Leaves
Photosynthesis
The process of making food by plants in the presence of sunlight, water, carbon dioxide aid chlorophyll is called photosynthesis. During photosynthesis, plants take carbon dioxide and release oxygen. Food is prepared by plants in the form of glucose. Plants store extra food in fruits and seeds as starch. Trees store food in their trunks in the form of cellulose. Cactus do not have leaves. Photosynthesis occurs in their stems.
Cactus
Some plants are not green. For example, mushroom. Another plant like croton plant has red coloured leaves. The red colour of the leaves is due to the presence of anthocyanin. But they have chlorophyll also. Photosynthesis takes place in these plants also.
Croton
Mushrooms do not have chlorophyll. They cannot make their food from photosynthesis. They get food from dead plants and animals.
Classification of Plants
Plants are of various types classified on the basis of where they grow.
Terrestrial Plants
Plant that grows on land are called terrestrial plants. They are further divided into various types such as:
Mango tree
Plants in hilly areas
In hilly areas, plants can make food easily as there is sufficient sunlight and rainfall in these places. Coniferous tree grows on hills and mountains. They have standing branches so that snow which falls on them gets down. Conifers are generally evergreen as they do not shed their leaves. They do not produce flowers. Their leaves have few stomata only.
Coniferous tree
Desert plants
Plants that grow in hot places like deserts are called desert plants. Their leaves are modified into spines. Instead of leaves, food is prepared in stems.
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Amphibians
Amphibians reproduce by laying eggs in water. The young frog which comes out of the egg is known as tadpole.
Fishes
Fishes also reproduce by laying thousands of eggs in water. But only few eggs grow into baby fishes.
Fishes
Reptiles
Reptiles lay eggs in the sand or rotting vegetation. They do not sit on the eggs to keep them warm. The sea makes them warm and the egg is hatched.
Animals Gluing Birth to Young Ones
Mammals are the animals which give birth to young ones and produce milk to feed them. They do not lay eggs. Dogs, monkeys, cats and human beings comes under the category of mammals. Bats are flying mammals. Whales and dolphins are also mammals living in water.
Habitat
The home or natural environment of a living thing is known as habitat. All living beings changes themselves to survive in the natural world, for example, birds and insects can fly. This is called adaptation.
Classification of Animals on the Basis of Their Habitat
Animals are classified on the basis of the place where they live.
Aquatic Animals
Animals which live in water are called aquatic animals. Fishes live in water. They have fins for swimming in water. They have gills for breathing. Aquatic animals like dolphins and whales do not have gills. They have lungs for breathing for which they have to come to the surface of water. Birds like ducks have webbed feet which more... 
Digestive System of Human Body
Parts of Teeth
A tooth has three parts. Crown, neck and root.
Crown: Crown is that part of tooth that we can see.
Neck: Neck is below the crown.
Root: through roots, tooth is fixed in the jaw. The gum covers the root.
The outer hard layer which covers the tooth is called enamel. Enamel is the hardest thing in a human body. Dentine is below it. The core of the tooth is called pulp. Pulp is soft and has blood vessels and nerves in it. The nerves are connected to the gum through a hole in the root.
Types of Teeth
There are four kinds of teeth in our mouth which are as follows:
Incisors
The teeth which have sharp straight edges are called incisors. These are four in number in each jaw. They are present in front of the jaw. They help to cut or bite the food.
Canines
Canines are located on either side more... 
Measurement of Length
In early days, people used body parts to measure lengths.
Cubit Hand span
The metre is what we normally use for measuring lengths. Smaller lengths are measured in centimetres. Metre is written as m and centimetre as cm.
Measurement of Mass
Mass tells us how heavy or light an object is. We use weighing scales to find the mass of an object.
Just as we use metre for measuring length, we use kilogram for measuring mass. Smaller weights are measured in grams. Kilogram is written as kg and gram is written as g.
Measurement of Capacity
Capacity of a container is the amount of liquid it can hold. Litre is the commonly used unit for measuring capacity. Smaller units are measured in milliliters. Liter is written as / and milliliters as ml.
Some Other Units of Measurement
In everyday life, we also need to measure things that do not involve length, mass, and capacity. Time and temperature are two such examples. Time is measured in seconds. Measure of hotness or coldness of an object is called temperature. Temperature can be measured with the help of a thermometer
A solid can change into a liquid. This will happen if you heat the solid. The solid will melt into a liquid. This process is called melting. If you continue to heat the liquid will change into a gas. This is called evaporation. If you fill water in an ice tray and keep it in the freezer, you will see that after some time the liquid water has turned into ice. We say that the water has frozen and the process is called freezing. When a gas cools it change into the liquid state we say that it has condensed. And, the process is called condensation. The formation of rain in the water cycle is a natural example of the change of state of matter.
Changes Around Us
Matter is constantly changing around us. Changes are of two types - physical changes and chemical changes. In physical change, no new substance is formed. Breaking or glass, melting of ice into water are some, examples of physical change. When ice melts the solid water turned to liquid water. It doesn't turn into food or cold drink or anything new. It remains water. Physical changes can be reversed. In a chemical change, new substance is formed. Changing of milk into curd is an example of chemical change. Similarly burning of paper, making of vegetable dishes from raw vegetables, bursting of crackers are some other examples of chemical changes. Unlike physical changes, chemical changes cannot be reversed.
Rocks
Our earth is made up of rocks. Rocks are hard stones.
Pebbles are small pieces of rock.
Rocks are useful to us in many ways. Rocks such as marble, granite and sandstone are used in making buildings.
World's seventh wonder Taj Mahal is made up of white marble.
Soil Formation
A man lifting a dumbbells
Elastic Force
It is the force exerted when an elastic material is stretched. For example, stretching of rubber band.
Stretching of a rubber band
Frictional Force
It is the force exerted by two surfaces on each other in opposite direction when one moves over the other, while they are in contact. For example, while walking on a road frictional force is acting between the road and the sole of our shoe.
Friction, between shoes and floor
Gravitational Force
The force exerted by the centre of the earth which pulls objects towards it. For example, when a ball is thrown in the air, it comes back towards the earth due to gravitational force, an apple falling from a tree, etc.
Falling of an apple due to gravitational force
Electrostatic Force
When we rub a comb through dry hair, the comb gets charged and is able to attract tiny bits paper. The force exerted by charged comb on the bits of paper is called electrostatic force.
Charged hairs exert force on balloon
Work
Work refers to an activity that involves applying force on an object and movement of the object in the direction of the force. For example, if a man lifts a bucket then some work is done. In this case, due to the force applied by the man, the movement of bucket takes place in upward direction.
Simple Machines
The tools which make our work easy are called simple machines. For example, pulley, wheel and axle, lever, inclined plane, etc.
Pulley Inclined plane
Energy
Energy is the capacity or ability to do work. Energy can be of various types.
Mechanical Energy
This is the energy of motion that does some work. For example, wind turns a windmill.
Heat Energy
Heat energy is produced when a fuel is burnt in the air. For example, when coal is burnt in the air, heat energy is produced. Heat energy is used in steam engines, in cooking, etc.
Atomic Energy
The energy obtained by splitting more... 
Sun has ultraviolet rays which are absorbed by ozone layer present in the atmosphere. These rays can cause skin cancer. Due to air pollution ozone layer is getting depleted.
Effects of Air Pollution
Air pollution has various effects which are explained below.
Breathing Problem
When we inhale polluted air, it causes breathing problems. Bronchitis and asthma are diseases caused by air pollution.
Global Warming
Human inhales oxygen and gives out carbon dioxide, when amount of carbon dioxide increases in air, it causes global warming. Global warming is the heating up of atmosphere due to excessive amount of carbon dioxide in the air.
Acid Rain
Sometimes harmful gases discharged by factories and vehicles mixes with water vapours in the clouds. When it rains, these harmful gases get mixed with water vapours and comes down as acid rain. It affects forests, soil and human health. It makes soil more acidic. It also damages buildings, monuments etc.
Water Pollution
When toxic substances enter lakes, rivers, oceans and other water bodies, it causes water pollution. There are many sources of water pollution. Sewage from cities is thrown into water resources without treatment. Polluted water causes diseases like jaundice, typhoid, diarrhea etc.
Factories discharges harmful chemicals directly into water which causes damage to aquatic plants and animals.
Soil Pollution
Land gets polluted when we dump garbage on it.
Wastes are of two types:
Biodegradable: Things like fruits, vegetable peels/ paper etc. get decayed by microorganisms and mixes with soil.
Non-biodegradable: Things like plastic, polythene which do not get decayed by microorganisms and remains as it is in the soil and pollute the soil.
The sun and the eight planets belong to a family called solar system. The eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. All of them revolve in fixed path called orbit. Planets rotate on their axis also. Most planets have their satellites which revolve around them. Satellite does not have its own light. Man has also made some satellites for weather forecasting and to help in communication which are known as artificial satellites, for example, Aryabhata, Rohini etc.
Stars and Planets
A star is a huge ball of hot gases. It gives out heat and light. Planets do not have any heat or light of their own. They appear bright because they reflect the light of the stars. They revolve around stars. The sun is actually a star because it has its own heat and light. It is a huge sphere of hot gases. The earth and other seven planets that revolve around the sun get heat and light from the sun.
The sun is the main source of energy in our solar system. The planet Mercury is closest of the sun, followed by Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. They revolve around the sun in fixed path called orbit. Stars are far apart from each other. Distance between stars is measured in light years. The distance travelled by light in one Year is called light year.
The planets also rotate on their axis. Most of the planets have satellites. A satellite is a heavenly body that revolves around planets. It does not have any light of its own. The moon is a natural satellite of the Earth. It shines as it reflects sunlight from its surface. The moon does not have an atmosphere to protect it from extreme heat or cold. Some satellites in the sky are artificial. They have been sent up by scientists of different countries to study space, to forecast weather or to help in communication. The first one of these was Sputnik 1. Some others are Aryabhata,
Rohini, INSAT, etc.
Here, if we want to separate out one animal then definitely that animal will be cow because cow is the only animal in the group which is a domestic animal. Rest of the animals (lion, tiger, panther, bear and wolf) are wild animals. Hence, rest of the animals (lion, tiger, panther, bear & wolf) form a group of wild animals separating out the domestic animal (cow).
Similarly, out of 6 letters A, M, N ,W, P and Q, we will take out A and form a group of 5 letters M, N, W, P & Q because out of given six letters only A is a vowel while remaining letters form a group of consonants.
Types of Classification
(i) Letter Based Classification
Such classification is based on letters of English alphabet. Many groups of letters are given in the question in which one group is different from remaining group and hence, the different group will be our answer.
Example
1. Find the odd one out of the following options.
(a) P Q T (b) U V Y
(c) D E H (d) U N
(e) F G J
Explanation: (a) 
(b) 
(c) 
(d) 
(e) 
It is clear that except option (d), all the other options have a gap of 2 letters between 2nd and 3rd letter and the 1st two letters are in consecutive order. While in case of option (d), 1st two letters are in consecutive order but there is a gap of 3 letters between 2nd and 3rd letter. This is the reason why option (d) separates itself out of the remaining options. Hence, more... 
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