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FSc Notes Biology Part 2 Chapter 15 Homeostasis Notes

FSc Notes Biology Part 2 Chapter 15 Homeostasis Notes


The maintenance of a constant internal environment by a living organism is called homeostasis. OR the ability of a living organism to maintain or nearly maintain constant internal body conditions is called homeostasis. Homeostasis means “Steady state” or “Staying similar”. According to Claude Barnard that living organisms face two environments:
  1. External Environment: That surrounds organisms.
  2. Internal Environment: Mostly tissue fluid where cells live.

External environment fluctuates continuously. But organisms resist external changes by adjusting the internal environment. The main organs of homeostasis are lungs, skin, liver and kidneys. Organisms make these adjustments with the help of various control system. Substances which must be kept constant in the body are salt, water, temperature and removal of toxic wastes.
Because external environmental changes may affect these substances. Homeostasis protect the organisms from the harms of changes in external environments.

Various Aspects of Homeostasis

There are three aspects of homeostasis.
  1. Osmoregulation: The mechanism of regulation of solutes and gain or loss of water between the organism and its environment is called osmoregualtion.
  2. Excretion: The removal of harmful wastes substances from the living body is called excretion.
  3. Thermoregulation: The maintenance of internal body temperature within a tolerable range is called thermoregulation.

Homeostasis Control System

A self regulating system in the body which operate by means of feedback mechanism is called homeostasis control system Changes occur in our bodies which always show opposite response to these changes. Many physiological processes in the body take part to maintain homeostasis. A check and balance system is necessary for homeostasis’s. Due to this system the internal body conditions remain constant and in regular form.
A homeostatic control system consists of three functional components.
  1. Detector: Those organs which any change inside the body are called Receptors.
  2. Controller: The receptors transfer messages to a control system called central control system.
  3. Effector: controls system send order to a particular organs called effectors.
Effector perform a particular action which is necessary to maintain the system constant. Any change from the normal condition is called stimulus.

Example of Homeostatic Control System

Blood glucose concentration in human is an example of homeostatic control system. Normal blood glucose level is 90 mg/ 100 ml. Any increase or decrease in this level is harmful to the cells. The glucose level rises after taking sugar rich meal while falls during physical exercise. Pancrease secrete two hormones insulin and glycogen. Both these hormones regulate the blood glucose level. When blood glucose level decrease than normal. It stimulate Pancrease which secrete a hormone into the blood. This hormone is called glucogon which is carried to the liver by blood. In liver glucogon convert stored glycogen into glucose. Thus glucose level increase in the blood and become normal. Similarly rise in blood glucose level than normal also stimulate pancreas. Pancrease secretes another hormone in the blood called insulin. Insulin converts the excess of glucose into glycogen which stored in the liver. Thus glucose level in the blood become normal.

Osmoregulation in  Plants

Water is important factors for plant which is used in different metabolic process. Plants are distributed in different habitats which depends on water. But the amount of water is different in different places. According to their habitat plants have special adaptation to regulate their salt and water level. On the basis of availability of water plants are classified into four groups.
  1. Hydrophytes: (Hydro = water, phyte = plant) Those plants which grow in or near water are called hydrophytes. Plant body is either completely found in water or partially submerged. Roots are either absent or poorly developed. Water is absorbed throughout their body surface. Plant body is covered by mucilage which protect them from rotting effect of water. Leaves have large surface area and numerous stomata on the upper surface . They remove extra water by excessive transpiration.
  2. Halophytes: (halo = salt, phyte = plant) Those plants which grow in salty soil are called halophytes. Halophytes are salt tolerator plants. Their leaves contain water storage cells. Leaves have thick cuticle which prevent transpiration. They absorb water by active transport from the soil because soil contains high percentage of salts. They produce respiratory roots called pneumatophores. They mostly grow on seashores forming special type of vegetation called mangrove. Example: Salsola, Rhizophora etc.
  3. Mesophytes: (Meso = middle, phyte = plant) Those plants which grow in places which are neither very wet nor very dry are called Mesophytes. They have well developed roots. Leaves are dark green and contain abundance chloroplast. Stomata are present on the lower surface of leaves. Their body is covered by cuticle to prevent lose of water. Their stomata open or closed according to the availability chloroplast. Stomata are present on the lower surface of leaves. Their body is covered by cuticle to prevent lose of water. Their stomata open or closed according to the availability chloroplast. Stomata are present on the lower surface of leaves. Their body is covered by cuticle to prevent lose of water. Their stomata open or closed according to the availability of water. Examples: Rose , Brassica, Citrus, etc.
  4. Xerophytes: Those plants which grow in dry hot and sandy place are called xerophyte. They are also called desert plants. Such habitat contain very less amount of water. These plants have long and deep roots to absorb undergroung water. Some xerophytes produce root on the soil surface or near surface absorb rain water rapidly. Stem also contain water storage tissues. In some plants leaves are modified into spines to reduce transpiration. Leaves and stem are covered with thick cuticle. Stomata are present in pits or very few in number. Some leaves have shining surface to avoid light.

Different Types of Environment for a Cell

Life is dependent on metabolism which requires balance of water and dissolved solutes. The environment outside the cell may be; hypotonic, hypertonic, isotonic.
  1. Hypotonic Environment: When the external environment is less concentrated than internal environment is called hypotonic. e.g. fresh water.
  2. Hypertonic Environment: When the external environment is more concentrated than internal environment is called hypertonic. e.g. sea water.
  3. Isotonic Environment: When the concentration of solutes is equal in external and internal environment is called isotonic.

Types of Animals on the Basis of Osmoregulation

  • Osmoconformers: Those animals whose body fluid concentration is equal to the concentration of solution in the external environment are called osmoconformer. These animals keep their body fluid isotonic. There is no net gain or loss of water. Because the body fluid and external solution are equally concentrated. Therefore equal amount of water move in and out the body. Examples: Hagfish, ray, shark, invertebrates.
  • Osmoregualtors: Those animals whose body fluid concentration is different from outside environment are called osmoregualtors. They use energy to keep balance of water and salt in their body. They excrete extra water in fresh water environment and excrete salt in marine environment.

Osmoregulation in Terrestrial Animals

The major problem faced by land animals is the evaporative loss of water which causes dehydration. Arthropods and vertebrates are successful animals which can property maintain osmoregualtion.

Terrestrial animal maintain balance of water by: Drinking water, eating moist food, concentrated urination and preventing dehydration.

Land animal lose water by: Excreting dilute urine, sweating, breathing.

Land animals show the following adaptation for osmoregualtion:
  1. Waterproof body covering: Insect have waterproof waxy exoskeleton which prevent dehydration. Vertebrate animal contain waterproof waxy epidermis or skin preventing loss of water from their body.
  2. Use of metabolic water: Some animal survive without drinking water. Kangaroo rat do not drink water and use metabolic water. They feeds on seed which produce water.
  3. Storage of water: Camel store water in the lumen of stomach. Uromastix store water in the large intestine.
  4. Amniotic cavity: Embryos of mammals, birds, and reptiles develop in water filled amniotic cavity.
  5. Anhydrobiosis: The ability of organism to tolerate dehydration for a certain period of time is called anhydrobiosis.
  6. Production of concentrate urine: Kangaroo rat produce much concentrated urine due to long loop of henle in kidney. Desert animal spent day in moist burrow and come out at night. Some insect lay eggs on humid and moist places to prevent embryo dehydration.

Osmoregulation in Fresh Water Animals:

Fresh water animal have higher salt concentration in their body fluid than in surrounding water. If they lose much salt or take in too much water they die. Therefore they expel water and retain salts. Fresh water fish are covered by scales and mucous secretion which preventing water entry into the body. They absorb salt by their gills and take in salt rich food. They remove extra water by producing large amount of dilute urine. Fresh water Amoeba and paramecium pump out extra water by contractile vacuoles.

Osmoregulation in Marine Animals:

Marine animal live in salty water, so their body fluid contain less salt concentration. Marine animals have different adaptations for osmoregulation:
  • Bony Fishes: Bony fished constantly loses water through their surface by osmosis. These fished during water continuously. They retain water and expel salt through their gills. They also save water by excreting small amount of concentrated urine.
  • Cartilaginous Fish: Most cartilaginous fishes maintain lower internal salt concentration than that of seawater. Shark and rays store high concentration of urea in their body. It make the body fluid slightly saltier than seawater. They also have trimethylamine oxide for protection against toxic urea. They do not face the problem of water loss. They contain special glands in their rectum called rectal glands. These glands help to remove excess amount of salts.
  • Salmon fish have remarkable osmoregulatory adaptation: Salmon fish can migrate between fresh and marine water.In ocean: they during more water and excrete extra salts from their gills. In freshwater: They stop drinking water and gills absorb salts from fresh water.
  • Invertebrates: Marine invertebrates and hagfishes are osmoconformers. They do not have osmoregulatory mechanism.


The removal of harmful or toxic material produced in metabolic process from the living body is called excretion. Many chemical reactions occur within the cell to keep the organism alive. The products of these reaction are called metabolites. Some products are harmful to a greater or lesser extent to the organism. Therefore these products must be removed from the body. Organisms have developed different specialized system for removal of such wastes from their bodies.

Excretion in Plants:

There is no proper excretory system in plants like animals . plants use different mechanism for removal of their waste products. In plants rate of catabolism is slow and waste products are produced in least amount.

Waste Products: The main waste products produce in plants are: carbon dioxide and oxygen, water, Nitrogenous wastes. Removal of CO2 and O2: CO2 is the waste product produce in respiration. Oxygen is the by product of photosynthesis. Plants remove these gases through stomata or whole body surface. Carbon dioxide is released at night and oxygen in the daytime.

Removal of water: Water in excess to the need of plant body is also considered as waste product extra water is removed from plant by two methods:

Transpiration: Removal of water vapors from aerial parts of plant.

Guttation: Removal of water drops from the tip or margin of leaves. Guttation occurs by special openings called hydathodes. This process occur when water absorption is high and transpiration rate is low.

Nitrogenous Wastes: A small amount of nitrogenous waste is also produce in plants due to oxidation of protein.

Waste products are not removed but stored in some parts of the plant:
  1. Some plants store these wastes in mature cells of barnacles and trunk especially in old dead xylem. e.g. Ebony.
  2. Some plants store tannin in dead tissues of bark. e.g. Oak.
  3. Some plants actively secrete waste products into the soil through roots.
  4. Plants also store glucosides and alkaloids in their leaves. These leaves become yellow and fall off in autumn and release these wastes products.
  5. Some plants have gland cells which secrete latix, resin, gum and mucilage These products are released when the plant is injured.

Excretion in Animals

Animals are very active group of organisms and need energy for life activities. They get energy from the break down of food. As a result many waste products are produced. They are harmful if remain in the body for long time. Therefore, excretion is necessary to keep the animal alive.

Types of waste products: Carbon dioxide: Produced by the break down of glucose during respiration. CO2 is removal by lungs. Ammonia, urea, Uric acid, Excess of water and salts.

Formation of waste products:
  • CO2: Produced by the breakdown of glucose during respiration.
  • Excess water: Removed by Kidneys and skin through sweating.
  • Nitrogenous wastes: Ammonia, Urea, Uric acid are collectively called nitrogenous wastes.They are produced from the breakdown of protein in the diet.

Types of Nitrogenous Wastes and Their Relation With Habitat of Animal

A general relationship exists between habitat of organism and nature of nitrogenous wastes. These nitrogenous wastes are ammonia, urea and uric acid. All these wastes are not excreted in the same animal. These wastes are produced and removed in different animal living in different habitats. The type of nitrogenous waste and their removal depend upon the habitat of an animal.

Ammonia (NH3):
  • It is the excretory product of aquatic animals.
  • It is produced by the break down of amino acids.
  • It is very harmful to the living cells.
  • It is the removed mostly by diffusion.
  • It is highly soluble in water.
  • About 500 ml of water is required to excrete one gram of ammonia.
  • Animals which excrete ammonia are called ammonotelic.
  • Examples: Protozeoan, Earthworm, Fishes, Sponges etc.

Urea {CO (NH2)2}:
  • Urea is the excretory products of mostly land animals with moderate supply of water.
  • It is produced in the liver from ammonia.
  • It is less toxic than ammonia and can be store in the body for some time.
  • One gram of urea need 50 ml of water for removal.
  • Animals which excrete urea are called ureotelic.
  • Examples: Mammals, Shark, Turtles, Adults Amphibians.

Uric Acid (C5O3N4H4):
  • It is the excretory product of animals which live in the environment with acute supply of water.
  • These animal do not use more water.
  • Uric acid is harmless and least soluble in water.
  • One ml of water is needed to remove 1 gram of uric acid.
  • It is excreted in the form of paste or urete crystal with little water loss.
  • Animals excreting uric acid are called uricotelic.
  • Example: Birds, insects, land snails, many reptiles.

Excretion in Planaria

Planaria is a fresh water invertebrate. Excretory product: planaria excrete ammonia and is ammonotlic. This excretion occurs by two ways, diffusion, specialized excretory system.

Excretory organs:
Planaria have simple tubular excretory system called protonephiridia. Protonephridia arranged in two longitudinal trunk one on either side of the body. Each track consists of a network of closed tubules without internal openings. These tubules divide into small branches which ends up in flame cells. Tubules open to the outside by small opening called nephridiophores.

Structure of flame cell:
Flame cells are club shaped hollow cells. Each flame cell contain nucleus, cytoplasm and internal cavity. Each flame cell contain nucleus, cytoplasm and internal cavity. A group of cilia is present in the cavity. Cilia perform a movement like a flame of candle. Flame cells also has many cytoplasmic elongations.

Mechanism of excretion:
Flame cells absorb wastes from the cells and push it into the cavity. From cavity the beating of cilia carried the waste to the excretory tubules. Finally the waste are removed to the upside by nephridiophore.

Excretion in Earthworm:

Earthworm live in moist soil.

Excretory product:
These are CO2, ammonia, urea.

Excretory organs:
In earthworm excretory system consists of coiled tubes called nephridia. Nephridia are present in all segments except first three and last segment. Each segment contain a pair of nephridia. Nephridia are open at both sides.
Structure of Nephridium:
Each nephridium consists of three parts:
  1. Nephrostome
  2. Main body
  3. Nephridiopore

Nephrostome: It is rounded and ciliated funnel. It open into the coelomic cavity and collect coelomic fluid. 

Main body : It consists of following two parts:
  • Coiled Tubular part: Nephrostome opens into this part.Blood capillaries surround these coiled tubes.
  • Bladder: The coiled tubular part open into a side part called bladder.

Nephridiopre: The bladder opens outside by a small pore called nephridiopore.

Mechanism of Excretion
Nephrostome collects wastes from coelomic fluid and transfer it into the main body. When fluid move along the coiled tubules, its cells reabsorb important substances from it. After reabsorption only urine is left in the tubule. From tubule urine is pushed into bladder. Finally urine is excreted out by nephridiopore.

Excretion in  Cockroach

Cockroach is a terrestrial animal. It has acute shortage of water.

Excretory Products:
In cockroach excretory product is uric acid. Cockroach excretes uric acid without losing water.

Excretory organ:
Excretory organ of cockroach is malpighian tubules.

Malpighian tubules are present at the junction of mid-gut and hind-gut. Malpighian tubules are the only excretory organs in animal kingdom that are connected with digestive tract. So excretory waste and digestive waste are excreted together.

Number: There are six groups of malpighian tubules in cockroach. Each group consist of about 15-20 malpighian in tubules.

Color: They are yellowish in color.

Shape: They are thread like or hairs like unbranched tubes.

Each malpighain tubule is blind and an inch long. Malpighian tubule consists of three parts:
  1. Proximal end: This end opens into the hind gut.
  2. Lumen or duct: This is the middle part.
  3. Distal end: This end is blind or closed.
Mechanism of Excretion:
Distal end float freely in the haemolymph (body fluid). It collect nitrogenous waste and push them into the hind gut. Hind gut reabsorb water and push the waste into the rectum. Rectum reabsorb large amount of water and salt. Thus uric acid become dry and excreted out with the feces without losing water.

Excretion in Human Body

The removal of metabolic waste products from the body is called excretion. A large number of chemical reaction occur in our body cells. The products of these chemicals reactions contain various wastes, which are called metabolic wastes.  
Waste Products: in human common metabolic wastes are: CO2, urea, uric acid, used hormones, drugs, bile pigments, excess of water and salt.
Excretory organs:
Those organs which remove metabolic wastes of the body are called organs. The excretory organs in human are:
  1. Kidney: Kidneys are the primary excretory organs. They remove, urea in urine, nitrogenous waste, drugs and hormones, toxins, excess of salt and water , bile pigments.
  2. Liver: Which excrete, bile pigment, cholesterol.
  3. Skin: Skin contain sweat glands which excrete sweat. Sweat formation causes cooling. In kidney failure, more urea is excreted by the sweat glands.
  4. Lungs: Lungs remove CO2 and also lose water vapors.

Urea Cycle

The cyclic chain of chemical reaction which produces urea from amino acid is called urea is also called ornithine cycle. Because ornithine play a vital role in urea formation. This cycle was first studied by Krebs and Henseleit. Protein in diet are converted into amino acids. Excess of amino acids are transported to the liver. Amino group is removed from these amino acids. This amino group is first converted into ammonia and then into urea.
Site of urea formation:
Urea formation is always take place in the liver. It was experimentally proved by a scientist named “ Mann” he found that when liver was removed form a dog, no urea is formed.
Rate of formation: Daily 25 – 30 grams urea is formed in the body.
Raw material for urea: in urea cycle two ammonia and one CO2 molecules enter the cycle.
  • Citrulline Formation: Ornithine combine with ammonia and C02 to form citrulline and H2O. Ornithine + NH3 + CO2 ------------------------- Citrulline + H2O
  • Argininosuccinate Formation: Citrulline then combine with another ammonia to form argininosuccinate.
  • Arginie Formation: Argininosuccinate is then spilt into arginine and fummeric acid.  Argininosuccinate ------------------- Arginine + Fummeric acid.
  • Urea Formation: Arginine is decomposed by an enzyme arginase in the presence of Water to form urea and ornithine. Ornithine to now again available to start another cycle.

Liver as Homeostatic Organ

Liver is the central factory of metabolism and help in homeostasis. It is the body central metabolic clearing house. It support the vital activities of the kidney. Liver perform the following homeostatic functions:
Bile Production: Liver produces a yellowish, green alkaline substance called bile. It neutralizes the acidic food. Bile is also antiseptic and acts as germ killer.

Internal structure of kidney

Internally each kidney consist of two parts:
  1. Cortex: it is the outer darker part of kidney.
  2. Medulla: is the inner lighter part of kidney. In medulla about 10 -15 cone like structure are present called renal pyramids. These pyramids open into a wide funnel shaped part called pelvis. The middle of medulla contains many collecting ducts which carry urine to the pelvis. Each kidney contain about one million nephrons or urinary tubules which form urine.
Cortical nephrons: Nephrons which are present only in cortex.
Juxta medullary nephrons: Nephrons arranged along the border of cortex and medulla are called juxta medullary nephrons. Tubular system of these nephron is present in the medulla.

 Structure of  Nephron

The structural and functional units of the kidney which produces urine is called nephron. Nephrons are held together by connective tissues. Each nephron is highly coiled tube and blind at one end. Each nephron consist of two parts:
  1. Renal carpsule
  2. Renal tubule
Renal Carpsule:
It is the blood filtering unit of nephron.
  1. Bowman s capsule: The blind end of nephron form double walled cup shaped structure called Bowman’s capsule.
  2. Glomerulus: Bowman’s capsule contain a network of blood capillaries called glomerulus. Blood enters the glomerulus through afferet arterioles and leaves through efferent arterioles.
Renal Tubule:
It is the tubular portion of nephron. It is also called filtrate refinery. It is surrounded by capillary network. Renal tubule consist of three parts:
  1. Proximal Convoluted tubule: This is the first coiled part of renal tubule. Most of the rebsorption take place here.
  2. Loop of henle: This the u – shaped narrow part of nephron. It helps in the reabsorption of water and salt.
  3. Distal convoluted tubule: It is highly coiled and expended part. It lies in the cortex and help in urine formation. Several nephrons open into one collecting duct.


Urine Formation: 

The function of nephron is the formation of urine.

Urine formation occur in the following steps:
  1. Glomerular Filtration: The process of separation of liquid from the blood in the glomerulus is called glomerular filtration. Blood flows under high pressure in glomerulus. As a result some fluid is filtered out from capillary wall into Bowman’s capsule. This liquid is called glomerular filtrate. This filtrate contain water, salts, glucose, amino acids, urea, vitamins. About 7.5 liter of glomerular filtrate are produced every hour.
  2. Tubular Reabsorption: Glomerular filtrate flow out from Bowman s capsule into the tubular part of each nephron. Here the useful substances are selectively reabsorbed back into blood amino acid. Loop of henle reabsorbed water and salt.
  3. Tubular secretion: In this step H+, K+, NH+ 4 and drug (penicillin) are removed from blood into the distal tubule of nephron. This process maintain the pH of blood.
  4. Excretion: After reabsorption the filtrate changes into urine. This urine is collected by collecting duct into the renal pelvis. Urine come out of the kidney through ureter into urinary bladder. From here urine passes to the outside by urethra.

Effect of Hormones on the Working of Kidney

The function of kidney is under the control of three hormones:

Reabsoption of glucose from filtrate occur in the proximal part of nephron. This function is under the control of a hormone – insulin. Insulin is secreted by islets of langerhans in the pancrease. It reduces the level of glucose in the blood. Normal level of glucose in blood is 70 mg / 100 ml of blood. It this level falls to 30 mg/100 ml of blood death will occur. If glucose level raises to 120 mg/ 100 ml of blood, it show secretion of insulin. Excess of glucose will not be reabsorbed and excreted in the urine. This is one symptom of diabetes mellitus.

Aniduretic Hormone:
The distal part of nephron is responsible for reabsorption of water. This function is under the control of a hormone – antidiuretic hormone. ADH is secreted by the pituitary gland. Dehydration of body stimulate ADH secretion. This ADH then increases the reabsorption of water. In old age the secretion of ADH reduces in some persons. The distal part of their nephron fail to absorb water. Such person excrete huge volume of watery urine daily.

It is secreted by the adrenal gland. It stimulates active reabsoption of Na+ ions in the ascending limb of loop of Henle.

Composition of Urine

Color: Urine is yellowish in color due to the presence of urochrome.
Volume: A normal person excretes about 1.5 liters/day.
pH: it varies from 4.6 – 8. Because it depends upon the presence of H+ ions in blood.
Composition: Urine is mainly composed of the following substances:
Water = 95%
Organic and inorganic salts = 2%
Urea = 2%
Uric acid = 1%
Small amount of ammonia and cretinine.

Kidney as osmoregulatory and Excretory Organ

Kidney act as both excretory and osmoregulatory organ. Kidney kept the body fluid concentration within narrow limits. It regulate the concentration of blood in the following way:
(i) Production of dilute urine:
If the blood contains more water then less water is reabsorbed from glomerulus filtrate. As a result large volume of dilute urine is produced.
(ii) Production of concentrated urine:
If the blood is too concentrated by the shortage of water. Then more water is absorbed back into the blood from the glomerulus filtrate. As a result a small amount of concentrated blood also stimulates thirst center in the brain causing drinking of water. This restores the blood correct concentration.
(iii) Regulate acid base balance:
Kidneys also maintain the acid base balance in the body. Kidney excrete acids in urine while prevent the excessive loss of water base.

Kidney Stone

The formation of some solid structure in the kidney is called kidney stone.

Chemical composition: These stones have specific chemical nature. These stones are usually composed of:

Causes: Kidney stones are formed by high level of calcium and oxilate in blood. Calcium is found in milk, egg, fruits etc. Oxilate is present in, green vegetables, tomatoes. Sometimes these substances are deposited in the kidneys and change into stones. About 70% Kidney stones are formed due to Calcium oxilate.

Treatment: Kidney stones are usually removed by surgery i.e. operation.

Lithotripsy: The technique to break up and remove kidney stone without surgery is called lithotripsy. In this process high concentration of x- rays are passed through the stones. The stones are broken into small pieces which are removed from the kidney with urine.

Renal Failure

When the Bowman s capsulte of the nephron is damaged the filtration process is weakened, which is called renal failure. In such conditions the harmful substances remain in blood. Thus the amount of urea is increased in blood.
Treatment: Renal failure can be treated by: Dialysis or Kidney transplant.


The filtration and purification of blood with the help of artificial kidney machine is called Dialysis. Dialysis is a Greek word which means, “ Separation” Dialysis is not a permanent treatment.
Types: Haemodialysis and Peitoneal dialysis.

In this process the patients blood is cleaned by a specialized machine called Dialyzer. Dialyzer contain a fluid called “Dialysate” This dialysate contain semi permeable tubes kept at body temperature. A plastic tube is surgically inserted into an artery and vein of leg or Blood from the body is transferred into the dialysis machine. This blood is allowed to flow through the tubing in the dialysate. The wastes like urea, extra water, salts diffuse out into the dialysate. After filtration the blood is returned back into body vein. Haemodialysis remove about 50 – 250 gm urea in six hours.

Peritoneal Dialysis:
Abdomen has a peritoneal cavity lined by a thin epithelium called peritoneum. Peritoneal cavity is filled with dialyssis fluid through catherter. A bag is attached to the patient abdominal cavity. Excess water and wastes pass through the peritoneum into dialysis fluid. This process require one hour and repeated several times a day.

Adaption in Plants to low and high Temperature

Temperature plays very important role in the plant life. Most of the physiological process in the plants require an optimum temp. Extremely high and low temperature causes some morphological and anatomical adaption in plants such as:

Adaptation for low Temperature:
In plant low temperature effect:
  1. Enzyme activities i.e. become inactive.
  2. Permeability of cell membrane or it become crystalline.
  3. Effect Cell transport.

Plants Living in Low Temperature Have The Following Adaptation

  1. Alternation of lipid composition in cell membrane: In low temperature the lipids of cell membrane become crystalline. But plant convert saturated fatty acid into unsaturated fatty acid which prevent crystal formation. However, it is a slow process so plant is effected upto some extent. 
  2. Change in solute concentration: Plant living in cool area bring changes in their solute concentration of the cell that prevent ice formation inside the cell.
  3. Short life cycle: Plants in such places have short life cycle. 
  4. Bark Protection: Such plants have well developed bark for protection against low temperature.

Adaptation for high temperature:

High temperature damages the cell by denaturing its enzyme. Plant have the following adaptation for high temperature.
  1. Transpiration: High temperature increases the transpiration rate because it makes the plant cool.
  2. Heat shock protein: Most plants produce special protein called heat shock protein. These proteins protect enzymes from denaturation at high temperature.
  3. Large Vacuole: their vacuole is large to store more water. They also have water storage tissues in the stem.
  4. Leaf modification: Sometimes leaves are modified into spines to reduce transpiration. Leaves are covered with thick cuticle. Stomata are sunken or mostly present on cuticle.

Heat Gain:

Organisms get heat by two sources:
  1. Internal source: Heat is produce by oxidation of food material. Muscular contraction or activities also produce more heat.
  2. External source: Body obtain heat, (i) Directly from sunlight, (ii) By hot drinking, (iii) By eating hot food.

Heat Loss:

Body loss heat by following ways:
  1. Radiation: Release of heat in the form of rays
  2. Convection: Transfer of heat by the movement of air or liquid from the body surface.
  3. Evaporation: loss of heat from lungs and skin in the form of gas.
  4. Drinking of cold water
  5. Intake of cold air.

Need For Maintaining Body Temperature

All body chemical reactions take place at a specific temperature. Variation in temperature disturbed internal system of the body. Sensory nerve ending in skin feel us hot and cold. Human body temperature below or above normal is dangerous. Normal body temperature is maintained by heat production and heat loss. Body temperature is regulated by the following mechanisms.

Over Heating: Rise in body temperature than normal due to heat gain or excessive heat production is called over heating. Vasodilatation: Widening or dilation of blood vessel by hormone is called vasodilatation. In this case blood vessel increase in diameter. As a result more blood flows to the skin and loses heat by radiation. Sweating: Sweat glands become active and water is exerted out through skin. About 70% heat is regulated by this process. Decrease urination: Over heating reduces urination to prevent dehydration. Conscious action: in summer we wear thin clothes and setting in shade to cool down.

Over Cooling: low body temperature than normal is called over cooling. It is due to more heat loss then produced by the body. Following mechanisms regulate it: Vasoconstriction: decrease in diameter of blood vessel is called vasoconstriction. Less blood flows towards the skin to reduce loss of heat. Reduce sweating: Winter, sweating is reduced or stopped preventing heat loss by evaporation. Increase Urination: Winter, volume of urine increase to keep body temperature near to normal. Shivering: Uncontrollable rapid muscular contraction in the body produces heat to regulate cooling. Increase Metabolism: Adrenaline and thyroxin hormones increase respiration and oxygen consumption to produce heat. Conscious action: In winter season we get heat by: Wearing thick and warm clothes. Rubbing of hands. Taking Exercise: Setting in the sun or hot places. Hot drinking: eating hot food.

Written by: Asad Hussain


  1. notes of NBF syllabus plzzz........Allah ap ka bhala kary

  2. plc endlish k notes bhi upload kar dy ........ class 12


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