Introduction
We know that there are different kinds of living organisms found on the earth surface. It varies from unicellular to multicellular organisms. These organisms are bacteria, protista, fungi, virus, plant and animals. The bodies of all the organisms are made up of smallest unit called cell. Thus, cell are the basic unit of all life forms found on the earth surface. The cell was first observed by Robert Hook in 1665. He saw that the cork resembled the structure of honey comb consisting of many compartments. He observed this cell for the first time in the self made microscope. At that time the structure was not clear as the microscope was not of very high power. Later on with improved microscope in 1674, Leeuwenhoek discovered the free living cell in ponds. It was Robert Brown in 1831 who discovered the nucleus of the cell. The term protoplasm was proposed by Purkinje in 1839. Later in the same year the cell theory was proposed by two biologists Schleiden and Schwann. This was expanded by Virchow in 1855 saying that all the cell arises from preexisting cell.. 
Animalia
These organisms are multicellular and heterotrophic. Most of them can move from one place to another and lacks ceil wall in their cell. They are further classified on the basis of body design and cell structures. Some of the phylum of the animal kingdom are discussed below:
Porifera
These organisms have smallest holes on their bodies and are non motile in nature. These small holes on their bodies forms the canal system in the body and helps in circulating water, oxygen, and food. They have hard outer covering on their body and are mainly founded in marine water. They are multicellular and diploblastic which have radial symmetry. They do not have any well developed organs like mouth, body cavity, and anus.
Coelenterata
They are multicellular and diploblastic animals having more organized tissue structure. Their body shows radial symmetry and are mostly founded in marine water, except for few, such as. Hydra. They have only cells of nervous system and can reproduce by both sexual and asexual methods. They possess central
gastrovascular cavity which consist of mouth surrounded by short and slender tentacles. Some of them live in colonies while other live independently. For example the jelly fish and Hydra shows independent existence.
Platyhelminthes
Their bodies shows bilateral symmetry and dorsoventrally flattened animals. Their bodies are triploblastic and have digestive cavity with a single opening called mouth. They have suckers for taking food and hooks for movements.
They do not have any circulatory system. They are either free living or parasitic in nature. For example, planaria are free living and liver flukes are parasitic in nature. They are also hermaphrodite i.e. both the sex male and female are present in the same individuals. They do not have true internal body cavity.
Nematoda
Their bodies shows bilateral symmetry and are triploblastic. Their bodies have tissues and have true body cavity, but no real organs. The body is covered with tough resistant cuticle that provides their bodies some sorts of shape and structure. Male and female are found in different individuals. Most of them are parasitic, but very few are free living. For example round worm, filarial worms are parasitic in nature.
Anneelida
These organisms show bilateral symmetry and are triploblastic. They also have true body cavity. The body is covered with thin cuticles and have lateral appendages for locomotion. more... 
Different Kingdoms of Organisms
Monera
These are basically the unicellular organism which do not have well defined nucleus and nor have any cell organelles. Some of these organisms have cell wall while other do not. They are either autotrophic or heterotrophic in nature. For example, the organism like blue green algae, halophiles, cocci, bacilli and spirilla.
Protista
This kingdom includes many kinds of unicellular eukaryotic organisms which uses appendages such as cilia and flagella for movement from one place to another. They are either autotrophic or heterotrophic. Most of them are aquatic in nature having irregular body design. Cytoplasm is divided into two parts, outer and inner parts. They reproduce either by sexual or asexual. For example, the organism like algae, diatoms and protozoa comes in this categories.
Fungi
Fungi are the non-green plants that are heterotrophic in nature. Some fungi are parasitic in nature and derive its food from the other organisms. For example, albugo, ustilago etc. Some others are saprophytic in nature. For example, Rhizopus, Agaricus etc. They are either unicellular or multicellular. Their cell wall is made up of chitin and cellulose and stores food in the form of glycogen. Some algae such as blue green algae, shows symbiotic relationship among them self and are also called lichens. The lichens are the green patches which grows on the rocks, and watery area around the drains and barks of the trees. The fungus absorbs water and minerals from the soil and supplies it to the algae which in turns prepare food and supplies it to the fungus.
Plant
These are the multicellular organisms which are autotrophic in nature. The plants are further subclassified into three subgroups such as Thallophyta, Bryophyte, and Pteridophyte. The first basis of classification is that whether the plant body has well differentiated body parts or not. The second basis of classification is wether the parts of the plant's body have special tissues for transportation of water and mineral or not. The third basis of classification is, if the plant produces seeds and fruits or not. We will discuss each of them in
Thallophyta
This group includes the most primitive plants which do not have well differentiated body design. The body cannot be differentiated into stem, roots and leaves and is in the form of undivided body, called thallus. These groups commonly includes algae which are aquatic in nature and are founded in both fresh water and more... 
Classification of Organisms
Since there is one or the other similarity and dissimilarity among the organisms and. also there are large number of organisms in this world and it is very difficult to identify and understand each of them separately. Hence we need to classify the organisms. The main advantage of classification of organism is that it makes the study of large variety of organism easier. It also tells us the interrelationship among the various organisms. In ancient times the classification was based on some basic criteria such as size, colour, and nature of the organism. Later on the system of classification was based on overall similarities and dissimilarities between the organisms.
In present time the organisms has been classified into two groups as plant Kingdom and animal kingdom. The main difference between plant kingdom and animal kingdom is that plant can manufacture their own food using sunlight and carbon dioxide, where as the animals derive its food from the plants. Later on it was found that there were some organism which fit into neither plants nor animals category. Hence the classification system was further modified.
At present time there are five kingdom of classification:
Hierarchy of Classification
The five kingdom of classification given by Whittaker was based on the cell structure of the organism, mode of nutrition and their body design. The classification is done by naming the subgroups at various level as:
\[\to \] Kingdom Phylum \[\to \] Class \[\to \] Order \[\to \] Family \[\to \] Genus \[\to \] Species
In broadest mode of classification the organisms has been classified into two categories as plant kingdom and animal kingdom. The next step is the phylum which includes all the organism having few common characters. The next is the mammals. Mammal is followed by order which includes the organism having few common character and are less similar, such as carnivorous and omnivorous. The next step is the family which includes the group having more similarity to each other, such as, the family of cat and lion is similar. The next is genus, which includes the organisms having similar reproductive organs, such as, plants producing flower and fruits. The last step is the species which include the group of organism having same structure and forms, but not necessarily the function and are able to breed among themselves and produce the fertile offspring of their own kind. 
Introduction
There are large variety of living organism in this world and each organism is unique in its own way. This uniqueness of each organism is called diversity.
Due to large diversity it is necessary to classify the organisms. The biological science which deals with the identification, naming and classification of organism is called Taxonomy. In science we normally follow binomial nomenclature i.e. each organism is given two name, the first name is called genus and the second name is called species. The genus represents the community to which the organism belongs and the second name represents specific organism to which it belongs. Linnaeus is considered to be the father of taxonomy as he developed the binomial system of nomenclature. The scientific name of some of the common organisms are given below:
| SL. No. | Common Name | Scientific Name |
| 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. | Lion Tiger Dog Cat Rat Mango Neem Potato Lotus Honey Bee Ant Peacock | Panther Leo Pinthra Tigress Canis Lupus Felis Catus Tattus Norvegicus Mangifera Indica Azadirachta Indica Solanum Tuberosum Nelumbo Nucifera Apis Mellifera Formicidae Pavo Cristatus |
Thrust and Pressure
Thrust
It is the force acting on the body perpendicular to the surface. Its unit is same as that of force. It is dyne in CGS system and Newton in SI system.
1 kgwt = 9.8 newton and 1 gm wt = 980 dyne
Pressure
It is the force applied normal to the surface per unit area. It is given by
Pressure \[(P)=\frac{Force}{Area}=\frac{F}{A}\]
The unit of pressure is \[N/{{m}^{2}}\] or pascal (Pa). 1 Pa = 1 \[N/{{m}^{2}}=10\,\,dyn/c{{m}^{2}}\].
Fluid Pressure
The pressure exerted by the fluid is called the fluid pressure. A fluid exerts pressure in all directions. Normally it exerts three types of pressure downward pressure, upward pressure, and lateral pressure.
Atmospheric Pressure
The pressure exerted by air on the surface of earth is called the atmospheric pressure. It can be measured with the help of an instrument called barometer. 1 atmospheric pressure is equal to 76 mm of Hg.
Pascal Law
It states that if a pressure is increased at any point inside the liquid at rest then it is equally transmitted in all directions of the liquid. This principle is used in designing the instrument like hydraulic press, Brahma press etc.
Buoyant Force
It is the force exerted in upward direction by the liquid on the object which is fully or partially immersed into the liquid. The property of liquid to exert buoyant force on the object is called buoyancy.
Archimedes Principle
It states that when a body is fully or partially immersed in a liquid at rest, it exerts an up thrust on the body which is equivalent to the volume of liquid displaced by the object. All the ships are designed on the principle of Archimedes principle.
Relative Density
We can compare the density of the substance relative to the density of the water at 4°C . The ratio of density of the substance to the density of the water is called the relative density.
Relative Density \[=\frac{\text{Density of substance}}{\text{Density of water}}\]
Find the depth in an ocean at which a bubble of air will have one fourth the volume as it have on the surface of ocean?
(a) 4.1560m
(b) 2.1002m
(c) 1.8908m
(d) 3.1008m
(e) None of these
Answer: (d)
Kepler’s laws of planetary motion
Kepler observed that different planets take different time to complete one revolution around the sun. From s this observation of planetary motion he deduced that square of time period is proportional to the cube ob its distance from the sun.
Kepler’s First Laws
Kepler’s first laws of planetary motion states that planets move around the sun in such a way that sun always remains at one of its focus.
Kepler’s second law
According to second law the line joining planet to the sun sweeps out equal area in equal time interval, as the planet revolve around the sun in a elliptical orbit.
Kepler's Third Law
It states that square of time period is proportional to the cube of its semi major axis.
Let A and B be the two planets whose time period are \[{{T}_{1}}\] and \[{{T}_{2}}\]. If \[{{r}_{1}}\] and \[{{r}_{2}}\] be their distance from the sun/then
\[\frac{{{T}_{1}}^{2}}{{{T}_{2}}^{2}}=\frac{{{r}_{1}}^{3}}{{{r}_{2}}^{3}}\]
Orbital Velocity
The velocity required for an object to revolve around the planet in its orbit is called its orbital velocity. The orbital velocity of the earth is given by \[V=\sqrt{g{{R}_{e}}}\].
Its numerical value is 7.92 km/sec. The orbital velocity is independent of the mass of the object. If the velocity is less than orbital velocity, then the object will fall back on the earth and if the velocity is more than the orbital velocity, then it will get lost into the space.
Escape Velocity
The minimum velocity with which an object must be projected so that it escapes the gravitational pull of the earth is called the escape velocity.
It is given by \[{{V}_{e}}=\sqrt{2g{{R}_{e}}}\] . The numerical value is 11.2 km/sec.
Find the weight of the object on the surface of moon whose weight on the surface of earth is 9.8 N,
(a) 2.2 N
(b) 1.63 N
(c) 3.2 N
(d) 4.1 N
(e) None of these
Answer: (b)
We know that escape velocity of earth is 11.2 km/s. Find the escape velocity of planet whose radius and mass is twice that of earth.
(a) 11.2 km/s
(b) 22.4 km/s
(c) 11.272 km/s
(d) 33.6 km/s
(e) None of these
Answer; (a)
A body whose weight is 120 kg on the more... 
Acceleration Due To Gravity
Let us consider al ball dropped from a certain height. As the ball falls towards the ground its velocity increases.
Let 'm' be the mass of the ball falling from a certain height freely under the influence of gravity. Then the force between the ball and the earth is given by
\[F=G\,\frac{m\times {{M}_{e}}}{R_{e}^{2}}\] …………. (1)
Where, \[{{M}_{e}}\] is the mass of the earth
\[{{R}_{e}}\] is the radius of the earth
During the fall there is no change in direction but there will be continuous change in velocity. Hence the object will be falling towards the earth with an acceleration due to the earth's gravitational force. This acceleration is called the acceleration due to the gravity. It is denoted by 'g'. Thus, force due to earth's gravity is given by
\[\mathbf{F=m\times g}\]……………. (2)
From equation (1) and (2) we have
\[m\times g=G\frac{m\times {{M}_{e}}}{R_{e}^{2}}\]
\[g=G\,\frac{{{M}_{e}}}{{{R}_{e}}^{2}}\]
Therefore, we see that acceleration due to gravity is independent of mass of the object. On putting the value we get the value of g=9.8m/s2 approximately. Since the earth is not perfectly spherical, the radius of earth increases from pole to the equator, hence the value of g decreases from the pole to the equator.
Equation of Motion Falling Freely under Gravity
We have three equations of motion, which describes the motion of the bodies on the surface of the earth. The three equations of motions are
\[v=u+at;\,\,s=ut+\frac{1}{2}\,a{{t}^{2}}\] and \[{{v}^{2}}={{u}^{2}}+2as\]
Motion of the object under the influence of gravity is such that the object will either fall towards the earth or will go up against the gravity. When the object falls towards the earth surface then g is positive and when it is thrown upward then g is negative. Hence in such cases we have a = +g or -g accordingly. The equations of motion under the influence of gravity is thus reduced to
\[v=u+gt\,;\,\,h=ut+\frac{1}{2}g{{t}^{2}}\] and \[{{v}^{2}}={{u}^{2}}+2gh\]
Mass and Weight
Mass of a body is defined as the total quantity of matter contained in the body. It can also be defined as the measure of inertia. We can, therefore, say that mass of the object remains the same everywhere in this universe. The weight of an object is defined as the force with which an object is attracted towards the centre of the earth. The relation between mass and weight can be reduced as follows. Let W be the weight of an object of mass 'm' on the earth/then
\[W=G=\frac{m\times {{M}_{e}}}{{{R}_{e}}^{2}}\]
Or, \[W=m\times \,\left( G\,\frac{{{M}_{e}}}{{{R}_{e}}^{2}} \right)\]
Or, \[W=m\times g,\] where \[g=\,\left( G\,\frac{{{M}_{e}}}{{{R}_{e}}^{2}} \right)\]
Weight of the Object on the Moon
Let \[{{M}_{m}}\] be the mass of the moon and \[{{R}_{m}}\], be the radius of the moon. Let us consider an object of more... 
Earth’s Gravitation Force
Let us consider an object of mass 'm' and let 'M' be the mass of earth. The distance between the object and the centre of earth is approximately equal to the radius of the earth. Let R be the distance between object and the centre of earth. Then by universal law of Gravitation we have,
\[F=G\,\,\frac{m\times M}{{{R}^{2}}}\]
Where, M = mass of earth \[=6\times {{10}^{24}}kg\]
R = radius of the earth \[=6.4\times {{10}^{6}}\] meters = 6,400 km
\[G=6.67\times {{10}^{-11}}\,N{{m}^{2}}/k{{g}^{2}}\]
The force between any object on the earth and the earth itself is very large, as compared to the force between any two object on the surface of earth, which is found to be negligible. The gravitational force exerted by the earth is called the force of gravity.
Importance of Gravitational Force
The universal law of gravitation has many importance such as :
Two objects of mass 200 kg and 800 kg separated by a distance of 50 m. Find the gravitational force between the two bodies.
(a) \[4.26\times {{10}^{-9}}N\]
(b) \[2\times {{10}^{-9}}N\]
(c) \[2.4\times {{10}^{-9}}N\]
(d) \[2.4\times {{10}^{-8}}N\]
(e) None of these
Answer: (a)
Explanation
We have, \[F=G\frac{mM}{{{r}^{2}}}\]
Or, \[F=\frac{6.67\times {{10}^{-11}}\times 200\times 800}{50\times 50}=4.26\times {{10}^{-9}}N\]
The mass of earth is \[6\times {{10}^{24}}kg\] and the mass of other planet is \[7.4\times {{10}^{22}}kg\]. If the distance between the earth and the other planet is \[3.84\times {{10}^{5}}km,\] find the force of attraction between the earth and the other planet.
(a) \[4.01\times {{10}^{20}}N\]
(b) \[3.31\times {{10}^{20}}N\]
(c) \[5.23\times {{10}^{20}}N\]
(d) \[2.01\times {{10}^{10}}N\]
(e) None of these
Answer: (a)
Explanation
We have \[F=G\frac{nM}{{{r}^{2}}}\]
Or, \[F=\frac{6.67\times {{10}^{-11}}\times 6\times {{10}^{24}}\times 7.4\times {{10}^{22}}}{(3.84\times {{10}^{5}})}=2.01\times {{10}^{20}}\,\] Newton
Bodies falling freely on the Earth
We know that the speed of a falling object increases as it comes down i.e. we can say that the object accelerates as it falls down. Suppose we drop a stone and a sheet of paper from a certain height, we find that the stone reaches the ground first and the sheet of paper later, which is quite expected. But we cannot generalized this concept that heavier object falls faster than the lighter one.
For example: if we drop two different masses say 2 kg and 3 kg from same height we will find that they reaches the ground almost simultaneously. Thus, we can say that it is the density and the surface area of the object which determine the more... 
Universal Law of Gravitation
According to universal law of gravitation, every two object in this universe attracts each other with a force, which is directly proportional to the product of their masses and inversely proportional to the square of distance between them.
Let us consider two object of mass \[{{M}_{1}}\] and \[{{M}_{2}}\] and d be the distance between their centre. If F be the force between the two object, then
\[F\,\alpha {{M}_{1}}\times {{M}_{2}}\] and \[F\,\alpha \,\frac{1}{{{d}^{2}}}\]
Combining the above two equation we get,
\[F\,\alpha \,\frac{{{M}_{1}}\times {{M}_{2}}}{{{d}^{2}}}\]
Or, \[F=G\,\frac{{{M}_{1}}\times {{M}_{2}}}{{{d}^{2}}}\]
Where, G is universal gravitational constant.
The value of G is found to be \[\mathbf{6}\mathbf{.67\times 1}{{\mathbf{0}}^{\mathbf{-11}}}\mathbf{N}{{\mathbf{m}}^{\mathbf{2}}}\mathbf{/k}{{\mathbf{g}}^{\mathbf{2}}}\]. The value of G is called universal constant i.e. it remains same everywhere in this universe. It does not depend on anything. It is applicable for all particle whether small or large. 
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