Showing posts with label CBSE-VII BIOLOGY. Show all posts
Showing posts with label CBSE-VII BIOLOGY. Show all posts

Sunday, January 3, 2021



A Material which is available in the form of thin and continuous stand is called Fibre. The thin strands of thread that we see are made up of still thinner strands called Fibres. 

The cloth produced by weaving or knitting textile fibre is called Fabric. There are two types of fibres,
1. Natural Fibre
2. Man – Made fibre or Synthetic Fibre            

Natural Fibre: The fibres which are obtained from pland and animals are called Natural Fibres. Example: cotton wool, jute & silk.

Man-Made or Synthetic Fibres: The fibres that are synthesized in laboratory are called Man-Made or Synthetic Fibres.  Example: Nylon, Polyester, Makmal, Fur etc.  

Natural Fibres
COTTON:  Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus Gossypium in the mallow family Malvaceae. The fiber is almost pure cellulose. Under natural conditions, the cotton bolls will increase the dispersal of the seeds.   

The fiber is most often spun into yarn or thread and used to make a soft, breathable textile. The use of cotton for fabric is known to date to prehistoric times; fragments of cotton fabric dated to the fifth millennium BC have been found in the Indus Valley Civilization. 

Process of Making Cotton: From field to fabric
The process of making cotton transforms the raw fibers into threads, yarn and fabric in three steps: Preparation, Spinning, and Weaving. 

Preparation: To be used for thread or fabric, raw seed cotton must cleaned and free of debris. Seeds, burrs, dirt, stems and leaf material are removed from the cotton during ginning (The process of separating cotton from seed).

Spinning: A Yarn is usually of substantial length & of small cross section. In the cross section of a yarn there are usually a multiple number of Staple fibers (short fibers) or Filaments (long fibers) of unlimited length.

Yarn made out of Staple fiber is known as Spun Yarn, because the staple fibers should undergo number of process stages so that a yarn can be made out of them. This procedure or process stages in correct sequence is called “Spinning”

Spinning is the twisting together of drawn-out strands of fibers to form yarn, and is a major part of the textile industry.  The yarn is then used to create textiles, which are then used to make clothing and many other products.

There are several industrial processes available to spin yarn, as well as hand-spinning techniques where the fiber is drawn out, twisted, and wound onto a bobbin. 
Staple Spun YarnThose are made by Twisting Staple Fibres together into a Strand. The length of the Fibre is limited. Given are some of the spun yarns.        

1. Mono Yarn: Solid, Single Strand of Unlimited Length. 
2. Multi Filament: Many continuous filaments with some twist
3. Staple Yarn: Many short fibers twisted together tightly. 
4. Two Plied Yarn: Two single yarn twisted together. 
5. Multi Plied Yarn: Plied Yarns twisted together. 
6. Thread: Hard, Fine, Plied Yarn. 
7. Cord or Cable: Many plied yarns twisted into a course structure. 
Weaving: Weaving is a method of textile production in which two distinct sets of yarns or threads are interlaced at right angles to form a fabric or cloth. Other methods are knitting, crocheting, felting, and braiding or plaiting. The longitudinal threads are called the warp and the lateral threads are the weft or filling.

SLIK: Silk is a natural protein fiber, some forms of which can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoons. 

There are different types of silk worm produce different silks in terms of luster and textile. Example: tassar silk, mooga silk, kosa silk etc. are produced by different types of silk moth. Mulbery silk is the most common silk moth.  

The rearing of silkworms for obtaining silk is called Sericulture. silk was discovered in chinna around 3500 BC. Silkworms are reared on mulberry leaves as they feed on mulberry leaves.

Life cycle of silkworm: There are four stages in the life cycle of silk moth. Egg, larva, pupa & adult.
Female silk moth- lays eggs- After about 14 days eggs are hatched into larva (called caterpillar) – Grow into pupa – Secretes fibres made of protein and weaves the fibres around itself completely- This covering is called cocoon.- Lives in the cocoon for some time- After coming out cocoon grows into silk moth. 
Stage 1: Egg
An egg is the first stage of the life cycle of the silkworm. The egg is laid by a female moth which is mostly the size of small dots. A female moth lays more than 350 eggs at a time. In the springtime, the eggs hatch due to the warmth in the air. This procedure happens once in every year. 
Stage 2: Silkworm
A hairy silkworm arises after the eggs crack. In this stage of silkworms, the growth happens. they feed on mulberry leaves and consume a large amount of these leaves for around 30 days before going to the next stage. 
Stage 3: Cocoon
In this stage, silkworms spin a protective cocoon around itself. It is the size of a small cotton ball and is made of a single thread of silk.
Stage 4: Pupa
The pupa stage is a motionless stage. In this stage, people kill the pupa by plunging the cocoon into boiling water and unwind the silk thread. 
Stage 5: Moth
In this stage, the pupa changes into an adult moth. The female moth lays eggs after mating and thus the life cycle of silkworm begins again. 
Silk moth to silk: After they are laid by the silk moth; eggs are stored over a clean cloth or paper strips. When larvae are hatched from eggs, they are kept in clean bamboo trays with fresh leaves of mulberry. Larvae feed on mulberry leaves for about 20 to 25 days.

After that, larvae move into tiny chambers of bamboo in which they start spinning cocoon. They do it by secreting liquid protein from their salivary glands.  Finally they enclose themselves in cocoon. Cocoons get hardened because of exposure to air. 

Process of silk:
The process of obtaining silk from silk moth involves- 
1) Rearing of silkworms :The process of keeping, feeding, breeding and medical care of useful animals is called rearing of animals. .
2) Reeling and Dyeing: Cocoons of silk moth are used to obtain the silk fibres. These cocoons are kept under the sun or boiled or exposed to steam. The silk fibres is then separated. This process of obtaining wool from the cocoons is called reeling the silk. This followed by spinning and weaving.

Wool is obtained from the fleece (hair) of sheep, sheep, goat, camel, yak, llama, alpaca and other animals. These animals have thick coat hair on their body because the hair traps the air and air is poor conductor of heat. So thick layer of hair keep their body warm and protect them from harsh cold. 

Rearing and breeding of sheep: Sheep are reared in many parts our country like Jammu and Kashmir, Himachal Pradesh, Uttaranchal, Sikkim, Arunachal Pradesh, Haryana, Punjab, Rajasthan, Gujarat etc. Rearing of sheep means to look after the sheep by providing them food, shelter and health care. Breeding is done to obtain animals with desired characters.

Processing of making wool:
The major steps necessary to process wool from the sheep to the fabric are: shearing, cleaning and scouring, grading and sorting, carding, spinning, weaving, and finishing. 
Shearing: Sheep shearing is the process by which the woollen fleece of a sheep is cut off. The person who removes the sheep's wool is called a shearer.

Cleaning and scouring: scouring is a way of cleaning textile fibres. Wool that's been shorn from a sheep is known as greasy, or raw wool. 
Grading and sorting: Grading should not be confused with wool classing: sorting fleeces into various lines according to fineness, length, strength, yield, color, and style. 
Carding: Short-stapled pieces of wool which result from the carding process, spun and woven to make standard-quality fabrics. 
Spinning: Spinning is the twisting together of drawn-out strands of fibers to form yarn, and is a major part of the textile industry. 
Dyeing: After sorting and picking out of burrs, these are dyed in desired colors. 
Weaving: The process of arranging two sets of yarn together to make a fabric is called weaving. 

JUTE: Jute is a long, soft, shiny vegetable fiber that can be spun into coarse, strong threads. It is produced primarily from plants in the genus Corchorus, which was once classified with the family Tiliaceae, and more recently with Malvaceae. Jute was used for making textiles in the Indus valley civilization since the 3rd millennium BC. 

Process of making jute: The jute fiber comes from the stem and ribbon (outer skin) of the jute plant. The fibers are first extracted by retting. The retting process consists of bundling jute stems together and immersing them in slow running water. There are two types of retting: stem and ribbon.  Manufacturing Process of Jute Yarn:   

Raw Jute: Raw jute in the form of bales are processed in jute mills to produce hessian, sacking, jute yarn, bags, and other useful products. 
Selection of Raw Jute: In the selection process, raw jute bales are opened to find out any defect and to remove the defective portion from the mora by experienced workers. Raw jute bales are of two types i.e. 150 kg weight and 180 kg weight with or without top portion cutting. The bales are assorted according to end use like Hessiean weft, Sacking wrap, Sacking weft etc. After selection, jute bales are carried to softning section by workers called Gariwala and Bajawala. 
Softning Process Jute: In softning process jute morahs are made soft and pileable. Two methods are used for softning; use of softening machine and use of jute good spreader. Generally an emulsion plant with jute softner machine is used to lubricate and soften the bark and gummy raw jute. The emulsion plant consists of gear pump, motor, vat, jet sprayer, nozzles, emulsion tank and the jacket. In this softning process jute becomes soft and pileable and suitable for carding. 
Carding: Carding is a combining operation where jute reeds are splitted and extraneous matters are removed. Jute fibres are formed into ribbon called "sliver". There are three different carding sections: 
(i) Breaker carding 
(ii) Inner carding 
(iii) Finisher carding 

In the Breaker carding machine soften jute after piling is feed by hand in suitable weight. The machine by action with different rollers turns out raw jute in the form of jute sliver for finisher carding. In this process root cutting is necessary before feeding the material to the hand feed breaker carding machine.  Finisher carding machine make the sliver more uniform and regular in length and weight obtained from the Breaker carding machine. 
             Finisher carding machine is identical to the Breaker carding machine, having more pair of rollers, staves, pinning arrangement and speed. The material thus obtained is send to drawing section. 
Drawing:  Drawing is a process for reducing sliver width and thickness by simultaneously mixing 4 to 6 sliver together. There are three types of Drawing Frame machine. In most mills 3 Drawing passages are used in Hessian and 2 Drawing passages are used in Sacking.

Spinning: Spinning is the process for producing yarn from sliver obtained from Third drawing. The jute spinning frame machine is fitted with slip draft zone and capable of producing quality yarns at high efficiency with auto-dofting arrangements also. 

These are also known as man-made fibers. Synthetic fibers are obtained by chemical processing of petrochemicals. The synthetic fibers can be woven into a fabric, just like natural fiber.  Synthetic fibers have a wide range of use ranging from household articles like ropes, buckets, furniture, containers, etc. to highly specialized uses in aircrafts, ships, spacecrafts, health care, etc.

Synthetic fibers and plastics are made up of molecules called polymers. A polymer is a large molecule formed by combination of many small molecules, each of which is called a monomer. 
Properties of synthetic fibers:The properties of synthetic fibres are as follows-  They quickly dry up.
1. It means that synthetic fiber dries easily after washing. They are durable. 
2. It means that they can be used for a longer period of time. They are less expensive.
They are readily available.
They are easy to maintain and do not need extra care.

Kinds of Synthetic Fibers: 
There are different kinds of synthetic fibers which are as follows-

Rayon: This is a type of synthetic fibre obtained from wood pulp. Rayon is soft, absorbent and comfortable. It is easy to dye in wide range of colors. Rayon is mixed with cotton to make bedsheets. Rayon is mixed with wool to make carpet.

Nylon: This type of synthetic fibre is obtained from coal, water and air. Nylon is very lustrous, easy to wash and elastic. It dries quickly and retains its shape. It finds its application in seat belts of car, sleeping bags, socks, ropes, etc.  Nylon is also used in ropes for rock climbing, making parachutes and fishing nets. 

Acrylic: Acrylic is warm and lightweight, soft and flexible fibre. It is often used for making sweaters, blankets, cashmere, jackets, shawls, and tracksuits. It is also used as linings for boots and gloves as well as in furnishing fabrics and carpets. It is used in craft yarns, boat sails and vehicle covers. 

Polyester: polyster is obtained from coal, water, air and petroleum. It is made from repeating units of chemical known as esters. It is easy to wash and it remains wrinkle free and it is quite suitable in making dress material. Polyester retains its shape and remains crisp. Polyester is used in making ropes, nets, raincoats, jackets, etc. 

Advantages of synthetic fibres: Synthetic fibres are very durable and do not wrinkle easily They are elastic and can be easily stretched out They are strong and can sustain heavy load. It is soft and hence it is used in clothing material. It is cheaper as compared to natural fibres. 

Disadvantages of synthetic fibres: Most synthetic fibres do not absorb moisture. Synthetic fibre can be affected if washed using hot water. It catches fire easily as compared to natural fibre. 


Sunday, March 6, 2016


Children we are going to learn about human digestive system and its function. Human digestive system starts from mouth, buccal cavity, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus are the parts in the human digestive system.

Mouth, salivary glands and their functions. Mouth is only an opening of the digestive system. Taking in of food digestive system. Taking in of food through mouth is called ingestion. The cavity or space in the mouth is called oral cavity or buccal cavity.

Digestion starts in buccal cavity. Teeth, tongue and openings of three pairs of salivary gland are present in baccual cavity.

Physical and chemical nature of the food changes when it is masticated with the help of teeth and mixed with saliva.

There are four types of teeth in man- incisors, canines, premolars and molars- each for a specific functions.

The arrangement of teeth is same on the upper and lower jaws.An adult human has thirty two teeth – 8 incisors, 4 canines, 8 premolars, and 12 molars.

Tongue is muscular and pushes the food on to the teeth during mastication. Taste buds on the tonge sense the taste of food.

Three pairs of salivary glands are present in the buccal cavity. They are parotid, sub-lingual and sub-maxillary  glands .

Parotid glands are present near the ear. Secretion 

from these glands is sent into buccal cavity through ducts.

Other two pairs of glands open below the tongue through ducts. Saliva is released when food is present in buccal cavity. It is also released at the sight, smell and even thought of food. Saliva contains large amount of waste small amounts of salts and mucous.

Saliva is slightly alkaline in nature. It contains an enzymes called salivary. Amylase converts starch into dextrin and maltose sugar. As the food stays only for short time in the buccal cavity, starch is partly digested here.

Mucous present in the saliva makes the food sticky and helps its passage easy through pharynx. The food in buccal cavity undergoes mainly physical changes. Saliva is also useful as a solvent for dissolving the chemical substance present in food.

Oesophagus is a narrow tube and connects pharynx and somach. It has both volume and involuntary muscles. These muscles are arranged circularly and longitudinally.

Internally, the wall of esophagus is lined with a mucous membrane which secretes mucous. Mucous acts as a lubricant and helps in the easy and smooth passage of food.

Swallowing means pushing food into oesophagus, is a voluntary act. Once food enters oesophages, swallowing becomes an involuntary act.

When food enters into oesophages, the muscles present in its wall contract and relax alternately producing wave like movements. These are called peristaltic movements.

They help in pushing the food down the oesophagus into the stomach. Peristaltic movements of oesophagus are involuntary.

There are no digestive enzymes in oesophagus. Oesophagus is only a passage through which food enters into stomach.

Hence, food does not undergo any change in pharynx and oesophagus. However, amylase present in the saliva continues to act on the starch present in the food.

Stomach as a muscular bag it is present on the left side in the abdominal cavity, below the diaphragm. Part of the stomach into which oesophagus opens is called cardiac stomach.

Part of the stomach that opens into duodenum is called pyloric stomach. Opening of the pyloric stomach into duodenum is protected by pyloric sphincter.

Muscles in the walls of the stomach are involuntary muscles. These are arranged longitudinally, diagonally and circularly.These muscles, contract in different directions. As a result food is churned in the stomach.

Stomach has three important roles:
1. It stores the food temporarily.
2. Mixing of various components in the food thoroughly – this occurs due to contraction and relaxation of muscles.
3. It brings about phusical and chemical changes in the food.

Internally stomach wall is lined by mucous membrane. A number of glands called gastric glands are present in this membrane. Each gastric gland opens by a small pore into the lumen of stomach. Gastric glands secrete gastric juice and mucin.

Gastric juice is a thick, clear and straw coloured fluid. Gastric juice contains hydrochloric acid and enzymes. The food gets mixed with hydrochloric acid present in the gastric juice.

Hydrochloric acid kills bacteria present in food. It also destroys the structure of proteins, so that enzymes can digest them easily.  Mucous membrane protects stomach wall from the action of acid present in the gastric juice.

Pepsin and lipase are the enzymes present in the gastric juice. When pepsin is secreted, it is inactive and is called as pepsinogen. Acids converts inactive pepsinogen to pepsin which is the active form of the enzyme.

Pepsin breaks down proteins into peptones and proteases. Lipase converts fats into fatty acids and glycerol. In children, another enzyme called rennin is secreted into the stomach. It curdling of milk. This enzyme disappears as the child grows.

Food is retained in the stomach for two to four hours and is partially digested in the stomach. As the food is undergoing changes in stomach, the pyloric sphincter closes the opening of stomach into duodenum.

The pyloric sphincter allows only small quantities of food into duodenum at a time. The food that enters the duodenum is called chyme. This is acidic and very soft.

Duodenum, pyloric sphincter, liver, gall bladder, pancreas
Duodenum is ‘U’ shaped and connects stomach with ileum. Bile from the live and pancreatic juice from pancreas reach duodenum through separate ducts.The pyloric sphincter remains closed until digestion of food in the stomach is completed.

It opens and allows small amounts of acidic chime to enter into duodenum, so that entire duodenum is not filled with chyme. Pyloric sphincter closes immediately after the chyme enters duodenum and this prevents the back flow of chyme into stomach. Opening and closing of pyloric sphincter is involuntary.

Liver: Liver is present on the right side of duodenum, below the diaphragm. It is brown in color there are four lobes in the liver. Cells present in the liver are called hepatocytes. Liver  produce bile duct through cystic duct.

Gall bladder: Gall baldder is a pear shaped dark coloured sack. Bile is stored temporarily and also concentrated – by the removal of water in the gall- bladder. Bile from the gall-bladder is sent to bile reaches duodenum through a duct called bile duct.

Bile : in human beings bile has a mixed colour of yellow and golden brown. Bile is thick and sticky fluid it has about 86% of water, bile salts and bile pigments.

Sodium cholate and sodium deoxycholate are the bile salts. Bilirubin and biliverdin are the bile pigments. Bile pigments are products during the degradation of hemoglobin. Color of bile depends on the amount of bile pigments.

There are no digestive enzymes in bile. But the bile salts change the fats into small microscopic colloidal particles. This is called emulsification. Emulsification of fats helps lipase to act in fats. Emulsification of fats by bile salts is an important step in the digestion of lipids and absorption of fatty acids .

When the bile duct is blocked, bile gets mixed with blood and circulates in the body. Because of this, the eyes and skin become yellow. This is called jaundice.

Pancreas :
Pancreas is an yellow grey gland and is present on the left side of duodenum, below the stomach. There are two parts in pancreas. One of them is called exocrine pancreas. Cells of exocrine pancreas open into ducts and secrete a juice called pancreatic juice.

All the small ducts join to form a pancreatic duct which opens into duodenum. Trypsin chymotrypisn, amylase and lipase are important enzymes present in pancreatic juice. Pancreatic juice also has large amounts of bicarbonate which neutralizes the acid present in the chime and makes the chime slightly alkaline. Trypsin and chymotrypisn hydrolyze protein. These two enzymes are produced in their inactive form called trypsinogen and chymotrypsinogen. These are converted into their active forms by another enzyme called enterokinase.

Enterokinase is present in the intestinal juice. Once a small amount of Trypsin is formed, it converts the rest of the inactive enzymes into active enzymes. This is called autocatalysis. Trypsin and chymotrypisn are active in alkaline medium. The proteins that are partially hydrolysed by pepsin are completely hydrolysed by chymotrypisn to polyidespepides.

Amylase present in pancreatic juice acts on carbohydrates, producing dextrines and finally convert them into maltose sugar. Lipase present in the pancreatic juice converts emulsified fats into glycerol and fatty acids.

The second part of the pancreas consists of islets of langerhans cells which help in secretion of insulin. This part comes under endrocine system.

Small intestine – structure and functions of enzymes. Small intestine is a tube of 6 meters length and 3cm width.

The anterior part is called duodenum. The middle part is called jejunum and posterior part is called ileum. Ileum joins large intestine.  The middle part of intestine is coiled.

Cells present in the intestinal wall secrete mucous and enzymes in the form of intestinal juice. This is called succusentericus. Enterokinesis, peptidase, lipase, sucrose, nuleotidase, nucleosidase are some of the enzymes present in the intestinal juice.

Partially digested food entering the intestine mixes with the intestinal juice. Enzymes present in the intestine completely digested the partially digested food.

Peptidases  convert peptides into amino acids. Intestinal lipase completely digests fats. Enzymes sucrose, maltase, lactase hydrolyse sucrose, maltase, lactase respectively converting them into glucose. Other sugars are also produced in this process. Nucleotidase and nucleosidase complete the digestion of nucleic acids.

Transport of the products of digestion from the intestine into blood is called absorption. Internally, intestinal wall has a number of finger like process called villi. The villi increase the surface area for absorption. Blood vessels are present in the form a network in the villi. Products of digestion are absorbed first into the villi and from there into the blood vessels and lymph vessels.

The diameter of large intestine is greater than the diameter of the small intestine. 

Large intestine is present between small intestine and rectum. The wall of colon is made of involuntary muscles. Movement of these muscles pushes the food large intestine.

Water and minerals salts present in the chime are absorbed in the colon and soft, solid faeces is formed. Faeces consists of undigested food material, dead material, bile salts and bile pigments. 

By the peristaltic movements of large intestine, faeces is pushed towards rectum. It is expelled out through the anus. This happens when the sphincter muscles that guard anus expand. This activity is called defecation.