Reproduction

Reproduction
Definition
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.
Variation in Cold Treatment
The duration of cold temperature (chilling) treatment may vary in different plants i.e. wheat requires cold treatment at seed stage while some plant need cold treatment when they become at least 10 days old.
Advantages of Vernalization

• Out of season flowers can be produced by vernalization.
• It can used to increase the yield of crops.
• Vernalization is an important method to protect plant from drought conditions.

Photoperiodism
Definition
The length of daily period of light to which is exposed is called photoperiod and the response of plant to the photoperiod is called Photoperiodism.
OR
The influence of relative lengths of day and night on the activities of an organism is called Photoperiodism.
Types of Plants on the Basis of Photoperiodism
On the basis of their differing responses to light and dark, flowering plants can be divided into three groups.
1. Long Day Plant
2. Long Day Plant
3. Day Neutral Plant
1. Long Day Plant
Those plants which required long days and short nights are called long day plant.
Examples
Petunias, Spinach, Radishes, Lettuce etc.
2. Short Day Plant
Those plants which required short days and long nights are called short day plant.
Examples
Chysanthemums, Cocklebur, Poinsettias etc.
3. Day Neutral Plant
Those plants which are in different to day length are called day neutral plant.
Example
Tomato and Cotton etc.
Inflorescence
Definition
The arrangement of flowers on a branch in the floral region or a group of flowers on the main axis is known as Inflorescence.
Types of Inflorescence
There are various types of Inflorescence but two major types are
1. Racemose
2. Cymose
1. Racemose
The type of inflorescence in which main axis called Peduncle continues to grow and its growth is indefinite is called Racemose.
Main Characteristics

• Flowers are produced in acropetal succession.
• No flower grow on the tip of peduncle.
• The opening of flower is centripetal.

Kinds of Racemose Inflorescence
Racemose is classified into three kinds on the basis of length of peduncle which are as follows
i. Peduncle Elongated
ii. Peduncle Shortened
iii. Peduncle Flattened
i. Peduncle Elongated
In this type of racemose inflorescence, penduncle is elongated. It includes following four types
a. Raceme
b. Spike
c. Catkin
d. Spadix
a. Raceme

• Flowers and pedicellate
• Flowers and bisexual

Example
Goldmohr
b. Spike

• Flowers are sessile or non-pedicellate
• Flowers are bisexual

Example
Amaranthus
c. Catkin

• Flowers are sessile
• Flowers are unisexual

Example
Mulberry
d. Spadix

• Flowers are sessile
• Flowers are unisexual
• Flowers are covered over by one or many large bracts called Spathe

Example
Banana
ii. Peduncle Shortened
In this type of racemose inflorescence penduncle is shortened. This includes following two groups
a. Corymb
b. Umbel
a. Corymb

• Flowers are pedicellate
• Flowers have pedicels of unequal length, lower having large pedicels and upper ones having small pedicel.

Example
Iberis
b. Umbel

• Flowers are pedicellate
• Length of pedicel is almost equal and they arise from a common point.

Examples
Onion, Corriander
iii. Peduncle Flattened
In this type of racemose inflorescence penduncle is flattened. This include following two groups.
a. Head (Capitulum)
b. Spikelet
a. Head (Capitulum)

• Main axis form a disc
• Flowers are very small (florets) which are sessile
• The florets are commonly of two kinds
• Ray Florets
• Disc Florets

b. Spikelet

• It is a kind of racemose, inflorescence
• There are three bracts at its base called “glumes”
• The lower two without flowers are called “empty glumes”
• The third glume has flower in its axil called “Lemma”
• Opposite to lemma are small bracteole called plea flower

Example
Family Poaceae
2. Cymose
The type of inflorescence in which main axis called Peduncle, not continue to grow and its growth is stopped by terminal flower is called Cymose.
Main Characteristics

• Flowers are produced in basipetal succession
• Flower grow on the tip of penduncle
• The opening of flower is centrifugal

Kinds of Racemose Inflorescence
Cymose inflorescence is classified into two kinds
i. Uniparous Cyme
ii. Biparous Cyme
i. Uniparous Cyme

• The main axis soon ends in a flower
• Only one lateral branch arises from the main axis, ending in flower and so on the process continues

Types of Uniparous Cyme
There are two types of uniparous cyme
a. Scorpoid Cyme
b. Helicoid Cyme
a. Scorpoid Cyme
In this type of cymose inflorescence, branches are produced on the alternate sides.
Examples
Cotton, Forget-me-not etc
b. Helicoid Cyme
In which type of cymose inflorescence the branches arise on one side only.
Example
Sundew
ii. Biparous Cyme

• The main axis ends in terminal flower.
• At the same time, two lateral branches arise from it.
• These two lateral branches repeat the same procedure.

Examples
Pink Jasmine, Teak-Night Jasmine.
Sexual Reproduction in Flowering Plants
Flower
Flower is the reproductive part of plant, which is actually the modified form of shoot.
Explanation
Flower develops from compressed shoots with four whorls of modified leaves separated by very short internodes. These floral leaves are called sepals, petals, stamens and carpels.
Microsporophylls
The stamens are also called microsporophylls. Each microsphylls contains following three parts.
Megasporophylls
Megasporophylls are also called carpels. The carpel is flask shaped body having stigma (head), style (neck) and ovary (basal swollen part). Inside the ovary, ovules (mega sporangia) are found and each ovules has an embryo sac (megaspore) in which a female gamete is present.
Pollination
Definition
The transfer of pollen grains from another to the stigma of carpel is called pollination.
Types of Pollination
There are two types of pollination
1. Self Pollination
2. Cross Pollination
1. Self Pollination
The transfer of pollen grains from the another of a flower to the stigma of the same flower is called self pollination.
2. Cross Pollination
The transfer of pollen grains from the another of a flower the stigma of another flower is called cross pollination.
Pollen Tube
Definition
The tube like structure arised from the male gametophyte contain make gamete (Sperm) called pollen tube.
Role of Pollen Tube
1. Pollen tube acts as a “Vehical for Sperms”.
2. Pollen tube grow down the carpels and discharge sperm into embryo sacs resulting in the fertilization of eggs.
3. The evolution of pollen tubes parallels the evolution of seeds.
4. The obstacle has been overcome by the development of pollen tubes.
Development of Male Gametophyte

• Inside the microsporangium (pollen sac) a large number of cells called microscope mother cells are present.
• Each microspore mother cell forms four haploid microspores by meiosis.
• Each microspore divides into two cells by mitosis. One cell is called generative cell and the other is known be cell. The microspore is surrounded by a thick resistant – wall.
• In this condition the microspore is considered as immature male gametophyte.

Development of Female Gametophyte

• The female gametophyte or embryo sac developers inside the mega sporangium or nucellus of ovule.
• The megaspore mother cell (2n) form four haploid cells by meiosis, which are called linear tetrad.
• Megaspore develops into female gametophyte.
• The haploid nucleus of megaspore form eight nuclei by the mitotic divisions.
• Out of these eight nuclei, two are fused to form a diploid secondary nucleus.
• In this stage, the embryo sac contains seven nuclei three nuclei towards chalaza are called antipoda three nuclei towards the micropylar end are called egg apparatus.
• In the egg apparatus, two synergids and one egg cell are found.

Double Fertilization

• After the pollination, the pollen grain is transfered into the stigma where it germinates. \
• During the germination inner layer intine rupture the exine at any germ pore and come out in the form tube, which is called pollen tube.
• The pollen tube grown downward towards the ovule and finally it enters into ovule through microspore.
• The nuclei of tube cell and generative cells are shifted into the pollen tube.
• When the generative nucleus enters into the pollen tube, it divides to form two male gametes.
• When the pollen tube penetrates into the embryo sac its tip bursts and both male gametes enter embryo sac.
• First male gamete is fused with egg nucleus to form diploid oospore. This fusion is called syngam second male gamete is combined with secondary nucleus to form triploid (3n) endosperm nucleus.
• In this way fertilization take place twice in an embryo sac, therefore this process is called fertilization which was discovered by Nawaschin in 1989.

Changes in Ovule after Double Fertilization

• After double fertilization, the ovule is converted into a seed. In this process following changes take place.
• The oospore is change into an embryo, cotyledons, plumule and radicle.
• The endosperm nucleus forms a nutritive tissue, which provides nourishment to the developing embryo the tissue is called endosperm.
• The integuments form seed coats.
• Micropyle also persists in seeds.
• The seed is dehydrated until its water contents become 5 to 15% of its weight.

Phytochrome
Definition
In the body of plant, there are certain compounds to get sunlight called Phytochrome.
OR
Special light sensitive pigments present in plant called Phytochrome.
Composition
These phytochromes consists of protein and a pigments.
Discovery
Phytochromes are light receptor, these are discovered in 1960.
Location
These are found in whole plant in little amount but these are abundant at growth tips.
Types of Phytochrome
These are two types of phytochrome
1. Phytochrome 660
2. Phytochrome 730
1. Phytochrome 660
Those phytochrome which absorbs red light having 660nm wave length are called phytochrome 660.
2. Phytochrome 730
Those phytochrome which absorbs infra red light having 730nm wave length care called phytochrome 730.
Effects of Red Light and Far-Red Light
Red Light
1. In this light phytochrome 660 is changed into phytochrome 730.
2. It increase the process of seed germination. E.g. Lettuce.
3. It help in the formation of plant pigment anthocyanine.
4. It increase the size of leaf.
5. It inhibit elongation of internode.
6. It promotes flower production in long day plant and reduced in short day plant.
Far-Red Light
1. In this light phytochrome 730 is changed into phytochrome 660.
2. It inhibits the process of seed germination. E.g. Germination
3. It prevents the formation of anthocyanine.
4. It decreases the size of leaf.
5. It increase the size of internode.
6. It promotes flower production in short day plant and reduced in long day plant.
Vitro Fertilization Plant
When the process of fertilization is performed outside the body of plant artificially by the help of scientific equipments it is called vitro fertilization.
Procedure

• In this process, ovules are removed from the ovary.
• They are placed in a solution containing all essential nutrients.
• After fertilization the zygote develops into embryo.
• When embryo matures, its development remains continue because it is autotroph.
• A new embryo matures when all necessary substances are provided to it like water and oxygen and suitable temperature.

Importance

• Vitro fertilization is important for new crops.
• In this process of development there is wider range of genotype.
• By this process there is better development of the plants which contain extra-ordinary genotype.

Asexual Reproduction in Animal
Asexual reproduction occurs in many ways. The common type in animals are
1. Fission
2. Budding
3. Regeneration
4. Parthenogenesis
5. Fragmentation
6. Cloning
1. Fission
Definition
The simplest type of asexual reproduction in which parent body divides into two or more parts and each of which develop into a new individuals is called Fission.
Types of Fission
There are two types of fission
i. Binary Fission
ii. Multiple Fission
i. Binary Fission
The type of fission in which parent body divides into two individuals is called binary fission.
Example
It is commonly observed in unicellular organisms like protozoa.
ii. Multiple Fission
The type of fission in which parent body divides into more than two daughter organisms is called multiple fission.
Example
It occurs in unicellular organisms like amoeba and paramecium during unfavourable conditions.
2. Budding
Definition
The type of asexual reproduction in which one or two small outgrowth develops on the part of parent body called bud which after some growth many separates from the parent body and develops into new individual is called budding.

Example
Budding is common in sponges, hydra and corals.
3. Regeneration
Definition
The type of asexual reproduction which involves the reformation of lost parts of the body is called as Regeneration.

Example
It is common in unicellular as well as multicellular animals like star fish for example, a lizard can regenerate its tail if it is cut away from the body. Similarly, a star fish regenerates it lost arms.
4. Fragmentation
Definition

The type of asexual reproduction in which parent body splits off into many pieces and each grow into new complete individuals is called fragmentation.

Example
It is common in sponges.
5. Parthenogenesis
Definition
The type of asexual reproduction in which one parent means female produces egg without fertilization which develops into new individual is called parthenogenesis.
Example
This reproduction is neither strictly asexual nor sexual parthenogenesis common in some insects like honey-bees, ants and wasps.
Twins
Definition
The two children which develop and born together is called Twins.
Types of Twins
There are two types of Twins
1. Identical Twins
2. Fraternal Twins
1. Identical Twins

• Identical twins are exactly alike and of the some sex because both of them develop from just one zygote (monozygotic).
• One zygote divides mitotically into two separate blastomeres, each of which develops into a new individual.
• Sine both of those develop from one zygote they share the same genes and arc exactly identical in features.

2. Fraternal Twins

• In fraternal twins, the children are develops from two independent eggs.
• As each egg is fertilized by a separate sperm they are dizygotic.
• The genotype of each zygote is different hence they are not identical and are said to be the product of sexual reproduction.

Significance of Sexual Reproduction
Sexual reproduction has much significance which is as follows
1. Sexual reproduction is important to avoid genetic monotony, which is the result of asexual reproduction where generation after generation exactly identical progeny develops.
2. Sexual reproduction maintains the chromosome number in a species.
3. Through sexual reproduction variety of organisms are produced.
4. The diversity of characteristics increases the chances of survival of a species are far brighter in an unfavourable environment or during the out break of disease.
5. The genetic variation thus produced by sexual reproduction is the foundation of evolutionary changes.
Necessities of Sexual Reproduction
Sexual reproduction is a complicated process and it occurs in following steps
1. Gametogenesis
2. Mating
3. Fertilization
1. Gametogenesis
Definition
The process of formation of sex-cell (gametes) is called Gametogenesis.
Types of Gametogenesis
There are two types of gametogenesis
i. Spermetogenesis
ii. Oogenesis
i. Spermetogenesis
Definition
The process of gametogenesis which involves the formation of male gamete i.e. sperm is called spermatogenesis.
Process of Spermatogenesis
i. Male Gonad Testes
The spermatogenesis takes place in male gonad called Testes. Which contain spermatocytes producing mother called germ cells.
ii. Spermatogonia
In the testes germ cells take part in the spermatogenesis. The germ cells produce spermatogonia.
iii. Primary Spermatocytes
The spermatogonia are changed into primary spermatocytes.
iv. Secondary Spermatocytes
Each primary spermatocyte divides into two cells by meiosis called secondary spermatocytes.
v. Spermatids
Secondary spermatocytes divide further into four haploid spermatids.
vi. Sperm
Spermatids change into sperms
ii. Oogenesis
Definition

The process of gametogenesis which involves the formation of female gamete i.e. ova or egg cell is called Oogenesis.
Process of Oogenesis
i. Female Gonad Ovary
The oogenesis takes place in female gonad called ovary which contain ova producing mother cells called germ cells.
ii. Oogania
In the ovary, the germ cells change into special cells called oogania.
iii. Primary Oocytes
The oogania convert into primary oocytes.
iv. Secondary Oocytes
Primary oocytes divide into two cells by meiosis called Secondary oocytes.
v. Ovum
Secondary oocytes divide further into four cells, one ovum and three polar bodies which degenerates while ovum takes part in fertilization.
Development
Internal fertilization show different types of development.
1. Oviparity
2. Viviparity
1. Oviparity
Definition
The animals which lay eggs in the environment are called oviparous animals and the process is called Oviparity.
Properties of Oviparous Egg

• Eggs of oviparous animals are usually large in number.
• In terrestrial animals, eggs are always protested by tough water proof shells.
• The egg of aquatic oviparous animals covered over by gelatinous membrane.
• The egg of oviparous animals are large size.
• Oviparous egg contain enough store nutrients and yolk for embryo.
• Oviparous animals completes its development inside the egg before hatching.

Examples
Birds and Reptiles
2. Viviparity
Definition
The animals which given birth to young ones are called viviparous animals and the process is called Viviparity.
Properties of Viviparous Egg

• Eggs of viviparous animals are usually small in number.
• Viviparous animal eggs required no shells because they are well protected inside the females body.
• Eggs of viviparous animals are small in size.
• Viviparous egg contain very small amount of yolk because developing embryo in viviparous animals is taken by its mother with the help of its placenta.

Example
Mammals (Pouch mammals and placental mammals)
Reproductive System
Definition
The group of organs which involve in the process of reproduction comprised a system called reproductive system.
Male Reproductive System
Male reproductive system consists of
1. Organs
2. Glands
1. Organs of Male Reproductive System
Male reproductive system consists of following organs
i. A pair of testes
ii. Epididymis
iii. Vas – Deferns
iv. Urethra
v. Penis
i. A Pair of Testes
The small solid, oval bodies and man male reproductive organ called testes.
Functions

• In the seminiferous tubules of testes, the repeated division by the germ cell produce spermatogonia which form primary spermatocycle which undergo meiotic division to form secondary spermatocytes and spermatids. Eventually the spermatids differentiate into mature sperms.
• Testes also produce testosterone hormone, which controls the development of secondary sex characters.

ii. Epididymis
End of the testes is a narrow, much coiled, 6 meter long, thin tube called Epididymis.
Function

• Sperms from the testes may be stored temporarily in an inactive form in the epididymis.

iii. Vas-Deferens (Spermduct)
Epididymis open in a tube from each side passes into the abdominal cavity called Vas-deferens.
Functions

• It receive the sperm from the Epididymis and transfer to urethra.
• It also receive secretion from seminal vesical and prostate gland.

iv. Urethra
The urethra is a tube, which comes from the bladder runs through the center of the penis to the exterior. The urethra also called urinogenital duct is a common tube for the urinary and reproductive discharge.
Function

• Urethra transports the sperm outside the body of male.

v. Penis
The penis is an erectile and copulatory organ. It contain erectile tissue with numerous.
Function

• The penis performs two main functions.
• To carry the urine
• To transport the semen

2. Glands
There are three glands involved in the process of male reproductive system.
i. Seminal Vesicle
ii. Prostrate Gland
iii. Cowper’s Gland
i. Seminal Vesicle
The seminal vesicle, the prostrate and the cowper’s gland secrete a slippery fluid which mixes with the sperms. The mixture of fluid and sperms is called Seminal Vesicle.
Functions

• The fluid in the semen contains nutrients and enzymes which serve to nourish the sperms.
• It activate them so that they begin to swim actively.
• The seminal vesicle also stores sperms temporarily before ejaculation.

Female Reproductive System
The female reproductive system consists of
1. A Pair of Ovaries
2. A Pair of Ovi-Ducts or Fallopian Tubes
3. Uterus
4. Cervix
5. Vagina
6. Vulva
1. Ovaries
The small solid pair of oval bodies and female reproductive organ called Ovaries.
Location
The ovaries are present in lower region of abdomen. They are attached to the dorsal body wall just below the kidneys.
Functions
i. Production of Ovum
Germ cell in the ovary produce many oogonia which divide mitotically to form primary oocytes. There are enclose in groups of follicle cells. The primary oocyte divides meiotically into haploid secondary oocyte and first polar body. Second meiotic division in oocyte proceeds until oocyte (ova) is produced.
ii. Ovulation
Ovary also perform the function of ovulation and discharged only one ovum from the ovary at one time.
iii. Hormones
Ovary produces two hormones i.e. oestrogen and progesterone.
2. Oviduct OR Fallopian Tubes
After ovulation, the ova are immediately sucked up by a pair of tubes called fallopian tubules. It leads from ovary to uterus. It has a funnel like opening lying close to the ovary called fallopian funnel. It makes easy for the eggs to enter the oviduct.
Function
The egg is fertilized in the oviduct.
3. Uterus
Both the oviducts open at their other end into a small pear shaped muscular but distensible sac called uterus. Its inner lining, the endometrium is soft and smooth.
Function
In the uterus development of embryo takes place. Uterus releases oestrogen hormone.
4. Cervix
At the narrow end of the uterus is a circular ring of muscles known as Cervix.
Function
The cervix dilates during birth and allows the head of the infant to pass through vagina the cervix also prevents from infections to developing embryo.
5. Vagina
Cervix opens into a long muscular tube called Vagina.
Functions
The vagina serves as birth canal.
6. Vulva
The opening of vagina is called Vulva.
Function
Semen is deposited in the vagina during intercourse.
Female Reproductive Cycle
The female reproductive cycle are as follows
1. Oestrous Cycle
2. Ovarian Cycle
1. Oestrous Cycle
The cycle in which egg mature and the hormonal secretion of female indicates their readiness for mating and animal is said to in heat a period of sexual receptivity during breeding season are called oestrous cycle.

• This cycle found in all animals except human beings.
• In some animal it is once twice or some time in a year.
• Oestrous cycle indicate that egg is ready for fertilization.

2. Ovarian Cycle
In female human being the reproductive cycle in which ova become mature and take part in fertilization are called ovarian cycle.

• In ovarian cycle one egg become mature and released from the ovary about once every 28 days.
• A human female contain around 200,000 oocytes in each of her ovary.
• Only about 450 of these oocyte develop into mature egg.
• Hormone help in this process.
• After 50 year of age maturation of ova and ovulation stop it is called menopause.

Menstrual Cycle
Definition
In female human beings the reproductive cycle involves certain uterine changes which occur to prepare it for a possible pregnancy this ovarian cycle is called uterine cycle. This monthly egg saturation and uterine preparation is collectively called menstrual cycle or menses.

• Menstruation begins around the age of thirteen and stops at menopause at the age of fifty.
• Menstruation cycle is controlled by hormones.
• Menstrual cycle completes in 28 days.

Phases of Menstrual Cycle
Menstrual cycle completes in four distinct phases
1. Menstruation Or “M” Phase
2. Follicle Or “F” Phase
3. Ovulation Or “O” Phase
4. Corpus Luteum Or “L” Phase
1. Menstruation Phase

• When fertilization does not occur, the inner lining of uterus which because thickened and well developed to received fertilized ovum is broken.
• The progesterone hormone is stopped to secrete from the ovary.
• These broken tissues along with unfertilized ovum, mucus and blood are discharged out of the body through vagina its is called menstrual stage.
• When menstruation starts it is considered as the beginning of menstrual cycle.
• It lasts for 4 to 5 days during which menstrual flow occur.

2. Follicle Phase
The following events occur during this phase
a. Maturation of follicle
b. Endometrium Re Building

• This phase starts just after the menstruation and ends with the release of ovum.
• It lasts about 7 days (day 6 to 12)
• During this stage one or more ova start to develop.
• Only one follicle matures to produce an egg. This egg producing follicle is sometimes called Graffian follicle, while rest of follicle degenerates.
• This process initiated by FSH secrete by pituitary gland.
• FSH stimulates the ovary to produce a hormone called Oestrogen while oestrogen inhibit the secretion of FSH.
• Oestrogen take part in thickening the uterine wall.
• Low FSH level and high oesrogen level in blood initiates the secretion of LH hormone from the pituitary gland.

3. Ovulation Phase

• It is a short phase and is lasts in three days (13 to 15).
• During this phase graffian follicle of the ovary recaptures and the mature ovum is released. This process is called ovulation.
• Mature ova enters into the oviduct.
• This stage is initiated by the increase of LH level.

4. Corpus Luteum Phase
During this phase, following events occur
a. Formation of corpus luteum
b. Development of Endometrium
c. Feed back control

• This phase is the longest period of menstrual cycle.
• It lasts about 12-14 day (16 to 28).
• LH causes the ruptured follicle to change into a yellowish body called corpus luteum.
• Corpus luteum start producing another hormone called Progesterone.
• Progesterone enhances the growth of the mucous lining (endometrium) of the uterus.
• If the mature ovum, in oviduct is not fertilized, the Corpus Luteum gradually degenerates. Progesterone secretion stops and the internal lining of uterus gradually degenerates. Progesterone secretion stops and the internal lining of uterus disintegrates and sloughs off with blood.
• Menstruation begins and the cycle starts again.

Sexually Transmitted Diseases (STD)
Definition
The diseases which are transferred from infected person to healthy person by sex are called Sexually Transmitted Diseases (STD).

Following are important sexually transmitted Diseases
1. Gonorrhoea

• Syphilis
• Genital Herpes
• Aids

1. Gonorrhoea
Causative Agent

• It is caused by gram positive bacteria Neisseria Gonorrhoea.
• The bacteria can enter the body via mucous membranes of urethra, cervix and anal canal during the sexual intercourse.

Symptoms
The main symptoms of Gonorrhoea are

• It mainly affects the mucous membrane of urinogenital tract.
• The new born infants may acquire serious eye infections if they pass through the infected birth canal.
• It may cause infertility in both male and female.
• In male, penis discharges yellow pus and also urination may be painful.
• In female, slight vaginal discharge or a burning sensation is noticed while passing urine.

Treatment and Precaution

• Sexual process should be avoided with affected persons.
• Proper antibiotics should be used for the treatment of disease.

2. Syphilis
Causative Agent
It is caused by a spirochete, treponema pallidum. Transmission sexual contact is the main cause for infection.
Symptoms
The main symptoms of syphilis are

• It damages the reproductive organs, eye, bones, joints, central nervous system, heart and skin.
• Spots are developed on skin.

Treatment and Precautions

• Use of antibiotics
• Sexual contact with affected persons should be avoided.

3. Genital Herpes
Causative Agent

• It is caused by a virus, herpes simplex.

Symptoms
The main symptoms of Genital herpes are

• Painful blisters and ulcers are produce around the external genital organ.
• It may cause inflammation and pain.
• The nervous system and eyes are also affected by the disease.

Transmission

• It is most frequently transmitted by sexual contact causing infection of the genitalia. In infected pregnant woman, virus can be transmitted to infant during birth, causing damage to eye and CNS of the infant.

Precautions and Treatment

• Sexual contact with affected person should be avoided.
• Use of antibiotics to develop immunity in the body.

4. Aids
Causative Agent

• It is a very dangerous disease, caused by a virus called Human Immune Deficiency Virus (HIV).

Symptoms
The main symptoms of AIDS are

• Flue like symptoms in the beginning, later on immune system is destroyed.
• Spots are developed on the skin called skin cancer.
• Blood become poisonous called Septocaemia.
• Nervous system is damage, loss of memory and ultimately death.

Transmission of Virus
HIV virus enters the body by the following ways

• By sexual contact
• By donations of infected blood
• From mother of baby
• By the reuse of used syringes

Precautions and Treatment

• Sexual contact with affected person should be completely avoided.
• Testing of blood before donation.
• Reuse of used syringes should be controlled.
• Use of antibiotics

Placenta
The tissue attaching the embryo to the wall of uterus is called Placenta.
Structure
The placenta looks lika a flat pie shaped structure. It has million of blood vessels that are the part of the embryo’s blood system. It is connection between mother’s body and embryo.
Functions
The main functions of placenta are

• Placenta provides food and O2 from mother body to the embryo.
• It helps in the excretion of CO2 and other harmful excretory products from embryo through the mother body.
• It allows the antibodies to diffuse from the mother’s blood into the embryonic blood capillaries. The antibodies protect the embryo against certain diseased.
• Placenta produces progesterone hormone which maintains uterine lining in healthy state during pregnancy.

Protective Coats of Embryo
Definition

The membrane that protect the embryo are called embryonic membranes.
These membranes often called extra-embryonic coats. The embryonic membranes found in reptiles, birds and mammals are
1. Amnion
2. Chorion
3. Allantois
1. Amnion
Amnion is a membrane that develops and surrounds the embryo completely. Amnion encloses the embryo in a fluid filled space known as amniotic cavity. The cavity is filled with amniotic fluid.
Functions
The amniotic fluid performs the following important functions

• It supports and cushions the embryo fetus before birth.
• It is a shock absorber.
• It also protect the embryo fetus against mechanical injury.

2. Chorion
It is embryonic membrane that covers the embryo completely and present on extreme outer side of the embryo near the egg shell.
Function

• It protects the embryo and assist it in nutrition and excretion.

3. Allantois
It is an embryonic membrane which arises from hind gut of embryo and protect the embryo.
Functions

• It stored food material and harmful nitrogenous waste.
• It help in the formation of umblical cord