M Ed Biology

 

Anatomical development of mammal from fertilization to organogenesis

The egg  or ovum of rabbit is 0.1 m in diameter while that of human being is 0.15 mm in diameter. It is oval in shape and on its outer surface, there is a thin vitelline membrane. The egg contains cytoplasm. In the cytoplasm, there is  eccentric  nucleus. The nucleus lies in the upper half or animal hemisphere. The egg of mammal is alecithal  or micro lecithal with almost no yolk or lower half or vegetal hemisphere has some particles of yolk distributed evenly in the cytoplasm.  The whole egg is surrounded by a striated secondary membrane called zona pellucida secreted by follicular cells. Outside zona pellucida, there are follicle cells forming corona radiata which is soon dissolved away.

The secondary oocyte is released from the Graafian follicle into the peritoneal cavity outside ovary. The wall of ovary ruptures to release the egg which is known as ovulation. In human beings, every month or every 28 days, one ovum generally is released either from right or left ovary alternating with one another. The development of ovary and development of egg or ovum within the  ovary is under the influence of Follicle Stimulating Hormone FSH produced from the Pituitary gland. The developing egg or ovum starts secreting female hormone called Estrogen.

Soon after the release of ovum, the follicular cells and blood clot forms the Corpus Luteum.  The Corpus Luteum acts as endocrine gland and produces important hormone known as Progesterone.  Both female hormones are responsible for development of secondary sex organs like the oviducts, uterus, vagina  and mammary gland etc. and tertiary sex characters like different pattern of distribution of hairs, high pitched voice and little bit of shyness  in case of  human beings and deposition of fat at different parts of body like thigh and broad hip in case of man and other  mammals.

The egg is fertilized in the upper part of oviduct called ampulla which is slightly swollen part after the fimbriated funnel. For fertilization, entire spermatozoon penetrates the egg but soon the tail is degenerated.  The penetration by sperm is brought about by an enzyme hyaluronidase present in the semen.  The haploid set of chromosome present in egg and sperm arranged into homologous pairs and diploid chromosomes is restored.  The restoration of diploid chromosome is called fertilization. With fertilization, the egg is changed into zygote.

The zygote undergoes second maturation division  and becomes mature ovum. Two polar bodies lie within the zona pellucida near the animal pole. The fertilization ensures the division of zygote and further development of it.

Cleavage

Cleave is complete and holoblastic but unequal. The first cleavage is vertical diving the zygote completely into two unequal blastomeres, one being smaller and more opaque than the other. The second cleavage is also vertical and at right angle to the first one.  Four celled structure is formed. After the third cleavage which is horizontal little above the equator, eight cells are formed. The further cleavages are irregular diving zygote vertically and horizontally at the same time. Then a solid ball of cells is formed called Morula.  The Morula is covered by dense coat of albumen. It passes down the oviduct and comes in contact with uterus of mother and absorbs liquid food from mother.

Blastocyst

A fully formd morula shows an outer or superficial layer of cells, the trophoderm or trophoblast, surrounding an inner cell mass of larger polyhedral cells. The Morula stage passes down the oviduct and implanted into the wall of uterus.

Morula absorbs fluid secreted by the uterine mucous membrane and swells up. The liquid food is collected in a cavity which separate an outer layer of smaller trophoblast cells from a solid inner mass of cells. The embryo is now called a blastocyst which appears like a blastula but is not comparable to it. Those trophoblast cells which lie above the inner cells mass are called cells of Rauber. The inner cell mass in sonly attached to the trophoblast at animal pole like a knob. It is called embryonal knob because all parts of embryo will be derived from it. Embryonal knob is comparable to the area pellucid of chick embryo. The embryo now forms a vesicular structure called blastocyst or blastosphere.

As cavity enlarges the knob like inner cell mass becomes flattened and known as germinal or embryonal disc, which gives rise to embryo proper. In case of rabbit and other mammals, the trophoblast cells (cells of Rauber) overlying embryonal disc disintegrate. As a result the embryonal disc comes to lie at the surface of blastodermic vesicle or blastoderm and its edge becomes continuous with trophoblast around it. The trophoblast is equivalent to extra embryonic ectoderm. The cavity of embryo is equivalent to sub germinal  cavity of chick. However blastocyst stage is  peculiar to mammalian development.

Implantation

The trophoblat cells opposite to the embryonal knob form small papillae of trophoblastic villi which penetrate into depression or crypts  in the uterine wall so the blastocyst becomes attached to or implanted in the uterus of the mother, the villi absorb food from uterus.

Gastrulation

Some cells separate from lower surface of the embryonal knob, these cells migrate and form a lining of the trophoblast, the new layer of  cells is endoderm. The blastocyst is now converted into a two layered gastrula. Its fluid filled cavity is a functionless yolk sac. However there is no yolk.

In the centre of embryonal disc, cells collect to form a primitive streak, movement of the cells of primitive streak on both sides result in the separation of mesoderm which at first are un segmented  and have no cavity. Cells move forward from the primitive streak  to form notochord. Formation of mesoderm and notochord is the same as in chick. Formation of mesodermal somites and splitting of lateral plate mesoderm with appearance of splanchnocoel proceed in the same manner as in chick. However in rabbit, the lateral plate mesoderm extends as far as the equator, so that the lower wall of yolk sac consists of only ectoderm. The primitive streak retreats towards hind end. After giving up the  chorda mesoderm cells of the notochord and mesoderm, the remaining cells of the embryonal disc are ectoderm. The ectoderm cells form neural plate and neural folds  which become a neural tube as in chick. The mammalian embryo in its later stages is called foetus.

 

Balanoglossus (tongue worm)

Hemichordata ( Gr.  Hemi = half, chorde = cord) has been treated as subphylum of Phylum Chordata ( or Protochordata).  Some authors regarded it to be independent phylum close to phylum Echinodermata.  But for convenience of comparative study of protochordates, hemichordate has been retained in the subphylum of Phylum choradata.  Sub phylum Hemichordata includes a group of soft, vermiform, marine and primitive chordates. The most popular hemichordate genus is Balanoglossus commonly known as tongue worm or acorn worm. Other genus is Saccoglossus. They belong to class Enteropneusta (Gr. Enteron, gut; pheustos, breathed), some characteristics in the animals of this class are  body large and worm like, gill slits numerous, intestine straight.

Systematic position

Phylum            Chordata

Group              Protochordata ( Acraniata)

Subphylum      Hemichordata

Class                Enteroneusta

Family             Ptychoderidae

Type                Balanoglossus ( tongue worm)

Delie Chaije in 1829 named and recorded Balanoglossus clavigerus.  The genus Balanoglossus was derived from two Greek words, Balanos and glossus. The term balanos means an “acorn” ( fruit of oak) and refers to the proboscis projecting from collar looking like acorn nut, therefore the common name acorn worm is given. The other term glossus means tongue which  refers to the shape of its proboscis, collar and genital wings bearing a close resemblance to an ox tongue so, tongue worm is given to it. The fisher men call Balanoglossus  by the name of ox tongue.

Geographical distribution

Balanoglossus  and other hemichordates are marine animal. It is cosmopolitan in distribution. Balanoglossus is found in tropical and sub tropical seas of world. Some other species of Balanoglossus are  B australiensis ( Australia), B carnosus ( Indo Pacific) B  misakiensis ( Japan), B jamaicensis (West Indies), B gigas (Brazil), B capensis ( South Africa),  B clavigerus ( Mediterrannean and British isles).

Habits and Habitat

Balanoglossus is a marine, tubiculous or burrowing hemichordates. It inhabits shallow waters of intertidal zone and few occur in deep water also.

Burrow

The animal may hide under stones, or sea weeds or excavate its own burrow in bottom sand or mud.  B clavegerus  makes a U shaped tube or burrow having two vertical limbs of  about  50 to 70 cm deep and two openings are 10 to 30 cm apart.  In Saccoglossus, the body of the animal and tube are twisted but the anterior and posterior extremities are   straight. The anterior opening of the burrow is funnel shaped and wide.  The anterior vertical limb may give out branches each having funnel like opening. The posterior opening  of the burrow is round and concealed below the spirally coiled faecal matter of the animal.

Protective device

The inner wall of the fragile burrow is smoothly lined by sand particles cemented together into a tough cast with sticky mucus secreted by the mucous gland present in the skin of the animal. Due to this the walls of the burrow are not collapsed and protects the delicate body of animal from burial in loose sand. They also secret foul smelling odour like iodoform for protection.

Movements

The tongue worm is sluggish in movement. It is little affected by the external stimuli.  It can move inside burrow with the help of cilia covering its body surface. The proboscis is the most active part of its body. The proboscis can be elongated or shortened by the action of muscle. The proboscis can help in burrowing.  When the tide is over, Balanoglossus protrudes its anterior end out of the burrow to explore the surrounding. The worm can extend the posterior end out of the burrow to cast the faecal material.

Feeding

Acorn worm takes a lot of sand or mud to obtain diatoms, protozoans and other microorganisms and organic detritus present in it. Sand or mud is not the food but as it cannot separate  food and sand or  mud they consume both. They take lot of sand or mud because  the sand or mud contains little amount of food.

External structure

• Shape – the shape of its body is cylindrical, worm like and bilaterally symmetrical.
•  Size – the body measures about 10 to 50 cm in length but it may differ according to species. B gigas attains about 1.8 m in its body length according to Sawaya 1951 or 2.5 m according to Spengel 1893.
• Color – color of its body is bright or drab with reddish or orange tint.
• Locomotory organ – the body is uniformly covered by short hair like cilia. Exoskeleton and external appendages are absent.

Division of body

The body of acorn worm is unsegmented.  It is divisible into three distinct regions or parts like proboscis, collar and trunk.

Proboscis

Proboscis is also known as protosome which  is the anteriormost part the body.  Proboscis is club shaped or conical.  It is circular in cross section.  It has thick muscurlar wall and cavity inside is proboscis coelom. The proboscis coelom  communicates to the exterior through minute proboscis pore situated mid dorsally near its base.  In some proboscis pore ends blindly or there are two pores. Posteriorly the proboscis narrows into a slender neck or proboscis stalk which is attached to the collar. Below the stalk, the base of proboscis  bears U shaped ciliated epidermal depression called the preoral ciliary organ which tests the quality or food and water entering the mouth.

Collar

Collar is also known as mesosome. It is middle, short and cylindrical part. The flap like or funnel like anterior margin is called as collarette. It completely surrounds and conceals the proboscis stalk and posterior part of proboscis. Ventrally, below the proboscis stalk, the collarette encloses a permanently open wide aperture called as mouth.  The mouth opens into a cavity called buccal cavity which lies inside collar. The collar is well demarcated  from the trunk by circular constriction. The wall of the collar is highly muscular. There is a cavity called collar coelom. The collar coelom opens to the outside through a pair of collar pores into the first  pair of gill pouches behind.

Trunk

Trunk is also called as metasome. It is the posteriormost and the largest part of the body. The trunk is flat and appears annulated due to circular constrictions on the surface.  The trunk bears a mid dorsal ridge and mid ventral ridge which correspond the nerve cord and blood vessel. The trunk is further divisible into three regions.

            Branchiogenital region

Branchiogenital region is marked  by a pair of lateral, thin, flat and longitudinal flaps called the genital wings which contains gonads. The gonopores are microscopic and cannot be seen by unaided eye. The anterior half of the branchiogental region bears two  longitudinal rows of branchial apertures or gill pores. The number of gill pores increases with the age of animal. Two genital wings can be curved to meet mid dorsally so as to conceal the gill pores.

Hepatic region

 The middle hepatic region of the body is somewhat smaller than  branchiogenital region. It is greenish in color and its dorsal surface is marked by presence of numerous irregular intestinal sacculations or hepatic caeca.

Posthepatic region

This is the posteriormost and  the longest part of the trunk. It is also called abdomen or caudal region. It is more or less of uniform diameter. The posterior end tapers somewhat and bears  terminal anus.

Life cycle

Sexes are separate. Male and female Balanoglossus live in separate burrows. When fully matured, they shed gametes in sea water.  The egg is microlecithal. The sperm fuses with egg in sea water. So, the fertilization is external. The fertilized egg or zygote undergoes cleavage. Embryo is formed. Embryo hatches into a free swimming planktonic larva called tornaria. It is ciliated larva. The development is indirect.

There is no asexual reproduction. The fragile body of Balanoglossus may get broken easily and they have considerable power of regeneration.

 

Pisces (osmoregulation and scales

Every organism in natute has a close relationship with its environment for water and salts. An optimum concentrations of water and salts is essential in the body for  proper metabolism. The maintainance of such a concentration is called osmoregulation. There may be three possible conditions of the concentration of waer and salts in the body of an organism in comparision to the concentration of the same substances in the environment.

1. isotonic  or iso osmotic- the cell or organism kept in it experiences no change in its volume. In this situation the osmotic pressure is same both inside and outside the cell or organism.
2. Hypotonic or hypo osmotic – which is more diluted as compared to the other. The solvent or water enters into the body of organism from surrounding environment.
3. Hypertonic or hyper osmotic – which is more concentrated as compared to the other. The solvent or water  comes out of the body of the organism into the surrounding environment.

Animals can be put in two categories according to their tolerance for osmotic changes.

• Stenohaline  - this includes the animals which can tolerate the narrow range of salinity. They change the osmotic pressure of their internal fluids according to the changes in their  external medium. This includes crustaceans and several mollusks.
• Euryhaline – this includes the animals which can tolerate the broad range of salinity. They do not change the osmotic pressure of their internal fluids according to the changes in their external medium. They can maintain the concentration of their body fluids at the same level in all situations. 

Marine elasmobranchs like sharks,  rays and skates have a special urea retention device. The migratory fishes have their own peculiarity of osmoregulation. For instance, when the fresh water eel reaches  the sea for spawning, there is a tendency for the fish to lose water and to increase the salt concentration in its body. The excess salts are removed to the outside by the active transport through the chloride –secreting cells of  the gills. The kidneys keep on reabsorbing water.  When they return to the rivers and grow into adults, they have to face the reverse problem where they remove the excess water along with the urine and reabsorb salts into the blood. These changes in the kidneys are regulated by the endocrine secretions.

Scales of fishes

In vertebrates, the exoskeletal covering of body is made on two types scales. They are epidermal and dermal. The epidermal scales are cornified derivatives of malpighian laer of epidermis and developed in terrestrial animals like reptiles , birds  and mammals. Dermal scales are mesenchymal in origin and especially developed in fishes. They are small, thin, calcareous or bony plates which fit closely together or overlap.  Primitive fossil fishes of Silurian and Devonian periods, possessed exoskeleton in the form of plates and scales which consist of three district layers. The innermost layer consisted of a compact bone, isopedine, the intermediate or middle layer of spongy vascular bone and the outer layer is of dentine.

According to the mode of origin, there are tow types of scales. (1) those which are formed due to the secretary activity of both epidermis  as placoid scales  of elasmobranch (ii) non placoid scales that are derived from dermis only as the scales of teleosts.. structurally the scales are classified as cosmoid, genoid or rhomboid, placoid, cycloid and ctenoid. The last two are called bony ridge scales.   

Cosmoid scales – the cosmoid scales are found in extinct Crossopterygii and Dipnoi.

Ganoid scales – ganoid scales are characteristic of the primitive acrinopterygians called ganoid fishes. These scales are heavy and have an outer layer of hard inorganic, enamel like material called ganoine. The middle layer  is cosmine containing numerous branching tubules. The innermost layer is thickest and is made up of lamellar bone called isopedine. 

Placoid scales – Placoid scales are characteristic of elasmobranch fishes( sharks). Each scale has a disc like basal plate embedded in the dermis and a spine projecting out through the epidermis. Placoid scale resembles the tooth.  The spine has an external covering of enamel like hard transparent material called vitrodentine. This is followed by a layer of dentine enclosing a pulp cavity from  which several branching dentine tubules radiate in different directions. Placoid scales are closely set in skin but do not overlap each other and fiving a sand paper like quality to skin.

Cycloid scales – cycloid   scales are thin flexible, translucent plates, rather circular in outline, thicker in the centre and marked with several concentric line of growth which can be used for determine the age of the fish. They are found in a large number of teleostean fishes having soft rayed fins, such as Labeo, Catla. The central part of the scale is called focus and is the first part to develop.  They form protective covering over the skin and project diagonally in an imbricating pattern.

Ctenoid scales -  Ctenoid scales are also circular and can be distinguished from the cycloid scales by having a more or less serrated free edge. Several spines are present on the surface of the posterior area of the scale.  These scales are characteristic of modern higher teleosteans such as perch, sunfish etc. They are firmly attached and their exposed free hind parts are not overlapped and bear numerous small comb like teeth or spines.

Economic  importance of Amphibia

Most of the amphibians are beneficial to mankind.  They are of great economic importance.  Specially  frogs and toads are of economic importance.

• Scientific study

Frogs and toads are included the syllabus of Proficiency certificate level of  different universities of world including  Nepal  from the past several years.  Specially in Nepal, the frogs are dissected in the laboratory to study the  general anatomy,  alimentary canal, reproductive organs, arterial system, venous system and brain etc. Amphibian developmental study is also included in the syllabus of University of Nepal.  The amphibians are studies mainly because they represent both lower and higher animals in many respects.  In USA, mud puppies( Necturus) are dissected  for the laboratory study.  Newt Diemictylus viridescens is widely used in research.

• As food

Frogs are mainly consumed as food by gourmets in USA and Japan and many other countries of the world. In Nepal also, frogs  (paha as local name) are eaten by the terrain people. Usually the fleshy  hindlimbs are eaten.  Other edible amphibians esteemed as food are Necturus and axolotls in America and giant salamander in Japan.

• Predation

Frogs and toads are destroyers of noxious insects. Toads are of great value because they live in gardens where insects are most injurious.  The French gardeners even buy toads to control harmful insects . Bufo marinus has been introduced in tropical sugarcane fields to destroy injurious insects. . in Nepal, farmers gave great resects fir   the frogs as they help to increase their production.

• Medicinal value

Toads are used in Chinese medicines. Skins of toad secretes a digitalis like substance that increases blood pressure when injected into humans.

• Trade, art and recreation

Skins of frogs are used for glue, book binding and making delicate purses. Amphibians and their larvae provide motifs in the art of American Indians, toads have played a role in religious beliefs of primitive people since ancient  times. Aesop 560 BC included frogs among his fables. Tribal magicians in America used parts of frog and toads in their magic. Bull frogs area said to participate in a jumping frog contest held every year in USA frogs and toads are kept as pet in household aquaria.

• Poisonous Amphibia

A wide variety of irritating toxic compounds Is produced by amphibians. Poison glands are located dorsally in  skin and defense postures of anurans and urodel present the dorsal glandular surface to their predators. Poisonous secretions (bufotoxins) of Bufo marinus are fatal to dogs and cats. Poison of Dendrobates a South American frog is used by tribal people to poison the points of their arrows.  Some poisonous amphibians such as Salamandra salamandra are warningly colored. Helbenders (Cyptobranchus ) are said to be poisonous but not dangerous to men.

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for class XII

Endocrine gland

Endocrine gland is the gland without duct for secreting. The secretions are defused into blood. Through blood circulation, reach various parts of body. These secretions or hormones control, coordinate and integrate various physiological processes and activities of body. Different endocrine glands together make endocrine system in the body.

Differences

Exocrine endocrine
Gland with ducts ductless gland
Found near site of action usually found way from the site of action also
Secretions are enzymes secretions are hormones

Glands are either endocrine or exocrine but pancreas is both exocrine and endocrine in function. The endocrine part produces insulin and glucagons that regulate metabolism of glucose. The exocrine part produces pancreatic juice for digestion of food. It is called heterocrine gland.

Differences between hormone and enzyme


Pituitary gland
This is important gland. The other endocrine glands are influenced by hormones of this gland. So pituitary gland is called master gland.
Locaton it is found at the base of brain below diencephalons and enclosed in a depression. It is also known as hypophysis. It is small about size of a pea na weighs about 5 gm.

It consists of three lobes
1. anterior lobe
2. intermediate lobe
3. posterior lobe
the anterior and intermediate lobes are together known as adenohypophysis. The posterior lobe is known as neurohypophysis.

Adenohypophysis secretes 7 hormones
1. Follicle Stimulating Hormone FSH
Functions in female, it stimulates development and maturation of ovarian follicles to produce eggs.
In males, promote spermatogenesis

2. Luteinizing Hormone
Functions in female, stimulate ovulation, formation of corpus luteum,
secretion of Progesterone and estrogen
in male, it is known as intersticial cell stimulating Hormone ICSH induces secretion of testosterone
3. lactogenic hormone or Prolactin

function stimulates lactation, milk production after child birth.
4. Adrenocorticotropin Hormone

Function stimulaes adrenal cortex to secrete adrenocorticosteroid hormone
Hyposecretion atrophy of adrenal gland
Hypersecretion excessive growth of adrenal cortex

5. Thyrotropin or Thyroid Stimulating Hormone TSH

Function stimulate thyroid gland
Hyposecretion thyroid atrophy
Hypersecretion stimulate thyroid gland to produce excessive thyroxine

6. Growth Stimulating Hormone GSH or Somatotropin
Function controls growth of body
Hyposcretion cause dwarfism in childhood
Myxoedema in adult reduce genital organ, reduce fertility

7. Melanocyte Stimulating Hormone MSH

Functions stimulate pigmentation of skin, secreted by intermediate lobe


Neurohypophysis

It stores and releases 2 hormones

1. Oxytocin (Pitocin) it affects uterine contraction during child birth in females

2. Vasopressin or Antidiuretic hormone ADH it increases BP it regulates reabsorption of water, hyposecretion large urine volume (diuresis) hypersecretion small urine volume (antidiuresis)

Thyroid gland

It is another important endocrine gland. It is found on either side of the trachea. There are two lobes which are joined by connective tissue called isthmus.

Structure - it is bilobed gland. It is about 5x3 cm in size. It weighs about 25 to 40 grams. Each lobe consists of follicles. The follicles secrete hormones. The hormones are:
o Thyroxine -- iodine is the major component of thyroxine.
o Thyrocalcitone -- it regulate the Calcium level in blood.

Thyroid gland produces hormone when it gets activated by thyroid stimulating hormone TSH from anterior lobe of pituitary gland.

Role of thyroxine hormone
o Regulate metabolic activities
1. general metabolism
2. growth and differentiation
3. metamorphosis
Less secretion or thyroidectomy(removal of thyroid gland) causes following
o cretinism -- in childhood, retard growth mentally and physically
o myxoedema – in adulthood, lowering of basal metabolism, sluggish appearance, dry, pale skin low temp. etc.
o simple goiter - due to deficiency of iodine leads to enlargement of thyroid gland, swelling of neck called simple goiter.
Hyperthyroidism
o Increased metabolic rate
o Exopthalmic goiter or Grave’s disease
o Bulging of eye ball
o Irregular heart beat
o Nervousness
o Loss of weight etc

Thyrocalcitonin
It is hypocalcemic, hypophosphatemic and secreted when Ca++

Parathyroid gland

It is found embedded in dorsal surface of thyroid gland. There are lobes two on each thyroid gland. These are rounded masses. Each is about 2 to 4 mm in size and 50 mg in weight . there are masses of polygonal cells called chief cells. These cells secrete parathormone or collip’s hormone. Low concentration of blood Calcium causes secretion of Parathormone.

Function
It increases Calcium level mobilizing from bone and reducing its elimination in urine, decreases phosphate level eliminating in urine, and affects growth of bones, membrane permeability, nerve functioning and muscular activity. The production of this hormone is controlled by concentration of Calcium level in blood. Excess Calcium inhibits its production.

Disorder
Low level of Parathormone leads muscle spasms, sustained contraction or tetany of muscle in larynx, face, hand and feet. Abnormally low levels may lead of death. High level of Parathormone causes excess Calcium in blood. As Calcium is taken from bone, bone becomes soft and porous. Decalcification is called Osteoporosis.



Adrenal glands

There are two small yellowish glands found at anterior tip o kidney. They are conical and have two distinct regions. The outer region is called cortex and inner region is called medulla.

Hormones of adrenal cortex

Cortex region secretes over 50 different hormones. They can be catagorised into three types.
• Mineralocorticoids
Functions
- regulate water
- Na + ,K+ metabolism
- Prevent loss of Na +
- Eliminate K+
- Increase water reabsorption
- Eg Aldosterone

• Glucocorticoids
Functions
- conversion of aminoacid, fatty acid into glucose called gluconeogenesis
- increase blood sugar level
- eg cortisol

• Sex corticoids
Fuctions
- have same functions as sex hormones
- promote secondary sex characters

Hyposecretion of adrenal cortex causes Addition’s disease
Symptoms
- muscular weakness
- ready fatigability
- loss of weight, dehydration
- hypotension
- anorexia( loss of appetite)
- vomiting, diarrhea
- mental confusion
- hypoglycemia
- decreased ability to withstand infection
- haemorrhage


Hypersecretion of adrenal cortex causes Cushing’s syndrome. It is mainly due to excess Glucocorticoids.
Symptoms
- protein depletion
- poor wound healing
- poor muscle development
- thin skin and red cheeks
- moon face fat pad, buffalo hump
- pendulous abdomen

Adrenal virilism it is due to disorder of secretion of adrenal cortex
symptoms
- produces masculine type like beards, moustache, male voice in female
- uterus and ovaries degenerate, menstruation stops

Hormones of adrenal medulla

Adrenaline or epinephrine
Functions
- prepares body for emergency or at the time of fight
- dilation of pupil
- Diversion of blood supply to organs
- Strenuous work of organs
- Decreased gastro intestinal activity
- Bronchodilation

Nor adrenaline or nor epinephrine
Functions
- increase BP by vasoconstriction
- CNS stimulation
- Heat production
- Decrease cardiac out put
- Powerful exciter
- Tonus hormone


Pancrease

It is heterocrine gland having both the exocrine and endocrine part in one. It is situated at the C shaped curve of duodenum. The endocrine part is found towards the tail of Pancreas. It consists of some specialized cells. The alpha cells produce Glucagon, Beta cells produce Insulin and delta cells produce Somatostatin.

Functions of Glucagon
It converts glycogen into glucose when glucose level falls down in blood

Functions of Insulin
It converts excess glucose into glycogen for storage in the liver. The hyposecretion of insulin causes rise in the glucose level in the blood. It causes a disease called Diabetes mellitus(DM)
Symptoms - increased thirst due to increased urination usually at night.
- appearance of glucose in urine( glucosuria) when it rises to about 200
mg in 100 cc of blood
- loss of body weight
- poor wound healing specially in foot
- attacks vision
- causes heart diseases
somatostatin controls the secretion of both glucagon and insulin

for class XII

Muscular tissue
Mesodermal in origin, except the ciliary muscle iridial muscle ectodermal)
639 types of muscle in human body.
Properties
o excitability – can excited by nerve impulse of stimulus of specific strength called threshold stimulus.
o Conductivity - can conduct waves of contraction along their length at the rate of 3-5 mitre/sec.
o All or none rule – muscle fibre can not be stimulated by sub threshold stimuli, single muscle twitch a muscle fibre contracts only once when stimulated
o Refractory period - undergoes refractory period of 0.005 second during which it recovers itself.
General structure
 A muscle cells are highly elongated and contractile called muscle fibres.
 Always contract along their longitudinal axis and can contract up to one third or one half of their length.
 Cytoplasm of muscle fibres – sacroplasm is highly conctractile, mitochondria collectively called sarcosomes, a network of modified SER sarcoplasmic reticulum and numerous glycogen granules to provide energy for its contraction and relaxation. Sarcoplasm contains large no. of fine longitudinal and contractile proteinaceous threads called myofibrils, each myofibril 1-2 um in diameter.
 Highly specialized for movement and locomotion, so no power of division and regeneration.
 Do not secrete intercellular subs almost no intercellular space, held together by connective tissue.
Functions
1. responsible for movements in hands, legs eye
2. equilibrium
3. prevents escape of food
4. helps in collecting information about changes in environment
5. brings about movement of food in digestive tract, urine in ureters, sperms in vasa diffrentia , ovum in fallopian tube, production of sound, beating of heart, respiratory movements .
6. provide support to skeletal structure.
7. locomotion of living organisms, which help protection from predators, to locate food and water, to find mating partner, to reach favorable area for egg laying or rearing the youngs.
8. also control facial expression and gesture.

In vertebrates, three kinds of muscular tissue are recognized.
1. smooth or unstriated or involuntary muscle
2. striated or voluntary muscle
3. cardiac muscle
smooth muscle - spindle shaped, rounded or polygonal in cross section, contain centrally placed oval or rod shaped nucleus, length of cell 1/20th of mm , width 1/60th of a mm. cytoplasm or sarcoplasm contain fine longitudinally arranged thread like elements known as myofibrils, found in visceral structure, part of digestive tube, blood vessels urinary bladder or ducts.
Striated muscle - because of their appearance, these are called striated or striped and because of their physiology, these are voluntary. Each striated muscle is composed of very large no. of long and cylindrical fibres measuring 100 microns in diameter and about 40 mm in length. These fibres are much wider, non tapering and their cells boundaries can not be clearly distinguished. The muscle fibres are coenocytic( multinucleate) with many elongated peripheral nuclei. The cytoplasm of each fibre contains large no. of myofibrils and sarcostyles which are relatively course and therefore not difficult to see under the microscope in a profusely stained preparation. Myofibrils are tightly packed. Each fibre has extensive sheath of sarcolemma which encloses contractile myofibrils. Just beneath the sarcolemma of each fibre occur in the sarcoplasm several elongated nuclei at regular intervals. When examined under the microscope each muscle fibre appears to be divided into an alternating dark and light bands which appear as such due to fact that each myofibril itself is formed of number of alternating light and dark sections . the dark bands or A discs are separated from one another by light band or I discs.
Stiated muscle fibres are united in parallel bundles. These muscles have power of contracting rapidly and strongly, are liable to fatigue and get their nerve supply from ventral roots of spinal cord. The striated muscles work in pair. A flexor causing bending at joint and extensor muscle causes straightening. Striated muscle is generally found attached to the bones except some of the muscle of tongue.
Cardiac muscle - cardiac muscles are characterized by branching and anastomosing fibres, central nuclei, transeverse striations and intercalated discs. Adult cardiac muscle consists of muscle fibres joined into a intricate network. Myofibrils appear to be similar to those of striated muscle. They usually present a staircase appearance. Cardiac muscle has as extremely rich blood supply. It contracts automatically and rhythmically. Cardiac muscles are found in walls of heart.

Nervous tissue

It consists of neurons, nerve fibers and neuroglia. Neurons are highly specialized cells. Neuroglia are more or less undifferentiated supporting cells which form packing around neurons.

Properties
Excitability - neurons have pre existing potential difference across their membrane called membrane potential. A stimulus of adequate strength called threshold stimulus can cause depolarization of neuron locally and initiates the nerve impulse. On stimulation, potential difference undergoes change and cell is said to be excited. The cell then transmits this change as a wave along the membrane.
Conductivity - message is transmitted along axon is called nerve impulse. It is conducted in the form of electric impulse. It always travels from cell body towards axon.

Structure of neuron
It possesses two distinct regions
1. cell body, perikaryon or soma
2. cytoplasmic extensions

Cell body contains nucleus, abundant granular cytoplasm. Cell organelles like mitochondria, golgi apparatus, rough endoplasmic reticulum and neurofibrils are present.
Cytoplasm contains conical, angular or rhomboidal granules called Nissl’s granule rich in RNA. These are concerned with protein synthesis. These are absent in axon.

Cytoplasmic extensions extend from the cell body. They are of two kinds.
o Dendron or dendrite - small wide processes that break up into numerous fine branches. They convey impulses toward cell body.
o Axon or nerve fibre - it is a long process, several meters long. It carries nerve impulse away from cell body. Terminal ends are swollen. These are neurosecretory. They release acetylcholine, adrenaline. They communicate with neuron through synapse.

Types of neuron
Neurons are of three types
o Unipolar neurons - they have just one process arising from cyton. These neurons have only axon. This type of neurons is found in the embryonic condition only. In the adult, there is presence of pseudo unipolar neurons. In pseudo unipolar neuron, the single process divides into two branches. They have axon at one branch and dendron at another branch.
o Bipolar neurons - these neurons have two processes arising from opposite poles of cyton. On one process there is dendron and on the other process there is axon. These are found in the retina of eye, nasal chamber etc.
o Multipolar neurons - they have many processes arising at different points of cyton. There are many dendrons and one axon. They are found in developed organisms.

Types of nerve fibres based on the presence or absence of myelin sheath
o Myelinated or medullated nerve fiber - in this, the nerve fiber is covered by myelinated sheath. They are white in color. These are found in white matter of Brain and spinal cord. They are involved in quick conduction of nerve impulse.
o Non myelinated or medullated nerve fiber - these nerve fibers are without myelin sheath. These are grey in color. They are found in the grey matter of brain and spinal cord. They conduct nerve impulse slowly.

Types of neurons on the basis of their functions
o Sensory or afferent - these neurons take impulses from the sensory organs to the brain or spinal cord. Some of the cranial nerves like optic nerve, auditory nerve are sensory in function.
o Motor or efferent - these neurons take information from brain to the target organ or muscles. Some of the cranial nerves like oculomotor nerve, trochlear nerve are motor in function.
o Mixed nerve - some are mixed in nature. They are both sensory and motor in function. The spinal nerves are all mixed in nature.

Neuroglia cells or glial cells
These are non nervous in nature. These are about 10 times more than the nerve cells. These are capable of division. These are cells from the connective tissue.
Functions
o Form packing between nerve fibres.
o Help in wear and tear.
o Insulate adjoining nerurons, prevent lateral transmission of nerve impulse.
o Provide nutrition.
o Act as phagocyte.
o Help in memory.

Types
o microglial or microgliocytes - these are small spindle shaped, make reticulo endothelial system.
o Astrocytes – large sized, highly branched and present around blood vessel.
o Oligodendrocytes – large sized, few branched processes, form insulating covering of nerve fibre.

Ependymal cells
These are also non nervous in nature. These are found in the central canal of spinal cord. These are ciliated and help in spreading of cerebrospinal fluid.
Neurosecretory cells
These are also non nervous in nature. These are found in hypothalamus of brain. These are special cells of endocrine nature. They secrete the neurohormones like Adreno cortico tropic hormone ACTH, thyroid stimulating hormone TSH etc.











Biotechnology
It is the new discipline of science. It is an application of scientific principles to the processing of materials using biological agents to provide goods and services. It is defined as “any technique that uses living organisms to make or modify products to improve plants and animals or to develop microorganisms for specific uses.

Antibiotics
These are chemical substances produced synthetically b micro organisms. It inhibits the growth of bacteria and other micro organisms and even destroy them.

First antibiotic - Penicillin
It was discovered by British Bacteriologist Alexander Flemming in 1928. Once he was working with Staphylococcus. It happened that some spores of mould floated in his laboratory. He threw them from window. Luckily these spores landed on one of his Staphylococcus colony. He observed that bacteria were quickly killed or destroyed. Later the mould was identified as Penicillium notatum. Due to this reason, the active substance which killed bacteria was named as Penicillin.

Commonly used antibiotics
Penicillin- prepared from Penicillium notatum and Penicillium chrysegenum. It is proved to be effective for treatment of bacterial infection such as pneumonia, meningitis, tetanus etc since 1940. It has saved millions of lives.

Streptomycin - it is obtained from mould Streptomyces griseus. It is effective for treatment of TB, Typhoid.

Tetracycline - it is broad spectrum, made up of group of antibiotics. It is effective for treatment of bacterial and viral infections.

Actions
Bacteriostatic (inhibiting the growth of microorganisms in the body. Later the immune system of body will kill the microorganism)
Bacteriocides (killing pathogenic microorganism directly)

Catogories
Broad spectrum - destroy several pathogen species eg Penicillin, Streptomycin
Specific antibiotics - have limited action.

Application
1. medicinal use – control no. of infectious diseases human and animal
2. food preservation – especially meat, fish, poultry
3. supplement in animal feed, some antibiotics have been used to enhance growth of animals




Vaccines
These are preparations of killed or living microorganisms which produce immunity when administered into body.
Dr Edward Jenner an Eighteenth century physician made an important observation in 1790. Small Pox was most dreadful disease in those days. Dr Jenner noticed that milkmaids and diary workers did not get the disease. He found that these people contacted cow pox from animal at some time earlier during life which appeared in the form of pustule on hand and left scar and nothing serious happened.
Dr Jenner experimented with the boy Philips and infected with first cow pox and later with small pox (after six month). To his surprise, the boy did not get small pox an survived the attack showing he was immunized to small pox. Jenner gave the term vaccine . vacca in Latin means cow ) to the fluid he inoculated.

Types of immunity
1. natural or inborn - it is present at birth. Some antibodies pass through placenta to foetus. It gives passive immunity for short time. However protects from no. of diseases like Polio, measles till body’s own immune system develops.
2. acquired immunity - it is developed after birth.
active - produced by injecting small quantity of antigen called vaccine into body. The process is called vaccination or immunization. Then body manufactures antibodies. It lasts for long time. When body is exposed to antigen, it contacts disease. The body not only produce antibodies also memory cells. When same antigen strikes for second time, memory cells produce large amount of antibodies and body does not contact disease. This is why some childhood disease like mumps, chicken pox occur only once in life.
Passive - body does not produce antibodies, instead readymade antibodies from some other organism is introduced

Types of vaccine

1. killed vaccine - it is prepared from killed pathogenic organism by heat or UV light or alcohol, formalin of phenol. Example Typhoid vaccine, cholera vaccine
2. toxoid - it is prepared by destroying toxic property of toxin retaining antigenic property. Example TT tetanus toxoid
3. attenuated living vaccines - pathogen weakened to make non virulent. Example oral Polio vaccine, BCG
4. antibodies as vaccine - serum used after a person or animal has been exposed to infection. Serum contains antibodies against pathogen. Example anti tetanus serum (ATS)
5. mild strain of virus - non pathogenic strain of virus. Vaccine developed through recombinant DNA Technology used to clone the gene for protective antigen protein. Example Hepatitis B, influenza, foot and mouth disease(FMD)



Tissue and organ transplantation

It is the process of removing tissue or organ from animal and planted to the other or from one individual to another. It is a process applied to replace injured or diseased tissue or organ with natural or artificial ones.

Tissue transplantation
Skin or part of bone -- highly successful.

Types
• autograft - from one part to another
• isograft – between genetically identicals - twins
• allograft - between different members of same species
• heterograft - between different species. Monkey to man

Organ transparent

Best known and successful one is cornea transplant.
Others include kidney, liver, heart etc.
Draw back - the transplanted organ contains about 40 antigens which can trigger the production of antibodies. The recipient recognizes the transplanted organ as foreign body. Does not accept, immune system activated and causes destruction or reject
Drugs used to force accept the transplanted organ.
Radiation to suppress immune system.
So usually between siblings
Cryopreservation - it is the preservation of organ at very low temp.
This technique involves the use of tissue taken form human and other animal for the purpose of reconstructive surgery.

The transplant of cornea is called keratoplasty. The credit of keratoplasty goes to Russian Dr Filotov.
The first heart transplant was done by Christian Bernard in 1967 in the USA
The first lung transplant was performed by JD Hardy in 1964.
The science of transplantation is new one and represent one of the major frontiers. Research and experimental transplant are done and attempted with all parts of human organs.

Benefit of organ and tissue plantation
• Millions of blind people can see the this beautiful world due to cornea transplant.
• Can give life to those patients where the hope of treatment has been given up.
• Skin transplantation, a successful one for those who have met accidents.








Amniocentesis

When a pregnant women is known to have chance of bearing a child with a genetic defect, it may be desirable to diagnose the condition of fetus. This can be done by taking some cells from the fetus by drawing about 10 cc of amniotic fluid with the help of hypodermic needle. This technique is called the amniocentesis. This is usually performed at 15th week of pregnancy to allow enough time for safe abortion if recommend . more than 30 genetic diseases have been detected.

Karyotype analysis - fetal cell analysis- useful for detection of chromosomal abnormalities.

Biochemical test – presence of absence of certain enzymes detection of prenatal disease

Termination of pregnancy is advised if there is serious congenital defect.
This technique has been misused to know the sex of the growing child and abort the normal female fetus. So it is banned.



Test tube baby

For those unable to conceive and give birth to a child normally. Fertilization not possible. Unfertilized ovum taken out , kept under sterile or septic condition. Fertilization carried out by the sperm from her husband out side body. Zygote developed in vitro up to 32 cells stage. Put into reproductive tract. The mother then can give birth to child in a normal way.

It is a great achievement of medical science. The first attempt was made by Italian scientist Dr Petrucci in 1959. He removed an ovum from a patient and put it in a glass tube among swarming millions of spermatozoa. One of which met and fertilized the egg. The embryo grew and survived for 29 days. It is credited to Gynecologist Patric Steptoe and physiologist Robert Edwards of England. The first test tube baby born on July 25, 1978 named Louse Joy Brown, a female child. Mrs. Brown gave birth at 28 weeks and 5 days.
This technique can help those female with obstruction in oviduct to carry down the ovum. In males, it can help if the sperm count is less. In some rare cases, a surrogate or substitute mother has been used to bring up in vitro fertilized ovum to maturity. In reality, ovum does not belong to substituted mother but she delivers the child. It has created ethical and legal problems such as right over child. In case of male infertility, sperms can be used from the sperm bank.

In Nepal, Om Hospital with the technical support of Assisted Reproductive Technology(ART) has started the technology of Test tube baby. The first test tube baby is Om mani Tamang born in 2005 March 3 at 8.52 am in Kathmandu, belonged to Mr Rajendra Tamang and Mrs. Sandhya Syanbo. Since then hundreds of test tube babies have been born.

for BLAS

Natural science

Science - this term has been derived from a Greek verb scire, meaning to know and a Latin noun scientia, meaning knowledge. It is an orderly and systematized body of knowledge based on observations, reasoning and experimental verification. The scientific knowledge is gathered by observations, inquiry and investigations. The main thing that distinguishes science from humanities such as art and culture is the use of the experiments to answer the questions.

The scientific reasoning and the experiments are often simple not mysterious at all. They are merely logical ways of trying to answer the problem as are used by business people, historians and each of us in everyday life. There is no need of any scientific training or knowledge to decide whether conclusions are justified from the data presented or not. We can request further tests of a theory that not appear to be well supported by evidence, and we can agree or disagree with the predictions from a theory.

The term science when used without any descriptive adjective refers to natural science. It deals with natural phenomena. It is different from social science such as sociology which deals with human relations or an abstract science such mathematics which deals with abstract relations.

Natural science is taken into a position of great importance in modern society. Scientific inventions and discoveries are inseparable from human life and welfare. Their applications in day to day problem provide solutions for them. Many decisions affecting our future depend on appropriate interpretation of scientific discoveries.

The government of a country requires that every one participate in decisions on such subjects as population control, pollution standards, protection of wildlife and immunization. The body of scientific knowledge is already so vast that everyone can not understand it all. However, as a responsible citizen, we can follow some studies that bear on public issues. By doing so, we can apply scientific reasoning to decide our own positions on these issues.

However, the natural sciences can be categorized into physical sciences and biological sciences. The physical sciences primarily deal with non-living matter and include subjects like Physics, Chemistry, geology, astronomy etc. The biological sciences include the living organisms, their interactions and relationship with the non – living things. It includes the subjects like Botany, Zoology and microbiology etc.









Scientific Method


The knowledge imparted by any science includes facts, laws and principles of the nature. The knowledge about these is acquired by a typical procedure which is sometimes called scientific method or method of science. This method is used to know about an unknown object or an unknown happening (event or phenomenon) in any science. Sequence of steps of this procedure are broadly classified as

• Observation
• Hypothesis
• Experimentation
• Conclusion
• Sometimes retesting


The scientific method begins with a set of observations with respect to an unknown object or an unknown happening (event or phenomenon) the set of observations activate observer’s (scientist’s or researcher’s ) mind and he wants to know about the unknown object or unknown happening. His natural reaction is to ask questions about it. Then considering his own thought, colleagues’ suggestion and information of the literature, he recognizes a problem to investigate on his observations.

With these information, the scientist or researcher puts forth a hypothesis. Hypothesis is an explanation of what he expects in the underlying original observation or a set or observations. The hypothesis is a tentative explanation or observations or event. It is confirmed through the experiment or refused.

The hypothesis is tested through experiment. It is called experimentation. The experiment is carried out in a specified fashion. The scientist attempts to hold all conditions constant except the one he is manipulating so that any result he observes should be exclusive function of the changed conditions. The result is compared with that of a control, an experiment that depicted all natural conditions.

From the data of experiment, a conclusion is arrived at. If the conclusion is contrary to the hypothesis the hypothesis is refuted, otherwise the conclusion establishes a fact law or principle about the unknown object or happening.


Physics, major science, dealing with the fundamental constituents of the universe, the forces they exert on one another, and the results produced by these forces. Sometimes in modern physics a more sophisticated approach is taken that incorporates elements of the three areas listed above; it relates to the laws of symmetry and conservation, such as those pertaining to energy, momentum, charge, and parity. See Atom; Energy.
Scopes of Natural Science
Divisible into pure science and applied science
Study , understanding of different laws, facts and principles of natural sciences is pure science
Application of the knowledge of pure science for the welfare of human beings is applied science
Scopes of physics
Simple machines
Lever pulley trolley wheel and axel screw wedge, water lifting pump
Computer which work like human brain
Light – microscope, telescope,
Heat – cook food
Sound - audio systems,
Electricity- machines, motors, television, fridge
Magnet – motors, sound systems, therapy
Scopes of chemistry – food, water, metals (ornaments), electric bulbs, metals used in machines, organic and inorganic substances, medicines, fertilizers, pesticides,
Scopes of biology

Nature of Biology

The word Biology comes from Greek words, Bios = life, logos= study, knowledge or discourse. It is the branch of Natural Science which deals with various aspects of living beings (animals and plants). Biology tries(seeks) to understand how animals and plants perform their life activities , how they interact with each other and with non living things. So, it is most appropriately called as the life science.

Though the definition of Biology is very simple, it is equally complex and extensive as it deals with various aspects of enormous number of living organisms spread in time and space.

This branch of science deals with structural organization of living organisms, functions of their body parts, habitat, relationship and interaction among themselves and surrounding. How they pass their specific characters to the next generation ? How do they evolve from simple or primitive to more advanced forms ?

Biology must have born very early in the remote past out of simple curiosity of man about himself and the living world around him. The study have begun in search of different articles of human use from living world so as to lead comfortable life. The science of living organism is as old as the history of man himself. However the first conceivable evidence of the study of living organisms comes from the work of great Greek philosopher Aristotle ( 384 – 322 BC) . He arranged all living organism in a hierarchy placing the simplest organism at the bottom and man at the top. Due to this creditable work, Aristotle is known as the Father of Biology. He is also known as the Father of Zoology and Founder of Embryology.

The term Biology was first used by French Naturalist Lamarck and Treviranus in 1801.

Scope of Biology

Biology is very much important branch of Natural Science. From the very ancient time, man has been benefited from the various parts of animals and plants found around him. The animals and plants are found to be helping man in various ways in making his life much easier.

• Understand human life -- We are curious to know about our own health. Why we eat? How we grow? How we see and hear? What is the importance of balanced diet? The knowledge of Biology can help us to get the right answer of all such questions and others like these.

• Understand natural phenomena -- Natural phenomena like flowering of plants, breeding mechanisms and seasons of animals, social behavior of some insects , dispersal mechanism of seed etc can better understood by the study of Biology.



• Understand mechanism of

Heredity - the transmission of characters from generations to generations.
Evolution - Development of higher organisms from simple ones
Adaptation – Adjustment of organisms.
Scientific theory- various experiment are carried out on crops, animals like mice, guinea pig and their application on man.

• Fulfill the basic need – Skillful biological techniques can be used to fulfill the need of food, shelter, clothes and drugs by improving farming practices.

• Control population -- The knowledge of reproductive physiology of man and other harmful animals and plants can be used in controlling their population.

• Control epidemics -- The epidemics like Malaria, Encephalitis, Sleeping sickness due to insects as vectors can be controlled by knowledge of feeding mode, life cycle, breeding habit etc.

• Conservation of wild life -- if we know the habitat, feeding habit, breeding season etc, we can easily conserve these rare type of wild life.

• Careers in Biology
A. Pure Science - Zoology, Botany, Microbiology, Genetics Entomology etc.
B. Medical Science - Homeopathy, Allopathy including Dental, Nutrition. Etc
C. Applied Science – Apiculture, Forestry, Fisheries, Diary technology, sericulture, soil science, Food technology, Animal husbandry etc


Branches of Biology

Biology is vast subject. We can not study Biology as a whole in our life. Our life is very short. To make the study of Biology much easier, it has been divided into various branches or fields or disciplines. We can study the branches of our interests.

The branches of Biology on the basis of the structure and function:

• Morphology -- the study of external features of organisms
• Anatomy -- the study of internal structure of organisms as seen by naked eye.
• Cytology – the study of structure and functions of cell and cell inclusions.
• Histology -- the study of structure and functions of cells that make up the internal organs of organisms.
• Physiology -- the study of the functioning of organs of organism.



The branches of Biology on the basis of the specific unit or field:

• Toxicology – the study of the toxic substances and their effects
• Embryology -- the study of the development of organism
• Evolution -- the study of origin of life and development into modern plants and animals.
• Microbiology -- the study of micro organisms or microbs.
• Parasitology – the study of parasites and their effects.
• Ecology – the study of relationship between living organism and environment.
• Paleontology – the study of animal or plant fossil

The branches of Biology on the basis of the specific group of organisms:

• Entomology – the study of insects.
• Protozoology -- the study of unicellular organisms
• Parazoology – the study of sponges.
• Cnidology – the study of Coelenterates like Hydra etc
• Bacteriology – the study of Bacteria.
• Virology – the study of Virus
• Ornithology – the study of Birds

The branches of Biology related to the medical science:

• Cardiology – the study of structure and function of heart
• Nephrology -- the study of structure and function of kidney
• Oesteology – the study of bones
• Endocrinology – the study of endocrine glands and hormones.
• Neurology – the study of functioning of brain
• Hematology – the study of blood.
• Enzymology—the study of enzymes



Relation of Biology with other branches of Science

Biology has relationship with other branches of science. We can not study biology without the help of other sciences. We need the knowledge of other sciences to understand biology.
Relation of Biology with Chemistry
• In side the cells as well as body of animals and plants there are inorganic substances and organic compounds.
• Enzymes, hormones , vitamins and minerals are all chemicals. They take part in different vital activities.
• The acid base balance maintains pH. It is required to carry out biological reactions in the body.
• Chemical processes like diffusion, osmosis, plasmolysis, solubility play important role in biological system. These chemical processes help in absorption, excretion, filtration , ascent of sap, transpiration in animals and plants,
• The electrolytes like Na + and K+ play role in conduction of nerve impulse in brain.
• The subject Biochemistry shows the relation of Biology and Chemistry.

Relation with Physics
• The bones and cartilages of body of animals provide the mechanical strength. They act as efficient levers with joints and muscle.
• The lens of eye is for focusing light during image formation, ears are sensitive to change in sound waves.
• Photobiology is related to the role of light in different biological processes like photosynthesis, photoperiodism, phototaxis and phototropism etc.
• Use of energy and maintaining certain temperature of body.
• The subject Biophysics shows the relation of Biology and Physics


Relation with Statistics and Mathematics
The researches in biology requires the knowledge of statistics and mathematics. Many interpretations in biology are based on the knowledge of statistics. The Mendelian ratio of monohybrid and dihybrid cross is the examples of relation of biology with statistics and mathematics.

Relation with Geography
Animals and plants are distributed at different regions of the earth. The north and south poles have similar climatic condition but only the south pole (Antarctica) has the Penguins. The polar bears are found only at the north poles. The Elephants are found only in Asia and Africa. This shows the relation of biology with the geography. It is called as Zoogeography or biogeography.

Biology as science of exception

Though there are different rules and regulations in the different branches of sciences, there are many exceptions in biology. So biology is called as the science of exceptions.
• The red blood corpuscles(RBC) of mammals are without nucleus except Camels.
• DNA is the hereditary materials in all except the Viruses.
• The heart of reptiles are three chambered except the Crocodiles.
• Fishes have gills for respiration but Protopterus (Nile lung fish) has lungs.
• Larva develops into adult but American Salamander larva becomes sexually matured and gives birth to larva.
• Birds are usually adapted for flying but certain birds like Kiwi, Ostrich can never fly.
• Stems are usually aerial but ginger, potato have underground stem.
• Mammals are viviparous but duck billed Platypus, Echidna is oviparous






Origin of life
From pre historical time, man of different walks of life has tried to define and explain life in their own ways and even biologist at some time attempted to define life
Philosophical definition of life
Ancient philosophers idealist view life possesses some supernatural source not comprehensible by experimental method. Plato called it ‘psyche’ , Aristotle called it as ‘ entelechy’ , Hindu philosophy ‘ atman ‘ immortal soul , as divine spark, universal reason by Hegel . idealist consider matter as non living and inert
Materialism based on facts derived from natural science confirms that life like rest of the world is material n its nature. It does not need any sort of spiritual origin for its understanding. There occur no biological laws. There exists one law alone reeling inorganic nature which directs all phenomena occurring in living bodies
Dialectical materialism special form of motion of the matter, qualitatively differentiated from objects of inorganic world. This form of motion is inherent only in living beings. According to rational definition of Oparin 1968 life is a special form of the motion of matter arising in a regular manner at certain stage in the development of matter.
Biological definition
Instead of defining life by exact words, provide an operational definition of life (Korn and Korn, 1971). They differentiate living system with non living objects by the set of properties that characterize living system.
1. the capacity for synthesis - convert different energy forms into chemical energy of ATP , which is then used to derive reactions for synthesis of macromolecules for maintaining growth
2. the capacity for self regulation - contain information content in the form of DNA which specifies polymeric synthesis and monomeric degradation that can occur through regulation of protein synthesis
3. The capacity to adapt genetically - the living system retain an identity apart from, yet within their environment while being inherently able to adapt to new environment or improve in their efficiency in the same environment by random changes in their information content. In short, living system undergo evolutionary changes.
Origin of life
The most complicated, puzzling problem for thinkers, philosophers naturalist



Different theories
Theories of origin of life

Theory of Special Creation

This theory was proposed by Hebrew et al and strongly supported by Father Suarez. According to Bible, God created this universe, all animals and plants including ocear, mountain etc. The life was created during 4004 BC in six consecutive days. The heaven and earth were created on 1st day. Sky was separated from water on the 2nd day. On the 3rd day, the land and plants were created. On the 4th day, the Sun, Moon and Stars were created. Te 5th day, fish and fowl were created. Animals were created on 6th day. The first human was Adam created from inanimate matter the clay which was furnished with soul. Then it started breathing. The first woman was Eve who was created from one of his ribs.
All existing animals and plants were created by God. According to Hindu Mythology, Brahma( God of Creation) created different forms of life. The body of all living beings was made up of five elements( pancha maha bhut) like the earth(Prithvi), water(jala), fire(Teja), sky(Akash) and air(Bayu). After the death, all these elements will be returned to pancha maha bhuta.

This theory states that
1. The life was created by God or Creater
2. Formed all of a sudden, out of nothing
3. No interrelationship among living beings and
4. Have not undergone any change
The life is a mysterious force or vital spirit that set living things completely apart from non living and originated due to some supernatural event. It is accepted on basis of faith. One should believe in the existence of God. However, this theory can not be proved experimentally. So biologists do not believe in this theory.



Objections
Charles Darwin condemned special creation theory saying that earth has not always been inhabited by plants and animals as we know now. It means there is always a change. This theory lacks sound logic, scientifically sound evidence, it could not convince scientists.




Theory of Spontaneous generation or abiogenesis

Before the end of the Seventeenth century, both biologists and philosophers believed that non living things could arise from the non living(inanimate) substance spontaneously. This remained true for centuries in the past. This theory was proposed by Von Helmont(1577-1644). In China, even from earliest time, there was belief that aphid and other insects under the influence of heat and moisture, come into existence. In sacred books of India, there are indication of sudden emergence of different parasites, flies, beetles from sweat and manure. The Babylonian cuneiform text showed the worms and other creatures were formed form the mud of canals. In ancient Egypt, the conviction prevailed that layer of humus deposited by Nile river in its flood gave birth to living creatures like toads and frogs.

o Frogs, toads, snakes etc were believed to be developed from mud
o Parasites, beetles flies etc from sweat and manures
o Aphids and other insects arose under the influence of heat and moisture
o Fly maggots from flesh
o Young mice could arise from wheat grains and when these are kept in a dark room along with dirty clothes
Anaximenes (586-524 BC) proposed that air as sole cause of life.
Aristtotle (384-322BC proposed that worms, insects, fish, tape worm from excreta, crab, salamanders from earth can be developed.

Experiment of Von Helmont
Von Helmont kept dirty shirt and few grains of wheat in a cup board for 21 days. He observed mice developed from sweat and wheat. So, he proposed that both sexes of mice will be developed directly from non living things. He conducted this experiment in the support of spontaneous generation.
We find the repetition of these tales in the writings of ancient Greeks like Thales(624-547 BC), Empedocles(485-425 BC), Democritus (460-370 BC), Plato (427-347BC ) and Aristotle(384-322 BC).
William Harvey(1578-1627) despite the statement that all life come from egg was not able to tear himself from the concept that lower forms of life may aboriginate by spontaneous generation from non living precursors.

Theory of biogenesis

This theory states that life is originated not from inanimate substance but from the preexisting forms only.

Redi’s Classical Experiment

Italian Physician Sir Francisco Redi (1621-1697) demonstrated that maggots were not created from meat or fishes. In his classical experiment, he placed lumps of boiled meat in jars, some uncovered, some covered with muslin cloth and some with parchment paper. After few day, he observed fly maggots only in the uncovered jars.


The discovery of microbs by Van Leeuwenhoek (1632-1723) brought the question that microbs are so simple and could arise by Spontaneous Generation. This idea was authoritatively maintained by German philosopher Leibniz (1646-1716), French naturalist Buffon (1707-1788) and Englishman John Ne dham (1713-1781).


The decline and fall of the theory of Spontaneous Generation

An Italian scholar Abbe Spallanzani tested the theory of Spontaneous Generation. In 1765, he prepared flasks of meat broth which were boiled for several hours and then sealed. This broth remained clear for months and when seals were broken and broth tested, it was shown to be free of microbs.

Spallanzani’s experiment were neither conclusive nor satisfying to many of his contemporary scientist. They claimed that by boiling, he had driven out the vital force needed for Spontaneous generation. And also the sealed flask contained no oxygen.


The period of Louis Pasteur(1822-1895) : Pasteur devised several experiment means by which Spontaneous Generation of microbs was disproved. The simplest and most sophisticated one was with the use of a swan- neck flask. He prepared meat broth in this flask and boiled for several hours. He then left the flask unsealed. The flask was not sealed and there was free exchange of air with environment and system did not lack oxygen. Still the swan –neck remained free of microbial contamination for months because their swan neck were so shaped to trap the viable microbial particles and allow only air to enter the flask. After several months, he broke the neck of the flask and did not find the microbs. This simple experiment thus altogether disproved the concept of Spontaneous Generation. Thus it was proved that life could arise only from the pre existing life which is known as Biogenesis.

Cosmozoic theory
This theory was proposed by Richter 1865 AD and supported by Arrhenius 1908 AD. It states that life came on this earth from other planet in the form of seed or spore or panspermia. So, spore theory finding the suitable environment it grows into life. He could not explain mechanism by which panspermia survived adverse condition of high temp and lethal radiation of inter planatery space during migration.

Catastrophic theory
It was proposed by G Cuvier 1769-1832 and Orbigney 1802-1837. This theory states that there have been several creation each preceded by a catastrophy due to some major geological changes. Each catastrophy destroyed previous life completely and was followed by next advanced creation.

Steady state theory
This theory states that organisms have been unchangeable not only through out existence but also they have existed and continue to exist unchanging till eternity. Hutton says there is no beginning and end. This theory was supported by Richter and Arrhenius etc.

Modern or Natural or chemosynthetic theory of origin of life
This theory was proposed by Russian biochemist Alexander Ivanovich Oparin (1923) and supported by JBS Haldane (1928). This theory is popularly known as Oparin Haldane theory. This theory has been explained in detail in Oparin’s book “The Origin of life on the earth” published in 1936.

It states that primitive life originated in the water bodies on the primitive earth by chemical evolution through a series of chemical reaction about 4200 million years ago.
Steps
A. Origin of Earth (Biopoiesis)
The earth is supposed to be originated about 4.6 billion (4x109) years ago. The sphere was filled with cloud masses of dust particles called ylem. The rotation and gravity caused condensation and formed entire solar system. The earth when formed was very hot (4000 – 8000 oC ), like a ball of fire. Gradually cooled in next few million of years. They started condensing forming solids, liquids and gases. Heavy elements shank at the centre forming core. The lighter one (Aluminum, silicon, sodium, potassium ) formed the middle core of earth. Thus, lithosphere was formed. Lightest gases N2 H2 CO2 He etc including water vapor with dust particle rose above the land surface and turned finally into atmosphere.
B. Origin of life on earth
It is expected that life originated on earth nearly 3.7 billion years ago and involved following changes.
I. Chemogeny
Volcanic gases like H2 N2 CO2 H2O He underwent many changes (chemical evolution) which took place in following steps.
i. Formation of original gases
The original gases like NH3, CH4, HCN etc would have formed by interaction of volcanic gases when primitive earth cooled down from 100 oC. The formation of prime component was the start of life in primitive earth
N2 + 3H2 ……… 2NH3
C + 2H2 ……… CH4
2C + N2 + H2 ….. 2HCN
ii. Formation of key bio micro compounds
Simple key bio micro compounds like pentose sugar, glycerol. Fatty acids aminoacids, nitrogen bases( adenine, cytosine, thymine, Guanine etc would have formed by interaction of original gases( NH3 CH4 HCN ) when the temp further went down to about 50 to 60 oC Such reaction took place under the action of heat coming from energy radiation of Sun lightning, lava, radio active elements like radium, uranium of rocks etc.
6CH4 + H2O …………….. C6H12O6 + 12H2
CO2 + 2NH3 …………….. CO(NH2)2 + H20
CH4 + H2O + NH3 +HCN ……….. Nitrogen bases
CH4 saturated hydrocarbon reacted with water there by forming unsaturated hydrocarbon like acetylene, ethylene etc. From these, aldehydes, ketones, alcohol, acid were formed spontaneously, still more complex organic compounds like glucose, amino acid, fatty acids etc and purine and pyrimidine were formed as key bio micro compounds.
iii. Formation of complex bio macro compounds
Complex bio macro compounds like starch, protein, lipid, nucleic acid would have formed by polymerization of key simple bio micro compounds in the presence of water.
C6H12O6 + C6H12O6+ + C6H12O6 + … Polysaccharides
Fatty acids + glycerol ……………………. Lipid(fat)
Amino acids + amino acids + amino acids + ……..Protein
Complex bio macro compounds thus formed did not undergo oxidation because primitive earth was reducing, no free O2 and no microbes present.
iv. Formation of coacervates
When earth further cooled down, water vapour turned into rain, earth surface shrunk and formed depression where rain water filled up and turned into lakes, sea, as hydrosphere. Up lands turned into mountains. In sea, bio macro compounds when mixed with sea water formed thin hot soup called “broth”. To this Haldane 1992 called ‘pre biotic soup’.



Miller Urey experiment

Stanley Miller and Harold C Urey in 1953 performed series of experiments and tested Oparin and Haldane theory. They devised an apparatus that simulated the conditions of the surface of pre biological earth and analyzed the molecular forms that arose. The apparatus consisted of exposing water vapor to electric spark of 75,000 volts(to represent the lightning of thunder storms) in an ammonia, methane and hydrogen atmosphere of the early earth. After two weeks of treatment, Miller chromatographed the final solution and found many organic compounds including both carbohydrates and amino acids. Many of the compounds were important metabolic intermediates of present day organisms.

Since free oxygen destroys most of the intermediate products, the presence of intermediate products supported the Oparin and Haldane’s hypothesis of reducing atmosphere of primitive earth. Abiotic synthesis of molecules is possible only in reducing atmosphere and abundance of free oxygen (as in earth today) prevents the abiotic origin of life. So, life is originated from the earth’s inorganic atmosphere in the past but is no longer happens today.




Classification
Grouping of living organisms according to their similarities and dissimilarities is known as classification. It is the important part of modern taxonomy. There are millions of living organisms on earth. No systematic study can be done without classifying them.
The classification is not only for identification but also to know the evolutionary trend. Different systems of classification
Artificial classification
It is the classical type of classification. Ancient people tried to classify plants and animals according to use to mankind. This type of classification is based on one or few characters. It is not based on natural characters and phylogenetic relationship. Artificial classification is put forwarded by different workers in pre Darwinian era.
Natural system of classification
Natural system is based on truly natural characters such as characters of resemblance or correlation, affinities among them etc. this system considers all aspects by which closely related plants and animals come together. The best and highly recognized natural system of natural classification was proposed by George Bentham (1800 to 1894) and Joseph Dalton Hooker (1817-19110). They made the thorough observation of the plants and presented classification.
Phylogenetic system of classification
The study of history of development of a race or simply evolutionary history is called phylogeny. It includes he knowledge of ancestor, place and time of origin. This is the most advanced type of classification. This system classifies the plants and animals according to their evolutionary sequence and genetic relationship. This system was put forwarded by A Engler(1844-1893) this system enables the taxonomists to trace out ancestor and evolutionary trend.

Hierarchic system in classification

Hierarchy is a system of arrangement where taxonomic categories are placed in major units of classification
8. Kingdom
This is the highest caterory. There are kingdoms like Monera, Protista, Fungi or Mycota, Plantae and Animalia etc.
9. Division or Phylum
The division or phylum includes classes of different organisms having common characters.
10. Class
It is the group of orders.
11. Order
Group of related Families
12. Family
Group of related genera
13. Genus
Aggregation of two or more species
14. Species
This is the basic unit of classification. The closely resembling individuals of same kind constitute species. They can freely interbreed and produce fertile offspring. Among the member of species, there may be presence of minor differences in color, form and size etc
Two Kingdom classification
Carolus Linnaeus (1707-1778) divided all living things into two Kingdoms for the first time.
Kingdom Plantae or Plant kingdom
Some characters
6. Autotrophic mode of nutrition
7. Immobility
8. Rigid cellulosic wall
9. Less sensitive
10. Includes all plants
Kingdom Animalia or Animal kingdom
Some characters
6. Heterotrophic mode of nutrition
7. Mobility
8. Made up of cells without rigid cellulosic wall.
9. More sensitive because of presence of nerve cell
10. Includes all animals
The two kingdom classification is appreciable effort. However it could not address a great variety of animals and plants. So, it is inadequate and unsatisfactory in modern age.

Five kingdom classification
RH Whittaker of USA (1969) gave five kingdom system of classification (Science,163:150-160)
This system focuses on
4. Complexities of cell structure and body organization
5. Mode of nutrition
6. Phylogenetic relationship
Features of five kingdom classification
4. Advancement over the two kingdom classification
5. Based on phylogenetic relationship
6. Solves many problems of two kingdom classification.
Characters of five kingdom classification
7. Separated prokaryotes from eukaryotes
8. Removed anomaly of positions of many transitional and intermediate forms
9. All multi cellular, photosynthetic, eukaryotic with cellulosic wall included in kingdom Plantae
10. All multi cellular, non photosynthetic, eukaryotic with cellulosic wall included in Animal kingdom
11. All multi cellular, non photosynthetic plants separated from photosynthetic plants and kept in kingdom Fungi.
12. Brought out phylogenetic relationship amongst the primitive forms
Kingdom Monera

Characters
6. Unicellular, microscopic, prokaryotic and found greatest in number on earth
7. Lack of well organized nucleus, not surrounded by nuclear membrane, nucleus consists of double stranded DNA, nuclear contents lie any where scattered in protoplasm.
8. Most of them rigid cell wall
9. Various mode of nutrition, autotrophic, parasitic, symbiotic or saprophytic known as decomposers which convert complex organic matter into simple and soluble forms.
10. Can tolerate extreme environmental conditions like temperature pH absence of O2.
Bacteria were first discovered by Dutch naturalist Anton Van Leeuwenhoek (1632-1723). He discovered the first microscope in the 17th C. He observed Bacteria in June 10, 1675. The term bacteria was given by Ehrenberg in 1838. The study of Bacteria is called Bacteriology. Bacteria can withstand temp up to 78 oC and -190 oC. There are two types of Bacteria Gram +ve and Gram –ve based on stain.

Kingdom Protista
Characters
6. Unicellular microscopic eukaryotic organism with well organized nucleus. Besides nucleus, mitochondria , endoplasmic reticulum, golgi bodies plastids etc present.
7. Both autotrophic and heterotrophic mode of nutrition.
8. Photosynthetic protists are chief prodders of ocean, fresh water bodies and known as phytoplankton .
9. The non photosynthetic protists are called zooplankton which are primary consumers.
10. Some act as decomposers
Reproduce both sexually and asexually. Some like Euglena exhibit flexible
Kingdom Animalia
Characters
9. Includes multi cellular, eukaryotic animals.
10. Heterotrophic mode of nutrition.
11. They are called consumers as they depend on others
12. Great variety ranging from invertebrates to vertebrates.
13. Lack of green pigment chlorophyll, cell wall.
14. Holozoic, parasitic
15. Reserve food in the form of glycogen
16. Have locomotory organ and sense organ.

Kingdom plantae
Characters
6. Includes multi cellular eukaryotic plants found on land, sea water or freshwater. They can be alga, bryophytes, pterydophytes, gymnospersm and angiosperm. All are photosynthetic hence called autotrophs and producers of ecosystem.
7. Cell wall is made up of cellulose
8. Some are parasitc(Cuscuta). Some insectivorous like Pitcher plant and others symbiotic( leguminous plants.
9. Fixed on land and no locomotory organ.
10. Have chlorophyll and can synthesize food.

Kingdom Fungi( Mycota)
Characters
14. Includes multi cellular eukaryotic plants with heterotrophic mode of nutrition. Size vary from microscopic to bracket fungi, toadstools. Puffballs which are seen
with unaided eye.
15. Mostly saprophytes feeding on dead and decaying organic matter also known as decomposers.
16. Cell wall is made up of chitin or cellulose or both
17. Exists as a mycelium made of network of branching multi cellular threads called hyphae
18. Some are parasitic eg. Puccinia
19. Body is thallus( not differentiated into root, stem and leaf.
20. Lack chlorophyll, cannot manufacture food
21. Non vascular
22. Reproduce by spore forming, asexual and sexual method
23. Reserve food in the form of glycogen and oil globules.
24. Some harmful, causes diseases
25. Some beneficial, used in industry like alcohol, enzymes. Vitamins, bread and antibiotics, some as food.
26. Found in almost all habitat where organic material is available.




Lamarckism

Organic evolution
The doctrine of organic evolution states that the present day organisms are modified but lineal descendants of species that lived in former geological times and that more complex and highly differentiated forms have evolved from simpler ones by gradual modifications. It is still in operation.

One of the first attempts to explain the organic evolution was made by French Biologist Jean Baptiste Lamarck n 1809. he outlined his ideas in his book Philosophie Zoologique published in 1809.

This theory is based on observation that the changes in the environment lead to the changed pattern in the species.

This theory consists of four postulates or facts
1. Tendency to grow - the internal forces of life tends to increase in size of parts of an organism on the whole up to a certain limit. The limit is determined by life itself.
2. Formation of new organs - new organ or a part in the body is formed due to long felt need or want. For example webbed toes in duck.
3. Effects of use and disuse - the more frequently and continuously and animal used an organ; the more it was strengthened, developed and enlarged. If an organ wan not used, it gradually weakened and finally disappeared. For example legs of snake.
4. Inheritances of acquired character -- all changes which organism acquire during life time are acquired characters. These characters are inherited in the generations. The acquire characters go on accumulating through generations and finally in long course of time produce organism entirely different from the pre existing ones. So, this theory is also known as Theory of acquired characters. For example, Giraffe developed long neck and long legs by continuous effort and stretching to reach the higher level of trees. The longer neck and legs produced, passed on to the next generations. Over long period of time after successive generations, the present day Giraffe with long neck and leg were evolved.


Draw backs

Lamarck’s theory is rejected because acquired characters are never inherited. Acquired characters can bring changes in body or somatic cells, but not in the germ cells.

August Weismann proved that acquired characters affect the body and are somatic; they can not be inherited since they do not affect germ cells. Any variation must be present in the germ cells if they are to be inherited. In one experiment, he cut tail of mice for 20 generations, mouse produced after that have same length of tail. No decrease in length at all.

This theory could not produce any example from plants.









Darwinism

Charles Darwin and Alfred Russell Wallace jointly contributed a paper in 1858 putting forward the view that species had evolved by process of natural selection of those races most fitted to survive in particular surroundings. According to this theory, living organisms have common origin and through a series of small changes in the organism generation after generation new species are formed. This theory is known as theory of Natural Selection or Darwinism.

The theory of Natural Selection can be explained under following observations and consequences.

1. over production of offspring
Every lining organism tends to increase in a geometrical manner. Such reproductive
Potential of different species may be easily observed in nature. A single pair of English sparrow would be the ancestor of over 275 billion individuals in 10 years if they and their descendants could reproduce at their natural rate without any check. In case of slowest breeding animals like elephants, one pair of elephants in 800 years could have 29 million descendants in the absence of any check.

2. Total number of survivors remain nearly constant
In spite of their capacity to increase, population remains nearly constant. In case of fishes, they can lay large no of eggs, all the eggs do not hatch. Large number of fingerlings dies or killed before they reach reproductive age. Even in case of human beings, the mortality of infants is much higher. Besides, these are different checks by which population can not increase so high.

3. struggle for existence
the available food and other resources can support only a limited number of organisms . So animals and plants have to struggle for their existence.
Intraspecific struggle
Intraspecific struggle or competition occurs among the individuals of same species. This type of completion is fierce due to similar requirements. This may be for food, shelter and mate.
Interspecific struggle
This type of competition is found between two individuals of different species. The very common object for this type of competition is food.
Predation
There are different carnivore animals which kill and feed on the herbivores. These animals are said to be predators. Due to predation also no o animals are kept within limit.
Environmental struggle
Living organisms struggle with adverse environmental conditions like drought, heat cold, lightening, earthquake, volcanic eruption heavy rainfall flood etc. Besides out break of diseases, war etc can kill large no. of animals and plants.

4. variations and heredity
Individuals always try to become better adopted to utilize the resources and to survive successfully. For this they may have certain modifications or changes in their bodies. These changes are called variations. Variations are of two types. Some variations are harmful which make the animal unfit but some variations are useful or favorable. Useful variations are quite significant and make organisms fit in their environment. The same variation may be harmful at one environment but useful at other environment. Variations are inherited in the progeny and therefore progeny have better chances of survival.

5. Survival of fittest or Natural Selection
Those individuals having favorable variations would survive and propagate their kind. They can increase their population. Herbert Spencer called it survival of the fittest. Those which are fit can survive. According to Darwin, it is Natural Selection. Only those animals having favorable variations are selected. The animals with harmful variations will decline and one day they will become extinct.

6. Origin of species
Useful variations are accumulated generation after generation for thousands of years. After long time, the generations produced will be quite different from parents. This is the emergence of new subspecies. These new subspecies later on form different species. In this way new species in originated. Some process of variations with heredity accompanied by natural selection was sufficient over the vast geological time to produce all the living animals of today.

Natural Selection is admitted today as the most probable explanation of evolution. With the scanty of knowledge of the nature of variations and heredity before 1900, little could be added to what Darwin knew of the phenomena.



Criticism

A. Mutation is the process in which sudden large variations occur in the animal’s body. It is now proved that mutation has powerful role in evolution. Darwin ignored mutation.

B. Darwin could not identify the heritable variation and non heritable variation. Because only the heritable variations are counted.

C. Natural selection is not a creating or initiating force but only directing or controlling factor. Natural selection operated only after variations have appeared. It accounts for preservation rather that origin of favorable variation.

D. Darwin’s theory does not show how natural selection is brought about nor does it explain the origin of non useful variations.

E. This theory explained the survival of the fittest but not arrival of the fittest.
Neo Darwinism
On these and several other grounds it is now held by many scientists that the theory of natural selection is not only the factor in evolution. Darwin and his contemporaries were not aware of cytological and genetic information which became available later on. Since Darwin’s time interest has not lessened in the matter of how evolution has taken place. At present, the most widely accepted theory of evolution incorporates many of Darwin’s ideas into a frame work of genetics. Neo Darwinism is modification of Darwin’s theory taking into account the results of more recent work.

Scientist like Dobzhansky, RA Fischer, Julian Huxley, JBS Haldane Sewell Wright, Hugo de vries etc contributed to the Neo Darwinism.

It is based on following facts.

Mutation -- it is the sudden heritable change which occur in the chromosome.

Genetic recombination -- crossing over in the meiotic division brings changes in the genetic composition. It is responsible for the variations in the population.

Natural Selection -- useful variations are preserved by natural selection.

Genetic drift or Sewell Wright Effect -- variation in gene frequencies within populations can occur by chance than by natural selection. It is important in small or isolated population.

Reproductive isolation -- it can help to bring more changes in new environment. When not mixed, they become more and more different from one another.

Origin of new characters
Heredity is the presence of characters in the off springs which are present in the parents. These characters are directly transmitted to children from parents. The children thus get some characters from father and some other characters from mother. Some children get more of the characters from father and less from mother and vice versa. So, any child is not the photocopy of the father or mother. The child is little bit different from the father as well from the mother.

In the sexually reproducing animals including human beings, at the time of gamete formation, there is meiosis. During this cell division meiosis, the chromosomes number is reduced to half. For example, in case of human beings, there are 23 pairs of chromosomes. It is said to be Diploid number of chromosomes, denoted as 2n. In the sperm and ova(eggs), there are only 23 chromosomes. This number of chromosomes is said to be Haploid number of chromosomes and denoted as n. At the time of fertilization, the chromosomes of sperm and egg together make Homologous pairs of chromosomes and thus make Diploid number of chromosomes. During the process of formation of Homologous pair of chromosomes, there is crossing over to make the new set of chromosomes. This new set of chromosomes are little bit different from the those of parents. This new set of chromosomes are responsible for the origin of new characters in the off spring or children.

The new set of chromosomes are formed because of meiosis. The pattern of transmission of characters depend on the way the new set of chromosomes are formed. The pattern of transmission of characters in the off spring is studied in Genetics. This term Genetics was first used by W Bateson in 1905. The foundation of Genetics was laid in 1865 by Gregor Johann Mendel. For his overriding contribution in Genetics he is called as Father of Genetics.

Biography of Gregor Mendel

Gregor Mendel was born on 22 July 1822 at Heinzendorf of Silesian village in Austria. He joined Augustinian monastery at Brunn in Austria in 1843. He was sent to University of Vienna to study Natural Science and Mathematics. He returned to Monastery in 1853. He conducted research on common garden pea plant (Sativum pisum) for eight years from 1956 to 1864. Mendel presented data and conclusion derived from his experiments in a paper entitled “ Experiments in plant hybridization” which was read before Brunn Natural History Society in 1865 and was published in Annual proceedings of Natural history Society in 1866. His work was not recognized in his life. Unrecognized and bitterly disappointed , he died in 1884. Mendel’s observations went unnoticed on account of
o He published his work in an obscure journal.
o Failure of he scientists to notice his work because scientific world was at that time busy in the controversy arisen by the Darwin’s theory of origin of species.
o His ideas were ahead of his time as the ignorance was prevalent in that period about cytological basis of heredity.
In 1900, three eminent biologists Hugo de Vries of Holland, Karl Correns of Germany and Eric Von Tshermak of Australia working independently on heredity discovered the same phenomena originally uncovered by Mendel. Thus the genius of Mendel came to be discovered after 16 years of his death. Mendel for his great contribution is now famous as “Gather of Genetics”.

Mendel’s experiment
Mendel selected garden pea (Pisum sativum) as plant material for his experiment since it had following advantages.
o Possess many varieties with well defined characters.
o Flowers are bisexual and can pollinated easily.
o Easily be grown and readily be crossed.
o Very short life span, many generations formed.
o Hybrid pea plants are fertile.
o Flowers completely closed by petal, so plants predominantly self pollinating and self fertilizing.
Reasons for Mendel’s success
o Studied the inheritance of one character at a time.
o Carried out experiments to F2 and F3 generations only.
o Maintained statistical records, analyzed carefully.
o Selected pure line parent plants.
o All possible precautions taken to prevent self pollination.
o Even reciprocal crosses conducted but no change in the expected ratio of off springs.
Seven pairs of contrasting characters of pea plant used by Mendel
Trait dominant recessive
1. Seed color yellow green
2. Seed shape round wrinkled
3. Pod color green yellow
4. Pod shape inflated constricted
5. Flower color purple white
6. Flower shape axial terminal
7. Plant height tall dwarf
These seven pairs of contrasting characters of pea plant mean that if one character is expressed the other is not expressed. If the character tallness is expressed the other character dwarfness cannot be expressed. In the same way, if dwarfness is expressed, the other character tallness is not expressed.

Some basic terms used in inheritance studies

Gene or Factor

Mendel called it factor which carry the character from the parent to offspring. In the modern sense an inherited factor that determines a biological character of an organism is called gene. This is the function unit of hereditary material. It is a segment of DNA. Gene is equivalent to the factor of mendel.

Allelomorphs or allele

Allele is abbreviated form of allelomorphs, which means one form or the other. It indicates the alternative forms of the same gene. Each character has two determiners called factor. In pure tall or pure dwarf plant, same allele is duplicated like TT or tt. But in the hybrid tall plant both alleles are present like Tt. An organism having same allele or two identical alleles is known homozygous and an individual with different alleles is called the heterozygous. For example an organism with both TT or tt is called homozygous and an organism with Tt is called heterozygous.

Homozygous plants are genetically pure or that character. They give rise to offspring having same character on self breeding. The heterozygous hybrid plants do not breed true on self fertilization. The heterozygous plants on self fertilization produce both tall and dwarf plant.

Homozygous organism bear either dominant or recessive alleles and never both. Where as heterozygous organism bear both dominant(T) and recessive(t) alleles. The homozygous organism(plant) produces one types of gametes either T or t only. But heterozygous organism produces two types of gametes nearly half with T and another nearly half with t. The homozygous plants do not show vigor but the hybrid or heterozygous plants show extra vigor.

Genotype and phenotype
It is the genetic composition of an organism. It can be like TT, Tt or tt for a particular character. The genotype can be ascertained from ancestry or progeny of individual. On the other hand, phenotype is character which can be observed from the outside like the tall plant or dwarf plant. Phenotype is expressed like form, sex, color, behaviour etc. phenotypes of organism is expression or observable structural traits or characters produced due to interaction of genes and environment. In some cases, the phenotype is not visible from outside. For example, the blood groups like Blood group A, B, O and AB and Rhesus Factor like Rh +ve or –ve is not expressed outside.

Monohybrid and dihybrid cross
In the monohybrid cross, Mendel considered only one pair of contrasting characters like tallness and dwarfness of plant. Similarly, the other characters like round or wrinkled seed or yellow or green seed etc. can be considered but only one pair of the contrasting characters. The other characters are not taken into consideration. In case of dihybrid cross, two pairs of contrasting characters are taken into consideration at the same time like the yellow or green and round or wrinkled seeds.

Reciprocal cross
The reciprocal crosses involve tow crosses concerning the same characteristics but with reversed sex. For example, if in first cross, A is as the female and B is as male, then in the second cross A is as male and B is as female.

The interpretation of Mendel’s results
The principles of inheritance as given by Mendel are as follows.
1. Principle of Dominance
Out of two contrasting characters only one is expressed itself in an individual. The factor which is expressed is called dominant while the other which has not shown its effect is termed as recessive. In monohybrid cross, when homozygous (true breed) tall pea plant is crossed with homozygous dwarf plant, all the plants appeared in F1 generation are tall although they receive both factors (Tt) T from tall plant and t from dwarf plant. In the F1 generation, the character of t is not expressed. The character which is expressed in the F1 generation is called the dominant character and the character which is not expressed in F1 generation is called the recessive. The factors responsible for certain character is always found in the pair like TT or Tt or tt. To these Mendel’s factors, Danish botanist Johansson introduced the term gene in 1909.
Importance of principle of dominance - the phenomenon of dominance is of practical importance as the harmful recessive characters remain hidden by normal dominant character in hybrids. In human beings, a form of idiocy, diabetes and hemophilia are recessive characters.
2. Principle of segregation ( purity of gametes)
The law of segregation states that when a pair of contrasting factors or allelomorphs or genes are brought together in a hybrid(heterozygote) these factors do not blend or mix up but simply associate themselves and remain together and separate at the time of gamete formation.



3. Principle of independent assortment.
the law states that the agaenes of different characters located in different pairs of chromosomes are independent of one anotrher in theeir segregation during gamete formation ( meiosis) . the principle of independent assortment can also be defined as “ if we consider the inheritance of tow or more genes at a time their distribution in the gametes and in progeny of subsequent generations in independent of each other.
in the experiment of dihybrid cross between the round yellow and wrinkled green seed plants, we can get the emergence of new characters like round green and wrinkled yellow seed plants. these new characters in combination were not present in the parents.we have the ratio of the dihybrid cross as follows. The round yellow:round green:wrinkled yellow:wrinkled green is 9:3:3:1 in the F2 generation. this showed that the factors responsible characters are separated during the segregation and they are free to combine with any other of the factors. they combine haphazardly. there is no any hard and fast rule for their combination. this is known as principle of independent assortment.



11. life style. In absence of light ingest food and in he presence of light show autotrophic mode of nutrition.