About 600 to 800 BC the people living in Magnesia in Asia Minor found a stone (an ore of iron Magnetite Fe₂O₃) which was capable of attracting iron pieces towards it. They called this stone as magnetite. During the course of time, the name changed to a magnet. Certain substances have a tendency to attract iron filings towards them, such substances are called magnetic substances and the property is known as magnetism. e.g. Iron, Steel, Cobalt, Nickel.

The pieces of loadstone, which show magnetism are called natural magnets. The natural magnets are of irregular and odd shapes. They don’t have strength. Magnetized iron pieces of iron or other magnetic material are called artificial magnets. They can be made of different shapes.

A magnet creates around it what is called a magnetic field. Thus the region around the magnet in which it exerts a force on other magnets or other magnetic materials is called a magnetic field. The magnetic force is a non-contact force.

Characteristics of Magnet:

Attractive Property:

A magnet attracts small pieces of iron. The magnetic field is stronger at the ends of a magnet and thus the ends of the magnet are the centres of attraction. These centres of attraction are called poles of the magnet.

Magnetic lines of force are crowded at the ends of a bar magnet. Actually, the poles are not at the ends of the geometric length of the magnet but they are slightly inside. The points of a magnet where the attraction appears to be maximum are called the poles of the magnet.

Directive Property:

When a bar magnet is suspended in the air such that it is free to rotate about the transverse axis passing through its centre, then it is found that the bar magnet always aligns itself in a north-south direction. The end of the magnet which is pointing towards the geographical north is called north-seeking pole or simply north pole, while the end of the magnet pointing towards the geographical south is called south-seeking pole or simply south pole.

Law of Magnetic Poles:

Like poles of magnets repel each other and unlike poles attract each other.

Pair Property:

When we cut a magnet into two parts two new magnets are formed. Thus it is impossible to separate the poles of a magnet. Isolated magnetic poles do not exist. i.e. magnetic poles always exist in pairs. Hence the magnets have to be necessarily regarded as dipoles.

Sure Test of Magnetization:

Repulsion is a sure test of attraction because an iron rod is always attracted towards the magnet and unlike poles always attract. Thus if a given rod is repelled we can definitely say that the rod is magnetized.

Types of Magnets:

Bar Magnet:

A bar magnet is a rectangular parallelepiped body which exhibits magnetic properties. Actually, the poles are not at the ends of the geometric length of the magnet but they are slightly inside.

• The length of the edge parallel to the magnetic axis is called the geometric length of the bar magnet.
• The line joining the poles of the bar magnet to called an axis of the magnet.
• The distance between the poles of the bar magnet is called magnetic length.
• Magnetic length of bar magnet × 1.2 = Geometric length of the bar magnet.
• A vertical plane passing through the magnetic axis of the freely suspended magnet is called magnetic meridian.
• A vertical plane passing through the magnetic equator of the freely suspended magnet is called equatorial meridian.

Magnetic Needle:

It is a magnet tapered towards both ends and pivoted at the centre.

It is used to check the direction of the magnetic field and to map magnetic lines of force of other magnets.

Horse Shoe Magnet:

It is in the shape of a horseshoe. This magnet is usually more powerful than a bar magnet. As both the poles of horseshoe magnet face each other, the attractive power is doubled.

The two poles can be made closer than any other type, hence these magnets can be used when a strong magnetic field is required in a small space. They are used in electronic valves of RADAR, electric motors, electric generators and moving coil galvanometers.

Disc Magnet:

It is in the shape of a disc.

Its poles are located each on its circular faces. i.e. if one face is acting as a north pole, other face will act as a south pole.

Magnetic Keepers:

If two magnets are placed side by side there will be mutual repulsion or attraction. This weakens the strength of the magnet. Similarly, a magnet is kept for a long time it loses its magnetic property. It is due to self-inductance and due to Earth’s magnetic field. To prevent this, bar magnets are placed side by side with opposite poles near. A soft iron piece called a keeper is placed across the poles as shown in the figure.

The magnet induces opposite polarity at the ends of the keeper.  Thus this soft iron piece provides a path for the magnetic field lines to form a continuous loop. Thus it helps in preserving the magnetic field.

Advantages of Artificial Magnets:

• Artificial magnets can be made up of different (convenient) shapes and sizes.
• Artificial magnets can be made of different strengths.
• Strong magnetism can be obtained by artificial magnets only.

Uses of Magnets:

• Its directive property is used to construct magnetic needles and mariner’s compass.
• Permanent magnets are used in dynamos, electric motors, generators, electrical accelerators, door locks.
• Electromagnets are widely used in electric bells, electric cranes, tape recorders and speakers.
• Magnets are used in separating iron particles from solid mixtures using the method of magnetic separation.
• It is used in pin holder to stock pins and makes easy to pick them when required.
• They are used as a magnetic lock to keep shutters of doors and cupboards to shut tightly.

Magnetic Compass OR Mariner’s Compass:

A magnetic compass consists of a small magnetic needle pivoted at the centre of a small brass box which has a glass top. Generally, the north end is painted in red.

It works on the principle that when a magnet is free to rotate about a transverse axis then under the action of Earth’s magnetic field, the needle aligns itself in North-South direction. Thus using Compass the North and South direction can be located and thus other directions can be obtained.

Uses of the magnetic compass are.

• To decide North-South directions.
• To find the direction of the magnetic field at a place.
• To plot or draw magnetic lines of force
• To test the polarity of a magnet.
• It is very useful for travellers, mariners a, d navigators to find direction when they sail through the unknown location.

Pin Holder:

Pin holder is used on writing tables to hold pins. It consists of a thin round magnet fitted at its mouth. When the pin holder is turned upside down, the pins at the bottom of the holder stick to the inside of the mouth of the holder. Now they can be easily picked out and be used.

Magnetic Locks for Shutters of Cupboards:

The magnetic lock is fitted on the frame of the cupboard, while a thin iron strip is fixed on the shutter, exactly opposite to the magnetic lock.

When the shutter is brought near the frame, the magnetic attraction between the iron strip and magnet click shut the shutter tightly to the frame.

Next Topic: Properties of Magnet

Science > Physics > Magnetism > Magnets

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When a human blood sample is prevented from clotting and spun in a test tube (centrifuged), in a machine called a centrifuge, the blood separates into a   straw coloured liquid called plasma and a dark brown mass of blood cells. The lower layer consists of white blood cells, blood platelets, and red blood cells. Collectively, these are the formed elements, which make up about 45% of the total volume of whole blood; the percentage of blood attributed to red blood cells is called the hematocrit. The hematocrit is defined as the percentage of blood volume that is occupied by erythrocytes. The normal hematocrit is approximately 45 percent in men and 42 percent in women.

The upper layer is plasma, which contains a variety of inorganic and organic molecules dissolved or suspended in water. Plasma accounts for about 55% of the total volume of whole blood.

Composition of Plasma:

Plasma is the straw-coloured non-living, liquid part of blood. It makes up about 55 – 60% of blood volume and 5.5 % of body weight. Blood corpuscles and platelets are suspended in it. Blood without clotting factor is called serum. The characteristic straw color of plasma is due largely to a waste product of hemoglobin breakdown called bilirubin.

It is the liquid portion of blood, and about 92% of plasma is water. The remaining 8% of plasma is composed of various salts (ions) and organic molecules. The salts, which are dissolved in plasma, help maintain the pH of the blood. Small organic molecules such as glucose, amino acids, and urea are also dissolved in plasma. The large organic molecules in plasma include hormones and the plasma proteins.

Water:

Plasma is composed of about 90 to 92% water. Acts as a solvent and suspending medium for blood components.  

Plasma Proteins:

Plasma proteins or serum proteins constitute 6 to 8% of plasma. Important plasma-proteins are. The plasma proteins constitute, by weight, most of the plasma solutes. They can be classified, according to certain physical and chemical reactions, into three broad groups: the albumins and globulins, and fibrinogen, which function in blood clotting. Most plasma proteins are made in the liver. An exception is the antibodies produced by B lymphocytes, which function in immunity. Certain hormones are plasma proteins made by various glands.  It must be emphasized that the plasma proteins normally are not taken up by cells; cells use plasma amino acids, not plasma proteins, to make their own proteins. Plasma proteins must be viewed quite differently from most of the other organic constituents of plasma, which use the plasma as a medium for transport to and from cells. In contrast, most plasma proteins perform their functions in the plasma itself or in the interstitial fluid.

• Fibrinogen and prothrombin: It constitutes 4% of the plasma proteins and required for blood clotting.
• Serum albumin: The albumins are the most abundant of the three plasma protein groups and are synthesized by the liver. It makes up 58% of the plasma proteins. They are partly responsible for blood viscosity, the regulation of water movement between tissues and blood and osmotic pressure; acts as a buffer; transports fatty acids,
  free bilirubin, and thyroid hormones.
• Globulins or Gamma globulins or Immunoglobins (Ig): It accounts for 38% of the plasma proteins. They act as antibodies and are associated with the defence mechanism of the body. They Transport lipids, carbohydrates, hormones, and ions like iron and copper; antibodies complement are involved in immunity

Inorganic Salts and Ions (Minerals):

They form 1-2 % of the plasma and includes electrolytes like Sodium, potassium, calcium, magnesium, chloride, iron, phosphate, hydrogen, hydroxide, bicarbonate. They are involved in osmosis, membrane potentials, and acid-base balance.

Dissolved Nutrients:

Glucose, lipids, vitamins, fatty acids, amino acids, and cholesterol. They act as sources of energy and basic “building blocks” of more complex molecules. Vitamins Promote enzyme activity.

Hormones and Enzymes:

Blood acts as the transport system for the transportation of regulatory substances called hormones secreted by different glands.  Thus plasma contains hormones and enzymes. Enzymes catalyze chemical reactions; hormones stimulate or inhibit many body functions.

Dissolved Gases:

Oxygen, It is necessary for aerobic respiration; terminal electron acceptor in an electron-transport chain, Carbon dioxide, a Waste product of aerobic respiration; as bicarbonate, helps buffer blood and nitrogen.

Excretory Substances:

Ammonia, urea, uric acid, creatine, and creatinine. Urea, uric acid, creatinine , and ammonia salts  are the breakdown products of protein metabolism; excreted by the kidneys. Bilirubin is the breakdown product of red blood cells; excreted as part of the bile from the liver into the intestine. Lactic acid is the end product of anaerobic respiration; converted to glucose by the liver.

Functions of Plasma:

Transport Nutrients:

Delivering nutrients to the body is a critical function of the circulatory system. Plasma of the blood is the carrier of all nutrients. After food is digested and assimilated, its component nutrients like carbohydrates, proteins, minerals, fats, and vitamins are absorbed into the bloodstream. Each of these nutrients is vital for healthy body function.

Transport of Waste Products:

The plasma collects metabolic waste products like urea, creatinine, and other chemical wastes and toxins and transports them to the liver, kidneys, skin, and lungs (excretory organs) for elimination from the body.

Transport of Hormones:

Hormones are chemical messengers produced by endocrine glands that affect distant organs. Hormones are released into the bloodstream through which they travel to target sites. The plasma collects the hormones from the endocrine glands and serves as the transportation connection between the glands and the organs or tissues.

Transport of Other Products:

Albumin transports the molecule bilirubin, a breakdown product of hemoglobin. Lipoproteins, whose protein portion is a globulin, transport cholesterol.

Body Temperature Regulation:

Plasma Picks up excess body heat from the deep-seated heat-producing organs and brings it to the skin to be excreted. If body temperature drops, surface blood vessels constrict(decrease in size) to conserve body heat. Thus it  helps in regulating the body temperature

Disease Protection and Healing:

There are three types of globulins, designated alpha, beta, and gamma globulins. The alpha and beta globulins, produced by the liver, bind to metal ions, to fat-soluble vitamins, and to lipids, forming the lipoproteins. Antibodies, which help fight infections by combining with antigens, are gamma globulins. The immunoglobins of plasma act as antibodies and attack the foreign intruder in the body. They neutralize these harmful foreign agents. Thus plasma is responsible for the immunity of the body.

Fibrinogen present in the plasma is responsible for clotting of blood which is important for stopping the blood flow from the wounds.

Maintain Haemostasis and Osmoregulation:

Plasma supplies water to different tissues at the same time and removes excess of water produced during metabolic activities. Thus it maintains water balance in the body. Osmotic pressure is a force caused by a difference in solute concentration on either side of a membrane. The plasma proteins, particularly the albumins, contribute to the osmotic pressure, which pulls water into the blood and helps keep it there.

Acid-Base Buffer:

Plasma proteins act as acid-base buffers and maintain blood pH within a range. Plasmaproteins are able to take up and release hydrogen ions; therefore, the plasma proteins help buffer the blood and keep its pH around 7.40.

Disorders Related with Blood Plasma:

Oedema or Edema:

Oedema is swelling that occurs when too much fluid becomes trapped in the tissues of the body, particularly the skin. It most often occurs in the skin, especially on the hands, arms, ankles, legs, and feet. However, it can also affect the muscles, bowels, lungs, eyes, and brain. It usually starts slowly, but the onset can be sudden.

In case of a person suffering from protein deficiency, a fall in plasma protein leads to escape of excess volume of water from the blood to tissues. Due to excess of fluid of fluid in tissues causes swelling of feet. The state is called oedema.  The condition mainly occurs in older adults and women who are pregnant. Symptoms include skin that retains a dimple after being pressed for a few seconds,  puffiness of the ankles, face, or eyes, higher pulse rate and high blood pressure.

Diuretics are a type of medication. They help get rid of excess fluid by increasing the rate of urine production by the kidneys.

Cholesterol:

Cholesterol is present in plasma. Cholesterol has a tendency to deposit on the walls of blood vessels leading to a condition called atherosclerosis. The liver is responsible for producing and clearing cholesterol in the body.

Dietary cholesterol increases plasma total cholesterol concentrations in humans. There is a relationship between increased plasma cholesterol concentrations and cardiovascular disease risk. Dietary guidelines have consistently recommended to such person limiting food sources of cholesterol. Potential sources of dietary cholesterol are limited to animal foods; eggs, dairy products, and meat.

LDL (low-density lipoprotein) cholesterol is also called “bad” cholesterol. LDL can build up on the walls of arteries and increase the chances of getting heart disease. HDL (high-density lipoprotein) cholesterol is also called “good” cholesterol. HDL protects against heart disease by taking the bad cholesterol out of the blood and keeping it from building up in arteries. Along with cholesterol, triglycerides form plasma lipids. Excess triglycerides in plasma have been linked to the occurrence of coronary artery disease in some people.

Everyone over the age of 20 should get their cholesterol levels checked at least once every 5 years by a test called “Lipid profile”. Everyone over the age of 40 should get their cholesterol levels checked at least once a year.

Lifestyle changes such as exercising and eating a healthy diet are the first line of defence against high cholesterol. The choice of medication for high cholesterol depends on individual risk factors, age,  current health and possible side effects. Common choices include Statins, Bile-acid-binding resins, Cholesterol absorption inhibitors, Injectable medications. The choice of medication for high triglycerides is Fibrates, Niacin, Omega-3 fatty acid supplements.

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Science > Biology > Human Anatomy and Physiology > Cardiovascular System > Composition of Blood: Blood Plasma

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In the Cardiovascular system, the ‘‘heart’’ (cardi) pumps the blood in a ‘‘little circle’’ (circul), which travels through ‘‘little vessels’’ (vascul). In human, the transportation is done through blood circulatory system and lymphatic system. Thus two fluids move through the circulatory system: blood and lymph. The blood, heart, and blood vessels form the Cardiovascular System. The lymph, lymph nodes and lymph vessels form the Lymphatic System. Human blood circulatory system has three main components. A fluid (blood), tubing (arteries, veins and capillaries) and a pump (the heart).

Study of blood is called haematology. It is a fluid connective tissue. It is bright red, slightly alkaline, salty viscous fluid heavier than water.

The Constituent of the Blood:

In this article, we shall only take an overview of the composition. In the next article, each constituent is discussed in detail.

When a human blood sample is prevented from clotting and spun in a test tube (centrifuged), in a machine called a centrifuge, the blood separates into a   straw coloured liquid called plasma and a dark brown mass of blood cells. The lower layer consists of white blood cells, blood platelets, and red blood cells. Collectively, these are the formed elements, which make up about 45% of the total volume of whole blood; the percentage of blood attributed to red blood cells is called the hematocrit. The hematocrit is defined as the percentage of blood volume that is occupied by erythrocytes. The normal hematocrit is approximately 45 percent in men and 42 percent in women.

The upper layer is plasma, which contains a variety of inorganic and organic molecules dissolved or suspended in water. Plasma accounts for about 55% of the total volume of whole blood.

Characteristics of Human blood:

Study of blood is called haematology. Blood is a fluid connective tissue. It is bright red, slightly alkaline (pH 7.3 to 7.5), salty viscous fluid heavier than water. the pH of blood is more in arteries than that in veins. The viscosity of blood is 5 to 6 times that of water. An adult has a blood volume of approximately 5.5 litres. It forms 6 to 10 % of the body weight. Blood is the only tissue that exists in both the liquid and solid state simultaneously.

Volume of Blood and Different Constituents:

The volume of blood in an average-sized person is approximately 5.5 L. Now hematocrit is 45 percent of the total volume,

Then, Erythrocyte volume = 0.45 x 5.5 L = 2.5 L

Since the volume occupied by the leukocytes and platelets is normally considered negligible, the plasma volume equals the difference between blood volume and erythrocyte volume; therefore, in our average person

Plasma volume = 5.5 L – 2.5 L = 3.0 L

Plasma:

The plasma consists of 90 to 92% water and 8% to 10% proteins, salts, hormones, enzymes, waste products and other various chemicals. Most of the solute part about 7% is proteins. These include antibodies that help to protect the body from diseases, fibrinogen that helps the blood to clot. The waste product includes urea and carbon dioxide. Hormones are the chemical messenger, which help to coordinate different body functions.

Plasma obtained from blood donation may be converted to a powdered form for storage. During the transfusion, it is dissolved in sterile distilled water and can be administered at once. This method saved the lives of many during World war.

Red Blood Cells (RBCs): 

They are also called erythrocyte. They are produced inside the bone marrow. They have a lifespan of about 100 to 120 days after which they are destroyed by the liver. They are the most common type of blood cell (5.1 to 5.8 million per cubic mm). They are non-nucleated, small in size, round and biconvex in shape. They are able to fold and bend as they are forced through the smallest blood vessels.

The strong red colour of blood is due to the large number of RBCs. Red blood cells contain haemoglobin which gives them their red colour and enables them to carry oxygen from lungs to different parts of the body. They also carry carbon dioxide from different parts of the body to the lungs. Their main function is to carry oxygen from the lungs to the tissues.

White blood cells (WBCs):

They are also called leucocytes. Many white cells are made in the bone marrow. Their lifespan is 3 to 4 days. They are colourless and they have a nucleus. WBCs are larger than red cells but they are lesser in number. (About 5000-7000 per cubic millimetre of blood). They are further classified as lymphocytes and phagocytes. The nucleus of each type has a characteristic shape. When they travel in the blood they are more or less spherical, but they flatten and continuously change their shape along the inside walls of the blood vessels.

WBC’s rid the body of pathogens in the process called phagocytosis. In this process, the WBC surrounds, engulfs and “eats” the invading pathogen.

Platelets : 

Platelets are also called thrombocytes. They are made in the bone marrow and have a lifespan of 8-14 days. They are much smaller than red cells. One cubic millimetre of blood contains about a quarter of million platelets. Their function is to help the blood clot. Clotting prevents loss of blood from wounds.

Observing Blood Under Microscope:

• Clean the skin of your finger with a swab of cotton dipped in ethanol. With a sterile needle prick your finger so that a drop of blood comes out.
• Place the drop of blood at one end of a microscope slide. With another slide spread the blood over the surface to form a smear. Let it dry and then examine it under a microscope. We can observe red blood corpuscles.
• Now cover the smear with Leishman’s stain and leave it for five minutes. Then wash the stain off with tap water gently. Let the slide dry and then examine it under the microscope again. Now, we can observe white blood corpuscles.

Functions of Human blood:

Transportation:

The blood moves from the heart to all the various organs, where exchange with tissues takes place across thin capillary walls. Blood collects oxygen from the lungs and nutrients from the digestive tract and transports these to the tissues. It delivers enzymes and chemical messengers to cells and tissues. Various organs and tissues secrete hormones into the blood, and blood transports these to other organs and tissues, where they serve as signals that influence cellular metabolism. It delivers water, vitamins and minerals to cells. It carries carbon dioxide from cells, tissues and carries it to lungs for disposal. It carries waste materials like urea and other chemical wastes and carries them to the liver and kidneys for disposal. It carries antibodies from place to place in the body. It carries vitamins and enzymes.

Protection:

The blood defends the body against invasion by pathogens (microscopic infectious agents, such as bacteria and viruses) in several ways. Certain blood cells are capable of engulfing and destroying pathogens, and others produce and secrete antibodies into the blood. White blood corpuscles  (WBC) fight against disease-causing germs that harm the body.

It prevents the loss of blood after an injury by clotting. Blood helps in the repair process after a cut or other injury. Without blood clotting, we could
bleed to death even from a small cut.

Regulation:

Blood Picks up excess body heat and brings it to the skin to be excreted. The sweat is formed on the skin. Which is evaporated and heat required for it is taken from the body. Hence the body cools down. It controls the amount of water in the body. The salts and plasma proteins in blood act to keep the
liquid content of blood high. In this way, blood plays a role in helping to maintain its own water-salt balance. It also helps to regulate the amount of chemical substance in the tissues of the body. Due to the presence of buffers in the blood, it also helps to regulate body pH and keep it relatively constant.

Blood Donation:

Anybody who is healthy weighs over 50 kg and is between the age of 18 years and 65 years can donate blood. An adult has a blood volume of approximately 5 litres. A donor may give up to half a litre of blood at one time. This is quickly replaced by the body.

Many donors give blood regularly. It is immediately mixed with a chemical which prevents it from clotting and also provides food for the living cells. The blood is then stored in a refrigerator until it is required. Similarly, sodium citrate is added to it to avoid coagulation. The place where the blood is stored is called a blood bank.

Blood groups:

Human blood group is determined by the antigens present on the surface of RBC’s.  Blood groups are inherited and do not change throughout life. Human blood is classified into 4 main groups: A, B, AB and O. Each can be either Rhesus + ve or Rhesus – ve, giving  8 groups in all. Blood grouping is the identification of the antigens in a blood sample. This system is called ABO system.

An individual’s RBC’s may carry an A antigen, a B antigen, both A and B antigens, or no antigen at all. These antigen patterns are called blood types A, B, AB and O, respectively. Type AB is known as a universal recipient, meaning that they can receive any type of blood, while O is the universal donor, meaning they can donate blood to anyone

Blood transfusion:   

Blood transfusion is the transfer of blood that is taken from one person, into the bloodstream of another person. The person who gives blood is called the donor. The person who receives blood is called the recipient. When there is a loss of blood suddenly due to an accident, or because of the bursting of a blood vessel, there is a danger that not enough blood will be left to maintain the circulation. In such a case, the patient may lose consciousness due to low blood pressure and hence less supply of oxygen to tissues. Losing blood is called haemorrhage. To restore the blood volume and to provide more red cells, a blood transfusion is carried out.

Before doing blood transfusion the compatibility between the groups of the donor and the recipient should be checked. If the blood of the donor is not compatible with the blood of the patient, the red cells in the patient’s blood will stick together. This may lead to death.

Clotting of Blood:

Human blood contains heparin and antithrombins as anticoagulants, it prevents the blood to clot inside the blood vessels. As soon as blood vessel ruptures, bleeding starts. The conversion of liquid blood into semisolid jelly is called blood coagulation or blood clotting. Platelets adhere to the site of the wound and release clotting factors known as prothrombin. Prothrombin is inactive. At the site of rupture the platelets and injured tissues release thromboplastin which initiates the formation of enzyme prothrombinase.  In the presence of Ca, ions prothrombinase converts inactive prothrombin to active thrombin. Thrombin converts soluble fibrinogen into fibrin. The fibrin forms a net to enmesh platelets blood cells and plasma to form a clot.

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Science > Biology > Human Anatomy and Physiology > Cardiovascular System > The blood, an Overview

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In living things, many substances such as food, gases, minerals salts, hormones and waste products have to be transported from one part of the body to another. Plants and animals have a system of transporting substances throughout their body. In animals (vertebrates), blood is the medium of transport. In small animals (lower animals) such as protozoa and Flatworms, Diffusion of gases takes place through their body surface. Due to their smaller size, they lack a special system for the transport of other materials such as oxygen for existence. Higher animals have higher metabolic activity, hence higher animals require an efficient and speedy supply of nutrients and oxygen for their tissues at the same time they require efficient and speedy disposal of respiratory products, nitrogen products. Hence such animals have developed a special fluid called blood in them and conducting system called circulatory system consisting of heart, vessels etc. This system is also called a vascular system. The circulatory system has two functional components viz. a) blood vascular system and b) lymph vascular system.

Functions of the Circulatory System

Transport of oxygen:

The main function of the circulatory system is supplying oxygen to the different parts of the body. Every cell requires oxygen for their survival. Particularly the brain cells are the most sensitive and begin to die in as little as 3 minutes if deprived of oxygen. During inhalation, air enters the lungs and oxygen is absorbed through the air sacs (alveoli) into the bloodstream. Oxygen combines with the haemoglobin of RBCs to form oxyhaemoglobin. This oxygen-rich blood is pumped through the heart into the arterial circulation. In the capillaries, unstable oxyhaemoglobin breaks down into haemoglobin and oxygen. The separated oxygen diffuses out of the blood into the cells of the body’s organs and tissues where it is utilized for metabolic activities.

Transportation of Carbon dioxide:

Carbon dioxide is a waste product produced by cells during its metabolic activities. A small amount of carbon dioxide combines with haemoglobin to for carbamino-haemoglobin. Some carbon dioxide dissolves in blood plasma.  The absorbed carbon dioxide in the blood is transported to the lungs through the venous circulation. When this oxygen-poor blood reaches the lungs, carbon dioxide diffuses through the air sacs (alveoli) and is then exhaled.

Transport of Nutrients:

Delivering nutrients to the body is another critical function of the cardiovascular system. After food is digested and assimilated, its component nutrients like carbohydrates, proteins, minerals, fats, and vitamins are absorbed into the bloodstream. Each of these nutrients is vital for healthy body function. Carbohydrates are a direct source of energy for the body while proteins (amino acids) are building blocks of new cells. Thus circulatory system supply nutrients wherever it is required. Like oxygen, nutrients diffuse from the bloodstream into body cells via the capillaries.

Transport of Waste Products:

The circulatory system collects metabolic waste products like urea and other chemical wastes and toxins and transports them to the liver, kidneys, skin, and lungs (excretory organs) for elimination from the body.

Transport of Hormones:

Hormones are chemical messengers produced by endocrine glands that affect distant organs. Hormones are released into the bloodstream through which they travel to target sites. Thus the cardiovascular system serves as the transportation connection between the endocrine glands and the organs or tissues. For example, Pituitary gland situated near the brain produces hormones which control other endocrine glands such as the thyroid, ovaries and testes and growth. Similarly, pancreas situated near liver produce hormone insulin which is required for maintaining blood sugar level throughout the body. The circulatory system delivers these hormones to the site of use of that hormone.

Body Temperature Regulation:

Blood Picks up excess body heat and brings it to the skin to be excreted. The sweat is formed on the skin. Which is evaporated and heat required for it is taken from the body. Hence the body cools down. Optimal function of the human body occurs within a relatively narrow temperature range, which is tightly regulated. If body temperature begins to rise, blood vessels close to the body surface dilate (increasing in size). This allows the body to get rid of an excess of heat through the skin. If body temperature drops, surface blood vessels constrict (decrease in size) to conserve body heat. Thus the cardiovascular system works in concert with the body’s sweating mechanism  to regulate the body temperature

Disease Protection and Healing:

The circulatory system serves as the path for disease-fighting cells and proteins, and messengers of the immune system. WBC’s rid the body of pathogens (invading germs) in the process called phagocytosis. In this process, the WBCs surround, engulf and “eats” the invading pathogen. Thus they fight against the pathogens. On entry of germs, antibodies are produced in the blood and a chemical alarm signal is created that travel through the bloodstream, which subsequently transports antibodies to the site of the infection. The circulatory system also carries chemical messengers that attract cells to heal tissues that have been damaged due to injury or disease. It helps in clotting to heal the wound.

Maintain Haemostasis and Osmoregulation:

Homeostasis is a property of cells, tissues, and organisms that allows the maintenance and regulation of the stability and constancy needed to function properly. Homeostasis is a healthy state that is maintained by the constant adjustment of biochemical and physiological pathways. Humans’ internal body temperature, the blood sugar level, blood pressure are all maintained through homeostasis. The circulatory system plays an important role in it. The maintenance of constant osmotic pressure in the fluids of an organism by the control of water and salt concentrations is called osmoregulation. The osmotic pressure and concentrations are maintained by the circulatory system.

Types of Circulatory Systems

Higher organisms have higher metabolic activity, hence higher animals require an efficient and speedy supply of nutrients and oxygen for their tissues at the same time they require efficient and speedy disposal of respiratory products, nitrogen products. Hence such animals have developed a special fluid called blood in them and conducting system called circulatory system consisting of heart, vessels etc. This system is also called a vascular system. The circulatory system has two functional components viz. a) blood vascular system and b) lymph vascular system.

The blood vascular system is of two types a) Open circulation and  b) Closed circulation

Open Circulatory System:

Open circulatory systems are the more basic type of circulatory system. In this circulatory system, the blood is not contained within an enclosed circuit of vessels. Blood (haemolymph) flows from the heart through open-ended vessels and, when it reaches the end of the vessels, The haemolymph enters into an open cavity called a haemocoel. The haemolymph mixes with interstitial fluid and moves around the haemocoel, thus bathing the internal organs and tissues. Haemolymph flows directly over the tissues delivering nutrients and in some cases, gases such as oxygen. Then the haemolymph freely flows back into vessels that direct the blood back to the heart.

The heart is simply an aorta or other blood vessels, and the haemolymph is pulsed throughout the body by muscle contractions. There are no arteries or major veins to pump the haemolymph, so blood pressure is very low and the volume of haemolymph is relatively high.

Examples: arthropods which include insects, spiders, prawns and most molluscs.

Characteristics of Open Circulatory System:

• Blood flows through large open spaces called lacunae and sinuses.
• No capillary system so tissues are in direct contact with haemolymph.
• Exchange of nutrients and gases takes place directly between haemolymph and tissue.
• The volume of haemolymph flowing through tissues cannot be controlled as hemolymph is flowing through open spaces.
• haemolymph flow is very slow. The blood pressure is very low
• Found in higher invertebrates like most arthropods such as prawns, cockroach etc. and in some molluscs.

Closed Circulatory System:

William Harvey (1578-1657)  discovered and published the first accurate description of the human circulatory system, based on his many years of experiments and observations as a scientist and physician. The humans have closed circulatory system. Unlike an open circulatory system, a closed circulatory system is more structured and controlled. The blood of a closed system always flows inside vessels. These vessels make up the vessel system of the body and can be found throughout the entire body.

Characteristics of Closed Circulatory System:

• Blood flows through a closed system i.e. heart and blood vessels.
• Capillary system present so blood is not in direct contact with tissues.
• Nutrients and gases pass through the walls of capillaries to tissue fluid which is then taken up by the tissues.
• Blood flow is controlled by contraction and relaxation of muscles of blood vessels.
• Blood flow is rapid here.
• Found in some molluscs, annelids and all vertebrates.

Importance of Human Circulatory System:

Most of the cells in the human body are not in direct contact with the external environment, so rely on the circulatory system to act as a transport service for them. Two fluids move through the circulatory system: blood and lymph. The blood, heart, and blood vessels form the Cardiovascular System. The lymph, lymph nodes and lymph vessels form the Lymphatic System. The Cardiovascular System and the Lymphatic System collectively make up the Circulatory System. The system in which blood is circulated throughout the body is called the circulatory system.

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Energy is required by living beings for performing different activities. Energy is contained in the food. Food can be defined as a collection of chemicals taken by an organism for the purpose of the growth, repair, and replacement of body cells, energy releases, and maintenance of all the life processes. The process by which organisms obtain and utilize food for their growth, development, and maintenance is called nutrition and the chemical constituents present in the food are called nutrients. Digestion is the breaking down of complex constituents of food by enzymes into simpler soluble forms that can be absorbed and utilized by the cells of the body.

Types of nutrition:

Autotrophic Nutrition:

It is a type of nutrition in which organisms synthesize their energy sources that are high energy organic molecules (food) from low energy inorganic raw materials available in their surroundings. The chief source of carbon and nitrogen are carbon dioxide and nitrates. Green plants (containing green pigment chlorophyll) and certain bacteria can manufacture their own food (organic substances) from inorganic substances (CO₂ and H₂O) using energy from sunlight. This mode of nutrition is called autotrophic mode of nutrition. The result of autotrophic nutrition is the formation of glucose.

Green plants and plants like blue-green algae and bacteria such as cyanobacteria are considered to be examples of autotrophs.

Symbiotic Nutrition:

In this case, two organisms or animals might live in association and derive nutrition from each other. This dependence on each other is called mutualism. For example, Escherichia coli that lives in the intestine of man synthesizes vitamin B12 which is used by man and E. coli receives in return, simpler food from the intestine of man. Rhizobium bacteria living in the roots nodules of leguminous plants fix atmospheric nitrogen in nitrates form in the soil, which is absorbed by the plant. Nitrates are useful for the growth of the plant. In turn, the rhizobium bacteria gets nutrition from the plant. In lichens fungus in it absorb moisture from the atmosphere and give into the algal part. In turn, it gets food from algae.

Heterotrophic Nutrition:

In this mode of nutrition the food (organic and inorganic substances) obtained by feeding on other organisms. Heterotrophic Nutrition is further classified as holozoic nutrition, saprophytic nutrition, and parasitic nutrition.

• Holozoic Nutrition: In this mode, the organisms engulf the food into the body, digest it and absorb the soluble products of digestion, e.g. humans.
• Saprotrophic Nutrition: Some organisms do not ingest solid food. Such organisms secrete digestive enzymes on to dead or decaying organic matter and absorb the products of digestion. The food is digested outside the body of the organism. e.g. certain bacteria and fungi. Other examples are spiders, houseflies, etc.
• Parasitic Nutrition: In this mode, the food is derived from other living organisms by living on or inside their bodies. The parasites thrive on liquid food materials obtained from the body of the host. The host may or may not suffer as a result of this relationship. e.g. certain bacteria, roundworm, tapeworm, Cuscuta, Plasmodium, Trypanosoma, Taenia, and Ascaris, etc.

Types of Nutrients:

Nutrients include both organic and inorganic compounds. The organic compounds include carbohydrates, proteins, fats, and vitamins. Inorganic compounds contain minerals and water.

Depending upon the quantity of nutrients in food the nutrients are classified as macronutrients and micronutrients.

• Macronutrients: Those nutrients which are needed in large amounts are called macronutrients. Carbohydrates (sugar), lipids (fats), and proteins are macronutrients. They are the main source of energy and source of carbon (sugars) and organic nitrogen (amino acids) to the organism.
• Micronutrients: They are nutrients which are needed in a small amount. Vitamins and minerals are micronutrients. They play important roles in human development and well-being, including the regulation of metabolism, heartbeat, cellular pH, and bone density. Lack of micronutrients can lead to stunted growth in children and increased risk for various diseases in adulthood.

Nutrition in Animals

Animals are heterotrophs and hence they depend on other organisms (plants and other animals) for their food. All animals can be divided into three groups on the basis of their food habits. These are:

• Herbivores: Those animals which eat only plants are called herbivores. Examples are Goat, Cow, and Deer etc.
• Carnivores: Those animals which eat only other animals as food are called carnivores. Examples are Lion, Tiger, and Lizard etc.
• Omnivores: Those animals which eat both, plants and animals are called omnivores. Examples are Man, Dog and Crow etc.

Steps in Animal Nutrition (Holozoic nutrition):

The breakdown of complex food constituents and their absorption is accomplished by the digestive system. The processes involved in nutrition are:

Ingestion:

In this step, food is taken from outside into the alimentary canal through the mouth. It involves taking in food, chewing or sucking it and swallowing. These animals are variously adapted, both internally and externally, fo the ingestion of the specific type of food they take in. Depending upon the gross size of food, feeding in animals is classified into two categories: Microphagy (feeding on microscopic organisms: e.g. Amoeba, Paramoecium) and macrophagy (feeding on larger forms of organisms, e.g. the majority of chordates and some non-chordates).

Digestion:

It is the breaking down of complex constituents of food by enzymes into simpler soluble forms that can be absorbed and utilized by the cells of the body. In this step, the covalent bonds in the organic food molecules like carbohydrates, lipids, protein, and carbohydrates are broken down by the process of hydrolysis. Different enzymes act as a catalyst at different stages of digestion.

Absorption:

The absorption step involves absorbing digested food through the intestinal wall to reach the body tissues.

Assimilation:

These absorbed molecules are then used for the construction of their own molecules or body substances. Utilization of digested food nutrients by the body tissues for energy and synthesis of new protoplasm for growth and repair.

Egestion:  

The whole food which we eat is not digested by our body, a part of the food remains undigested which cannot be used by the body and so it is removed from the body. The process of removal of undigested and unabsorbed food from the body is called egestion or defecation.

Types of Digestion:

Generally, two types of digestion are seen in heterotrophs: (a) Intracellular (b) Extracellular

Intracellular Digestion (Intra = inside):

In this type of digestion, all the five steps of nutrition (ingestion, digestion, absorption, assimilation, and egestion) occur inside the cell itself, as in Amoeba, Paramecium and other unicellular animals. Intracellular digestion is defined as the process in which animals that lack a digestive tract bring food items into the cell for digestion and for nutritional needs.

Intracellular digestion in Amoeba:

Food particles such as minute bacteria are enclosed (caught) by pseudopodia to form a food vacuole (Ingestion). Enzymes from the cytoplasm are secreted into the food vacuole (phagosome) to break down complex food. (Digestion). The food vacuole changes into a digestive vesicle (phagolysosome) within a cell by the fusion of phagosome containing ingested material and a lysosome containing hydrolytic enzymes. It leads to the digestion of food.

Digested food is absorbed into the cytoplasm. (Absorption). The absorbed food is used up wherever required in the cell. (Assimilation). The undigested unabsorbed food is expelled, when the food vacuole comes near the cell surface and bursts open. (Egestion). Food vacuoles are temporary structures and every time the Amoeba feeds, a new food vacuole is produced.

Extracellular Digestion (extra = outside):

In this type, the digestion occurs outside the cell. All animals (excluding sponges) carry out extracellular digestion.

The animals showing extracellular digestion have either a cavity, a tube, or a food canal (alimentary canal) which receives the ingested food. Digestive enzymes are poured over the food during its passage through the alimentary canal, and the products of digestion are absorbed back into the cells through the walls of the intestine. The undigested, unabsorbed food is thrown out of the digestive cavity.

Fungi and other decomposers perform extracellular digestion. They suck the life out of their host by releasing chemicals which break down the food they are living on. Once broken down their cells absorb the nutrients released.

Joint Intracellular and Extracellular Digestion:

In Hydra and other Cnidarians, the food (tiny prey) is caught by the tentacles and ingested through the mouth into the single large digestive cavity, called a gastrovascular cavity.

Enzymes are secreted from the cells bordering this cavity and poured on the food for extracellular digestion. Small particles of the partially digested food are engulfed into the vacuoles of the digestive cells lining the gastrovascular canal for intracellular digestion. Any undigested and unabsorbed food is finally thrown out of the mouth.

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Depending upon the interaction between the bodies and level of contact forces are classified a) Contact forces b) Non-contact forces. Muscular force is a contact force. Electrostatic force is non contact force.

Contact Forces:

A force which can be applied only when it is in contact with an object is called a contact force. All mechanical forces are contact forces. The following are the examples of contact force.

Muscular Force: The force resulting due to the action of muscles is known as muscular force. Muscular force can be applied only when it is in contact with the object. For ease, a rope or handle may be used. We use muscular force to different activities using hands like lifting, throwing, catching, etc. We use the muscular force of animals to simplify our work. We use instruments with the help of muscular force. Examples of the use of muscular force are cutting of vegetables or fruits using a knife, hammering of a nail, kneading of the dough, bullocks ploughing in the field, horse pulling a cart, etc.

Friction: The force of friction always acts on all the moving objects and its direction is always opposite to the direction of motion. It always acts a point of contact between the two bodies. i.e. It arises due to contact between the two surfaces. Examples: When a vehicle is moving on a road, there is a force of friction between the surface of the road and tyres at the point of contact. Other examples are a ball rolling on ground stops after some time due to friction between the ball and the ground. If we stop pedaling a bicycle. It stops after some distance. It is due to friction between the road surface and the tyres. It is difficult to slide heavier objects on the ground. After some time the tyres of vehicle wear and tear.

Types Of Contact Forces

There are 6 kinds of forces which act on objects when they come into contact with one another. Remember, a force is either a push or a pull.

• Normal Force: A book resting on a table has the force of gravity pulling it toward the Earth. But the book is not moving or accelerating, so there must be opposing forces acting on the book. This force is caused by the table and is known as the normal force.
• Applied Force: Applied force refers to a force that is applied to an object such as when a person moves a piece of furniture across the room or pushes a button on the remote control. A force is applied.
• Frictional Force: Frictional force is the force caused by the relative motion of two surfaces that come into contact with each other.
• Tension Force: Tension force is the force applied to a cable or wire that is anchored on opposite ends to opposing walls or other objects. This causes a force that pulls equally in both directions.
• Spring Force: The spring force is the force created by a compressed or stretched spring. Depending upon how the spring is attached, it can pull or push in order to create a force.
• Resisting Forces: The air resistance is a special type of frictional force that acts upon objects as they travel through the air. The force of air resistance is often observed to oppose the motion of an object. This force will frequently be neglected due to its negligible magnitude (and due to the fact that it is mathematically difficult to predict its value). It is most noticeable for objects that travel at high speeds (e.g., a skydiver or a downhill skier) or for objects with large surface areas.

Non-Contact Forces:

A force which can be applied without any contact with two bodies is called a non-contact force. The following are examples of non-contact force.

• Magnetic Force: The force exerted by a magnet is called a magnetic force e.g. Like poles of a magnet repel each other, while unlike poles attract each other. These forces exist without contact between the two magnets. e.g. i) Magnet attracts Cobalt, Nickel, Iron and steel towards itself. ii) When two magnets are brought near then South-South, North – North poles repel each other. While North and South pole attracts each other.
• Electrostatic force: The force exerted by a charged body is called an electrostatic force e.g. Like charges repel each other, while unlike charges attract each other. These forces exist without contact between the two bodies. e.g. i) When a comb is run through dry hair, then the comb can attract small pieces of paper. ii) If we bring a charged comb near our hair, they rise towards the comb. iii) A charge is developed on synthetic fibre due to rubbing. iv) We can hear the cracking sound of sparks when taking off or putting on woolen or synthetic clothes.
• Gravitational force: The force exerted by the earth on a body is called gravitational force. Actually this force exists between any two bodies in the universe. This force is always of attraction. e.g. When a body is dropped from a height it moves in a downward direction towards the Earth with increasing speed (with constant acceleration). This constant acceleration by which all bodies fall down is called acceleration due to gravity. Its value is 9.8 m/s² (approx 10  m/s² )on the surface of the earth. e.g. i) A fruit from tree falls down; ii) Water falls down on the ground from a tap. iii) We feel the weight of a bucket full of water holding in our hand.

Force field:

Region or space in which non-contact force such as magnetic force, gravitational force, electrostatic force acts is called force field. The region surrounding a magnet, where magnetic substance experiences force is called the magnetic field. The region surrounding an electric charge, where electric charge experiences force is called the electric field. Thus a field is a sphere of influence of non-contact force.

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The body of a typical flowering plant can be divided into the underground root system and aerial shoot system. The shoot system is heterogeneous.  The shoot system (stem) is an aerial and erect part of the plant body that grows upwards. It is usually above the soil and develops from the plumule of the embryo of a germinating seed. It consists of a stem, branches, leaves, flowers, fruits, and seeds. In this article, we shall very important of a plant, the leaf.

The leaf is lateral, generally flattened structure borne on the stem. A leaf may be defined as “A dorsoventrally compressed, lateral appendage of the stem, produced at the nodes and is specialized to perform photosynthesis. It develops at the node and bears a bud in its axil. The axillary bud later develops into a branch. Leaves originate from shoot apical meristems and are arranged in an acropetal (outward) order. They are the most important vegetative organs for photosynthesis.

Characteristics of Leaf:

• The leaf is a thin, expanded, green structure. The green colour is due to the presence of chlorophyll pigment.
• An auxiliary bud is present at the axil of each leaf.
• It is borne on the stem at the node, hence it is exogenous.
• It does not contain apical bud required for continuous growth hence it has limited growth.
• The lamina possesses prominent vascular strands called veins.
• Leaf bears abundant stomata for the exchange of gases.

The Structure of the Leaf:

A typical leaf consists of three main parts: leaf base, petiole, and lamina. The leaf is attached to the stem by the leaf base (hypo-podium) and may bear two lateral small leaf-like structures called stipules. The leaves with stipules are called stipulate leaves and the leaves without stipules are called ex-stipulate leaves. The main functions of stipules are to protect the bud and carry out photosynthesis. In monocotyledons, the leaf base expands into a sheath covering the stem partially or wholly. In some leguminous plants, the leaf base may become swollen, which is called the pulvinus. It protects the young axillary bud.

The petiole (mesopodium) is a cylindrical or sub-cylindrical smooth or grooved stalk of the leaf which lifts the lamina above the level of the stem.  Leaves that possess petiole are called petiolate leaves and those without petioles are called non-petiolate or sessile leaves. In papaya the petiole is hollow. The petiole help to hold the blade to light and also in conduction. Long thin flexible petioles allow leaf blades to flutter in wind, thereby cooling the leaf and bringing fresh air to the leaf surface.

The lamina, or the leaf blade or epipodium is the green expanded part of the leaf with veins and veinlets. There is, usually, a middle prominent vein, which is known as the midrib. Veins provide rigidity to the leaf blade and act as channels of transport for water, minerals and food materials. The shape, margin, apex, surface, and extent of incision of lamina varies in different leaves. The main functions of the lamina are photosynthesis and transpiration.

In dicots, the leaves are dorsiventral because its dorsal and ventral surfaces are structurally different. In monocots the dorsal and ventral surfaces of leaves are structurally identical, hence they are called isobilateral.

In some plants the shape and form of leaves are such that it is difficult to distinguish between the two surfaces, such leaves are called centric or cylindrical leaves. e.g. onion, garlic, etc.

Venation:

The arrangement of veins and the veinlets in the lamina of a leaf is termed as venation. Veins and veinlets are skeletal as well as conducting prominences visible on the surface of the lamina, especially the under surface in dorsiventral leaves.

Functions of Venation:

• Venation provides skeletal support to the lamina so that it can remain stretched for its optimum functioning,
• Veins and veinlets reduce the effect of wilting.
• They are important for the conduction of water and nutrients.

Types of Venation:

Reticulate Venation:

When the veinlets form a network, the venation is termed as reticulate. e.g. leaves of dicots,  Peepal (Ficus religiosa) (पीपल), Shoe-Flower (Hibiscus rosasinensis) (जास्वंदी), etc.(exceptions: Calophyllum, Corymbium, Eryngium).  It is further divided into two types.

Pinnate or Unicostate Reticulate Venation: 

The lamina has a single principal vein or midrib which extends from its base to apex. It gives rise to lateral veins along its entire length. Veins bear veinlets. The veinlets form reticulations. e.g. Mano, Peepal.

Palmate or Multicostate Reticulate Vena­tion: 

A number of prominent or principal veins arise from the tip of the petiole and reach either the apex or margins of the lamina. They give rise to lateral veins connected by reticulations of veinlets. It may be convergent (as in Ziziphus (बेर), Smilax) or divergent ( as in grapevine, lufia).

Parallel Venation:

When the veins run parallel to each other within a lamina, the venation is termed as parallel venation. There is a single principal vein or midrib that runs from base to the apex of the lamina. The lateral veins run parallel to one another without forming anastomoses e.g. leaves of monocots, maize, grass, banana (Musa paradisiaca), canna. etc. It is further divided into two types.

Pinnate or Unicostate parallel Venation: 

There is a single principal vein or midrib that runs from base to the apex of the lamina. The lateral veins run parallel to one another without forming anastomoses e.g. banana, canna

Palmate or Multiicostate convergent parallel Venation: 

Several parallel principal veins arise from the base of the lamina and converge towards the apex, e.g., Bamboo, Grass, etc.

Palmate or Multiicostate Divergent parallel Venation: 

Several parallel principal veins arise from the base of the lamina and proceed towards the margins, e.g., Fan Palm (Livistonia).

Furcate Venation:

The veins branch dichotomously. The finer branches do not form a reticulum. (e.g., ferm Adiantum, Circeaster)

Types of Leaves:

A leaf is said to be simple, when its lamina is entire or when incised, the incisions do not touch the midrib.

When the incisions of the lamina reach up to the midrib breaking it into a number of leaflets, the leaf is called a compound.

A bud is present in the axil of petiole in both simple and compound leaves, but not in the axil of leaflets of the compound leaf.

Types of Compound Leaves:

Pinnately Compound Leaves:

In a pinnately compound leaf, a number of leaflets are present on a common axis, the rachis, which represents the midrib of the leaf as in neem. They are further classified as

Unipinnate Compound Leaves: If the leaflets arise on primary rachis itself then it is known as unipinnate compound leaf. If the number of leaflets is odd it is known as imparipinnate compound leaf and if it is an even then it is known as a paripinnate compound leaf. Example: Azadirachta indica (Neem)

Bipinnately Compound Leaves: In this type, the primary rachis gets branched once and the leaflet arises on the secondary rachis. Example: Mimosa pudica (Touch me not)

Tripinnately Compound Leaves: In this type, the rachis gets branched twice and the leaflet arises on the tertiary rachis. Example: Moringa oleifera (drumstick)

Decompound Compound Leaves:

In this type, the rachis gets branched thrice or more than thrice and the leaflets arise on the ultimate branches. Example: Coriandrum sativum (coriander)

Palmately Compound Leaves:

In palmately compound leaves, the leaflets are attached at a common point, i.e., at the tip of the petiole, as in silk cotton.  On the basis of the number of leaflets they are further classified as

• Unifoliate Palmately Compound Leaves: With a single leaflet. Examples: Citrus limon (lemon), Citrus maxima (papanas).
• Bifoliate Palmately Compound Leaves: With two leaflets. Example: Bauhinia Yunnanensis (butterfly tree / kanher).
• Trifoliate Palmately Compound Leaves: With three leaflets. Example: Clover (Ran methi).
• Quadrifoliate Palmately Compound Leaves: With four leaflets. Example: Oxalis, MarsileaMultifoliate Palmately Compound Leaves: With more than four leaflets. Examples: Baobab, Umbrella plant.

Phyllotaxy:

Phyllotaxy is the pattern of arrangement of leaves on the stem or branch. This is usually of three types alternate, opposite and whorled.

• In an alternate type of phyllotaxy, a single leaf arises at each node in an alternate manner, as in China rose, mustard and sunflower plants.
• In the opposite type, a pair of leaves arise at each node and lie opposite to each other as in Calotropis and guava plants.
• If more than two leaves arise at a node and form a whorl, it is called whorled, as in Alstonia.

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In this article, we shall study the modification in stem in some plants for performing the functions other than its primary function. Primary functions of the stem are

• To support and orient the leaves in a manner that they are exposed to maximum sunlight and for efficient gaseous exchange during photosynthesis and respiration.
• To conduct water and minerals from roots to leaves and manufactured food from leaves to different parts of the plant.
• To bear flowers and fruits

Some stems perform the function of storage of food, support, protection, and vegetative propagation. The secondary functions of the stem are

Underground Modification of Stem:

Since underground, they may seem like roots but they have characteristics of the stem, like the presence of nodes and internodes, scaly non-green leaves and buds. This modification serves two functions it acts as perennating structures by remaining leafless and dormant in winter but giving off aerial shoots under favourable conditions (next season) and Store food and become thick and fleshy.

Rhizome:

It is a prostrate, dorsoventrally thickened brownish stem, which grows horizontally under the surface of the soil. It shows distinct nodes and internodes. It shows distinct nodes and internodes. It bears scale leaves on nodes, It possesses terminal bud and axillary buds in the axil of each scale-leaf present at the node. Adventitious roots are present. e.g. Ginger (अद्रक), Turmeric (हलदी).

Stem Tuber:

Tubers are actually the swollen tips of ends of special underground branches swollen due to the storage of food as starch. The tubers show nodes and internodes. Nodes bear scale leaves with axillary buds, commonly called eyes. Under favourable conditions eyes sprout and produce aerial roots. Thus tubers help in vegetative propagation. They do not produce adventitious roots. e.g. Potato (आलू).

Bulb:

It is a condensed disc like an underground stem. The upper surface of the disc-like stem is conical and bears centrally placed apical bud and many concentrically arranged overlapping scale leaves. Scale leaves store food.  When the scale leaves surround the apical bud in the form of concentric rings, it is called a tunicated bulb. The lower surface of the stem produces adventitious roots. e.g. onion (प्याज).

When the scale leaves partially surround the apical bud by overlapping each other, it is called a scaly bulb. The lower surface of the stem produces adventitious roots. e.g. garlic (लहसुन).

Corm:

It is condensed disc-like underground, fleshy, spherical stem with flattened base, It grows vertically, bears many scale leaves, distinct nodes and internodes, buds and adventitious roots. e.g.  Saffron (केसर), yam (जिमीकंद), gladiolus.

Sub Aerial Modification Of Stem:

Stems are weak, therefore lie prostrate on the ground or may get partially buried in the upper layer of soil. The plants bearing such stems are called creepers. Their stems serve the function of vegetative propagation.

Runner:

The basal internodes of the bud elongate horizontally and trail along the soil carrying the bud to a distance from the mother plant where it gets fixed to the soil by means of adventitious roots and develops a new daughter plant. This branch carrying the bud is called a runner.  It grows in all the direction and a single plant soon covers a large area by its pro­geny. e.g. Grass, Oxalis, Centella asiatica, strawberry, etc.

Stolon:

When a weak lateral branch which grows upwards then arches down to meet the soil, strike roots and produce daughter plants. The difference between the runner and stolon is, runner grows horizontally, while stolen grow obliquely upward and then arches to the ground. e.g. Mint (‘Pudina’), Jasmine.

Offset:

Like runner but thicker and shorter, grow for a short distance then produce cluster (rosette) of leaves above and adventitious roots below; generally in aquatic plants. It is just like the runner, only it is shorter and thicker. e.g. water hyacinth (Eichhornia crassipes), pistia (Pistia stratiotes), water lettuce

Sucker:

An underground runner that grows horizontally for a distance under soil then emerges obliquely upwards, strikes roots and forms daughter plants. e.g. Chrysanthemum, Mentha arvensis, banana, pineapple etc.

Aerial Modification of Stem:

The whole stem or its part (axillary or terminal bud) gets modified to perform definite functions. It is a stem because they show characteristics like a) Arise in the axil of leaf b) Bear nodes and internodes c) may bear leaves, buds, flowers.

Stem Tendrils:

Stem or its branches get modified into green threadlike, spirally coiled leafless structures called tendrils which are meant for climbing. They twine around neighbouring objects and help weak plants to climb. These may be branched or unbranched. A scale leaf is always present at the point of branching of the tendril. e.g. Grapevine, cucumber, pumpkins, watermelon, etc.

Thorns:

These are straight, pointed, hard or woody structures sometimes they bear leaves, flowers or may be branched. Axillary buds of stems get modified into thorns (e.g. Citrus, Duranta, and Aegel). In Carrissa, terminal buds get modified into thorns. Thorns are used as organs of defence against grazing animals or climbing (e.g. Bougainvillea) and to check transpiration.

Phylloclade:

These are fleshy, green flattened or cylindrical branches of unlimited growth with nodes and internodes. The leaves are modified into spines or scales to check transpiration. This modification of stem is observed in plants growing in dry regions. The stem takes part in photosynthesis and stores water. e.g. Opuntia, Euphorbia, Casuarina, Cocoloba etc.

Cladode or Cladophylls:

It is a phylloclade with limited growth i.e. with only one or two internodes; help in photosynthesis. These are a green cylindrical or flattened leaf-like branches. In Asparagus, the cladodes are one internode long and in Ruscus, the cladodes are two internodes long. They help in photosynthesis.

Bulbil:

These are modified vegetative or floral buds with stored food and meant for vegetative propagation. In Dioscorea, bulbils are condensed axillary buds while in Agava and lily the floral buds develop into bulbil. They detach to develop into a new plant.

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The body of a typical flowering plant can be divided into the underground root system and aerial shoot system. The shoot system is heterogeneous. The shoot system (stem) is an aerial and erect part of the plant body that grows upwards. It is usually above the soil and develops from the plumule of the embryo of a germinating seed. It consists of stem, branches, leaves, flowers, fruits, and seeds.

The Stem:

The stem is negatively geotropic (moves above the soil), negatively hydrotropic (moves away from the water) and positively phototropic (moves towards the light). Branches arise from axillary buds present in the axil of leaves. Each axillary bud is a small, compact, underdeveloped shoot covered with a large number of overlapping leaf primordia. Internodes of this bud enlarge and develop into a branch. Therefore the development of branches is exogenous (exo = outside).

Characteristics of Stem:

• Stem arises as a prolongation of plumule (one end of an embryo).
• The shoot system is heterogeneous and consists of stem, branches, leaves, and flowers.
• The stem is negatively geotropic (moves above the soil), negatively hydrotropic (moves away from the water) and positively phototropic (moves towards the light). 
• The stem bears nodes and internodes. The regions of the stem where leaves are born are called nodes while internodes are the portions between two nodes.
• The stem bears vegetative buds which could be terminal (apical bud) for the plant to grow upwards or axillary (bud in the axil of the leaf) which give rise to lateral branches. The stem bears floral buds (terminal or axillary) that grow into flowers
• The young stem is green in colour and thus it is photosynthetic. The mature stem is generally green when young and later often become woody and dark brown.
• Lateral branches of the stem are exogenous in origin.

Functions of the Stem:

Primary functions of the stem are

• To support and orient the leaves in a manner that they are exposed to maximum sunlight and for efficient gaseous exchange during photosynthesis and respiration.
• To conduct water and minerals from roots to leaves and manufactured food from leaves to different parts of the plant.
• To bear flowers and fruits

Some stems perform the function of storage of food, support, protection and vegetative propagation. The secondary functions of the stem are

• Storage:  Some stems store food and water in some plants e.g. potato
• Perennation: The underground stems help tide over the unfavourable growing periods e.g. ginger, turmeric.
• Vegetative propagation: e.g. rose, and sugarcane the stem can be used for vegetative propagation.
• Photosynthesis: In xerophytes (desert plants) the leaves are reduced to thorn, the stem possessing chlorophyll takes up the function of photosynthesis. e.g.Opuntia
• Protection: In some plants, the axillary bud modifies into the thorn and protects the plants from grazing animals e.g. citrus, Duranta.
• Support, Climbing and Clinging: Tendrils or hooks are modified branches or buds. They coil around
  the support and help the plant to climb e.g. grapevine.

Types of Stem: 

The stem may be

• aerial (erect, rigid, strong and upright as in herbs, shrubs, and trees) or
• subaerial (weak, unable to stay upright and trail on the ground as creepers or climb up as climbers) or
• underground (buried in soil and produces aerial branches under favourable conditions only

Branching of Stem:

There are three main forms of branching.

• Excurrent:  the main trunk goes the entire height of the tree, with branches forming patterns; e.g. Evergreens, pinus.
• Decurrent: The main trunk continues up about halfway, then splits into more than one main branch; eg. fruit trees.
• Columnar or Coudex: The main trunk continues the full height of the tree, with the branches forming only at the top; eg. Palm trees, coconut tree.

Lateral Branching:

Branching is racemose or cymose according as the lateral buds are less vigorous or more vigorous than the apical bud.

Racemose Branching:

In racemose or monopodial branching the apical bud of the plant grows indefinitely giving rise to a straight stem axis or podium on which the lateral buds grow in acropetal succession, i.e. older branches are borne near the base and younger branches towards the apex.

This type of branching is the commonest among young Phanerogams. as the plant grows older, the apical bud often gets lost and some side branches become very strong so that the plant loses its monopodial character.

Instead of there being a single leaf at each node there be a whorl of leaves, the branches at each node will also be whorled. Then it is called whorled racemose.

Types of Buds:

Small lateral or terminal protuberance on the stem of a vascular plant that may develop into a flower, leaf, or shoot is called bud. Buds arise from meristem tissues. Flower buds are modified leaves. Buds are classified as follows:

Types of Buds on the Basis of Their Function:

Vegetative buds:

They contain embryonic leaves or shoots. They grow into new branches and shoots.

Floral buds:

They contain embryonic flowers. They grow into flowers. They are also referred as reproductive buds.

Mixed buds:

They contain both embryonic leaves and flowers. They may gro into vegetative parts like soot or leaf or into a flower part.

Tendrillar buds:

They grow into tendrils.

Types of Buds on the Basis of Its Position:

On the basis of the position of the buds, they are classified as terminal or apical buds and lateral buds.

Terminal or apical buds:

They develop at the apex of the main stem or branch. e,g, cabbage is a large apical bud

Lateral buds:

They develop into lateral branches or flowers. They are further classified as axillary buds, accessory buds, and sub-petiolar buds. Axillary buds are lateral buds that arise in the axil of the leaf, e.g. Sunflower, Citrus, Rose. Accessory buds are more than one bud that arises in the axil of a single leaf. e.g. Cucurbita, Luffa, Brinjal, Chilly, Bougainvillaea. Subpetiolar buds are axillary buds those are covered by a sheathing leaf base and appear to arise from the leaf base. As they remain dormant for a quite long time they are also referred as dormant buds. When they gro they are referred as sprouting buds. e.g. Dalbergia sissoo (Shisam) and Mulberry.

Bud Scales:

In some plants, buds are covered by overlapping scales, these scales are called bud scales. These bud scales are tough and may be modified leaves, leaf bases, petioles or stipules. e.g. Jackfruit, Ficus, and Magnolia.

Winter Buds:

In extremely cold regions plants bear specially protected buds called winter buds. During cold period leaves fall but the winter buds remain intact. During spring the bud opens with developing young leaves. e.g. Cauliflower, Cabbage.

Adventitious Buds:

They arise at a position other than their normal position. Epiphyllous or foliar buds arise on leaves. e.g. Begonia, Bryophyllum, etc. Cauline buds arise from the cut or pruned end of branches. e.g. Sweet potato, Coffee, Aegle, etc. Radical buds develop on the roots. e.g. Sweet potato, Dahlia, Dalbergia.

Turions Buds: 

A turion bud is a resistant plant bud that is found in certain aquatic plants and can allow the plant to survive winter in the vegetative state. e.g. Ultricularia, Potamogeton.

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In this article, we shall study the modification of roots for the purpose of food storage, respiration, support, etc. Roots in some plants change their shape and structure and become modified to perform functions other than absorption and conduction of water and minerals. They are modified for support, storage of food and respiration. We shall study the modification of roots for tap root system and adventitious system.

Modification of Tap Roots:

Modifications of Tap Root for Storage of Food:

Taproots of carrot, turnip and adventitious roots of sweet potato, get swollen and store food. The secondary roots remain thin. Hypocotyl, i.e. the embryonic region between cotyledons and radicle may also join the taproot in storing food. The stem is reduced and disc-shaped in the beginning and bears radical leaves.  Depending upon their shapes they are further classified into four types.

Modifications of Tap Root for Better Respiration:

The plants growing in saline, swamps, marshy places, and salt lakes are called halophytes. Such plants e.g.  Rhizophora growing in swampy areas (mangroves), many roots come out of the ground (negatively geotropic) and grow vertically upwards. Such roots, called pneumatophores. They help to get oxygen for respiration. The roots appear like conical spikes coming out of the water.  They occur in large numbers near the tree trunk. Exposed root tips possess Rhizophora minute pores (lenticels or pneumatothodes) through which roots respire. e.g. Rhizophora, Avicennia, Sonnerita, Heritiera (सुंद्री found in Sunderbans, Bengal).

Characteristics of Respiratory Roots:

• These are modified tap roots.
• These are non-green and non-photosynthetic
• They are found in marshy habitats like swamp and mangroves near seashores
• They grow vertically upward in response to gravity i.e. they are negatively geotropic.
• These roots are covered with cork and the gaseous exchange takes place through pores called lenticels

Nodulated Roots:

In legumes (pea family), the secondary roots of primary tap root bear small tubercles or swellings which are called root nodules. These nodules shelter nitrogen-fixing bacteria Rhizobium leguminosarum. They help in fixing atmospheric nitrogen into nitrates which can be absorbed by the roots.

Modifications of Adventitious Roots:

Modifications of Adventitious Root for Storage of Food:

Simple Tuberous Roots: 

These roots are creeping and become swollen and do not assume any shape. They are always borne singly. These roots arise from nodes of prostrate stem and enter in the soil. e.g. sweet potato (Ipomoea batatus) (शकरकंद).

Fasciculated Tuberous Roots: 

It is a cluster of adventitious roots for the storage of food. These roots have a definite shape. e.g. Dahlia, Asparagus (शतावरी)

Nodulose Roots:

Only apices of roots become swollen like single beads. e.g. mango, ginger, turmeric

Beaded or Moniliform Roots:

Roots alternately swollen and constricted which has beaded or moniliform appearance. e.g. Grasses, sedges, momordica.

Annulated Roots:

Looks like number of disc placed one above the other. e.g. Ipecac

Modifications of Adventitious Roots for Support:

Prop Roots:

The hanging structures that support a banyan tree are called prop roots. Roots develop from tree branches hang downwards and ultimately penetrate the ground, thus provide support to heavy branches. A banyan growing in Indian Botanical garden, Owrah (Kolkata) has nearly 1700 such prop roots and has a very large spread. The tree is about 200 years old. Another example is the mangrove plant Rhizophora.

Characteristics of Prop Roots:

• They arise from the branches of the stem.
• They hang down vertically and enter the soil.
• They are quite long.
• They behave like a pillar and give support to the plant.

Stilt Roots:

The stems of maize and sugarcane have supporting roots coming out of the lower nodes of the stem. These are called stilt roots. They are mainly found in monocots, shrubs and small trees. They grow obliquely downwards and penetrate the soil. Their primary function is to provide support to the plant. In plants like maize, bajra, sugarcane, jowar, they grow in whorls.  In screwpine(केवडा) or Pandanus (a tropical palm-like tree) these roots arise only from the lower surface of the obliquely growing stem to provide support. Another example is bamboo.

Characteristics of Stilt Roots:

• They develop from basal nodes of the stem.
• They grow obliquely from the stem.
• They are shorter in length
• They provide support to the plant as the ropes provide to the tent.

Climbing Roots:

Such plants produce roots from their nodes, by which they attach themselves to some support and climb over it. Weak climbers twine around and clasp the support with the help of climbing roots arising from their nodes. e.g. Money plant, black pepper (kali mirch), betel (pan). In Ivy, adhesive disc grows from climbing roots.

Clinging Roots: 

Special clinging roots arise, enter the crevices of support and fix the epiphyte. e.g. epiphytes orchids

Buttress Roots:

They are present at the basal part of the stem and spread in different directions in the soil. They are vertically elongated and horizontally compressed. They look like planks e.g. Ficus, Bombax, Terminalia.

Modifications of Adventitious Roots for Special Functions:

Epiphytic Roots:

Some plants like orchids grow on horizontal branches of big trees in the forest to get sunlight. They are autotrophic. These plants are called epiphytes. They develop special areal hanging roots called epiphytic roots. These roots are spongy. Due to the presence of velamen tissue are hygroscopic and have a porous wall. They absorb moisture from the atmosphere. e.g. vanda, dendrobium, etc. These roots are also called assimilatory roots due to their partial capacity of photosynthesis.

Sucking Roots or Haustoria or Parasitic Roots:

These are highly specialized and microscopic roots, developed by parasites to absorb nourishment from the host. In partial parasites penetrate only xylem element of the host and absorb water and minerals. E.g. Viscus album. In total parasites, they establish contact with both xylem and phloem of the host. Thus absorb water, minerals, and nutrients. e.g. Cuscuta, Orobanche, Viscum, Lorathus.

Floating Roots: 

Spongy, floating roots filled with air, arise from nodes of some aquatic plants, and help in floating and respiration. eg. Jussiaea

Photosynthetic or Assimilatory Roots: 

Roots which when exposed to sun develop chlorophyll, turn green and manufacture food. e.g. Tinospora (gilo) and orchids. In Tinospora, the roots arise as green hanging threads. Other examples are Taeniophyllum, Trapa ( Singhara), and Podostemon.

Characteristics of Assimilatory Roots:

• These are modified adventitious roots.
• These are green and photosynthetic
• They are found in diverse habitats like aquatic, terrestrial and epiphytes.
• They grow horizontally in response to gravity and hence referred as diageotropic similarly, they show branching pattern and hence they are also referred as plagiotropic.
• Gaseous exchange takes place through the general surface.

Mycorrhizal Roots: 

This is a symbiotic association between higher plants and fungus. In some plants, roots become associated with fungal hyphae. This association of a fungus with higher plants is called mycorrhiza. The fungus absorbs water and minerals from the soil, in turn, the plant provides organic food to the fungus. Example: Pinus, Monotropa

Reproductive Roots:

Adventitious roots of some plants develop buds that give rise to leafy shoots. These roots help propagation. Example: sweet potato

Contractile Roots:

These roots can be found on underground rhizome, bulb, tuber, corm, etc. of some plants. They maintain a proper level of the plant in the soil. Example: Cracus, Freesia, Canna.

Root Thorns:

In some plants, roots are modified by hard pointed thorn-like structures called root thorns. e.g. Pothos armatus and Acanthorrhiza.

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