Class 11th PCMB Notes

Class 11 Biology Revision Notes for Excretory Products and their Elimination of Chapter 19

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• Elimination of metabolic waste products from the animal body to regulate the composition of body fluids and tissues is called excretion. These waste products include ammonia, uric acid, urea, carbon dioxide and ions like Na+Na+, K+K+, Cl^– and phosphates and sulphate.
• Ammonia is the most toxic and uric acid is the least toxic. The process of removing ammonia is called ammonotelism and organisms that excrete ammonia are called ammonotelic (bony fishes, aquatic amphibians and insects).
• The organism that release urea as nitrogenous wastes are called ureotelic (mammals, terrestrial amphibians). The organism that excretes uric acids is called uricotelic (reptiles, birds and land snails).

Animals	Excretory organs
Flat worms, some annelids and cephalochordates.	Protonephridia or flame cells.
Earthworms and annelids	Nephridia
Insects including cockroaches	Malpighian tubules
Mammals	Kidney

Human Excretory System
Human excretory system consists of:

1. A pair of kidneys
2. A pair of ureters
3. A urinary bladder
4. A urethra

• Kidneys are reddish brown bean shaped structure situated between last thoracic and lumber vertebra. Each kidney has a notch on its inner side called hilum through which ureter, blood vessels and nerves enter.

• Inside the hilum has broad funnel shaped space called renal pelvis with projection called calyces.

• Inside the kidney are two zone- outer cortex and inner medulla. Medulla is divided into medullary pyramids projecting into calyx.
• Cortex extends between medullary pyramids as renal column called Columns of Bertini.

• The functional unit of kidney is nephron. Each kidney contains about one million nephrons.
• Each nephron has two parts- the glomerulus and renal tubules. Glomerulus is the tuft of capillaries formed by afferent arteriole. Blood from glomerulus is carried away by efferent arteriole.
• Renal tubules starts with Bowman’s capsule continue with tubular parts divided into Proximal Convoluted tubules, Henle’s loop and Distal Convoluted tubule.

• The malpighian tubules, PCT and DCT of nephron are situated in cortical region where as loops of Henle’s into medulla.

Juxta medullary Nephrons	Cortical Nephrons
a. Loop of Henle’s is short and extend only a little into medulla.	a. Loop of Henle’s are very long and extend deep into medulla.
b. The glomeruli lie close to the inner margin of the cortex.	b. The glomeruli lie in the outer cortex.

Urine formation

• Glomerular capillaries blood pressure cause filtration of blood through 3 layers (endothelium of glomerular blood vessels, epithelium of Bowman’s capsule and basement layer between two membranes as ultra-filtration.
• The amount of filtrate formed by kidneys per minute is called glomerular filtration rate (GFR) which is 125 ml/minute.
• Glomerular Filtration rate is controlled by Juxta glomerular apparatus (JGA).
• 99% of filtrate has to be reabsorbed by renal tubules called reabsorption.

Function of Tubules

1. Proximal Convoluted Tubules (PCT) – all the important nutrients, 70-80% electrolytes and water are reabsorbed.
2. Henle’s Loop– maintains high osmolarity of medullary interstitial fluid.
3. Distal Convoluted Tubules (DCT) – conditional reabsorption of Na+ and water. Maintains pH and sodium- potassium balance.
4. Collecting Duct– large amount of water is reabsorbed to produce concentrated urine.

Mechanism of concentration of urine– The flow of filtrate in two limbs of Henle’s loop is in opposite direction to form counter current. The flow of blood in two limbs of vasa recta increase the osmolarity towards the inner medullary interstitium in the inner medulla.

• The transport of substance facilitated by special arrangement of Henle’s loop and vasa recta is called counter current mechanism.

Regulation of kidney function–

• Functioning of kidney is monitored by hormonal feedback mechanism of hypothalamus and JGA. Change in blood volume, body fluid and ion concentration activates the osmoreceptors in the body that stimulate the hypothalamus to release ADH or vasopressin hormones. The ADH facilitates water absorption in tubules.
• Decrease in glomerular blood pressure activate JG cells to release renin which converts angiotensinogen to angiotensin I and II that increase the glomerular blood pressure and release of aldosterone that increase absorption of Na+ ions and water.

Micturition – The process of expulsion of urine from the urinary bladder is called micturition. The neural mechanism that causes it is called micturition reflex. Urine formed in nephron is stored in urinary bladder till a voluntary signal is given by CNS. This initiates the contraction of smooth muscles of the bladder and simultaneous relaxation of the urethral sphincter causing the release of urine.

• Lungs, liver and skin also play important role in process of excretion. Lungs remove CO2CO2 and water, liver eliminates bile containing substances like bilirubin, biliverdin. Sweat glands remove NaCl, small amount of urea and lactic acid. Sebaceous glands excrete sterol, hydrocarbons and waxes.

Disorders of Excretory System

• Uremia– there is high concentration of non-protein nitrogen (urea, uric acid, creatinine). Urea can be removed by hemodialysis.
• Renal failure– also known as kidney failure where glomerular filtration is ceased and both kidney stops working. Kidney transplant is the ultimate method in correction of acute kidney failure.
• Renal Calculi– formation of stone or insoluble mass of crystallized salts formed within the kidney.
• Glomerulonephritis (Bright’s Disease)-inflammation of glomeruli of kidney due to entry of protein or red blood corpuscles in to filtrate due to injury.

Class 11 Biology Revision Notes for Body Fluids and Circulation of Chapter 18

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Body fluids are the medium of transport of nutrients, oxygen and other important substances in the body.

Blood is the most commonly used body fluid in most of the higher organisms. Lymph also transports certain substances like protein and fats.
Blood
Blood is a fluid connective tissue composed of a fluid matrix, plasma and the blood corpuscles. It forms about 30-35% of the extracellular fluid. It is slightly alkaline fluid having pH7.4.

• Plasma is straw coloured viscous fluid that constitutes 55% of blood volume. It consists of 90-92% water, 6-8% protein (fibrinogens, albumins and globulins), glucose, amino acids and small amount of minerals like Na+, Ca++, Cl^– etc.
• Erythrocytes, leucocytes and platelets are collectively called formed elements.
• Erythrocytes are most abundant cells in human body. Total blood count of RBCs is 5-5.5 million, which is slightly less in females due to menstruation. It is formed in bone marrow. Nucleus is absent in mammalian RBCs having biconcave shape.
• Every 100 ml of blood contain 12-16 gm. of haemoglobin. They have life span of 120 days. They are destroyed in spleen( graveyard of RBCs)
• Leucocytes or WBCs are colourless due to absence of haemoglobin. 6000-8000 of WBCs are present in each ml. of blood.

• Neutrophils are most abundant and basophils are least abundant WBCs. Monocytes and neutrophils are phagocytic cells which destroy foreign organisms.

• Basophils secrete histamine, serotonin and heparin that are involved in inflammatory reactions.
• Eosinophils resist infection and allergic reactions. B and T lymphocytes are responsible for immune response of the body.

Thrombocytes or platelets are cell fragments produced from megakaryocytes in bone marrow. 150000-350000 platelets are present in each ml of blood. Platelets are involved in clotting or coagulation of blood in case of injuries.
Blood Groups – blood of human beings differ in certain aspects although it appear same in all individuals. Two main types of grouping are ABO and Rh.
ABO grouping is based on presence or absence of two surface antigens RBC, antigen A and antigen B. The plasma of an individual also contains two antibodies produced in response of antigens.

• During blood transfusion, blood of donor has to be matched with blood of recipients to avoid clumping of RBCs.
• Group ‘O’ blood can be donated to any individual with any blood group, so it is called universal donor.
• Person with ‘AB’ blood group can receive blood from any person of any group, so it is called universal recipient.

Rh grouping – Rh antigen (similar to Rhesus monkey) are observed on surface of RBCs of majority of individuals (about 80%). Such people are called Rh positive (Rh+Rh+) and those in whom this antigen is absent are called Rh negative (Rh−Rh−).

• Erythroblastosis foetalis– if father blood is Rh+ and mother blood is Rh−Rh−, the foetus blood is Rh+. During the delivery of first child there is a possibility of exposure of mother blood with foetus blood to develop antibodies in mother blood. In subsequent pregnancy the mother’s blood can leak into foetus blood and destroy the foetus RBC. This case is called erythroblastosis foetalis.

Coagulation of blood (Blood Clotting)
When an injury is caused to a blood vessel bleeding starts which is stopped by a process called blood clotting. An injury or trauma stimulates the platelets in the blood to release certain factors that activate the mechanism of coagulation. Calcium play important role in blood clotting.
Lymph
During flow of blood through capillaries, some water soluble substances move out in the space between cells of tissues. This fluid released out is called interstitial fluid or tissue fluid. It is similar to the blood but has fewer blood proteins, less calcium and phosphorus and high glucose concentration.

• It is a colourless fluid containing specialized lymphocytes that provide immune response to body.
• Main function of lymph is to provide immunity, carry proteins and fats molecules and transport oxygen, food materials, hormones etc.

Circulatory Pathways

• All vertebrates have a muscular chambered heart.

Fish – 2 chambered heart
Amphibian and Reptiles (except crocodile) – 3 chambered heart.
Crocodile, Birds and Mammals – 4 chambered heart.
Human Circulatory System – consists of 4 chambered muscular heart, closed branching blood vessels and circulatory fluid blood.
Heart is the mesodermally derived muscular organ, present in thoracic cavity between the two lungs protected by double membrane of pericardium.

• The upper two chamber is called atria and lower two chambers are called ventricles. Interatrial septum separate the right and left atrium and thick walled inter ventricle septum separate the ventricles.
• The opening between right atrium and right ventricle is guarded by a three muscular flaps called tricuspid valve. Bicuspid or mitral valve guards the left atrium and ventricle.
• The opening of right and left ventricle to pulmonary artery and aorta respectively is controlled by semilunar valve.
• The nodal tissue present on upper right corner of right atrium is called SAN (sino-atrial node) and those on lower left corner of right atrium is called AVN ( atrio-ventricular node).
• The purkinje fibres along with right and left bundles form the bundle of HIS. The nodal musculature has ability to generate action potential.
• SAN generate maximum number of action potential and is responsible for rhythmic contraction of heart. Therefore it is called pace maker.

Cardiac Cycle

• To begin with, all four chambers are in relaxed state called joint diastole. As the bicuspid and tricuspid valves are open, blood from pulmonary vein and vena cava flows to left and right ventricle respectively. Semilunar valves are closed at this stage.
• SA node generates action potential that contracts both atria (atrial systole). The action potential passes to AV node and bundle of HIS transmit it to ventricular musculature to cause ventricular systole. At the same time atria undergoes relaxation diastole to close the bicuspid and tricuspid valve.
• Semilunar valves open into circulatory system that relax the ventricle and close the valves to prevent back flow of blood.
• As the pressure inside ventricle decreases the bicuspid and tricuspid valve open to repeat the process or cardiac cycle.
• During each cardiac cycle two sounds are produced. The first sound (lub) is due to closure of bicuspid and tricuspid valve and 2nd heart sound (dub) is due to closure of semilunar valve.

ECG (Electrocardiograph) is a graphical representation of electrical activity of heart during cardiac cycle. The electrocardiograph machine is used to obtain electrocardiogram. The patient is connected to three electrical leads to wrists and left ankle.

• The P-wave represents the electrical excitation of atria (depolarisation) which leads to contraction of atria.
• The QRS-wave represents the depolarisation of ventricles, which initiates the ventricular contraction.
• The T-wave represents the return of ventricle from exited to normal state (repolarization). The end of T-wave marks the end of systole. Counting the number of QRS complex in given period of time determine the heartbeat rate.

Double Circulation
Flow of same blood twice through the heart once in oxygenated form and other in deoxygenated form is called double circulation. It includes systematic and pulmonary circulation.
Systematic circulation includes flow of oxygenated blood from the left ventricle to all parts of body and deoxygenated blood from various body parts to the right atrium. All systematic circulation starts form aorta and ends at superior vena cava, inferior vena cava or coronary sinus to right atrium.
The systematic circulation provides oxygen, nutrients and other substances to the tissues and take CO2 and other harmful substances away for removal.

Pulmonary Circulation
The flow of deoxygenated blood from the right ventricle to the lungs and the return of oxygenated blood from the lung to the left atrium is called pulmonary circulation.
Two pulmonary veins from each lung transport the oxygenated blood to the left atrium.
Double circulation prevents the mixing of oxygenated and deoxygenated blood.
Regulation of Cardiac Activity

• Normal activities of heart are regulated by nodal tissue (SA and AV node), so the heart is myogenic.
• A special neural centre in medulla oblongata moderates the cardiac function by ANS. Sympathetic nerve can increase the rate of heart beat and parasympathetic nerve of ANS decrease the rate of heart beat.
• Adrenal medullary hormone also increases the cardiac output.

Disorder of Circulatory System

1. Hypertension (high blood pressure) – Blood pressure higher than (120/80) . 120 mm Hg is the systolic that is pumping pressure and 80 mm Hg is the diastole, resting pressure. It leads to heart disease and affect vital organs like brain and kidney.
2. Coronary Artery Disease (CAD)- commonly called atherosclerosis that affects the blood vessels that supply blood to heart muscles due to deposition of fat, calcium, cholesterol that makes the arteries lumen narrower.
3. Angina- also called angina pectoris, acute chest pain due to less supply of oxygen to heart muscles. It may occur in elderly male and female. It occurs due to restricted blood flow.
4. Heart failure– heart does not pump enough blood to meet the requirement of body. It is also known as congestive heart failure because congestion of lung is one of its causes. Heart failure is different from heart attack ( heart muscle is damaged by inadequate blood supply) and cardiac arrest ( when heart stops beating).
5. Coronary Thrombosis- formation of clot in the coronary artery is coronary thrombosis. It occurs most frequently in the left anterior descending coronary artery.

Class 11 Biology Revision Notes for Breathing and Exchange of Gases of Chapter 17

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The process of exchange of O₂ from the atmosphere with CO₂ produced by the cell is called breathing. It occurs in two stages of inspiration and expiration. During inspiration air enters the lungs from atmosphere and during expiration air leaves the lungs.

Breathing	Respiration
a. It is simply an intake of fresh air and removal of foul air.  b. It is a physical process. c. No energy is released. d. It is an extracellular process.	a. It is the oxidation of food to form carbon dioxide, water and energy.  b. It is a biochemical process. c. Energy is released in form of ATP. d. It is an intracellular process.

Respiratory Organs – Mechanism of breathing varies in different organism according to their body structure and habitat.

Respiratory Organs	Organisms
Entire Body surface	Sponges, coelenterate, flatworms.
Skin	Earthworm.
Tracheal system	Insects
Gills	Pisces, aquatic arthropods.
Lungs	Amphibians, mammals.

Human Respiratory System

• Human respiratory system consists of a pair of nostrils, pharynx, larynx, bronchi and bronchioles that finally terminates into alveoli.
• Nasal chamber open into pharynx that leads to larynx. Larynx contains voice box (sound box) that help in sound production.
• The trachea, primary, secondary and tertiary bronchi and initial bronchioles are supported by incomplete cartilaginous rings to prevent collapsing in absence of air.
• Each bronchiole terminates into an irregular walled, vascularized bag like structure called alveoli.

• The branching network of bronchi, bronchioles and alveoli collectively form the lungs.
• Two lungs are covered with double layered pleura having pleural fluid between them to reduce the friction on lung surface.

• Conducting parts include nostrils, pharynx, larynx and trachea. Main functions include-

1. Transport of atmospheric air to alveoli.
2. Removing foreign particles from air, humidifying it and bringing it to body temperature.

• The exchange parts are alveoli. It is the site of actual diffusion of O2O2 and CO2O2 between blood and atmospheric air.

Steps of Respiration

1. Breathing in which Oxygen rich atmospheric air is diffused in and CO2O2 rich alveolar air is diffused out.
2. Diffusion of gases across alveolar membrane.
3. Transport of gases by blood.
4. Diffusion of O2O2 and CO2O2 between blood and tissues.
5. Utilization of O2O2 by cells to obtain energy and release of CO2O2 (cellular respiration).

Mechanism of Breathing

• Breathing involves inspiration and expiration. During inspiration atmospheric air is drawn in and during expiration, alveolar air is released out.
• Movement of air in and out takes place due to difference in pressure gradient.
• Inspiration occurs when pressure inside the lung is less and expiration occurs when pressure is more in lungs than outside.
• The diaphragm and external and internal intercostal muscles between the ribs help in developing pressure gradient due to change in volume.

• The contraction of intercostal muscles lifts the ribs and sternum causing an increase in volume of thoracic cavity that results in decrease in pressure than the atmospheric pressure. This causes inspiration.
• Relaxation of the diaphragm and intercostal muscles reduce the thoracic volume and increase the pressure causing expiration.
• The volume of air involved in breathing movements is estimated by using spirometer for clinical assessment of pulmonary functions.

Respiratory Volume and Capacities
Tidal volume (TV) – volume of air inspired or expired during a normal respiration. It is about 500mL in healthy man.
Inspiratory Reserve Volume (IRV) – additional volume of air a person can inspire by forceful inspiration. It is about 2500 mL to 3000mL.
Expiatory Reserve Volume (ERV) – additional volume of air a person can expire by forceful expiration. It is about 1000 mL to 1100mL.
Residual Volume (RV) – volume of air remaining in lungs even after a forcible expiration. It is about 1100mL to 1200mL.
Inspiratory Capacity (IC) – TV + IRV
Expiratory Capacity (EC) – TV + ERV
Functional Residual Capacity (FRC) – ERV + RV
Vital Capacity (VC) – maximum volume of air a person can breathe in after a forceful expiration. ERV+ TV+ IRV
Total Lung Capacity (TLC) – total volume of air accommodated in lung at the end of forced inspiration. RV+ ERV+ TV+ IRV or Vital capacity + Residual Volume.

Exchange of Gases

• Exchange of gases takes place at two sites

1. Alveoli to blood
2. Between blood and tissues.

• Exchanges of gases occur by simple diffusion due to pressure/ concentration gradient, solubility of the gases and thickness of membrane.
• Pressure contributed by individual gas in a mixture of gas is called partial pressure represented by pCO2O2 and pO2O2 .
• Partial pressure of Oxygen and carbon dioxide at different part involved in diffusion varies from one part to another and moves from higher partial pressure to lower partial pressure.
• Solubility of CO2O2 is 20-25 times more than solubility of O2O2 , so CO2O2 diffuse much faster through membrane.
• Diffusion membrane is three layered thick, that is alveolar squamous epithelium, endothelium of alveolar capillaries and basement substance between them.

Transport of Gases

• Blood is the medium of transport for CO2O2 and O2O2 . Most of oxygen (97%) is transported through RBC and remaining 3% by blood plasma.
• 20-25% of CO2O2 is transported by RBC, 70% as bicarbonate and rest 7% in dissolved state by blood plasma.

Transport of Oxygen

• Haemoglobin in RBC combines with O2O2 to form Oxyhaemoglobin. Each haemoglobin combine with four oxygen molecules.
• Binding of O2O2 is related with partial pressure of O2O2 and CO2CO2, hydrogen ion concentration and temperature.
• Percentage saturation of haemoglobin and partial pressure of oxygen forms sigmoid curve (oxygen dissociation curve).
• In the alveoli, pO2O2 is more and pCO2O2 is less, less H+ ions concentration and lower temperature favour the binding of O2O2 with hemoglobin. Where opposite condition in tissues favour the dissociation of Oxyhaemoglobin.

Transport of Carbon dioxide

• Carbon dioxide is transported by haemoglobin as carbamino-haemoglobin. In tissues pCO2O2 is high and pO2O2 is less that favour the binding of carbon dioxide with haemoglobin. Opposite condition help in dissociation of carbamino- haemoglobin in alveoli.
• Enzyme carbonic anhydrase help in formation of carbonate ions to transport carbon dioxide.

Regulation of Respiration

• Human beings have ability to maintain and moderate the rate of respiration to fulfill the demand of body tissues by neural system.
• Respiratory rhythm centre is located in medulla region of hind brain. Pneumotaxic centre in pons moderate the function of respiratory rhythm centre.
• Chemo-sensitive area near rhythm centre is highly sensitive to CO2O2 and H+ ions that ultimately control the respiratory rate. Oxygen do not play major role in controlling rate of respiration.

Functions of Respiration–

1. Energy production
2. Maintenance of acid-base balance.
3. Maintenance of temperature
4. Return of blood and lymph.

Mountain Sickness is the condition characterised by the ill effect of hypoxia (shortage of oxygen) in the tissues at high altitude commonly to person going to high altitude for the first time.
Symptoms-

• Loss of appetite, nausea, and vomiting occurs due to expansion of gases in digestive system.
• Breathlessness occurs because of pulmonary oedema.
• Headache, depression, disorientation, lack of sleep, weakness and fatigue.

Disorder of Respiratory System

1. Asthma– it is due to allergic reaction to foreign particles that affect the respiratory tract. The symptoms include coughing, wheezing and difficulty in breathing. This is due to excess of mucus in wall of respiratory tract.
2. Emphysema– is the inflation or abnormal distension of the bronchioles or alveolar sacs of lungs. This occurs due to destroying of septa between alveoli because of smoking and inhalation of other smokes. The exhalation becomes difficult and lung remains inflated.
3. Occupational Respiratory Disorders– occurs due to occupation of individual. This is caused by inhalation of gas, fumes or dust present in surrounding of work place. This includes Silicosis, Asbestoses due to exposer of silica and asbestos. The symptom includes proliferation of fibrous connective tissue of upper part of lung causing inflammation.
4. Pneumonia– it is acute infection or inflammation of the alveoli of the lungs due to bacterium streptococcus pneumoniae. Alveoli become acutely inflamed and most of air space of the alveoli is filled with fluid and dead white blood corpuscles limiting gaseous exchange.

Class 11 Biology Revision Notes for DIGESTION AND ABSORPTION of Chapter 16

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The process of conversion of complex food into simpler absorbable form is called digestion and is carried out by digestive system by mechanical and biochemical methods.
Digestive System- Human digestive system consists of alimentary canal and associated glands.

• Alimentary canal begin with anterior opening mouth and opens out posteriorly through anus. It comprises of following parts:-

1. Mouth- leads to oral cavity or buccal cavity which contains teeth and tongue.
   Upper surface of tongue has small projections called papillae, some of which contain taste buds.
   Each teeth is embedded in socket of jaw bone (thecodont). Milk teeth is replaced by permanent or adult teeth, this type of dentition is called diphyodont. Four different types of teeth (Heterodont) are incisors (I), canine (C), premolar (PM) and molar (M).Dental formula: Each half of the upper and lower jaw has following number of teeth- 2123212321232123
2. Pharynx – oral cavity opens into pharynx which acts as common passage for food and air. Cartilaginous flap called epiglottis prevents the entry of food into wind pipe (glottis) during swallowing.
3. Stomach- Oesophagus leads to stomach. The opening of stomach is guarded by a sphincter (gastro-oesophageal). Stomach is divided into three parts- cardiac, fundic and pyloric.
4. Small intestine- is the longest part of alimentary canal divided into duodenum, jejunum and ileum. Pyloric sphincter is present between stomach and duodenum.
5. Large intestine- ileum opens into large intestine, which is divided into caecum, colon and rectum. Caecum is a blind sac which host microbes. Vermiform appendix arises from caecum. Rectum opens through anus.

Histology of Alimentary canal-
The wall of alimentary canal from Oesophagus to rectum consists of four layers.

1. Serosa– it is the outermost layer made up of squamous epithelium and areolar connective tissue.
2. Muscularis– it is composed of outer longitudinal and inner circular muscle fibres. Muscles fibres are smooth and have network of nerve cells.
3. Submucosa– it consists of loose connective tissue richly supplied with blood and lymphatic vessels. Meissner’s plexus is present between the muscular coat and mucosa that controls the secretion of intestinal juice.
4. Mucosa– is innermost layer lining the lumen of the alimentary canal. It has irregular folding in stomach called rugae and villi in small intestine. Mucosa forms glands in the stomach (gastric glands) and crypts in between the bases of villi in the intestine (crypts of Lieberkuhn).
   

Salivary Glands- secrete saliva in oral cavity. In human beings salivary glands are three pairs- parotid, sublingual, and submandibular.
Liver- it is the largest gland in human body lies in upper right side of the abdominal cavity just below the diaphragm. Hepatic lobules, covered by Glisson’s capsule, are structural and functional unit of liver made up of hepatic cells. The secretion is stored and concentrated in gall bladder. Bile duct and pancreatic duct open together in duodenum by common duct guarded by sphincter of Oddi.

Pancreas- It is soft lobulated greyish pink gland which weighs about 60 gm., consists of exocrine and endocrine portion. The exocrine portion secretes alkaline pancreatic juice and endocrine secretes hormones insulin and glucagon.
Digestion of food
Carbohydrates, fats, proteins and nucleic acids occur in food in the form of large and complex insoluble macromolecules (polymers). These macromolecules are converted into small monomers by the action of enzyme.

• In buccal cavity, teeth and tongue help in mastication and mixing of food. Mucus in saliva mix with masticated food to form bolus.
• Bolus is passed to pharynx and Oesophagus by swallowing or deglutition.
• Chemical digestion of food starts in oral cavity by the action of enzyme salivary amylase and lysozyme.
  Lysozyme acts as antibacterial agent in mouth to prevent infection.
  Salivary amylase breaksdown starch into maltose
• Mucosa of stomach have gastric glands having three types of cells- mucus neck cells that secrete mucus, peptic or chief cells that secretes proenzyme pepsinogen and pariental or oxyntic cells that secretes HCl.
• Food mixes with gastric juice due to churning action of muscular wall to form chyme. HCl activates the pepsinogen to pepsin to digest protein into peptones  and proteoses
• Mucus and bicarbonates present in gastric juice play important role in lubrication and protecting inner wall of stomach from the action of HCl. Renin is a proteolytic enzyme found in gastric juice of infants to digest milk protein.
• The Bile, pancreatic juice and intestinal juice are released in small intestine. Pancreatic juice contain inactive trypsinogen, chymotrypsinogen, procarboxypeptidases, amylases, lipases and nucleases.
• Trypsinogen is activated by enzyme enterokinase in to trypsin, which further activates the other enzyme of intestinal juice.
• Bile contains bile pigments (bilirubin and bil-verdin), bile salts, cholesterol and phospholipids which help in emulsification of fats.
• Secretion of brush border cells of mucosa and goblet cells contain enzyme succus entericus, containing variety of enzymes to complete the process of digestion.

Function of large intestine

1. Absorption of water, minerals and certain drugs.
2. Secretion of mucus for adhering of the undigested food and lubricating it for easy passage.

Absorption of Digested Food
Absorption is the process by which nutrients pass from the alimentary canal into the blood and lymph through its mucous membrane.

• Amino acids, monosaccharide, fatty acids, glycerol, salts, vitamins and water are to be absorbed. About 90% of absorption occurs in small intestine and rest 10% in stomach, mouth and large intestine.
• The passage of different absorbent depends upon concentration gradient for some substances like glucose and amino acids and electrolytes.

Absorption in different part of alimentary canal-

Mouth	Certain drugs coming in contact with the mucosa of mouth and lower side of tongue are absorbed into the blood capillaries lining them.
Stomach	Absorption of water, simple sugar and alcohol takes place.
Small intestine	Glucose, fructose, fatty acids, glycerol and amino acids are absorbed through the mucosa into the blood stream and lymph.
Large intestine	Absorption of water, some minerals and drug takes place.

Disorder of Digestive System
The inflammation of intestinal tract due to bacterial infection, fungal infection and parasitic infection caused by tapeworm, round worm, threadworm and pin worms.

1. Jaundice– it is a disease of liver. In jaundice the skin and the eyes turn yellow due to large quantities of bilirubin pigments in the extra cellular fluid.
2. Vomiting – it is the ejection of stomach content through the mouth. This reflex action is controlled by the vomit Centre in the medulla.
3. Diarrhoea- frequent defection of liquid faeces is known as Diarrhoea. It reduces the absorption of food.
4. Constipation– in constipation the faeces are retained within the rectum as the bowel movements occur irregularly.
5. Indigestion– incomplete digestion usually accompanied by one or more of the following symptoms- pain, nausea, vomiting, heartburn, acid regurgitation, accumulation of gas and escape of gas from the stomach.

Class 11 Biology Revision Notes for Plant Growth and Development of Chapter 15

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• Root, stem, leaves, flowers, fruits and seeds arise in orderly manner in plants. The sequence of growth is as follows-
• Plants complete their vegetative phase to move into reproductive phase in which flower and fruits are formed for continuation of life cycle of plant.
• Development is the sum of two processes growth and differentiation. Intrinsic and extrinsic factors control the process of growth and development in plants.

• Growth is a permanent or irreversible increase in dry weight, size, mass or volume of cell, organ or organism. It is internal or intrinsic in living beings.
• In plants growth is accomplished by cell division, increase in cell number and cell enlargement. So, growth is a quantitative phenomenon which can be measured in relation to time.
• Plant growth is generally indeterminate due to capacity of unlimited growth throughout the life. Meristem tissues are present at the certain locality of plant body.
• The plant growth in which new cells are always being added to plant body due to meristem is called open form of growth.
• Root apical meristem and shoot apical meristem are responsible for primary growth and elongation of plant body along the axis.
• Intercalary meristem located at nodes produce buds and new branches in plants.

• Secondary growth in plants is the function of lateral meristem that is vascular cambium and cork cambium.

Growth is measurable

• At cellular level, growth is the increase in amount of protoplasm. It is difficult to measure the increase in amount of protoplasm but increase in cell, cell number and cell size can be measured.
• The parameter used to measure growth is increase in fresh weight, dry weight, length, area, and volume and cell number. All parameters are not used for every kind of growth.
• Formative phase is also called as the phase of cell formation or cell division. It occurs at root apex, shoot apex and other region having meristematic tissue. The rate of respiration is very high in the cells undergoing mitosis division in formative phase.
• Phase of Enlargement- newly formed cells produced in formative phase undergo enlargement. Enlarging cells also develops vacuoles that further increase the volume of cell.
• Cell enlargement occurs in all direction with maximum elongation in conducting tissues and fibres.

• Phase of maturation- the enlarged cells develops into special or particular type of cells by undergoing structural and physiological differentiation.
• Growth Rate- increase in growth per unit time is called growth rate. Growth rate may be arithmetic or geometrical.
• Arithmetic Growth- the rate of growth is constant and increase in growth occurs in arithmetic progression- 2,4,6,8 ……. It is found in root and shoot elongation.

L_t = L₀ + rt
Length after time = length at beginning + growth rate x time.

• Geometric Growth- here initial growth is slow and increase rapidly thereafter. Every cell divides. The daughter cells grow and divide and the granddaughter cells that result into exponential growth.
• Geometrical growth is common in unicellular organisms when growing in nutrient rich medium.

• Sigmoid growth curve consists of fast dividing exponential phase and stationary phase. It is typical of most living organisms in their natural environment.

Exponential growth can be represented as follows-
W₁ =W₀e^rt. W1 = final size, W0 = initial size, r = growth rate, t = time of growth and e is the base of natural logarithms (2.71828).

• Quantitative comparison between the growth of living system can be made by

1. Measurement and comparison of total growth per unit time is called the absolute rate.
2. The growth of given system per unit time expressed on a common basis is called relative growth rate.

Condition for growth

• Necessary condition for growth includes water, oxygen and essential elements. Water is required for cell enlargement and maintaining turgidity. Water also provide medium for enzymatic conditions.
• Protoplasm formation requires water and micro and macronutrients and act as source of energy.
• Optimal temperature and other environmental conditions are also essential for growth of the plant.
• Cells produced by apical meristem become specialized to perform specific function. This act of maturation is called differentiation.
• The living differentiated cells that have lost ability of division can regain the capacity of division. This phenomenon is called dedifferentiation. For example interfascicular cambium and cork cambium.
• Dedifferentiated cells mature and lose the capacity of cell division again to perform specific functions. This process is called redifferentiation.

Development
It is the sequence of events that occur in the life history of cell, organ or organism which includes seed germination, growth, differentiation, maturation, flowering, seed formation and senescence.

Sequence of development process in plant cell

• Different structures develop in different phases of growth as well as in response to environment. The ability to change under the influence of internal or external stimuli is called plasticity. Heterophylly in cotton plant is the example of plasticity.

Plant Growth Regulators are simple molecules of diverse chemical composition which may be indole compounds, adenine derivatives or derivatives of carotenoids.

• Auxin was isolated by F.W. Went from tips of coleoptiles of oat seedlings.
• The ‘bakane disease’ of rice seedlings is caused by fungal pathogen Gibberella fujikuroi. E. Kurosawa found that this disease is caused due to presence of Gibberellin.
• Skoog and Miller identified and crystallized the cytokinesis, promoting active substance called kinetin.

Auxin- was first isolated from human urine. It is commonly indole-3-acetic acid (IAA). It is generally produced at stem and root apex and migrate to site of action.
Functions-

1. Cell enlargement.
2. Apical dominance
3. Cell division
4. Inhibition of abscission
5. Induce Parthenocarpy

Gibberellins- are promotery PGR found in more than 100 forms named as GA1GA1, GA2GA2, GA3GA3…. GA100GA100. The most common one is GA3GA3 (Gibberellic Acid).
Functions-

1. Cell elongation.
2. Breaking of dormancy.
3. Early maturity
4. Seed germination.

Cytokinins- the plant growth hormone is basic in nature. Most common forms include kinetin, zeatin, etc. They are mainly synthesized in roots.
Functions-

1. Cell division and cell differentiation.
2. Essential for tissue culture.
3. Overcome apical dominance.
4. Promote nutrient mobilisation.

Ethylene – it is a gaseous hormone which stimulates transverse or isodiametric growth but retards the longitudinal one.
Functions–

1. Inhibition of longitudinal growth.
2. Fruit ripening
3. Senescence
4. Promote apical dominance

Abscisic Acid – it is also called stress hormone or dormin. It acts as a general plant growth inhibitor. Abscisic acid is produced in the roots of the plant and terminal buds at the top of plant.
Function-

1. Bud dormancy
2. Leaf senescence
3. Induce Parthenocarpy
4. Seed development and maturation.

Photoperiodism- the effect of photoperiods or day duration of light hours on the growth and development of plant, especially flowering is called Photoperiodism. On the basis of photoperiodic response, flowering plants have been divided into the following categories-

1. Short Day Plants– they flower when photoperiod is below a critical period (continuous duration of light which must not be exceeded in short day plants and should always be exceeded in long day plants in order to bring them flower). Example- Xanthium, Rice, Sugarcane, Potato etc.
2. Long Day Plants– these plants flower when they receive long photoperiod of light, greater than critical period. Example- Radish, Barley, Lettuce.
3. Day Neutral Plants – the plant can blossom throughout the year. Example- Bean, Wild Kidney.

Vernalisation– is the process of shortening of the juvenile or vegetative phase and hastening of flowering by cold treatment. The stimulus of Vernalisation is perceived by meristematic cells.

• Vernalisation helps in shortening of vegetative period of plant and brings about early flowering.
• It is applicable to temperate plants like Wheat, Rice, Millets, etc.

Class 11 Biology Revision Notes for Respiration in Plants of Chapter 14

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Respiration is an energy releasing, enzymatically controlled catabolic process which involves a step-wise oxidative breakdown of food substance inside living cells.
C6H12O6+6O2→6CO2+6H2O+EnergyC6H12O6+6O2→6CO2+6H2O+Energy

• Living organism require energy for all activities like absorption, movement, reproduction or even breathing. Energy required is obtained from oxidation of food during respiration.
• Cellular respiration is the mechanism of breaking down of food materials within the cell to release energy for synthesis of ATP.
• Breaking down of complex molecules takes place to produce energy in cytoplasm and in the mitochondria.
• Breaking down of C-C bond of complex compounds through oxidation within the cells leading to release of energy is called respiration. The compounds that get oxidized are called respiratory substrates.
• Energy released during oxidation is not used directly but utilized in synthesis of ATP, which is broken down when energy is required. Therefore, ATP is called energy currency of cells.
• The process of respiration requires oxygen. In plants oxygen is taken in by stomata, lenticels and root hairs.
• Plants can get along without respiratory organs because:
  1. Each plant part takes care of its own gas-exchange needs.
  2. Plants do not present great demands for gas exchange.
  3. Distance that gases must diffuse in large plant is not great.
  4. During photosynthesis O2 is released in leaves and diffuse to other part of leaves.

• During process of respiration oxygen is utilized and carbon dioxide and water is released along with energy molecules in form of ATP.
• Respiratory Quotient is the ratio of the volume of carbon dioxide produced to the volume of oxygen consumed in respiration over a period of time. RQ is equal to one for carbohydrate and less than one for protein and peptones.

 
Aerobic Respiration is an enzymatically controlled release of energy in a stepwise catabolic process of complete oxidation of organic food into carbon dioxide and water with oxygen acting as terminal oxidant.

Glycolysis

• The scheme of glycolysis is given by Gustav Embden, Otto Meyerhof, and J. Parnas. It is also called as EMP pathway.
• Glycolysis is the partial oxidation of glucose or similar hexose sugar into two molecules of pyruvic acid through a series of enzyme mediated reaction releasing some ATP and NADH2. It occurs in cytoplasm.
• In plants glucose is derived from sucrose or from storage carbohydrates. Sucrose is converted into glucose and fructose by enzyme invertase.
• Glycolysis starts with phosphorylation of glucose in presence of enzyme hexokinase to form Glucose-6-phosphate. One molecules of ATP is used in this process.
• In next steps Glucose-6-phosphate is converted into fructose-6-phosphate, catalysed by enzyme phosphohexose isomerase.
• Fructose-6-phosphate uses another molecule of ATP to form Fructose-1-6 biphospahte in presence of enzyme phosphfructokinase.

• In glycolysis two molecules of ATP are consumed during double phosphorylation of glucose to fructose 1,6 biphosphate. Two molecules of NADPH2 are formed at the time of oxidation of glyceraldehyde 3-phosphate to 1,3 biphosphoglycerate. Each NADH is equivalent to 3ATP, so that net gain in glycolysis is 8 ATP.
• Pyruvic acid is the key product of glycolysis, further breakdown of pyruvic acid depends upon the need of the cell.
• In animal cells, like muscles during exercise, when oxygen is insufficient for aerobic respiration, pyruvic acid is reduced to Lactic acid by enzyme lactate dehydrogenase due to reduction by NADH2.

• In fermentation by yeast, pyruvic acid is converted to ethanol and CO2. The enzyme involved is pyruvic acid decarboxylase and alcohol dehydrogenase catalyse this reaction.
• In both lactic acid fermentation and alcohol fermentation very less amount of energy is released.
• Yeasts poison themselves to death if concentration of alcohol reaches above 13%.
• Final product of glycolysis, pyruvate is transported from the cytoplasm into mitochondria for further breakdown.
• Oxidation of Pyruvate to Acetyl-CoA is done to produce CO2 and NADH. The reaction catalyzed by pyruvic dehydrogenase requires the participation of several Coenzymes including NAD+ .

Pyruvicacid+CoA+NAD+Pyruvicacid+CoA+NAD+−→−−−−−−−−−−−−−PyruvatedehydrogenaseMg2+AcetylCoA+CO2→PyruvatedehydrogenaseMg2+AcetylCoA+CO2+NADH+H++NADH+H+

• The Acetyl CoA enters a cyclic pathway called TCA cycle or Kreb’s cycle.

Tricarboxylic Acid Cycle/Krebs Cycle

• TCA cycle was discovered by Hans Krebs in 1940. This cycle is called TCA cycle because initial product is citric acid.
• Acetyl CoA combine with OAA ( Oxaloacetic acid) and water to yield citric acid in presence of enzyme citrate synthase to release CoA.
• Citrate is then isomerised to isocitrate. It is followed by two successive
  steps of decarboxylation, leading to the formation of α-ketoglutaric acid and then succinyl-CoA.
• In the remaining steps, succinyl-CoA is oxidised to OAA allowing the cycle to continue.
• There are three points in the cycle where NAD + is reduced to NADH2 and one point where FAD + is reduced to FADH2 .
• A molecule of glucose produces two molecules of NADH2NADH2, 2ATP and two pyruvate while undergoing glycolysis. The two molecules of pyruvate are completely degraded in Krebs cycle to form two molecules of ATP, 8NADH28NADH2 and 2FADH22FADH2.

pyruvic + 4NAD⁺ + FAD⁺ + 2H₂O + ADP + Pi −→−−−−−−−−−−−−MitochondrialMatrix→MitochondrialMatrix 3CO₂ +4NADH+4H+FADH2ATP+4NADH+4H+FADH2ATP
Terminal Oxidation is the name of oxidation found in aerobic respiration that occurs towards end of catabolic process and involves the passage of both electrons and protons of reduced coenzyme to oxygen to produce water.

Electron Transport Chain

• The metabolic pathway through which the electron passes from one carrier to another inside the inner mitochondrial membrane is called ETC or mitochondrial respiratory chain.
• Electrons from NADH produced during citric acid cycle are oxidized by NADH dehydrogenase and electrons are transferred to ubiquinone located within the inner membrane. Ubiquinone also receives electrons from FADH2 which is transferred to cytochrome c via cytochrome bc₁ complex.
• When the electrons pass from one carrier to another via electron transport chain, they produce ATP from ADP and inorganic phosphate. The number of ATP molecules synthesized depends upon electron donor.
• Oxidation of one molecule of NADH gives rise to 3 molecules of ATP, while oxidation of one molecule of FAD2FAD2 produce two molecules of ATP.

Oxidative phosphorylation	Photophosphorylation
a) It occurs in respiration process.  b) Energy of oxidation-reduction is used for production of proton gradient required for phosphorylation.	a) It occurs in photosynthesis.  b) Light energy is utilized for production of proton gradient for phosphorylation.

• The energy released during ETC is used to make ATP with the help of ATP synthase, which consists of two major parts F1 and F0.
• F1 is a peripheral membrane protein complex having site for synthesis of ATP from ADP and inorganic phosphate. F0 is integral membrane protein that form channel for proton.
• For each ATP produced 2H+ passes through F0 from the intermembrane space to the matrix down the electrochemical proton gradient.

Fermentation	Aerobic Respiration
a. It accounts for incomplete oxidation of glucose.  b. In fermentation, there is net gain of only two molecules of ATP. c. NADH is oxidized to NAD+ very slowly.	a. It accounts for complete oxidation of glucose.  b. In aerobic respiration, there is more net gain of ATP. c. NADH is oxidized to NAD+ very fast.

Amphibolic Pathway

• Glucose is the favored substrate for respiration. All carbohydrates are usually converted into glucose before used for respiration.
• Fats needs to be broken down into glycerol and fatty acid, which is further broken converted into Acetyl CoA and enter the respiratory pathway.
• Proteins are broken into amino acids and further enter into Krebs cycle.
• Breaking down process within living organism is called catabolism and synthesis process is called anabolism process. So, respiration is an Amphibolic pathway.

Class 11 Biology Revision Notes for Photosynthesis in Higher Plants of Chapter 13

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Photosynthesis is a physico-chemical process by which green plants use light energy to drive the synthesis of organic compounds. It is an enzyme regulated anabolic process.
6CO2+12H2O−→−−LightC6H12O6+6H2O+6O26CO2+12H2O→LightC6H12O6+6H2O+6O2

• Photosynthesis is the basis of life on earth because it is the primary source of all food on earth and it is responsible for release of O2O2 in the atmosphere.
• Chlorophyll, light and CO2CO2 is required for photosynthesis. It occurs only in green part of leaves and in presence of light.

Early Experiments

• Joseph Priestley in 1770, on the basis of his experiments showed the essential role of air in growth of green plants. A mouse kept in closed space could get suffocated and die but if a mint plant is kept in bell jar neither candle will extinguish nor will the mouse die. He concluded that foul air produced by animal is converted into pure air by plants. Priestley discovered Oxygen gas in 1774.

• Julius Von Sachs in 1854 shows that green part in plants produces glucose which is stored as starch. Starch is the first visible product of photosynthesis.
• T.W.Engelmann (1843-1909) used prism to split light into its components and then illuminated Cladophora (an algae) placed in a suspension of aerobic bacteria. He found that bacteria accumulated in blue and red light of the split spectrum. He thus discovered the effect of different wavelength of light on photosynthesis (action spectrum).
• Cornelius Van Neil (1897-1985) on the basis of studies with purple and green sulphur bacteria showed that photosynthesis is a light dependent reaction in which hydrogen from an oxidisable compound reduces CO2CO2 to form sugar.

2H2A+CO2−→−−Light2A+CH2O+H2O2H2A+CO2→Light2A+CH2O+H2O
In green sulphur bacteria, when H2SH2S , instead of H2OH2O was used as hydrogen donor, no O2O2 was evolved. He inferred that O2O2 evolved by green plants comes from H2OH2O but not from CO2CO2 as thought earlier.
Where Does Photosynthesis Takes Place?

• Chloroplasts are green plastids which function as the site of photosynthesis in eukaryotic photoautotrophs. Inside the leaves, chloroplast is generally present in mesophyll cells along their walls.
• Within the chloroplast there is a membranous system consisting of grana, the stroma lamellae and the fluid stroma.

• The membrane system is responsible for synthesizing light energy for the synthesis of ATP and NADPH. In stroma enzymatic reactions incorporate CO2CO2 in plants leading to synthesis of sugar.
• The reaction in which light energy is absorbed by grana to synthesis ATP and NADPH is called light reaction. The later part of photosynthesis in which CO2CO2 is reduced to sugar, light is not necessary and is called dark reaction.

Pigments involved in Photosynthesis – Chromatographic separation of leaf pigments are as follows-
 
Maximum absorption by chlorophyll a occurs in blue and red regions having higher rate of photosynthesis. So, chlorophyll a is the chief pigment.

• Other thylakoid pigments like chlorophyll b, xanthophyll and carotenoids are called accessary pigments that absorb light and transfer energy to chlorophyll a and protect them from photo-oxidation.

Light reaction

• Light reaction(photochemical phase) includes:

1. Light absorption
2. Water splitting
3. Oxygen release
4. Formation of high energy chemical intermediates (ATP and NADPH).

• The pigments are organized into two discrete LHC( light harvesting complex) within photosystem I and photosystem II.
• LHC are made up of hundreds of pigments molecules containing all pigments except single chlorophyll a molecules in each PS.

• The pigments in photosystem I and photosystem II absorbs the lights of different wavelength. Single chlorophyll a molecule makes the reaction centre. In PS I reaction centre has highest peak at 700nm, hence called P700. And PS II reaction centre has highest peak at 680 nm, so called P680.

The Electron Transport System

• Reaction centre of photosystem II absorbs light of 680 nm in red region and causing electron to become excited. These electrons are picked by an electron acceptor which passes to electron transport system consisting of cytochromes.

• Electrons are passed down the electron transport chain and then to the pigment of PS I.
• Electron in the PSI also get excited due to light of wavelength 700nm and are transferred to another accepter molecule having a greater redox potential.
• When electron passes in downhill direction, energy is released. This is used to reduce the ADP to ATP and NADP+ to NADPH. The whole scheme of transfer of electron is called Z-scheme due to its shape.
• Photolysis of water release electrons that provide electron to PS II. Oxygen is also released during this process.

2H2O→4H++O2+4e−2H2O→4H++O2+4e−

• Difference between cyclic and non-cyclic photophosphorylation

Cyclic photophosphorylation	Non-cyclic photophosphorylation
It is performed by photosystem I independently.An external source of electron is not required.It synthesizes only ATP.It occurs only in stromal or intergranal thylakoids.	It is performed by collaboration of both PS I and PS II.The process requires an external electron donor.It synthesizes ATP and NADH both.It occurs in the granal thylakoids only.

 
Chemiosmotic Hypothesis of ATP FORMATION
This hypothesis was proposed by Mitchell in 1961. ATP synthesis is linked to development of proton gradient across the membrane of thylakoid and mitochondria.
The process that causes development of proton gradient across the membrane is-

1. Splitting of water molecules occurs inside the thylakoid to produce hydrogen ion or proton.
2. As electron passes through the photosystems, protons are transported across the membrane because primary acceptor of electron is located towards the outer side the membrane.
3. The NADP reductase enzyme is located in the stroma side of membrane. Electrons come out from the acceptor of electron of PSI, protons are necessary for reduction of NADP+ to NADP + H+. These protons are also removed from the stroma. This creates proton gradient across the thylakoids membrane along with pH in the lumen.
4. Gradient is broken down due to movement of proton across the membrane to the stroma through trans-membrane channel of F0 of ATPase. One part of this enzyme is embedded in membrane to form trans-membrane channel. The other portion is called F1that protrudes on the outer surface of thylakoid membrane which makes the energy packed ATP.
5. ATP and NADPH produced due to movement of electron is used immediately to fix CO2 to form sugar.

• The product of light reaction used to drive the process leading to synthesis of sugar are called biosynthetic phase of photosynthesis.

Calvin Cycle/C3 cycle/Reductive Pentose Sugar Phosphate Pathway
Malvin Calvin, Benson and their colleagues used radioactive 14C and Chlorealla and Scenedesmus algae to discover that first CO2CO2 fixation product is 3-carbon organic compound (3-phosphoglyceric acid) or PGA. Later on a new compound was discovered which contain 4-carbon called Oxaloacetic Acid (AAO). On the basis of number of carbon atoms in first stable product they are named C3 and C4 pathway.
Calvin cycle can be described under three stages: carboxylation, reduction and regeneration.

• Carboxylation is the fixation of CO2CO2 into 3-phosphoglyceric acid (3-PGA). Carboxylation of RuBP occurs in presence of enzyme RuBP carboxylase (RuBisCO) which results in the formation of two molecules of 3-PGA.
• Reduction is series of reaction that leads to formation of glucose. Two molecules of ATP and two molecules of NADPH are required for reduction of one molecules of CO2CO2. Six turn of this cycle are required for removal of one molecule of Glucose molecules from pathway.
• Regeneration is the generation of RuBP molecules for the continuation of cycle. This process require one molecules of ATP.

Fig-Calvin Cycle/ C3 Cycle

• For every molecules of CO2CO2 entering the Calvin Cycle, 3 molecules of ATP and 2 molecules of NADPH is required. To make one molecules of glucose 6 turns of cycle is completed so total energy molecule required is

In	Out
Six CO2CO2  18 ATP 12 NADPH	One glucose  18 ADP 12 NADP

C4 pathway/Hatch Slack Pathway

• This pathway was worked out by Hatch and Slack (1965, 1967), mainly operational in plants growing in dry tropical region like Maize, Sugarcane, Sorghum etc.
• In this pathway first stable product is a 4-carbon compound Oxaloacetic acid (AAO) so called as C4C4 pathway. C4C4 plants have Kranz Anatomy (vascular bundles are surrounded by bundle sheath cells arranged in wreath like manner), characterized by large no of chloroplast, thick wall impervious to gases and absence of intercellular spaces.
• The primary CO2CO2 acceptor is a 3-carbon molecule Phosphoenol Pyruvate present in mesophyll cells and enzyme involved is PEP carboxylase.
• OAA formed in mesophyll cell forms 4-carbon compound like malic acid or aspartic acid which is transported to bundle sheath cells.
• In bundle sheath cell, it is broken into CO2CO2 and a 3-carbon molecule. The 3-carbon molecule is returned back to mesophyll cells to form PEP.
• The CO2CO2 molecules released in bundle sheath cells enters the Calvin cycle, where enzyme RuBisCO is present that forms sugar.

Photorespiration

• It is a the light dependent process of oxygenation of RuBP and release of carbon dioxide by photosynthetic organs of plants.
• Photorespiration decreases the rate of photosynthesis when oxygen concentration is increased from 2-3% to 21%.
• Presence of light and higher concentration of Oxygen results in the binding of RuBisCO enzyme with O2 to form.

RuBisCO + O2→O2→ PGA + phosphoglycolate
This pathway involves Chloroplast, Peroxisome and Mitochondria. Photorespiration do not occurs in C4C4 plants.

C3 plants	C4 plants
The leaves do not have Kranz anatomy.Photorespiration occurs.RuBisCO is the first acceptor of CO2.PGA is the first stable product.Plants are adapted to all climates.Mesophyll cells perform complete photosynthesis.	The leaves show Kranz anatomy in leaves.Photorespiration does not occur.PEP is the first acceptor of CO2.OAA is the first stable product.Plants are adapted to tropical climate.Mesophyll cells perform only initial fixation.

Factors affecting photosynthesis

1. Light- as light intensity increases, the rate of photosynthesis also increases until light saturation point.
2. Carbon dioxide concentration– with increase in concentration of CO2CO2 rate of photosynthesis increase till the compensation point.
3. Temperature- it does not influence the rate of photosynthesis directly but at higher temperature enzyme activity is inhibited due to denaturation of enzymes which affect the dark reaction.
4. Water– due to increase in amount of water, rate of photosynthesis does not increase proportionally as after saturation no more water is required during photosynthesis.

Blackman’s Law of Limiting Factors states:
If a chemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value: it is the factor which directly affects the process if its quantity is changed.

Class 11 Biology Revision Notes for Mineral Nutrition of Chapter 12

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Mineral nutrition is the study of source, mode of absorption, distribution and metabolism of various inorganic substances (minerals) by plants for their growth, development, structure, physiology and reproduction.
Methods to study the Mineral Requirement of Plants

• Hydroponics is the technique of growing plants in nutrient solution in complete absence of soil. This method is used to determine the nutrients essential for plants.
• In this method plant is cultured in soil-free, defined mineral solution. These methods require purified water and mineral nutrients.
• Essential elements are identified and their deficiency symptoms are discovered by hydroponics methods. It is also used for commercial production of vegetables, like tomato and cucumber.

Essential mineral nutrients- About 65 elements are found in different plants. Following criteria is used to determine the essentiality of an element.

1. Element must be absolutely necessary for the normal growth and reproduction to complete their life cycle.
2. The requirement of element must be specific and not replaceable.
3. Element must be directly involved in the metabolism of plants.

• Macronutrients are present in plants tissues in larger quantity. C, H and O is obtained from water and rest are absorbed from soil.
• Micronutrients or trace nutrients are required in very small quantity.

On the basis of diverse functions, essential elements are divided into following categories-

Role of Macro and Micro nutrients-

1. Essential elements participate in various metabolic processes in plants such as permeability of cell membrane, maintenance of osmotic potential, ETS. Etc.
2. Act as major constituents of macromolecules and co-enzymes.

Various forms and function of essential nutrients-

1. Nitrogen- required by plants in greatest amount, it is absorbed by plants as NO₂^–, NO₃^– and NH₄⁺ . It is one of the major constituent of proteins, nucleic acids and vitamins.
2. Phosphorus- Absorbed by plants from soil in the form of phosphate ions. It is the constituent of cell membrane. All nucleic acids and nucleotides require phosphorus.
3. Potassium – absorbed as potassium ions (K⁺). Help to maintain cation-anion balance in cells. It is involved in protein synthesis, opening and closing of stomata.
4. Calcium – absorbed by plants from soil in form of Calcium ions (Ca²⁺). Used in synthesis of cell wall. It activates certain enzymes.
5. Magnesium- absorbed by plants in form of Mg²⁺ ions. It activates the enzymes for respiration, photosynthesis, and involved in synthesis of DNA and RNA. It is constituent of chlorophyll.
6. Sulphur- plants obtain sulphur in form of sulphate (SO₄^2-). Present in amino acids (cysteine, methionine) and is main constituent of coenzymes and vitamins.
7. Iron- obtained in the form of ferric iron (Fe³⁺). It is important constituent of protein involved in transport system.
8. Manganese-absorbed in form of Mn²⁺ ions. Main function is splitting of water to liberate Hydrogen and Oxygen during photosynthesis.
9. Zinc-obtained as Zn²⁺ ions. Activate enzymes like carboxylases. Needed in formation of Auxin.
10. Copper –absorbed as cupric ions(Cu²⁺). Involved in various metabolic activities and redox reactions.
11. Boron-absorbed as BO₃^3- or B₄O₇^2- ions. Required for uptake of calcium, cell elongation and pollen germination.
12. Chlorine – it is absorbed in form of Cl^– ions. Determine the solute concentration and splitting of water during photosynthesis.

Deficiency Symptoms of Essential elements

• When supply of essential elements becomes limited, plant growth is retarded. The concentration of essential elements below which plant growth is retarded is called critical concentration.
• In absence of any particular element, plant shows certain morphological changes. These morphological changes are called deficiency symptoms.
• The parts of plant that show deficiency symptoms depend upon mobility of elements in the plants. Elements that are actively mobilized (N,Mg,K) show deficiency in older regions. On the other hand, symptoms appear first in young region if the elements are relatively immobile (Ca) and not transported out of mature tissues.
• Kinds of deficiency syndrome are as follows-

Deficiency Disease	Symptoms	Deficient elements
Chlorosis	Loss of chlorophyll leading to yellowing of leaves.	N, K, Mg, S, Fe, MN, Zn, Mo
Necrosis	Death of tissue (leaf).	Ca, Mg, Cu, K.
Stunted plant growth	Less height of plant	Fe, K.
Premature fall of leaves and buds.	Falling of leaves and buds.	P, Mg, Cu
Inhibition of cell division	Less elongation in stem.	Low level of N, K, S, Mo.

• Deficiency of any element may cause many symptoms or same symptoms may be caused by different elements. To identify the deficient elements various symptoms are compared with standard chart.Toxicity of micronutrients- in higher doses, micronutrients become toxic. Any tissue concentration which reduces dry weight of tissue by 10% is called toxic concentration. Critical toxic concentration is different for different elements.
  Mechanism of absorption of elements
• It takes place in two phases. In first phase, rapid intake of ions occurs in free space or outer space of the cells, apoplast. In second phase, ions are taken slowly into inner space, the symplast of the cells.
• Passive movement of ions in apoplast occurs through ion channels and trans-membrane protein. On the other hand, movement of ions into symplast occurs by expenditure of energy by active process.
• The movement of ion is called flux. The inward movement is called influx and outward movement is called efflux.

• Translocation of solutes occur through xylem along with ascending stream of water

Soil as reservoir of essential elements- most of the nutrients required for growth and development is obtained from soil by roots. These minerals are formed by weathering of rocks. Soil also harbours nitrogen fixing bacteria and other microbes, holds water and supplies air to roots. Deficiency of essential elements affects the crop yield. So, fertilisers are used to supplement these elements.
Metabolism of Nitrogen

• Nitrogen is the most prevalent element in living world along with C, H and O. It is the main constituent of proteins, nucleic acids, fats, hormones, enzymes etc.
• The process of conversion of nitrogen to ammonia is called nitrogen fixation. In nature lightening and ultraviolet radiation provide energy to convert atmospheric nitrogen into nitrogen oxide ( No, NO₂ and N₂O).
• Industrial combustion, forest fire and automobiles along with thermal power plants produce nitrogen oxides.
• The decomposition of organic nitrogen of dead plants and animals into ammonia is called ammonification.
• Ammonia is first oxidized to nitrite by bacteria Nitrosomonas or Nitrococcus which is further oxidized to nitrate with help of bacteria Nitrobactor. These processes are called nitrification.

2HN3+3O2→2NO−2+2H++2H2O2NO−2+O2→2NO−32HN3+3O2→2NO2−+2H++2H2O2NO2−+O2→2NO3−

• Nitrates formed is absorbed by plants and transported to leaves. Nitrates is converted into free nitrogen by the process called denitrificaion by bacteria Pseudomonas and Thiobacillus.
• Reduction of nitrogen to ammonia by living organism is called Biological Nitrogen Fixation. The enzyme nitrogenase is present in prokaryotic organism called nitrogen fixer.

N≡N−→−−−−−−NitrogenaseNH3N≡N→NitrogenaseNH3

• Nitrogen fixing microbes may be symbiotic (Rhizobium) or free living (Nostoc, Azotobactor, Anabaena).
• Symbiotic biological nitrogen fixation includes legume-bacteria relationship in which rod shaped Rhizobium lives with symbiotic relation with nodules of Leguminous plants.
• Central portion of nodule is pink or red due to presence of leguminous haemoglobin or leg-haemoglobin.

Nodule formation involves sequence of interaction between root and Rhizobium as follows-

• Rhizobia increase in number and attach with epidermis of roots. Root hairs curls and bacteria invade it. An infection thread is formed that carries the bacteria into cortex of root.
• Nodule formation starts in cortex of root. Bacteria is released from thread to cells which leads to formation of specialized nitrogen fixing cells.
• Nodules establish direct vascular connection with host for exchange of nutrients.
• Nodule contains all necessary biochemical components like enzyme nitrogenase and leg-haemoglobin.

• Enzyme nitrogenase is a Mo-Fe protein and catalyses the conversion of atmospheric nitrogen into ammonia.

The reaction is as follows-
N2+8e−+8H++16ATPN2+8e−+8H++16ATP→2NH3+H2+16ADP+16P1→2NH3+H2+16ADP+16P1

• The enzyme nitrogenase is highly sensitive to molecular oxygen and needs anaerobic condition. To protect this enzyme from oxygen, the nodules contain an oxygen scavenger called leg-haemoglobin.
• The ammonia synthesized by nitrogenase enzyme require large amount of energy (18ATP) for each NH3 produced.

Fate of ammonia- at physiological pH, ammonia is converted into ammonium ions (NH₄⁺).It is toxic for plants in larger concentration and ammonium ion is converted into amino acids by two methods-

1. Reductive amination– in this process ammonia reacts with α-ketoglutaric acid to form glutamic acid.

α−ketoglutaricacid+NH+4+NADPHα−ketoglutaricacid+NH4++NADPH−→−−−−−−−DehydrogenaseGlutamateglutamate+H2O+NADP→DehydrogenaseGlutamateglutamate+H2O+NADP

1. Transamination– it involves the transfer of amino group from amino acids to keto group of keto acid. Glutamic acid is the main amino acid from which transfer of NH3 takes place and other amino acids are formed by transamination. The enzyme transaminase catalyses all such reactions.

Two important amides asparagine and glutamine found in plants as structural part of proteins. They are formed from aspartic acid and glutamic acid by addition of another amino group to it.

Class 11 Biology Revision Notes for Transport in Plants of Chapter 11

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Plant transport various substances like gases, minerals, water, hormone and organic solutes to short distance (one cell to another) or long distance as water from roots to tips of stem.

• Long distance transport occurs through vascular system, xylem and phloem called translocation through mass flow.
• The direction of translocation may be unidirectional as in case of water and multidirectional as in minerals and organic solutes.

Simple Diffusion-

• Movement by diffusion is passive and slow along the concentration gradient through permeable membrane.
• No energy expenditure takes place. It occurs in liquid and gases.
• Rate of diffusion are affected by gradient of concentration, permeability of membrane, temperature and pressure.

Facilitated Diffusion-

• Lipid soluble particles easily pass through cell membrane but the hydrophilic solutes movement is facilitated.
• For facilitated diffusion, membrane possesses aquaporins or water channels. Aquaporins are membrane proteins for passive transport of water soluble substances without utilization of energy.
• The protein forms channels in membrane for molecules to pass through. The porins are proteins that forms huge pores in the outer membrane of the plastids, mitochondria etc.
• Water channels are made up of eight different types of aquaporins.

Symport, Antiport and Uniport-

• In Symport, both molecules cross the membrane in the same direction.
• In Antiport, both molecule moves in opposite direction.
• When a molecule moves across a membrane independent of other molecules, the process is called uniport.

Active Transport

• Uses energy to pump molecules against the concentration gradient. It is carried out by membrane proteins.
• In active transport movable carrier proteins are called pumps.
• The pumps can transport substance from low concentration to high concentration. The carrier proteins are very specific in what it carries across the membrane.

Comparison between Transport mechanisms-

Simple diffusion	Facilitated diffusion	Active transport
Special membrane protein is not required.	Special membrane protein is required.	Special membrane protein is required.
Not selective	Highly selective	Highly selective
Transport do not saturate	Transport saturate	Transport saturate
No uphill transport	Uphill transport	Uphill transport
No ATP energy is required.	No ATP energy is required.	ATP energy is required.

Plant Water Relationship

• Water is essential for all physiological activities of plants along with all living organisms. It provide medium for most substances to dissolve in it.
• Protoplasm of cells contains water in which different molecules are dissolved and suspended.
• Terrestrial plants take lot of water and release most of it in form of water vapour by the process of transpiration.
• Water is the limiting factor for plant growth and productivity in both agricultural and natural environments.

Water Potential (ΨwΨw)- is a concept fundamental to the understanding of water movement. Water potential is determined by solute potential (ΨsΨs) and pressure potential (ΨpΨp).

• Water molecules possess kinetic energy. The greater the concentration of water in the system, the greater is its kinetic energy or water potential. So pure water has greatest water potential.
• Water potential is denoted by Greek symbol Psi (ΨΨ) and is expressed in pressure unit Pascal (Pa).
• Water pressure of pure water is taken as zero at standard temperature and pressure. A solution has less water potential due to less water concentration.
• The magnitude of lowering of water potential due to dissolution of solute is called solute potential (ΨsΨs). Solute potential is always negative. More the solute molecules in the solution lesser the solute potential.
• If a pressure greater than atmospheric pressure is applied to pure water or solution, its water potential decreases. Pressure potential is usually positive. Pressure potential is denoted by (ΨpΨp).
• Water potential of a cell is affected by both solute and pressure potential. The relationship is as follows.

ΨwΨw = ΨsΨs + ΨpΨp
Ψw=Ψs+ΨpΨw=Ψs+Ψp
Osmosis is the diffusion of water across a semi-permeable membrane. The net direction and rate of osmosis depends upon the pressure gradient and concentration gradient. Water will move from its region of higher concentration to region of lower concentration until equilibrium is reached.

• Solute A has more water and less solutes so high water potential in comparison to the solution in B container.
• Osmotic potential is the pressure required to prevent water from diffusing. More the solute concentration greater will be the pressure required to prevent water from diffusing it.
• Numerically osmotic pressure is equal to osmotic potential but sign is opposite. Osmotic pressure is the positive pressure while osmotic potential is negative.
• If the surrounding solution balances the osmotic pressure of cytoplasm, the solution is called isotonic.
• If the external solution is more dilute than cytoplasm, it is hypotonic. The cells swell up when placed in hypotonic solution.
• If the external solution is more concentrated than cytoplasm, it is hypertonic. Cell will shrink in hypertonic solution.
• Plasmolysis is the shrinkage of the cytoplasm of the cell away from its cell wall under the influence of hypertonic solution. The pressure of plasmolysis is usually reversible when the cell is placed in hypotonic solution.
• The pressure build up against the wall due to movement of water inside is called turgor pressure. It is responsible for enlargement and extension growth of cells.
• Imbibition is a special type of diffusion when water is absorbed by solid colloids causing them to increase in volume. For example absorption of water by seeds and dry woods. Imbibition is also a kind of diffusion because movement of water is from higher concentration to lower concentration.
• Water potential gradient between the absorbent and liquid imbibed is essential for imbibition.

• Long distance transport of water in plants takes place by mass or bulk flow system. It is the movement of substance in bulk from one point to another as a result of pressure difference between two points.
• The bulk movement of substances through the conducting or vascular tissue of plants is called Translocation. Xylem is associated with translocation of water and mineral salts, some organic nitrogen and hormone from roots to aerial parts of plants.
• Phloem transport organic and inorganic solutes from leaves to other part of plants.

Absorption of water by plants

• Water is absorbed along with mineral solutes by root hairs by diffusion. The absorbed water passes to deeper layer by two pathways.

Apoplast pathway	Symplast pathway
It consists of nonliving parts of plants body such as cell wall and intercellular spaces.There is little resistance in movement of water.It is faster.Metabolic state of root does not affect apoplast pathway.	It consists of living parts of plant body such as protoplast connected to plasmodesmata.Some resistance occurs in the movement of water.It is slightly slower.Metabolic state of root directly affect symplast pathway.

• Most of the water flows in roots via apoplast pathway because cortical cells are loosely packed and offers no resistance to water movement.

• The inner boundary of cortex, endodermis is impervious to water due to suberised matrix called Casperian strip. Water molecules are directed through wall regions that are not suberised.
• Water flows through the different layers of roots to reach the xylem tissues as follows-

• A mycorrhiza is the symbiotic association between a fungus and angiospermic roots. The fungal filaments forms a network around the young root to have large surface area that help to absorb mineral ions and water from the soil. The fungus provide minerals and waters and roots in turn provide organic and nitrogen containing compounds.

Ascent of saps (Translocation of water)
The upward movement of water from roots towards the tips of stem, branches and their leaves is called ascent of sap.

• Vital force theory was forwarded by J.C.Bose in 1923. This theory believes that the innermost cortical cells of the root absorb water from the outer side and pump the same into xylem channels.
• Root pressure theory was forwarded by Priestley in 1916. Root pressure is positive pressure that develops in the xylem sap of the root of plants. It can be responsible for pushing up water to small heights in plants.
• Loss of water in liquid phase by herbaceous plants from the tips of leaf blades is known as guttation.
• Water rises in tubes of small diameters, kept in vessels having water due to force of surface tension. Similarly water rises up in the walls of xylem channels due to adhesion and cohesion. This theory is called Theory of Capillarity.
• Cohesion Tension theory was put forwarded by Dixon and Joly in 1894. According to this theory water is mostly pulled due to driving force of transpiration from the leaves. The water molecules remain attached with one another by cohesion force. The water molecule does not breaks in vessels and tracheid due to adhesive force between their walls and water molecules. On account of tension created by transpiration, the water column of plant is pulled up passively from roots to great heights.
• Transpiration is the loss of water in the form of water vapour from aerial parts of plants. The following purpose is fulfilled by transpiration-

1. Creates transpirational pull for absorption and transport in plants.
2. Supplies water for photosynthesis.
3. Transport minerals and salts from soil to other parts of plant.
4. Cool the leaves and maintain their shape and size.

• Photosynthesis is limited by available water. C4C4 plants are twice as efficient as C3C3 plants in term of fixing carbon. Although C4C4 plants uses half as much water as C3C3 plants for the same amount of CO2CO2 fixed.

Uptake and transport of mineral nutrients

• Most of the minerals enter the roots by active absorption into the cytoplasm of epidermal cells because-

1. Minerals are present in the soil as charged particles (ions) which cannot move across cell membranes.
2. The concentration of ions in soil is usually lower than concentration in roots.

• Active absorption needs energy in form of ATP. Active uptake of ions is also responsible for water potential gradient in roots.
• Transport proteins of epidermal cells are control point where quantity and type of solutes that reach the xylem is adjusted.
• The ions that reaches to xylem by active or passive transport moves further upward along with transpirational pull.
• The chief sink of mineral elements are growing region of plants like apical meristem, young leaves, growing flower and fruit, and the storage organs.
• Minerals are frequently remobilized from older senescing part of the plants to young growing parts of plant.
• The elements most readily mobilized include phosphorus, sulphur, nitrogen and potassium. The element like calcium is not mobilized as it is the structural components of plant body.

Phloem transport: Flow from Source to Sink

• Food (sucrose) is transported by phloem from source to sink. The part of plant that synthesize the food is called source and part where food is used or stored is called sink.
• The source and sink can be reversed by the plants depending upon the season or plant’s need. So, the direction of movement in the phloem is bi-directional.
• Phloem sap is mainly water and sucrose but other sugars, hormones and amino acids are also translocated through it.

Pressure flow or Mass flow hypothesis

• It is the most accepted theory for the translocation of sugar from source to sink. Glucose is prepared at source by photosynthesis which is converted into disaccharides (sucrose). Sucrose moves into companion cells and then into sieve tube cells by active transport.
• Loading of phloem at source creates a water potential gradient that facilitates the mass movement in the phloem.
• Sieve tube cells of phloem forms a long column with holes in their wall called sieve plates. Cytoplasmic strands pass through the hole in the sieve plates to form continuous filament. Hydrostatic pressure developed in sieve tube cells moves the sap in the phloem.
• At sink, incoming sugar is actively moved out of the phloem as complex carbohydrates. The loss of solute produces a high water potential in the phloem and water passes out and returning into xylem.

Class 11 Biology Revision Notes for Cell Cycle and Cell Division of Chapter 10

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• The sequence of events by which a cell duplicates its genome, synthesizes the other constituents of cells and eventually divides into two daughter cells is called cell cycle.
• DNA synthesis occurs in one specific stage of cell division but distribution of chromosome in cells occurs in complex series of events during cell division.

Phases of Cell cycle
Human cell divides once in approximately 24 hours, which may vary in different organisms. In yeasts it takes about 90 minutes to complete the cell division process.
Cell cycle is divided into two basic phases-

1. Interphase– it is the phase between two successive M phases. Interphase lasts for 95% of a cell cycle. This phase is called as resting phase but during this period the cells prepare itself for nuclear division by cell growth.
2. M Phase– when the actual cell division or mitosis occurs. It starts with karyokinesis (nuclear division) or duplication of chromosome and end with cytokinesis or division of cell matrix (cytoplasm division).The interphase is divided into three further phases:

• G1 phase represents the interval between mitosis and initiation of DNA replication. Cell is continuously active and grows in size.

• During synthesis phase, replication or synthesis of DNA takes place and amount of DNA get doubles per cell.
• During G2 phase protein is synthesized in preparation for mitosis.
• In adult animals, some cells do not divide or may divide occasionally. These cells do not divide further and exits the G1 phase to enter an inactive stage called Quiescent Stage (G0) of cell cycle.
• In animals mitotic division is present in only somatic diploid cells but in plants it is seen in both haploid and diploid cells.
• Mitosis cell division is also known as equational division because the numbers of chromosome remain same in parental and progeny cells.

• Prophase is the first phase of mitosis followed by G2 phase. It involves following events-

1. Initiation of condensation of chromosomal materials.
2. Movement of centrioles towards opposite poles of the cell.
3. At the end of prophase, endoplasmic reticulum, nuclear membrane, Golgi complex disappears.

• Metaphase starts with complete disappearance of nuclear membrane. The most suitable stage for study of morphology of chromosomes. It involves

1. Condensation of chromosomal materials in to compact and distinct chromosomes made up of two sister chromatids attached with spindle fibres with kinetochores.
2. Chromosomes arrange at centre of cell called metaphase plate.

• Anaphase involves following steps:

1. Splitting of each chromosome at centromere into two sister chromatids.
2. Two chromatids start moving towards opposite poles.

• Telophase is the last stage of mitosis which involves

1. Chromosomes reach at opposite poles and loose its identity as discrete unit.
2. Nuclear membrane reassembles around the chromosome clusters.
3. Nucleolus, Golgi complex and ER reappear.

• Cytokinesis is the division of cytoplasm of a cell after karyokinesis (division of chromosome) into two daughter cells. In animal cells, appearance of furrows in plasma membrane that deepens gradually and joins to divide cytoplasm into two parts.
• In plant cells, wall formation starts at the centre and grows outwards to meet lateral walls. The formation of cell wall begins with formation of cell plate.

Significance of Mitosis

1. Mitosis produces diploid daughter cells with identical genetic complement.
2. It helps in repair of cells, especially in lining of gut and blood cells.
3. Meristematic division in apical and lateral cambium results in continuous growth of plants.

Meiosis- The cell division that reduces the number of chromosome into half and results in the production of haploid daughter cells is called meiosis. It helps in production of haploid phase in the life cycle of sexually reproducing organism. It involves following events.

1. Two sequential cycles of nuclear and cell division called meiosis I and meiosis II but single cycle of DNA replication.
2. It involves pairing of homologous chromosome and recombination of them.
3. Four haploid cells are formed at the end of meiosis II.

Meiosis I	Meiosis II
Prophase I	Prophase II
Metaphase I	Metaphase II
Anaphase I	Anaphase II
Telophase I	Telophase II

• During Leptotene, the chromosome becomes distinct and visible under microscope. Compaction of chromosome continues throughout the leptotene phase.
• During Zygotene stage, chromosomes start pairing together (synapsis). The paired chromosomes are called homologous chromosome. Synaptonemal complex formed by a pair of homologous chromosome is called bivalent or a tetrad.
• During Pachytene stage, crossing over between non-sister chromatids of homologous chromosome occurs for exchange of genetic materials. The crossing over is enzyme –mediated process which involves enzyme recombinase.
• Diplotene is recognized by dissolution of synaptonemal complex and tendency to separation of bivalent except at the site of crossing over. This forms an X like structure called chiasmata.
• Diakenesis is marked by terminalisation of chiasmata. The nuclear membrane breaks and nucleolus disappear.
• In metaphase I the bivalent chromosome align at equatorial plate and microtubules from the opposite poles of the spindle get attached to the pair of homologous chromosomes.
• Anaphase I – homologous chromosome separate but sister chromatids remain attached at centromere.

• During Telophase I, nuclear membrane and nucleolus reappears and cytokinesis follows. This is called as diad of the cells.
• The stage between two meiotic divisions is called interkinesis and it is short lived that follows Prophase II.

Meiosis II

• It is initiated immediately after cytokinesis before chromosome gets elongated.
• In prophase II, nuclear membrane disappears and chromosome becomes compact.
• At metaphase II stage, the chromosomes align at equator and microtubules attach with kinetochores of sister chromatids.
• Anaphase II start with splitting of centromere of each chromosome to move towards opposite poles.

• Meiosis ends with Telophase II in which two groups of chromosomes get enclosed by nuclear membrane followed by cytokinesis to form tetrad of cells (four haploid daughter cells).

Significance of meiosis–

1. Meiosis forms the gametes that are essential for sexual reproduction.
2. Crossing over introduces new recombination of traits.
3. Helps in maintenance of chromosome number of sexually reproducing organism.
4. Provides evidence of basic relationship of organisms.

Difference between Mitosis and meiosis

Mitosis	Meiosis
Takes place in the somatic cells.It is a single division which produces two cells.Haploid and diploid both kind of cells may undergo mitosis.Crossing over absent.Pairing of chromosome does not occur.	Takes place in reproductive cells.It is a double division which produces four cells.Only diploid cells undergo meiosis cell division.Crossing over takes place.Pairing of homologous chromosome occurs.