Introduction
Every organisms living on this earth is unique in itself. This uniqueness of each living individual is the basis of the great differences or diversity of the living world. The type of living organism found in one place is entirely different from organisms found in another place. For example, animals found in plains is different from the animals found in mountains or hilly regions. In fact different places, in different part of the world have their own typical kind of living Organisms. The degree of diversity in the living world is endless.
Different Types of Animals
With such vast differences and large number, it is very difficult to study each and every living organism separately, at the individual level. Therefore to study and understand the life of animals effectively they have been classified into different groups, on the basis of certain criteria.
Classification of Animal Kingdom
The animals are broadly divided into two major groups based on the presence or absence of the major characteristic feature, that is, the back bone.
Invertebrates
Invertebrates are those animals which do not have a backbone or vertebral column. They are considered to be primitive form of life on the earth. A large variety of small animals like insects, worms, slugs, snail, spider and scorpion etc. belong to this group. A surprising fact is, earth is home to more insects than any other kind of animal. Insets are very unique, among all living creatures on the Earth.
Different Types of Invertebrates
The body of an insect is divided into three parts head, thorax and the abdomen. The head contains the mouth, the eyes and the antennas. Some insects use their antennas for smelling. The thorax of an insect is similar to our chest. If an insect has wings, they are attached to this portion of the body i.e. thorax. The abdomen contains the large part of the digestive system. As the invertebrates lack bones, they have hard outer covering to support the body called chitin. This outer layer is waxy and waterproof. All insects have six legs. Invertebrates are found everywhere on the earth, land, water, air etc.
Vertebrates
The animals which have a back bone or a vertebral column are called vertebrates. These animals are highly evolved and have well developed organ system. Vertebrate is a large group. To study and understand the animals in this group, vertebrates are further divided into five major groups.
Fish
As the name suggest, these animals live more... 
Animals and Their Habitat
Animals are found everywhere on the earth. They are found on the highest of mountains and in the deepest of the sea. They are found in the hottest deserts or in the cool poles (Antarctica). Animals live in the wild and even in our homes. They live in air too. The surrounding or the environment in which an animal lives and survive is called its habitat. Animals develop certain features, which help them to survive in their specific environment, or habitat. If they are not properly adapted to their surrounding, they either die or they move to places where they are better suited and can adjust in a much better way for survival and growth. The process of developing special features in order to adjust to the changes in the surrounding or the habitat of an animal is called adaptation. Depending on the habitat of animals, they can be differentiated from one another into five different groups.
Terrestrial Animals
Terrestrial animals are animals which live on land. These animals have developed specific features that help them to survive and live on land. Most of these animals have legs, which help them to run fast. They have to run fast to catch their prey or to protect themselves from becoming prey of other animals (predators). They breathe through well-developed lungs.
Tiger
Some terrestrial animals have sharp teeth with pointed canines and sharp claws to catch their prey. These animals have well developed sense organ, which helps them to look for food in the dark night or by mere movement of their prey. These special adaptive features are common to most of the terrestrial animals.
Condition on the land is not uniform everywhere. It varies from place to place. Mountain region and the Polar regions are very cold. Animals living there have developed several adaptations to adjust to these climatic conditions. Polar bear living in the polar region and Yak living at high mountain range have thick coat of fur on their body, which protects them from the chilling cold. Animals like Walrus, Seals and Penguins also live in freezing conditions. These animals have special adaptation called blubber (thick layer of fat).
Polar bear
Conditions in the deserts are also very harsh. Here the temperature is very hot during the day but the nights are cold. Animals living here has to adapt to the changing temperature and scarcity (i.e. very little) of food and water. Camel is the very good example of an animal which has very well adapted itself to the life in a desert.
Camel
Camel has thick skin and very more... 
Food of Animals
We all need food to live and grow. Animals cannot prepare their own food like plants. Hence they have a heterotrophic form of nutrition. The large and the diverse groups of animals living in this world have different food habits. It is for this difference that all the forms of life are surviving. Can you guess what will happen if all the animals eat the same type of food? Different animals eat different kind of food and their body parts are accordingly adapted. Adaptability and availability are the two main reasons for an animal to have a specific food habit. Based on the type of food that an animal eats, they have been divided into five major groups.
Herbivores
Plants i.e. herbs, bushes, leaves, grasses, fruits or seeds etc., of a plant are eaten by animals. These plant eating animals are called herbivores. Herbivores have adaptation to break, graze, chew and digest plant products. These animals have sharp front teeth which help to cut grass or leaves, and very strong flat grinding teeth at the back. These grinding teeth help to chew the grass.
Cow Buffalo
Herbivore like cows continuously eat grass and store it in their stomach. The partially digested grass, called cud, is stored in stomach. Later the cud is returned to the mouth in small lumps and the animal chew it. This is the reason why a cow is continuously chewing even when they are not eating. The grass is rich in cellulose, a type of carbohydrate. Cellulose cannot be digested by all the animals. The special adaptation of the cow to digest cellulose is that they have a large sac between large intestine and small intestine. Cellulose is digested in this sac by the action of certain bacteria present there. Common examples of herbivores animals are cow, sheep, goat, zebra etc.
Carnivores
Carnivores are animals that eat the flesh of other animals. Latin worm 'carne' means flesh. Carnivores are solely dependent on animal's tissues (flesh) for their need of energy and nutrients. Lion, a carnivore has developed special characteristics which help them to adopt the life that they lead. Lions have sharp canines for hunting and tearing out the flesh of its prey. Eyes of lions are faced in front of the face, which allows it to have a correct idea about the location of the prey. They have sharp, pointed long claws in their front legs, this helps them to pounce and hold on to their more... 
Adaptation for Protection
The living world is full of challenges. Organisms have to adopt all the harsh conditions of the environment, in order to live and reproduce. Apart from the harsh environmental conditions like high and low temperature, little or lots of water etc., a major struggle of the animals is for food. Many of the animals are the food for other animals. Mostly the carnivores or omnivores hunt herbivores for their requirement of foods. However, many of the animals have adopted special features that help them to protect themselves from enemies. Let us look and understand at some of the special adaptive features of animal have evolved specially for their protection against their enemies.
Large Size
Huge sizes of some animals are enough to scare away their enemies. For example, bear, elephant and hippopotamus are so gigantic that their mere sizes scare away most of their enemies. It is not a common that a lion is attacking an elephant.
Hippopotamus
Strong Legs
Some animals have very strong legs and are able to run very fast. These animals due to their great speed run away from their enemies. Dear is a good example.
Deer
Position of Eyes and Ear
The long ears help them to hear the slightest of the movement. Hearing the slightest of movement they run for their life. The position of eyes on the side of its head allow them to look in all direction for danger. The large ear of the elephant helps them to hear even very soft sounds. This alarms them much in advance and they move away from danger. The position of eyes and ears help deer to move quickly away from the enemies.
Move in Herds
Most of the animals protect themselves from their enemies by moving in large groups. This large group is known as herd. It becomes difficult for the enemies to attack such a large group. Hence animal remain safe. For example, dear, wild buffaloes, monkeys, elephants move in herd.
Elephant Herd
Different Body Covering
Many animals such as tortoise, turtle, snail, crab have hard outer covering on their body known as shell. This shell protects their soft body parts from injury and also from the attack of the enemies. These animals also have a special characteristic of withdrawing their body parts into their shell at the time of danger. Some animals such as porcupines or hedgehogs have spines more... 
Reproduction in Animals
Like any other living thing, animals are born, grow, give birth to their own kinds, get old and die. The ability to produce more of their own kind is known as reproduction. Reproduction is very essential for the continuation of a species or a group of animal. It ensures the continuation of similar kind of individuals (animals) generation after generation. Animals have mainly two different ways of reproduction. Animals, which give birth to their young one, the baby develops inside the body of the mother. Second group of animals are those which lays eggs, baby hatches out from the egg. Now let us understand these two ways of reproduction in detail.
Reproduction
Egg Laying Animals
Many of the animals reproduce by laying eggs. The eggs are laid in a safe place like nest, borrows, holes etc. Either of the parents sit on the egg to keep it warm. After a fixed period of time the egg gets matured and the young one hatches out. In the centre of the egg, is a yellow portion called yolk. It contains the developing baby called embryo. Yolk is rich in fats, vitamins and minerals which is the food for the growing embryo.
Hen’s Egg
Yolk is surrounded by a white jelly like substances called albumen. It is rich in protein. Albumen protects the embryo and provides water to it. These substances are protected all together in a thin protective shell called the egg shell. The embryo develops into a chick.
Birds
All birds reproduce by laying eggs. Birds build nests to lay eggs and to raise their young ones. Within the egg, embryo goes through various developmental stages. Mostly the mother sits on the egg to keep it warm. The baby bird hatches out. The parent birds feed and protect the young bird until they can look after themselves. The baby bird grows into an adult. All the stages of development from the embryo to a mature adult make up a complete cycle. This cycle is called life cycle of an animal.
Frog
Female frog lays hundreds of eggs at a time in a lake or pound. These large clusters of eggs are called spawns. Tiny tadpoles hatch out of the egg. They swim in water and look like fishes. A tadpole starts to grow legs after a few weeks. Tadpole's tails becomes shorter and shorter and finally disappear, and they develop into an adult frog.
more... 
Introduction
To do any kind of work we have to apply force and to apply force we require energy. It shows that these three terms (Work, Force and Energy) are related and dependent on one another.
Work Force Energy
Done <————— Applied <————— Needed
Thus we can say that work is only done, when we have the energy to apply force.
Force
Think of the normal activities like catching a ball, throwing a ball, pulling or pushing a chair. Have you ever thought, why a chair moves when we push it or pull it? The chair moves because we apply a force on it.
Force is push or pull acting on an object. Force is used not only to move an object, but also to stop it. Force is also used to change the direction and position of an object. It is also used to increase or decrease the speed of moving object. While playing cricket, many of you must have been given caught out. The friend of yours who caught the ball has applied force to stop the ball, which was moving in the air by your hitting. The force applied by you is to move the ball and the force applied by your friend is to stop the ball. Both you and your friend has applied force but to do different kinds of work.
Force is applied to hit the ball
Every one of you must have enjoyed your bicycle ride. You can increase or decrease the speed of the bicycle when you want to. The speed of the bicycle depends on the rider. The rider apply force to increase or decrease the speed of the cycle.
Force is used to increase or decrea.se the speed of moving object. Children, while playing with football or basketball have the habit of sitting on it or pushing it against the hard surfaces. While doing so shape of ball gets changed. Force is use to change the shape of the object. Therefore, force is push or pull acting on an object. Force is used to move objects, to stop the moving object, to change the direction of the moving object, to decrease or increase the speed of the object and also to change the shape of the object.
Force applied can make the ____________.
(a) Body move
(b) Body stop
(c) Change the direction of motion
(d) Change shaped
(e) All of the above
Answer: (e)
Explanation
Force applied can move the object, stop the moving object, change the direction of motion, and change the shape of the object.
more... 
Types of Force
In this chapter, we will study about two types of forces:
(i) Frictional force
(ii) Gravitational force
Friction
Friction is a type of force exerted when two surfaces are in contact with each other. Lets us understand it in a simpler way with an example.
A bicycle gradually slows down and finally stops, when we stop pedaling. A ball that you have rolled, gradually slows down and then comes to rest. When you push your toy, it moves for some distance and then slow down and finally stops after some time. These are few of the events that most of you have experienced. Can you guess why the moving object comes to rest automatically?
In all the above cases there is no force that appears to act on the object, then why the object's speed slows down and finally stops? Or, is there some force acting on these objects? Yes, the force is known as friction.
Friction always acts on all the moving objects, but the direction of force of friction is always opposite to the direction of motion of the object. In all the above cases, it is the force of friction which slows down the speed and finally stops the moving objects, like moving a ball, bicycle or a moving toy. Surfaces in contact with each other, exert force on each other. This force exerted by the surface is in the opposite direction to the other. This causes resistance of motion of one surface on the other. This opposing force is called the force of friction or even as force of resistance. This opposing force is the main cause of slowing down of the movement of the object and its complete stop.
We need this force of friction in all our actions. If there was no friction we would not be able to walk, run, play or doing any such activities. Anything that started to move would never stop, a toy would keep moving or the ball would keep rolling. Imagine how the world would be with object once set in motion always remaining in the same condition.
Force of friction depends on the surface of the moving object. In general, rough surfaces like, stoned or kacha road, floor with carpet has more friction as compared to smooth floor
Gravity
Gravity is the force with which objects are pulled downwards towards the centre of the earth. Let us understand it better with an example.
Body released Forces on body more... 
Work
When force is used to move an object from its position, we say that work is done.
To move a table from its one positions to another, we require to apply force on the table. You must have pushed a chair many a times. Why the chair moves? The chair moves because of the force applied by you. You apply the force on the chair and move it from its original position to a new position of your choice. This is the process of doing work.
Work done by moving an object
Work is always done by a force. We often name the agent that has applied this force and say that the agent has done work.
When a girl pushes a notebook on the table, we say that the girl has done work on the notebook. Actually the work is done by the force exerted by the girl.
Energy
Any kind of work can only be done when we have the energy to apply force. Energy can also be defined as the ability to apply force which in turn does the work.
Reading, writing, sitting, eating, playing these are some activities that we? All do. Now think of activities like climbing, riding a bicycle, carrying load, and lifting heavy items. To do all those works, even the simplest one, we need energy. We use energy even while we are sleeping. Energy is also required by matter to change its states. We need heat energy to change water into vapor. Ice is changed into water, which again requires energy.
Changing state of matter
Energy is present in different form like heat energy, light energy, sound energy, electrical energy, mechanical energy, chemical energy and nuclear energy. Energy has the ability to be converted from one form to another. 
Types of Energy
There are two major types of energy. The energy present in a resting body is the potential energy and the other is the kinetic energy, which is present in the objects in motion.
Potential Energy
Potential energy is the energy of an object due to the position of its body. The S.I. unit of potential energy is
When a rubber band is stretched to the left, it exerts a force to the right so as to return to its original un -stretched position. When a mass is lifted up, the force of gravity on the object brings it back to the ground. Roller coaster climbs a hill, it has maximum potential energy at the top of the hill. When the Roller coaster speeds down the hill it starts to loose potential energy.
Kinetic Energy
In simple way, we can say that kinetic energy is the energy of motion. When we walk, run or jump, our body shows kinetic energy. A rubber band flying through the air has kinetic energy. You all must have played with yoyo. How does it work? A yoyo at the rest position has potential energy, at the top has the maximum potential energy. When the yoyo starts to fall, the potential energy begin to change into kinetic energy. At the bottom, its all potential energy has been converted into kinetic energy.
Yoyo at different position.
Body showing different types of energy at different position
When an object is dropped from rest from some height above the ground, it has some potential energy but no kinetic energy. As the object starts to fall towards the ground, it losses its potential energy and gains kinetic energy. Just before the object reaches the ground, it has lost all its potential energy and is full of kinetic energy. We all enjoy the view of a water fall. The water comes down from the height to the ground with high speed and the gushing sound. Have you even thought of the type of energy water posses? The water at the top of the hill has stored potential energy. When the water begins to fall, its potential energy is changed into kinetic energy. Kinetic energy can easily be passed from one object to another. Let us see an example to understand it better.
In the game of billiards the players give kinetic energy to the cue ball by striking it with the cue stick. If the ball, which is hit, collides with another ball, it slows down, and the ball it collided with, starts to move. This is because the kinetic energy is passed on more... 
Sources of Energy
Any system from where energy is tapped is called a source of energy. Sun is the ultimate source of almost all energy. Energy that the earth receives from the sun is in the form of heat and light. Some of the main sources from where we get energy are as follows:
Different source of Energy
Solar Energy
Solar energy is the energy that we get from the sun. It is in the form of heat and light. The green plants use this solar energy to make food for all living things on the earth. Animals eat the food made by the plants and get energy to do work. Animals can't use the solar energy directly. We depend on plants for this process. Thus we can say that all living things are dependent on solar energy directly or indirectly for their energy need.
Energy from the sun
Wind Energy
Wind, as we understand, is the movement of air around us. As we have seen earlier in this chapter that any moving substance has energy, so wind also have energy. The energy of the blowing wind is called wind energy. As the energy is due to movement of substance, the energy associated is the kinetic energy. Wind energy is also used by boatman to sail boats and to generate electricity.
Windmill used to harness wind energy to produce electricity
Tamil Nadu is the state in our country, which produces largest amount of electricity using wind energy. Wind energy is an eco-friendly and efficient mode of production of electricity.
Water Energy
Moving water like any moving substance has energy. Many natural processes like weathering of rocks and pebble formation is due to moving water. We use this energy of moving water to produce electricity. Electricity, produced by this process is environment friendly and position free.
Use of moving water to produce electricity
Atomic or Nuclear Energy
Each atom has a centrally located nucleus, which consists of protons and neutrons. When nucleus of an atom breaks down or two or more nuclei combines together to form a single nucleus, huge amount of energy is released. This energy is called atomic energy.
Structure of an atom
Energy of the atoms can be used to produce electricity for our use. In India Nuclear Power Corporation (NPC) produces electricity from the energy of the atoms. The sun also gets its heat and light energy from more... 
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