Class 9

RBSE Class 9 Science Notes Chapter 11 Sound

July 12, 2019 by Prasanna Leave a Comment

Rajasthan Board RBSE Class 9 Science Notes Chapter 11 Sound

Production of Sound:
Sound is a form of energy which produces a sense of hearing in our ears. Sound is produced by striking, plucking, scratching, rubbing, blowing or shaking of different objects.

Propagation of Sound:

Sound is produced by vibrating objects. The matter or substance through which sound is transmitted is called a medium. The vibration of all the particles of a material medium, sets up the vibration in the object(s) placed in the medium. The medium around its vibrating the medium in contact with the vibrating object is first displaced from its equilibrium position. It then exerts a force on the adjacent particle. As a result, the adjacent particle gets displaced from its position of rest. Disturbance created by a source of sound in the medium travels through the medium and not the particles of the medium. A wave is a disturbance that moves through a medium. Sound waves are characterised by the motion of particles in the medium and are called mechanical waves.
When a vibrating object moves forward, it pushes and compresses the air in front of it, creating a region of high pressure. This region is called compression. When the vibrating object moves backwards, it creates a region of low pressure called rarefaction.
A series of compressions and rarefaction’s facilitates propagation of sound waves through the medium.
Sound needs a material medium like air, water, etc. for its propagation. It can not travel through vacuum.

Nature of Sound Waves:

All waves-mechanical and non mechanical waves are classified into two types. These are: Longitudinal waves (b) Transverse waves.
Longitudinal waves: A wave in which the particles of the medium oscillate to and fro about their mean positions, in the direction of propagation of the wave is called a longitudinal waves. Examples:
Sound waves
Waves produced in a spring.
Transverse waves: A wave in which the particles of the medium oscillate about their mean position in a direction perpendicular to the direction of propagation, of the wave is called a transverse wave.
Examples:
All electromagnetic waves, i.e., light waves, etc.
When a string of sitar or guitar is plucked, transverse waves are produced in the string.
Transverse wave occurs in the form of crests and troughs.
As we have already discussed, in transverse waves the particles of the medium oscillates in the direction perpendicular to the direction of propagation. The highest point on the hump in a transverse wave is called crest or in other words, we can say that the point of maximum positive displacement on a transverse wave is called crest.
The lowest point on the depression in a transverse wave is called trough, or in other words we can say that the point of maximum negative displacement on a transverse wave is called trough.

Characteristics of a sound wave:
A wave is characterized mainly in terms of the following parameters.
• Frequency
• Amplitude
• Speed

Frequency: The number of complete waves (or oscillations) produced in one second is called frequency of the wave. It is the number of vibrations that occur per second. It is denoted by the Greek letter v. Its S.l. unit is Hertz (symbol, Hz), named in honor of Heinrich Rudolf Hertz, who discovered photoelectric effect.1 Hz = 1 vibration per second 1 kHz = 1000 Hz
Amplitude: The maximum displacement of the particles of ti medium from their original mean position, on passing a wave through the medium is called amplitude of the wave. It is used to describe the size of the wave. It is usually denoted by the letter A. Its S.l. unit is meter.
Speed: The distance traveled by a wave in one second is called speed of the wave under the same physical conditions. The speed of sound is same for all frequencies. It is represented by the letter V. Its S.l. unit is meter/ second.Relationship between speed, frequency and wave length of a wave From the definition of velocity
Velocity $=\frac{\text { Distance travelled }}{\text { Time taken }}$
So for a wave,
Wave velocity $=\frac{\text { Distance travelled by a wave }}{\text { Time taken }}$
A wave takes time equal to its time period (T), to travel a distance equal to its wave length.
So, wave velocity $=\frac{\text { Wave length of the wave }}{\text { Time neriod of the wave }}$
$\mathrm{V}=\frac{\lambda}{\mathrm{T}}$
As per definition:
Frequency of the wave,
$v=\frac{1}{\text { Time period of the wave }}$
$v=\frac{1}{T}$
From (i) and (ii) , we have
$\mathrm{V}=\lambda \times \frac{1}{\mathrm{T}} \Rightarrow \mathrm{V}=\lambda \mathrm{v}$
⇒ wave velocity = wave length × frequency
The above equation is known as wave equation. This statement is true for all the types of waves. Velocity of the wave depends on the medium.

Intensity:
The amount of sound energy passing each second through unit area is known as the intensity of sound. Intensity of sound can be measured. The relation of intensity of sound is with its energy. The S.l. unit of intensity is watt per square meter (w/m²).

Loudness:

The loudness of a sound depends on the amplitude of the vibration producing that sound. Greater the amplitude of vibration, louder is the sound produced by it.
The loudness of a sound also depends on the quantity of air that is made to vibrate.
Loudness of sound is measured in decibels (dB) unit.

Pitch:
The characteristic of sound by which a shrill note can be distinguished from a flat note is called pitch. The pitch of the sound depends upon its frequency. Higher the frequency of sound, higher is its pitch.

Quality OR Timber:

Quality of a sound is also known as timber.
The quality or timber of sound is that characteristic which enables us to distinguish one sound from another, having the same pitch and loudness. The sound which is more pleasant is said to be of a rich quality.

Reflection of sound:
Sound bounces off a solid or a liquid, just like a rubber ball bounces off the wall. The directions in which the sound is incident and reflected, make equal angles with the normal to the reflecting surface at the point of incidence and they are in the same plane.

Echo:
If we shout or clap near a suitable reflecting object such as a tall building or a mountain, we will hear the same sound again, a little later. This sound which we hear is called an echo. To hear a distinct echo, the time interval between the original sound and the reflected one must be at least 0.1s.

Reverberation:
A sound created in a big hall will persist by repeated reflections from the walls, until it is reduced to a value where it is no longer audible. This persistence of sound is called reverberation.

Audible range:
The audible range of sound for human beings extends from about 20 Hz to 20000 Hz (one Hz = one cycle/s). Sound of frequencies below 20 Hz are called infrasonic sound or infra sound. Sound frequencies higher than 20 kHz are called ultrasonic sound or ultrasound.

Applications of Ultrasound:
Ultrasound are used extensively in industries and for medical purposes. Ultrasound is generally used to clean hard-to-reach places; to detect cracks or flaws in metal blocks; echo-cardiology; scanning; etc.

SONAR:
The acronym SONAR Stands for Sound Navigation and Ranging. This technique is used by ships to detect the presence of submarines, icebergs, sunken ships, etc. in the sea. SONAR is a device that uses ultrasonic waves to measure the distance, direction and speed of underwater objects. Sonar can also be used for determining the depth of the sea.

Determination of the depth of a sea using SONAR:
Let the time interval between transmission and reception of ultrasound signal be t and the speed of sound through seawater be v. The total distance, 2 d traveled by the ultrasound is 2 d = v x t

Structure of Human Ear:
Sound waves from outside are collected by external ear (known as Pinna) and reaches the eardrum, through the auditory canal. When the sound waves strike the eardrum, it starts vibrating. These vibrations are transmitted across the middle ear by the three ossciles called (the hammer, anvil and stirrup). The vibrations produced by the eardrum are amplified. The amplified vibrations are then transmuted to the cochlea. Cochlea is coiled and fluid filled tube, having the sense organ for thousands of auditory nerves, which send messages to the brain.

RADAR:

The word RADAR is an acronym derived from the words Radio Detection and Ranging. It refers to the technique of using radio waves to detect the presence of objects in the atmosphere. The electronic principle on which radar operates is very much similar to the principle of sound wave reflection. In 1922, A. Hoyt Taylor and Leo.C.Young discovered the scientific device RADAR. RADAR is an object detection system that uses radio waves to determine range, angle or velocity of objects. It can be used to detect air craft, ships, space craft,guided missiles, formation of weather focuses and terrains.
Once the radio waves have been generated, an antenna working as a transmitter, focuses them into the air, in front of it. The antenna is usually curved. So, it focuses the waves into a precise, narrow beam, but RADAR antennas also typically rotate so. they can detect movements over a large area.
The radio wave travel out ward from the antenna at the speed of light (186000 miles or 300000 km/s) and keep going, until they hit something. Then, some of them bounce back towards the antenna in a beam of reflected radio waves, also travelling at the speed of light. If an enemy jet plane is approaching at over 3000 km/h, the RADAR beam needs to travel much faster than this to reach the plane, so it returns to the transmitter and trigger the alarm in time. That is no problem, because radio waves travels fast enough to go seven times around the world in a second. Any reflected radio waves picked up by the antenna are directed into a piece of electronic equipment that processes and displays them in a meaningful form, on a television like screen, watched all the time by a human operator. Using RADAR an operator can see nearby ships,planes, where they are, how quickly they are travelling and where they are heading.

Summary of how does a RADAR works:

An instrument, magnetron generates high frequency radio waves.
Duplexer switches magnetron to the antenna.
Antenna acts as transmitter, sending narrow beam of radio waves through the air.
Radio waves hit energy airplane and reflect back.
Antenna picks up reflected wave during a break between transmission.
Duplexer switches antenna through to receiver unit.
Computer in receiver unit processes reflected waves, and draw them on a T.V screen.
Enemy plane shows up on TV radar, also displaying any other nearly targets.

Uses of RADAR:

In navigation of aeroplane and ships.
In launching of rockets and missiles.
In GP.S system.
In locating the enemies aeroplane, missiles and ships.

RBSE Class 9 Science Notes

RBSE Class 9 Science Notes Chapter 10 Gravitation

July 12, 2019 by Prasanna Leave a Comment

Rajasthan Board RBSE Class 9 Science Notes Chapter 10 Gravitation

Gravitation:
The force by which one particle attracts the other particles in the universe is called the force of gravitation.

Newton’s Law of Gravitation:
Newton’s law of gravitation may be stated as follows:
Every particle in the universe attracts every other particle with a force, which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
This force of attraction is along the line joining the two particles. Let us consider two objects A and B of masses m1 and m2 separated by a distance R. The force of gravitation (F) acting on these two particles, according to Newton’s law
$\mathrm{F} \propto m, \times m_{2} \text { and } \mathrm{F} \propto \frac{1}{\mathrm{R}^{2}} \text { or } \mathrm{F} \propto \frac{m_{1} m_{2}}{\mathrm{R}^{2}} \Rightarrow \mathrm{F}=\mathrm{G} \frac{m_{1} m_{2}}{\mathrm{R}^{2}}$
where, G is called the universal gravitational constant
(Value of G = 6.67 × 10^-11 Newton m² / kg²)
Example: Two objects of 25 kg and 75 kg are situated 1 meter apart. Calculate the gravitational force between them.
[G = 6.67× 10^-11Nm²/ kg² ]

Solution:
Mass of first object, m₁= 25 kg
Mass of second object, m₂ = 75 kg
Distance between both the objects, R = 1 m

Formula: $F=G \frac{m_{1} m_{2}}{R^{2}}$ Or $F=\frac{6.67 \times 10^{-11} \times 25 \times 75}{(1)^{2}} \text { or } F=1.25 \times 10^{-7} .$ Newton

Freely falling bodies:

Experiment: A long and wide tube filled with air is kept vertically, as shown in figure (A). We drop a coin and a feather in this tube simultaneously. We see that the coin reaches the bottom of the tube earlier, because the coin is heavier. The feather being lighter reaches a bit later.
Now, keeping the coin and feather in the tube, fit a vacuum pump and seal the mouth of the tube, making it air tight as shown in figure (B). Take out air from the tube with the help of the vacuum pump and thus create vacuum in the tube. Again, let the coin and feather drop, simultaneously. We see that they reach the bottom of the tube simultaneously now. From the above experiment we conclude that all bodies(lighter or heavier) in vacuum fall with the same acceleration towards the earth.
Acceleration of the bodies falling freely under the action of gravity does not depend upon their mass.
On the basis of experiments, it was found that all the bodies fall towards the earth with an acceleration of 9.8 m/s². This acceleration is produced in a body due to force of gravity. Therefore, this acceleration is called acceleration due to gravity and it is represented by the symbol ‘g’. It is constant at a place, but varies from place to place on the earth.

Value of acceleration due to gravity:
The gravitational force acting on a body of mass ‘m’ near the surface of the earth is given by
$F=\frac{G \cdot M \cdot m}{R^{2}}$ ……….(i)
where, m is the mass of body, M is the mass of the earth and R is the radius of the earth.
If g is the acceleration produced in the body, of mass m, then
F= mg ……(ii)
From the equation (i) and (ii), we have
$m g=\frac{G \cdot M \cdot m}{R^{2}} \text { or } g=\frac{G M}{R^{2}}$
Thus, acceleration due to gravity does not depend on the mass of the falling body. Hence, all bodies fall towards the earth with same acceleration

Relation between ‘g’ on the earth and on a planet:
If the value of acceleration due to gravity on the surface of the earth is g_e, the mass of earth is M_e and radius of earth is R_e, then
$g_{e}=\frac{G \cdot M_{e}}{R_{e}^{2}}$
If the value of acceleration due to gravity on the surface of the planet is g_p, the mass of planet is M_p and radius of planet is R_p, then
$g_{\rho}=\frac{G \cdot M_{0}}{R_{p}^{2}}$
On dividing equation (ii) by equation (i), we get
$\frac{g_{\rho}}{g_{e}}=\frac{\mathrm{G} \cdot \mathrm{M}_{\mathrm{p}}}{\mathrm{R}_{\mathrm{p}}^{2}} \div \frac{\mathrm{G} \cdot \mathrm{M}_{\mathrm{e}}}{\mathrm{R}_{\mathrm{e}}^{2}}$
$\frac{g_{p}}{g_{e}}=\frac{M_{p}}{M_{e}} \times\left(\frac{R_{e}}{R_{p}}\right)^{2}$
From this equation, weight of the planet can be calculated.
Example: Both the radius and mass of a planet are half of the radius and mass of the earth. What would be the value of acceleration due to gravity on the planet, in comparison to that on the earth?
Solution:. Mass of earth = M_e
Mass of planet = M_p = $=M_{p}=\frac{M_{e}}{2}$
Radius of earth = R_e
Radius of planet = R_p $=\frac{R_{e}}{2}$
We have to find out the acceleration due to gravity, g_p
Formula: $\frac{g_{p}}{g_{e}}=\frac{M_{p}}{M_{e}} \times\left(\frac{R_{e}}{R_{p}}\right)^{2}$ Or $\frac{g_{p}}{g_{e}}=\frac{M_{e}}{2 M_{e}} \times\left(\frac{2 R_{e}}{R_{e}}\right)^{2}$
Or $\frac{g_{p}}{g_{e}}=\left(\frac{1}{2}\right) \times\left(\frac{4}{1}\right)=2$
∴ $g_{p}=2 g_{e}$
The value of acceleration due to gravity on the planet would be twice the value on the earth.
Acceleration due to gravity on Moon is 1 /6 th of that on the earth

Mass:
Mass of a body is defined as the quantity of matter contained in the body. Its SI unit is kilogram and it is a scalar quantity.

Weight:
The force with which a body is attracted by the earth is known as the weight of the body. Weight of a body (w) = mass × acceleration due to gravity
w = mg
The S.l. unit of weight is the same as that of force, i.e., Newton.

Weightlessness:

The force with which the earth attracts a body on it is called weight of the body. Consider a person standing on a weighing machine, placed inside an elevator which is at the uppermost storey of a multi storeyed building. When the elevator is at rest, the machine reads the true weight of the person, because weight of the man is pressing the spring in the machine downwards and machine gives the reaction. As the elevator moves downwards, the machine shows less weight. When falling freely, both the person and the weighing machine are attracted by the earth with the same acceleration, and no force acts on the machine due to the person. As a result, the machine will read zero.
Thus, the apparent weight of the freely falling person is zero, i.e., a person appears weightless when falling under the action of gravity. When a body falls down under the acceleration due to gravity of earth, then it becomes weightless.

Weightlessness in space:
The spaceships, satellites and astronauts orbiting the earth at a certain height are actually, in a state of free fall towards the earth. During the free fall, both travel downwards with the same acceleration, equal to the acceleration due to gravity. As a result, the astronaut does not exert any force on the sides/ floor of spaceship and the floor/side does not push them up. As a result, the astronaut experiences weightlessness while orbiting around the earth in a space-vehicle.

Equation of motion for an object under free fall:
Initial velocity of the object remains zero, when the object is under free fall. In this situation, the three equations of motion, i.e., v = u + gt
$s=u t+\frac{1}{2} g t^{2}$
$v^{2}=u^{2}+2 g h$
Will become equal to
v= gt
$s=\frac{1}{2} g t^{2} \quad \text { and } v^{2}=2 g h$
Here, v = final velocity, t = time, g = acceleration due to gravity, h = height attained by the body. If an object is thrown upwards then acceleration due to gravity will be negative. So, equation of motions will become
v = u – gt
$\mathrm{s}=\mathrm{ut}-\frac{1}{2} \mathrm{gt}^{2}$
$v^{2}=u^{2}-2 g h$

RBSE Class 9 Science Notes

RBSE Class 9 Science Notes Chapter 9 Force and Motion

July 12, 2019 by Prasanna Leave a Comment

Rajasthan Board RBSE Class 9 Science Notes Chapter 9 Force and Motion

Scalar and vector quantities
The physical quantities which have only magnitude and need no idea of direction are called scalar quantities. For example: Speed, mass, time, length, area, volume, density, work, energy etc. are scalar quantities.

Vector quantities:
There are certain quantities which require magnitude as well as direction to express them clearly. That is, the physical quantities which have magnitude as well as direction are called Vector quantities.

Unit Vector:
Unit vector of any $\vec{A}$ is a vector whose magnitude is unit and direction is the direction of vector $\vec{A}$ Unit vector’s denoted as $\hat{\mathrm{A}}$ and is read as A cap
$\hat{A}=|\overline{A}| \hat{A} \Rightarrow \frac{\overline{A}}{|\overline{A}|}$
Motion:

An object is said to be in motion, if its position from the reference point, changes with time. We require two measurements, to describe the position of an object.
The distance of the object from a fixed reference point called origin.
The angle which the line joining the origin and object makes with a reference axis.

Relative nature of motion:
We take an example to explain the nature of motion . A person with his companions is sitting inside a compartment of a running train. The person is at rest relative to other passengers but the person is in motion with respect to the trees and telegraph poles.

This example shows that the same object may be at rest with respect to one reference point and in motion with respect to another at the same time. So, we can say that motion is actually a relative term.

Distance and displacement:

The distance traveled by an object is actual length of the path, traced by it. Distance is a scalar quantity.
The minimum straight line distance between the first position and the last position of an object, in a particular direction
is called displacement. Displacement is a vector quantity.

Speed:
Distance traveled by a body in unit time is called speed of body. Unit of speed is meter per second. Speed is a scalar quantity because it gives idea of magnitude only and not of direction.
Speed = $\frac{\text { Distance travelledby the body }}{\text { Time interval }}, \text { i.e., } \mathrm{S}=\frac{d}{t}(\mathrm{m} / \mathrm{sec})$

Velocity:
• The displacement of a moving body per unit time in a definite direction is called its velocity. Its unit is also meter per second. It is a vector quantity.
Velocity $=\frac{\text { Displacement Vector }}{\text { Time Interval }} \text { or } \overline{v}=\frac{\overline{d}}{t}$

Difference between Speed and Velocity:

Speed

Velocity

1. The distance covered by a moving body per unit time is called speed.

2. Speed is scalar quantity. It has magnitude only, direction is not required.

1. The distance covered by a moving body per unit time, in a definite direction is called velocity.

2. Velocity is a vector quantity. It has a meaning both with magnitude and direction.

Uniform acceleration:
When the change in the velocity of a moving body is the same per unit interval of time, then its acceleration is said to be uniform. Such motion is said to be a uniformly accelerated motion.

Non-Uniform acceleration:
When the change in velocity of a moving body is not the same per unit interval of time, then its acceleration is said to be non uniform acceleration and the moving body is said to be moving with non-uniform acceleration.

Graphical representation of motion:
Velocity time graph:
When a body moves with a constant velocity in a straight line:
Let us consider a body moving with a constant velocity, v. Since velocity remain constant with time, therefore, velocity-time graph is obtained as a straight line parallel to x axis. Let distance covered by the body moving with constant velocity v in time t is s. then the s = v × t.

In the adjoining-figure, let OC represents time t, on x-axis and OA represents velocity v, on y-axis. Therefore, Area of rectangle (OABC) = OC× OA = v × t. This area called the area under the velocity-time graph, represents the total distance traveled by the body in time t.

When a body is moving with uniform acceleration. How to derive the three equations of motion from velocity time graph?:
The velocity time graph for a body under uniform acceleration is shown in figure.
Let initial velocity of the body = u
Final velocity of the body = v
Time taken by the body = t
Acceleration of the body = a

Derivation of the first equation of motion:
According to definition:
Acceleration of a body = Rate of change of velocity, i.e., slope of velocity time graph.
The velocity time graph for a uniformly accelerated body is given by the straight line AB. So, accelerated of the body is equal to the slope of the line AB.
Acceleration = Slope of line
$A B=\frac{B D}{A D}=\frac{B C-D C}{A D}$
From the velocity time graph
BC = v, DC = OA = u, AD = OC = t
$a=\frac{v-u}{t} \Rightarrow a t=v-u \Rightarrow v=u+a t$ This is the first equation of motion

Derivation of the second equation of motion:
Under uniform acceleration, from figure, one can write
Distance travelled (s) = Area of trapezium OABC
s = Area of the triangle ABD + Area of rectangle OADC
$\frac{1}{2} \times \mathrm{AD} \times \mathrm{BD}+\mathrm{OC} \times \mathrm{OA}$
Here, AD = OC = t and BD = BC – DC = v – u
BD = u + at – u = at and OA = u
$s=\frac{1}{2} \times t \times a t+t \times u \Rightarrow s=u t+\frac{1}{2} a t^{2}$ This is the second equation of motion

Derivation of the third equation of motion:
Distance travelled, s = Area of the trapezium OABC
$s=\frac{1}{2}(\text { sum of the parallel sides }) \times$ perpendicular distance between the two parallel sides
$s=\frac{1}{2} \times(\mathrm{OA}+\mathrm{BC}) \times \mathrm{OC} \quad s=\frac{1}{2}(u+v) \times t$
But, $a=\frac{v-u}{t} \Rightarrow t=\frac{v-u}{a} \Rightarrow s=\frac{1}{2}(v+u) \times \frac{v-u}{a}=\frac{v^{2}-u^{2}}{2 a}$ = $s=\frac{v^{2}-u^{2}}{2 a} \Rightarrow v^{2}-u^{2}=2 \mathrm{as}$ This is the third equation of motion.

When a body is moving with non-uniform acceleration:
In case of non-uniform motion, the velocity-time graph is shown in figures (i) and (ii).
In figure (i), in time f; velocity increases from zero to v. Here, graph AB shows the body is moving with the positive acceleration, whereas BC shows the body in negative acceleration.
In figure (ii) the body is moving with positive acceleration in first 2 seconds and in between 2 to 6 seconds the body is moving with constant velocity, i.e., acceleration is zero and from 6 to 8 seconds the body is moving with negative acceleration, i.e., retardation. After 8 seconds, the velocity will become zero.

Force and its units:

In simple words, we can say push or pull is called force.
On applying force, a stationary body sets in motion and the velocity of the moving body or its direction of motion or both can change.Hence, force is an agent which sets a stationary body in motion or can change the velocity of a moving body. Force is a vector quantity.

Units of Force:
In M.K.S system, the unit of force is Newton. In C.G.S system, the unit of force is dyne. In F.P.S system, the unit of force is poundal.

Balanced and Unbalanced Forces:
In the game of tug of war when the two teams pull with equal effort, the position of the rope is not changed at all. The forces exerted by two teams in this case are balanced. Only when one of the team pulls harder, it is able to pull the weaker team towards it. In this case, forces are unbalanced. Unbalanced forces acting on an object can changes its speed or direction of motion.

Newton’s laws of motion:
Scientist Newton propounded three laws of motion:

First law of motion: According to this law, a body remains at rest or in the state of continuous uniform motion, until and unless it is compelled by an external force to change its state of rest or uniform motion.
Second Law of motion: The acceleration produced in the body by the action of force acting on it is directly proportional to the force and inversely proportional to the mass of the body. In other words, Newton’s second law of motion can be stated as: The rate of change of momentum is equal to the force applied to the body and the change in momentum always takes place in the direction of force.
Third Law of Motion: According to this law, “For every action there is an equal and opposite reaction” (Law of action and reaction).
Inertia: Inertia is the property of a body due to which it resists a change in its state of rest or of uniform motion.

Momentum:
The vector product of mass and velocity of a moving body is called momentum.
Momentum = Mass of body x Velocity
$\vec{p}=m \vec{v}$

Law of conservation of momentum:

The law states that, in absence of external forces the momentum of the system is conserved. It means that total momentum before the collision is equal to the total momentum after the collision.
Suppose two bodies A and B of masses m₁ and m₂are moving in a straight line in the same direction with velocities u₁and u₂, velocity of the body A is more than that of B. So, both the bodies will collide, after sometime. Let velocity of the bodies A and B after collision become v₁and v₂, respectively. Let the time of collision equal to t.

If during the collision, the force exerted by body A on body B is F₁ and force exerted by body B on body A is F₂. From second law of motion.
For the body A, $F_{1} t=m_{1}\left(v_{1}-u_{1}\right)$ …. (i)
For the body B, $\mathrm{F}_{2} t=m_{2}\left(v_{2}-u_{2}\right)$ …..(ii)
From the third law of motion, F₁and F₂are equal, but their direction will be opposite. Hence
$F_{1}=-F_{2}$ …….(iii)
From equation (i), (ii) and (iii), we have $m_{1}\left(v_{1}-u_{1}\right)=-m_{2}\left(v_{2}-u_{2}\right)$
Or $m_{1} v_{1}-m_{1} u_{1}=-m_{2} v_{2}+m_{2} u_{2} \text { or } m_{1} u_{1}+m_{2} u_{2}=m_{1} v_{1}+m_{2} v_{2}$
i.e. Total momentum before collision = Total momentum after the collision This is what we call the law of conservation of momentum

Friction:

When a body slides or rolls over any surface, a force will develop between the surfaces in contact, which tends to oppose the motion. This force is known as force of friction. The effect of frictional force is more on rough, uneven surfaces than on smooth, even surfaces.
Bodies moving in air or in liquids also feel the force of friction (though less than that on solid surfaces).
Initially, when we try to push a body on a surface, it does not move, so long as the force is small, because the frictional force developed is more than the applied force. On gradually increasing the force, a stage will come, when the body begins to move. The maximum force opposing the motion of a body on a surface, when it is just on the verge of moving (by overcoming the frictional force) is called limiting friction. When a body moves sliding on the surface, the force of friction between them is called Sliding Friction. When the body moves on the surface rolling on it (like a ball or wheels) the friction between their surfaces in contact is called rolling friction. Rolling friction is much less than sliding friction.
Frictional force is a necessary evil. It has many advantages as well as disadvantages. We use methods to increase or decrease the frictional force according to necessity.

Thrust and Pressure:

Thrust: Thrust is the total force acting perpendicular to the surface of a body.
S.l. unit of thrust: Since thrust is a force. Its S.l. unit is same as that of force, i.e., Newton (N). It is a vector quantity.
Pressure: Pressure is defined as the force acting perpendicular per unit area of the surface or in other words, we can say that, thrust per unit area is called pressure.
Pressure $\propto \frac{1}{\text { area }}$ ……(i)
Pressure (P) ∝ Force (F) ……..(ii)
From (i) and (ii), we have
$P=K \cdot \frac{F}{A}$ ,where K is proportionality constant
When K = 1, F = 1N, A = 1m², and P = 1 Pascal, then Force (Thrust) = Pressure × Area
Unit of pressure = $=\frac{N}{m^{2}}, \text { i.e., } N m^{-2}$
1 N m^-2 is also known as 1 Pascal (Pa)
1 N m^-2 = 1 Pascal
i.e., Unit of pressure is also pascal (Pa).

Buoyant Force:

The upward force extended by a liquid on the body which is immersed in the liquid is known as buoyant force.
The tendency of a fluid to exert an upward force on an object placed in it is called buoyancy.
Factors on which buoyand force depends:
- The size or volume of the body immersed in a fluid.
- The density of the fluid in which the body is immersed.

Archimedes’ Principle:
When a body is wholly or partially immersed in a liquid at rest, it experiences an upthrust (or an apparent loss in weight), is equal to the weight of the liquid displaced by the body. This is the statement of Archimedes principle.

Applications of Archimedes principle:

Designing of ships and submarines.
Designing lactometers, to test the purity of milk.
Designing hydrometer, to find the densities of liquid.

Density:
Mass per unit volume of a body is known as density.
density $=\frac{\text { Mass }}{\text { Volume }}$
$D=\frac{M}{V}=\frac{k g}{m^{3}}$
∴ Unit of density is kg.m^-3

RBSE Class 9 Science Notes

RBSE Class 9 Science Notes Chapter 8 Major Activities of Living Organisms

July 12, 2019 by Prasanna Leave a Comment

Rajasthan Board RBSE Class 9 Science Notes Chapter 8 Major Activities of Living Organisms

Concept of Nutrition and its importance

Energy is required by all the living organisms for growth and development. This requirement is fulfilled by food. Thus, nutrition is the process in which all those activities which are concerned, like ingestion, digestion, absorption of digested food, egestion, oxidation of simple food to produce energy for growth, development and maintenance of living organisms. In other words,the process in which all the food materials eaten by an organism, is utilized for cellular respiration to obtain energy, is called nutrition.
Nutrient are the substances, like oxygen, food and water, which are required to sustain life. These are the only substances that nourishes a living being.
Types of Nutrition:
On the basis of method of nutrition, living organisms have been classified in two groups:
Nutrition is the whole process by which an organism utilize its food to produce energy, for growth, development and maintenance. Nutrition is mainly of two types: Autotrophic and Heterotrophic.
Autotrophics are living organism which synthesis their own food, by taking simple inorganic substances such as carbon dioxide, ammonia, water, etc. They are called autotrophs.

Autotrophs are of two types:

Photosyhthesisers: The living organisms which synthesis their own food, by taking carbon dioxide from atmosphere and water from the soil, in presence of sunlight and chlorophyll on the form of carbohydrates are called photosynthesisers. Example-Green plants.
Chemosynthesisers: These organisms oxidizes hydrogen sulfide,ammonia,nitrates, etc. inorganic substances, to produce energy.
Example: Sulfur bacteria, nitrite bacteria and nitrate bacteria are chemosynthesisers.

Heterotrophic

Many organisms cannot synthesis their own food and get ready made food from other creatures, by eating them, such organisms are called heterotrophs.
Herbivore: These are the animals who depends upon plants for their food, e.g., cow, goat, deer, etc.
Carnivore: Those animals who eat the flesh of other animals are called carnivores. For example, lion, tiger, etc.
Saprophyte: Organisms like bacteria and fungi feed on dead, decaying organic matter. Such organisms are called saprophytes.
Omnivores: Animals who feed on plants as well as other animals, for their food are called omnivores, e.g., Rat, Pig, Man, etc.
Parasite: Some plants and animals live on or inside the body of another their hosts. Such organism called as Parasites, e.g., Cuscuta, Tapeworm, Plasmodium, etc.
Sanguivore: Some animals depends upon the blood of other animals for food. Such animals are called Sanguivore, e.g., Mosquito, Leech, etc.

Nutrition in Plants:

Photosynthesis is the process of manufacture of simple carbohydrates from CO₂ and H₂O, in the presence of sunlight and chlorophyll. The main events of photosynthesis are (i) absorption of light energy by chlorophyll, (ii) Use of light energy in photolysis of water, (iii) Conversion of light energy into ATP and NADPH₂in chlorophyll. It is used in dark reaction.
Photosynthetic pigments found in plants are of three types
- Chlorophyll
- Carotenoids
- Phycobillins.
They are found in chloroplast and trap energy.
Photosynthesis is a oxidation-reduction process conduct in mesophyll cells in a leaf. When sunlight falls on leaf, light energy is trapped by the chlorophyll. This energy is utilized in the chemical process, in the manufacture of food. The chemical reaction of this process is
$6 \mathrm{CO}_{2}+6 \mathrm{H}_{2} \mathrm{O} \frac{\text { Light }}{\text { Chlorophyll }} \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}+6 \mathrm{O}_{2}$
Photosynthesis is divided into two major steps:
- Light reaction,
- Dark reaction.
Light reaction is also known as photo chemical reaction. It takes place in thylakoids present in chloroplasts.

This reaction can be divided into four steps:

Absorption of sunlight by chlorophyll.
Photolysis of water.
Evolution of oxygen,
Synthesis of ATP and reducing agent (NADPH₂)
Dark reaction is also known as biochemical reaction. This take place in stroma present in the cavity of chloroplast. In this reaction, reduction of carbon dioxide take place and first formed stable product is a molecule of 3 carbon, so called as C₃ or Calvin cycle.
The factors affecting photosynthesis is of two types (a) External Factors and (b) Internal factors.
In External factors, light, oxygen, carbon dioxide, temperature, water and air pollutants affects photosynthesis.
In Internal factors, chlorophyll contents, protoplasmic factors, accumulation of carbohydrates, etc. affect photosynthesis.
Bacterial photosynthesis is a special kind of photosynthesis which take place in certain bacteria.
The main methods of procurement of food in animals are- Holozoic, Holophytic, Parasitic, Saprophytic and Coprophagy. On the basis of procurement of nutrition or nature of food material, animals are categories as: Herbivorous, Carnivorous, Omnivorous and Sanguivorous.

Main Components of Food:

Food is that substance which we intake, digest and assimilate. It thus, provide energy for growth, development and maintenance. Food is an essential component for keeping the body healthy.
Nutrients play a major role or are directly linked with body, growth, development and maintenance.

Nutrients are divided into six components:

Carbohydrates,
Fats,
Proteins,
Mineral salts,
Vitamins,
Water

Water is not actually a nutrient, but it plays an important role in digestion, excretion and thermo-regulation. Dietary intake of water is very essential. Roughage is the fibrous part of plant food. All the vegetable and fruits, which we take in diet, contain cellulose, which is non-digestible for humans, so it passes out through the digestive tract unchanged in the form of faces.

Nutrition in animals:
The animals get ready made food for energy from green plants. Plants get CO₂ from atmosphere and converted into sucrose, by the process of photosynthesis.

Digestion:
Digestive system of man comprises of the following parts:

Alimentary canal,
Digestive glands

Mouth:

Buccal cavity: Oral cavity is known as the buccal cavity. The floor of the buccal cavity has tongue, bearing taste buds on it.
Tongue: Tongue is a voluntary, glandular and muscular structure, found on the floor of the mouth. It helps in swallowing. It is essential for creating a distinct speech, mastication and mucus secretion. Taste bud, sensation of sweetness, saltness, sourness and bitterness are found on the human tongue.
In the mouth, food gets mixed up with saliva, secreted by salivary glands. Saliva contains enzyme ptyalin, an amylolytic enzyme, which breaks polysaccharide starch into disaccharide maltose.
Starch $\stackrel{\text { Ptyalin }}{\longrightarrow}$ Maltose

Pharynx:
It is a short, conical region, beyond the soft palate.

Oesophagus:
Oesophgus is a long, narrow, muscular tube, which directly leads to the stomach. It is about 25 cm long and passes downwards through the neck, the thorax and the abdominal cavity.

Stomach:

Stomach is the dilated portion of the alimentary canal, situated between the oesophagus and beginning of the small intestine. Stomach leads into the small intestine through pyloric aperture, guided by a valve called pyloric sphincter or pylorus. Pyloric sphincter does not open, till the food in the stomach is fully mixed and churned.
In the stomach, food is churned by the action of muscles of the stomach. Moreover, the food gets mixed with the gastric juice which contains dil. HCI and two enzymes, namely, rennin and pepsin. A weak gastric lipase enzyme is also secreted by peptic cells.

Functions of HCl:

Softens food.
Kills the bacteria present in the food.
Stops the action of saliva.
Provides acidic medium for the enzymes present, in the gastric juice to act.
Rennin: It is only present in infants. It coagulates or curdles milk.
Pepsin: It is a proteolytic enzyme, which breaks proteins into proteoses and peptones.
Proteins $\stackrel{\text { Pepsin}}{\longrightarrow}$ Proteoses and peptones
Churning of food and action of enzymes in the stomach leads to the formation of a milky white sludge, called chyme, which is poured through the pyloric sphincter into the duodenum. Imbalance in the rate of secretion of gastric juice leads to peptic ulcer, which are depressed lesions in the mucous membrane of the stomach. Excessive secretion of HCI causes irritation in the wall of the stomach, because of which there is less formation of mucus which forms a protective lining. Finally, mucus layer is totally eroded leading to lesions or ulcers.

Small Intestine:

The small intestine is a convoluted tube, extending from the pylorus of the stomach to the ileo-caecal valve, where it joins the large intestine. It is approximately 5 m (16 ft) long and consists of three parts:
- Duodenum,
- Jejunum,
- Ileum
Duodenum: It is the first part of the small intestine. It is approximately 25-30 cm long and lies in a C-shape portion, around the head of the pancreas.
Jejunum: The jejunum forms two-fifths of the small intestine.
Ileum: The Ileum forms the remaining three fifths part of small intestine.

Duodenum receives juices from : (a) Liver, i.e., bile, (b) Pancreas (pancreatic juice)

Bile: Bile does not contain any enzyme. It is an alkaline juice, yellowish-green in color. It consists of H₂O, sodium bicarbonate, bile pigments and bile salts. Bicarbonate ions make the medium alkaline.

It has three main functions:

It emulsifies fats.
It helps in fat absorption.
It makes the medium alkaline by first neutralising the acid from the stomach, so as to enable the enzymes present in the pancreatic juice to show their action on food.
Pancreatic juice: It consists of proteolytic enzyme, namely, trypsin and amylolytic enzyme, namely, amylase and lipolytic
enzyme, namely, lipase.
Trypsin breaks proteins, proteoses, peptones and peptides into amino acids.
Proteins, Proteoses, Peptones $\stackrel{\text { tripsin}}{\longrightarrow}$ Amino acids
Amylase breaks starch to maltose: Starch $\stackrel{\text { Amylase}}{\longrightarrow}$ Maltose
Lipase breaks fats to fatty acids and glycerol: Fats $\stackrel{\text { Lipase}}{\longrightarrow}$ Fatty acids + Glycerol
Enzymes present in the intestinal juice breaks carbohydrates, proteins and fats, as shown below
Peptides $\stackrel{\text { Peptidases}}{\longrightarrow}$ Amino acids
Maltose $\stackrel{\text { Maltase}}{\longrightarrow}$ Glucose
Lactose $\stackrel{\text { Lactase}}{\longrightarrow}$ Glucose + Galactose
Fats $\stackrel{\text { Lipase}}{\longrightarrow}$ Fatty acids + Glycerol
Sucrose $\stackrel{\text { Sucrose}}{\longrightarrow}$ Glucose + Fructose
Large Intestine: Small intestine leads to the large intestine or colon. There is present a blind dilated sac, situated right at the place where the small intestine opens into the large intestine. This sac is known as caecum. Caecum terminates into a fine finger like projection, known as vermiform appendix.
Ileum: From the duodenum, food slowly moves toward ileum, where it gets mixed with intestinal juice called succus entericus, secreted by intestinal glands. Intestinal juice consists of amylolytic, proteolytic and lipolytic enzymes. In the small intestine, food becomes an alkaline emulsion, called chyle.
Rectum: It is slightly dilated part, about 13 cm long and concerned with temporary storage of undigested food.
Anus: Rectum leads to anus, which helps in elimination of undigested wastes

Knowledge of digestion in Animals:
An ameoba there is no mouth, therefore, intake of food may occur at any part of the body, but it usually takes place at the advancing end, i.e., pseudopodia. This process of obtaining food is called phagocytosis. The alimentary canal is in the form of a tube-like structure which communicates with the exterior, at the anterior end through the mouth and at the posterior end through the anus. The food is ingested through the mouth, digested in the alimentary canal and undigested food is expelled out of the body through the anus.

Respiration:

Respiration is a catabolic process involving the burning up of food substances such as carbohydrates fats, and proteins, within the tissues to produce energy. The released energy is temporarily stored as ATPs i.e. Adenosine triphosphate molecules. The organic compounds which are oxidised during respiration are known as respiratory substrate. It is an exergonic reaction.
In respiration and combustion processes, substance consumed are organic compounds and energy is released. Both these processes, require oxygen and carbon dioxide and water is formed.
Respiration occurs in living cells only, while combustion does not occurs in living cells. Most of the energy released during respiration is stored in ATP, while energy released in combustion is lost in the form of light and heat. Respiration takes place at ordinary temperature, while combustion takes place at high temperatures.
The total process of cellular respiration or oxidation and break down of glucose takes place into two steps-(a) Anaerobic respiration, (b) Aerobic respiration.
Anaerobic respiration takes place in the absence of oxygen. In this type of respiration ethyl alcohol or lactic acid is produced by fermentation of glucose. This respiration is also called fermentation of sugar. During this process, only a small amount of energy is released. One molecule of glucose produces two molecules of ATP.

Aerobic respiration takes place in the presence of oxygen. In this type of oxidation, atmospheric oxygen is used in the oxidation of glucose. As a result, glucose on decomposition gives carbon dioxide and water, and energy is evolved

The respiratory system of human body includes all the organs which use oxygen. For example, respiratory tract and lungs. According to the work, respiratory organs are divided into two groups,
- Accessory respiratory organ,
- Mainrespiratory organ.
The main accessory respiratory organs are- external nares, nasal passages, larynx, trachea.
Main respiratory organ are two lungs, present in the chest box on either side of the heart. Lungs are spongy. Exchange of gases takes place in air sacs. Each lung is covered by two membranes called pleural membrane. The outer pleural is in contact with the muscles of the ribs. The membrane keeps lungs in a normal position on the inner side of the chest box.
The breathing mechanism is due to expansion and contraction of thoracic cavity.

It is divided into two parts:

Inspiration: Chamber of chest is made up of ribs with active muscles. Due to contraction of diaphram and ribs, the lungs expand. As a result, pure air of atmosphere rushes into the lungs.
Expiration: With the relaxation of ribs and muscles of diaphram, chest box contracts and air of lungs goes out with pressure, through the nostrils.
We inhale and exhale, due to alternate order of pressure caused by movement of chest muscles, about 15 to 20 times per minute.

Circulation:

The process of transporting the absorbed food, water and waste products from one place to another in the body is called circulation. In animals, two types of circulatory systems are found:
- Open circulatory system,
- Closed circulatory system.
In lower organisms like cockroach and snail, blood vessels from the heart pour blood into open tissue spaces known as sinuses. This is known as open circulatory system. The open tissue spaces are called haemocoel and the blood flowing through them is known as haemolymph.
In higher animals, the blood remains only in the vessels and carried to various organs through vessels and capillaries. The blood remains in blood vessels during its circulation around the body and does not come in direct contact with the tissue cells. Such system is called closed circulatory system.
In earthworm, closed circulatory system is found, blood acts as a medium of transport. A red ionized pigment, haemoglobin is found for transportation of oxygen and found in plasma fluid.
In cockroach, nutrients and waste products are transported by open circulatory system. In cockroach, there is a main dorsal vessel termed as heart or aorta. It is a muscular tube which has 13 chambers. Heart is pulsating. In it, blood flows from the posterior portion to anterior portion. Heart or aorta opens at the apex of the anterior portion. Blood has no pigment, so it is not helpful in exchange of gases. For exchange of gases, there is a tracheal system.
In human beings, circulatory system is divided into two systems:
- Blood vascular system,
- Lymphatic system.
Blood vascular system contains blood, heart and blood vessels. Blood is composed of Plasma, RBCs, WBCs and Blood platelets. Blood carries oxygen, nutrients, hormones to cells, waste products to excretory organs. It regulates the body temperature and helps in repairing injured tissues.
Human heart is situated in thoracic cavity between the lungs, slightly on the ventral surface. It is, a triangular muscular organ enclosed in double membrane, pericardium. Pericardial fluid is present between these membranes. Internally it is divided into two main parts, right and left, each consist of two parts, an upper thin walled auricle and lower thick walled ventricle.

The four chambers of heart are:

Left Auricle,
Left Ventricle,
Right Auricle,
Right Ventricle.
Internally partition between right and left auricle is known as interauricular septum, while partition between two ventricles is known as interventicular septum.
The main function of heart is to circulate blood. It is a double pump. Impure blood fills the right auricle by way of superior vena cava and inferior vena cava. From the right auricle, blood passes into right ventricle through valve. Then, the right ventricle contracts. Impure blood is forced into pulmonary artery, which carries the blood to the lungs. Then, oxygenated pure blood comes into left auricle through pulmonary veins. The left auricle contracts and blood passes through the valve into left ventricle. From here, blood passes into the aorta and is distributed to all parts of the body by its branches.
All the pressure caused due to the contraction of heart can be felt by putting finger over the arteries of wrist. This is called pulse. The pressure of blood in arteries is called blood pressure. In a normal young man, the blood pressure is 120 mm/80 mm of mercury. High or low blood pressure is harmful. The blood pressure is measured in left bronchial artery, just above the elbow by an instrument called sphygmomanometer. Heart contracts 72 times a minute and 1 lac times day.
Three types of blood vessels found in man are:
- Arteries,
- Veins, and
- Capillaries.
Arteries have thick wall with elastic connective tissues, while veins have thin wall with less connective tissues. Arteries contain oxygenated blood, while veins have deoxygenated blood. Arteries do not have valves, while veins have valves. The large arteries branch many times to form arterioles and end in capillaries. Veins divide to form venules and in the end form capillary network.
Lymphatic system is accessory and another circulatory system. It circulates lymph. It comprises of lymph capillaries, lymph vessels, lymph organ and lymph nodes. Lymph is a part of blood, which is filtered from the blood through capillaries. It is a straw coloured liquid. The lymph or tissue fluid bath, the cell supply materials for the cells and removes waste from them. Thus, the lymph or tissue fluid acts like a middle-man between body cells and blood. Lymph mainly contains leucocytes, respiratory gases, nutrients and hormones. The tissue fluid after circulating in open spaces among the cells, is reabsorbed by special vessels called lymph capillaries. Thus, lymph consists of a fluid that has escaped from blood. Lymph capillaries merge with one another to form large vessels. Finally, two prominent lymph vessels join veins in the arm-region of the body. Here the lymph re-enters the blood stream. At some places in lymph vessels, are present swollen parts called the lymph nodes. These nodes store lymph and filter lymph WBCS are also produced in these nodes.
Tissue fluid and lymph have many functions in the body. Tissue fluid supplies nutrients and oxygen to the tissue cells and collects C02, waste products, metabolic intermediates and synthesised products from tissue celis to reach them to the blood, through lymph. Lymph carries these materials as also lymphocytes and antibodies to the blood. Lymph also transports food fat from intestines to the venous blood.
Lymph nodes, spleen, thymus tonsils are the organs made up of lymph tissue. Lymph flows from organs to heart.

Conduction in plants:

Conduction is a life process, in which a substance absorbed or synthesised in one part is moved to other part of the body. In plants, leaf is the main part of photosynthesis. The main parts of a flowering plant or a seed plant are root, stem, leaves and flowers. The vegetative parts of plants are root, stem and leaves and the reproductive organ is flower.
The main functions of leaves are photosynthesis, transpiration, exchange of gases and food storage. Leaf is made up of parenchyma tissue, in which plastids containing green pigment chlorophyll are present. On the lower epidermis, minute pores called stomata are present. Guard cells are present around stomata, through which gaseous exchange take place.
Each leaf has a network of veins, formed by phloem and xylem.
Stem is the main route for the conduction of mineral salts and food materials.Stem provides a support to branches, which hold spreading crown of leaves.Other functions of stem are food storage, photosynthesis and vegetative propagation.
The cross section of a woody dicot stem shows three regions:
Outer region: It consists of bark and cortex, Bark is made of super-sized cell, while cortex is made of thin walled living storage cells
Vascular cylinder: It consists of conducting tissues-Xylem and Phloem
Pith: It consist of thin walled, cells, which store food.
Vascular tissues: The transport of water, dissolved minerals and liquid food is carried out by vascular tissues.
They are of two types:
- Xylem and
- Phloem.
Xylem tissue is somewhat complex in structure. There are special tube like cells called vessels and tracheids.
The main function of xylem is to conduct water and dissolved minerals from roots to the top leaves of the plants.
Phloem conducts food materials from leaves to different parts of plants. Phloem consists of four main types of cells.
- Sieve tubes,
- Companion cells,
- Phloem parenchyma, and
- Phloem fibers.
A herb plant has one prominent main tap-root. From tap root are given out a number of secondary roots. From secondary root are given out tertiary roots. Such a root system is called tap root system.

Main functions of root are:

To absorb water and dissolved minerals from the soil.
To support the aerial parts of the plant.
To store food.
Soft and slender apical part is the growing region of the root. In this region, new cells are formed. On the apex of the root, is present a cap like structure called root cap. It protects the delicate growing region from injury. Just above the root apex are present, densely distributed unicellular root hairs.
The transverse section of a mature root observed through a microscope, shows the following structures:
- Outermost layer of cells form the bark
- Below the bark, a zone of thin walled parenchyma, called cortex
- In central part is the vascular zone, comprising of vascular tissues- xylem and phloem.
The transport of solution across the membrane involves following two processes.
- Passive absorption, and
- Active absorption
In Active absorption, the cells use metabolic energy to move substances through the cell membrane towards a region of higher concentration. It is a living process.
Passive absorption, involves a number of physical processes, such as diffusion, osmosis, capillary and imbibition.
Diffusion: Diffusion is a physical process in which molecules move from higher concentration to lower concentration, leading finally to uniform concentration. Transport of substances occur in plant and animal cells through diffusion.
Capillarity: Rise of liquid into a vacant space of its own accord is called capillarity. The force of capillarity helps in absorption and transport material, within the organism.
Imbibition: It is a process by which rise of water occurs due to attraction between water molecules and molecules of the substance. Water is mostly absorbed by cell wall and hard seed coats by inhibition.
Osmosis is the movement of water and sugar molecules through a semi permeable membrane, from low solute concentration to the region of high solute concentration.
Osmosis is of two types
- Endosmosis : The entry of water into the cell by osmosis is called endosmosis.
- Exosmosis: Outward movement of water from the cell is called exosmosis.
If a cell is placed in a solution having higher concentration, then the water molecules will move from the cell sap to outer solution and turgidiy of cell wall will go on decreasing and cell wall begin to shrink. The shrinking of protoplasma is called plasmolysis.
The movement of molecules of water from cell sap to outer medium is called exosmosis.
Soil water is infact a dilute solution of mineral salts, the concentration of cell of root hair is more, as compared to soil water. Hence, water enters into root hair by endosmosis .As a result, the cell sap of root hair becomes more dilute as compared to neighbouring adjacent cells, hence water move into this cell by osmosis. In this way smotic pressure gradient is established. Because of this gradient, soil water with dissolved salts continuously move from soil to xylem.
The pressure which cause water to rise in xylem is called root pressure. It is produced due to the absorption of water by root cells and the osmotic pressure gradient moves the soil solution from soil to xylem. Root pressure is a vital pressure, which pushes water upwards.
Transpiration-cohesion-hypothesis: How water rises up from root to leaves in xylem? This hypothesis is based on three factors.
Plant physiologist Munch, put forward a plausible hypothesis: The mass flow hypothesis: The food in liquid or dissolved form is transported from higher concentration to cells with lower concentration through pholem. The food glucose is synthesized in cells of leaves. Hence, the sap in these cells becomes more concentrated. Glucose is either used up or stored in other parts of the plants. So, their cell sap is less concentrated. Osmotic pressure gradient is formed between leaves and cells of the part and food is transported to these parts.

Excretion:

The biological process involved in removal of the excess or toxic wastes from the body is called excretion. On the basis of nature of nitrogenous waste products, animals are categorised as follows:
Aminotelic: The animals which excrete amino acids are called aminotelic, e.g., Unio, Pila, Starfish, etc.
Ammonotelic: The animals which excrete nitrogenous waste in the form of ammonia are called ammonotelic, e.g., Amoeba, Hydra,Tadpole of frog, etc.
Ureotelic: The animals which excrete nitrogen nous wastes mainly as urea are called ureotelic, e.g., Adult amphibians and Mammals.
Uricotelic: The animals which excrete uric acid as end product are termed as uricotelic, e.g., Insects, Snakes, Lizards, etc.
Amoeba is a single celled animal. It lives in fresh water and removes waste and excess water by diffusion, through contractile vacuole. Waste C02 and ammonia produced in the cell and surplus water enter into contractile vacuole from the cytoplasm. As more and more water and waste collect, the contractile vacuole increase in size and moves close to the plasma membrane. Now, contractile vacuole burst and release the contents in the surrounding water. Later a new contractile vacuole appears and the same process starts.
There are no excretory organs in hydra. Ammonia and carbon dioxide are diffused out of the body. The undigested residue is thrown out of the body through single opening, which works as mouth and anus.
The body of earthworm divided into series of similar segments, separated internally by septa. The excretory organs in earthworm are specialised tubules called nephridia, which are attached to the septa. Nephridia pour the nitrogenous wastes into the alimentary canal, to be finally excreted out along with faeces.
In insects, carbon dioxide, uric acid and undigested food are the main excretory products. Carbon dioxide is excreted by respiration, while the undigested food is excreted by anus.
In Cockroach, about 60 to 150 yellow coloured thread like malpighian tubules open in the alimentary canal. These tubules collect nitrogenous products from the body cavity and pass it into the intestine, from where these are passed out of the body through anus.
The excretory organs present in our body are-skin, liver, spleen, intestine, lungs and kidney. In our skin, very minute pores with hairs are present. They are the opening of sweat duct, which excrete sweat and dissolved salts. Liver is the controlling centre of metabolic activities. Urea, the main nitrogenous waste is formed in liver. The cells of spleen and liver destroy the damaged blood cells. Intestine itself does not actively take part in excretion. But, large intestine help faeces and other waste products to excrete from the body. Lungs remove carbon dioxide from the body, during respiration.
Kidneys are the principal organs of excretory’system. They are bean-shaped and lie on either side of the back bone in the lower part of the body cavity.
Internal structure: Each kidney is divided into two parts, the outer cortex and the inner medulla.
In each kidney, there are about one million small tubules called nephrons. Each nephron represents an excretory unit. Each nephron is a coiled duct, with a cup like structure called Bowman’s Capsule. The capillaries of arterioles and venuoles form a ball like structure called glomerulus.
The method of excretion is very complex.

There are two actions in it:

Synthesis of urea: It takes place in liver from carbon dioxide and ammonia. In one molecule of urea formation, there is need of 2 molecules of ammonia, 1 molecule of carbon dioxide and 3 molecules of A.T.P.
Formation of Urine: Nephrons are separate and independent unit of urine formation.
Man’s kidney performs two functions-filtration and reabsorption. Due to blood pressure, the excess quantity of water, glucose uric acid, urea and some salts pass from blood to the Bowmans capsule by the process of ultra-filteration. When this filterate passes through the glandular part of nephron, glucose, useful salts and some part of water are re-absorbed. The liquid left after the re-absorption is now called urine.
This urine then passes through the urethra into the urinary bladder, where it is stored. When the bladder is full of urine, the muscular walls of bladder contract, expelling the urine out of the body through urethra.
Urine is light yellow and slightly acidic in nature. It consists of 95% water and 5% are salts of uric acid and other nitrogenous compounds, including sodium and potassium salts. A normal young man excretes about 1.5 litres of urine per day.
The following two hormones regulate the working of kidneys.
The anti diuretic hormone which controls the re absorption process of water in nephron duct.
Minerals corticoid and Gluco corticoid hormones, which are secreted by adrenal gland. These hormones control and regulate the metabolism of water and salts.

Excretion in Plants:

The phenomenon of discarding waste substance from the body is known as excretion.
The process of excretion is quiet simple in plants. Hence, excretory organs are not found in plants. In all the organisms two type of process take place: catabolic and aanabolic. These process are collectively known as metabolic processes. Waste substance are produced during metabolic processes.
The excretion is simple in plants, because the rate of metabolic processes is less as compared to animals. Green plants use much of the waste in their anabolic processes. The metabolism in plants is mainly based on carbohydrates. The end product is less harmful and poisonous. In land plants, waste products are given out through stomata. So, excretion in plants is much simpler and less complicated than animals.
There are lens shaped pores called lenticles, in the back of periderm. Lenticles have thin walled cork cells with intercellular spaces. Lenticles are always open and gases can easily diffuse in thick trunk of trees and they have no specific structure, like guard cells.
Some waste products such as carbonic acid (citric acid, tartaric acid, oxalic acid) are stored in vacuoles of the cells, in dissolved forms. In this way, they do not put obstacle in the different biochemical reactions of the cells.
Alkaloids such as quanine, cocaine and ephedrene are wastes for plants, but we use them as medicines. Gum is also a plant waste, which is formed due to dissolution of cellulose.
Cystolith of calcium carbonate and calcium oxalate is found in epidermal cells of the leaf of rubber. Needle shaped crystals called raphides are found in petiole of nymphacea. Star shaped bunch called sphaeroraphides are found in leaf stalk of papaya.
Water in form of drops, oozes out from apex and margin of leaves of peepal, tomato and lawn grass. This process is called guttation. In plants which show guttation, there are special stomata called hydathodes, located on margin and apex of leaves. Guttation increases when absorption rate is more than the rate of transpiration.

Reproduction:
Reproduction is not a necessary process to maintain the life of an individual organisms,unlike other essential life processes such as, nutrition,respiration or excretion. However, it is essential for the existence of the organisms. If there were to be only one, non-reproducing member of a particular kind, it is doubtful that we would have noticed its existence. It is the large numbers of organisms belonging to a single species that bring them to our notice.

Reproduction at its most basic level involves making copies of the blue prints of body design. A basic event in reproduction is the creation of DNA copy. DNA copying is accompanied by the creation of an additional cellular apparatus, and then the DNA copies separate. Effectively, a cell divides to give rise to two cells. These two cells are similar, but not absolutely identical. DNA copies generated will have some variations, each time. This inbuilt tendency for variation during reproduction is the basis for evolution. Variation is useful for the survival of species, over the period of time.

Reproduction in Animals:

Humans uses sexual mode of reproduction. Human beings develop special tissues for this purpose. While the body of the individual organism is growing to its adult size, the resources are mainly directed at achieving this growth. Reproductive tissue is not likely to be a major priority. As the rate of general body growth begins to slow down, reproductive tissue begin to mature. This period during adolescence is called puberty.
Reproduction is a process by which all living beings propagate or duplicate their own kinds to maintain the continuity of the race. Sexual reproduction takes by the fusion of special sex cells or gametes. In animals, gametes are of two types, male gametes known as sperms and female gametes known as ova. Both the sex cells are extremely small in size.
There are many different ways of sexual reproduction in animals. In a unicellular organism there is no difference in shape and size between the two individuals, taking part in sexual reproduction.
In Amoeba, binary fission takes place. In this method, the parent animal gets divide into two similar animals. It is a complex process.
Asexual reproduction in hydra takes place by Budding. In this method, an outgrowth called bud is formed on the body of the animal. It grows in size and separates from the parent body, to develop into a new animal.
In the month of February and March, male and female reproductive organ occurs in the form of nodes on the body of hydra. Female and male gametes fused and formed zygote, which develops into new hydra.
In earthworm, a single individual has both male and female sex organs, so they are called bisexual or hermaphrodite. The female genital pore is located ventrolaterally, upon its 18th segment. The same organism produce ova at one time and sperms at another time.
The human reproductive system is well developed and divided into two parts. Male reproductive system: It consist of testes, seminiferous tubules, vasdeference and urethra.
Female reproductive system: It consist of a pair of ovaries, oviduct, uterus and vagina. The ovary secrete two hormones progesterone and estrogen. Periodically, progesterone hormone decreases in the blood, resulting in the bursting of blood vessels and the blood along with uterine fluid comes out. This is called menstruation. Its time duration is 4-7 days. It repeatedly occurs after 28-30 days. During oestrous cycle, a desire for reproduction increases tremendously in females, after ovulation.
In the process of coition, seminal fluid is discharged by penis in the vagina. Only a few sperms are able to enter into the oviduct. The egg produced by the ovary also reaches the oviduct, where only one sperm enters the egg. There is a fusion of nuclei of sperm and egg, as a result of which zygote is formed. This process is called fertilisation. As this type of fertilisation occurs in the body of female, so it is called internal fertilisation.
Zygote moves from the oviduct to the uterus, where it gets attached to the walls of uterus. This process is called implantation. The inner walls of uterus and the embryo form a structure called placenta, through which the embryo remains connected with the mother. Placenta provides, nourishment, respiration and excretion facilities to the foetus.

Reproduction in plants:
Reproduction is the process of producing new organisms from the existing organisms of the same species.

Broadly there are two types of reproduction:
1. Asexual,
2. Sexual reproduction.

Asexual reproduction means without sex. The production of a new organism from only one parent, without the involvement of sex cells is called asexual reproduction. For example, amoeba, hydra and in plants-vegetative propagation mode.
Sexual reproduction means with sex. The production of a new organism from two parents, by making use of their sex cells is called sexual reproduction. In this reproduction, two sexes male and female are very much required. For example, in humans, cats, dogs etc. Most of flowering plants also reproduce sexually.
Asexual reproduction in plants is achieved by several methods. Each new organism begins life as a single cell. If this cell is derived from one parent cell, this form of reproduction is asexual.

The different types of asexual reproduction are as follows:

Fission: The unicellular body divides into two daughter cells. Each daughter cell grows to full size, as in bacteria.
Fragmentation: Spirogyra and Riccia plants breaks up into two or more pieces, called fragments. Each fragment develops into a new organism.
Budding: This is also a type of fission, in which the nucleus divides into two equal parts, but the division of cytoplasm is unequal, as in yeast.
Spore formation: Asexual reproduction occurs in several plants like some algae, fungi, bryophyta and pteridophyta by special small rounded structures called spores.
Spores are of two types: (a) non-motile spores, and (b) motile spores.
When a new plant develop from vegetative part like root, stem or leaf, it is called vegetative reproduction. Artificially, vegetative reproduction is carried by following methods:
Cuttings: Cuttings or strips are parts of short length of stem or branch. New plants of rose, sugarcane are obtained by placing the cuttings obliquely, making an angle of about 45 degree with the soil surface.
Budding: In ordinary variety of rose, a T shaped groove is curved out. Bud of superior rose is fitted into the groove and tied with a soft thread. Within a few days, the bud sprouts into a new branch. Other branches of this ordinary plant are later cut off.
Grafting: By this method, varieties of mango, seedless grapes, guava, etc. are developed. In this method, branch of better quality called scion is grafted into groove made on the stem of ordinary quality called stock. The tissue of both plants are fused, and a new plant of better variety develops.
Layering: In this method, branch or branches which are near the ground are made to bend downwards in wet soil and pressed. After some days, root proliferates from the underground part. Part of branch with roots is cut off and develops into a new independent plant. Garden plants like Jasmine (Chameli) and Mogra are obtained by this method.
Vegetative reproduction is the only method to maintain and multiply the desired varieties at commercial level. It results is more production, and flower and fruits can be obtained in short time. The production is high in the plants and new plants produced by this method are exactly similar in characteristics to that of mother plant.
Sexual reproduction in plants take place by gametes obtained from two parents. Flower bears the sex organs of a plant. When male and female sex organ are present in same plant, it is called bisexual, when they are present in different plants it is called unisexual.
The angiospermic flower consist of four sets of modified leaves, arranged in whorls. They are: (i) Sepals, (ii) Petals, (iii) Stamens, (iv) Carpels.
Sepals and petals which are also known as calyx and corolla are the outermost floral part of the flower.
Androecium constitute the male part of the flower and consists of a certain number of stamens. Each stamen comprises a lobed structure, called the anther, borne on a stalk or filament. The another contains four pollen sacs, each of which has a number of microspores, mother cells. Meiotic division takes place in these mother cells, resulting in the formation of four microspores or pollen grains from each. Pollen grains are small structures that produce the male gametes or sperm cells.
The gynoecium or pistil constitutes the female part of flower. It consists of carpels which may be either single and solitary, many and separate from each or few, or joined together. Each carpel consists of three parts. A slightly swollen and sticky stigma is present at the top and a slender stalk, called style and a swollen ovary is present at the bottom. Inside the ovary are, located a fixed number of ovoid structures, the ovules. These ovules contain eggs.
The transfer of pollen grains from the anther of a stamen to the stigma of a carpel is called pollination. Pollination is done by insects (like bees and butterflies), birds, winds and water. Pollination can occur in two ways, self-pollination and cross-pollination. When the pollen grains from the anther of a flower are transferred to the stigma of the same flower (or another flower on the same plant), it is called self-pollination. When the pollen grains from the anther of a flower on one plant are transferred to the stigma of a flower on another plant, it is called cross pollination.
The pollen grains are deposited on the stigma by pollination. The pollen grains germinate on stigma, producing a tube known as pollen tube. The pollen tube grows downward into the style and reaches ovary. Finally, it enters into the ovule, through a minute pore. Here, one male gamete fuses with egg. It is the act of actual fertilization, by which production of zygote and development of embryo take place.
The fusion of second male gamete takes place with the two polar nuclei-situated in the embryo sac. Whereby a triploid structure is formed, fusion is called as triple fusion. Thus, in embryo sac, fusion of two male gametes with 3 nuclei, take place twice, which is called as double fertilization. After fertilization further development take place, whereby ovule is converted into seed and ovary into fruit. In this way, the sexual reproduction in flower is accomplished.

Regulation:

In our body, there are two system for regulation; co-ordination and control.
- Nervous system,
- Endocrine system.
Nervous system contains series of tissues. The signals are transmitted from one part to another of the body, through nerves. Endocrine system consist of ductless or endocrine glands, which secrete hormones.
Change in the environment of an organism is called stimulus. Organism react to stimulus to survive in changed environment and this is called response.

Response in lower animals:

Amoeba: Amoeba receives stimulus through its protoplasm and respond and reacts, accordingly. Amoeba can respond to the external stimulus like light, heat and other chemical substances.
Hydra: The body of hydra is made up of two layer of cells. In between these layers, are present network of nerves. These nerves carry impulses in all directions. The stimulus is conducted to all parts of the body, through the nerve net. There is no directional control over the impulse.
Cockroach: Developed nervous system is found in cockroach and other insects. Different type of sensory organs are found in cockroach.
Nervous system is another major system of co-ordination and control of the body. It consist of nervous tissue, which is mainly made up of nerve cells. The basic functional unit of nervous system is the neuron. It has three parts-soma, dendrites and axon. The dendrites are small and branched. They receive impulses and conduct them towards soma. Axon is the impulse travelling along a single fiber from the cyton of neurons. The outgoing fiber is called axon. Axon is longer and thicker than dendrites.

There are three major steps In the conduction of impulses and Its response:

Receipt of stimulus by the sense organs.
Stimulus in the form of impulse is carried from the place of origin to the place of controlling organ, by electro-chemical reaction.
Appropriate response of the impulse is given by the controlling organ, brain or spinal cord. When the impulse reaches the end of axon, three hormones are secreted-
- adrenaline,
- acetylcholine and
- serotonin.
These hormones create depolarisation in the dendrites of nearby neuron, resulting in the passing of impulse through the synapse, from one neuron to another neuron.
The brain and nerve network are collectively called nervous system. Human nervous system can be divided into three parts.
Central nervous system: It consisted of brain and spinal cord. Brain is located in the head and enclosed in cranium.

The main parts of brain are:

Cerebrum: It is divided into two cerebral hemispheres. The surface of these hemispheres is folded into a large number of irregular wrinkles and furrows called convolutions, which increase the surface area of cerebrum. In human beings, the cerebral area is the largest among all the animals, that is why, man is the most intelligent of all animals.
Cerebrum is the seat of intelligence, memory and will-power. It controls and regulat speech, sight, hearing and touch.
Cerebellum: It is located just below the cerebrum. The main function of cerebellum is to control and coordinate the movement of body muscles. It also helps us to maintain our body balance.
Medulla oblongata: It is the lower most part of the brain. At the anterior end, it is joined to cerebellum. Its posterior part is extended into spinal cord. It controls involuntary actions, such as heart beat, food digestion, breathing, etc.
Spinal cord: The spinal cord is a long and cylindrical nerve, extending from the posterior end of the medulla oblongata to the end of the lumber region of our body. It is well protected by vertebral column. 31 pair of spinal nerves are given off by this end. The main function of spinal cord is to control reflex action.
Peripheral nervous system: It consists of 12 pair of cranial, 31 pair of spinal nerves and their branches. Their main function is to transmit impulses from sense organs to the brain and spinal cord.
Autonomous nervous system: It controls many voluntary and involuntary activities of the body.It Is divided into two sub- divisions: (a) Sympathetic nervous system, (b) Para-sympathetic nervous system.
Reflex action is involuntary activity. These involuntary actions are controlled by spinal cord. When our hand comes in contact with a hot body, the stimulus of hotness is received by sensory nerves of the skin. The sensory nerves carry the impulse to the spinal cord. In the spinal cord, the impulse is analysed. The spinal cord sends order through motor nerves to the concerned muscles for removing the hand.
A structure which makes hormones in the body is endocrine glands.

There are six endocrine glands:

Pituitary gland: It is located on the ventral surface of posterior cerebrum and it is stalked. This is our main endocrine gland. It secretes various hormones, which are called pituitary hormones. These hormones control hormones secreted by thyroid, adrenal, testes and ovary. Thus, this gland control the functions of other endocrine glands. The growth hormone secreted by this gland controls the development of bones and muscles. The over-secretion of this hormone leads to gigantic body, while under-secetion leads to dwarfism. The vasopressin hormone secreted by the gland, increases the re-absorption of water in kidney tubules. It also controls water and electrolyte balance. Its under secretion increases the quantity of urine, and this is called diabetes insipidus.
Thyroid gland: It is ‘H’ or butterfly shaped, bilobed gland situated on the ventral side in the neck, just below the larynx. The colour of this gland is dark red. It secretes a hormone called thyroxine. Thyroxine hormone regulates the basal metabolic rate. It increases the rate of cellular breathing. When the thyroid gland becomes over active, then quantity of thyroxine increases, as a result of which the rate of oxidation of food increases and the heart-beat also increases. When the thyroid gland becomes less active, then the quantity of thyroxine in the blood decreases. Deficiency of thyroxine hormone leads to the deficiency of iodine in blood. As a result, a disease called ‘goitre’ is caused.
Adrenal gland: Adrenal gland is present on the upper end of each kidney, fitting like a cap. It is also called supra- renal gland. The gland consists of two regions- the outer is called cortex and the inner one is called medulla.Cortex: The cortex secretes three hormones.
Mineralocorticoid: It regulates concentration of carbohydrate, fat and protein in the blood, and also secretes male hormone androgen and female hormone. The adrenal medulla secretes adrenaline hormone. The secretion of adrenaline increases in the situation of stress, such as during fear, anger, mental tension, injury, etc., affecting rise in blood pressure.
Thymus gland: This endocrine gland is found in new-born child, close to the heart. With advancing age, it gradually becomes smaller and the adult is atrophied. Thymus gland secretes the hormone called thymosin, which stimulates the proliferation of lymphocytes and also restores cell mediated immunological functions, such as the ability to reject first or second set skin grafts. Thymus also produces lymphocytes known as T-Lymphocytes, which produce antibodies.
Parathyroid gland: These small glands are four in number. They lie embedded in thyroid on its dorsal surface. They secrete the hormone, parathormone which acts to keep calcium dissolved in blood. Calcium helps to build bones and teeth. It also helps blood to clot, cells to adhere, muscles to contract and nerves to conduct signals properly. The bones act as a storage place for calcium. Parathormone, assisted by vitamin D and blood phosphate, controls the movements of bone calcium and not the blood, where it becomes available for all its other functions.
Pineal gland: It is a small round structure on the upper surface of the thalamus, lying between the cerebral hemispheres. This light sensitive gland secretes melatonin hormone, that inhibits ovarian growth and ovulation, i.e., to regulates sexual cycle of mammals.
Pancreas: It is a double gland. The bulk of pancreas consists of exocrine portion, which secretes a variety of digestive enzymes of pancreatic juice. Round or oval patches of cells, called islets of Langerhans act as endocrine glands. They secrete the insulin hormone, that helps to lower the blood glucose level and secrete another hormone, glucagon, which functions to elevate the blood glucose level. Thus, both the hormones interact to maintain a steady level of glucose in blood.Ovary: Main function of ovary is to produce ova. It secretes estrogen and progesterone hormones. Due to estrogen
hormone, secondary sexual characters like development of mammary glands, initiation of menstruation cycle, occurs in females. The progesteron hormone maintains the pregnancy.
Testes: Like ovaries, testes have two functions: The production of sperms and secretion of the male sex hormone, the testosterone. This hormone is secreted by the interstitial cells of the testes. Under the influence of anterior pituitary hormone. L.H. testosterone promotes the development of the masculine secondary sexual characters: enlargement of penis and scrotum, appearance of pubic hair, deepening of the voice and development of sexual desire.
The chemical substance which regulate and control the growth of plant parts are called as plant hormones or phytohormones. These hormones are produced mainly in stems, roots, apical meristem of buds and young leaves. These are transported from one place to another by phloem. They act in very small quantity. These have less molecular weight and are soluble in water. They control metabolic activities of plants. They regulate the action of genes, functions of enzymes and regulate respiration. They are said to be chemical co-ordinators.
Application of hormones in agriculture are: Auxins helps in root formation of cuttings and checks abiscission. By the use of auxins, parthenocarpic fruits, i.e., seed less varieties of fruits like oranges, grapes, guava, apples, etc., have been developed. They check untimely fall of fruits. In cold storage, NAA (Nepthalin Acetic Acid) is sprayed on potato tubers to prevent the sprouting of buds. To produce resistance for low temperature, to grow more crops to ripen fruits, to check sterility and to store seed, plant hormones are extensively used.

RBSE Class 9 Science Notes

RBSE Class 9 Science Notes Chapter 7 Bio-Diversity

July 11, 2019 by Prasanna Leave a Comment

Rajasthan Board RBSE Class 9 Science Notes Chapter 7 Bio-Diversity

Meaning and Significance of Biodiversity:
The variety of life around us has evolved on the earth over millions of years. However, we do not have more than a tiny fraction of its knowledge, to try and understand all the living organisms. So, we classify the living organisms into groups or classes, and then study different classes or groups, as a whole.

Major characteristics considered for classification are:

Whether they are made of prokaryotic or eukaryotic cells.
Whether the cells are living single or organised into multicellular complex organisms.
The cells have a cell wall or not.
Whether they prepare their own food.
Various types of organisms in the world differ in shape, structure and physiology. Division of organisms in groups, on the basis of similarities and dissimilarities is called classification. The science of studying classification is called Taxonomy. The different types of organisms with variations in structure constitutes the bio-diversity.

Need of classification:
The main purpose of classification is to inform us about the inter-relationship between different groups of plants & animals and a natural evolutionary relationship, is based on natural affinity among organisms and their evolution.

Major groups of animals and plants
Carolus linnaeus classified the living organisms into two kingdoms:

Plant kingdom
Animal Kingdom
German Zoologist, E.H Haeckel raised third kingdom for unicellular organisms called protista, Later on, an American ecologist. Robert. H. Whittaker proposed a fourth kingdom, Monera for bacteria and fifth kingdom, fungi.

To arrange organisms into these kingdoms, three criteria were considered:

Complexity of cell structure,
Complexity of the organisms body, and
Method of obtaining nutrition.

The five kingdoms are:

Monera: In it, are included all prokaryotic cell organisms. Examples: Bacteria, Blue green algae, mycoplasma etc.
Protista: In it, all unicellular organisms with nucleus and nuclear membrane are included. Example: Protozoans.
Fungi: They are unicellular or multicellular. Nucleus is present, but chlorophyll is absent. They can not perform photosynthesis.
Plant Kingdom (Plantae): They are multicellular plants. They have chlorophyll, so they can synthesise their own food. Examples: Members of Bryophyta, Pteridophyta, Gymnosperms and Angiosperms.
Animal kingdom(Animalia): They are multicellular animals. They do not have chlorophyll. Examples: Sponge, hydra, earthworm, frog, snake, man, etc.
Kingdom plantae is a large group of organisms include all the coloured multicellular, simple and complex plants. On the basis of Phylogeny and evolution, Oswald Tippo in 1942, classified this kingdom into two subkingdoms
- Thallophyta,
- Embryophyta.
Thallophyta plants do not form embryos. Embryophyta plants form embryo. Based on certain common trails, such as whether they produce seeds or not and whether the seeds are contained in fruits or are exposed, this kingdom is grouped into four phyla.
Thallophyta: e.g. (bacteria, fungi, lichens, and algae)
Bryophyta: (Liver worths, Hornworts and mosses)
Pteridophyta: (lycopodium, pteridium and ferns)
Spermatophyta: (a) Gymnosperms e.g., pinus, cycas, etc (b) Angiosperms, e.g., Wheat, Rice, etc.
Thallophyta: Plant body is not differentiated into root, stem and leaves. Body is called thallus. Reproductive organ is unicellular. It has three sub-divisions.
Algaes are unicellular or multicellular. They have chlorophyll, so they can manufacture their own food, by photosynthesis. They are aquatic.
Example: Spirogyra,Chlamydomonas, Chlorella, etc.
Fungi plants do not have chlorophyll. They are saprophytes or parasites. Example: Yeast, Mucor.
Bacteria are unicellular, prokaryotic organisms. Nuclear membrane and membrane bound cell organelles are absent.
In Bryophyta, body is more developed in comparison to thallophyta. They have rhizoids, instead of root, which absorb water and salts from soil. Mostly the plants are found in moist and shady places. Their body is made of parenchyma tissue. Sex organs are multicellular. Examples: Funaria, Riccia etc.
In Pteridophyta, the body of plants is differentiated into root, stem and leaves. Xylem and phloem are found in the conducting tissues of the plants. Reproducive organs are multicellular. Male sex organ is called antheridia and female sex organ is called archegonia.
Examples: Lycopodium, Pteridium and other ferns.
In Gymnosperms, body is differentiated into root, stem and leaves. The seeds of the plants are naked (exposed), because fruit is not formed in these plants. The reproductive organs are cone shaped. Examples: Pinus,Cycas etc.
In Angiosperms body is differentiated into root, stem and leaves Flowers, Fruits and Seeds are formed. Seeds are formed inside the fruits. Example: Wheat, Rice, Mustard, Neem, Pea, Gram, etc.
The two major group of animals are non chordates and chordates. In non chordates, animals do not have notochord, dorsal solid nerve chord and pharengeal gill clefts.

They are further divided into following phylums:

Protozoa: They are unicellular, microscopic, simple and primitive animals. Example: Amoeba, Paramecium.
Porifera: They are multi cellular with minute pores on their body and found in sea water. Example: Sycon, Euspongia.
Coelentrata: They are radially symmetrical, diploblastic. Gastro vascular cavity is found and mouth is surrounded by hollow tentacles. Example: Hydra, Obelia.
Platyhelminthes: They are parasites of vertebrates. Animals are bilaterally symmetrical, triploblastic and organisation is of organ system level. Example: Fasciola, Taenia.
Aschelminthes: They are long, cylindrical, worm like triplobastic, bilaterally symmetrical. Alimentary canal is found completely. Example: Ascaris, Bucheria.
Annelida: They are long, cylindrical, segmented, bilaterally symmetrical and triploblastic
Example: Nereis, Leech, Earthworm.
Arthropods: They are multicellular, triploblastic, bilaterally symmetrical. Their body is divided into head, thorax and abdomen. Jointed appendages are found, which are modified for different functions. Example: Scorpion, Cancer, etc.
Mollusca: They are aquatic, bilaterally symmetrical. In most of the animals shell is found. Example: Unio, Pila.
Echinodermata: They are found in sea, skin is spiny, True body cavity is entrocoel type. Tube feet is found for locomotion. Example: Starfish, Sealily, etc.
In chordata, animals have notochord in some stage of their life. Heart is present on ventral surface and blood circulatory system is of closed type.

They are divided into five classes:

Pisces: It includes fishes and other aquatic animals. They are cold blooded, body is spindle shaped, divided into head, thorax and tail and covered with scales. Heart is two chambered and respiration takes place through gills. Example: Dog fish, Rohu, Seahorse, etc.
Amphibia: It include frogs. They can live both on land and water. Their body is divided into head, thorax and abdomen. Respiration takes place through skin and lungs. Heart possess two auricles and one ventricle. Example: Frog, Toad, Tree frog, etc.
Reptilia: It includes snakes. They crawl on the ground and respire through lungs. Their body is divided into head, neck, thorax and tail, covered with endodermal scales. Their heart has two auricles and one incompletely divided ventricle. They lay eggs. Example: Tortoise, Lizard, etc.
Aves: It include aerial animals, like birds. Their body is boat shaped, stream-lined, divided into head, thorax, neck and tail, covered with feathers, horny beak is found, teeth are not found and bones are hollow. Example: Pigeon, Crow, etc.
Mammalia: It includes big animals. Developed mammary glands are found in females. Their body is divided into head, thorax, neck and tail. They are warm blooded, respire through lungs, and heart is four chambered. Example: Bat, Man, Rat, etc.

Adaptation of Animals and Plants on the basis of habitat:

Habitat is a place where an organism lives. The special characteristics which help the plants and animals to live successfully in a particular environment are called adaptations. Owing to the basis of availability of water in the environment, different plants are classified into following categories:
- Hydrophytes,
- Xerophytes,
- Halophytes,
- Mesophytes.
Hydrophytes are the plants which live in abundance of water or grow in wet habitat, aquatic plants.

Adaptation in Hydrophytes:

Roots: The root system is poorly developed, which do not play any significant important role in water absorption due to availability of plenty of water. Roots of these plants do not have root caps and root hairs. The roots of these plants contain air cavity.
Stems: The stems are long, slender, soft and spongy, due to large air cavity. The conducting tissues, xylem and phloem are poorly developed.
Leaves:The leaves of submerged plants are thin, long, ribbon shaped or linear. Floating leaves are large and flat and are often coated with wax or covered with hairs. Leaves of emergent and rooted plants below water, are long, narrow and dissected, while those which lie outside the water, are broad and non-dissected.
Reproduction: In hydrophytes, reproduction is mostly asexual and where flowers develop, seeds are rarely formed. In some plants and vegetables, cuticle is absent.
Reproduction is also found.
Mucilage is secreted from all parts of the plants, thus plants is not palatable.
Osmotic pressure is less, in hydrophytes plants.

General characters of Xerophytes:
Xerophytes are the plants which grow in deserts. Deserts are a typical example of dry habitat. The places which receives little rainfall and where there is no water for irrigation are Xerophytic habitats. The main feature of this habitat are bright light, lack of moisture, high temperature and fast blowing dry winds.

Morphological characters:

Non-succulent Xerophytes have long tap root, while in succulent xerophytes, roots are on the upper surface of soil. Root hair and root cap are poorly developed.
Stems are short, irregular, woody and hard. The stem is modified into under-ground rhizome.
In Asparagus, axial branches are modified into needle like structures, called cladode.
In Xerophytes, there is cover of wax and silica on the surface of stem and in some xerophytes, the stem surface is covered with hairs, e.g., Argemone.
Leaves of majority of xerophytes are smaller in size and very less in number, e.g., Acacia, Opuntia.

Anatomical characters:

Leaves and stems are provided with thick cuticle.
The conducting tissues are highly developed and vessels are in large number in xylem tissue.
The cells of epidermis of xerophytes are smaller in size and outer walls are thick.
Chloroplast and columnar tissues are found in the outer cortex of stem, of xerophytes.

General characters of Halophytes:

Halophytes are special type of xerophytes, which grow in saline soils. The soil has high concentrations of sodium chloride, magnesium sulphate and magnesium chloride. The plants that grow in saline and marshy soil are called halophytes.
Halophytes of sub-tropical places are herbs, while those in tropical zone are shrubs and trees.
The roots do not penetrate much deeper.
Adventitious roots that develop from the main stems of halophytes, support these plants, after entering into the soil.
Special type of roots develop from Mangrove are called respiratory roots or pneumetophores. These are negatively geotrophic roots. Each root is provided with numerous pores, towards the upper end for the exchange of 02 and C02.
Stem of some plants are fleshy and covered with hairs.
Leaves of halophytes are absent or little developed and fleshy.
Thick cuticle is found on the epidermis of stems and leaves.
The rate of evaporation is very less in these plants.
Carbonic acid is formed during respiration, due to special metabolic activities.
Mangrove plants show a special type of germination of their seeds, known as, vivipary. The seeds germinate inside the fruit, which is still attached to the parent tree. When germinated, seeds fall on the soil, and begines to development soon., e.g., Rhizophora and Sonneratia.
There are diverse group of animals that are found in different habitats. There are favourable characteristics (structural and functional) which the organism develops over a period of time, which enables them to survive, breed and prosper. Adaptations may be in the form of modifications in shape, structure of organs, colour, size, behaviour and food habits.

Adaptations in animals are of the following three main types:

Aquatic,
Terrestrial,
Aerial.

Aquatic adaptations is one of the most important habitat, where large number of animals live. The aquatic habitat include, both fresh water and salt water habitats.

The adaptive features of aquatic animals are:

Body shape: Body is streamlined and it offers least resistance to motion, as swimming.
Swimming organs: Body is covered by waterproof scales and a slippery substance, for reducing surface tension. The flippers of whale, fins and tail of a fish helps in increasing speed and changing the direction.
Air bladders: They are present in some fishes. It communicates with pharynx and filled with air.
Respiratory organs are gills, in fishes. Gills have large surface area, to extract oxygen dissolved in water.
In amphibious adaptation, frog is adapted for both aquatic and terrestrial life.
limbs, through webbed feet, are adopted for swimming.
Hind limbs are longer than fore limbs.
Skin is always moist, which helps in breathing, when the animal is on land.

Fertilisation is external.
Animals living on land, differs in their habits of living. The walkers and runners have cursorial adaptations, the burrowers have fossorial adaptations, climbers and fliers have arboreal adaptations. Animal living in deserts have desert adaptations.

Some adaptations found in Mesic habitat animals are:

All fast moving animals, have streamlined body and strong limbs for running.
Certain animals have protective coloration mechanism, such as the ability to change the body color to deceive the predator or prey, e.g., green lizard.
Insects and certain worms have modified mouth parts for feeding, e.g., wall lizard, which catches insects using its long, sticky tongue.

Xeric adaptations of Desert animals:
Animals such as camels, desert rats, rabbits, foxes, etc., have to adapt in order to overcome, the xeric conditions.

Some xeric adaptations are as follows:

Moloch absorbs water, like blotting paper. Its surface is covered by thorn like scales.
Water cells are developed in the walls of camel. It uses its entire foot, while walking.
The desert animals do not perspire and conserve water.
The nostril of camel can be closed like eyelids. The eyelids are modified into window, like structure which covers the eye.
The ear openings are either small or protected by scales.
Sense of light, hearing and smell are highly developed.
The animals who live and flourish, mainly on land, but come to the trees or branches for safety and shelter are called arboreal animals, e.g., monkey, flying lizard, flying squirrel, bats, birds, etc.

The bird and bats are adapted for aerial mode of life. Some adaptation of birds
are as follows:

The body of birds is streamlined, i.e., spindle shaped, for the easy and swift passage through air.
Forelimbs are modified into wings, for flying.
The entire body of birds are covered by light, elastic and water-proof feathers. They also help in maintaining the body temperature.
Birds have hollow bones, strong flight muscles, light body covering, sharp eyesight, modified beaks and tails. Birds do not have teeth and urinary bladder.
Ovary and oviduct is single, lungs are provided with air sacs, which are air filled and make the body light.
The feet of birds are modified for climbing and perching.

Classification give a scientific name:

A name is used for every living organism throughout the world. Common name does not serve the purpose, because a particular animal is known by different names in different parts of the world. On the other hand, scientific name is universally accepted and used for a particular group of animals.
As the binomial name indicates, the naming is done by two words. The first word is generic and the second is specific. The generic word starts from capital letter and specific starts from small letter.
In some species, some special type of dissimilarities are found, which are called subspecies. So, first name is of genus, second one is species and then another name is added, that is of subspecies

RBSE Class 9 Science Notes

« Previous Page