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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.