• NCERT नवा अभ्यासक्रमनु BEST मटेरियल ALL IN ONE
  • 22 August 2018



    Mixture of rocks particles, sand and humus is known as soil. Soil supports the growth of plants by holding their roots and supplying water to them.
    Formation of soil: Soil is formed by weathering. Weathering is the process of breaking down of rocks by the action of wind, water and climate. Formation of even one inch of soil takes many years.
    Composition of Soil: Soil contains humus, water, clay, sand and gravel.
    Humus: The decaying dead matters in soil are called humus. Humus makes the soil fertile and provides nutrients to the plants.

    Soil Profile

    Soil Profile: Different vertical layers of soil are known as soil profile. The feel (texture), colour and chemical compositions of soil are different in each layer.
    soil profile


    Layers of soil are referred as horizons. Horizons of soil are categorized into four types: A-horizon, B-horizon, C-horizon and Bedrock.
    A horizon: Top layer of soil is called A-horizon. It is also called top-soil. A-horizon is generally dark in colour. It is rich in humus. A horizon is generally soft and porous. It retains more water.
    Roots of small plants are entirely embedded in topsoil. Topsoil also provides shelter to many living organism, such as worm, insect, moles, rats, snakes, etc.
    B-horizon: The next layer of the soil from top is known as B-horizon. This layer is harder and more compact than the top soil. This is generally known as the middle layer of soil. This is less rich in humus but contains most of the minerals present in the soil.
    C-horizon: The third layer of soil is known as C-horizon. C-horizon is made of small lumps of rocks with cracks and crevices.
    Bedrock: The layer below the C-horizon is known as bedrock. Bedrock is composed of rocks and is hard to dig with spades.

    Types of Soil

    Size of particles of soil is very important for the properties of soil. So, soils are categorized mainly in three types based on the proportion of size of particles. These are Sandy Soil, Clayey Soil and Loamy Soil.
    Sandy Soil: Particles of sandy soil are larger in size. Because of being larger in size, sand particles cannot fit close together and hence there is enough space among them. These spaces are filled with air. Water drains quickly through sandy soil. So, sandy soil is called well aerated, light and dry.
    Sandy soil is not fit for vegetation as it does not retain water. However, millets can be grown on sandy soil.
    Clayey Sol: Particles of clayey soil are very small in size. This makes the particles of clayey soil packed tightly. There is very little space among the particles. Water does not drain quickly through clayey soil because of less space among particles. So, clayey soil is not well aerated and retains more water.
    Clayey soil is used in making of toys. Clayey soil is good for growing paddy.
    Loamy Soil: Particles of loamy soil are smaller than sand and larger than clay. Loamy soil is the mixture of sandy soil, clayey soil and silt. Silt is the deposit in river beds.
    Loamy soil has right water holding capacity and is well aerated. This is considered as the best soil for the growth of plants.

    Properties of Soil:

    Percolation Rate of Water: Amount of water drained through water in unit time is known as percolation rate of water in soil. Percolation rate of water can be calculated using the formula given here.
    Percolation rate (mL/min) = Amount of water in mL/Time taken to percolate
    The percolation rate of water in sandy soil is fastest and in clayey soil is slowest.
    Moisture present in soil: Amount of water present in soil is called moisture present in soil. The amount of moisture present in clayey soil is highest and that in sandy soil is lowest.
    Absorption of water: Different soil absorbs different amount of water. Clayey soil absorbs the highest amount of water because of its higher water retention capacity. On the other hand, sandy soil absorbs the least amount of water because of its lower water retention capacity.

    Soil and Crop

    Different types of soil are found are found at different places. A particular soil type may not be suitable for certain types of crop. That’s why different types of crop are grown in different parts of the world.
    Sandy soil: Sandy soil is not fit for any crop as it does not retain water. However, some thorns and bushes do grow on sandy soil. Millets can be grown on sandy soil.
    Clayey Soil: Clayey soil is best suited for paddy, as it can retain water for a longer time. This is also suitable for wheat and grams.
    Loamy Soil: Loamy soil is considered the best for almost all types of crops. It is suitable for lentils and other pulses.
    Sandy Loam: Sandy loam soil is suitable for the growth of cotton plants as it can easily drain water and is well aerated.

    Soil Erosion

    Removal of topsoil by weathering agents; such as wind, water and ice is known as soil erosion. Soil erosion affects the fertility of soil, as humus present in the soil is eroded along with soil. It is important to prevent soil erosion.

    Preventive measures for soil erosion:

    • Deforestation should be prevented at all cost to prevent soil erosion.
    • Shelter belt plantation of trees is good for preventing soil erosion.
    • Terrace farming in hilly areas is effective in preventing soil erosion.


    Wind Storm

    Air: Air is a mixture of gases.
    Wind: Moving air is called wind.
    Air exerts pressure: The fact that Air exerts pressure can be understood by many examples.
    • Tube of bicycle gets inflated when air is filled in it. This happens because air exerts pressure.
    • It is difficult to move the bicycle against the direction of wind. Similarly, a sailor feels it difficult to sail his boat against the direction of wind. This happens because air exerts pressure.
    • When boiled water is filled in a tin can and its mouth is closed with the lid; followed by cold water being poured over it, the can gets distorted. This happens because air inside the can gets condensed and creates low pressure. The higher pressure from outside distorts the shape of the can.
    • You can fly a kite because air exerts pressure from the rear portion of the kite.
    • Aeroplane can fly because air exerts pressure.
    • Birds can fly because air exerts pressure.
    • High speed wind creates area of low air pressure:
    • Thatched roof is blown off because of high speed wind. This happens because high speed wind creates an area of low pressure. Due to this, the thatched roof is sucked up and finally gets blown away. Thus, increase in wind speed is associated by decrease in air pressure.


    Weather Climate


    The day to day condition of atmosphere at a particular place is called weather. The weather can be comfortable, or can be too hot or cold.
    Weather Report: The daily report about weather; usually released by the meteorological department is called weather report. Weather report is often shown along with the news on television.
    Elements of Weather: The various elements of weather are: temperature, humidity, rainfall, wind-speed, etc.
    • Temperature: Temperature depends upon the duration of sunshine. During the summer season, the duration of the sunshine is longer. Due to this, the temperature is high in summer. The day temperature is minimum in the morning and maximum at noon.
    • Humidity: Humidity is the amount of moisture present in air. Humidity is generally measured in percentage. Humidity is generally at the highest level; during the rainy season.
    • Rainfall: Amount of rainfall is measured in terms of mm. For this, an apparatus; called rain gauge is used.
    • Wind-speed: Speed of wind also affects the condition of weather.

    Department of Meteorology: This is a Government Department. The Meteorological Department measures the elements of weather and keeps their record. Meteorologists use data from satellites and analyse the data to forecast about the weather.


    Climate is the average weather condition of at least 25 years; in a given geographical part.
    The climate of India is said to be hot and humid, because the temperature is usually high and so is the humidity for most parts of the year. The climate of Rajasthan is said to be hot and dry because temperature is very high but humidity is very low. On the other hand, the climate of Kashmir is said to be cold because temperature is low.
    Rainforest: Rainforest is found generally near the equator. Places near the equator receive more sunshine and hence more rainfall. This makes the place hot and humid. Temperatures vary from 15⁰C to 40⁰C near the equator. Rainforests are also present in some tropical areas.

    Desert: Temperature in desert is generally higher and it receives less or little rain fall. So deserts are hot and dry.
    Polar Region: Polar Region is at high latitude and hence do not receive adequate sunshine. Due to this, temperature is very low in the Polar Regions. The Polar Region is covered with snow, because of the low temperature.

    Climate and Adaptation:

    At several places, such as desert, polar region, etc. climate is very harsh. Many organisms live and thrive at these places, in spite of the harsh climate. Animals and plants; living in such places; develop certain features which help them survive the harsh climate. To develop certain features in order to survive the given climate is called adaptation.

    NCERT STD 7 SCIENCE UNIT 6 Physical and Chemical Changes UNIT TEST PDF

    Physical and Chemical Changes

    We see different types of changes; every day in our surrounding. Growth of tree, rising of sun, setting of sun, different shape and size of moon, burning of coal, paper, wood, etc. are the examples of changes around us.
    Before knowing the scientific meaning of changes; it is necessary to understand some terms, i.e. physical properties, chemical properties, reversible and irreversible.
    Physical Properties: Shape, Size and State of substance are known as physical properties. For example; when a sheet of paper is folded, its shape changes and this is an example of change in physical property.
    Chemical Properties: The internal properties of a substance are known as chemical properties. For example curd is the product of milk but the internal properties of milk and curd are completely different.

    Reversible: Things or processes which can be reversed are called reversible. For example, a folded sheet of paper can be unfolded and hence folding a sheet of paper is reversible.
    Irreversible: Things or processes which cannot be reversed are called irreversible. For example, when milk turns into curd; it cannot be changed back to milk and hence is an irreversible change.

    Physical Change:

    Change in which only physical properties of a substance change and no new substance is formed is called Physical Change.
    Most of the physical changes are reversible, this means we can get the substance back even after the change.


    Acid Base Salt

    Substances can be divided into three types – Acid, Base and Salt.
    ACID: Taste of acid is sour. There are many substances that contain acid and so taste sour. For example – lemon, curd, pickles, orange juice, vinegar, etc.
    Substances that taste sour are called acidic. The chemical nature of such substance is known as ACIDIC.
    The word acid comes from Latin ‘ACERE’ which means sour.
    BASE: Taste of base is bitter. Substances that contain base taste bitter. For example; soap or soap solution, baking soda, washing soda, etc.
    The chemical nature of substances that contain base is known as BASIC.

    INDICATOR: A substance which detects the acidic or basic nature of another substance by change in colour is called acid-base indicator. It is not advisable to taste any substance in laboratory because it can be harmful. Hence, acid-base indicators are used to check if a given substance is acid or base.

    Types of Indicator:

    Indicators can be divided into two types.
    Natural Indicator: Indicators that are obtained from naturally occurring substance are called NATURAL INDICATORS. Example: litmus, turmeric, China rose, etc.
    Synthetic Indicator: Indicators that are made in laboratory are called SYNTHETIC INDICATORS. Example: phenolphthalein, methyl orange, etc.


    Litmus: Litmus is extracted from Lichens. Lichen is a composite organism. Lichens consist of fungi and algae living in symbiotic relationship.
    Litmus is a purple coloured liquid in distilled water. Litmus comes in the form of strips of two colours. One is called blue litmus paper and another is called red litmus paper. Litmus liquid and litmus paper are used to detect the acidic or basic nature of a substance.
    Colour of litmus paper in acid: Blue litmus paper turns into red when dipped in acidic solution.
    Colour of litmus paper in base: Red litmus paper turns into blue when dipped in basic solution.

    Turmeric: Turmeric is also used as natural indicator. Turmeric is of yellow colour. Turmeric paper turns into red when it is dipped into basic solution. Turmeric paper does not change its colour with acid.
    China Rose: China rose is another natural indicator. China rose solution gives dark pink (magenta) colour with acid and green colour with base.
    Acid Rain: Carbon dioxide, sulphur dioxide and nitrogen dioxide which are released from vehicles and chimneys mix with droplets of rain and turn the rain water acidic. When this acidic rain water falls over earth, it is known as acid rain. Acid rain damages the buildings and is harmful for plants and animals.
    The Taj Mahal; which is made of marble; is under threat because of acid rain. Many parts of Taj Mahal and many other historical buildings and monuments have got damaged due to acid rain.

    Characteristics of Acid:

    • Sour in taste.
    • Turns blue litmus paper red.
    • Turns the solution of China rose to dark pink colour (magenta).

    Characteristics of Base:

    • Bitter in taste.
    • Turns red litmus paper blue.
    • Turns solution of China rose to green.
    • Turns turmeric paper to red.



    Heat is the transfer of energy from a hot body. The sense of touch can be used to understand the degree of hotness or coldness of something. But the sense of touch is not reliable and cannot be always used to say how much hot anything is. Moreover, using the sense of touch can be risky in case of something being very hot. Thus, hotness of anything is measured in terms of TEMPERATURE in reliable way. To measure temperature a device called THERMOMETER is used.

    Unit of heat:

    There are three units which are used to measure the temperature: Degree Celsius, Fahrenheit and Kelvin.
    Degree Celsius: Degree Celsius is written as °C and read as degree Celsius or simply Celsius. For example 20°C; it is read as twenty degree Celsius.
    Fahrenheit: Fahrenheit is written as °F and read as degree Fahrenheit. For example 25°F; it is read as twenty five degree Fahrenheit.
    Kelvin: Kelvin is written as K. For example 100K; it is read as hundred Kelvin.


    Thermometer is a device which is used to measure temperature. Thermometer is made of a long narrow glass tube; with a bulb at one end. The narrow tube appears as a continuous silver line; because it is filled with mercury. Mercury is a metal which is in liquid state at room temperature and it readily expands or contracts at the slightest change in temperature. Hence, mercury is used in thermometer.

    Types of thermometer:

    Laboratory Thermometer: Laboratory thermometer is used to measure the temperature. The scale of temperature is graduated generally from –10°C to 110°C over the glass tube. Each division of temperature scale is further divided into 10 parts to read fraction of temperature.
    structure of thermometer

    Clinical Thermometer: Clinical thermometer is used to measure the body temperature. The scale of temperature is graduated from 35°C to 42°C and or from 94°F to 108°F. The temperature of human body always remains within this range and this is the range on the clinical thermometer. There is a kink near the bulb of clinical thermometer which prevents the automatic fall of mercury level.
    Digital Thermometer: In digital thermometer, reading of temperature is displayed digitally as in digital watches. This is safer because no mercury is used in this. It is important to note that mercury is a highly toxic substance.
    Maximum-Minimum Thermometer: Maximum – minimum thermometer is used to measure the daily temperature to prepare weather reports.
    Reading of thermometer and measuring of temperature:
    • Take a clinical thermometer and hold it horizontally with reading scale towards your eye.
    • Do not hold the thermometer from the bulb.
    • Rotate the thermometer slightly clockwise and anticlockwise. By doing this you will see a shiny thin silvery thread.
    • The end of the silvery thread shows the reading of temperature. If mercury lining ends at 37, the reading is 37°C.
    • Wash the bulb end of thermometer with an antiseptic solution.
    • Give two or three jerks slightly. By doing this the mercury level would fall. When it falls to 35°C or below, put it below the tongue and wait for one minute.
    • Take out the thermometer and read the temperature. Temperature would be near 37°C.
    • The normal body temperature is 37°C. This can differ from person to person.


    Animal fibres

    → Wool and silk fibres are obtained from animals.

    → Wool is obtained from the fleece (hair) of fleece sheep or yak.

    Silk fibres come from cocoons of the silk moth.


    → Wool comes from sheep, goat, yak and some other animals who are having hair on their body.

    → Wool is derived from these hairy fibres.

    Animals that yield wool

    → Breeds of sheep are found in different parts of our country are the main source of obtaining wool.

    • Yak wool: Obtained from Yaks which is common in Tibet and Ladakh.
    • Angora wool: Obtained from Angora goats found in hilly regions such as Jammu and Kashmir.
    • The under fur of Kashmiri goat is soft which is woven into fine shawls called Pashmina shawls.
    • The fur (hair) on the body of camels.
    • Llama and Alpaca, found in South America.
    Rearing of Sheep and obtaining fibre
    • Sheep are reared in hilly areas of Jammu & Kashmir, Himachal Pradesh, Uttaranchal, Arunachal Pradesh and Sikkim or the plains of Haryana, Punjab, Rajasthan and Gujarat.
    • Sheep are herbivores so mainly feed on grass and leaves. They are also provided pulses, corn, jowar, oil cakes and other materials.
    • In winter, sheep are kept inside and fed leaves, grass and dry fodder.
    • Sheep having thick coat of hair on their body yields good quality wool in large quantities.
    • Hair of sheep is shaved off for getting wool, once the reared sheep have developed a thick growth of hair.
    List of India breeds of sheep
    Processing of Wool from Fibre
    → Obtaining wool is very long process which involves various steps.
    Step 1(Shearing)
    → Fleece of the sheep along with a thin layer of skin is removed from its body which is called Shearing.
    → Shearing is done during hot weather so that sheep survive without protective hair.
    →The hair or the fleece of the sheep are dead cells so it doesn't hurt the sheep.
    → The instrument used to remove the fleece is similar to the shaving instrument.
    Step 2 (Scouring)
    → Washing of sheared skin with hair in tanks to remove grease, dust and dirt is called scouring. Nowadays scouring is done by machines.
    Step 3 (Sorting)
    → The hairy skin is sent to a factory where hair of different textures are separated or sorted. This is called sorting.
    Step 4
    → The small fluffy fibres, called burrs, are picked out from the hair. These are the same burrs which sometimes appear on your sweaters. 
    →The fibres are scoured again and dried. This is the wool ready to be drawn into fibres.
    Step 5
    → The fibres can be dyed in various colours, as the natural fleece of sheep and goats is black, brown or white.
    Step 6
    → The fibres are straightened, combed and rolled into yarn. 
    → The longer fibres are made into wool for sweaters and the shorter fibres are spun and woven into woollen cloth.
    → Silk fibres are also animal fibres. The rearing of silkworms for obtaining silk is called sericulture.
    Life history of silk moth
    → For obtaining silk, silkworms are reared on a large scale. A female silk moth gives hundreds of eggs on the mulberry leaf. 
    → The eggs are then hatched by keeping them under the right temperature and humidity conditions. 
    → Then, the silk caterpillars are fed on mulberry leaves. After 20-25 days, caterpillars stop eating and start spinning cocoons around them.
    → Further development of the moth continues inside the cocoon. The moth leaves the cocoon after its development is complete.

    → Once the moth has left the cocoon, it is collected to obtain silk.

    → The cocoons are kept under the sun or boiled or exposed to steam to separate the silk fibres. This process is known as reeling the silk.

    → Silk fibres obtained after reeling are spun into silk threads.

    From cocoon to silk

    → For obtaining silk, moths are reared and their cocoons are collected to get silk threads.

    Rearing silkworms

    → A female silk moth lays hundreds of eggs at a time.

    → The eggs are stored carefully on strips of cloth or paper and sold to silkworm farmers.

    → The farmers keep eggs under hygienic conditions and under suitable conditions of temperature and humidity.

    → The eggs are warmed to a suitable temperature for the larvae to hatch from eggs.

    → This is done when mulberry trees bear a fresh crop of leaves.

    → The larvae, called caterpillars or silkworms, eat day and night and increase enormously in size.

    → The worms are kept in clean bamboo trays along with freshly chopped mulberry leaves.

    → After 25 to 30 days, the caterpillars stop eating and move to a tiny chamber of bamboo in the tray to spin cocoons.

    → Small racks or twigs may be provided in the trays to which cocoons get attached.

    → The caterpillar or silkworm spins the cocoon inside which develops the silk moth.

    Processing silk

    → A pile of cocoons is used for obtaining silk fibres.

    → The cocoons are kept under the sun or boiled or exposed to steam.

    → The silk fibres separate out. The process of taking out threads from the cocoon for use as silk is called reeling the silk.

    → Reeling is done in special machines, which unwind the threads or fibres of silk from the cocoon.

    → Silk fibres are then spun into silk threads, which are woven into silk cloth by weavers.



    • In the previous chapter we learned that plants can prepare their own food by photosynthesis but animals cannot.
    • Animals get their food from plants, either directly by eating plants or indirectly by eating animals that eat plants. So animals exhibit heterotopic mode of nutrition.
    • Again from previous chapter it is clear that all living organisms (both plants and animals) need certain nutrients to stay alive and grow and these nutrients are obtained from food.
    • Since this Chapter is about nutrition in animals so in this chapter we will learn about the process of intake and utilization of food in animals.
    • All the animals can be divided into three groups on the basis of their food habits. These are:
      1. Herbivores: Those animals which eat only plants are called herbivores. Examples are Goat, Cow, and Deer etc.
      2. Carnivores: Those animals which eat only other animals as food are called carnivores. Examples are Lion, Tiger, and Lizard etc.
      3. Omnivores: Those animals which eat both, plants and animals are called omnivores. Examples are Man, Dog and Crow etc.

    Process of nutrition in animals

    Holozoic nutrition: It is a process by which animals take in their food. It involves different steps namely, ingestion, digestion, absorption, assimilation and egestion. Human beings exhibit holozoic mode of nutrition involving five basic steps.
    • Ingestion: The process of taking food into the body is called ingestion.
    • Digestion: the process in which the food containing large, insoluble molecules is broken down into small, water soluble molecules is called digestion.
    • Absorption: The process in which the digested food passes through the intestinal wall into blood stream is called absorption.
    • Assimilation: The process in which the absorbed food is taken in by the body cells and used for energy, growth and repair is called assimilation.
    • Egestion: The process in which the undigested food is removed from the body is called egestion.

    Nutrition in Simple organisms

    In this section we will learn about simple organisms like amoeba, paramecium, hydra, spider and frog.

    Nutrition in Amoeba

    • Amoeba is a microscopic organism which consists of only a single cell.
    • Amoeba is mostly found in pond water.
    • Figure given below shows the structure of amoeba.
      structure of amoeba
    • Amoeba eats tiny plants and animals as food which floats in water in which it lives.
    • The mode of nutrition in Amoeba is holozoic.
    • The process of obtaining food by Amoeba is called phagocytosis.
    • Steps involved in the nutrition of Amoeba:
      1. Ingestion: Amoeba ingests food by forming temporary finger-like projections called pseudopodia around it. The food is engulfed with a little surrounding water to form a food vacuole (‘temporary stomach’) inside the Amoeba.
      2. Digestion: In Amoeba, food is digested in the food vacuole by digestive enzymes which break down the food into small and soluble molecules by chemical reactions.
      3. Absorption: The digested simple and soluble substances pass out of food vacuole into the surrounding environment.
      4. Assimilation: The absorbed food materials are used to obtain energy through respiration and make the parts of Amoeba cell which leads to the growth of Amoeba.
      5. Egestion: The remaining undigested material is moved to the surface of the cell and thrown out of the body of Amoeba.

    Nutrition in Paramecium:

    • Paramecium is also a tiny unicellular animal which lives in water.
    • Ingestion: Paramecium uses its hair like structures called cilia to sweep the food particles from water and put them into mouth.
    • Ingestion is followed by other steps such as digestion, absorption, assimilation and egestion which are same as those we studied in Amoeba

    Nutrition in Hydra

    • Hydra is a simple multicellular animal.
    • It has a number of tentacles around its mouth, which are used for ingestion of food.
    • These tentacles entangle small aquatic animals and kill them with their stinging cells.
    • After this they push them into their mouth. Now inside their body cavity digestive juices are secreted by the surrounding cells.
    • These juices digest the food and the digested food is absorbed through the cavity walls and assimilated in the cells.

    Nutrition in frog

    • The frog uses its long sticky tongue to catch insects. Frogs have well developed digestion system in which the digestion of food takes place.

    Nutrition in Spider

    • In spiders digestion of food actually takes place outside their body.
    • A spider weaves a sticky web in which small insects get stuck.
    • It then injects digestive juices into the body of the insect, which digests the body part of the insects.
    • The spider then sucks up the digested food.

    Human Digestive system

    • We take food through our mouth, digest and utilise it.
    • Figure given below shows the human digestive system
      human digestive system
    • Human digestive system consists of alimentary canal and its associatedhuman-digestive-system.png glands.
    • Various organs of human digestive system in sequence are
      1. Mouth (Buccal Cavity)
      2. Oesophagus (food Pipe)
      3. Stomach
      4. Small intestine
      5. Large intestine
      6. Rectum
      7. Anus.
    • The glands which are associated with human digestive system are
      1. Salivary glands- Located in mouth or Buccal Cavity
      2. Liver- It is the largest gland situated in the upper part of abdomen on the right side.
      3. Pancreas- located just below the stomach
      The ducts of various glands open into the alimentary canal and pour secretion of their juices into the alimentary canal.

    Digestion in the mouth

    • We take food through our mouth and the process of taking food into the body is called ingestion.
    • The mouth or buccal cavity contains teeth, tongue and salivary glands.
    • Digestion begins in the mouth when we chew the food with the help of our teeth.
    • The teeth cut the food into smaller pieces, chew and grind it.
    Chewing breaks down the food into smaller pieces and mixes them with saliva. This process is called mastication.
    • The salivary glands secrete watery liquid called saliva. Saliva is a digestive juice that helps to partially digest the starch present in the food.
    • The tongue helps in mixing saliva with the food.
    • Tongue is a muscular organ that helps you eat the food. It mixes saliva with the food during chewing and helps in swallowing it.
    • We also taste food with our tongue as it has taste buds that detect different tastes of food.


    • Teeth are used for cutting, grinding and tearing the food before you swallow it.
    • You have different types of teeth to do the job.
    • Milk teeth:- A child has only 20 teeth, 10 in each jaw. These are known as milk teeth. They begin to fall at the age between 6 to 8 and then new set of teeth grows.
    • Permanent teeth:- This set contains 32 teeth, 16 in each jaw. There are 4 incisors, 2canines, 4 premolars and 6 molars in each jaw. As shown below in the figure:
      prtmanent teeth
      1. Your front teeth are incisors. They are used for biting and cutting.
      2. Next to incisors are canines. These are pointed and are used for piercing and tearing pieces of food.
      3. Teeth at the back of your mouth are broad with almost flat surface. These teeth crush and grind food and are called the premolars and molars. Molars are larger then premolars
      4. White substance that covers your teeth is called enamel.

    The food pipe/Oesophagus

    • The swallowed food passes into the food pipe or oesophagus as shown below in the figure
    • This figure shows the movement of food in food pipe which runs along the neck and chest.
      the food pipe
    • So, the oesophagus leads from your mouth to the stomach. It is made up of the muscles.
    • Food is pushed down by movement of the wall of food pipe.
    • This movement called peristalsis, takes place throughout the alimentary canal and pushes the food downwards.


    • Stomach is the thick walled bag present on the left side of the abdomen. (see human digestive system figure)
    • It is the widest part of the alimentary canal. Oesophagus brings slightly digested food from mouth into the stomach.
    • The stomach walls contain s three tubular glands in it walls which secrete gastric juice.
    • The gastric juice contains three substances: Hydrochloric acid, the enzyme pepsin and mucus.
    • The hydrochloric creates an acidic medium which facilitates the action of the enzyme pepsin that is the digestion of protein into simple substances.
    • The acid kills many bacteria that enter along with the food.
    • The mucus helps to protect the stomach wall from its own secretions of hydrochloric acid.
    • The partially digested food then goes from the stomach into the small intestine.

    Small intestine

    • Small intestine is highly coiled and is about 7.5 m long.
    • After leaving stomach food enters small intestine and last steps of digestion takes place in small intestine.
    • It receives secretions from liver and pancreas and wall of small intestine also secrets juices.
    • Liver:- Liver is the largest gland in the body and is situated in the upper part of the abdomen on the right side. It secrets bile juice that is stored in gall bladder
    • Pancreas:- It is the large cream coloured gland located just below the stomach. The pancreatic juice acts on carbohydrates, fats and proteins and converts them into simple form.
    • The partly digested food now reaches the lower part of the small
    • The walls of the small intestine contain glands which secretes intestinal juice.
    • The enzymes present in it finally convert the proteins into amino acids, complex carbohydrates into glucose and fats into fatty acids and glycerol.


    • The small intestine is the main region for the absorption of digested food.
    • The inner surface of the small intestine has numerous finger-like projections called villi which increase the surface area for rapid absorption of digested food.
    • The digested food which is absorbed through the walls of the small intestine goes into our blood.


    • The blood carries digested and dissolved food to all the parts of the body where it becomes assimilated as part of the cells and is utilised for obtaining energy, building up new tissues and the repair of old tissues.


    • The unabsorbed food is sent into the large intestine where more villi absorb water from this material.
    • The rest of the material is removed from the body via the anus.
    • The exit of this waste material is regulated by the anal sphincter.

    Digestion in grass eating animals

    • Buffaloes and other grass eating animals swallow grass and store it in a separate part of stomach called Rumen. These animals have complicated stomach.
    • In rumen food is partially digested and is called cud.
    • Later cud returns to the mouth in small lumps and the animals chews it. This process is called rumination and these animals are called ruminants.
    • Grass is rich in cellulose and we humans cannot digest it.



    • All living organisms such as plants and animals require food. So food is essential for all living organisms.
      why organisms need food
    • Plants are capable of making their food themselves but humans and animals cannot.
    • Carbohydrates, proteins, fats, vitamins and minerals are essential components of food, these components are called nutrients.

    Mode of nutrition in plants

    • Plants prepare their food by using raw materials like water, carbon dioxide and minerals.
    • The process of utilization of food by a living organism to obtain energy is called nutrition.
    • There are two modes of nutrition as shown below in the figure
      modes of nutrition
      1. Autotrophs or Autotrophic: - In this mode of nutrition organisms make their food themselves from simple substances. All green plants are Autotrophs (Auto means self and trophos means nourishment)
      2. Heterotrophs or heterophobic: - Heterotrophic organisms are those who obtain food from other organisms. Since these organisms depend on other organisms for their food, they are called consumers. All animals and non-green plants like fungi come under this category.


    • Photosynthesis is food making process in plants from simple substances like carbon dioxide and water in the presence of sunlight.
      photosynthesis definition
    • Oxygen is released during photosynthesis.

    The process of photosynthesis can be represented as:

    process of photosynthesis
    • The process of photosynthesis takes place in the green leaves of a plant.
    • The food is prepared by the green leaves of a plant in the form of a simple sugar called glucose.
    • The extra glucose is changed into another food called starch. This starch is stored in the leaves of the plant.
    • The green plants convert sunlight energy into chemical energy by making carbohydrates.

    The photosynthesis takes place in the following three steps:

    1. Absorption of sunlight energy by chlorophyll.
    2. Conversion of light energy into chemical energy, and splitting of water into hydrogen and oxygen by light energy.
    3. Reduction of carbon dioxide by hydrogen to form carbohydrate like glucose by utilizing the chemical energy.

    Conditions necessary for photosynthesis:

    The conditions necessary for photosynthesis to take place are:
    1. Sunlight
    2. Chlorophyll
    3. Carbon dioxide
    4. Water

    Raw materials for photosynthesis:

    The raw materials for photosynthesis are:
    1. Carbon dioxide
    2. Water
    How the plants obtain carbon dioxide?
    Nutretion in plants
    • There are a large number of tiny pores called stomata on the surface of the leaves of plants.
    • The carbon dioxide gas enters the leaves of the plant through the stomata present on their surface.
    • Each stomatal pore is surrounded by a pair of guard cells. The opening and closing of stomatal pores is controlled by the guard cells.
    How the plants obtain water for photosynthesis:
    • The water required by the plants for photosynthesis is absorbed by the root of the plants from the soil through the process of osmosis.
    • The water absorbed by the roots of the plants is transported upward through the xylem vessels to the leaves where it reaches the photosynthetic cells.
    1. The plants also need other raw materials such as nitrogen, phosphorus, iron and magnesium, etc., for building their body.
    2. The plants take these materials from the soil.
    3. Nitrogen is essential element used by the plants to make proteins and other compound.
    Site of photosynthesis: Chloroplasts
    • Photosynthesis takes place in the leaves of the plants.
    • Leaves have green pigment called chlorophyll
    • It helps leaves capture the energy of the sunlight which is then used to prepare food from carbon di oxide and water.
    • Here, you see that solar energy is captured by the leaves and is stored in the plant in the form of food.
    • So, we can say that Sun is ultimate source of energy for all living organisms.

    Other Notes on photosynthesis

    • Photosynthesis in plants can also takes place in other green parts like green stems, green branches.
    • Glucose (simple carbohydrates) is the simplest food synthesized by plants. This glucose made by plants is converted into complex carbohydrates which are known as starch.
    • These simple carbohydrates are used to synthesise other components of food such as proteins and fats.
    • Proteins are nitrogenous substances. Plants prepare proteins with the help of nitrogen which is obtained from the soil. 
    • Plants use the minerals dissolved in water to convert Glucose (simple carbohydrates) into carbohydrates, proteins and fats.
    • Photosynthesis is important because
      1. It provides food to animals including human beings
      2. It puts oxygen gas into the air which is essential for breathing and respiration in animals including human beings

    Other modes of nutrition in plants

    • Most of the plants have green pigment called chlorophyll and can make their own food.
    • Some plants do not have chlorophyll and cannot synthesize their own food and are known as Heterotrophic plants
    • This type of nutrition can be categorized into
      1. parasitic mode of nutrition
      2. Insectivorous mode
      3. saprophytic mode of nutrition 
      4. Symbiotic mode of nutrition
    • Let us now explain these modes in detail


    • In parasitic mode of nutrition, plants depend on other plants or animals for their nourishment.
    • Such dependent plants are called as parasites and the ones on which parasites depend are called as hosts
    • A parasite plant climbs on the host plant from which they get all the food.
    • The host does not get any benefit from the parasite.
    • Some examples of parasites are Cuscuta (akash-bel), Cassytha (amar-bel), hookworms, tapeworms, leeches, etc.

    Insectivorous Plants

    • The insectivorous mode of nutrition is observed in plants like pitcher plant and the Venus fly trap.
    • These types of plants purely depend on other insects and small animals for their nutrition.
    • Pitcher plants trap small insects inside the pitcher and insects are digested by the digestive juices secreted in the pitcher.
    • Insectivorous plants grow in those soils which do not contain sufficient nitrogen mineral.
    • These types of plants are green and carry out photosynthesis to obtain a part of food.


    • Mode of nutrition in which organisms or plants that obtain their nutrition from dead and decaying organic matter is called Saprophytic mode
    • The plants which exhibit saprotrophic mode of nutrition are called as saprotrophs
    • Saprotrophs secrete digestive juices onto dead and decaying matter to dissolve it and then absorb nutrients from it.
    • Examples of saprotrophs are moulds, mushrooms, yeasts and some bacteria.

    Symbiotic plants

    • In this mode of nutrition there is a close association between two different plants of different categories.
    • In such type of association both the plants get benefited.
    • For example certain fungi live in the roots of the trees. In this case tree provides nutrients to fungi and in return receives help from it to take up water and nutrients from the soil.

    How nutrients are replenished in the soil

    • We know that plants continuously take nutrients from the soil in order to synthesize food. As a result of this amount of nutrients in the soil decreases.
    • Nutrients in the soil are replenished by adding fertilisers and manures.
    • Fertilisers and manures contain plants nutrients and minerals like nitrogen, phosphorus and potassium.
    • Another way to replenish soil is to grow leguminous crops (for example gram, peas, pulses etc.) in the soil.
    • The bacterium called Rhizobium can take atmospheric nitrogen and convert it into a soluble form.
    • But Rhizobium cannot make its own food. So it lives in the roots of gram, peas, moong, beans and other legumes and provides them with nitrogen. In return plants provide food and shelter to the bacteria.
    • Thus plants and bacteria have a symbiotic relationship here.
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    19 August 2018



    There are many instances when we notice a substance being separated from a mixture of materials.
    Tea leaves are separated from the liquid with a strainer, while preparing tea (Fig. 5.1).

    Fig. 5.1 Separating tea leaves with a strainer
    Grain is separated from stalks, while harvesting. Milk or curd is churned to separate the butter (Fig. 5.2). As we learned in Chapter 3, we gin cotton to separate its seeds from the fibre.
    Perhaps you might have eaten salted daliya or poha. If you found that it had chillies in it, you may have carefully taken them out before eating.
    Suppose you are given a basket containing mangoes and guavas and asked to separate them. What would you do? Pick out one kind and place them in a separate container, right?
    Seems easy, but what if the materials we want to separate are much smaller than mango or guava?

    Fig. 5.2 Butter is taken out by churning milk or curds
    Imagine you are given a glass of sand with salt mixed in it. Impossible, even to think of separating salt from this mixture by picking out grains of sand by hand!
    But, why would we need to separate substances like this at all, is what Paheli wants to know.
    Activity 1 In Column 1 of Table 5.1, are given a few processes of separation. The purpose of separation and the way separated components are used is mentioned in Column 2 and 3 respectively. However, the information given in Columns 2 and 3 is jumbled up. Can you match each
    Table 5.1 Why do we separate substances?
    Separation process Purpose for which we do the separation What do we do with the separated components?
    1) Separat stone from rice a) To separate two different, but useful components i) We throw away the solid components
    2) Churning milk to obtain butter b) To remove non-useful components. ii) We throw away the impurities.
    3) Separate tea leaves c) To remove impurities or harmful components. iii) We use both the components.
    process with its purpose and the way separated components are used?
    We see that, before we use a substance, we need to separate harmful or non-useful substances that may be mixed with it. Sometimes, we separate even useful components if we need to use them separately.
    The substances to be separated may be particles of different sizes or materials. These may be solids, liquids or even gases. So, how do we separate substances mixed together if they have so many different properties?


    We will discuss some simple methods of separating substances that are mixed together. You may come across some of these methods being used in day to day activities.

    Hand Picking

    Activity 2 Bring a packet of grain purchased from a shop to the classroom. Now, spread the grain on a sheet of paper. Do you find only one kind of grain on the sheet of paper? Are there pieces of stone, husks, broken grain and particles of any other grain in it? Now, remove with your hand the pieces of stone, husks and other grains from it.
    This method of handpicking can be used for separating slightly larger sized impurities like the pieces of dirt, stone, and husk from wheat, rice or pulses (Fig. 5.3). The quantity of such impurities is usually not very large. In such situations, we find that handpicking is a convenient method of separating substances.

    Fig. 5.3 Handpicking stones from grain


    You must have seen bundles of wheat or paddy stalks lying in fields after harvesting the crop. Stalks are dried in the sun before the grain is separated from them. Each stalk has many grain seeds attached to it. Imagine the number of grain seeds in hundreds of bundles of stalk lying in the field! How does the farmer separate grain seeds from those bundles of stalks?
    One may pluck mangoes or guavas from the trees. But, grain seeds are much smaller than mangoes or guavas. So, plucking them from their stalks would be impossible. How does one separate grain seeds from their stalks?
    The process that is used to separate grain from stalks is threshing. In this process, the stalks are beaten to free the grain seeds (Fig. 5.4).

    Fig 5.4 Threshing
    Sometimes, threshing is done with the help of bullocks. Machines are also used to thresh large quantities of grain.


    Activity 3 Make a mixture of dry sand with sawdust or powdered dry leaves. Keep this mixture on a plate or a newspaper. Look at this mixture carefully. Can the two different components be made out easily? Are the sizes of particles of the two components similar? Would it be possible to separate the components by handpicking?
    Now, take your mixture to an open ground and stand on a raised platform. Put the mixture in a plate or sheet of paper. Hold the plate or the sheet of paper containing the mixture, at your shoulder height. Tilt it slightly, so that the mixture slides out slowly.
    What happens? Do both the components — sand and sawdust (or powdered leaves) fall at the same place? Is there a component that blows away? Did the wind manage to separate the two components?.
    This method of separating components of a mixture is called winnowing. Winnowing is used to separate heavier and lighter components of a mixture by wind or by blowing air.

    Fig. 5.5 Winnowing
    This method is commonly used by farmers to separate lighter husk particles from heavier seeds of grain (Fig. 5.5).
    The husk particles are carried away by the wind. The seeds of grain get separated and form a heap near the platform for winnowing. The separated husk is used for many purposes such as fodder for cattles.


    Sometimes, we may wish to prepare a dish with flour. We need to remove impurities and bran that may be present in it. What do we do? We use a sieve and pour the flour into it (Fig. 5.6).
    Sieving allows the fine flour particles to pass through the holes of the sieve while the bigger impurities remain on the sieve.
    In a flour mill, impurities like husk and stones are removed from wheat before grinding it. Usually, a bagful of wheat is poured on a slanting sieve. The sieving removes pieces of stones, stalk and husk that may still remain with wheat after threshing and winnowing.

    Fig. 5.6 Sieving
    You may have also noticed similar sieves being used at construction sites

    Fig. 5.7 Pebbles and stones are removed from sand by sieving
    to separate pebbles and stones from sand (Fig. 5.7).
    Activity 4 Bring a sieve and a small quantity of flour from home, to the class. Sieve the flour to separate any impurities in it. Now, make a fine powder of chalk pieces and mix it with the flour. Can we separate the flour and the powdered chalk by sieving?
    Sieving is used when components of a mixture have different sizes.

    Sedimentation, Decantation and Filtration

    Sometimes, it may not be possible to separate components of a mixture by winnowing and handpicking. For example, there may be lighter impurities like dust or soil particles in rice or pulses. How are such impurities separated from rice or pulses before cooking?
    Rice or pulses are usually washed before cooking. When you add water to these, the impurities like dust and soil particles get separated. These impurities go into water, which becomes a little muddy. Now, what will sink to the bottom of the vessel — rice or dust? Why? Have you seen that the vessel is tilted to pour out the dirty water?
    When the heavier component in a mixture settles after water is added to it, the process is called sedimentation. When the water (along with the dust) is removed, the process is called decantation (Fig. 5.8). Let us find a few other mixtures that can be separated through sedimentation and decantation.
    The same principle is used for separating a mixture of two liquids that do not mix with each other. For example, oil and water from their mixture can be separated by this process. If a mixture of such liquids is allowed to stand for some time, they form two separate layers. The component that forms the top layer can then be separated by decantation.
    Let us again consider a mixure of a solid and liquid. After preparing tea, what do you do to remove the tea leaves? Try decantation. It helps a little. But, do you still get a few leaves in your tea? Now, pour the tea through a strainer.

    Fig. 5.8 Separating two components of a mixture by sedimentation and decantation
    Did all the tea leaves remain in the strainer? This process is called filtration (Fig. 5.1). Which method of separating tea leaves from prepared tea is better, decantation or filtration?
    Let us now consider the example of water that we use. Do all of us, at all times, get safe water to drink? Sometimes, water supplied through taps may be muddy. The water collected from ponds or rivers may also be muddy, especially after rains. Let us see if we can use some method of separation to remove insoluble impurities like soil from the water.
    Activity 5 Collect some muddy water from a pond or a river. If it is not available, mix some soil to water in a glass. Let it stand for half an hour. Observe the water carefully and note your observations.
    Does some soil settle at the bottom of water? Why? What will you call this process?
    Now, slightly tilt the glass without disturbing the water. Let the water from the top flow into another glass (Fig. 5.8). What will you call this process?
    Is the water in the second glass still muddy or brown in colour? Now filter it. Did the tea strainer work? Let us try filtering the water through a piece of cloth. In a piece of cloth, small holes or pores remain in between the woven threads. These pores in a cloth can be used as a filter.
    If the water is still muddy, impurities can be separated by a filter that has even smaller pores. A filter paper is one such filter that has very fine pores in it. Fig. 5.9 shows the steps involved in using a filter paper. A filter paper folded in the form of a cone is fixed onto a funnel (Fig. 5.10). The mixture is then poured on the filter paper. Solid particles in the mixture do not pass through it and remain on the filter.

    Fig. 5.9 Folding a filter paper to make a cone

    Fig 5.10 Filtration using a filter paper
    Fruit and vegetable juices are usually filtered before drinking to separate the seeds and solid particles of pulp. The method of filtration is also used in the process of preparing cottage cheese (paneer) in our homes. You might have seen that for making paneer, a few drops of lemon juice are added to milk as it boils. This gives a mixture of particles of solid paneer and a liquid. The paneer is then separated by filtering the mixture through a fine cloth or a strainer.


    Activity 6 Heat a beaker containing some water. Allow the water to boil. If you continue heating, would the water turn into steam

    Fig. 5.11 Heating a beaker containing salt water
    and disappear completely? Now, add two spoons of salt to water in another beaker and stir it well. Do you see any change in the colour of water? Can you see any salt in the beaker, after stirring? Heat the beaker containing the salt water (Fig. 5.11). Let the water boil away. What is left in the beaker?
    In this activity, we used the process of evaporation, to separate a mixture of water and salt.
    The process of conversion of water into its vapour is called evaporation. The process of evaporation takes place continuously wherever water is present.
    Where do you think, salt comes from? Sea water contains many salts mixed in it. One of these salts is the common salt. When sea water is allowed to stand in shallow pits, water gets heated by sunlight and slowly turns into water vapour, through evaporation. In a few days, the water evaporates completely leaving behind the solid salts (Fig. 5.12). Common salt is then obtained from this mixture of salts by further purification.

    Fig. 5.12 Obtaining salt from sea water

    Use of more than one method of separation

    We have studied some methods for separation of substances from their mixtures. Often, one method is not sufficient to separate the different substances present in a mixture. In such a situation, we need to use more than one of these methods.
    Activity 7 Take a mixture of sand and salt. How will we separate these? We already saw that handpicking would not be a practical method for separating these.
    Keep this mixture in a beaker and add some water to this. Leave the beaker aside for some time. Do you see the sand settling down at the bottom? The sand can be separated by decantation or filtration. What does the decanted liquid contain? Do you think this water contains the salt which was there in the mixture at the beginning?
    Now, we need to separate salt and water from the decanted liquid. Transfer this liquid to a kettle and close its lid. Heat the kettle for some time. Do you notice steam coming out from the spout of the kettle?
    Take a metal plate with some ice on it. Hold the plate just above the spout of the kettle as shown in Fig. 5.13. What do you observe? Let all the water in the kettle boil off.
    When the steam comes in contact with the metal plate cooled with ice, it condenses and forms liquid water. The water drops that you observed falling from the plate, were due to condensation of steam. The process of conversion of water vapour into its liquid form is called condensation.
    Did you ever see water drops condensed under a plate that has been used to cover a vessel containing milk that has just been boiled?
    After all the water has evaporated, what is left behind in the kettle?
    We have thus, separated salt, sand and water using processes of decantation, filtration, evaporation and condensation.
    Paheli faced a problem while recovering salt mixed with sand. She has mixed a packet of salt in a small

    Fig. 5.13 Evaporation and condensation
    amount of sand. She then tried the method suggested in Activity 7, to recover the salt. She found, however, that she could recover only a small part of the salt that she had taken. What could have gone wrong?

    Can water dissolve any amount of a substance?

    In chapter 4, we found that many substances dissolve in water and form a solution. We say that these substances are soluble in water. What will happen if we go on adding more and more of these substances to a fixed quantity of water?
    Activity 8 You will need a beaker or a small pan, a spoon, salt and water. Pour half a cup of water in the beaker. Add one teaspoonful of salt and stir it well, until the salt dissolves completely (Fig 5.14). Again add a teaspoonful of salt and stir well. Go on adding salt, one teaspoonful at a time, and stir.
    After adding a few spoons of salt, do you find that some salt remains undissolved and settles at the bottom of the beaker? If yes, this means that no more salt can be dissolved in the amount of water we have taken. The solution is now said to be saturated.
    Here is a hint as to what might have gone wrong when Paheli tried to recover large quantity of salt mixed with sand. Perhaps the quantity of salt was much more than that required to form a saturated solution. The undissolved salt

    Fig 5.14 Dissolving salt in water
    would have remained mixed with the sand and could not be recovered. She could solve her problem by using a larger quantity of water.
    Suppose, she did not have sufficient quantity of water to dissolve all the salt in the mixture. Is there some way that water could be made to dissolve more salt before the solution gets saturated?
    Let us try and help Paheli out.
    Activity 9 Take some water in a beaker and mix salt in it until it cannot dissolve any more salt. This will give you a saturated solution of salt in water.
    Now, add a small quantity of salt to this saturated solution and heat it. What do you find? What happens to the undissolved salt in the bottom of the beaker? Does it dissolve, now? If yes, can some more salt be dissolved in this solution by heating it?
    Let this hot solution cool. Does the salt appear to settle at the bottom of the beaker again?
    The activity suggest that larger quantity of salt can be dissolved in water on heating.
    Does water dissolve equal amounts of different soluble substances? Let us find out.
    Activity 10 Take two glasses and pour half a cup of water in each of them. Add a teaspoon of salt to one glass and stir till the salt dissolves. Go on adding salt, one teaspoon at a time, till the solution saturates. Record the number of spoons of salt that dissolved in the water, in Table 5.2. Now, repeat the same activity with sugar. Repeat this with some other substances that are soluble in water.
    What do you notice from Table 5.2? Do you find that water dissolves different substances in different amounts?
    Table 5.2
    Substance Number of spoons of substance that dissolved in water
    We have discussed a few methods of separating substances. Some of the methods of separation presented in this chapter are also used in a science laboratory.
    We also learnt that a solution is prepared by dissolving a substance in a liquid. A solution is said to be saturated if it cannot dissolve more of the substance in it.
    • Churning
    • Condensation
    • Decantation
    • Evaporation
    • Filtration
    • Handpicking
    • Saturated solution
    • Sedimentation
    • Sieving
    • Solution
    • Threshing
    • Winnowing
    • Handpicking, winnowing, sieving, sedimentation, decantation and filtration are some of the methods of separating substances from their mixtures.
    • Husk and stones could be separated from grains by handpicking.
    • Husk is separated from heavier seeds of grain by winnowing.
    • Difference in the size of particles in a mixture is utilised to separate them by the process of sieving and filtration.
    • In a mixture of sand and water, the heavier sand particles settle down at the bottom and the water can be separated by decantation.
    • Filtration can be used to separate components of a mixture of an insoluble solid and a liquid.
    • Evaporation is the process in which a liquid gets converted into its vapour. Evaporation can be used to separate a solid dissolved in a liquid.
    • A saturated solution is one in which no more of that substance can be dissolved.
    • More of a substance can be dissolved in a solution by heating it.
    • Water dissolves different amount of soluble substances in it.


    Solid Liquid & Gas

    solid liquid and gas
    Fig:States of Matter
    Solid: Solid has definite shape and definite volume. Examples: Stones, wood, plastic, common salt, steel, ice, glass, etc.
    Liquid: Liquid has indefinite shape but definite volume. Examples: Water, milk, oil, etc.
    Gas: Gas has indefinite shape and indefinite volume. Examples: Oxygen, nitrogen, carbon dioxide, etc.

    Other Criteria For Sorting Materials:


    Appearance: Different materials look different from each other. The appearance depends on colour, hardness, texture, and lustre.
    Hardness: hardness is another property of materials. Some materials are very hard while some are very soft.
    Hard: Material which are difficult to compress are called hard, e.g. diamond, stone, wood, steel, etc. Diamond is the hardest natural substance.
    Soft: Materials which can be compressed easily are called soft, e.g. chalk, cotton, rubber, etc.


    Human beings exhibit locomotion. Locomotion is brought about by the combination of muscular and skeletal system. The bending and movement of the skeleton is brought about by special structures called as joints.

    Joint is a point at which two separate bones meet.
    Joints are held at position by strong cords called as ligaments. Joints can be classified based on the type of movement they bring about. There are three main types of joints in the human body. They include fixed or immovable joints, slightly movable joints and freely movable joints.

    a) Fixed or immovable joints are the joints which do not allow the structure to move but they offer protection for the structure in which they are present. Examples are the sutures between the bones of the cranium,ribs in the breast bone, bones of the hip girdle.

    b) Slightly movable joints provide support to the structure in which they are present. They also help the structure to move slightly. 
    Example includes joints of the lower jaw which are slightly movable.

    c) Freely movable joints are the joints which solely help in the movement of the structure or organ in which they are present. Four immovable joints present in our body are Ball and socket joint, Pivot joint, hinge joint and the gliding joint.
    • Ball and socket joint: This joint is formed by two bones in which one end of a bone is rounded and ball-like. It fits into a cup-like depression of the other bone. This joint provides movement in any direction. Examples of a ball and socket joint are shoulder joints and hip joints.
    • Pivot joint: This is the joint in which one bone fits into a ring formed by the other bone. It rotates over the pivot-like end of the other bone. Example is the joint which joins the neck to the head. Head rotates over the neck.
    • Hinge joint: This is a joint which moves like a hinge in a single plane not more than 180 degrees.  It provides back and forth movement of the structure. This is a joint which can be compared to that of a hinge in the door. Examples of a hinge joint are the elbow joint and the knee joint.
    • Gliding joints: This is a joint which allows bones to glide over each other. These types of joints provide little movement in all directions. These are the joints present at the ankles,wrist and between vertebrae.
    Movement in bones
    Joints along with muscles can bring about movement in bones.
    • One end of the muscle is attached to a movable bone and the other end of the muscle is attached to a fixed bone.
    • Muscles are attached to bones by tough cords called as tendons.
    • Muscles work in pairs and bring about movement by contraction and relaxation.
    • The paired muscles are biceps and triceps which together help in the movement of the structures like arm, leg etc.
    • Contraction brings in the shortening of the muscle and relaxation brings about lengthening of the muscle. It makes the muscle short, thick and stiff to pull the bone .
    • When the arm is folded, biceps contract and triceps relaxes and lengthens. 
    • When the arm is straightened, biceps relax and lengthen whereas triceps contract. 
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