4th Class

       States of Matter   Matter is divided into three groups according to the state in which they exist.              Solid In solids, the molecules are very close to one another and the force of attraction among the molecules is great. Arrangement of molecules in solid Because of this close packing and great attraction among the molecules, solids are hard and has a definite volume and definite shape. For example, ice, book, table, etc.                                                         Books                                 more...

     Molecules   A smallest particle of matter, which can exist in a free state is called a molecule. Structure of molecules of some elements has been given below.                        Molecules of any given substance are all similar. A molecule is defined as a group of at least two atoms in a definite arrangement. Molecules are formed by the combination of two or more atoms. The Properties of a substance are the properties of its molecule. Molecules can be subdivided to individual atoms. The atoms are bounded together in a molecule. Molecules also are not visible to the naked eye. It can be seen through highly magnifying microscopes and other scientific devices.     more...

     Introduction   All the things that we can see around us, whether living or non-living, are matter if it takes up space and has weight. It can be dog, cat, bat, ball, air, water, etc.                                                                                    Matters  Matter is made up of tiny particles. These tiny particles are too small to be seen. Millions and millions of these tiny particles put together to form a matter. These tiny particles are known as molecules. A molecule is the smaller unit of any substance that has all the properties of that particular substance. A molecule of aluminum has all the properties of aluminium. The molecule of different substances are different from each other. more...

     Nervous system   Nervous system co-ordinates all our body functions. It consists of brain, spinal cord and the nerves. Brain is our body's control system. Brain sends messages and receives them from all organs, all over the body. Brain is divided into 3 parts         Human Brain Accounts for 85% of our brain's weight. It consists of two -halves, right half and left half. The right half, which helps to think about things like colour, different shapes, etc. The left half is responsible for speech, maths, and logic. It is also known as the forebrain.            Cerebellum It is also called the Hindbrain, and is much smaller than forebrain. It is responsible for the movement of our body and maintaining body balance.   more...

     Excretory system   Excretory system throws out waste from our body. Human excretory system consists of kidneys, ureter urinary bladder and urethra.                 Excretory System We have a pair of kidneys which is bean shaped. When the blood reaches the kidney it has both useful and harmful substance present in it. The kidneys absorb harmful substance from the blood. The waste is dissolved in water and is removed as urine. The urine from the kidney goes to the urinary bladder through tube like urethras. Urethra has an opening at end of the muscular tube through which urine passes out. The skin also helps in removing waste from our body in the form of sweat. Lungs act as excretory organ by removing carbon dioxide (harmful gas) from the body.       more...

     Circulatory System   Circulatory system circulates blood throughout the body. It takes oxygen and food to every body cells and sweeps out carbon dioxide and other waste materials. It also helps in fighting infection and keeps our body warm. The circulatory system consists of the heart, blood vessels and the blood. Our heart is a powerful pump made of muscle. It contracts and relaxes automatically about 72 times a minute to pump blood around the body. Our heart is placed in the middle of our chest, slightly to the left.    Circulatory System              Our heart Our heart has two sides, the right and the left one. The right side pumps blood only to the lungs. The left side, which is the bigger of the more...

     Respiration in Human   Respiration is a process by which body burns organic matter (glucose) in the presence of oxygen to release energy. This energy is needed for work, growth, development and maintenance of the body. The human respiratory system consists of nose, windpipe and lungs. We breathe air through our nose. The air has oxygen in it. This air now moves down from windpipe to the lungs. The lungs are present inside our rib cage. We have a pair of them. It is a soft spongy bag like organ. Each of our lungs has millions of branching air sacs known as bronchioles.   Respiration in Human At the end of each bronchioles there are bunches of air sacs known as alveoli. During the process of respiration, oxygen from the air seeps through the air more...

     Digestion of Food   Digestion is the process of breaking down food into simple form so that it is easily absorbed by the body. Digestion of food takes place in a number of steps. There are several organs of our body, which are involved in this process. They all together make up our digestive system. Digestion of food starts in the mouth. The food is broken down by chewing and grinding into a paste. The paste next moves to the stomach through the food pipe. Food is churned by the stomach muscles with more digestive juices. It is then broken down into simple soluble form. The simpler food now passes to the intestine. Here the food is mixed with more digestive juices and breaks down further. Some of these digestive juices come from the intestine, while other is made in other body organs more...

     Nutrients   All living thing needs food for its growth, maintenance and development. Food has different components. These components are called nutrients. Each nutrient is required in specific amount and has a specific function. Food is divided into different groups according to the function they perform in the body.              Carbohydrates Carbohydrates provide energy to our body. We need energy to do any kind of work. Example bread, chocolates, sweet Potatoes and Banana.                  Carbohydrate Rich Food                Proteins They are the body building nutrients. We need protein for our growth. They build muscles and repair the damaged parts of our body. Children need more protein than adult because their body parts need more...

     Functioning of Human Body   Human body is a complex, well-coordinated, wonderful and a beautiful looking machine. We have different systems working independently and doing its work without any fuss or irregularities.          We can say that our body follow the rule of division of labour. We have different systems like the digestive system whose function is digesting of food, circulatory system which supplies food and oxygen to the required cells and collects waste from all body parts. Nervous systems which coordinates all our body function. Respiratory system is concerned with the release of energy from the food. Excretory systems excretes the waste material from our body. Reproductive system is involved in reproduction, i.e., producing young ones. The functions of these systems are monitored by the brain. more...