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JAC Class 9 Science Notes Chapter 11 Work and Energy

September 10, 2024September 9, 2024 by Bhagya

JAC Board Class 9th Science Chapter 11 Notes Work and Energy

→ Work: When a force acts upon an object to cause a change in its position, work is said to be done. It is expressed as the product of force and displacement in the direction of force.
W = F × s
Here, W = work done on the object
F = force on the object
s = displacement of the object
The SI unit of work is newton metre (N m) or joule (J).
1 joule is defined as the amount of work done by a force of 1 N to cause a displacement of 1 m in the object.

→ Sign Conventions for Work Done
a. When both force and displacement are in the same direction, work done is positive.
W = (F × S)

b. When force acts in a direction opposite to the direction of displacement, the work done is negative.
W = – (F × S)
Angle between force and displacement is 180°.

c. If force and displacement are inclined at an angle less than 180°, the work done is given by:
W = Fs cos θ
where θ is the angle between force and displacement.

d. If force and displacement act at an angle of 90°, the work done is zero.

→ Necessary Conditions for Work to be done
Two conditions are required for the work to be done:
a. A force should act on the object.
b. Object must be displaced.

→ Energy: The capacity of a body to do work is called energy of the body. It is a scalar quantity.

→ Unit of energy: As energy is measured by the amount of work that a body can do, so the unit of energy is same as that of work. The SI unit of energy is joule (J). One joule of energy is the energy required to do 1 J of work.
1 kilojoule = 1 kJ = 1000 J.

→ Forms of energy: The various forms of energy are potential energy, kinetic energy, heat energy, chemical energy, electrical energy and light energy.

→ Kinetic energy: It is the energy possessed by a body by the virtue of its motion. Kinetic energy of an object increases with its speed. Kinetic energy of a body moving with a certain velocity is equal to the work done on it to make it acquire that velocity.

→ Derivation
Let an object of mass’m’, start from rest and attain a uniform velocity ‘v’, after a force ‘F’ is applied on it.
Let, during this period, the object be displaced by a distance ‘s’.
Thus, work done on the object,
W = F × S …(i)

Let the acceleration produced after applying force on the object be ‘a’.
So, using third equation of motion, we have:
v² – u² = 2as ……….(ii)

Substituting F and s from equations (ii) and (iii) in equation (i), we get:
W = F × s
W = ma × \(\frac{v^{2}-u^{2}}{2 a}\)
W = \(\frac{1}{2}\)mv² [As, initial velocity, u = 0]
∴ K_E = \(\frac{1}{2}\)mv²
[Work done is stored as kinetic energy]

→ Potential energy: The energy possessed by a body due to its position, shape or configuration is called its potential energy.

→ Gravitational potential energy (P_E): The gravitational potential energy (P_E) of an object at a point above the ground is defined as the work done in raising it from the ground to that point, against gravity.
JAC Class 9 Science Notes Chapter 11 Work and Energy 1

→ Derivation:
Consider a body of mass m, raised through a height ‘h’ from the ground.
Force required to raise the object = weight of the object = mg.
Object gains energy equal to the work done on it.
Work done on the object against gravity is ‘W’.
W = force × displacement = mg × h
W = mgh
P_E = mgh
[Work done is stored as potential energy]

→ Mechanical energy:
The sum of kinetic energy and potential energy is called mechanical energy.

→ Law of Conservation of Energy:
It states that energy can neither be created nor destroyed, but it can be transformed from one form to another. The total energy before and after the transformation always remains constant in an isolated system.
JAC Class 9 Science Notes Chapter 11 Work and Energy 2
Potential energy + Kinetic energy = Constant (Mechanical energy)
Consider a body of mass ‘m’, raised to a height ‘h’ as shown in the figure. At A, its potential energy is maximum and kinetic energy is 0 as it is stationary.

When body falls at B, ‘h’ is decreasing, hence potential energy decreases. Also, v is increasing, therefore, kinetic energy is increasing.
When the body is about to reach the ground level, h = 0 and ‘v’ will be maximum. Hence, kinetic energy > potential energy.
This shows that decrease in potential energy = increase in kinetic energy.
Thus, there is a continuous transformation of gravitational potential energy into kinetic energy.

→ Power: The rate of doing work is called power.
Power = \(\frac{\text { Work }}{\text { Time }}\) or P = \(\frac{\mathrm{W}}{\mathrm{t}}\)
Work, power and energy are all scalar quantities.

→ Watt: It is the SI unit of power. The power of an agent is one watt if it does work at the rate of 1 joule per second.
1 watt = \(\frac{1 \text { joule }}{1 \text { second }}\) or 1 W = 1 J s^-1
1 kilowatt = 1000 watt or 1 kW = 1000 W
1 horsepower = 746 watt or 1 H.P. = 746 W

→ Kilowatt-hour (kWh): It is the commercial unit of electric energy. It is defined as the electric energy consumed by an appliance of power 1000 watt in one hour.
1 kWh = 3.6 × 10⁶ J

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 10 Gravitation

September 10, 2024September 9, 2024 by Bhagya

JAC Board Class 9th Science Chapter 10 Notes Gravitation

→ Gravitation:
The universal law of gravitation’ states that any two bodies having mass, attract each other with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. The force acts along the line joining the centres of the objects.
JAC Class 9 Science Notes Chapter 10 Gravitation 1
Here, G is universal gravitational constant with a value of 6.673 × 10^-11 N m² kg². The value of G was found out by Henry Cavendish.

Note:

If mass of an object is large, force will be more. If mass of an object is small, force will be less.
If distance between two objects is more, force exerted will be less and vice versa.

→ Importance of Gravitational Force

It binds us to the earth.
Moon revolves around the earth due to gravitational force. Planets revolve around the sun due to gravitational force.
Tides in oceans are caused due to gravitational force of the moon on earth.

→ Centripetal acceleration of the moon:
If the moon is revolving with speed v in a circular orbit of radius r, then the acceleration acting on it along the radius and towards the centre of its orbit is
a_c = \(\frac{\mathrm{v}^{2}}{\mathrm{r}}\)

→ Free fall: The earth attracts objects towards it due to gravitational force. When an object moves under the influence of gravitational force alone, it is said to be in a ‘free fall’.

→ Acceleration due to gravity: The acceleration produced in the bodies due to earth’s gravity is called acceleration due to gravity. Its value on the earth’s surface is 9.8 m/s².

→ Relations between g and G: If M is the mass of the earth and R is its radius, the acceleration due to gravity at the surface of the earth is given by
g = \(\frac{\mathrm{GM}}{(\mathrm{R})^{2}}\)

The value of g depends on:

shape of the earth
height above the earth
depth inside the earth
latitude on the earth

→ Mass of the earth:
It is given by
M = \(\frac{g^{2}}{G}\)

→ Centre of mass:
The centre of mass of a body may be defined as the point at which whole mass of the body may be assumed to be concentrated.

→ Centre of gravity:
The centre of gravity of a body is a point at which the resultant of all the parallel forces due to gravity, experienced by various particles of the body, acts or at which whole weight of the body acts.

→ Equations of motion for freely falling bodies: The three equations of motion are:
v = u + at ……..(ii)
s = ut + \(\frac{1}{2}\) at² …..(ii)
v² – u² = 2as
For free fall, the value of acceleration (a)
= g = 9.8 ms^-2

→ Projectile: Any object thrown into space with some initial velocity and which thereafter moves under the influence of gravity alone is called a ‘projectile’. The path of a projectile is a parabola. Its horizontal range is maximum when the angle of projection is 45°.

→ Mass: Mass of an object is the measure of its inertia. It is the amount of matter present in it. It remains the same everywhere in the universe.

→ Weight: The force with which an object is attracted towards the centre of the earth is known as the weight of that object. Its SI unit is newton.
W = m × g
where W = weight of the object, m = mass of the object, and g = acceleration due to gravity.
The weight of an object can change from one place to the other and from one planet to the other.

→ Thrust: It is the net force applied in a particular direction. Its SI unit is N.
Pressure = \(\frac{\text { Thrust }}{\text { Area }}\)
The SI unit of density is kg/m³.

→ Relative density: It is the ratio of the density of a substance to the density of water at 4°C.
Density of substance Density of water at 4°C
Since relative density is a pure ratio, it has no units.

→ Pressure in fluids:
All liquids and gases are fluids as they can flow. The pressure exerted by a fluid is transmitted in all directions.

→ Buoyancy:
The upward force exerted by water (fluid) on the body immersed in it is known as upthrust or buoyancy. The magnitude of the buoyant force depends of the density of the fluid.

→ Archimedes’ principle: It states that when a body is immersed fully or partially in a fluid, it experiences an upward force that is equal to the weight of the fluid displaced by it.
It has following applications:

Used in designing ships and submarines.
In lactometers to find purity of milk.
In hydrometers to determine the density of a liquid.

→ Density: The density of a substance is its mass per unit volume.
Density = \(\frac{\text { Mass }}{\text { Volume }}\)
The SI unit of density is kg/m³.

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 9 Force and Laws of Motion

September 10, 2024September 9, 2024 by Bhagya

JAC Board Class 9th Science Chapter 9 Notes Force and Laws of Motion

→ Force: It is a push or pull on an object that produces acceleration in the body on which it acts. The SI unit of force is ‘newton’. Forces are used in our daily life actions like pushing, lifting, pulling, stretching, twisting and pressing.

→ A force cannot be seen. It can be judged only by the effects which it can produce in several bodies (or objects) around us.

→ Force has both magnitude and direction, making it a vector quantity. It is measured in the SI unit of newton and represented by the symbol ‘F’

→ Effects of Force:
a. Force can set a stationary body in motion. For example, a football can be set in motion by kicking it, i.e. by applying a force.

b. Force can stop a moving body. For example, by applying brakes, a running cycle or a running vehicle can be stopped.

c. Force can change the direction of a moving object. For example, by applying force, i.e., by moving handle, the direction of a running bicycle can be changed. Similarly by moving steering, the direction of a running vehicle is changed.

d. Force can change the speed of a moving body. For example, by accelerating, the speed of a running vehicle can be increased or by applying breaks, the speed of a running vehicle can be decreased.

e. Force can change the shape and size of an object. For example, by hammering, a block of metal can be turned into a thin sheet. Also by hammering, a stone can be broken down into pieces.

→ Balanced forces: If the resultant force of several forces acting on a body is zero, the forces are said to be ‘balanced forces’.

→ Unbalanced forces: If the resultant force of the several forces acting on a body is not zero, the forces are said to be ‘unbalanced forces’. An object in rest can be moved by applying unbalanced forces. Only an unbalanced force can produce the effects of force.

→ Newton’s First Law of Motion: An object remains in its state of rest or of uniform motion in a straight line unless acted upon by an external unbalanced force.

→ Inertia: The natural tendency of an object to resist a change in its state of rest or of uniform motion is called its inertia.

Inertia of rest: It is the tendency of a body to remain in its state of rest.
Inertia of motion: It is the tendency of a body to remain in its state of uniform motion in a straight line.
Inertia of direction: It is the inability of a body to change, by itself, its direction of motion.

→ Newton’s Second Law of Motion: The rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of force.
Mathematically,
Force = Mass × Acceleration or,
F ∝ \(\frac{P_{1}-P_{2}}{t}\) or \(\frac{\mathrm{m}(\mathrm{v}-\mathrm{u})}{\mathrm{t}}\) or ma
This law defines the unit of force. One unit force is that force which produces unit acceleration in a body of unit mass.

→ Newton (N): It is the SI unit of force. One Newton is that force which produces an acceleration of lm/s2 in a body of mass 1 kg.

→ 1 newton = 1 kg × 1 m/s² or 1N = 1 kg m/s²

→ Momentum: The momentum of an object is the product of its mass and velocity and has the same direction as that of the velocity. Its SI unit is kg m/s.
Momentum = Mass × Velocity or p = mv

→ Newton’s Third Law of Motion: To every action, there is an equal and opposite reaction and they act on two different bodies.

→ Law of Conservation of Momentum:
It states that the total momentum of any system of objects remains constant in the absence of any external force. According to the law of conservation of momentum, for collision between two bodies:
Total momentum before collision = Total momentum after collision
m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂

→ Frictional force: Whenever a body slides or rolls over the surface of another body, a force comes into action which acts in the opposite direction as that of the motion of a body. This opposing force is called ‘friction’.

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 8 Motion

September 10, 2024September 9, 2024 by Bhagya

JAC Board Class 9th Science Chapter 8 Notes Motion

→ An object is said to be in motion if it changes its position with the passage of time with respect to a fixed point in the background.

→ Types of Motion
a. Linear motion: A body is in linear motion if it moves in a straight line or path.
b. Circular motion (rotational): A body is in circular motion if it moves around a fixed point. A vertical line passing through the fixed point around which the body moves is known as axis of rotation.
c. Vibratory motion: A body has vibratory motion if it moves to and fro about a fixed point.

→ Concept of a Point object, Rest and Motion a. Point object: An extended object can be treated as a point object when the distance travelled by the object is much greater than its own size.
“A point object is one, which has no linear dimensions but possesses mass”.
b. Rest: A body is said to be at rest when its position does not change with time with respect to the observer.
c. Motion: A body is said to be in motion when its position changes with time with respect to the observer.

→ Vector and Scalar Quantities
a. Vector Quantities: The physical quantities that have magnitude as well as direction are called vector quantities.
Examples: Velocity, acceleration, force, displacement, momentum, weight, electric field, etc.

b. Scalar Quantities: The quantities that have only magnitude and no direction are called scalar quantities.
Examples: Mass, time, distance, speed, work, power, energy, charge, area, volume, density, pressure, potential, temperature, etc.

→ Distance and Displacement
a. Distance: It is the actual path travelled by an object from its initial position to its final position.
b. Displacement: It is the shortest straight line path between initial and final positions.
– If the initial and final points are same, displacement will be zero.
– Distance depends on path but displacement does not.
– Distance is always greater than or equal to displacement. They are equal only in straight line motion in a definite direction.
JAC Class 9 Science Notes Chapter 8 Motion 1

→ Uniform and Non-uniform Motion
a. Uniform motion is a motion in which equal distances are covered in equal time intervals.
b. Non-uniform motion is a motion in which unequal distances are covered in equal intervals of time.

→ Speed and Velocity
a. Speed: Speed is the distance travelled by an object in unit time.
Speed = \(\frac{\text { Distance travelled }}{\text { Time taken }}\)
or v = \(\frac{\mathrm{s}}{\mathrm{t}}\)
[where v = speed; s = distance; and t = time taken]
The SI unit of speed is m/s.

→ Average speed: It is the total distance travelled by the body divided by the total time taken to cover this distance.
Average speed = \(\frac{\text { Total distance travelled }}{\text { Total time taken }}\)

→ Uniform speed: When an object covers equal distances in equal intervals of time, however small these intervals may be, it is said to be in ‘uniform speed’.

→ Non-uniform speed: When an object covers unequal distances in equal intervals of time, it is said to be in ‘non-uniform speed’.

b. Velocity: It is the displacement of the body per unit of time. It is the distance travelled by a body per unit time in a given direction.
Velocity = \(\frac{\text { Displacement }}{\text { Time }}\)
The SI unit of velocity is m/s.

→ Important note: Velocity has both magnitude and direction while speed has only magnitude and no direction. Velocity has same direction as that of displacement.

→ Average velocity: The ratio of total displacement to the total time taken by the body gives its average velocity.
Average velocity = \(\frac{\text { Total displacement }}{\text { Total time taken }}\)

Average speed is always greater than average velocity, except in case of straight line motion without U – turn, when both are equal.
If body returns to its initial position, average velocity will be zero but average speed-will not be zero.
When direction of motion changes, velocity also changes.

→ Instantaneous Speed and Velocity
a. Instantaneous speed: It is the speed of an object at a particular moment (instant) in time.
b. Instantaneous velocity: It is the velocity of an object in motion at a specific point in time.

→ Acceleration: Acceleration is the measure of change of velocity with time. It is also called rate of change of velocity. The SI unit of acceleration is m/s2. It is a vector quantity.
Acceleration = \(\frac{\text { Final velocity – Initial velocity }}{\text { Total time taken }}\)
If the velocity of an object changes from an initial value ‘u’ to the final value ‘v’ in time ‘f, the motion is called accelerated motion. In this case, acceleration ‘a’ is given by
a = \(\frac{\mathrm{v}-\mathrm{u}}{\mathrm{t}}\)

Accelerated motion is a motion in which acceleration is not equal to zero.
a. Acceleration has same direction as that of velocity, if velocity increases.
b. Acceleration has opposite direction as that of velocity, if velocity decreases. In this case, acceleration will be negative. Negative acceleration is also called retardation or deceleration.

→ Uniform and Non-uniform Acceleration
a. When velocity of a body changes by equal amounts in equal time intervals, acceleration is said to be uniform.
b. When velocity of body changes by unequal amounts in equal intervals of time, acceleration is said to be non-uniform.
Examples: A freely falling ball is under uniformly accelerated motion. A car driving by applying brakes frequently, is under non-uniformly accelerated motion.

→ Equations of Uniformly Accelerated Motion:
Relation among velocity, distance, time and acceleration gives the equation of motion. There are three equations of motion for bodies moving with uniform acceleration.
a. First Equation of Motion: v = u + at

b. Second Equation of Motion:
s = ut + \(\frac{1}{2}\) at²

c. Third Equation of Motion:
v² = u² + 2as
Here,
v = final velocity of the body
u = initial velocity of the body
a = acceleration of the body
t = time taken by the body
s = distance travelled by the body in time ‘t’

→ Average velocity in Uniformly Accelerated Motion: If a body moves a distance ‘s’ in time ‘t’
Average velocity = \(\frac{\text { Displacement }}{\text { Time }}=\frac{\mathrm{s}}{\mathrm{t}}\)
= u + \(\frac{1}{2}\)at (∵ s = ut + \(\frac{1}{2}\)at²)
or, u + \(\frac{1}{2}\)at = u + \(\frac{1}{2}\)(u – v) (∵ v = u + at)
= u + \(\frac{\mathrm{v}}{2}-\frac{\mathrm{u}}{2}=\frac{\mathrm{u}+\mathrm{v}}{2}\)
Here, ‘a’ is uniform acceleration of body.
Average velocity = \(\frac{u+v}{2}\)

→ Graphical Representation of Motion: To describe the motion of an object, we can use different graphs. Graphical representation of motion shows dependence of one physical quantity, such as distance or velocity, on another quantity such as time.
a. Distance-time Graph: The change in the position of an object with time can be represented on the distance-time graph. The s-t graph for a moving body can be used to calculate the speed of the body.
JAC Class 9 Science Notes Chapter 8 Motion 2

b. Velocity-time Graph
– If a body moves with a uniform velocity (no acceleration), its speed-time graph would be a straight line parallel to time axis.
If a body moves with a non-uniform velocity (uniform acceleration), its speed time graph would be a straight line. If velocity increases (positive uniform acceleration) with time, graph would be a straight upward slope. If velocity decreases (negative uniform acceleration) with time, graph would be a straight downward slope.
JAC Class 9 Science Notes Chapter 8 Motion 3
We can find out the magnitude of displacement (distance) and acceleration of a body using the velocity-time graph. The distance travelled by a moving body in a given time will be equal to the area under the speed-time graph.

→ Velocity-time graph of an object moving with constant velocity
For the above graph,
Distance travelled = area of rectangle ABCD = AB × BD
s = v(t₂ – t₁)
Acceleration of body = \(\frac{\text { Change in velocity }}{\text { Time taken }}\)
As in above graph, velocity is constant, so in this case, acceleration will be zero.

→ Derivation of equation of motion using graphs:
Let an object move from A to B in time interval ‘f.
Acceleration of moving object = \(\frac{v_{2}-v_{1}}{t_{2}-t_{1}}\)
a. If initial velocity is u and final velocity is v then
a = \(\frac{v-u}{t-0}\)
at = v – u
v = u + at …(1)
Hence proved
JAC Class 9 Science Notes Chapter 8 Motion 5

b. Distance travelled by object = area under graph
= area of rec. ADCO + area of triangle ABD
= (AO) (OC) + \(\frac{1}{2}\) (AD) (DB)
= ut + \(\frac{1}{2}\) (OC) (BC – CD)
= ut + \(\frac{1}{2}\) t (v – u)
= ut + \(\frac{1}{2}\) t (at)
or
s = ut + \(\frac{1}{2}\)at² ….(2)

c. Distance travelled by object = area under graph
= area of trapezium AOCB
s = \(\frac{1}{2}\) (sum of ∥ sides) × t
S = \(\frac{1}{2}\) (u + v) × t …(i)
From first equation of motion, (v-u)
t = \(\frac{(v-u)}{a}\)
Equating equations (i) and (ii)
s = \(\frac{(v+u)(v-u)}{2 a}\) ……..(iii)
Hence proved

→ Circular Motion
a. Uniform circular motion is the motion in which an object moves on a circular path with constant speed. For example: moon revolving around the earth.
b. Non-uniform circular motion is the motion in which an object moves on circular path with varying speed. When an object is in circular motion, direction of its velocity keeps on changing.

→ Speed in the case of circular motion
Suppose a body is moving in a circular path of radius r.
Speed (v) = \(\frac{\text { Distance }}{\text { Time }}\)
= \(\frac{\text { Circumference of circle }}{\text { Time }}\)
= \(\frac{2 \pi r}{t}\)
JAC Class 9 Science Notes Chapter 8 Motion 6

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms

September 10, 2024September 9, 2024 by Bhagya

JAC Board Class 9th Science Chapter 7 Notes Diversity in Living Organisms

→ Biodiversity: The word ‘biodiversity’ is used to define the diversity of life forms. Biodiversity is a word more often used to refer to the variety of life forms found in a particular geographic region.

→ Diversity: Diversity of life forms in a geographic region provides stability in that region.

→ Taxonomy: It is a branch of biology . which deals with identification, nomenclature and classification of organisms. Carolus Linnaeus is called the father of taxonomy.

→ Classification: The method of arranging organisms into groups or sets on the basis of similarities and differences is called classification.

→ Importance of Classification
a. It makes the study of a wide variety of organisms easy and systematic.
b. It helps to understand how the different organisms have evolved with time.
c. It helps to understand the inter-relationships among different groups of organisms.
d. It forms a base for the study of other biological sciences, like biogeography.

→ Classification of organisms by Aristotle: Greek philosopher, Aristotle first classified the animals based on their place of residence, i.e., whether they lived on land, in water or in the air. However, this was not an appropriate way to group organisms as animals living in the same habitat can have very different characteristics.

→ Later, all the living organisms were identified and categorised on the basis of their body structure and function. The idea of evolution was first described by Charles Darwin in 1859 in his book ‘The Origin of Species.’

→ Basis of Classification: There are certain features or properties used for the classification of living organisms which are known as characteristics. Organisms with same characteristics are placed in same groups.

→ The major characteristics considered for classification of all organisms into five major kingdoms are:
a. Type of cellular organisation
i. Prokaryotes: The organisms which have cells without well defined nucleus are called prokaryotes.
ii. Eukaryotes: The organisms which have cells with well defined nucleus are called eukaryotes. Presence of nucleus and membrane bound organelles give better efficiency to the cells.

b. Body organisations
i. Unicellular: The organisms made up of a single cell alone are termed as unicellular organisms. In them, the single cell is responsible for carrying out all the necessary functions to maintain life.
ii. Multicellular: The organisms made up of more than one cell are called multicellular organisms. Because of more number of cells, there can be some division of labour to gain more efficiency.

c. Mode of obtaining food
i. Autotrophs: Organisms producing their own food are called autotrophs. All green plants are examples of autotrophs. They have a pigment called chlorophyll, which facilitates photosynthesis.
ii. Heterotrophs: Organisms who are dependent on either plants or animals are called heterotrophs. They do not have chlorophyll. All animals, fimgi, various bacteria and protozoa belong to this group.

→ Hierarchy of Classification:
Linnaeus proposed a classification system that arranged organisms into taxonomic groups at different levels according to the characteristics they have. The groups or the levels from top to bottom are:
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 1

→ Nomenclature: An organism can have different names in different languages. This creates confusion in naming the organism. So, a scientific name is needed which is accepted globally. Binomial system of nomenclature given by Carolus Linnaeus is used for naming different organisms.

→ Following are some conventions in writing the scientific names:
a. Genus should be written first, followed by the name of the species.
b. First letter of the genus should be capital and that of the species should be in small letter.
c. When printed, the name should be written in italics and if hand written, the genus and the species should be underlined separately.
For example – Homo sapien for human, Panthera tigris for tiger.

→ Classification System
a. Two Kingdom Classification: Carolus Linnaeus in 1758 classified the living organisms into two groups, viz., plants and animals.
b. Five Kingdom Classification: Whittaker in 1959, further classified the organisms into five kingdoms,viz. Monera, Protista, Fungi, Plantae and Animalia.

→ Carl Woese in 1977 further divided kingdom Monera into Archaebacteria (or Archaea) and Eubacteria (or Bacteria).

→ Kingdom Monera
a. Prokaryotic, unicellular.
b. Can be autotrophic or heterotrophic.
c. May or may not have a cell wall.
d. Examples: Anabaena and bacteria (heterotrophic), Cyanobacteria or blue green algae (autotrophic).
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 3

→ Kingdom Protista
a. Eukaryotic, unicellular.
b. Can be autotrophic or heterotrophic.
c. Have cilia, flagella or pseudopodia for locomotion.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 4
d. Examples: Plant like – unicellular algae, diatoms; Animal like – protozoans (Amoeba, Paramecium, Euglena); Fungi like – slime moulds and water moulds.

→ Kingdom Fungi
a. Heterotrophic, eukaryotic organisms.
b. Saprophytic. They use.decaying organic materials as food.
c. Some fungi live in a symbiotic relationship with cyanobacteria. They are called lichens. The algal part provides food and the fungal part provides minerals and substratum.
d. Cell wall is made up of chitin.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 5
e. Examples: Mushrooms (Agaricus), green mould (Penicillium), smut (Aspergillus).

→ Kingdom Plantae:
a. Multicellular, eukaryotic.
b. Autotrophs, use chlorophyll for photosynthesis.
c. Cellulosic cell wall present.

→ Kingdom Animalia:
a. The organisms of Animalia include all organisms which are multicellular, eukaryotic and without cell wall.
b. Organisms of kingdom Animalia are heterotrophs.

→ Classification of Kingdom Plantae
Based upon body differentiation, types of vascular tissues (xylem or phloem), reproductive structures (seeds or spores) and type of seeds, (covered or naked), kingdom plantae is divided into the following divisions:

→ Division 1: Thallophyta
a. The plants of thallophyta do not have well differentiated body.
b. The plants in thallophyta are known as algae and they are predominantly aquatic.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 6
c. Examples: Spirogyra, Ulothrix, Cladophora, Chara, etc.

→ Division 2: Bryophyta
a. The plants of this group are called amphibians of plant kingdom.
b. Though not distinctly developed, plant body can be differentiated to form stem and leaf like-structures.
c. Examples: Moss (Funaria) and Marchantia.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 7

→ Division 3: Pteridophyta
a. Plants of Pteridophyta have defined roots, stems and leaves.
b. These plants have specialised tissues that transport water and other materials from one part to another part of the plant.
c. Examples: Marsilea, fem and horse-tails.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 8
d. The similarity among the thallophytes, the bryophytes and the pteridophytes is that all of them have naked embryos, which are known as spores.
e. The plants of these groups are known as ‘cryptogams’, which means ‘hidden reproductive organs’.

→ Division 4: Gymnosperms
a. The plants of this group bear naked seeds and are usually perennial, evergreen and woody.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 9
b. Examples: Pine, Cycas and Deodar.

→ Division 5: Angiosperms
a. This word is made from two Greek words: angio- meaning covered and sperma- meaning seed.
b. The seeds develop inside an organ which is modified to become a fruit. These are also called flowering plants.
c. Plant embryo in seeds has structures called cotyledons. Cotyledons are called ‘seed leaves’ because in many instances they emerge out and become green when the seed germinates.
d. The angiosperms are divided into two groups on the basis of the number of cotyledons present in the seed:

Monocots (Monocotyledonous): These seeds have a single cotyledon. E.g., onion.
Dicot (Dicotyledonous): These seeds have two cotyledons. E.g., musturd.

JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 10

→ Classification of Kingdom Animalia
Based on the extent and type of the body design differentiation, Animal kingdom is classified into the following phyla:

→ Phylum Porifera
a. Cellular level of organisation.
b. Non-motile animals.
c. Holes on the entire body surface which lead to a canal system for circulation of water and food.
d. Hard outside layer known as skeleton.
e. Examples: Sponges (Spongilla, Sycon).
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 11

→ Phylum Coelenterata
a. Tissue level of organisation.
b. No coelom.
c. Radial symmetry’, diploblastic.
d. Hollow gut, move from one place to another.
e. Examples: Hydra, sea-anemone, jelly fish, corals.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 12

→ Phylum Platyhelminthes
a. Well-developed organs.
b. No coelom.
c. Known as flatworms.
d. Bilateral symmetry, triploblastic.
e. Free living or parasitic.
f. Digestive cavity has a single opening for ingestion and egestion.
g. Examples: Planaria, liverfluke, tape worm, etc.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 13

→ Phylum Nematoda
a. Cylindrical body.
b. No well-developed body (i.e., no real organ).
c. False coelom.
d. Bilateral symmetry, triploblastic.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 14
e. Many are parasitic worms living inside human body and can cause various diseases, like filarial worms cause elephantiasis, round worms and pin worms living in human intestine cause infection.
f. Examples: Ascaris, Wuchereria.

→ Phylum Annelida
a. Found everywhere including fresh water, marine water as well as on land.
b. Bilaterally symmetrical and triploblastic body.
c. True body cavity present.
d. Segmented (segments specialised for different functions).
e. Extensive organ differentiation.
f. Examples: Earthworm, Nereis, leeches.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 15

→ Phylum Arthropoda
a. The largest group of animals.
b. Open circulatory system.
c. Generally known as insects.
d. Bilateral, triploblastic.
e. Segmented, sometimes fused.
f. Jointed appendages like feet, antenna.
g. Examples: Prawns, butterflies, houseflies, spiders, scorpions, etc.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 16

→ Phylum Mollusca
a. Coelom present.
b. Triploblastic, bilateral symmetry.
c. Soft bodies, sometimes covered with shell.
d. Generally not segmented.
e. No appendages present.
f. Kidney-like organs for excretion.
g. Examples: Chiton, Octopus, Pila, Unio.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 17

→ Phylum Echinodermata
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 18
a. Spiny skinned.
b. Free-living marine organisms.
c. Triploblastic with coelom present.
d. Skeleton of calcium carbonate.
e. Water vascular system for locomotion.
f. Bilateral symmetry before birth.
g. Examples: Starfish, sea cucumber,
feather star, etc.

→ Phylum Hemichordata
a. Small group of marine animals.
b. Cylindrical, bilateral symmetry, triploblastic.
c. Coelom present.
d. Gills for respiration.
e. Examples: Balanoglossus.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 19

→ Phylum Chordata
a. Bilateral symmetry, triploblastic.
b. Coelom present.
c. Notochord present.
d. Gills presented at some phase of life.
e. Dorsal nerve chord.
f. Post-anal tail present at some stage of life, e.g., in human beings during embryonic stages.

Phylum chordata is further subdivided into three sub-phyla, namely, urochordata, cephalochordata and vertebrata. Urochordata and cephalochordata are together called as Protochordata.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 20
a. Protochordata

Bilaterally symmetrical, triploblastic.
Coelom present.
Marine.
Examples: Herdmania, Amphioxus,

JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 21

b. Vertebrata

Notochord is replaced by vertebral column
Two, three, four chambered heart. Examples: Human (4 chambered), frog (3 chambered), fishes (2 chambered).
Organ for excretion, e.g., kidney, is present.
Paired appendages.

→ Classification of Vertebrata
The organisms of this kingdom have a true vertebral column and an internal skeletal structure. Vertebrates are further classified into the following classes:

Cyclostomata:
a. Jawless vertebrates.
b. Elongated body.
c. Circular mouth, slimy skin, scaleless.
d. Ectoparasites or borers of other vorebebrates.
e. Example: Petromyzon, Myxine (Hagfish).
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 22

Pisces:
a. The organisms of this group are typically different types of fishes.
b. Fishes can live only in water.
c. The skin of fishes is covered with scales/plates.
d. Fishes use oxygen dissolved in water to breathe with the help of the gills.
e. The tail of a fish helps in its movements.
f. Fishes are cold-blooded organisms and their hearts have only two chambers.
g. Fishes lay eggs (oviparous).
h. Examples: Rohu, Catla, Scoliodon, etc.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 23

Amphibia:
a. The organisms of Amphibia have mucus glands in the skin, and they have three- chambered heart.
b. Amphibians can live in water as well as on land.
c. These organisms respire through either gills or lungs.
d. They lay eggs.
e. Examples: Salamander, toad, frog, etc.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 24

Reptilia:
a. The organisms of Reptilia are cold blooded. They cannot maintain a constant body temperature.
b. They have three-chambered heart, except crocodiles which have four- chambered heart.
c. These organisms lay eggs with tough coverings (oviparous).
d. They have scales.
e. Examples: King cobra, turtle, chameleon, lizard, etc.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 25

Aves:
a. Aves are warm-blooded.
b. These organisms lay eggs.
c. Most of the Aves have feathers.
d. Four-chambered heart is present.
e. They have hollow bones which help them to fly.
f. Examples: Pigeon, crow, etc.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 26

Mammalia
a. The organisms of Mammalia are warmblooded and they have four-chambered heart.
b. Mammalia are typically characterised for their mammary glands.
JAC Class 9 Science Notes Chapter 7 Diversity in Living Organisms 27
c. Mammary glands produce milk to nourish the young ones.
d. Most of the mammals give birth to young ones. However, a few mammals, such as the Platypus and the Echidna, lay eggs.
e. Skin of mammals has hair along with sweat and oil glands.
f. Examples: Human, bat, cat, whale, etc.

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 6 Tissues

September 10, 2024September 9, 2024 by Bhagya

JAC Board Class 9th Science Chapter 6 Notes Tissues

→ A group of cells having a common origin and similar function are termed as tissues.

→ Plant tissues: They are primarily classified into two groups:
a. Meristematic tissues
b. Permanent tissues

Meristematic tissues: They are capable of dividing continuously to produce new cells. The meristematic tissues are present only at the growing regions such as shoot tip. root tip and at the base of intemodes and leaves.
JAC Class 9 Science Notes Chapter 6 Tissues 1
Depending on the area where they are present, meristematic tissues are classified as apical, lateral and intercalary. Meristematic tissues are very active, have dense cytoplasm, thin cellulosic walls and prominent nuclei. They lack vacuoles.

Permanent tissues: Formed from meristematic tissues, the cells in the tissue lose the ability to divide. They have differentiated and attained a permanent shape suitable for their functions. Permanent tissues are divided into two categories. Simple permanent tissues: Tissues which are made up of only one type of cells are called simple tissues.

Parenchyma, collenchyma and sclerenchyma are examples of simple tissues,
a. Parenchyma: Composed of unspecialised cells with relatively thin cell walls, large intercellular space, present in soft parts of the plant. Their main function is storage.
JAC Class 9 Science Notes Chapter 6 Tissues 2

b. Collenchyma: It is composed of living and elongated cells with cell walls and irregularly thickened at the comers. There is very little intercellular space. It provides mechanical support and elasticity to plant. It helps in bending of leaves and stems.

c. Sclerenchyma: It is composed of long, narrow and thick-walled cells. This tissue is made up of dead cells, and there are no intercellular spaces. Sclerenchyma cells are dead. They are present in seeds, nuts, husk of coconut- fibre of jute, etc.
JAC Class 9 Science Notes Chapter 6 Tissues 3

→ Complex permanent tissues: Made up of more than one type of cells (conducting tissues).
a. Xylem: It is composed of tracheids, vessels, xylem parenchyma and xylem fibres. Xylem conducts water and dissolves minerals from roots to all parts of the plant. Except xylem parenchyma, xylem cells are dead cells.
JAC Class 9 Science Notes Chapter 6 Tissues 4
b. Phloem: It conducts food from the green leaves/parts to other parts of the plant. It is composed of four elements-sieve tubes, companion cells, phloem parenchyma and phloem fibres. Except phloem fibres, phloem cells are living cells.

→ Animal tissues: Animal tissues are of four types in higher animals including human beings.
JAC Class 9 Science Notes Chapter 6 Tissues 6
a. Epithelial tissues: They are present for the covering of the external surfaces, internal cavities and organs of the animal body. Various types of epithelial tissues are:

Squamous epithelium in the lining of mouth and oesophagus.
Cuboidal epithelium in the lining of kidney tubules and salivary glands.
Columnar epithelium in the intestine and columnar epithelium with cilia in the lining of respiratory tract.
Glandular epithelium in the glands aids in a special function as gland cells, which can secrete at the epithelial surface.

b. Muscular tissues: They are made up of muscle cells, called muscle fibres. There are three types of muscle fibres:

Striated muscles (skeletal muscles or voluntary muscles): Cells are cylindrical, unbranched and multinucleate.
Smooth muscles (involuntary muscles): Cells are long, spindle-shaped and possess a single nucleus.
Cardiac muscles (involuntary muscles): Cells are cylindrical, branched and uninucleate.

c. Connective tissues: They connect various tissues and organs. They provide support to different parts of the body by forming packaging around different organs of the body. The different types of connective tissues in our body are bone, cartilage, tendon, ligament and blood.

d. Nervous tissues: The tissue responds to stimuli. The brain, spinal cord and nerves are composed of nervous tissues or neurons. A neuron consists of cell body, cytoplasm, nucleus, dendrite, axon and nerve ending. The neuron impulse allows us to move our muscles when we want to respond to stimuli.

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 5 The Fundamental Unit of Life

September 10, 2024September 9, 2024 by Bhagya

JAC Board Class 9th Science Chapter 5 Notes The Fundamental Unit of Life

→ All organisms consist of tiny building blocks which are known as cells. The term ‘cell’ was coined by Robert Hooke from the Latin word ‘cella’ which means a Tittle room’.

→ Cell is the basic structural and functional unit of all organisms. Cell is the lowest level of organisation that is ‘alive’.

→ Cell theory states that: All living organisms are composed of cells. Cell is the fundamental unit of life. All new cells arise from pre-existing cells.

→ Shape and size of cells: Cells vary in shape and size. They may be oval, spherical, rectangular, spindle shaped or totally irregular like the nerve cell. The size of cells also varies in different animals and plants. Most of the cells are very small in size, like red blood cells (RBCs), while some cells are fairly large, like nerve cells. Average size of a cell varies from 0.5 to 20 pm.

→ Cell Structure: Cell is a compound of same basic constituents.
1. Plasma membrane: Plasma membrane is the covering of the cell that separates the contents of the cell from its external environment. It is the living part of a cell. It is a very thin, delicate, elastic and selectively permeable membrane. As it is a selectively permeable membrane, it allows the flow of certain selected substances in and out of the cell. The plasma membrane is flexible and is made up of organic molecules called lipids and proteins. The flexibility of cell membrane also enables the cell to engulf food and other materials from its external environment. Such process is known as endocytosis. It is observed in Amoeba.

→ Transport of Substances through Plasma Membrane: Substances can pass through plasma membrane by two processes: diffusion and osmosis.
a. Diffusion: It is the process of movement of substances from their higher concentration to their lower concentration. During respiration, CO₂ is given out as a waste product and accumulates in higher concentration inside the cell as compared to the outside medium. Due to the difference in concentration inside and outside the cell, CO₂ starts moving out of the cell.

b. Osmosis: The movement of water moleculas through a selectively permeable membrane is called osmosis. Osmosis is the movement of water from a region of higher water concentration, through a semi-permeable membrane, to a region of lower water concentration.

→ If the medium surrounding the cell has a higher water concentration than the cell, the cell will gain water by osmosis. Such a solution is known as a hypotonic solution.
JAC Class 9 Science Notes Chapter 5 The Fundamental Unit of Life 1

If the medium has exactly the same water concentration as the cell, there will be no net movement of water across the cell membrane. Such a solution is known as an isotonic solution.
If the medium has a lower water concentration than the cell, it will lose water by osmosis. Such a solution is known as hypertonic solution.

→ Cell wall: Cell wall is a non-living, thick and freely permeable covering made up of cellulose. It is available in eukaryotic plant cells and in prokaryotic cells as well. It determines the shape of the cells. It protects the plasma membrane. It prevents desiccation or dryness in cells. It helps in the transport of various substances in and out of the cell.

→ Nucleus: Nucleus is covered by a double¬layered membrane. The fluid inside the nucleus is called nucleoplasm. Nucleus consists of chromosomes which are important for the functioning of a cell. Chromosomes consist of genes which are the carriers of genetic information. Nucleus controls all the metabolic activities of the cell. It is the storehouse of genes. Without nucleus, cell can neither survive nor show specialised activities.

→ Type of cells: The cells can be categorised in two types:

Prokaryotic cell: In some organisms, DNA and RNA (genetic substances) are bound by a membrane. This membrane bound nucleus is termed as true nucleus. Prokaryotic cells are the cells in which true nucleus and membrane bound organelles are absent. They are primitive and incomplete cells. Prokaryotes are always unicellular organisms. Bacteria and blue-green algae are examples of prokaryotes.
Eukaryotic cell: Eukaryotic cells are the cells in which true nucleus and membrane bound organelles are present. They are advanced and complete cells. Eukaryotes include all living organisms (both unicellular and multicellular) except bacteria and blue green algae.

JAC Class 9 Science Notes Chapter 5 The Fundamental Unit of Life 2

→ Protoplasm: It is a jelly-like, viscous, colourless semi-fluid substance present in various cell organelles in colloidal form. Protoplasm consists of two parts:

Cytoplasm: It is that part of protoplasm which surrounds the nucleus. It contains the various cell organelles.
Nucleoplasm: It is that part of protoplasm which is located inside the nucleus.

Protoplasm stores vital chemicals like amino acids, proteins, sugar, etc. It is the site of some metabolic reactions.
JAC Class 9 Science Notes Chapter 5 The Fundamental Unit of Life 3

→ Cell organelles: These are small membrane bound structures suspended in the cytoplasm. They perform lots of chemical activities to support the structure and functioning of a cell. Some cell organelles are described below:
1. Endoplasmic Reticulum: Endoplasmic reticulum is a mesh-like structure which is composed of numerous tubes. It extends from the plasma membrane to the nuclear membrane. There are two types of endoplasmic reticulum, viz, smooth ER (synthesises lipids, detoxify drugs) and rough ER (synthesises proteins). Rough ER has ribosomes on its surface which give it the characteristic rough appearance.
It serves as the transport channel in the cell. Substances are transported from cell membrane to cytoplasm and to nucleus and vice-versa. ER also serves the role of packing many substances in the cell. It helps in the formation of plasma membrane and Golgi-bodies. Smooth ER helps in synthesis and transport of lipids.
JAC Class 9 Science Notes Chapter 5 The Fundamental Unit of Life 4
2. Golgi body: The Golgi apparatus, first described by Camillo Golgi, consists of a system of membrane-bound vesicles arranged approximately parallel to each other in stacks called cistemae. The materials synthesised near the ER are packaged and dispatched to various targets inside and outside the cell through the Golgi apparatus. The Golgi bodies store, modify, pack and dispatch the substances. They help in the formation of lysosomes.
JAC Class 9 Science Notes Chapter 5 The Fundamental Unit of Life 5
3. Lysosomes: Lysosomes are small sac-like structures. They are derived from Golgi complex. Lysosomes contain digestive enzymes. They are found in eukaryotic cells, mostly in animals. Lysosomes help in digestion of foreign substances and wom-out cell organelles. They provide protection against bacteria and vims. They help to keep the cell clean. During the distribution in cellular metabolism, e.g., when they get damaged, lysosomes may burst and the enzymes digest their own cell. Therefore, lysosomes are also known as suicidal bags of a cell.

4. Ribosomes: These are extremely small, dense and round bodies interspersed in the cytoplasm. Ribosomes are made up of ribonucleic acid (RNA) and proteins. In prokaryotic cell, ribosomes are of 70 S type. In eukaryotic cells, ribosomes are of 80 S type. Ribosome is responsible for protein synthesis. They are not membrane bound.

5. Mitochondria: Mitochondria are small sausage-shaped organelles. It is a double-membrane structure. Outer membrane is smooth whereas inner membrane is projected into numerous finger-like structures called cristae. Mitochondria contain their own DNA and ribosomes. They provide energy for the vital activities of living cells. They produce energy due to chemical reactions, in the form of ATPs (Adenosine Triphosphate – energy currency of the cell). Therefore, it is called ‘powerhouse of the cell’.
JAC Class 9 Science Notes Chapter 5 The Fundamental Unit of Life 6

6. Centrosome and centrioles: Centrosome is found only in eukaryotic animal cells. It is not bounded by any membrane but consists of centrioles. Centrioles are hollow cylindrical structures arranged at right angle to each other and are made up of microtubules. Centrioles help in cell division and also help in the formation of cilia and flagella.

7. Plastids: Plastids are present in most of the plant cells and absent in animal cells. They are usually spherical or discoidal in shape. These are double membrane bound organelles. Plastids also have their own DNA and ribosomes. Plastids are of three types:

Chloroplast: They are green coloured plastids containing chlorophyll. Chloroplasts manufacture food by the process of photosynthesis.
Chromoplast: They are colourful plastids. They provide colour to flowers and fruits.
Leucoplast: They are colourless plastids. They help in the storage of various substances like starch, proteins and fats.

8. Vacuoles: Vacuoles are fluid filled chambers and are often seen in many cells. Vacuoles are very large in plant cells. A plant cell usually has a single but large central vacuole. Such a vacuole fills almost the entire space inside the cell. Vacuoles are much smaller and few in number in animal cells.
Cell division: A cell divides by one of the following two processes:
i. Mitosis: Each cell divides into two daughter cells and each new cell has same number of chromosomes as the mother cell.
JAC Class 9 Science Notes Chapter 5 The Fundamental Unit of Life 7
ii. Meiosis: Each cell divides into four daughter cells, each having half the number of chromosomes as the mother cell.

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 4 Structure of the Atom

September 10, 2024September 9, 2024 by Bhagya

JAC Board Class 9th Science Chapter 4 Notes Structure of the Atom

→ Atoms are made up of three fundamental particles or sub-atomic particles called electrons, protons and neutrons. Protons and neutrons of an atom are almost of same mass. The mass of proton is approximately 2000 times as that of an electron.

→ Electron (e): These negatively charged particles were discovered by J.J.Thomson in 1897. In the experiment, a gas at low pressure was taken in a discharge tube made up of glass.
JAC Class 9 Science Notes Chapter 4 Structure of the Atom 1

→ At the ends of the discharge tube, two electrodes were placed, connected to a battery for high voltage supply. The electrode connected to the negative end was known as cathode and that to the positive end as anode.

→ A stream of negatively charged particles was observed coming out of the cathode towards the anode. These particles were called electrons. The collection of negatively charged particles emitted from the cathode in the discharge tube are called cathode rays.

→ Proton (p⁺): In 1886, Goldstein observed in the same experiment, with different situation that, anode emitted positive particles which were called protons.

→ Canal rays: The positively charged radiations produced in the discharge tube from anode are called canal rays.

→ Difference between electron and proton:

Electron	Proton
Its mass is negligible.	Its mass is 1 unit.
Charge is negative.	Charge is positive.
J.J Thomson discovered it.	E. Goldstein discovered it.

→ Neutron (n): These neutrally charged particles were discovered by James Chadwick in 1932. Neutrons are present in atoms of all elements except hydrogen.

→ The structure of an atom:
1. Thomson’s Model of an atom: An atom is a positively charged sphere and the electrons are embedded in it. The magnitude of positive and negative charge is same inside an atom, so the atom is electrically neutral.
JAC Class 9 Science Notes Chapter 4 Structure of the Atom 2
2. Rutherford’s α-particle scattering experiment’: α-particles are doubly charged helium ions. Since they have a mass of 4 u, the fast moving α-particles have a considerable amount of energy. A thin gold foil with thickness of about 1000 atoms was taken. A lot of fast moving α-particles were bombarded on this thin gold foil. After passing through the foil, α-particles hit the screen.
JAC Class 9 Science Notes Chapter 4 Structure of the Atom 3

Following are the observations and inferences made:

Observation	Inference
a. Most of the α-particles pass through the foil without getting deflected.	a. Most of the space inside the atom is empty.
b. Some particles were deflected by small angles.	b. Positive charge of the atom occupies very little space.
c. One out of 12,000 particles rebound back.	c. All the positive charge and mass of the gold atom were concentrated in a very small volume within the atom.

Rutherford, on the basis of this experiment, suggested ‘the nuclear model of an atom’. According to the nuclear model of an atom:
a. Most of the space inside the atom is empty.
b. At the centre of an atom, a small, heavy, positively charged nucleus is present.
c. Electrons revolve around the nucleus.
d. Total positive charge in nucleus is the same as total negative charge on all electrons of the atom as atom has net zero charge.

→ Drawback of Rutherford’s model of an atom: If any charged particle undergoes accelerated motion, it must radiate energy. Therefore, if a charged body (e;) rotates around another charged body (nucleus), it will radiate energy. Due to energy loss through the radiation, speed of electrons will decrease and eventually jt will fall into the nucleus. But such collapse does not occur and atoms are found to be quite stable.

3. Bohr’s Model of Atom: In 1913, Neils Bohr overcame the limitations of Rutherford’s model and proposed a model of atomic structure.
Following are the postulates:
a. Electrons revolve around a centrally located heavy, small and positively charged nucleus in certain discrete orbits.
b. While revolving in discrete orbits, electrons do not radiate energy.
c. These discrete orbits or shells are called energy levels. These orbits or shells are represented by the letters K, L, M, N …
JAC Class 9 Science Notes Chapter 4 Structure of the Atom 4

→ Distribution of Electrons in Different Orbits: Distribution of electrons in different orbits (shells) is given by Bohr and Bury:
a. Maximum number of electrons present in a shell is given by 2n² (n = shell number).
For example,
n = 1 (K shell). 2n² = 2 (1)² = 2 electrons
b. The maximum number of electrons that can be accommodated in the outermost orbit is 8.
c. Electrons are not accommodated in a given shell, unless the inner shells are completely filled.

→ Atomic Number: The number of protons present in the nucleus of an atom is called its atomic number. It is denoted by Z.

→ Mass Number: Mass number is equal to the number of nucleons present inside the nucleus of an atom. It means, it is the sum of the total number of protons and neutrons of an atom. It is denoted by the letter A.
‘Mass number of element = Number of protons + Number of neutrons’
JAC Class 9 Science Notes Chapter 4 Structure of the Atom 6

→ Isotopes: Isotopes are atoms of same element having same number of protons but different number of neutrons. Isotopes have similar chemical properties but different physical properties.
For example: ¹²₆C, ¹⁴₆C

→ Uses of Isotopes:
a. An isotope of uranium (²³⁵₉₂C) is used in nuclear power plants to generate electricity.
b. An isotope of cobalt is used in treatment of cancer.
c. An isotope of iodine is used in treatment of goitre.
Isobars: Atoms of different elements having same mass number but different atomic numbers are called isobars.
For example: ⁴⁰₂₀Ca, ⁴⁰₁₈Ar

→ Valency: The electrons in the last shell of the atom are called valence electrons. These govern the chemical properties of elements. The number of valence electrons that take part in a chemical reaction is called valency of the atoms.
For example, hydrogen has only one electron in its outermost orbit, thus it requires one more electron to fill its outermost orbit (K shell). For this, hydrogen atom shares one electron with another hydrogen atom and forms Hr

→ When an electron from a higher energy level falls in an orbit of lower energy level, the difference in energy is radiated in the form of electromagnetic radiation or light. This explains why different atoms on heating or under other conditions emit light of different colours.

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 3 Atoms and Molecules

September 10, 2024September 9, 2024 by Bhagya

JAC Board Class 9th Science Chapter 3 Notes Atoms and Molecules

→ In 430 B.C., Democritus postulated that matter is made up of very small particles calLed “Atomos’ which means ‘indivisible’. Later, Antoine Lavoisier, from his experimental observations, established the laws of chemical combinations.

→ The Law of Conservation of Mass: This law of conservation of mass states that, the total mass of reactants is equal to the total mass of products.
For example:
A + B → C + D
(Reactants) → (Products)
Total mass of reactants = Total mass of products

→ Law of Definite Proportions: According to the law of definite proportions, in a chemical substance, the elements are always present in definite proportion by mass. For example. in water, the ratio of the mass of hydrogen to the mass of oxygen is always 1: 8.

→ After a series of experiments, Dalton concluded that all matter must be composed of tiny particles, which cannot be further divided. He called them atoms.

→ “The smallest particle of an element is called an atom.”
Atomic radius is measured in nanometer (nm).
1nm = 1 × 10⁹m
1 m = 10⁹nm
Atomic radii of hydrogen atom 1 × 10^-10 m

→ Dalton’s Postulates:

Matter is made up of atoms.
Atoms are indivisible and indestructible.
Atoms of a given element are identical in mass and in properties.
Compounds are formed by a combination of two or more same or different kinds of atoms and a chemical reaction is a rearrangement of atoms.
Atoms of different elements have different masses and chemical properties.
Atoms combine in the ratio of small whole numbers to form compounds.
The relative number and kind of atoms are constant in a given compound.

→ Elements and symbols: Dalton proposed a scheme of notation to represent elements.
JAC Class 9 Science Notes Chapter 3 Atoms and Molecules 1

→ Symbols for some elements as proposed by Dalton Symbols of some common elements

Name of the element	Latin name	Symbol
Hydrogen	–	H
Helium	–	He
Carbon	–	C
Copper	Cuprum	Cu
Cobalt	–	Co
Chloride	–	Cl
Cadmium	–	Cd
Boron	–	B
Barium	–	Ba
Bromine	–	Br
Bismuth	–	Bi
Sodium	Natrium	‘ Na
Potassium	Kalium	K
Iron	Ferrum	Fe
Gold	Aurum	Au
Silver	Argentum	Ag
Mercury	Hydrargyrum	Hg

→ Molecule: A molecule is a group of two or more atoms that are chemically bonded together and form the smallest part of an element or a compound. This can exist independently and shows all the properties of that substance.

→ Atomicity: The number of atoms constituting a molecule is referred to as its atomicity. Molecules of an element constitute same type of atoms. They may be monoatomic, diatomic or polyatomic.

Name of the element	Atomicity	Molecular formula
Helium	Monoatomic	He
Neon	Monoatomic	Ne
Argon	Monoatomic	Ar
Krypton	Monoatomic	Kr
Xenon	Monoatomic	Xe
Radon	Monoatomic	Rn
Hydrogen	Diatomic	H₂
Chlorine	Diatomic	Cl₂
Nitrogen	Diatomic	N₂
Phosphorus	Polyatomic (Tetra)	P₄
Sulphur	Polyatomic (Octa)	S₈

→ Ion: Ion is a charged particle and can be positively or negatively charged. A positively charged particle in a molecule is called cation, for example, Na⁺, Ca²⁺. An anion is a negatively charged particle in a molecule, for example, F^–, Cl^–.

→ Valency: The combining capacity of an element is known as valency. The combining capacity of the atoms to form molecules either with same or different elements is defined as valency. Valency is used to find out the number of atoms of an element that will combine with the atom of another element to form a chemical compound.

Every atom wants to become stable. To do so, it may lose, gain or share electrons.
a. If an atom consists of 1,2 or 3 electrons in its valance shell, then its valency is 1, 2 or 3 respectively, and it will lose 1, 2 or 3 electrons respectively.
b. If an atom consists of 5, 6 or 7 electrons in the outermost shell, then it will gain 3, 2 or 1 electron respectively, and its valency will be 3, 2 or 1 respectively.
c. If an atom has 4 electrons in the outermost shell, then it will share these electrons and hence its valency will be 4.
d. If an atom has 8 electrons in the outermost shell, then its valency is 0.
JAC Class 9 Science Notes Chapter 3 Atoms and Molecules 2

→ Variable valency: Some elements show more than one valency, hence, termed as variable valency elements.
For example:
Iron shows
valency II – Fe²⁺ (Ferrous ion)
valency III – Fe³⁺ (Ferric ion)

Copper shows
valency I – Cu⁺ (Cuprous ion)
valency II – Cu²⁺ (Cupric ion)

→ Chemical Formulae: The chemical formula of a compound is a symbolic representation of its composition.
Rule 1: Cross multiply the valency of elements to form a compound.
JAC Class 9 Science Notes Chapter 3 Atoms and Molecules 3

Rule 2: If compound consists of both metal and non-metal, then metal is written first. For example: In calcium chloride (CaCl₂) and zinc sulphide (ZnS), Calcium and Zinc are metals, so they are written first, whereas chloride and sulphide are non-metals.

Rule 3: If a compound is formed with polyatomic ions, then polyatomic ions are written in brackets.
For example: In aluminium sulphate [Al₂(SO₄)₃], the polyatomic sulphate ion, SO₄^2- is enclosed in a bracket before writing the subscript 3.
Here, the bracket with a subscript 3 indicates that three sulphate groups (SO₄^2-) are joined to two aluminium atoms.

Note: Compounds made up of a metal and a non-metal are called salts or ionic compounds. All the above examples are of salts.

→ Mole Concept: The quantity of a substance is expressed in terms of mole. 1 mole is also defined as the amount of substance which contains 6.022 × 10²³ units (Avogadro’s number denoted by NA).
For example 1 mole of oxygen atoms represents 6.022 × 10²³ atoms of oxygen and 5 moles of oxygen atoms contain 5 × 6.022 × 10²³ atoms of oxygen.

→ Molar Mass: The mass of 1 mole of a substance is called molar mass. Atomic mass or molecular mass in gram is equal to molar mass.
For example: Atomic mass of Fe is 56 u. Molar mass of Fe is 56 g.
Atomic mass of H₂O is 18 u. Molar mass of H₂O is 18 g.
Number of moles = \(\frac{\text { Given mass }}{\text { Molar mass }}\)

For example, number of moles in 122 g of iron will be
\(\frac{\text { Given mass }}{\text { Molar mass }}=\frac{112}{56}\) = 2 × 6.022 × 10²³ atoms.

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 2 Is Matter Around Us Pure

September 10, 2024September 9, 2024 by Bhagya

JAC Board Class 9th Science Chapter 2 Notes Is Matter Around Us Pure

→ A pure substance consists of a single type of particles.

→ A mixture has more than one substance (element / compound) mixed in any proportion.

→ Mixtures can be separated into pure substances by appropriate separation techniques.

→ A solution is a homogeneous mixture of two or more substances. The major component of a solution is known as the solvent and the minor one is the solute. For example, sugar dissolved in water or alloy of copper and zinc or ethyl alcohol in water.

Mass percentage of a solution
= \(\frac{\text { Mass of solute }}{\text { Mass of solution }}\) × 100
Volume percentage of a solution
= \(\frac{\text { Mass of solute }}{\text { Mass of solution }}\) × 100

→ Materials which are insoluble in a solvent and have particles which are visible to naked eyes form a suspension. A suspension is a heterogeneous mixture.

→ When solids are dispersed in liquids to form a heterogeneous mixture or an opaque medium, it is called suspension.

→ Colloidal solutions are heterogeneous mixtures where particles of 1 × 10⁹ to 1 × 10^-6 m diameter, called dispersed phase, are distributed uniformly in a solvent, called dispersing medium.

→ Difference between true solutions, suspension and colloidal solutions.

True Solution	ColloidalSolution	Suspension
It is a homogeneous mixture of solute and solvent.	It appears to be homogeneous but actually it is a heterogeneous mixture of dispersed phase and dispersing medium.	It is a heterogeneous mixture.
The solute particles are very small, i.e., less than 10⁹ m in diameter.	The solute particles are between 10⁹and 10⁶ m in diameter.	The solute particles are quite large, i.e., larger than 10⁶m in diameter.
Particles of true solution are not visible to naked eye.	Particles are not visible to naked eye but can be seen with ultramicroscope.	Particles are big enough to be seen by naked eye.
The entire solution passes through filter paper.	The particles can pass through ordinary filter paper.	The particles cannot pass through filter paper.
The solute particles do not show Tyndall effect.	The particles show Tyndall effect.	The particles may or may not show Tyndall effect.
The particles do not settle down.	The particles do not settle down.	The particles may settle due to gravity.

→ Different Types of Colloids
JAC Class 9 Science Notes Chapter 2 Is Matter Around Us Pure 1

→ Separation of a mixture can be done by hand-picking, sieving, winnowing, sedimentation, decantation, filtration, evaporation, distillation, fractional distillation, centrifugation, crystallisation and chromatography.

→ A physical change brings about a change in the state of matter without change in the composition or chemical nature of the substance.

→ A chemical change brings about a change in chemical properties of matter because one or more substances are transformed into a new substance.

→ Pure substances can be elements or compounds.

→ An element is a form of matter which cannot be broken down by chemical reactions into simpler substances.

→ A compound is a substance composed of two or more different types of elements, chemically combined in a fixed proportion.

→ Properties of a compound are different from its constituent elements whereas a mixture shows the properties of its constituting elements or compounds.
JAC Class 9 Science Notes Chapter 2 Is Matter Around Us Pure 2

JAC Class 9 Science Notes

JAC Class 9 Science Notes Chapter 14 Natural Resources

September 10, 2024September 8, 2024 by Bhagya

JAC Board Class 9th Science Chapter 14 Notes Natural Resources

→ Various material resources derived from the nature for the benefit of mankind are called natural resources.

→ The life supporting zone of earth is called biosphere. It has two components:
a. Biotic components: include all the living things, e.g., forests, animals, humans, etc.
b. Abiotic components: include all the non-living things, e.g., air, water, land, etc.

→ Air: It is an inexhaustible natural resource essential for the sustenance of life. The thick blanket of air that surrounds the earth is called atmosphere. This atmosphere keeps the average temperature of the earth fairly steady.

→ Wind: Moving air is called wind. In coastal areas, the uneven heating of land and water creates winds. During day, the direction of wind is from sea to land (sea breeze) while at night, wind blows from land to sea (land breeze).

→ Rain: When water bodies are heated during the day, water vapour goes into the air. As air rises, it expands and cools forming tiny water droplets? These droplets grow bigger by condensation and fall down as rain.

→ Air pollution: Presence of undesirable and harmful substances in the air causes air pollution. Burning fossil fuels release oxide of nitrogen and sulphur in air which in turn causes acid rain. Smoke and fog in air reduce visibility and form smog.

→ Water: 97% of the water on earth is in oceans and only 3% is fresh water. Of this 3%, only 1 % is available for use and the rest is present in glaciers. Rainwater harvesting improves the availability of fresh water. It is essential for the growth and sustenance of plants and animals.

→ Water pollution: Pollution of water can occur in three ways;
a. by addition of undesirable substances,
b. by removal of desirable substances, and
c. by change in temperature.

→ Chemical fertilizers and pesticides pollute underground water. Chemicals released by industries and water released by dams also pollute water. This also destroys the life- forms in those water bodies.

→ Soil: Soil is formed by various physical, chemical and some biological processes. Sun, water and wind, all contribute to the formation of soil. Some organisms, like lichens, grow on rocks and release chemicals which cause the rock surface to powder down into soil.

→ Soil is composed of different sizes of particles which decide the soil type.

→ Soil pollution: Modem farming practices which use chemical fertilizers and pesticides are harmful for the soil. We should use the soil sustainably and plant trees to prevent soil erosion.

→ Biogeochemical cycles: The cycles in nature which keep replenishing the various natural resources in atmosphere and on the earth’s crust are called biogeochemical cycles.
a. Water-cycle: It is the constant exchange of water among the air, land and sea and between living organisms and their surroundings.
JAC Class 9 Science Notes Chapter 14 Natural Resources 1
b. Nitrogen-cycle: Nitrogen, an important nutrient for all life forms, is circulated through the living and non-living components of the biosphere through various processes like nitrogen fixation (by nitrogen fixing bacteria), ammonification, nitrification and denitrification.
JAC Class 9 Science Notes Chapter 14 Natural Resources 2
c. Carbon-cycle: Carbon is incorporated into life forms by the process of photosynthesis and returns to the atmosphere through respiration, decomposition, combustion, etc.

d. Oxygen-cycle: Green plants release oxygen by photosynthesis which is cycled during combustion and respiration.
JAC Class 9 Science Notes Chapter 14 Natural Resources 4

→ Greenhouse effect: Greenhouse gases like CO₂, CH₄, etc., trap the solar energy and keep the earth warm. This is called greenhouse effect. However, excess of such gases in atmosphere results in heating up of the earth and increase the average temperature across the globe. This is called global warming which has numerous ill-effects like melting of glaciers, floods, draughts, etc.

→ Ozone (O₃): Ozone layer is present like a blanket around the earth in the stratosphere. It absorbs the harmful UV radiations from the sun and hence protects us. However, the presence of compounds like CFCs in the atmosphere depletes the amount of ozone. An ozone hole, formed by thinning of ozone, is found over Antarctica. Hence, there is a need to take precautionary measures and lifestyle changes to conserve and procure the nature.