an animal virus or
zoophage. In animal viruses DNA or RNA is present as a genetic material. In addition
to capsid, envelope is also present in animal virus. Retro virus, Rhino virus, Polio virus,
Rabies virus, Paramyxo virus, etc. are some examples of animal viruses.
Retro virus Rhabdo virus Rhino virus Paramyxo virus
Differences between bacteria and viruses.
SN Bacteria SN Viruses
1 Bacteria are very small 1 Viruses are smaller than bacteria. They
microorganisms which can be seen can be seen only under the electron
under a compound microscope. microscope.
2 Bacteria are living organisms. 2 Viruses are the borderline between
living and non-living organisms.
3 They show metabolic activities. 3 They do not show metabolic activities.
4 Bacterial cell has cell organelles. 4 Viruses do not have cell organelles.
218 Living Beings
ACTIVITY 1
Take two chart papers and draw the well labelled diagrams of bacteriophage and tobacco mosaic virus
separately in each chart paper. Compare the characteristics of these two viruses and discuss with your
friends in the class.
16.5 Fungi
Fungi are unicellular or multicellular eukaryotic organisms without chlorophyll. The cell wall
of fungi is composed of chitin. The fungal cells are multinucleated. They are found mainly in
soil or on the plant material rather than in freshwater and sea water. Most fungi grow in an
acidic medium with a pH value of about 5. They grow at about 25°C temperature, except for
pathogens, which grow at 37°C.
Yeast is a unicellular fungus while mucor, rhizopus, mushroom, etc. are multicellular fungi.
The main body of the most fungi is made up of fine, branching and usually colourless threads
called hyphae. Each multicellular fungus has vast numbers of hyphae. All these hyphae
interlock to make a twisted web called mycelium.
Mushroom Yeast Bread mold
Since fungi lack photosynthetic pigments, they depend upon other organisms to derive their
nutrition.Therefore, they are called heterotrophs. Most of the fungi are saprophytes which
derive nutrition from dead organic matter. Saprophytes are also called decomposers as they
decompose organic materials of the dead body and cycle the elements in nature. Few fungi are
parasites which absorb food from the host body. Parasites cause various diseases in animals
and plants. Mildews, rusts, scabs or canker, etc. are most common fungal diseases in plants
and skin diseases, hair disease, ear disease, eye diseases, etc. are most common fungal diseases
in animals. Few fungi are also symbiotic. They live in association with other organism without
hampering them. Lichen is an example of mutual association of algae and fungi.
Fungi reproduce through both sexual and asexual reproductions. Asexual reproduction
involves fragmentation, budding, sporulation and fission. Similarly, sexual reproduction
occurs by the union of opposite cells within a single or different mycelium.
Characteristics of fungi
i) Fungi are eukaryotic organisms without chlorophyll.
ii) They may be unicellular or multicellular.
Modern Concept Science and Environment – 8 219
iii) The plant body of fungi is thallus. It means that they Memory Tips
are not differentiated into root, shoot and leaves. 1. In order to prevent food from all
iv) The cell wall of fungi is made up of fungal cellulose. types of fungal decay, it should
v) The fungal body is made up of hyphae. be in temperature lower than
vi) Theymostlyreproducebyasexualreproductioninvolving -18°C, as they remain active
fragmentation, budding, sporulation and fission. even at 0°C.
Economic importance of fungi 2. Yeast is a unicellular fungus
which is mostly used in
a) Useful effects of fungi
fermentation.
i) Fungi are very useful in different industries like,
bakeries, wine industries, making cheese, commercial production of citric acid, etc.
ii) Antibiotics like Penicillin can be extracted from penicillium.
iii) Fungi contain a number of alkaloids which are utilized in medicine and useful in
controlling haemorrhage during child birth.
iv) Fungi like mushrooms, mor els, truffles, etc. are used as food.
v) Fungi decompose the dead bodies of the organisms and help in recycling the nutrients.
b) Harmful effects of fungi
i) Fungi cause various diseases in animals and plants. Examples: Late blight of
potato, black stem rust of wheat, brown spot of rice, mycosis, skin disease, vaginal
yeast infection, hair disease, etc.
ii) They spoil food, fruits, vegetables, etc.
16.6 Modifications of Different Parts of Plants
There are different parts of a plant such as root, stem, leaves, flowers, fruits, seeds, etc. Among
them, root, stem and leaves are the major parts. Flowers, fruits, seeds, etc. are also the parts of a
plant. The roots anchor a plant in the soil and fix the plant. They also absorb water and minerals
from the soil. Stem holds, branches, leaves, flowers, fruits and other parts of a plant. It also
serves as a path for the flow of water, mineral, nutrients, food, etc. in a plant. Similarly, leaves
perform photosynthesis to prepare food. In this way, different parts of a plant perform specific
functions according to their surrounding environment. However, some plants and their parts
modify themselves to do some extra function according to the surrounding environment. So,
the change in structure of leaves, stem and roots of plants to perform various functions and
to adopt according to the changing environment is called modification of parts of plant. Here,
some modifications of parts of the plants and their function have been described.
Modification of roots
Roots are the underground parts of plants. The first root of Taproot Adventitious root
a plant is called the radicle. It originates from the embryo of
a seed. Radicle elongates during germination of a seed and
forms the primary root. The roots that come out from the
primary root are called secondary roots. According to the
structure, the roots of plants are classified into two groups.
They are taproots and fibrous or adventitious roots.
220 Living Beings
In many plants the primary root is known as taproot. The taproot is much larger than secondary
roots. It penetrates deeper into the soil. Examples of plants with taproots are mustard, bean,
pea, peepal, banyan, etc. Beets and carrots are the examples of plants with very large taproots.
The bunch of roots arising from the stem is known as adventitious roots. They are also called
fibrous roots. Fibrous roots look like a group of fibres arising from a single root. They do not
have branches. Roots of maize, wheat, paddy, grasses, etc. are some examples of fibrous roots.
Roots fix the plants firmly to the soil. They also absorb water and minerals form the soil.
Besides these primary functions, roots are also modified to perform other functions. Some
modifications of the roots are described below:
a) Modification of roots for mechanical support
Many plants have strong and wide root systems to provide mechanical support to the
plants. The roots of most trees go deep into the soil and spread over a large area. These
roots provide strong mechanical support to the plants. Plants like, sugarcane, maize,
bamboo, etc. have roots coming out from their stem. Any of the modified roots that
arise from the stem of certain plants and provide extra support are called prop roots.
Orchid, banyan, mangrove, etc. have aerial roots (roots formed high up in the stem) that
tie themselves to other things. All these modifications in the roots provide mechanical
support to the plant.
Roots of banyan Roots of maize Roots of sugarcane
FACT WITH REASON
Why has a banyan tree prop roots?
The long prop roots of a banyan tree penetrate the soil to provide an additional support to it. So, a
banyan tree has prop roots to provide mechanical support.
b) Modification of roots for storage of foods
Apart from mechanical support to the plants, taproots of some plants are modified into
food storage organs. Plants like carrot, radish, turnip, cassava, etc. store excess of food
in their roots. In carrot, the upper part of the root is wider and the lower part is tapered.
In turnip, the upper part of the root is round and the lower part is pointed. Similarly,
in radish the middle part of the root is swollen and the lower part is pointed. In case of
sweet potato, the root is irregularly swollen to store food.
Root of carrot Root of turnip Root of radish Root of sweet potato
Modern Concept Science and Environment – 8 221
FACT WITH REASON
Why do plants like carrot, radish, turnip, cassava, etc. have swollen roots?
Plants like carrot, radish, turnip, cassava, etc. have swollen roots to store excess food. It is a kind of
modification of roots to store food.
c) Modification of roots for vital functions
Prop roots of few plants like trapa contain chlorophyll. These roots help in photosynthesis
to prepare food. Some aquatic plants like water hyacinth have spongy roots that help in
floating. Plants like cuscuta have parasitic roots arise from their stem. They penetrate
into host plant and derive nutrients. Rhizophora and other swamp plants have pores
in their roots. Such roots help in respiration. Epiphytes like orchids have aerial roots.
These aerial roots absorb moisture from the atmosphere.
Root of hyacinth Root of orchid Root of rhizophora
FACT WITH REASON
Floating plants like water hyacinth have spongy roots, why?
Floating plants like water hyacinth have spongy root because in the spongy roots, air is trapped inside.
It makes roots light and flexible. As a result, they can easily float in water.
Modifications of stem
Stem is the part of plant that grows above the ground. In vascular plants, the stem commonly bears
branches, leaves, buds, flowers, fruits, seeds, etc. The stem is usually aerial, upright and
elongate. In stem, branches, leaves and buds come out from the nodes of the stem. The major
functions of the stem are production and support to the branches, leaves, buds, flowers, seed,
etc. It also helps in conduction of water, minerals and food in different parts of the plant.
Besides these primary functions, the stems of some plants Memory Tips
are modified into different shapes, size and structure Perennation is a process in plants
to perform some special functions such as perennation, that is why they can survive during
vegetative propagation, storage, food production, etc. unfavourable conditions.
FACT WITH REASON
In sugarcane, roots are developed from the base of the stem, why?
In sugarcane, roots are developed from the base of the stem because sugarcane reproduce asexually
through stem called vegetative propagation.
222 Living Beings
a) Underground modification to store food
In some plants, the underground parts have the characteristics of stem. They have nodes
and internodes, scales, adventitious roots at the nodes, etc. These underground stems
are modified for perennation, vegetative propagation, food production and storage, etc.
Some modified underground stems are given below:
Garlic Ginger Onion Potato
i) Rhizomes: Rhizomes are underground modified stems. They bear nodes and
store food. Examples of rhizomes are ginger, grass and canna.
ii) Tuber: Tubers are the fleshy swollen parts of the underground stem. They store
food in winter season and produce new growth in spring season. In these stems,
there are buds. These buds are popularly known as eyes. For example: potato,
yam, etc.
iii) Corm: Corm is an underground stem. It bears leaves. Saffron, gladiolus, etc. are
its examples.
iv) Bulb : It is a modified underground stem. It occurs in the form of disc-like
structure. It bears fleshy leaves which store food.Examples: onion, lilies, etc.
b) Sub-aerial modification for reproduction
The sub-aerial stems are weak and unable to stand straight. These stems are usually
modified for the purpose of vegetative propagation. Some modifications in sub-aerial
stem are given below.
Dog’s tooth grass Menthe Pistia
i) Runner: Runners are modified stems produced from the auxiliary buds.
They spread in all directions. They are slim and horizontal branches with long
internodes. They creep on the ground. Adventitious roots are developed at their
nodes.Examples: Oxalis, marsilea, dog grass, etc.
ii) Stolon: It is a branch developed at the base of the stem under the soil. It first
grows upwards and then bends downwards to meet the soil. A common example
is Menthe plant.
Modern Concept Science and Environment – 8 223
iii) Offset: This type of modification is found in aquatic plants like Pistia. Just like a
runner,offset develops from the leaf axil and grows horizontally up to the some
extent. It bears a bunch of leaves upwards and adventitious roots downwards.
After sometimes, it detaches from the mother plant and grows independently.
iv) Sucker: Like a stolon, sucker is produced from the underground part of the stem.
But it is much shorter. The sucker grows obliquely upwards bearing adventitious
roots. It produces leafy shoot when reaches to the soil surface. For example:
chrysanthemum.
c) Aerial modification to support the plant
Stem is known as the aerial part of a plant. Some of these aerial stems are modified to
support the plant. Tendrils are the aerial modification in the stem of climbers. They are
long, thin, coiled and spring shaped in structure. Tendrils are the organs of attachment
for the certain climbing plants. Examples: grapes, cucumber, pumpkin, cucurbits, etc.
Grapes Cucumber Pumpkin
d) Aerial modification to protect the plant
In some plants like orange, lemon, cactus, etc. have needle shaped, hard, thick, straight,
deep seated and pointed defensive organs called thorns. They are the modification in
stem for protection.
Cactus Lemon Orange
e) Aerial modification for reproduction
Bulbil is a structure that develops at the leaf axil. It is a modification
of vegetative bud or floral bud. It is a multicellular structure
for vegetative propagation. It sheds from the mother plant and
grows up into a new independent plant. For example: dioscorea
f) Aerial modification to store food and water Dioscorea
Some desert plants like cactus, opuntia, aloe, etc. have thick and
fleshy stem. Their stems look like leaves and leaves modified into
224 Living Beings
needle shaped structure. These stems have chlorophyll and perform photosynthesis. In
these plants, stems store food and water.
Cactus Opuntia Aloe vera
FACT WITH REASON
The stems of cactus, opuntia, aloe, etc. have thick and fleshy leaves, why?
The stems of cactus, opuntia, aloe, etc. have thick and fleshy leaves because these stems are modified
to store food and water. They also contain chlorophyll and perform photosynthesis.
Modification of leaves
Leaves are the flat structures that develop from the nodes of the stem or branch. Most of the
leaves have green colour due to chlorophyll. The primary function of leaves is photosynthesis.
They also help in breathing and transpiration. But in some plants, the whole leaves or parts of
leaves are modified for special functions. For example, the leaves of some plants are modified
for climbing, attachment, storage, protection against predation or climatic conditions, trapping
and digestion of insects, etc. There are following modification in the leaves.
Agava Bryophyllum Peas
a) Modification of leaves to check water: In a dry environment, leaves of some plants
either reduced like in cactus or become succulent. The reduced and succulent leaves
retain water by decreasing transpiration. Examples: cactus, agave, aloe, etc.
FACT WITH REASON
Some plants bear thorns, or small leaves, why?
The thorns or small leaves reduce the loss of water from plants by transpiration. So, some plants bear
thorns or small leaves.
b) Modification of leaves for defence : Stipules of some plants are modified into spines.
These spines act as defensive organs. For example, the non-photosynthetic leaves of
cacti have modified for defence.
Modern Concept Science and Environment – 8 225
c) Modification of leaves for climbing : In plants like peas, the terminal leaflet of the leaf
modify into tendril. These tendrils lock themselves to the substratum and help in climbing.
d) Modification of leaves for reproduction : The leaves of some plants are modified for
reproduction. For example: the leaves of Bryophyllum, Kalanchoe, African violets, etc.
grow into new plants under favourable conditions.
e) Modification of leaves for nutrition absorption: Some plants like bladderwort, Pitcher
plant, Venus flytrap, Sundew, etc. are insectivorous plants. The leaves of Bladderwort
trick small animals like daphnia and larval fish for their food. Pitcher plants, Venus fly
trap, Sundew, etc. are adapted in nitrogen poor soil. Hence, they trick insects to fulfil
nitrogen requirements.
Pitcher plant Venus flytrap Sundew
16.7 Seed
A seed is a ripened ovule of a flowering plant. The seeds of different plants have different
shape, size, colour and number. Seeds of angiosperm are enclosed in the fruit while in
gymnosperm seeds are exposed on the scales of the cones. Cotyledons are the germinating
leaves inside seed.
Types of seeds (on the basis of cotyledons)
On the basis of number of cotyledons, seed are of two types. They are:
a) Monocotyledonous seeds
b) Dicotyledonous seeds
a) Monocotyledonous seed: The plants having one cotyledon in their seed are called
monocotyledonous plants. Wheat, oats, rye, maize, paddy, grasses, etc. are some
examples of monocotyledonous plants. Monocotyledonous plants have long and
slender leaves with parallel venation. They have fibrous or adventitious roots.
Maize seeds Wheat seeds Paddy seeds
226 Living Beings
Structure of a monocotyledonous seed
A monocot seed consists three major parts. They are testa, endosperm and embryo.
Testa: Testa is a tough and hard outer coat of the seed. It protects the seed from fungi,
bacteria and insects. Testa
Endosperm: Below the testa there is a major part of the
seed called endosperm which is filled with reserve food
materials. Endosperm is a source of nutrients for the Cotyledon
embryo. Inner starchy layer of the endosperm separates it Plumule
from embryo. Radicle
Embryo: Embryo is a baby plant that germinates in
favourable condition. It contains a single cotyledon. It
consists of three parts: radicle, plumule, and Epicotyl/ Structure of a maize seed
hypocotyl.
i) Radicle (young root): Radicle is the embryonic root. The part of an embryo which
develops into the plants primary root is called radicle. It is present at the basal tip
of hypocotyl.
ii) Plumule (young shoot): Plumule is the embryonic shoot. The part of an embryo
which develops into the shoot and first true leaves of a plant is called plumule. It is
present at the tip of epicotyl.
iii) Epicotyl/ hypocotyl: Epicotyl is the part of an embryo above the point of attachment
of the cotyledon(s). The part of an embryo below the cotyledon attachment site is
called the hypocotyl. Depending on the type of germination, one of these sections
will be the first to emerge out of the soil. Memory Tips
Micropyle, hilum and hypocotyl are not clearly visible There is one cotyledon in monocot,
in monocot seed. In case of maize seed, plumule faces two cotyledons in dicot and one or
towards the upper wider end of the seed while radicle more cotyledons in gymnosperms.
faces towards the narrow end of the seed. During
seed germination, radicle develops into root and plumule develops into shoot.
b) Dicotyledonous seeds
The plants having two cotyledons in their seed are called dicotyledonous plants.They
are also called dicotyledons or dicots. Large groups of plants are docotyledons. Gram,
pea, soayabean, mustard, mango, apple, orange, plum, etc. are few examples of dicots.
Doicot plants have short leaves with reticulate venation. They have taproot system.
Seed of pea Seed of mango Seed of pumpkin
Modern Concept Science and Environment – 8 227
Structure of a dicotyledonous seed
Some major parts of a dicotyledonous seed are described below:
Testa: The seed is covered with a tough protective outer covering called testa. The testa
is very thin in some plants like pea nut whereas it is hard and thick in coconut, walnut,
peach, etc. Cotyledon Testa
Tegmen: In flowering plants, there is thin and Radicle Tegmen
membranous covering inside the testa called Plumule
tegmen.
Endosperm: Endosperm is absent in most of the Epicotyl
dicotyledonous seeds. Hypocotyl
Structure of a gram seed
Cotyledons: A cotyledon is the seed leaf. It lies below the testa in non-endospermic
seeds. In dicotyledons there are two cotyledons. Depending on the type of germination,
the cotyledon may remain below the ground or be pulled above ground. Cotyledons
often contain reserve food which is used during the early stage of the germination. In
most of the plants the cotyledons are brought out of the testa above the ground. They
become green and make food by photosynthesis.
Hilum: The scar left by stalk which attaches the ovule with the wall of ovary is called
hilum.
Micropyle: A tiny pore in the testa opposite to the tip of the radicle is called micropyle.
It allows water to enter into the embryo before active germination.
Embryo: An embryo is the immature plant which will grow within the seed. The radicle
is the embryonic root which grows and develops into the root system of the plant. The
plumule is the embryonic shoot. It grows into the shoot system. Hypocotyl which is
present between the plumule and radicle grows into stem.
Differences between monocotyledonous seed and dicotyledonous seed.
SN Monocotyledonous seed SN Dicotyledonous seed
1 Monocotyledonous seed contains single 1 Dicotyledonous seed contains two
cotyledon. cotyledons.
2 The cotyledon of this seed is thin and 2 The cotyledons of this seed are large and
small which lacks food material. store food materials.
3 Seeds are endospermic. 3 Seeds are non-endospermic.
4 Micropyle and hilum are not visible. 4 Micropyle and hilum are visible.
5 Plumule is small in size. 5 Plumule is large in size.
Types of seeds (on the basis of endosperm)
On the basis of food storage tissues, there are two types of seeds. They are:
a) Endospermic seeds
b) Non-endospermic seeds
228 Living Beings
a) Endospermic seeds : The seeds in which food is stored in endosperm are called
endospermic seeds. All monocot seeds are called endospermic seeds. Examples: Seeds
of wheat, maize, rice, bajra, barley, etc.
b) Non-endospermic seeds : The seeds in which food is stored in cotyledons are called
non-endospermic seeds. All dicot seeds (except castor) are called non-endospermic
seeds. Examples: Seeds of pea, gram, orange, apple, soyabean, etc.
ACTIVITY 2
1. Collect some seeds of plants from your home and surrounding.
2. Keep these seeds in water for about one day.
3. Try to separate out these seeds into equal parts.
4. On the basis of structure, classify these seeds into :
a. Monocot seeds and dicot seeds. b. Endospermic seeds and non-endospermic seeds.
Functions of seeds
The major functions of the seed are given below:
a) Seed protects embryo
Seeds are covered with a tough outer covering called testa. Embryo is present inside the
seed. Seed coat protects embryo from various injuries and microorganisms. Due to this
reason seeds can remain dormant for a long time.
b) Seed provides nourishment to the embryo
Seed contains endosperm and cotyledons in it. Endosperms and cotyledons store food
materials for the development of embryo.
c) Seed helps in dispersal of seed itself
Some seeds are modified for easy dispersal. Some seeds can float easily in air and water.
Some seeds cannot be digested by animals. Some seeds are carried easily by animals,
birds, insects, etc. As a result, it becomes easy in dispersal.
d) Seed helps in germination
Seed helps in germination of a plant. The germinated seed develops into a new plant
and continue its life cycle.
Dispersal of seeds
Dispersal of seed means distribution or scattering of seeds away from the position of their
origin. Seeds need favourable environmental condition to germinate. So, they have tendency
to disperse in search of favourable conditions. Fruits or seeds are modified in various shapes
and sizes to help in dispersion. Different modes of dispersion of seeds are given below:
a) Dispersal of seeds by wind
The seeds of pine, simal, orchids, grass, milkweeds cotton,
dandelion, etc. have wings or hairy structures or dusty seeds.
They disperse here and there by wind.
Seeds of dandelion
Modern Concept Science and Environment – 8 229
b) Dispersal of seeds by water
Seeds of some plants like coconut, water lily, lotus, betel nut, mucuna,
dioclea, etc. have buoyant seeds that float in water. Seeds of these plants
do not decay in water for a long time. These seeds are dispersed by water
to search favourable condition.
c) Dispersal of seeds by animals Seeds of coconut
Some seeds are dispersed through animals and birds. They have
hooks or sticky structures on their surface. Seeds of acaena, burdock,
tomato, guava, apple, etc. attach to the fur of animal, clothes of
human beings, feathers of birds and disperse from one place to
another. Seeds of fleshy fruits are eaten by animals and dispersed
from one place to another. Round seeds like acorns, hazelnuts,
walnuts, etc. are rolled down by animals and reach far away from Dispersal by animal
their origin.
d) Mechanical dispersal of seeds
Some seeds are dispersed by their mechanical bursting. Examples:
Seeds of mustard, peas, sesame, Tiuri, Aalas, etc.
e) Dispersal of seeds by human beings Seeds of Pea
Human beings transport different kinds of fruits and seeds from one
place to another place and from one country to another country. It is a major method of
dispersal of seeds in wide range of distance.
Germination of seed
After dispersal of seeds, if the environmental conditions are suitable then the embryo gets
activated. It uses the stored food in the seed and begins to grow into a new seedling or young
plant. The development of a seed into a young plant is called germination of seed. If a seed
does not get suitable conditions for germination immediately, it will not die. It germinates
only when the conditions become suitable. Seeds survive in a resting state. Such a resting
period of seeds is called dormancy. Dormancy of a seed will continue if the embryo in the
seed does not experience the suitable conditions.
Conditions necessary for seed germination
Water, air and suitable temperature are necessary for seed germination.
Process of seed germination
The first step in the process of seed germination is absorption of water. When conditions are
suitable the seed starts to take in water. As water is taken in, the seed swells bigger and bigger
until the testa (coat) splits apart. Water and oxygen enter through gaps in the testa. Oxygen
and glucose enable aerobic respiration, which releases energy. The embryo is able to grow as
it receives raw materials and energy.
Types of seed germination
There are two types of seed germination: epigeal germination and hypogeal germination.
a) Epigeal germination
In this type of germination, the hypocotyl elongates rapidly upward pulling the
cotyledons above the soil. The type of germination where cotyledons emerge out of
230 Living Beings
the soil is called epigeal germination. The cotyledons turn green and act as the first
leaves of the young plant. These leaves are called foliage leaves. Photosynthesis takes
place in these leaves. They give the baby plant energy, until it gets its own leaves
for photosynthesis. The energy for growth is primarily derived from cotyledon. For
example, seed of bean, cotton, papaya, gourd, castor, etc. have epigeal germination.
b) Hypogeal germination
In this type of germination, the epicotyl elongates and the cotyledons remain below
the soil. The type of germination where cotyledons remain inside the soil is called
hypogeal germination. In hypogeal germination, the cotyledons do not have any role in
photosynthesis. The energy for growth is primarily derived from endosperm. For example,
seeds of pea, mango, maize, rice, gram, groundnut, etc. have hypogeal germination.
Epicotyl
Cotyledon Epicotyl
Hypocotyl Hypocotyl
Cotyledon
Hypocotyl
Epigeal germination Hypogeal germination
ACTIVITY 3
OBJECTIVE : To show the conditions necessary for germination of seeds.
REQUIREMENT : Three bean seeds, glass slide, thread, beaker, water
METHODS : Seed in air
1. Tie three bean seeds at three different places on a glass Seed
slide with the help of a thread. partially in
water
2. Keep that slide in a beaker with water in such a way that Seed Water
one seed is completely immersed in water, the middle one inside
water
is half immersed in water and upper one is in air.
3. Leave this experiment for 3 to 4 days.
OBSERVATION: After 3 to 4 days, we can observe that germination has occured in the middle seed only.
RESULT: The middle seed has germinated because it got air, water and favourable temperature.
CONCLUSION: This experiment shows that, air, water and temperature are the necessary conditions
for the germination of a seed.
FACT WITH REASON
A seed enclosed in an air tight bottle or inside water does not germinate, why?
Seeds need suitable amount of air, water and heat to germinate. A seed enclosed in a bottle does not
get water and a seed inside water does not get air. So, a seed enclosed in an air tight bottle or inside
water does not germinate.
Modern Concept Science and Environment – 8 231
16.8 Life cycle of a flowering plant
Plants that bear flowers in them are called flowering plants. Similar to the other organisms,
flowering plants also complete their life cycle. Most of the flowering plants reproduce by
means of sexual reproduction. However, science and technology also discovered different
kinds of artificial vegetative propagation in plants such as layering, grafting, tissue culture,
etc. In flowering plants, flower is the main reproductive organ. Flowers of one kind of plants
are the same in structure but different plants have different kinds of flowers in terms of shape,
size, colour and odour. A flower having both male and female reproductive parts in the same
flower is called a bisexual flower. The flower having only one reproductive part is called
unisexual flower. Flower produces fruit which contains one or more seeds. Seed germinates
into a new plant. This whole process is called life cycle. Thus, life cycle of an organism is a
series of changes that an organism spends to develop from its embryonic stage to its maturity.
Flower
Flower is a colourful and the most attractive part of plant. Different types of flowers have
different shape, size and colour. Most of the flowers have very sweet and pleasant smell. Due
to the colour and smell of the flowers bee, butterfly, animals, birds, insects, etc. are attracted
towards them.
Structure of a flower Anther Stigma
A plant can have many flowers as it matures. All the flowers Filament Style
present in a plant have common shape, size and colour. But
different flowers present in different plants may have different Petal
shape, size and colour. A flower is attached with the stem or Ovary Sepal
branch of the plant with the help of a stalk called pedicel. Most of
the flowers have pedicel. Pedicel may be absent in some flowers.
In a flower, there is a basal swollen part called thalamus. On the
thalamus, different parts of the flower are arranged in a ring called whorl. A complete flower
has four whorls. They are calyx, corolla, androecium and Memory Tips
gynoecium.
The flower containing all four parts
a) Calyx : Calyx is the outermost whorl of the flower. It i.e., calyx, corolla, androecium and
is generally green in colour. Calyx is present at the gynoecium is called a complete
base of a flower. Each individual part of the calyx is flower. Similarly, the flower which
called a sepal. Calyx protects the flower in bud stage does not contain all four parts is
and prepares food by photosynthesis. In some flowers
the sepals are free called polysepalous and in some called an incomplete flower.
flowers the sepals are fused called gamosepalous.
calyx
Sepal
epicalyx
Different types of calyx
232 Living Beings
b) Corolla: Corolla is the second whorl of a flower. It is made up of colourful and attractive
structures called petals. Petals may have scent. Due to colourful structure and unique
scent, corolla attracts insects and birds for pollination. Corolla also protects the flower.
In some flowers, petals are free called polypetalous and in some flowers petals are fused
called gamopetalous.
petal
limb
claw
Different types of corolla
c) Androecium : Androecium is the third whorl of the flower. It is a male reproductive
part of the flowering plants. Androecium consists of one or more stamens. Each stamen
is made up of swollen anther and a long and filamentous stalk called filament. The
anthers are the orange or yellow structures often seen at the centre of a flower. Each
anther is made up of four pollen sacs which are connected by a connective tissue.
Matured anther produces fine, powdery structures called pollen grains. Pollen grains
are the male gametes of the flower. They are transferred from the anther of one flower
to the stigma of the same or different flower by insects, wind, water or animals.
anther pollen
connective
anther
filament nectar gland
Different types of androecium
d) Gynoecium : Gynoecium is the innermost whorl of the flower. It is the female
reproductive part of a flower. It consists of one or more pistils (carpels). A pistil is made
up of an ovary, style and stigma. Ovary is the swollen basal part of the pistil. It contains
ovule. On maturity, ovule develops female gamete called ovum or egg. A long tubular
structure extended from the ovary is called style. At the top of the style, there is a flat
surface which receives pollen grains is called the stigma.
Stigma
Style
Ovary Placenta
Ovule
Different types of gynoecium
Modern Concept Science and Environment – 8 233
16.9 Pollination
When a flower becomes mature, androecium releases pollen grains form its anther. These
pollen grains reach to the stigma of the flower by various agents called pollination. Thus,
pollination is a process of transfer of pollen grains (male gametes) from the anther to the
stigma of a flower. It can be done by the various external agents like insects, wind, birds,
animals, water, etc. Insects are the most common agents that help in pollination. Pollination is
of two types. They are self-pollination and cross pollination.
a) Self-pollination
The process of transfer of pollen grains (male gametes) from the anther to the stigma of
the same flower or different flower of the same plant is called self-pollination.This process
is common in bisexual flowers where pollinating agents are not effective. Examples: pea,
mustard, china rose, etc.
b) Cross pollination
The process of transfer of pollen Self-pollination Self-pollination
grains (male gametes) from the
anther to the stigma of the different Cross-pollination
flower of the different plants is
called cross-pollination. Cross Pollination
pollination is common in bisexual
as well as unisexual flowers where
pollinating agents like air, water,
insects, animals, etc. are effective.
Examples: cucumber, pumpkin,etc.
Differences between self-pollination and cross-pollination.
SN Self-pollination SN Cross-pollination
1 The process of transfer of pollen grains 1 The process of transfer of pollen grains
(male gametes) from the anther to the (male gametes) from the anther to
stigma of the same flower or different the stigma of the different flower of
flower of the same plant is called self- the different plants is called cross-
pollination. pollination.
2 This pollination is common in bisexual 2 This pollination is common in bisexual
flowers where pollinating agents are not as well as unisexual flowers where
effective. Examples: pea, mustard, china pollinating agents like air, water, insects,
rose, etc. animals, etc. are effective. Examples:
cucumber, pumpkin, etc.
FACT WITH REASON
Some insects like the honey bee are the helpers of the farmers, why?
Insects like honey bees help in pollination. As a result, crops are produced easily.
234 Living Beings
16.10 Fertilization
Fertilization is a process of union of a male gamete and a female gamete to form a zygote. The
male and female gametes are haploid (n), so the zygote formed after their fusion is diploid (2n)
in nature. After pollination, the pollen grain germinates forming a pollen tube. The nucleus of
the pollen tube controls the growth of the pollen tube.The growth of pollen tube is an example of
chemotropism since it is growing toward the chemicals produced from the ovule. The haploid
male nucleus moves downwards through the pollen tube. In the course of its movement, it
undergoes mitosis cell division and forms two haploid male nuclei. The pollen tube enters
into the ovule through the micropyle and releases male gametes into the embryo sac. Now, the
tube nucleus disintegrates. In the embryo sac, one male gamete fuses with egg cell(ovum) to
form zygote (2n) while other male gamete fuses with secondary nucleus to form an endosperm
nucleus (3n). Therefore, the fertilization in flowering plants is called double fertilization.
FACT WITH REASON
The fertilization in flowering plants is called double fertilization, why?
In the embryo sac of the flowering plants, one male gamete fuses with egg cell (ovum) to form zygote
(2n). Similarly, another male gamete fuses with secondary nucleus to form an endosperm nucleus
(3n). Therefore, the fertilization in the flowering plants is called double fertilization.
Germinated pollen grain
Mature plant with Anther at tip of stamen Zygote
flowers Pollen tube Embryo
Ovary (base or carpel)
Seedling Ovule
Embryo sac
Simple fruit
Egg (develops from
Sperm ovary)
Germinating seed Seed
Seed (develops
from ovule)
Fertilization
Changes in the flower after fertilization
After fertilization, the ovary turns into fruit and the fertilized ovule becomes a seed. The
integument becomes the wall of the seed called testa. The micropyle closes. The endosperm
nucleus divides and forms an endosperm which is a food tissue. The diploid zygote divides
Modern Concept Science and Environment – 8 235
mitotically and develops into a baby plant called an embryo. The developing embryo draws
nourishment from the endosperm. Now, the embryo stops developing and goes into dormancy.
After getting favourable conditions the seed germinates into a new plant. In this way, the life
cycle of a flowering plant completes.
Differences between pollination and fertilization.
SN Pollination SN Fertilization
1 Pollination is a process of transfer of 1 Fertilization is a process of union of
pollen grains (male gametes) from the male gamete and female gamete to form
anther to the stigma of a flower. a zygote.
2 It occurs before fertilization. 2 It occurs only after pollination.
ANSWER WRITING SKILL
1. What is a cell without developed nucleus called?
Ans: A cell without developed nucleus is called a prokaryotic cell.
2. Which organism contains mycelium?
Ans: Fungi such as mushroom, mucor, etc. contain mycelium.
3. What is a complete flower?
Ans: The flower which has all four whorls such as calyx, corolla, androecium and gynoecium is called a
complete flower. For example, flower of a mustard plant.
4. What are unisexual and bisexual flowers?
Ans: The flower which has either male (androecium) or female (gynoecium) part of the flower is called a
unisexual flower. Similarly, the flower which has both male and female parts of the flower is called
a bisexual flower.
5. Write down any three functions of a fruit.
Ans: The three functions of fruits are:
i) Fruit stores food for a seedling.
ii) Fruit protects seeds from insects and germs.
iii) Fruit helps in dispersal of seeds.
6. How are seeds dispersed?
Ans: Seeds are dispersed by different agents such as air, water, animals, birds, human beings, etc.
7. Write any two differences between radicle and plumule.
Ans: Differences between radicle and plumule are:
S.N. Radicle S.N. Plumule
1 Radicle is an embryonic root. 1 Plumule is an embryonic shoot.
2 It develops root and root hairs. 2 It develops stem and leaves.
236 Living Beings
8. Write any two differences between bacteria and fungi.
Ans: Differences between bacteria and fungi are:
S.N. Bacteria S.N. Fungi
1 Bacteria are prokaryotic organisms. 1 Fungi are eukaryotic organisms.
2 They show both autotrophic and 2 They show only heterotrophic nutrition.
heterotrophic nutrition.
9. Write any two differences between androecium and gynoecium.
Ans: Differences between androecium and gynoecium are:
S.N. Androecium S.N. Gynoecium
1 It is the male reproductive organ of a flower. 1 Itisthefemalereproductiveorganofaflower.
2 It has stamen. 2 It has carpels.
10. Some seeds contain fluffy parachute like structure, why?
Ans: Some seeds contain fluffy parachute like structures. These are modification of seeds. As a result,
these seeds become light to be dispersed by the wind.
STEPS EXERCISE
STEP 1
1. Fill in the blanks with appropriate words.
a) ………… is a connecting link between living and non-living entities.
b) Yeast reproduces by ……………
c) ………… are the adventitious roots that arise from the upper part of stem.
d) Bulb of onion is an example of underground modification of ……….
e) Rhizome is an example of ………. modification of ………..
f) ………… is the part of an embryo above the point of attachment of the cotyledon(s).
2. Write True for the correct and False for the incorrect statements.
a) A bacteriophage infects bacteria.
b) Bacteria are prokaryotic organisms.
c) Fungi are autotrophic organisms.
d) Bacteria are responsible for many diseases.
e) Stamen is a female reproductive part of a flower.
f) Zygote is a haploid(n) structure.
g) Embryo is a baby plant.
3. S elect the best answer from the given alternatives.
a) Which is the group of symbiotic bacteria?
i) Cyanobacteria ii) E. coli
iii) Salmonella typhi iv) Rhizobium
Modern Concept Science and Environment – 8 237
b) Which is an example of prokaryotic organism?
i) Bacteria ii) Yeast iii) Ameoba iv) Mushroom
c) Which plant uses roots to respire?
i) Cactus ii) Vanda iii) Banyan iv) Rhizophora
d) Which plant has modified underground stem to store food?
i) Cactus ii) Potato iii) Corn iv) Pea
e) Which part of the seed allows water to enter inside the embryo?
i) Hilum ii) Cotyledon iii) Micropyle iv) Plumule
4. Match the following.
a) Carrot i) Fungi
b) Mushroom ii) Modified root
c) Tendril iii) Catch insect
d) Pitcher plant iv) Embryonic shoot
e) Plumule v) Embryonic root
f) Radicle vi) Cucumber
STEP 2
5. Answer the following questions in one word.
a) Name a fungus which is unicellular.
b) What is a cell without developed nucleus called?
c) Write down full form of TMV.
d) Which fungus does not contain mycelium?
e) Name any two plants whose underground stem modified to store food.
f) Write down any two plants which catch insects.
g) What is the female reproductive part of a flower called?
6. Write any two differences between:
a) Bacteria and virus
b) Bacteria and fungi
c) DNA virus and RNA virus
d) Endospermic seeds and non-endospermic seeds
e) Monocot seed and dicot seed
f) Plumule and radicle
g) Epigeal germination and hypogeal germination
h) Pollination and fertilization
i) Self-pollination and cross pollination
j) Stamen and pistil
7. Give reasons.
a) Viruses are called borderline organisms.
b) Viruses are called obligatory parasites.
238 Living Beings
c) Some seeds contain fluffy parachute-like structures.
d) Aquatic plants have spongy roots.
e) Parts of plants modify into different structures.
f) Desert plants have fleshy and green stem.
g) Fertilization in flowering plants is called double fertilization.
8. Write down the name of the following organisms and mention any two characteristics of each.
a) b) c) d)
STEP 3
9. Answer the following questions.
a) What are bacteria? Write down any five characteristics of bacteria.
b) Describe different kinds of bacteria with the help of examples.
c) Describe the structure of bacteria with diagram.
d) Explain economic importance of bacteria.
e) What are viruses? List the living and non-living characteristics of a virus.
f) Classify viruses on the basis of host.
g) What are TMV and bacteriophage?
h) Classify viruses on the basis of genetic materials.
i) What are fungi? Write down any four characteristics of fungi.
j) Explain economic importance of fungi.
k) What do you mean by modification of parts of plants?
l) Explain the underground, sub-aerial and aerial modification of stems with at least
one example of each.
m) Describe the different modifications of roods with examples.
n) Explain the modification of leaves.
o) Explain the structure of monocot and dicot seeds.
p) What is dispersal of seed? Explain the different agents which help in dispersal seeds.
q) List the major functions of a seed.
r) What is germination? Explain an experiment to demonstrate that water and air
are necessary for the germination of seed.
s) Describe the structure of a complete flower.
t) Explain how fertilization occurs in flowering plants.
10. Draw the labelled diagrams for the following. Dicot seed
a) Bacteria b) Bacteriophage virus c) Gynoecium
d) Monocot seed e) Androecium f)
g) Complete flower
UNIT Estimated teaching periods Theory MPoradecrtnicCaolncept Science and Environment – 8 239
6 3
17
Cell and Tissue
Syllabus issued by CDC Robert Hooke
Introduction to cell and tissue
Animal tissue
Epithelial tissue and its types
Plant tissue
Meristematic tissue and its types
Interrelationship among cell, tissue and organ in human body
LEARNING OBJECTIVES
At the end of this unit, students will be able to:
Introduce cell and tissue.
Introduce different types of animal tissues.
Describe different types of epithelial tissues present in human body.
Introduce different types of plant tissues.
Describe different types of meristematic tissues present in plant.
Explain interrelationship among cell, tissue and organ in human body.
Key terms and terminologies of the unit
1. Cell : Cell is the basic, structural and functional unit of life which is capable of independent
existence.
2. Cytology : The branch of biology which deals with cell is called cytology.
3. Tissue : The group of large number of specialized cells with a common origin and similar
structure and function is called tissue.
4. Histology : The study of tissues and their function is called histology.
5. Animal tissue : Tissues that are found in the body of animal are called animal tissue.
6. Epithelial tissue : Epithelial tissue (Epithelium) is a thin protective tissue which is made up one or
more layers of cells covering internal and external body organs.
7. Pavement epithelium : The single-layered, thin epithelial tissue which has cells with centrally placed
nucleus is called pavement epithelium or squamous epithelium.
8. Cubical epithelium : The single-layered, epithelial tissue which has cubical cells with similar dimensions
is called cubical epithelium.
9. Columnar epithelium : The single-layered, epithelial tissue which has column-shaped elongated cells is
called columnar epithelium.
10. Glandular epithelium : The columnar epithelium with goblet cells is called glandular epithelium.
11. Stratified epithelium : The epithelium which is composed of several layers of cells to withstand from wear
and tear is called compound or stratified epithelium.
240 Cell and Tissue
12. Sensory epithelium : The modified form of columnar epithelium which consists of elongated cells with
sensory hairs on their free surface is called sensory epithelium.
13. Plant tissue : Tissues that are found in the body of plants are called plant tissue.
14. Meristematic tissue : The simple and undifferentiated plant tissue which has actively dividing cells is
called meristematic tissue.
15. Apical meristem : The meristematic tissue which is present at the tip of root, stem and branch is
called apical meristem.
16. Lateral meristem : The meristematic tissue which is present along the side of the root and stem is
called lateral meristem.
17. Intercalary meristem : The meristematic tissue which is present at the base of leaf, fruit, internode, etc. is
called intercalary meristem.
18. Organ : Organ is a group tissues working together for a particular function.
19. System
: A system is a group of specialized organs working together to achieve a major
physiological function.
17.1 Introduction
Cell is the basic, structural and functional unit of life which Memory Tips
is capable of independent existence. It is a microscopic Cell is derived from the Latin word
unit. Each and every cell of the living body is capable of cella, means compartments.
conducting various processes required in the body. The
cell is a building block unit of the multicellular organisms. Different types of cells have
different shape, size and structure depending upon their function. Cell was first discovered
by Robert Hooke in 1965 AD while observing the thin slice of wooden cork under his own
made microscope. In the slice, he observed different rectangular to hexagonal honey comb
like compartments over there and named them cells. The branch of biology which deals with
cell is called cytology.
Pinocytotic vesicle Mitochondrion Ribosome Cell wall
Lysosome Golgi apparatus Cell membrane
Nucleolus Smooth endoplasmic Golgi apparatus
Rough endoplasmic reticulum (ER) Chloroplast
reticulum (ER) Nucleus Nucleolus Vacuole membrane
Smooth ER Nucleus
Rough (ER) Raphide crystal
Cell membrane Druse crystal
Centrioles Mitochondria
Large central vacuole Cytoplasm
Microtubules
Cytoplasm
Ribosome
Animal cell Plant cell
A cell is composed of different organelles like cell wall, cell membrane, cytoplasm, plastids,
mitochondria, vacuoles, nucleus, ribosomes, endoplasmic reticulum, Golgi bodies, etc. Each
organelle has its own function in the cell. All these cell organelles work together to make a cell
living. In animal cell, the cell organelles like plastids and cell wall are absent.
Modern Concept Science and Environment – 8 241
FACT WITH REASON
Why do cells have different size and shape?
Cells have different shapes and sizes because they are found in different parts of the body and
specialized for different functions.
17.2 Tissue
The group of large number of specialized cells with a common origin, similar structure and
function is called tissue. The cells of a tissue have related intercellular substances. Each tissue
has the cells which are originated form the common parents. The cells of the tissue have more
or less same shape, size and structure. Their arrangement is also the same. So, the cells of
a tissue are organized to perform a particular function. There are different types of tissues
in animals and plants. Examples: epithelial tissue, muscular tissue, connective tissue, blood,
meristematic tissue, xylem, phloem, etc. The group of specialized tissues makes organs and
group of associated organs make the body. The study of tissues and their function is called
histology. Broadly, the tissues are categorized into two types. They are animal tissues and
plant tissues.
FACT WITH REASON
Blood is called a tissue, why?
Blood is called a tissue because it consists of a group of cells having a common origin and perform
similar functions. Blood is also called a connective tissue because it connects different tissues in the
body.
Differences between cells and tissues.
SN Cells SN Tissues
1 Cell is the structural and functional 1 Group of large number of specialized
unit of life. cells with similar structure and function
is called tissue.
2 The study of cell is called cytology. 2 The study of tissues is called histology.
3 Cells make tissue. 3 Tissues make organ.
17.3 Animal Tissue
The tissues that are found in the body of animals are called animal tissues. On the basis of
structure and function, animal tissues are classified into following four types. They are:
i) Epithelial tissue ii) Muscular tissue Memory Tips
iii) Connective tissue iv) Nervous tissue Connective tissue holds other
different kinds of tissues together in
various ways. For example, blood.
242 Cell and Tissue
Animal tissue
Epithelial tissue Muscular tissue Connective tissue Nervous tissue
Pavement epithelium Voluntary muscle
Cubical epithelium Involuntary muscle
Columnar epithelium Cardiac muscle
Glandular epithelium
Sensory epithelium Soft connective tissue Hard connective Fluid connective
tissue tissue
a) Epithelial tissue Fibrous tissue
Adipose tissue Cartilage Blood
Bones Lymph
Epithelial tissue (Epithelium) is a thin protective tissue which is made up one or more layers
of cells covering internal and external body organs. It is specialized with the cells of closely
packed and arranged in one or more layers. It makes the covering or lining of all internal and
external body surfaces. The epithelial tissue that occurs in the interior surface of the body
organs is known as endothelium. The tissue that line the interior surface of blood vessels is
an example of endothelium.
Characteristics of the epithelial tissue
i) The cells of epithelial tissue generally have large nuclei, clear outline and a large amount
of granular protoplasm.
ii) Epithelial cells are packed tightly together with almost no intercellular spaces.
iii) Epithelial tissue is usually separated from the underlying tissue by a thin sheet of
connective tissue called basement membrane.
iv) Epithelial tissues do not contain blood vessels.
v) The free surface of the epithelial tissue may be smooth or may have hair-like cilia or microvilli.
Functions of the epithelial tissues
a) Protection
Epithelial tissue protects underlying tissue from mechanical injury, harmful chemicals,
invading bacteria and from excessive loss of water.
b) Sensation
The sense organs like skin, eyes, ears, nose, tongue, etc. contain sensory epithelial
tissues. It receives sensory stimuli.
c) Secretion
The glandular epithelial tissue is specialized to secrete specific chemical substances
such as enzymes, hormones, lubricating fluids, etc.
The words you are searching are inside this book. To get more targeted content, please make full-text search by clicking here.
Science book class 8
Discover the best professional documents and content resources in AnyFlip Document Base.
Search