NCERT Solutions Class 9. 203 Pages. Free Flip-Book by Study Innovations

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If α-particle scattering experiment is carried out using a foil of any metal
as thin as gold foil used by Rutherford, there would be no change in
observations. But since other metals are not so malleable so, such a thin
foil is difficult to obtain. If we use a thick foil, then more α-particles
would bounce back and no idea about the location of positive mass in
the atom would be available with such a certainty.

1. Name the three sub-atomic particles of an atom.

Answer

The three sub-atomic particles of an atom are:
(i) Protons
(ii) Electrons, and
(iii) Neutrons

2. Helium atom has an atomic mass of 4 u and two protons in its
nucleus. How many neutrons does it have?

Answer

Number of neutrons = Atomic mass - Number of protons
Therefore, the number of neutrons in the atom = 4 - 2 = 2

Page No: 50

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1. Write the distribution of electrons in carbon and sodium atoms

Answer

► The total number of electrons in a carbon atom is 6. The distribution
of electrons in carbon atom is given by:

First orbit or K-shell = 2 electrons
Second orbit or L-shell = 4 electrons

Or, we can write the distribution of electrons in a carbon atom as 2, 4.

► The total number of electrons in a sodium atom is 11. The
distribution of electrons in sodium atom is given by:

First orbit or K-shell = 2 electrons
Second orbit or L-shell = 8 electrons
Third orbit or M-shell = 1 electron

Or, we can write distribution of electrons in a sodium atom as 2, 8, 1.

2. If K and L shells of an atom are full, then what would be the total
number of electrons in the atom?

Answer

The maximum capacity of K shell is 2 electrons and L shell can
accommodate maximum 8 electrons in it. Therefore, there will be ten
electrons in the atom.

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Page No: 52

1. How will you find the valency of chlorine, sulphur and magnesium?

Answer

If the number of electrons in the outermost shell of the atom of an
element is less than or equal to 4, then the valency of the element is
equal to the number of electrons in the outermost shell. On the other
hand, if the number of electrons in the outermost shell of the atom of
an element is greater than
4, then the valency of that element is determined by subtracting the
number of electrons in the outermost shell from 8.
The distribution of electrons in chlorine, sulphur, and magnesium atoms
are 2, 8, 7; 2, 8, 6 and 2, 8, 2 respectively.

Therefore, the number of electrons in the outer most shell of chlorine,
sulphur, and magnesium atoms are 7, 6, and 2 respectively.
► Thus, the valency of chlorine = 8 -7 = 1
► The valency of sulphur = 8 - 6 = 2
► The valency of magnesium = 2

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1. If number of electrons in an atom is 8 and number of protons is also 8,
then (i) what is the atomic number of the atom and (ii) what is the
charge on the atom?
Answer
(i) The atomic number is equal to the number of protons. Therefore, the
atomic number of the atom is 8.
(ii) Since the number of both electrons and protons is equal, therefore,
the charge on the atom is 0.

2. With the help of Table 4.1, find out the mass number of oxygen and
sulphur atom.

Answer

Mass number of oxygen = Number of protons + Number of neutrons
=8+8
= 16

Mass number of sulphur = Number of protons + Number of neutrons
= 16 +16
= 32

Page No: 53

1. For the symbol H, D and T tabulate three sub-atomic particles found
in each of them.

Answer

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Symbol Proton Neutron Electron

H 10 1

D 11 1

T 12 1

2. Write the electronic configuration of any one pair of isotopes and
isobars.

Answer

12C6 and 14C6 are isotopes, have the same electronic configuration as (2,
4)22Ne10and 22Ne11 are isobars. They have different electronic
configuration as given below:
22Ne10 – 2, 8
22Ne11 – 2, 8, 1

Page No: 54

Excercise

1. Compare the properties of electrons, protons and neutrons.

Answer

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Particle Nature of Mass Location
Charge

Electrons are 9 x 10–31 kg Extra nuclear part
Electron negatively distributed in different
shell or orbits.
charged.

Proton Protons are 1.672 x 10–27 kg Nucleus
positively (1 µ)
charged. (approx. 2000
times that of the
electron)

Neutron Neutrons are Equal to mass of Nucleus
neutral. proton

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2. What are the limitations of J.J. Thomson's model of the atom?

Answer

The limitations of J.J. Thomson's model of the atom are:
→ It could not explain the result of scattering experiment performed by
rutherford.
→ It did not have any experiment support.

3. What are the limitations of Rutherford's model of the atom?

Answer

The limitations of Rutherford's model of the atom are
→ It failed to explain the stability of an atom.
→ It doesn't explain the spectrum of hydrogen and other atoms.

4. Describe Bohr's model of the atom.

Answer

→ The atom consists of a small positively charged nucleus at its center.
→ The whole mass of the atom is concentrated at the nucleus and the
volume of the nucleus is much smaller than the volume of the atom.
→ All the protons and neutrons of the atom are contained in the
nucleus.
→ Only certain orbits known as discrete orbits of electrons are allowed
inside the atom.
→ While revolving in these discrete orbits electrons do not radiate

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energy. These orbits or cells are represented by the letters K, L, M, N
etc. or the numbers, n = 1, 2, 3, 4, . . as shown in below figure.

5. Compare all the proposed models of an atom given in this chapter.
Answer

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Thomson’s model Rutherford’s model Bohr’s model

An atom consists An atom consists of a Bohr agreed with almost all
of a positively positively charged points as said by
charged sphere center in the atom Rutherford except
and the electrons called the nucleus. regarding the revolution of
are embedded in The mass of the electrons for which he
it. atom is contributed added that there are only
mainly by the certain orbits known as
The negative and nucleus. discrete orbits inside the
positive charges atom in which electrons
are equal in The size of the revolve around the
magnitude. As a nucleus is very small nucleus.
result the atom is as compared to the
electrically size of the atom. While revolving in its
neutral. discrete orbits the
electrons do not radiate
energy.

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6. Summarize the rules for writing of distribution of electrons in various
shells for the first eighteen elements.
Answer
The rules for writing of the distribution of electrons in various shells for
the first eighteen elements are given below.
→ If n gives the number of orbit or energy level, then 2n2 gives the
maximum number of electrons possible in a given orbit or energy level.
Thus,
First orbit or K-shell will have 2 electrons,
Second orbit or L-shell will have 8 electrons,
Third orbit or M-shell will have 18 electrons.
→ If it is the outermost orbit, then it should have not more than 8
electrons.
→ There should be step-wise filling of electrons in different orbits, i.e.,
electrons are not accompanied in a given orbit if the earlier orbits or
shells are incompletely filled.

7. Define valency by taking examples of silicon and oxygen.

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Answer

The valency of an element is the combining capacity of that element.
The valency of an element is determined by the number of valence
electrons present in the atom of that element.→ Valency of Silicon: It
has electronic configuration: 2,8,4
Thus, the valency of silicon is 4 as these electrons can be shared with
others to complete octet.
→ Valency of Oxygen: It has electronic configuration: 2,6
Thus, the valency of oxygen is 2 as it will gain 2 electrons to complete its
octet.

Page No: 55

8. Explain with examples (i) Atomic number, (ii) Mass number, (iii)
Isotopes and (iv) Isobars. Give any two uses of isotopes.

Answer

(i) Atomic number: The atomic number of an element is the total
number of protons present in the atom of that element. For example,
nitrogen has 7 protons in its atom. Thus, the atomic number of nitrogen
is 7.

(ii) Mass number: The mass number of an element is the sum of the
number of protons and neutrons present in the atom of that element.
For example, the atom of boron has 5 protons and 6 neutrons. So, the
mass number of boron is 5 + 6 = 11.

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(iii) Isotopes: These are atoms of the same element having the same
atomic number, but different mass numbers. For example, chlorine has
two isotopes with atomic number 17 but mass numbers 35 and 37
represented by

(iv) Isobars: These are atoms having the same mass number, but
different atomic numbers i.e., isobars are atoms of different elements
having the same mass number. For example, Ne has atomic number 10
and sodium has atomic number 11 but both of them have mass
numbers as 22 represented by -

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Two uses of isotopes:
→ One isotope of uranium is used as a fuel in nuclear reactors.
→ One isotope of cobalt is used in the treatment of cancer.
9. Na+ has completely filled K and L shells. Explain.
Answer
The atomic number of sodium is 11. So, neutral sodium atom has 11
electrons and its electronic configuration is 2, 8, 1. But Na+ has 10
electrons. Out of 10, K-shell contains 2 and L-shell 8
electrons respectively. Thus, Na+ has completely filled K and L shells.

10. If bromine atom is available in the form of, say, two isotopes 79 /
35Br (49.7%) and 81 / 35Br (50.3%), calculate the average atomic mass
of bromine atom.
Answer
It is given that two isotopes of bromine are 79 / 35Br (49.7%) and 81 /
35Br (50.3%). Then, the average atomic mass of bromine atom is given
by:

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Chapter 6
Tissues
Intext Questions

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On Page 69

Question 1:What is a tissue?

Solution:Group of cells that are similar in structure and are organized
together to achieve a particular function is called tissue.

Question 2:What is the utility of tissues in multicellular organisms?

Solution:In multicellular organisms, the body system is based on the
division of labour( like muscle cells form muscular tissue to which helps
in movement ). It means the cells performing a specific function are
grouped together to form a particular tissue. The different tissues are
organized in a way to provide highest efficiency in functioning of the
body.

On Page 74

Question 1:Name the types of simple tissues.

Solution:The three main types of simple tissues are:
1. Parenchyma
2. Collenchyma
3. Sclerenchyma

Question 2:Where is apical meristem found?

Solution:Growing tips of stems and roots of plants are the main are
where apical meristem is present . It helps in increasing the length of the

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stem and the root.

Question 3:Which tissue makes up the husk of coconut?

Solution:The husk of coconut is made up of sclerenchymatous tissue.

Question 4:What are the constituents of phloem?

Solution:The constituents of phloem tissue are:
1. Sieve tubes (tubular living cells with perforated end walls)
2. Companion cell (living cells)
3. Phloem parenchyma (living cells)
4. Phloem fibres (non-living and sclerenchyma cells)

On Page 78

Question 1:Name the tissue responsible for movement in our body.

Solution:Muscular tissue.

Question 2:What does a neuron look like?

Solution:A neuron consists of a cell body with a nucleus and cytoplasm.
It has two important extension name as axon and dendrites. Each
neuron has a single long part, called the axon and many short, branched
parts called dendrites. Many nerve fibres bound together by connective
tissue to make up a nerve.

Question 3:Give three features of cardiac muscles:

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Solution:Below are features of cardiac muscles:

1. These are involuntary, show rhythmic contraction and relaxation
throughout life.
2. The cells are cylindrical, branched, and uninucleate having faint cross
striations.
3. These muscles do not get fatigued under normal conditions.

Question 4:What are the functions of areolar tissue?

Solution:Functions of areolar tissue:

1. It fills the space inside the organs, thus acts as a packing tissue
between the organs.
2. It supports many delicate organs in the body.
3. It plays role in repair of tissues.

Exercises

Question 1:Define the term 'tissue’

Solution:Group of cells that are similar in structure and are organized
together to achieve a particular function is called tissue.

Question 2:How many types of elements together make up the xylem
tissue? Name them.

Solution:The following four types of elements make up xylem tissue:
1. Xylem tracheids.
2. Xylem vessels.

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3. Xylem parenchyma.
4. Xylem fibres.

Question 3:How are simple tissues different from complex tissues in
plants?

Solution:

Simple Tissue
Made up of only one type of cells.
Mainly responsible for mechanical support and storage.
Examples : Parenchyma, collenchyma and sclerenchyma
Complex Tissue
Made up of more than one type of cells.
Mainly responsible for the transport of water, minerals, sugars and
other metabolites.
Examples Xylem and phloem.
Question 4:Differentiate between parenchyma, collenchyma and
sclerenchyma on the basis of their cell wall.

Solution:Differences between parenchyma, collenchyma and
sclerenchyma

Parenchyma
These are living cells with thin walls.

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Cells are uniformly thin.
The cells are loosely packed with large intercellular spaces.
Collenchyma
These are living cells with slightly thick walls.
Cells are elongated.
The cells are irregularly thickened at the corners with very little
intercellular spaces.
Sclerenchyma
These are dead cells with thick cell walls.
Cells are long and narrow.
The cells are thickened due to lignin. These are so thick that there is no
internal space inside the cell.
Question 5:What are the functions of the stomata?

Solution:Stomata are essential for gas exchange with the atmosphere
and help in transpiration in the form of water vapour through leaves.

Question 6:Diagrammatically show the difference between the three
types of muscle fibres.

Solution:The three type of muscles fiber are:
1. Streated muscle
2. Smooth muscle
3. Cardiac muscle

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Diversity in Living Organisms
Page No: 80
1. Why do we classify organisms?
Answer
There are millions of organisms on this earth. So, it is harder to study
them one by one. Therefore, we look for similarities among them and
classify them into different classes to study these different classes as a
whole. Classification makes our study easier.
2. Give three examples of the range of variations that you see in life-
forms around you.

Answer

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Examples of range of variations observed in daily life are:
→ Organisms vary greatly in size-from microscopic bacteria to
elephants, whales and large trees.
→ The colour of various animals is quite different. Some worms are even
colourless or transparent. Various types of pigments are found in plants.
→ The life span of different organisms is also quite varied. For example,
a crow lives for only 15 years, whereas a parrot lives for about 140 years.

Page No: 82

1. Which do you think is a more basic characteristic for classifying
organisms?
(a) The place where they live.
(b) The kind of cells they are made of. Why?

Answer

The more basic characteristic for classifying organisms is the kind of cells
they are made of because different organisms may share same habitat
but may have entirely different form and structure. So, the place where
they live cannot be a basis of classification.

2. What is the primary characteristic on which the first division of
organisms is made?

Answer

The primary characteristic on which the first division of organisms is
made is the nature of the cell – prokaryotic or eukaryotic cell.

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3. On what basis are plants and animals put into different categories?

Answer

Plants and animals are put into different categories on the basis of Mode
of nutrition.Plants are autotrophs. They can make their food own while
animas are heterotrophs which are dependent on others for food. Also,
locomotion, absence of chloroplasts etc. make them different.

Page No: 83

1. Which organisms are called primitive and how are they different from
the so-called advanced organisms?

Answer

A primitive organism is the one which has a simple body structure and
ancient body design or features that have not changed much over a
period of time.As per the body design, the primitve organisms which hav
simple structures are different from those so-called advanced organisms
which have complex body structure and organization.

2. Will advanced organisms be the same as complex organisms? Why?

Answer

Yes, because the advanced organisms also were like the primitive ones
once. They have acquired their complexity relatively recently. There is a
possibility that these advanced or 'younger' organisms acquire more
complex structures during evolutionary time to compete and survive in

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the changing environment.
Page No: 85
1. What is the criterion for classification of organisms as belonging to
kingdom Monera or Protista?
Answer
The organisms belonging to Kingdom Monera are unicellular and
prokaryotic whereas the organisms belonging to Kingdom Protista are
unicellular and eukaryotic.
2. In which kingdom will you place an organism which is single-celled,
eukaryotic and photosynthetic?
► Kingdom Protista

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3. In the hierarchy of classification, which grouping will have the smallest
number of organisms with a maximum of characteristics in common and
which will have the largest number of organisms?
Answer
In the hierarchy of classification,a species will have the smallest number
of organisms with a maximum of characteristics in common, whereas
the kingdom will have the largest number of organisms.
Page No: 88
1. Which division among plants has the simplest organisms?
► Division Thallophyta
2. How are pteridophytes different from the phanerogams?
Answer

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Pteridophyta Phanerogams

They have inconspicuous or less They have well developed
differentiated reproductive organs. reproductive organs.

They produce naked embryos called They produce seeds.
spores.

Ferns, Marsilea, Equisetum, etc. are Pinus, Cycas, fir, etc. are

examples of pteridophyta. examples of phanerogams.

3. How do gymnosperms and angiosperms differ from each other?
Answer

Gymnosperm Angiosperm

They are non-flowering plants. They are flowering plants.

Naked seeds not enclosed inside Seeds are enclosed inside fruits.
fruits are produced.

Pinus, Cedar, fir, Cycas, etc. are Coconut, palm, mango, etc. are
some examples of gymnosperms. some examples of angiosperms.

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Page No: 94
1. How do poriferan animals differ from coelenterate animals?
Answer

Porifera Coelenterate

They are mostly marine, non- They are exclusively marine animals

motile, and found attached to that either live in colonies or have a

rocks. solitary life-span.

They show cellular level of They show tissue level of organisation.
organisation.

Spongilla, Euplectella, etc. are Hydra, sea anemone, corals, etc. are

poriferans. coelenterates.

2. How do annelid animals differ from arthropods?
Answer

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Annelids Arthropods

The circulatory system of annelids Arthropods have an open

is closed. circulatory system.

The body is divided into several The body is divided into few
identical segments. specialized segments.

3. What are the differences between amphibians and reptiles?
Answer

Amphibian Reptiles

They have a dual mode of life. They are completely terrestrial.

Scales are absent. Skin is covered with scales.

They lay eggs in water. They lay eggs on land.

It includes frogs, toads, and It includes lizards, snakes, turtles,
salamanders. chameleons, etc.

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4. What are the differences between animals belonging to the Aves
group and those in the mammalia group?

Answer

Aves Mammals

Most birds have They do not have feathers and the beak is
feathers and they also absent.
possess a beak.

They lay eggs. Hence, Some of them lay eggs and some give birth
they are oviparous. to young ones. Hence, they are both
oviparous and viviparous.

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Page No: 97
Excercise
1. What are the advantages of classifying organisms?
Answer
Following are the advantages of classifying organisms:
→ It makes us aware of and gives us information regarding the diversity
of plants and animals.
→ It makes the study of different kinds of organisms much easier.
→ It tells us about the inter-relationship among the various organisms.
→ It helps us understanding the evolution of organisms.
→ It helps in the development of other life sciences easy.
→ It helps environmentalists to develop new methods of conservation
of plants and animals.

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2. How would you choose between two characteristics to be used for
developing a hierarchy in classification?

Answer

We choose that characteristics which depends on the first
characteristics and determines the rest variety.

3. Explain the basis for grouping organisms into five kingdoms.

Answer

The basis for grouping organisms into five kingdoms are:
→ Complexity of cell structure - There are two broad categories of cell
structure: Prokaryotic and Eukaryotic. Thus, two broad groups can be
formed, one having prokaryotic cell structure and the other having
eukaryotic cell structure. Presence or absence of cell wall is another
important characteristic.
→ Unicellular and multicellular organisms - This characteristic makes a
very basic distinction in the body designs of organisms and helps in their
broad categorizations.

→ Cell Wall: Presence and absence of cell wall leads into grouping.

→ Mode of nutrition -Organisms basically have two types of nutritions -
autotrophic who can manufacture their own food and heterotrophic
who obtain their food from external environment, i.e., from other
organisms). Thus, organisms can be broadly classified into different
groups on the basis of their mode of nutrition.

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4. What are the major divisions in the Plantae? What is the basis for
these divisions?

Answer

The major divisions in Kingdom Plantae are:
→Thallophyta
→ Bryophyta
→ Pteridophyta
→ Gymnosperms
→ Angiosperms

The following points constitute the basis of these divisions:
→ Whether the plant body has well differentiated, distinct components.
→ whether the differentiated plant body has special tissues for the
transport of water and other substances.
→ The ability to bear seeds.
→ Whether the seeds are enclosed within fruits.

5. How are the criteria for deciding divisions in plants different from the
criteria for deciding the subgroups among animals?

Answer

The characteristics used to classify plants is different from animals
because the basic design are different, based on the need to make their
own food (plants) or acquire food (animals).
Criteria for deciding divisions in plants are:
→ Differentiated/ Undifferentiated plant body

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→ Presence/ absence of vascular tissues
→With/without seeds
→ Naked seeds/ seeds inside fruits
But the animals can't be divided into groups on these criteria. It is
because the basic designs of animals are very different from plants. They
are divided on the basis of their body structure.

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6. Explain how animals in Vertebrata are classified into further
subgroups.

Answer

Animals in Vertebrata are classified into five classes:

(i) Class Pisces: This class includes fish such as Scoliodon, tuna, rohu,
shark, etc. These animals mostly live in water. Hence, they have special
adaptive features such as a streamlined body, presence of a tail for
movement, gills, etc. to live in water.

(ii) Class Amphibia: It includes frogs, toads, and salamanders. These
animals have a dual mode of life. In the larval stage, the respiratory
organs are gills, but in the adult stage, respiration occurs through the
lungs or skin. They lay eggs in water.

(iii) Class Reptilia: It includes reptiles such as lizards, snakes, turtles, etc.
They usually creep or crawl on land. The body of a reptile is covered with
dry and cornified skin to prevent water loss. They lay eggs on land.

(iv) Class Aves: It includes all birds such as sparrow, pigeon, crow, etc.
Most of them have feathers. Their forelimbs are modified into wings for
flight, while hind limbs are modified for walking and clasping. They lay
eggs.

(v) Class Mammalia: It includes a variety of animals which have milk
producing glands to nourish their young ones. Some lay eggs and some

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give birth to young ones. Their skin has hair as well as sweat glands to
regulate their body temperature.

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