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Life of every organism depends on certain basic processes. Excretion is one among them. Different organisms follow different modes of excretion. In complex organisms including humans, there is a specialized system for excretion called human excretory system.

We all obtain our nutrients from different sources which are later digested and metabolized in our body. After metabolic reactions, the body starts to sort out useful and toxic substances in an individual. As we all know, the accumulation of the toxins may be harmful and the body removes all the metabolic wastes by the process called excretion.

Different organisms follow different modes of excretion such as kidney, lungs, skin and eyes depending on their habitat and food habit.

For example- Aquatic animals excrete waste in the form of ammonia, while birds and insects excrete mainly uric acid. Humans produce urea as the major excretory product.

Let us have a detailed look at the excretory system notes to explore the excretory system in human beings, different organs of the excretory system and the mechanism of excretion in humans.

Excretory System Organs

The human excretory system organs include:

• A pair of kidneys
• A pair of ureters
• A urinary bladder
• A urethra

Kidneys

Kidneys are bean-shaped structures located on either side of the backbone and are protected by the ribs and muscles of the back. Each human adult kidney has a length of 10-12 cm, a width of 5-7 cm and weighs around 120-170g.

The kidneys have an inner concave structure. The blood vessels, ureter and nerves enter the kidneys through the hilum, which is a notch at the inner concave surface of the kidney. The renal pelvis, a large funnel-shaped space is present inner to the hilum, is has many projections known as calyces.

Structure of Kidney

The structure of the kidney is explained below:

Capsule

The outer layer is called the capsule. Inside the kidney, there are two zones- the outer zone is the cortex and the inner zone is the medulla. The cortex extends in between the medullary pyramids as renal columns called columns of Bertin.

Nephrons

Nephrons are the functional units of the kidney. Each nephron has two parts- glomerulus and renal tubule.
Glomerulus consists of a bunch of capillaries formed by afferent arterioles. Blood from glomerulus is carried away by efferent arterioles.
The renal tubule starts with a cup-like structure called Bowman’s capsule and this encloses the glomerulus. The malpighian body consists of glomerulus and Bowman’s capsule. The highly coiled structure in the tubule next to the Bowman’s capsule is the proximal convoluted tubule.

Henle’s loop

The next part of the tubule is Henle’s loop which has an ascending and a descending limb. The ascending loop continues as a distal convoluted tubule. The distal convoluted tubules of many nephrons open into the collecting duct.
The cortical region of the kidney comprises of malpighian corpuscle, proximal convoluted tubule and distal convoluted tubule and the medullary region contains a loop of Henle.
There are two types of nephrons – cortical and juxtamedullary. In the case of cortical, the loop of Henle is very short and extends only a little into the medulla. In juxtamedullary, the loop of Henle is very long and runs deep into the medulla.

Ureter

A pair of thin muscular tubes called the ureter comes out of each kidney extending from the renal pelvis. It carries urine from the kidney to the urinary bladder.

Urinary Bladder

It is a muscular sac-like structure, which stores urine. The urinary bladder is emptied by the process of micturition, i.e. the act of urination.

Urethra

This tube arises from the urinary bladder and helps to expel urine out of the body. In males, it acts as the common route for sperms and urine. Its opening is guarded by sphincter muscles.

Human Excretory System Diagram

The diagram below represents the different parts of the human excretory system.

Excretion in Humans

Excretion is the process where all the metabolic wastes are removed from the body. Excretion in humans is carried through different body parts and internal organs in a series of processes.

Diffusion is the most common process of excretion in lower organisms. A human body is an exceptional machine, where different life-processes (respiration, circulation, digestion, etc.) take place simultaneously. As a result, many waste products produced in our body are in various forms that include carbon dioxide, water, and nitrogenous products like urea, ammonia, and uric acid.

In addition to these, the chemicals and other toxic compounds from medications and hormonal products are also produced. Simple diffusion is not sufficient to eliminate these wastes from our body. We need more complex and specific processes in order to eliminate waste products.

Blood contains both useful and harmful substances. Hence, we have kidneys which separate useful substances by reabsorption and toxic substances by producing urine.

Kidney has a structural filtration unit called nephron where the blood is filtered. Each kidney contains a million nephrons.

Capillaries of kidneys filter the blood and the essential substances like glucose, amino acids, salts, and the required amount of water get reabsorbed and the blood goes into circulation.

Excess water and nitrogenous waste in humans are converted to urine. Urine thus produced is passed to the urinary bladder via the ureters. The urinary bladder is under the control of the Central Nervous System. The brain signals the urinary bladder to contract and through the urinary opening called the urethra, we excrete the urine.

Mechanism of Excretion in Humans

The process of excretion in humans takes place in the following steps:

Urine Formation

The urine is formed in the nephrons and involves the following steps:

• Glomerular Filtration
• Tubular Reabsorption
• Secretion

Glomerular Filtration

It is the primary step in urine formation. In this process, the excess fluid and waste products from the kidney are filtered out of the blood into the urine collection tubules of the kidney and eliminated out of the body.

The amount of filtrate produced by the kidneys every minute is known as Glomerular Filtration Rate (GFR).

Tubular Reabsorption

It is the absorption of ions and molecules such as sodium ions, glucose, amino acids, water etc. Water involves passive absorption, while glucose and sodium ions are absorbed by an active process.

Secretion

Potassium ions, hydrogen ions, and ammonia are secreted out to maintain the equilibrium between the body fluids.

The functions of the various tubules involved in the process are:

• Glomerulus- filters the blood
• Proximal Convoluted Tubules (PCT)- reabsorb water, ions and nutrients. They remove toxins and help in maintaining the ionic balance and pH of the body fluids by secretion of potassium, hydrogen and ammonia to filtrate and reabsorbing bicarbonate ions from the filtrate.
• Descending Loop of Henle- is permeable to water and the filtrate gets concentrated as it is impermeable to electrolytes.
• Ascending Loop of Henle- it is impermeable to water and permeable to electrolytes. The filtrate gets diluted due to the movement of electrolytes from the filtrate to the medullary fluid.
• Distal Convoluted Tubule (DCT)- allows reabsorption of water and sodium ions. It also helps in maintaining pH and ionic balance by secretion and reabsorption of ions like PCT.
• Collecting Duct- a large amount of water is reabsorbed from the filtrate by the collecting duct.

Micturition

The urinary bladder is stretched and gets filled with urine formed in the nephrons. The receptors present on the walls of the urinary bladder send signals to the Central Nervous System, thereby, allowing the relaxation of sphincter muscles to release urine. This is known as micturition.

Dialysis

Under certain circumstances such as poor blood flow to the kidneys, infections, injuries, etc. the kidneys fail to perform their functions. In such situations, artificial kidneys are used for blood filtration and this process is called dialysis.

Other than the urinary system, skin, lungs, and even eyes helps in excreting waste products in different forms. Sweating is a mode of excretion where water, urea, and other salts are excreted through the skin. Lungs help us to exhale gaseous wastes such as carbon dioxide, nitrogen, etc.

Key Points On Human Excretory System

• Human excretory system includes organs that facilitate the removal of nitrogenous wastes from the body.
• The main excretory organs include kidney, ureter, urinary bladder and urethra.
• Kidneys filter the blood and urine is the filtrate obtained.
• Urine passes to the urinary bladder via ureter and is expelled out of the body. This is known as micturition.
• Kidneys also regulate the osmotic pressure of a mammal’s blood through excessive purification and filtration. This is known as osmoregulation.

This was a detailed analysis of the human excretory system.

Photosynthesis

Plant makes their food by the process of Photosynthesis. Photo means Light and synthesis
means to build. They use energy of sunlight to prepare food from CO2 and water in presence
of chlorophyll.
 Entire process is carried out in chloroplast, where the whole photosynthesis
machinery lies.
 Storma: Site for complex dark reaction in the process of photosynthesis.

Photosynthesis mainly occurs in two steps:

Light reaction

Dark reaction
Light Reaction
o Light energy causes the flow of electron from water to two Photosystems,
which contain chlorophylls and emits electron when they absorb light energy.
o Light energy get converted into chemical energy in the form of ATP and
NADPH2.
o Water splits into hydrogen and oxygen.
Dark Reaction
Co2 is converted into carbon compound like carbohydrates using energy in ATP and
hydrogen in NADPH2.
Co2 get fixed into glucose with the help of enzymes such as Rubisco.

Factors affecting photosynthetic rate:

• Light intensity

• Availability of Co2

• Temperature

• Availability of water

• Chlorophyll
• Respiration

To carry out various life processes food must be used as fuel. The process of releasing
energy from food is called Respiration.
Food + O2 CO2 + water + energy

o Respiration includes breathing and oxidation of food in cells.
o Respiration is characterized by three acts:
Food is used up.
Energy is produced.
Exchange of gases, oxygen is inhaled and CO2 is exhaled (breathing).

Oxidation of food can occur in presence or absence of oxygen, on this basis respiration can
be of two types:
1) Aerobic
2) Anaerobic

Aerobic respiration

Occurs in presence of oxygen
Glucose in completely broken into Co2 and H2O
Energy gets stored in the form of ATP

Anaerobic respiration

Occurs in absence of oxygen
Glucose is broken down into Co2, ethanol and releases energy.
Usually occurs in micro-organisms like yeast
Process of Respiration
Occurs in mainly two stages:
1) Breathing or External respiration
2) Cellular respiration or Internal respiration
Note:
All parts of plant perform respiration individually unlike animals

Animals are eukaryotic, multicellular, species belonging to the Kingdom Animalia. Every animal has its own unique characteristics. They obtain their energy either by feeding on plants or on other animals. There are millions of species which have been identified, few share similar characteristics while others differ drastically

Classification of Animal Kingdom

Animals are classified based on their characteristics. They are eminent from algae, plants, and fungus where rigid cell walls are absent. Some are also heterotrophic, in general, they digest their food within the internal chambers which again distinguish them from algae and plants. Another elite character of these species is that they are motile, except in certain life stages.

Protozoa

Protozoa are the different group of eukaryotic organisms which are unicellular having some similar characteristics of animals such as motility and predation. Protozoa take in food by the process of osmotrophy that is by engrossing the nutrients through the cell membranes or also they feed on phagocytosis, either by the process of engulfing the particles of the food with the help of pseudopodia.

Bryozoans

Bryozoans are normally acknowledged as moss animals.  They are filter feeders which sift food particles out of the water using a crown of tentacles lined with cilia and most of them dwell in humid waters, few in glacial waters and some in marine trenches. Most of them are colonial and one genre is solitary. Zooids are individuals in bryozoans and they are not completely independent species. All colonies have auto zooids, which are accountable for feeding and excretion.

Vertebrates

Vertebrates are the animals possessing backbones. Some include jawed vertebrates and jawless fish. For example sharks, ray fish, and bony fish.  A bony fish named clad also further falls into the class of amphibians, reptiles, mammals, and birds.  Extant vertebrates vary in size beginning from the frog species named Paedophryne amanuensis to the blue whale. Amphibians are species that live in the land and move to water for breeding. Reptiles are covered by scutes. Mammals are terrestrial, aquatic or aerial. Birds are covered with feathers and have streamlined avenues.

1. Organ Level of Organization: Animal tissues comprising of similar capacity are classified into shaped organs. Every organ is definite for particular capacity. For example Platyhelminthes.
2. Tissue Level of Organization: Animal cells displaying division of exercises among themselves.Cells performing the same function cooperate to form tissues.
3. Organ framework Level of Organization: The organ framework level of organization are displayed in those organisms where organs define the shape of functional frameworks and each framework is with a distinct physiological capacity.
4. Cellular Level of Organization: This organization consists of animals with cells which are formed as free cell lumps

Organ Systems Patterns

Circulatory System: They are 2 types of the Circulatory framework – open type and closed type.

• Open Type: In this type of circulatory system the blood is pumped out of the heart. For example Mollusca and Arthropods.
• Closed Type: In this type of circulatory system the blood flows through a progression of vessels that is capillaries, arteries, and veins.

Digestive System:  There are 2 types of digestive system.  Complete and Incomplete digestive systems.

• Complete Digestive System: In this type of digestive system there are 2 openings to the outside of the body, a rear-end and a mouth. For instance: Chordates and Arthropods.
• Incomplete Digestive System:  It consists of only one open to the outside of the body a solitary opening which serves as both rear-end and mouth. For example Platyhelminthes.

Body Symmetry: There are 3 types of symmetry. Bilateral, Radial, and Asymmetrical.

1. Bilateral Symmetry: Animals, where a body can be partitioned into indistinguishable left and right parts, are known to be bilaterally symmetrical.
2. Radial Symmetry: Animals tend to display spiral symmetry. For example Coelenterates, Echinoderms, and Ctenophores.
3. Asymmetrical: Asymmetry is the finished nonappearance of symmetry. That is a few animals cannot be divided into two equivalent parts along with any plane going through the focal point of the organism. For example Sponges.

Plant Kingdom – Plantae

Kingdom Plantae includes all the plants. They are eukaryotic, multicellular and autotrophic organisms. The plant cell contains a rigid cell wall. Plants have chloroplast and chlorophyll pigment, which is required for photosynthesis.

Characteristics of Kindom Plantae

The plant kingdom has the following characteristic features:

1. They are non-motile.
2. They make their own food hence are called autotrophs.
3. They reproduce asexually by vegetative propagation or sexually.
4. These are multicellular eukaryotes. The plant cell contains the outer cell wall and a large central vacuole.
5. Plants contain photosynthetic pigments called chlorophyll present in the plastids.
6. They have different organelles for anchorage, reproduction, support and photosynthesis.

Classification of Kingdom Plantae

A plant kingdom is further classified into subgroups. Classification is based on the following criteria:

1. Plant body: Presence or absence of a well-differentiated plant body. E.g. Root, Stem and Leaves.
2. Vascular system: Presence or absence of a vascular system for the transportation of water and other substances. E.g. Phloem and Xylem.
3. Seed formation: Presence or absence of flowers and seeds and if the seeds are naked or enclosed in a fruit.

The plant kingdom has been classified into five subgroups according to the above-mentioned criteria:

1. Thallophyta
2. Bryophyta
3. Pteridophyta
4. Gymnosperms
5. Angiosperms

Thallophyta

Thallophytes lack a well-differentiated body structure and the plant body is thallus like.

Thallophytes: Primitive plants where the body is not differentiated into stem, roots and leaves

Thallophyta includes plants with primitive and simple body structure. The plant body is thallus, they may be filamentous, colonial, branched or unbranched. Examples include green algae, red algae and brown algae. Common examples are Volvox, Fucus, Spirogyra, Chara, Polysiphonia, Ulothrix, etc.

Bryophyta

Bryophytes: Small, non-vascular plants that prefer moist environments

Bryophytes do not have vascular tissues. The plant body has root-like, stem-like and leaf-like structures. Bryophytes are terrestrial plants but known as “amphibians of the plant kingdom” as they require water for sexual reproduction. They are present in moist and shady places. Bryophyta includes mosses, hornworts and liverworts. Some of the common examples are Marchantia, Funaria, Sphagnum, Antheoceros, etc.

Pteridophyta

Pteridophytes have a well-differentiated plant body into root, stem and leaves. They have a vascular system for conduction of water and other substances. Some of the common examples are Selaginella, Equisetum, Pteris, etc.

Pteridophytes: Spore-dispersing vascular plants

Gymnosperms

Gymnosperms: Vascular plants that possess “exposed” seeds

Gymnosperms have a well-differentiated plant body and vascular tissues. They bear naked seeds, i.e. seeds are not enclosed within a fruit. Some of the common examples of gymnosperms are Cycas, Pinus, Ephedra, etc.

Angiosperms

Angiosperms: Vascular plants that possess special characteristics such as  flowers and fruits

Angiosperms are seed-bearing vascular plants with a well-differentiated plant body. The seeds of angiosperms are enclosed within the fruits. Angiosperms are widely distributed and vary greatly in size, e.g. Wolffia is small measuring about 0.1 cm and Eucalyptus trees are around 100 m tall. Angiosperms are further divided into monocotyledons and dicotyledons according to the number of cotyledons present in the seeds. Some of the common examples are mango, rose, tomato, onion, wheat, maize, etc.

Cryptogams and Phanerogams

The plant kingdom is also classified into two groups:

Cryptogams – Non-flowering and non-seed bearing plants. E.g. Thallophyta, Bryophyta, Pteridophyta

Phanerogams – Flowering and seed-bearing plants. E.g. Gymnosperms, Angiosperms

Frequently Asked Questions

Name the pigment responsible for photosynthesis in plants.

Chlorophyll is the pigment responsible for photosynthesis in plants.

Describe the criteria for levels of classification in plants.

The plant kingdom is further classified based on the following three criteria:

• Plant body
• Vascular system
• Seed formation

Explain the characteristic of Thallophytes.

Members of this class lack a well-differentiated body structure, or in other words, the body is not clearly divided into stem, leaves and roots.

Explain the significant features of Gymnosperms.

Gymnosperms include plants that possess a vascular system and a well-differentiated body structure. Furthermore, they bear seeds like the angiosperms, but they are not encased within a fruit. Hence, the term “Gymnosperm”, which is derived from Greek word, gymno = naked and Sperma = seed.

List the characteristics of Angiosperms.

• Seed-bearing plants
• Seeds are enclosed within fruits
• Presence of  well-differentiated plant body
• Produce flowers during their lifespan
• Presence of two subtypes – monocots and dicots

Introduction
Cells are joined to each other to form a secondary level of an organisation called Tissue.
The term ‘Tissue’ was first used by Marie Francois Xavier Bichat in 1792.
Histology: Study of tissue is called Histology.
The tissues are classified as follows on the basis of occurrence in living things:
(1) Animal Tissues
(2) Plant Tissues
Animal tissues: divided into four types on the basis of function

1. Epithelial – work as protective tissues over other tissues. Example: Our skin
2. Connective – hold other tissues or organs. Example: Cartilage
3. Muscular – help in movement and locomotion. Example: Heart muscles
4. Neural or Nervous – responsible for the response against the stimulus with the help of a
   sensory organ like Eyes, ears or tongue.
   Epithelial Tissue: on the basis of cell shape and structure classified as:
   (a) Squamous epithelium or Pavement epithelium
    Has a layer of flat, thin and scale-like cells
    Occurs in alveoli of lung
   (b) Columnar epithelium
    Appears rectangular in vertical view and polygonal in surface view
    Occurs in stomach and intestine
   (c) Cuboidal epithelium
    Cuboidal in shape and with rounded nucleus
   (d) Ciliated epithelium
    Columnar or cubical type cells are present
    Found in respiratory track and uterus

Connective Tissue:
Matrix: embedded cells in intercellular fluids of connective tissue.
On the basis of nature of matrix they are divided as:
(1) Connective tissue proper: soft matrix is present
 Areolar tissue
 Adipose tissue
 Tendon
 Ligament
(2)Fluid connective (Vascular) tissue: has ground matrix (plasma) and specialised free cell.
 Blood
 Corpuscles
(3) Supportive tissue: composed of tough matrix.
 Cartilage
 Bone
Muscular tissue:
These are mainly composed of the cells called myocytes.
On the basis of location, function and structure divided as:
(1) Striated or voluntary muscles
(2) Non-striated or non-voluntary muscles
(3) Cardiac muscles
Neural tissue:
Neurons are the units of nervous tissue.
Neuron is composed of:
 Cyton or cell body
 Dendrons
 The axon
Plant Tissues: Constitute plant body.
Some plant tissues divide throughout their lifespan and some not.
On the basis of development, plant tissues are classified as:
(1) Meristematic
(2) Permanent
Meristematic Tissues:
In initial stage of embryo development in plant, all cells are capable of divisions for plant
growth in length as well as width. These divisible embryonic regions are called meristems.
Meristematic cell can be oval, rectangular, spherical or polygonal in shape.
On the basis of position in plants, they are of three types:
(a) Apical meristems
(b) Intercalary meristems
(c) Lateral meristems
Permanent Tissues: originates from meristematic tissue
On the basis of types of cell divided as:
(i) Simple permanent tissue
(ii) Complex permanent tissue

Simple permanent tissue: contain only one kind of cell
 Parenchyma
 Collenchyma
 Sclerenchyma
Complex permanent tissue: made of more than one kind of cell
 Xylem
 Phloem
Tissue system in Plants
(A) Dermal Tissue system – form outer protective covering of plant
(B) Ground Tissue system – form main bulk of plant
(C) Vascular Tissue system – vascular bundles present in stems and roots
(D) Epidermal Tissue system – it forms outer covering of plant

Living things cannot live without air.
Air is present everywhere on earth surface up to 300 km above it as well as in water in
dissolved state.

Antoine Lavoisier performed experiment to show the air
components:
He used mercury in this experiment to detect the oxygen from air.
The active part of air used by mercury on heating named as “Oxygen” as it reacts to formed
mercury oxide giving rise to red coloured appearance.
And the remaining 4/5th part is named as “Nitrogen”
He concluded that ration of nitrogen and oxygen in air found to be 4:1 by volume along with
little amount of other gases.

Composition of Air :

 Air is mixture of gases as composition changes with respect to place.
 Nitrogen found to be 71% and oxygen as 21% and remaining 1% carbon dioxide
along with the 0.03% of other gases.
Oxygen:
Composition: About 21% that is 1/5th of the volume of atmospheric air.
 It is colourless, odourless and tasteless.
 Soluble in water in little extend and heavier than air.
 Supports the combustion.
 Chemically very reactive
Uses of Oxygen:

1. It is used for respiration .
   (a) Plants and animals take up the oxygen for undergoing aerobic respiration to
   generate energy , this is natural way.
   (b) Miners, sea divers , fireman use oxygen cylinders along with mask to breath in
   artificial way.
2. It is use in burning process:
   
3. As oxygen support burning to fuels containing nitrogen , called as oxidation along with
4. liberation of heat , light and carbon dioxide.

3. Medical uses:
   (a)Breathing problems like asthma, pneumonia etc. Are given oxygen from oxygen
   cylinders to enhance the artificial way of respiration.
   (b) Mixture of oxygen and nitrous oxide given to dental patient to render numbness
   on applied area that is anesthetic.
4. Industrial use:
   (a)In the process of welding and cutting
   (b)In rocket it is used as fuel
   (c)In manufacturing of chemicals such as sulphuric acid , nitrous acid.
   Nitrogen :
   Composition: 78-79% , means about 4/5th of the volume of atmospheric air.
   Properties:
    Colourless , odourless and tasteless
    Heavy as air but slight soluble in water.
    Chemically inert or not reactive at low temperature.
   Uses of Nitrogen:
5. Use in preservation of food as it is inert so packed food’s container can be filled.
6. It is used in manufacturing of ammonia , fertilizers such as urea.
7. It is very good refrigerant.
8. Manufacturing of chemicals , trinitrotoluene explosive and nitroglycerine.
9. It controls the combustion as it act as dilator in case of active oxygen.
10. It is essential in growth of plants as nitrates , requires to form plant proteins.
    Carbon dioxide:
    Composition: 0.02-0.03% by volume
     Properties:
    Colourless , odourless and tasteless
     Heavier about 1.5 times than air
     Slightly acidic in nature
     Chemically reactive

Uses of carbon dioxide:

1. It is widely used in aerated soft drinks
2. It is used as refrigerant as dry ice form.
3. It is use in manufacturing of chemicals like baking soda and baking powder.
4. It is used as fire – extinguisher
5. In case of plant for the process of photosynthesis, plays crucial role.
6. It is contributed role in the global warming as it traps the heat.
   Utility of water vapour:
7. In controlling evaporation as it minimizes the rate of evaporation.
8. It is used in detection of climatic conditions, rain, water dew.
9. It is useful in animal and plant growth as it is part of water cycle.
   Nobel gases contribution is less than 1% in air and they are found to be inert chemically.
   Argon, Xenon, Krypton are the Nobel gases found in air.
   Uses of Inert Gases:
10. Helium is used in weather observational ballons
11. It is used in electrical bulbs to provide environment to filament.
12. Neon as it shines used in advertising boards.
13. Xenon as well as krypton are used in photography.
    Polluting Gases :
     such as sulphur dioxide and oxides of nitrogen causes acid rain and serious
    respiratory problem
     Smoke and dust particle causes respiratory issues but help in formation of cloud.
    When metal and non-metal burns in oxygen it forms an oxide.
    A. Formation of Non-Metallic Oxides:
    Sulphur dioxide formed when sulphur burns with brilliant blue flame.
    Other example includes: formation of carbon dioxide when charcoal burns.
    B. Formation of Metallic Oxides:
    Molten sodium burns brightly with golden yellow flame in oxygen to form sodium
    oxide
    Other example includes: Formation of calcium oxide when calcium burns with brick
    red flame.
    

Combustion:
It is rapid chemical change in which a substances combines with oxygen to release
heat along with light.
Example: candle burns in air to produce light and heat along with liberation of
Carbon dioxide and water vapour.
 Combustion is useful in many ways , as cooking of food is the result.
Rusting:
It is the process in which exclusively iron combines with oxygen in the presence of
moisture to form a reddish brown flaky substances called as rust.
Rust: (Fe2O3.H2O)
 It is destructive and weakens the objects.
 Rusting takes a longer duration of time to form the final product.
 It is form of oxidation process in which no liberation of heat and light take
place.
 Rusting can be prevented by oiling, painting and galvanization.
Air pollution:
The contamination of air with undesirable substances leads to some harmful effects on
living and non-living organism called as Air pollution.
Sources of air pollutions:

1. Volcano eruption leads to liberation of sulphur dioxide , carbon mono oxide along
   with dust.
2. Decay of animals causes the emission of oxides of nitrogens
3. Forest fire result into formation of carbon monoxide, sulphur dioxide and carbon
   dioxide
   In manmade sources,
4. The uses of Automobile exhaust leads to liberation of various pollutants such as
   carbon monoxide , carbon dioxide , nitrogen and lead compounds.
5. Chemical industries and iron –steel industries also generates above mentioned
   pollutants in large extent.
6. Burning of fuels leads to increase the amount of carbon monoxide , sulphur dioxide
   along with carbon dioxide.
   

Leaking of chlorofluorocarbon from refrigerants, air conditioners and sprays cans causes
ozone layer depletion and global warming.

Acid Rain:
Acid rain is a result of air pollution. When any type of fuel is burnt, lots of different
chemicals are produced.
Power stations, factories and cars all burn fuels which increase polluting gases. These gases
like nitrogen oxides and sulphur dioxide get react with the tiny droplets of water in clouds to
form respective acids.
The rain from these clouds then falls as very weak acid, known as “Acid rain”..

Harmful effects of Acid Rain:
Acidic rain displaces the minerals from soil and such soil is lack in nutrients, reduces the soil
fertility
Water bodies get toxic as heavy metals such as cadmium, lead from soil get dissolved in it.
Because of these aquatic plants and animals get affected.
There are damaging effect seen on buildings, monuments and statues.
Eg. Whiteness of Taj mahal decreases day by day as there is chemical change occurring
there because of sulphuric and nitric acid

Metals and Nonmetals
All the elements found on the earth can be divided into metals and nonmetals. Metals generally have one or two or three electrons in their outermost shell. Metal atoms therefore lose one or two or three electrons and become positively charged ions called cations. Non-metals have four or more valence electrons and so they gain one or more electrons and form negatively charged ions called as anions.

Elements can be classified into metals and non-metals on the basis of their properties:

Physical Properties include
* Appearance
* Density
*Melting and boiling point
* Conductivity of heat and electricity
*Tensile strength
* Malleability (ability to be beaten into thin sheets by hammering)
* Ductility (ability to draw into thin wires)

Chemical Properties include
* Charge on ions formed from elements
* Types of bonding and properties of oxides

Metals are
*Lustrous or give shining
* Have moderate to high density
* Generally solid with exception of mercury being liquid at room temperature.
* Have generally moderate to high melting point.
* Generally good conductors of heat and electricity.
*High tensile strength.
*Malleable and ductile.
* Forms positive ions and generally form ionic compounds.
* Oxides of metal are basic with exception of zinc and aluminium which forms amphoteric oxides.

Non Metals
* Are dull in appearance
* Density is low to moderate
*Can exist in solid, liquid and gaseous state (liquid non-metal is Bromine)
* Have wide range of melting and boiling point.

* Generally are bad conductors of heat and electricity exception is graphite which is good conductor.
* They are generally brittle exception being diamond.
* Non-malleable and non-ductile
* Generally forms negative ions
* Bonding is covalent
*Oxides are generally acidic in nature.

Metals are placed on the left side of periodic table where as non-metals are placed on right side of periodic table.
*There are elements which have both metallic and non-metallic properties called as metalloids. e.g. Si, Ge, As, Sb, etc.
* Metals like gold and silver are called as noble metals because they are found in native states and are least reactive.
* Non-metals like alc. He, Ne, Ar, Kr, Xe and Rn are called inert gases or noble gases because they are unreactive elements.

Some common ores of metals Ores are those minerals from which metals are extracted profitably and with highest purity through processes of metallurgy are called Ores.

USES OF METALS

a) Iron: It is used in making pipes, tanks, cylinders, agricultural tools, nail, etc. Steel is used to make bridges, ships, buildings, utensils and machine parts. Steel is formed by mixing iron with carbon while stainless steel have Fe, C, Ni and Gr.

b) Copper: It is a good conductor of heat and electricity. It is used in making electric wires, cables and utensils.

c) Aluminium: It is light, strong and has high tensile strength. It is used to make bodies of aircraft, automobiles, machine tools and parts.

d) Zinc: Zinc does not rust easily and is used to coat iron sheets by a process known as galvanization.

e) Mercury: Property of not wetting glass and expanding a lot when heated make a mercury ideal for being used in thermometers.

f) Silver: The lustre of this metal has made it popular for making jewellary. Things made of other metals are often coated with a protective layer of silver called electroplating.

g) Gold: Gold is used for making jewellary, plating metals and in medicines. The purity of gold is measured in carats. Pure gold is 24 carat.

USE OF NON-METALS

a) Carbon: Both graphite and diamond are allotropic forms of carbon. Graphite is used to make lead of pencil and crucibles. Diamond is used to make tools for cutting and grinding glass and rocks. It is also used in jewellary.

b) Sulphur: Sulphur is used in the manufacture of sulphuric acid, gunpowder, dyes, matches and fireworks. It is also used to treat rubber in a process called as vulcanisation.

c) Phosphorus: Match-heads and fertilizers contain phosphorus.

d) Hydrogen: It is used to manufacture ammonia and hydrogen chloride. Vegetable oil is treated with hydrogen, it becomes solid like butter. This process is known as hydrogenation of vegetable oils.

e) Silicon (Metalloid): It is a semiconductor. It is used to make water proof materials, polishes and as an insulator in the electrical appliances.

Alloys: Alloys are homogenous mixtures of two or more metals. Some of them may contain traces of nonmetals also

a) Brass: It contains 60% copper and 40% zinc. It is used to make electronic equipment parts of telescopes and microscopes.

b) Bronze : It contains 80% copper 10% Zn and 10% tin. It is used to make statues, coins, bells and parts of some machines.

c) Solder: This alloy is made of lead and tin. It is used for joining electric wires.

d) Stainless steel : It consists of iron, carbon, chromium and nickel. It is used to make ships, bridges, railway lines, machinery, buildings, etc.

e) Duralumin: It consists of aluminium, copper, magnesium and manganese. It is used to make bodies of aeroplanes, automobiles, spacecraft, ships and pressure cookers.

Corrosion of metals
The slow destruction of material by chemical reaction is called as corrosion.

Preventing corrosion

1. Use paint or grease to prevent the contact with air,

2. Coating with another metal like Zn

3. Alloying.

Introduction

You would need many words to describe a chemical change in ordinary language. But you can do so with only a few letters and numbers in the language of chemistry.

J J Berzelius laid the foundation of this language in the early nineteenth century. It gradually developed into its present form. In this language, an atom is represented by a symbol, a molecule by a formula, and a chemical change (i.e., a reaction) by a chemical equation.    

Symbol

A symbol is an abbreviation of the name of an element.

The symbols of elements have been derived in three different ways.

1.The first letter (in capital) of the English name of an element 

2. The first letter along with one more letter of the English name of an element (this becomes necessary when the names of two or more elements begin with the same letter)

◊  What does a symbol represent ?

The symbol of an element represents the following.

1. An element in particular For example, you know that the symbol of sodium is Na and that of chlorine is Cl. So, instead of saying that the compound common salt is made up of the elements sodium and chlorine, you can say that it is made up of Na and Cl. You can also say that Cu is red-brown whereas Au is yellow, and that Ca is a metal whereas Cl is a nonmetal.

2. An atom of an element In formulae and equations, a symbol represents an atom of an element. More than one atom in a molecule is shown by a numeral subscript. This is explained in the next section.

→ FURMULAE 

Atoms usually do not exist independently. They generally combine among themselves to form molecules.

A molecule is the smallest part of an element or a compound that can exist independently. It is represented by a formula

The formula of a molecule gives the numbers(s) of atoms of the same or different elements present in the molecule.

→ FORMULAE OF ELEMENTS

When an atom of an element combines with another atom(s) of the same element, a molecule of the element is formed.

For example, two atoms of hydrogen combine to form a molecule of hydrogen. The formula of hydrogen is H₂, 2 being the subscript showing the number of H atoms in the molecule. Similarly, molecules of nitrogen, oxygen, fluorine, chlorine, bromine and iodine contain two atoms of the element. So they are represented as N₂, O₂, F₂, Cl₂, Br₂ and I2 respectively. As these molecules have two atoms of the element, they are said to be diatomic, A common example of a triatomic gas is ozone (O₃).

There are a few highly inactive gases present in very small amounts in the air. These gases, viz., helium (He), neon (Ne), argon (Ar), krypton (Kr) and xenon (Xe), are called noble gases. A molecule of a noble gas contains only one atom of the element. In other words, noble gases are monoatomic. So the formula of a noble gas is the same as its symbol.

◊ Valency–the combining capacity of an element

When atoms of two or more elements combine, a molecule of a compound is formed. The capacities of these elements to combine with each other determine the formula of the compound formed.

◊ The capacity of an element to combine with other elements is known as its valency.

It will be evident from the following that the combining capacities of all elements are not the same.

1. One atom of Cl combines with one atom of H to form a molecule of hydrogen chloride.

2. One atom of O combines with two atoms of H to form a molecule of water.

3. One atom of N combines with three atoms of H to form a molecule of ammonia.

Thus, the combining capacity of O is twice that of Cl, and that of N is thrice that of Cl.

H is assigned a valency of 1. So the valencies of Cl, O and N are 1, 2 and 3 respectively. However, many atoms do not combine with H. Their valencies are calculated by the number of Cl atoms they combine with, since Cl and H have the same valency, i.e., 1.

◊ The valency of an element is given by the number of H or Cl atoms that an atom o the element combines with.

(You will learn in higher classes that the valency of an element can be expressed in many ways.) Elements with valencies 1, 2, 3, etc., are said to be monovalent, divalent (or bivalent), trivalent, and so on. The valencies of some common elements are indicated in Table

Table: The valencies of some common elements.

◊ Obtaining the formulae of compounds

The formula of a binary compound, i.e., a compound formed by two elements only, is obtained by transposing their valencies. Suppose an element A has a valency y and element B has a valency x. Then the compound formed between A and B usually has the formula AxBy. The subscripts should be divided by a common factor, if any.

There are some exceptions like H2O2 (hydrogen peroxide) in which the numeral subscripts are not divided by the common factor. 

The formulae of some common compounds are given in table Table: Formulae of some common compounds.

→ VARIABLE VALENCY

Some elements have variable valency. For example, iron has valencies of 2 (e.g., in FeCl₂) and 3 (e.g., in FeCl₃). FeCl₂ is named iron(II) chloride, and FeCl3 is named iron(III) chloride. This method of naming a compound is adopted if it contains an element with variable valency.

Table: Some elements with variable valencies

→WHAT ARE COMPOUND RADICALS

Certain groups of atoms of different elements remain intact in many chemical reactions. In fact, they behave like single atoms and have a valency. They are called compound radicals. They do not exist independently, but only as parts of compounds. Common examples of monovalent radicals are hydroxide (OH) and nitrate (NO₃). Carbonate (CO₃) and sulphate (SO₄) are examples of divalent radicals. The phosphate (PO₄) radical is trivalent.

The formulae of compounds containing compound radicals are also obtained by transposing valencies (Table)

Table: Formulae of some compounds containing compound radicals.

→ CHEMICAL EQUATIONS

You know that an element is represented by a symbol and a compound, by a formula. A chemical change is represented by an equation called a chemical equation. For example, the burning of carbon in a sufficient supply of oxygen to form carbon dioxide is represented by the following equation.

If the supply of oxygen is insufficient, carbon monoxide (CO) is formed. Let us express the reaction thus:
C + O₂ → CO
The substances that react among themselves are called reactants and those that are formed are called products. Remember that no atoms are lost or gained in a chemical reaction. So the number of atoms of each element on the reactant side must be the same as that on the product side.

An equation satisfying this rule is called a balanced chemical equation. For example, the equation showing the formation of carbon dioxide is a balanced chemical equation. But the one showing the formation of carbon monoxide is not. Because there are two O atoms on the reactant side, the only one on the product side. To balance this equation, we place the numeral 2 before C on the reactant side and CO on the product side.

2C + O₂ → 2CO

Only balanced chemical equations are acceptable. Here are a few examples of such equations.

H₂ + Cl₂ → 2HCl

2H₂ + O₂ → 2H₂O

2Mg + O₂ →2MgO

Sometimes, an equation is made more informative by mentioning the conditions o the reaction above the arrow.

C + O₂ —→ ^heat CO₂

POINTS TO REMEMBER

◊ A symbol is an abbreviation of the name of an element.

◊ A symbol represents an element and an atom of the element.

◊ The formula of an element or a compound represents a molecule of the element or compound. It gives the number(s) of atoms of the same or different elements present in the molecule.

◊ Noble gases (helium, neon, argon, krypton and xenon) are monoatomic, whereas hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine are diatomic. Ozone(O3) is a triatomic gas.

◊ The capacity of an element to combine with other elements is known as its valency.

◊ The formula of a compound containing two elements is obtained by transposing their valencies.

◊ Some elements like iron (Fe), copper (Cu), lead (Pb), phosphorus (P) and sulphur(S) have variable valency.

◊ A group of atoms of two or more elements, which behaves like a single atom and has a valency, is known as a compound radical.

◊ Chemical changes are represented by chemical equations.

◊ The number of atoms of each elements on the reactant side must be the same as that on the product side.

An equation that satisfies this rule is called a balanced chemical equation

The smallest particle that exhibit the properties of matter and may or may not have
independent existence are termed as Atom.

The atomic structure of matter is made up of protons, electrons and neutron, called as
fundamental particles.

Atomic structure is the structure of atom consist of a nucleus which is at center in which
the protons (positively charged) and neutrons (neutral) are present. The negatively charged
particles called electrons revolve around the center or present as electron cloud of the
nucleus.
Neutral atoms have equal numbers of protons and electrons.

Atoms may gain or lose electrons in order to increase their stability, and after loss or gain of
electrons the resulting charged entity is called an ion.

Dalton’s Atomic Theory:
 Every matter is made up of atoms, which are very small particles.
 Atoms are indivisible, cannot be divided further.
 Specific elements have only one type of atoms in them means they are identical to
all aspect.
 Each atom has its own constant mass that varies from element to element.
 Atoms undergo rearrangement during a chemical reaction and in simple ratio.
 Atoms can neither be created nor be destroyed but can be transformed from one
form to another.

Fundamental Particles:

Protons
 Discovered by Goldstein.
 Protons are positively charged subatomic particles. The charge of a proton is 1e,
which corresponds to approximately 1.602 × 10-19
 The mass of a proton is 1.672 × 10-24
 The total number of protons in the atoms of an element is always equal to the
atomic number of the element.

Neutrons
 Discovered by Chadwick
 These are neutral particles.
 Located inside the nucleus.
 The mass of a neutron is almost the same as that of a proton i.e. 1.674×10-24
 Neutrons are electrically neutral particles and carry no charge.

Electrons
 Discovered by J.J. Thomson.
 They possess unit negative charge.
 Located in orbits or shell
 The charge of an electron is -1e, which approximates to -1.602 × 10-19
 The mass of an electron is approximately 9.1 × 10-31
.
Atoms of each element contain a characteristic number of protons.
The number of protons is equal to the number of electrons.
The number of protons in an atom is called the Atomic number.
Atomic number = Number of proton + Number of electrons
(Z) = ( p ) + ( e )

Molecules:
Atoms of the same element or different elements combine to form a molecule.
Example: hydrogen atom combines with chlorine atom giving rise to hydrogen chloride
molecule.

A molecule is the smallest particle of pure substances.
 Molecules of elements:
Two or more atoms of same kind of element combine to form molecule of element.
Example: two atoms of nitrogen get combine to form one molecule of nitrogen

 Molecule of compound:
Two or more elements of different elements combine in fixed ratio in chemically to form
molecule of compound.
Example: two oxygen atoms and one carbon atoms combine to form one whole carbon
dioxide molecule.

Atomicity:
The number of atoms present in one molecule is called as atomicity of that molecule.

1. Monoatomic Molecule :
   If there is only one atom present in molecule is called as monoatomic
   molecule
   Eg. Metal- sodium(Na) , Metalloid- Antimony(Sb) , Nobel gas- Xenon (Xe)
2. Diatomic Molecule :
   A molecules contains two atoms of elements are termed as diatomic
   molecule
   Example: Oxygen (O2) , Nitrogen (N2)
3. Triatomic Molecule:
   A molecule containing three atoms is called triatomic molecule.
   Example : ozone (O3)
4. Polyatomic Molecule:
   A molecule containing more than three atoms is termed as polyatomic
   molecule.
   Example: sulphur (S8)
   Radicle:
   An atom of element or groupe of atoms of different elements behaving as a single unit with
   positive or negative charge Eg. Cl-
   , NH4
   +
    Acid Radicle:
   The negatively charge radicals are called as radicle or anion Eg. (CO3)
   2-
   , Cl-
    Basic radicle:
   The positively charged radicles termed as Basic radicles Eg. NH4
   +
   , sodium (Na+
   )
   

Valency:
It is the combining capacity of an atom of an element with another atom.
Defined as in two ways as per following :
(A) In terms of replaceable or combined hydrogen atoms:
It is calculated as, the number of hydrogen atoms which can combine with or displace one
atom of element or radicle that is charged one forming a compound.
In case of water , two atoms of hydrogen combines with one oxygen atom the vacancy of
oxygen is 2.
(B) In terms of loss and gain of electrons
Atom is positive when it losses the electron whereas it is negative when gain the electron.
On the basis how much electron gain or loss by an atom its valency is calculated.
Example: Na2+ , Zn2+ , Cl-1
Writing the chemical formula of a chemical compound:
Aluminum oxide
Valencies of elements: Al = 3 , O = 2
Lowest common multiple of valences = 6
Al = 2 x 3 = 6
O = 3 x 2 = 6
Therefore the chemical formula = Al2O3

Periodic table:
Mendeleev arranged the elements in tabular manner in order to their increasing order of
atomic masses in particular rows and column.
Then Mosley arranged elements in order of their increasing order of atomic number called
as (Modern periodic table)
Periodic means some properties arte repeated in elements after certain interval of time or
period.

Relation between valency and group number :
The number of valence electrons increases from left to right in the periodic table.
If the number of valence electrons of an element is equal to 4 as that of carbon, the the
element would also have same valency that is 4.
For Group 13 : The valence electron are given as (Group number – 10)= (13 – 10 = 3)
Therefore group 13 has valency 3.

Matter : Objects are made up of substances or matter

The particulate nature of matter and properties of matter :

The matter may be in the solid, liquid or gaseous states but their properties are due to the matter by which they are made. e.g., Chalk is in solid form, ink is in liquid and perfume is in gaseous state. The colour of a chalk, the blue colour of ink, the fragrance of a perfume are the properties of their matter which remain unchanged.

• Objects have mass. This means the matter from which this object is made also has a mass.
• Objects occupy space.
• Objects acquire properties from the matter from which they are made of.
• Substance : Many kinds of matter contain only one constituent. These are found in pure form in the nature. Matter made of only one constituent is called ‘substance’. e.g., Gold, diamond, water, chalk.
• Mixtures : Matter made of two or more substances are called ‘mixtures’.

Element :Molecules :

Molecules : The smallest particles of substances are molecules.

• Molecules are formed by the combination of two or more atoms.
• Molecules can be subdivided to individual atoms. e.g., Water molecule can be further divided into oxygen and hydrogen atoms.
• When similar molecules combine together in any numbers, a simple product is formed.
• A molecule is usually stable to exist by itself.

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Element : A substance whose molecules are made of exactly alike one or more atoms are called element. There are 92 elements in nature. Scientists have produced 26 man-made elements. Therefore totally, there are 118 elements. Scientists have discovered 118 elements

• The element cannot be decomposed further to obtain different substances.
• The smallest particles of elements are made of only one type of atoms.
• Atoms cannot be seen with the naked eyes, but when crores of atoms come together they form volume large enough to be visible to our eyes.
• The mass and volume of atoms of different elements are different.
• Some important natural elements : Hydrogen, oxygen, nitrogen, carbon, iron, mercury, copper etc.
• Oxygen is in the gaseous state and in molecular state in the nature. Two atoms of oxygen are joined to form a molecule of oxygen.
• Elements can occur in solid, liquid or gaseous state.
• Atoms and molecules cannot be seen with the naked eyes.

Atom :

Atom : An atom is smallest particle in an element that has the properties of the element.

• It is not possible to breakdown the atom further retaining the properties of the element.
• The atoms are bonded together in a molecule.
• An atom is not stable by itself
• Atomos means invisible in Greek language. Therefore, Democritus named the small particle of elements as ‘atom’.
• John Dalton’s theory (1803) :Atoms cannot be created or divided into smaller particles or destroyed.

[collapse]Symbols for elements :

Symbols for elements : Berzelius introduced the method of using symbols for elements.

• Every element has its own symbol. To show this symbol the first letter of symbol’s name is used. e.g., for hydrogen, H is used, for nitrogen N is used.
• When the first letter in the names of two or more elements is the same, then a pair of letters is used to write the symbol. e.g., C is for carbon hence for chlorine, Cl is used and for calcium Ca is used.
• In such symbols, first letter is capital and the second is written in small script.

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Metals, Non-metals and Metalloids : Elements are generally classified into metals and non-metals

• Non-metals : The elements which lack the properties such as malleability, ductility, conductivity of heat and electricity, density, lustre and sonority are called non-metals. e.g., phosphorus, sulphur, chlorine.
• Metals : The elements which show all the above properties are called metals, e.g., iron, copper, gold, silver
• Metalloids : The elements having some properties of metals and some properties of non-metals are called metalloids. e.g., Arsenic, silicon, selenium are examples of metalloids.

Alloy :

Alloy : Some metals cannot be used in their pure form. In such case, the properties of the original metal are modified by mixing one or more elements in it. This type of a mixture of metals is called an alloy. e.g., Brass, steel, twenty-two carat gold.[collapse]

Compound : A compound is made of two or more elements chemically combined in a fixed proportion.

• A compound can be further subdivided into simpler substances by chemical means only.

• If the atoms in the molecule are of different types, then compound is formed. e.g. Water. In one molecule of water there are two hydrogen atoms and one oxygen atom.
• The properties of a compound are different from those of the constituent elements. e.g. common salt, sugar, water. Hydrogen is combustible and it can burn. Oxygen supports combustion. But in water, even if these both atoms are present, water does not support combustion.

Molecular formula :

Molecular formula : A molecular formula of a compound is a short form of its name written with the help of the symbols of the constituent elements and the number of their respective atoms.[collapse]

Mixture : A mixture is obtained by just mixing two or more substances in any proportion.

• By mixing different elements or compounds, a mixture is formed
• A mixture can be further subdivided into simpler substances by simple physical processes.
• There is no fixed proportion of various components in a mixture.
• While preparing the mixture, no chemical change takes place and no new substance is formed. e.g., air, sea water.

Separation of substances :

• Mixing unwanted substances in any foodstuff is also a type of mixture. This is known as adulteration.
• To separate the unwanted ingredients from the mixture, the simple and easy method are straining (filtering), sifting, picking, sorting, winnowing, combing with a magnet and sublimation.
• The properties of matter and the effects of heat can also be used for separating the components of a mixture.

Some Methods of Separation of substances :

[collapse]Method of Distillation :

Method of distillation :

• The method of distillation is used to separate solute from solution. It can also be used to remove impurities from the solution and make it pure.

• The sea water in the round bottom distillation flask is heated. This produces the steam.
• As this steam is passed through the condenser, it turns into liquid due to condensation.
• The pure water which drips down in the conical flask can be separated. The salts in the sea water remains in the distillation flask.

[collapse]Method of separation using separating funnel :

Method of separation using separating funnel :

• When two immiscible liquids are to be separated from one mixture then the separating funnel is used.
• The immiscible mixture of two liquids is left undisturbed in the separating funnel.
• In the mixture, two layers are clearly seen.
• The lighter liquid floats on top in the separating funnel while the heavier of the liquids always remains below.
• By opening the stopcock without disturbing the funnel, the lower solution can be separated. e.g. Kerosene and water can be separated by such technique.

[collapse]Method of centrifugation :

Method of centrifugation :

• To separate solids from a mixture of a liquid and solid, the method of centrifugation is used in the laboratory.

• A centrifuge machine is used for this purpose. It has a disc, which rotates in circular motion with a great speed. Test tubes are attached to the rim of this disc.
• When theses tubes attached to the disc rotate at the high speed, there is a centrifugal force generated. This force is pushes the particles away from the centre.
• Due to this the solid particles in the mixture are thrown to the bottom of the tubes and are thus separated from the mixture.
• In this way the small and lighter particles in the mixture get assembled together.

The other methods of separation such as filtering or settling do not become useful for separation of such fine particles.[collapse]Method of chromatography :

Method of chromatography :

• If two or more substances are dissolved in small proportions in the same solution, the method of chromatography is used to separate these substances.
• In chromatography, two mutually opposite properties of substances are used.
  • Solubility of the substance in the solvent that moves up.
  • Ability of the substance to stick to the stationary filter paper.
• These properties are different for different substances. Therefore, all the components of the mixture do not rise for different heights.
• This method is used in pharmaceutical science, factories and scientific laboratories for detecting new ingredients and for identifying and separating components of a mixture.