Homeostatis DefinitionHome means same and statis means state. So the regulatory mechanism which maintained the internal environment of a organism is called homeostatis.

Important Aspects of Homeostatis

There are three important aspects of homeostatis.

Osmoregulation

Thermoregulation

Excretion

Feed Back SystemThe check and balance system in a body is called feed back system. In a feed back system three organs are involved.

1. Receptor The organ which receive any change in the internal environment of the body are called Receptor.

2. Effector The central nervous system which send the message to a particular organ are called effector. Take part in particular action. 3. Central Nervous System The receptor transfer message to a central nervous system such as brain.

Types of Feed Back System

There are two type of feed back system.

Positive Feed Back System

Negative Feed Back System

1. Positive Feed Back System When there is a change in the internal environment and it is further increase by the process are called positive feed back system.

2. Negative Feed Back System When there is a change in the internal environment and it is further decreased by the process called negative feed back system.

Osmoregulation

DefinitionThe regulatory mechanism which maintain the balance between water and solute context of a cell is called osmoregulation.

Osmoregulation in Plant

Due to the availability of water there are four groups of plant.

Hydrophyte

Halophyte

Xerophyte

Mesophyte

Hydrophyte The group of plant which is grow in fresh water are called hydrophyte.

Characteristic of Hydrophyte

The plant do not have layer of cuticle.

The leave have stomata in the upper surface with take part in transpiration.

The root are either absent or poorly developed.

Example

Hydrilla, Lotus, Lily plant

Halophytes The group of plant which is grow in marshy soil or salty soil are called halophyte.

Characteristic of Halophyte

These plant absorb water from such a soil, which is higher salt concentration and low water potential.

Halophyte actively absorption salt into their roots.

In the leaves of plants salt glands are present which helps in the removal of salt and water from the body.

Some halophytes absorb humidity by leave.

Example Glass wort, Cord grass

Mesophyte The group of plant which is grow in well watered soil are called mesophyte.

Characteristics of Mesophyte

Their roots are well developed.

Their body is covered by a layer called cuticle.

They contain stomata for evaporation of extra water.

Some mesophyte excrete out water in the form of drop this process is called guttation.

Xerophyte

The group of plant which is grow in dry places such as desert are called Xerophyte.

Characteristic of Xerophyte

Some plants do not face dry consition and produce seed are called ephemeral plant. During raining season seeds germinate.

Their root are well develop which go deep into the soil to absorb water.

Some plant have horizontal root on the surface to absorb rain water rapidly.

Some plant leaves are modified into spine to prevent transpiration.

Stem and leave covered by cuticle.

Some plant store water in cell (succulent)

Example Cacuts, Euphorbia. xcretion

DefinitionThe removal of harmful substance produce in the metabolic process from the body is called Excretion.

Excretion in PlantIn plant rate of catabolic process is very slow and waste product are produce in less amount. They are used again in their anabolic process.

Waste Substance of Plant

The substance which are produce in excess amount are

Water

CO2 and O2

Ions

Removal of Water

Extra water is removed from the body of plant by two methods.

Transpiration

The extra amount of water removed in the form of vapor through stomata is called transpiration.

Guttation

When water is removed from plant in the form of drop this process is called Guttation. Guttation occur special opening called hydathods. Guttation take place in those plant which grow in tropical rain forest.

Release of Oxygen and Carbondioxide

In day time plant used CO2 for photosynthesis process and released O2.

In night time plant released CO2 and inhale O2 gas.

Ions

Excess amount of ion are deposit into dead cell of plant body such as bark.

Thermoregulation

The maintained the temperature of the body with in a range is called thermoregulation.

Thermoregulation in Plant

The normal range of temperature in plant is 10oC to 35oC. The adaption of plant to low and high temperature are as follows.

Low Temperature

At low temperature the nature of plasma membrane is changed and produce crystalline structure due to which transport of solute is slow.

To control this condition plant cell produce unsaturated.

At freezing point ice crystal are formed in the cell. But the plant of cold region change the composition of solute of cell so ice crystal are not formed in cytoplasm they form in cell wall. This condition is known as freezing tolerance.

High Temperature

High temperature has more harmful than low temperature for plant.

Due to high temperature all enzyme are denature and metabolic process stop. So plant increase rate of transpiration and cool the body.

At above 40oC plant produce heat shock protein. They protect the enzyme from destroying.

In some plant shiny cuticle is present which protest them from high temperature.

In some plant leaves are reduce in size.

Support and Movement

Irritability

The ability of an living organism to produce response against any stimula are called Irritability it is also called Sensitivity.

Movement

Living organism shown the responses towards stimuli are called Movement.

Support in Plant

Plants require proper strength and support it is necessary to maintain their shape, increase in size and keep them straight and strong. The support maintains balance. In plant body support is provided by two ways.

Turgidity in soft parts of plants

Mechanical tissues

Support Through Turgor Pressure

The living cell of epidemics, cortex and pith take in water by osmosis. Thus an Internal hydrostatic pressure called "Turgor Pressure", which keeps them rigid and resistant to bending. If they loose turgidity stem wilts. The turgor pressure is extremely important to maintain the turgidity in plants.

Support Through Supporting Tissue

In plants there are certain tissue called Mechanical tissues. These tissue provide strength to the plant body.

1. Parenchyma

2. Collenchyma

3. Sclerenchyma

1. Parenchyma

Structure

Parenchyma is a simple tissue. It is composed of thin walled spherical, oval or elongated cells.

They are with or without Intercellular spaces.

They are living cell.

Location

They are found in cortex, pith and epidemics, mesophyll region of leaves.

Functions Their function is synthesis of food and storage of food. They may serve as a supporting tissue in soft plant due to internal turgor pressure.

2. Collenchyma

Structure

Collencym is a simple permanent tissue. It is composed of rounded, oval or polygonal cells.

They are living cells with protoplasm.

Intra cellular spaces are absent and these cells thickened at the corners due to deposition of cellulose and protopectin.

Location

These tissues are found in the dicot stem below the epidermis.

Functions Collenchyma cell provide support to young herbaceous part of the plant. It elongate with the grow stem and leaves.

3. Sclerenchyma

Structure

Sclerenchyma is a simple permanent tissue. It is composed of long, narrow thick walled cell.

They have no intracellular spaces.

They are dead cell without protoplasm.

A thick materials is deposit along the wall of cell called pectin and lignin.

Location Sclerenchyma tissues are found in xylem which are vascular tissue.

Functions They provide strength and Mechanical support to the plant parts.

Types of Sclerenchyma

There are two type of sclerenchyma

1. Fibers 2. Sclerides 1. Fibers

The sclerenchyma elongated cell with tapered ends. They are tough and strong but flexible Fibers.

2. Sclerides

The variable often irregular in shape sclerenchyma are called sclereids. Simple unbranched sclerids are generally called stone cell.

Secondary Growth

An increase in plant girth due to the activity of cambium ring is called secondary growth.

Secondary TissueTissues which are formed by the activity of cambium ring are called secondary tissue.

Significance of Secondary Tissue

Cambium Ring

The ring of activity dividing cells responsible for lateral growth in plant are called cambium ring.

Secondary growth occurs due to cell division in cambium ring. There are two type

i. Vascular Cambium Ring

The cambium present between xylem and phloem is called Vascular Cambium Ring. The cell within the vascular bundles are called fusiform initials.

Vascular cambium gives rise to two new tissues.

Secondary Xylem (Toward the inside)

Secondary Phloem (Toward the outside)

Growth Rings The secondary Xylem causes most of the increase in stem thickness. Over the year a woody stem get thicker and thicker as it vascular cambium produce layer upon payer of secondary Xylem. These layers are visible as rings.

Sap Wood and Heart Wood

The outer region of secondary wood is of lighter color and take part in the conduction of water from root to leaf are called Sap Wood.

The inner region of secondary wood is dark brown in color and do not take part in the conduction of water are called Heart Wood.

In most plant heart wood accumulate a variety of chemical such as resins, oil, gum and tannins. Which provide a resistant to decay and insect attack.

ii. Cork Cambium Ring

The cambium ring present in cortex region and increase the diameter of stem are called cork cambium ring.

Cork cambium cell divide and form new cells on both side.

Cork / Phellem ------> Outerside

Secondary Cortex ------> Inner Side

Cork / Phellum

Cork is formed on the outer side by the cork cambium. Which is an insulating layer prevent transpiration. Cork cell are dead and thick wall.

Secondary Cortex

It is formed on the inner side by cork cambium. It is consist of few layers of parenchymatous cells. They contain chloroplast.

Bark

Epidemics, lenticels and cork collectively called bark which is the outer part of stem.

Callus

Another important function of the cambium is to form callus or wood tissue on over the wound. The tissue are rapidly formed below the damage surface of stem and root.

Movement in Plant

Definition

Any action taken by living organs to reduce its irritability produce by stimuli are called Movement.

Type of Movement

There are two type of movement in plant.

1. Autonomic Movement 2. Paratonic Movement

1. Autonomic Movement

Movement which occurs due to internal stimuli factor inherent inside the plant body itself are called Autonomic or spontaneous movement.

Types of Autonomic Movement

There are three type of autonomic movement.

i. Locomotory Movement

ii. Growth Curvature Movement

iii. Turgor Movement i. Locomotory Movement

Movement of whole plant body or an organ or material within plant cell from one place to another due to internal stimuli is called movement of locomotion.

Example

The streaming movement of cytoplasm (Cyclosis).

Movement of chromosome during cell division.

ii. Growth Curvature Movement

Change in the form and shape of plants or plant organs due to the differences in the ratio of growth of different parts are called growth and curvature movement.

Types of Growth Curvature

There are two type of growth movement.

Nutation

Nastic

Nutation

The growth tip of young stem moves in zigzag manner due to alternate changes in growth on opposite side of the apex. This type of growth is called nutation.

Example

Movement of climber around any rope as found in railway crupper.

Nastic

When the process of growth occurs in different manner in the parts of a plant and slow in other part it is called Nastic Movement.

There are two type of Nastic movement

Epinastic

Hyponastic

Epinastic

When faster growth occurs on the upper side of the organ is known as epinastic.

Hyponastic

When faster growth occurs on the lower side of the organ is known as hyponastic.

iii. Turgo Movement

Movement occur due to change in the turgidity and size of cells as a result of loose or gain of water called Turgo Movement.

Example

Movement of leaves of touch me not.

2. Paratonic Movement

The movement occurs due to external stimuli are called paratonic or Induce Movement.

Type of Paratonic Movement

There are two type of paratonic movement.

i. Nastic Movement

ii. Tropic Movement

i. Nastic Movement

The non directional movement of parts of plant in response to external stimuli are called Nastic Movement.

Usually this movement occur in leaves or petals of flower.

Type of Nastic Movement

There are two of nastic

i. Photonastic

ii. Haptonastic

i. Photonastic

The nastic movement occurs due to light are called photonastic.

Example

The flower open and close due to light intensity.

ii. Haptonastic

The nastic movement occurs due to the touch of any living organism are called Haptonastic.

ii. Tropic Movement

Tropic ------> Tropos mean "to turn"

The movement in response of growth of whole organ toward and away from stimuli are called

tropic movement. It is also known as directional movement.

Type of Nastic Movement

The main type of tropic movement are as follow

Phototropism

Geotropism

Chemotropism

Hydrotropism

Thigmotropism

Phototropism

Photo ------> Light Tropos ------> turn

The movement of part of plant in response to stimulus of light are called phototropism.

Example

Positive phototropism in stem

Negative phototropism in root

Geotropism

Geo ------> earth Tropos ------ turn

The movement of part of plant in response to force of gravity are called Geotropism.

Example

Root display positive Geotropism and shoots negative geotropism.

Chemotropism

Chemo ------> Chemical Tropos ------> turn

The movement in response to some chemicals is called Chemotropism.

Example

The hyphase of fungi show chemotropism.

Hydrotropism

Hydro ------> Water Tropism ------> turn

The movement of plant parts in response to stimulus of water is called hydrotropism.

Example

The growth of root toward water is due to positive hydrotropism and shoots negative hydrotropism.

Thigmotropism

Thigmos ------> touch Tropos ------> turn

The movement of plant parts in response to stimulus of touch are called Thigmotropism.

Example

The movement in climber

Definition

Certain chemical produced by plants have profound effect on their subsequent growth and development. Such chemicals are called Plant Hormones or Phytohormone.

Phytohormone are synthesized by plants in minute concentration and exert their effect by activating gene expression or inhibiting enzyme or changing properties of membrane.

Types of Phytohormone

There are five kind of plant hormones

1. Auxins

2. Gibberellins

3. Cytokinins

4. Abscisic Acid

5. Ethene

1. Auxins

Discovery

the first auxin was discovered by Fret Went in 1926.

Chemical Nature

Indol Acetic Acid (I.A.A)

Indol Acetic Acid (I.B.A)

Nephthalene Acetic Acid (N.A.A)

Site of Synthesis

It is synthesize at the apices of stem and foot, young leaves and young embryo.

Role of Auxin

i. Cell division and cell enlargement

It stimulate teh cell division and cell enlargement and plant in increase the length of plant.

ii. Initiation of Root

Auxins also initiates development of adventitious roots when applied at the cut base of stem.

iii. Abscission

In mature leaves and fruits when auxin production diminishes, a layer of thin walled cells is formed at the base of petiole and stake of fruit. This layer is called Abscission layer and causes fall of leaves and fruit with slight jerk.

iv. Growth of Fruit

Auxins produced in young embryo promotes the growth of fruit.

v. Parthenocarpy

Use of auxin helps in producing parthenocarpic or seedless fruits.

vi. Apical Dominance

Besides growth promoting function on Auxin, also has inhibitory effect on growth. Growth of apical bud inhibits growth of lateral buds beneath the stem. This phenomenon is termed as apical dominance removal of apical buds initiates growth of lateral buds with more leaves and axillary bud.

vii. Weedicide

Auxins are selective weed killer 2-4 dichlorophenoxy acetic acid (-2-4-D) is used to kill weeds in lawn's and cereal crops.

2. Gibberellins

Discovery

Gibberellins was discovered by T.Yabuta and I.Hayashu in a fungus called Gibberellins funjikuroi. This fungus causes foolish seedling (Bakanae) disease in rice. In this disease the

infected rice seedling elongated and ultimately fallover without producing grains.

Chemical Nature

The chemical nature of Gibberellins is Gibberellins acid 70 types of gibberellins have been discovered.

Role of Gibberellins

i. Cell division and cell enlargement

Like auxins Gibberellin also promotes cell division and elongation.

ii. Control of Dwarfism

Gibberellins can control genetic and physiological dwartism plants.

iii. Seed Germination

They promote the synthesis of a-amylase enzyme is dorman seeds due to the production of this enzyme, the seed starts germination.

iv. Parthenocarpy

These hormones help in the formation of seedless fruit which are called Parthenocarpic fruits.

v. Increase of Crop Yield

The crop yield of sugar can can be increased by the application of gibberellin about 50 tons/ acre.

vi. Formation of Flower and Growth of Pollen Tube

They stimulate flowering and the growth of pollen tubes during fertilization

3. Cytokinins

Discovery

Cytokinins are discovered by Miller in coconut milk.

Chemical Nature

Chemically there are two types of cytokinins.

Kinetin It is found in coconut milk etc.

Zeatin It is found in maize.

Role of Cytokinins

i. Cell Division

They initiate rapid cell division only in the presence of auxin.

ii. Delay in Senescence

They also caused delayed senescence (old age).

iii. Breaking of Seed Dormancy

They break seed dormancy and promote fruit development some species.

4. Abscisic Acid (A.B.A)

In contrast to growth promoting hormones, abscisic acid is growth inhibitor, produced by plants during adverse environment conditions such as drought conditions.

Role of Abscisic Acid

It increases dormancy in buds and seeds.

It causes stomata to close.

It turn leaf primordia into scale.

5. Ethene

It is a gas which also acts as a growth inhibitor.

Role of Ethene

It triggers ripening of fruits.

It contributes in leaf abscission and also breaks the dormancy of seeds and buds.

It also initiates flowering in plants e.g. pineapple.

Responses to Environmental Stress

Changes in environmental conditions are the big threats for living organisms especially for plants. These factors which change the normal condition of light, CO2, nutrients, temperature etc. causes severe stresses on plants. The common environmental stresses for plants are

1. Water Shortage (Drought condition)

2. Less Oxygen Supply

3. High Concentration of Salt in the Soil

4. High Temperature

5. Low / Cold Temperature

6. Herbivory / Over Grazzing

1. Water Shortage

In dry condition, the guard cells of leaf become flaccid to close the stomata.

In this way the transpiration is stopped.

The dry condition also stimulates increased synthesis and release of abscisic acid.

This hormone help in keeping stomata close.

These plants produce deeper root system.

2. Oxygen Deficiency

Those plants which grow in wet habitat or marshes, they develop aerial roots to absorb oxygen.

Some plants developed air tubes that provide oxygen to submerged roots.

3. Salt Stress

The plants especially halophytes, have salt glands in their leaves where desalination occurs.

4. Heat Stress

In plants there are two methods to tolerate the heat stress.

Transpiration has a cooling effect on the plant body. By this method the effects of heat are reduced.

Above 40oC plants cell start synthesizing relatively large quantities of special protein called heat shock proteins.

5. Cold Stress

Plants respond to cold stress by altering the lipid composition, changes in solute composition is altered also by producing different polymers of pentose (Fructose) which allow the crystals to super cool without compound formation.

6. Herbivory / Over Grazzing

Plants overcome excessive herbivory by developing horns and production of distasteful or toxic compounds.

Defence Against Pathogens

Diseases of plants may arise from infections by viruses, bacteria or fungi and other pathogens in most cases. Against these diseases the plants produce immune system in their body.

First Line Efence

The outer layer epidermis is a protective covering around the body of plant. This is the First Line Defence.

Second Line Defence

When pathogens enter the body through stomata or any other way, then plants produce certain chemicals to kill them. This is called Second Line Defence.

Phytoalexins

In infected plants an antibiotic phytoalexins is produced which is effective to all micro-organisms.

Reproduction

The process through which organisms produce young ones of their own kind to maintain their species are called as Reproduction.

Types of Reproduction

There are two types of reproduction.

1. Asexual Reproduction

2. Sexual Reproduction

1. Asexual Reproduction

The type of reproduction in which fusion of gamets does not take place and requires only a single parental organism and the offspring produced are exact copies of their parents. This type of reproduction is called Asexual Reproduction.

Asexual Reproduction of Plants

There are two methods of asexual reproduction in plants.

1. Natural Method of Asexual Reproduction

2. Artificial Method of Asexual Reproduction

1. Natural Method of Asexual Reproduction

In nature, plants reproduce asexually by following methods.

i. By Spores or Sporulation

ii. Vegetative Propagation

iii. Apomixis

i. By Spores or Sporulation

During alternation of generation plant produce haploid cell by meiosis called Spores. Each spore can develop into new organism without fertilization. The process of formation of unicellular spores is called Sporulation.

Example

Sporulation occurs in bacteria, protozoans, algae, fungi, mosses and fern as well as plants.

ii. Vegetative Propagation

The process which involves the separation of the part of the parent plant which then develop into new plant is called as Vegetative Propagation.

OR

When a new plant develops from tissue, organs of a plant or outgrowth of a plant. This type of reproduction is called Vegetative Propagation.

Process

In this process a plants part is separated which develops into new plant such as stem, leaves roots or buds may take part in the formation of new plant.

Methods of Vegetative Propagation

There are various method of propagation of plant by vegetative reproduction for improving crops, orchads and ornamental plants are as follows

i. By Cutting

ii. By Grafting

i. By Cutting

In this method stem or branch is cut from the plant. At the cut end of the shoot a mass of dividing undifferentiated cells called a callus forms and then adventitous roots develop form the callus. If the shoot fragment includes a node, then adventitous root forms without callus stage.

Example

Sugar cane, sweet potato and rose can be propagated by cutting. In raspberry and black berries root cutting are also used for artificial vegetative propagation.

ii. By Grafting

This is a technique whereby a branch from a desired variety of plant is joined to another plant with well established root system. The plant from which the branch is taken is called Scion and the plant to which it is joined is called Stock. The two plants involved are normally the different varieties of same species.

Example

Orange, lime and mango can be propagated by grafting.

iii. Apomixis

The modified form of asexual reproduction in which seeds are formed without fertilization is called Apomixis.

Mechanism

In apomixis, a diploid cell in the ovule gives rise to the embryo without any fertilization and the ovules mature into the seeds.

Example

In Dandelions and other plants seed formation take place without fertilization.

2. Artificial Method of Asexual Reproduction

In plant vegetative reproduction is performed by artificial method, which are as follows

i. Tissue Culture or Test Tube Cloning

ii. Protoplast Fusion Technique

i. Tissue Culture or Test Tube Cloning

Tissue culture or cloning is a special technique which is used to produce varieties of plants. By this technique, a group of genetically identical offspring produced by asexual method called Clones.

Procedure

In this method, pieces of tissues are cut from the parent plant or

from a single parenchymatous cell in a medium containing all the

nutrients and hormones.

The culture cells divide and form an undifferentiated Callus.

The callus then produces root and shoot with fully differentiated

cells.

The test tube plant can be transferred to soil where they continue

their growth.

Application

In plants tissue culture is also used in genetic engineering. To introduce new genes in plant body pieces of tissue or cells are used. By this technique, we produced a new variety of plant by introducing new DNA molecule.

Example

By cloning many thousand plants are produced from one plant. This method is used in Orchards and pinus trees to obtain wood.

Advantages of Tissue Culture

The main advantages of tissue culture are as follows

i. Development of Strong Plant: By this technique plants of Agriculture and horticulture are produced. These plants are strong than other plants produced by seeds.

ii. Development of Similar Plant: By this technique plants of similar character are developed.

iii. Development of Defence System in Plant: These plants have developed defence mechanism against any disease.

iv. Production of Useful Chemicals: By this technique, many useful chemicals are obtained such as shikonin (a dye used in silk and in the treatment of injuries caused by burning.

Disadvantages of Tissue Culture

There are also some disadvantages of tissue culture where are as follows

i. Production of Sterile Plant: The plant produced by this technique may be genetically sterile, do not reproduce by sexual method.

ii. Variation in Chromosome: This technique may cause change in the structure and number of chromosome.

ii. Protoplast Fusion Technique

Another technique known as protoplast fusion technique is developed to produce new varieties of plants.

Procedure

In this technique, outer cell wall is removed around the protoplast. After protoplast of one or more cells are fused together, then their protoplast are for culture. These protoplast produce a wall around them, then they are change into new plant. Protoplast of either same or different species may used for this technique.

Example

In potato and wild night shade plant this technique is used.

2. Sexual Reproduction

The type of reproduction in which fusion of gametes (sperm and ova) take place and two parents (male and female) are involved is termed as Sexual Reproduction.

Sexual Reproduction in Plant

In plants sexual reproduction takes place by three methods.

i. Isogamy

ii. Oogamy

iii. Heterogamy

i. Isogamy

The simplest type of sexual reproduction in which two morphologically similar gametes take part in fertilization to produced zygospore which then develop into new plant is called Isogamy.

It is also known as conjugation which means marriages of equals.

Example

This process occurs in algae and lower plants.

ii. Oogamy

The type of sexual reproduction in which a flagellated motile sperm fertilizes with non motile egg to produced a diploid zygote which then develop into new individual is called Oogamy.

Example

Some species of algae undergoes Oogamy.

iii. Heterogamy

The type of sexual reproduction in which two different structure gamets fused i.e. non flagellated large size female gamete fuses with small size flagellated male gamete to produced zygote which then develop into new plant is called Heterogamy.

It is also known as anisogamy.

Example

In higher plants such as bryophyte, heterogamy is present.

Germination

The process in which dormant or sleeping embryo awakes up renews its life and develops into a seeding is called as Germination.

OR

The breaking of dormancy of seed to produce seedling is called Germination.

Kinds of Germination

Seed can germinate into three ways i.e.

1. Epigeal Germination

2. Hypogeal Germination

3. Viviparous Germination

1. Epigeal Germination

Epi => above, geo => earth

The kind of germination in which cotyledons came above the soil due to rapid growth of hypocotyl is called Epigeal Germination.

Example

Caster oil seed, tomato, cotton etc.

2. Hypogeal Germination

Hypo => below, geo => earth

The kind of germination in which cotyledons remain under the soil due to rapid growth of epicotyl is called Hypogeal Germination.

Example

Maize-grain, Pea-gram etc.

3. Viviparous Germination

The special of germination in which seed germinates within fruit is called Viviparous Germination.

Process

The fruit is still attached to parent plant. Redicle comes out of the fruit which becomes swollen and heavy due to increasing weight the seedling gets detached and falls vertically into the soft mud gets embeded and starts growing.

Example

Rhizophora, coconut, date palm etc.

Seed

Seed may be defined as

A ripened ovule or a part of a plant body in which embryo lives in dormant condition is called Seed.

Structure of Seed

Structure of seed can be divided into two parts

1. External Structure

2. Internal Structure

1. External Structure

Externally seed consists of following parts

Seed Coat

The seed is covered from outside by a coat called Seed Coat.

The seed coat is formed by integuments. It is made up of two layers.

Testa

The outer thicker layer is called Testa.

Tegmen

The inner thin layer is called Tegmen.

Chromosomes as Carrier of Genes

Genes are small bodies found in the chromosome.

Chromosome are considered as the carrier of genes.

The chromosomes can be separately identified visually but the

genes are very small units. And so far have not been seen even

with the best microscope.

The chromosome and gene behave as hereditary units but the

genes can not be considered outside the chromosome.

At the time of meiosis, the separation of homologous

chromosomes takes place which result in the segregation of gene

pairs.

In the genotype of every individual one member of each pair of

genes is contributed by one parent and the other by the other

parent.

Chromosomal Theory of Heredity

Introduction

The chromosomal theory of inheritance was first formulated by the American Biologist "Walter Sutton" in 1902.

Postulates

The main postulates of this theory are as under

1. Hereditary Materials

Reproduction involves the initial union of only two cells, egg and sperm. If Mendel's model is correct then these two gametes must make equal hereditary contributions. Sperm, however contain little cytoplasm, therefore the hereditary material must reside within the nuclei of the gametes.

2. Segregation of Chromosomes

Chromosomes segregated during meiosis in a manner similar to that exhibited by the elements of Mendel's model.

3. Number of Chromosome

Gametes have one copy of each pair of homologous chromosomes, diploid individuals have two copies.

4. Independent Assortment

During meiosis each pair of homologous chromosomes orients on the metaphase plate independent of any other pair.

Objection

The objection on chromosomal theory of hereditary is that when there is independent assortment of chromosomes in meiosis, the number of factors (genes) is more than the number of chromosomes. This is considered as a fatal objection about Sutton's theory.

Evidence

The material which transmits the parental characters into the coming generation is called Hereditary Material.

Fredrick Griffith's Experiment

Introduction

Fred Griffith in 1928 provided the evidence of hereditary material in bacteria.

Experimental Material

He was working on strains of steptococcus pneumoniae, which occurs in two distinct different forms.

R-Type

Rough surfaced, non-capsulated bacteria, without the capability of producing pneumonia.

i.e. non-virulent

S-Type

Smooth surfaced, capsulated bacteria, with the capability of producing pneumonia i.e. virulent.

Steps of Experiment

He observed that when the injected R-type bacteria in the mice,

there was no ill effect.

When he injected the S-type, they proved to be fatal.

He also observed, when he injected both the bacteria separately

after killing them by heating under high temperature, the mice did

not develop the disease.

He also observed that, when the injected the living R-type with

heat-killed S-type, there was a high morality among the mice.

Conclusion

Fred Griffith concluded that the R-type bacteria gained genetic property of S-type inactive bacteria when they kept together, so R-type bacteria converted into virulent S-type by the activity of DNA. Hence by this experiment, it can be proved that DNA is a genetic material.

A Very, Macleod and McCarty's Experiment

Introduction

In 1944, after a decade of research, Oswald Avery, Maclyn McCarty and Colin Macleod discovered that the transforming agent had to be DNA.

Experiment

They performed various experiments and found out that the only substance, which carried the transforming capability, was DNA because if the enzyme deoxyriba-nuclease was added to the bacteria, the transforming capability was lot.

Hershey and Chase's Experiment

Introduction

In 1952, Hershey and chase performed experiment to proof that DNA is a hereditary material.

Experience at Material

Hershey and chase labeled protein coat and DNA of Bacteriophage separately. Protein coat labeled with radioactive sulphur and DNA with radioactive phosphorus. These two viruses use to attack bacterial cells.

Steps Experiment

Hershey and chase observed that if cultures of bacteriophage are

labeled with radioactive phosphorus [P32 labeling DNA] or with

sulphur [S35 for labeling protein coat].

bacteriophage is ruptured, the DNA is released and treated with

deoxyribsonucleas, the DNA breaks up into fragments in the

solution.

The empty protein coats of the ruptured membrane appear as

coats all the P32 or S35 were made to inject bacteria and multiply

by the help of special technique, all the S35 labeled protein were

removed.

The new phage formed contained only P32 indicating the

presence of DNA molecule.

Conclusion

The conclusion appears similar to the transforming principle in bacteria, showing that DNA is the genetic material in phage, transmitted from one generation to the next.

Watson and Crick's Model of DNA

Introduction

James Watson and Francis crick, in 1953 proposed structure of the DNA molecule.

Structure of DNA

Watson and Crick suggested a ladder like organization of DNA.

1. Double Helix

Each molecule of DNA is made up of two polynucleotide chains which twisted around each other and form a double helix.

2. Backbone of DNA

The uprights of the ladder are made up of sugar and phosphate parts of nucleotide and the rungs are made up of a paired nitrogenous bases.

3. Pairing of Bases

The pairs are always as follows

Adenine always pairs with thymine and cytosine with Guanine.

The two polynucleotide chains are complimentary to each other

and held together by hydrogen bonds.

Hydrogen Bonding

There are two hydrogen bonds between Adenine and Thymine (A=T) and three between Cytosine and Guanine (C≡G).

Distance

Both polynucleotide strands remain separated by 20 Aº distance.

The coiling of double helix is right handed and complete turn

occurs after 34 Aº. In each turn 10 nucleotide pairs are present,

therefore the distance between two pairs is about 3.4 Aº.

Genes - The Unit of Hereditary Information

Introduction

Archibald Garrod discovered in 1902, that certain diseases were more prevalent among some families and were inherited as a recessive Mendelian trait.

Alkaptonuria

Alkaptonuria is a disease in which the urine contained a substance called "Alkapton" now known as "Homogentisic acid" which was immediately oxidizes to black when exposed to the air.

Causes

He suggested that this disease occurred due to absence of an

enzyme, which could break the "Alkapton" down to other

products so it would not build up in the urine.

He proposed that the condition was "An inborn error of

metabolism" which is occurring due to changes in the hereditary

information, which must have occurred in one of the ancestors of

the affected families.

Conclusion

He concluded that the inherited disorders might reflect enzyme deficiencies.

Genome

Definition

The total genomic constitution of an individual is known as Genome.

Example

In a bacterial cell, a single circular chromosome along with plasmid is genome of bacteria, while in a human being all twenty two pairs of autosome along with a pair of sex-chromosomes constitute genome.

Replication of DNA

Definition

The mechanism in which DNA prepares its copies is called DNA replication.

OR

When the formation of new DNA molecule takes place in the cells without any change, it is known as Replication of DNA.

Semi Conservative Replication

Definition

The type of replication in which new daughter double helical duplex contain one stand old and another newly synthesized is called Semi Conservative Replication.

The Meselson Stahl Experiment

Introduction

Mathew meselson and Frank Stahl performed experiments to test the semi-conservative method of DNA replication.

Experiment

They grew bacteria in a medium containing Nitrogen-15 (N15), a

heavy isotope of the nitrogen.

The DNA after several generations became denser than normal

because the entire bacterial DNA now contained Nitrogen-15

(N15).

They then transferred the bacteria into a new medium containing

lighter isotope Nitrogen 14 (N14) and analyzed the cultures for

changes in the DNA.

At first DNA, which the bacteria synthesized, was all heavy.

After one round the density of the DNA fell exactly to the value

one half between the all heavy isotope DNA and all light isotope

DNA.

Result

This showed that after one round of replication, each of the daughter DNA duplex contained one strand of heavy isotope, after two rounds half contained none of the heavy isotope strand to form light duplex and half contained one of the heavy strand isotope.

It was now confirmed that the semi conservative method of the replication of DNA replication was true.

One Gene One Enzyme Hypothesis

Introduction

George Beadle and Coworker Edward L. Tatum proved that the information coded within the DNA of a chromosome, is used to specify particular enzymes.

Method of Study

Beadle and Tatum created Mandelian mutation in the

chromosomes of the fungus called Neurospora by the use of the x-

rays.

They studied the effect of the mutations caused by them and

suggested "One Gene One Enzyme Hypothesis".

Choice of Material

They choose the bread mold, neurospora crassa as an

experimental organism. It had a short life cycle and was easily

grown on a defined medium, containing known substances, such

as glucose and NaCl.

The nutrition of Neurospora could be studied by its ability to

metabolize sugars and other chemicals the scientist could add or

delete from the mixture of the medium.

Production of Mutations

They induced mutations in Neurospora spores by using x-rays.

The mutated spores were placed on complete growth media

enriched with all necessary metabolites, so keeping the strains

alive because the strains were deficient in producing certain

compounds necessary for fungus growth due to damaged DNA by

earlier irradiation, hence called Mutants.

Identification of Mutant Strains

To test the mutations, they grew the mutated strains on the animal

media containing sugar, ammonia, salt, a few vitamins and water.

A strain that had lost the ability to make a necessary metabolite,

failed to grow on such media.

Using this approach, they succeeded in identifying and isolating

the different mutants.

Identification of Specific Mutations

To determine the specific nature of each mutation, they added

various chemicals to minimize media, to make the strains grow.

Using this technique, they were able to pinpoint the biochemical

problem and thus the genetic deficiency of the mutants.

Many of the mutants were unable to synthesize a single amino

acid or a specific vitamin.

If a spore lacked the ability to synthesize a particular amino acid,

such as Arginine, it only grew if the Arginine was added in the

growth medium. Such mutants were called as arg mutants.

Chromosome mapping studies on the organism facilitated their

work and they mapped three areas clusters of mutant Arginine

genes.

For each enzyme in the arginine biosynthetic pathway, they were

able to isolate a mutant strain with a defective form of that

enzyme and mutation always proved to be located at one of a few

specific chromosomal sites, different for each enzyme.

Conclusion

They concluded that genes produced effects by specifying the structure of enzymes and that each gene encodes the structure of a single enzyme. This was called "One Gene One Enzyme Hypothesis".

RNA

Definition

The single stranded helical polynucleotide contain ribose sugar and uracil instead of thymine is called RNA.

Location

RNA is formed in the nucleus (in nucleolus 10%) as well as in the cytoplasm (90%).

Types of RNA

There are three types of RNA.

1. Ribosomal RNA (rRNA)

The class of RNA found in ribosome is called ribosomal RNA.

Function

During polypeptide synthesis it provides the site on the ribosome where the polypeptide is assembled.

2. Transfer RNA (tRNA)

A second class of RNA is called transfer RNA is much smaller. Human cell contains more than 40 different kinds of tRNA molecules.

Functions

During polypeptide synthesis tRNA molecules transport the amino acid into the ribosome for the synthesis of polypeptide chain.

3. Messenger RNA (mRNA)

It is long strand of RNA that passes from the nucleus to the Cytoplasm.

Function

During polypeptide synthesis, mRNA molecules brings information from the chromosome to the ribosomes to direct the assembly of amino acids into a polypeptide.

Gene Expression

Definition

All functions in the body of an organism are controlled by genes. A function expressed or performed by a gene is called Gene Expression.

Process of Gene Expression

The process of gene expression occurs in two phases.

1. Transcription

2. Translation

1. Transcription

Definition

The process in which an RNA copy of DNA sequence encoding the gene is produced with the help of an enzyme, RNA polymerase is called Transcription.

Step of Transcription

Transcription is initiated when a special enzyme called RNA

polymerase binds to a particular sequence of nucleotide on one of

the RNA strands. This strand is known as Template Strands or

Antisense Strands while the other strand is called Coding or Sense

Strand.

RNA polymerase proceeds to assemble a single strand of RNA

with a nucleotide sequence complementary to that of the DNA

pairing Adenine to Uracil and Guanine Cytosine and vice versa.

Only one strand of DNA is transcribed and when the RNA

polymerase reach specific stop sequence at the far end of the

gene, it disengages itself from the DNA release the newly

assembled RNA chain.

This RNA chain is called the primary RNA transcript copy of the

DNA nucleotide sequence of the gene or simply mRNA.

Translation

'The process of formation of the polypeptide chains using the messenger RNA is called Translation.

Step of Translation

1. Binding of mRNA

The process of translation begins with the binding of one end of the mRNA with a rRNA on a ribosome.

2. tRNA Binds Amino Acids

A tRNA molecule possessing the complementary three nucleotide sequence or anticodon, binds to the exposed codon on the mRNA, because this tRNA molecule bind with a particular amino acid and put amino with a particular amino acid and put amino acid and put amino acids at correct place on the elongated polypeptide chain.

3. Reading or Decoding of mRNA

The ribosome then starts to move along the mRNA molecules in increment of three nucleotide, adding a specific amino acid at each step through tRNA.

4. Polypeptide Chain Synthesis

It continues until it reaches the stop sequence, after which it stops the process. It then disengages itself from the mRNA and releases the newly assembled polypeptide.

Genetic Code

Definition

The sequence of nitrogenous bases that specify the amino acids and the positions of the starting and stopping of chain of the translation is called Genetic Code.

Type of Genetic Codes

The nitrogen base and amino acids from different codes by their combined functions. The types of codes are as follows.

1. Single Code System

2. Double Code System

3. Triple Code System

1. Single Code System

When one nitrogen base works for one amino acid, then only four types of genetic codes are formed. There are 20 basic amino acid not synthesized by only four codes.

2. Double Code System

When two nitrogen bases work for one amino acid, it is called double code system. In this system 16 possible codes may be formed.

3. Triple Code System

There must be at least three base sequence to code for 20 amino

acids.

Sine the total no of possibilities of variations is 64 (4 x 4 x 4 =

64). They can code for all the amino acids and also code for the

start and stop sequences.

They above hypothesis was found to be correct by Francis Crick

and coworkers in 1961.

Other scientists took one step forward and found the specific

codes for the specific amino acids by adding artificial messenger

RNA to the bacteria and getting the particular amino acids e.g.

RNA composed entirely of Uraeil (UUU......) directed the mixture

of synthesize a protein composed solely of phenylalanine.

Therefore the triplet UUU specify phenylalanine amino acids.

These mRNA triplets are called Codons.

The research showed that codon AUG codes for start and three

codons UAG codes for start and three codons, UAG. UAA and

UGA code for the stop signal.

It was further found out that the amino acids may specifically

coded by more than one but specific codons, so there were more

than one combinations possible for a single amino acids e.g. six

different codons, all codes for arginine amino acids.

Decoding

Definition

Messenger RNA (m-RNA) contains gentic code in three nitrogen bases and t-RNA contains anticodon triplet and it transfers amino acids to the ribosome, if anticodon triplet is attached the codon triplet of m-RNA. This process is called Decoding.

Mutation

Any change in the amount, structure and content of genetic material is called Mutations.

Mutations can appear in both sex chromosomes as well as in

autosomes.

Types of Mutations

There are two main types of mutations.

1. Chromosomal Mutation

2. Gene Mutation

1. Chromosomal Mutation

The change in amount arrangement and the nature of genetic material on a chromosome is called Chromosomal mutations. It is also called Chromosomal aberration.

This mutation is visible under the microscope.

Types of Chromosomal Aberration

There are following types of this mutation.

i. Deletion

ii. Duplication

iii. Inversion

iv. Translocation

i. Deletion

Definition

When a small portion of a chromosome is missing the situation is called Deletion.

Effects of Deletion

Pseudo-Dominance

Deletion may cause Pseudo dominance in heterozygous condition.

Lethal Effect

If deletion takes place in both homologous chromosomes then it has the lethal effect on the organism.

ii. Duplication

Definition

The repetition of a segment on a chromosome is called Duplication.

Effects of Duplication

Due to the duplication different physiological and morphological functions are disturbed.

iii. Inversion

Definition

When the arrangement of genes on a chromosome is changed then the mutation is called Inversion.

Effect of Inversion

Inversion reduced crossing over.

iv. Translocation

Definition

The transfer of a chromosomal segment to a non-homologous chromosomes is called Translocation.

Effect of Translocation

Translocation may give rise to varieties within species.

2. Gene Mutation

When small changes occur in the molecular structure of DNA, these are called Gene-Mutations.

This mutations can not be detected by the microscope.

These changes can produce drastic changes in the expression of

the genetic messages.

Types of Gene Mutations

There are following types

i. Point Mutation

ii. Transposition

i. Point Mutation

Definition

The change of the sequence of one or a few nucleotides is called Point Mutation.

ii. Transposition

Definition

Individual genes may move from one place to another place on their own chromosome which is called Transposition.

Effects

This chromosomal rearrangement often brings alternation in the expression of the genes or that of neighboring genes.

DNA Damage (Causes of Mutation)

There are three major important causes of DNA damage, they are

1. Ionizing Radiation

2. Ultra Violet Radiation

3. Chemical Mutagens

1. Ionizing Radiation

High energy radiations such as X-rays and Gamma rays are highly

mutagenic Nuclear radiation is also of this sort.

These radiations release unpaired electrons which are called free

radical.

These free radicals are highly reactive chemically, reacting

violently with the other molecules of the cell including DNA.

2. Ultra Violet Radiation

Ultra violet radiation is the component of sunlight.

When molecules absorb UV radiation little damage is produce in

these molecules.

Mostly certain organic ring compounds are affected by UV-

radiation.

3. Chemical Mutagens

The chemicals which are capable of damaging DNA are called Mutagens.

There are three main types of mutagens.

Chemicals resembling DNA nucleotides but pair incorrectly when

they are incorporated into DNA.

Chemicals that remove the amino group form Adenine or

cytosine, causing them to pair wrongly.

Chemicals that add hydrocarbon group to nucleotide bases also

causing them to pair wrongly.

Vernalization

Definition

Promotion o flowering by a cold treatment give to the imbeded seeds or young plant is called Vernalization.

OR

The phenomenon of cold treatment which shortens the vegetative period and hastens flowering is known as Vernalization.

Chourd (1960) defined vernalization as

The acceleration of the ability to flower by a chilling cold treatment.

Stimulation of Hormone

The process of vernalization does not induce flowering but prepares the plant for flowering. It stimulates the production of vernalin hormone which induce vernalization.