Plant Reproduction

Plants can reproduce asexually vegetative or sexually.  To reproduce asexually, plants use rhizoides fragmentation or budding.  Strawberries, crab grass and Barmuda grass are examples of plants that reproduces with rhizoids.  The creeping Charlie is an example of a plant that reproduces through fragmentation.

The banana is an example of a plant that reproduces through budding.

Vegetative Propagation

In this case plants parts root, stem and leaves develop into new plant under favourable conditions.

Only mitotic divisions are involved in vegetative or asexual reproduction.  It is takes place by following methods.

  1. Cutting : The division of any plant organ (stem/root/leaf) used for its propagation is called cutting, e.g., stem cutting in sugarcane, grapes, cocos, rose Bougainvillea, etc.
  2. Layering: A ring of the bark is removed from lower branch and bent down. This part is covered by soft soil.  After 2-3months, root develop and the branch is cut off to grow independently, e.g., lemon, grapes, strawberry, etc.
  3. Grafting: In grafting a plant (scion) is inserted into another plant (stock) so as to be nourished by it and united with it. Grafting is especially successful in dicotyledonous plants, where stem has cambium layer, e.g., citrus, mango, rose, apple, etc.
  4. By leaves: It is found in species of Bryophyllum (plantlets develop along the emerging of intact leaves), e.g., Begonia, Saintpaulia, etc.
  5. Tissue culture: In this case, new plants are grown by removing tissue or cells from the growing tip of a plant and placed in an artificial medium, where they divides and form a small group of cells or callus. After this the callus is transferred to another medium for growth and differentiation than the plantlets are placed in the soil so that plantlets can grow in the soil so that plantlets can grow into mature plant.

Sexual Reproduction

Sexual reproduction in plants involves male and female plant organs.  The female structure involved in sexual reproduction is the stigma, style and ovary.

The stigma is the sticky portion of the pistil that captures pollen.  The style is long and slender and supports the stigma.

The ovary is composed of one or more ovules.  Each ovule consists of a haploid egg and other associated cells. The male structures involved in sexual reproduction are the filament and the anther.

The filament supports the anther, which is responsible for storing and producing pollen.


Transfer of pollen grains form anther to the stigma is called pollination.  If the pollen grains are transferred to the stigma of the same flower, the pollination is called self-pollination or auto gamy.  If the pollen grains are transferred to the stigma of another flower of the same species, the pollination is called cross-pollination or allogamy.

On reaching the stigma, the pollen grains put out a tube.  This is called germination of the pollen grain.  The tip of the tube contains the male nuclei.  The tube grows and enters the ovule, where it burst at the tip releasing the male gametes. One of the male gametes fuses with the egg of the female gamete.

Double Fertilisation

It occurs in angiosperms only. It was first discovered by Nawaschin (1898) in Fritilaria and Lilium. On e male gamete fuses with egg (syngamy) forming a diploid zygote (2n) and the second male gamete fuses with two polar nuclei (or secondary nucleus) forming a triploid primary endosperm nucleus (3n).

The first fusion is called true fertilization and the second fusion is called triple fusion.  Five nuclei are involved in double fertilization. The division of the endosperm nucleus results in the formation of the endosperm triploid that nourishes the growing embryo.  The ovules then become the seed and the ovary change into fruit.  The petals, sepals, stamen, style and stigma may fall off

Reaching the age of Adolescence

Adolescence and Puberty

  • The word ‘Adolescence’ derived from the Latin word ‘adolescere’ whichmeans ‘to grow’.
  • The World Health Organization (WHO) defines adolescence as the periodof live between 11 and 19 years of age.
  • Generally, boys attain puberty at the age of 14 to 15 years, while girlsreach puberty at a comparatively lower age of 11 to 12 years.

Changes at Puberty

  • Increase in Height
  • Change in Body Shape
  • Change in Voice
  • Increased antivity of Sweat and Sebaceous glands.

Ductless Glands

  • The word gland means having some secretions. There are two types ofglands

Endocrine gland – gland with duct

Endocrine gland – gland without duct

  • The exocrine gland secretes enzymes which are important for digestion.The ductless or endocrine glands secretes hormones. They are special chemical substances that make wonder in our body

Pimple: A small papule or pastule .Pimples are sebaceous glands that areinfected by bacteria, become inflamed  and fill with pus.

Pituitary Gland   

  • It is located just below the brain
  • It is called as the master gland because it secretes number of hormoneswhich control the functioning of all other glands.
  • Your growth depends on the secretions of the pituitary gland
  • ln adults, excess secretion leads to a condition called acromegaly.

Thyroid gland

  • It is located in the throat region.
  • It secretes a hormone called thyroxine.
  • The function of thyroxine is to control the rate of Metabolism, growth and respiration `
  • The deficiency of thyroxine hormone in children is known as cretinism.
  • Someiirnes the gland may enlarge causing a disease called’Goitre’


  • Pancreas is both exocrine and endocrine. The endocrine part is called lslets of langerhans. lt has alpha and beta cells, which secretes glucagon and insulin.
  • Deficiency of insulin in the body causes a disease known as diabetes mellitus.

Adrenal gland

  • It secretes adrenalin hormone .This hormone is produced during stress or emergency situations. It regulates  heart beat, breathing rate, blood pressure etc.

Tastes and ovaries

  • Testes and ovaries secrete sex Testes produce testosterone and ovaries produce oestrogen hormones

Role of Hormones in Reproduction

The following are the various reproductive phases in the life of a female.

  1. Ovulation
  2. Menstruation or the period
  3. Pregnancy
  4. Menopause

Sex Determination

  • All the cells contain 23 pairs of chromosomes, the last pair of chromosome is different in males and females.

Sex chromosomes

  • Sex chromosomes are of two types, these are names as X. and Ychromosomes. Usually a woman has two ‘x’ chromosomes (XX) and malehas one ‘X’ and one Y chromosome (XY), in their cells.
  • During gamete (reproductive cell) formation the number of chromosomesis reduced into half. (46 chromosomes are reduced into 23).
  • When a sperm containing ‘X’ chromosome fertilizes the egg, the zygotewill have two ‘X’ (XX) chromosomes. The zygote will develop into afemale child.

Reproductive Health

  • During adolescence growing children need special attention towards diet, exercise and personal hygiene. The personal hygiene includes female and male reproductive health.

Nutritional Needs

Minerals: Since thereis an increase  in skeletal mass and blood volume, the body needs calcium ,phosphorous and iron

Calcium: Calcium intake needs to be increased o prevent  osteoporosis in later life.It is present in milk and  milkproducts.

Iodine: it helps to prevent  thyroid gland related diseases.

Iron: lack of iron in the diet results in anemia. To make up for the loss,have a diet rich in iron.


  • Sprouts are a living, enzyme-rich food, natural and low in calories.
  • Their vitamin A content will usually double, various B group vitamins will be 5 – 10 times
  • higher, and vitamin C will increase by a similar order.

Cancer and its prevention

  • Cancerous cells create lots of problem in our metabolism and invade to the other areas through blood streams, where they cause secondary tumours. This stage is called metastasis.
  • Treatment involves surgery, chemotherapy radiotherapy and hormonaltherapy.

Major types of reproduction

Asexual Reproduction

Sexual Reproduction

It invoves a single parent

It involves two parents (male and female) each capable of producing gametes

It does not involve the fusion of gametes

It involve the fusion of male and female gametes [(i.e) sperm and ovum ] resulting in the formation of zygote

Asexual Reproduction

  • These include multiple fission,binary fission,budding,regeneration gemmule and spore formation,etc.,
  • Binary fission:e.g Paramoecium

Multiple Fission

  • Many protozoans reproduce by multiple fission under unfavourable condition


  • Hydra reproduces asexually by budding


Gemmules are internal buds found in sponges and are resistant  tounfavourable condition. _

Spore and cyst formation

  • This type of reproduction is common among protozoan parasites such a plasmodium (malarial parasite).
  • This method is also called sporulation.


Animals like sponges, Hydra, Planaria and Star fish exhibit regeneration.


It refers to the power of self cutting of body parts  for defense. Examples  Regeneration of arms in star fish, regeneration of tail in house lizar

Regeneration in man

Examples of regeneration in man

  1. Healing of wounds
  2. Replacement o blood cells ,
  3. Replacement of horny layer of the skin

Advantages of Asexual reproduction

  1. It requires only one parent
  2. It donot involve gametes and fertilization
  3. The young ones have identical characteristics of their parents.

Disadvantages of Asexual reproduction

  • It does not result in large variations and hence donot lead to speciationand evolution.
  • Transmission of undesirable characters from parent of offspring without any change

Sexual reproduction

All higher animals and a few lower organisms can reproduce sexually

1.Unisexual organism – with only one type of gonad (i.e. either testis or  ovary) e. g. Human beings.

  1. Bisexual organisms or Hermophrodites – Organism with both testis andovary) e. g. Tapeworm, Hydra.

Conjugation in paramecium

Lower organisms like paramecium reproduce sexually by conjugation

Schematic representation of sexual reproduction









Young individual

  • In higher organisms, who individuals of a species (male and female) are involved in sexual reproduction.
  • The male reproductive organ is the testis which produce the sperms.The female reproductive organ is the ovary which produce the ova or eggs.
  • The fusion of sperm and ovum is called fertilization The zygote further develops into an embryo and later becomes an adult.

Reproduction in human

Male reproductive system

  • The primary sex organs are the testis and the accessory organs are seminal vesicles, prostrate glands, urethra and  Penis
  • Each testis contains a coiled mass of tubules known as seminiferous tubules which produce sperms.
  • The process of formation of sperms is known as spermatogenesis.
  • The interstitial cells of the testis also secretesecrete the male sex hormone (androgens which control spermatogenesis and the appearances of male sexual char such as growth of beard moustache, body hair, hoarse voice,etc.,
  • The sertoli celss of e testis provide nourishment of the developing sperms.
  • The sperms are delivered through the vas deferens which unites with theurethra which form a common passage for both sperms and urine.
  • Sperms are released in fluid called semen. This fluid provides nutritionand helps in the transport of sperms.

Structure of a mature sperm

  • The sperm consists of four parts namely head, neck, midpiece and tail.
  • The head contains a condensed nucleus containing haploid set (n) ofchromosomes and a terminal acrosome
  • The neck contains a proximal and a distal centriole.
  • The distal centriole is continuous with axial filament.
  • Midpiece contains the spirally coiled mitochondria.
  • The tail represents the remnants of Cytoplasm and propels the sperm in the liquid medium.
  • Anton Van Leeuwenhock (1632-1723) was the first and draw sperm cells.

Female reproductive system

  • The female reproductive system consists of ovaries and accessaory organsuch as fallopian tubes, uterus, cervic and vagina
  • The ovary produces an egg for every 28 days (menstrual cycle) as well asfemale sex hormones oestrogen and progesterone.
  • Each ovary produces the ovum by a process known as oogenesis.
  • The uterus is a hollow,thick walled muscular organ fertilized ovum isembedded and nourished in the uterus.
  • Vagina serves to receive sperms and as a birth canal
  • The oestrogen is responsible for oogenesis and for the appearance offemale secondary sexual characters such as development of breasts ,growth of hair, feminine voice, etc.,

Structure of egg of human ovum

  • The egg of human is alecithal without yolk.
  1. Vitelline membrane
  2. Zona pellucid
  3. Corona radiate

Menstrual cycle

  • The rhythmic series of changes in the female sex organs that occur for about 28 days throughout the reproductive life of women from puberty to menopause (except during pregnancy) is known as menstrual cycle.
  • When the ovum is not fertilized, the ovum along with the uterine wall is ruptured and discharged with blood and uterine.

It involves three phases namely

  1. The follicular phase (5th day-14th day)
  2. The luteal phase or Premenstrual phase (15th -28th day)
  3. The menstrual phase (1st -5th day)

Menstrual cycle

  1. Follicular phase
  • This phase is initiated by the secretion of Follicle Stimulating Hormone(FSH) of pituitary
  • During this phase primary ovarian follicles begin to grow and the mature graffian follicles burst and release the ovum into the fallopian lube(ovulation).
  1. Lateal Phase
  • This stage is influenced by Lutenising Hormone (LH) of pituitary gland.
  • After the release of the ovum, the ruptured part of graffian follicle istransformed into a transitory endocrine gland called corpus luteum. It secretes the pregnancy hormone called progesterone.
  • This hormone causes the thickness of endometrium and prepares the uterus to receive the fertilized ovum.
  • If the ovum is not fertilized, the ovum and uterine wall gets ruptured anddischarged during menstrual phase

Menstrual phase

  • The decline in progesterone and oestrogen initiates the shedding of unfertilized egg and endometrium with severe bleeding in a process called mensus or menstruation.
  • At the termination of menstruation, the corpus luteum is converted into ascar tissue called corpus albicans.


  • Fertilization is process of fusion of male gamete to form adiploid zygote.

Types of fertilization

  • External fertilization: The fusion of the gametes occurs outside the body ofthe animal (e.g.Frogs Echinoderms)
  • Internal Fertilization:The fusion of the gametes occur within the body of the female.(e.g Reptiles and Mammals)

Mechanism of fertilization

  • Internal Fertilization:The fusion of the gametes occur within the body of the female.(e.g Reptiles and
  • Fertilization of the ovum occurs in the ampulla of the uterine tube. Onlyone spermatozoan pierces the egg membrane Zona pellucid and enters the ovum.
  • Polygarny (entry of more sperms) is prevented by the fertilization membrane around the ovum.

Development of Embryo

  • The fertilized ovum is called the zygote.
  • The first phase of ernbryo’s development called cleavage.
  • As a result a ball of cells called the blastula is fanned. The outer surface forms the trophoblast and the embryo gets attached to the wall of the uterus. This process is known as implantation.
  • The implanted embryo develops the extra embryonic membranes such as anmion, allantois, chorion and yolk sac.
  • Amnion provides a fluid medium to the developing embryo. It prevents dessication of the embryo and function as a shock absorber.
  • The chorion and allantois fuse to form the placenta. It helps in the exchange of gases between the mother and the foetus and also the elimination of nitrogenous wastes foetus
  • The embryo and the placenta are connected by the umbilical cord which is derived from the allantois

Stages in the development of the human foetus

  • Gestation period:From the fertilizationof the ovum to the birth of the baby it takes about nine months

First trimester

  • The proliferation of cells takes place and gradually a single cell is transformed into a foetus
  • Organogenesis takes place resulting in the formation of organs.

Second trimester

  • The respiratory and circulatory systems become well developed and functional. The bones and muscles are well formed.

Third trimester

  • The length and weight of the foetus increases very rapidly and the development is completed.

Child birth

  • At the onset of childbirth, the uterus begins to contract rhythmically underthe influence of oxytocin hormone.
  • This marks the onset of laour pain. With continued powerful contractions.
  • Finally the muscular contractions of the uterus and the abdomen expel thechild through the dilated cervix and vagina.
  • A few minutes later, the placenta breaks away from the uterus and isexpelled as ‘after birth’.


  • The first milk which comes out from the mammary gland just after childbirth is known as colostrums
  • It is rich in proteins and nutrients also contain antibodies that provideimmunityforthe newborn infant
  • The secretion of milk is stimulated by the pituitary hormone prolactin.

Advantages of mother’s milk

  • It is easily available, clean, uncontaminated and strile.
  • It contains antibodies
  • In rural areas breast milk is used as eye drops for viral conjunctivitis
  • The calorific value of breast milk is 70 per 100 ml of milk.
  • Lactoferin a protein in breast milk provides considerable protectionagainst intestinal and respiratory infections.

Viviparous animals

  • Vivipary means directly giving birth to young ones(e.g .Placental mammals).The young ones directly receives food and oxygen from the mother through the placenta and also excretes the wastes through it


  • Oviparous animals lay eggs laden with yolk
  • Land dwelling animals lay eggs with shell(Cledoic eggs)
  • In these animals the embryos develop inside the eggs that are retained within the mother ‘s body until they are ready to hatch
  • There is no placental connection e.g vipers

Young ones to Adult

  • The young one has to pass through morphological,anatomical and physiological changes and get transformed into an adult.Thsese changes which transform the young ones into adults are known as metamorphosis

Metamorphosis in insects

  • In insects the outer skin in cast off periodically and this process is known as moulting or ecdysis
  • The larval stages between two successive moultings are called stadia(singular-stadium)


  • Chromosomes are thread-like condensed chromatin fibres which containhereditary information and the visible only only during cell division.
  • Each chromosome consists of two similar structure called chromatids.Both the chromatids are joined at a particular point called centromere.
  • The primaryconstriction is the region of chromosome occupied by the centromere. The terminal part of chromosome is telomere.

Types of chromosomes 

  1. Metacentric Chromosome .
  • The centromere lies in the middle of the chromosome.
  • The two arms are almost equal in length. It is a V-shaped chromosome.
  1. Submetacentric Chromosome
  • It’s one arm is slightly shorter than the other. It is a ‘J’ shapedchromosome.
  1. Acrocentric chromosome
  • One arm is very short and the other arm is very long. It is a rod-shaped chromosome.
  1. Telocentric Chromosome
  • There is only one arm on one side. It is also a rod-shaped chromosome.

DNA Structure

  • DNA (Deoxy ribonucleic acid) is the genetic material in most of the organisms and higher organisms. DNA is made up of millions ofnucleotides. 
  • Each nucleotide is made up of a pentose sugar Phosphate group and a nitrogenous base.
  • The nitrogenous bases are of two kinds- Purines and Pyrimidines. Adenine and guanine are the purines and Thyamine and cytosine are the pyrimidines.
  • The structure of DNA was proposed by Watson and Crick. DNA is a double structure in whichthe two strands are coiled around each other forming a double helix
  • The backbone if the helix is formed of sugar and phosphate molecules.The nitrogenous bases are attached to sugar molecules.
  • The nitrogenous bases are attached to sugar molecules. The two poly nucleotide strands are held together by hydrogen bonds between specificpairs of purines and pyrimidines.
  • The two strands run in antiparallel and opposite directions. (i.e. they run in opposite direction 5′ to 3′ and 3′ to 5′ ‘end). The two strands are intertwined in clockwise direction. The diameter of DNA molecule is 20A°.

Cell Division and Types

  • Plants or animals make their beginning from a single celled zygote. Thiszygote divides several times. to produce a plant or an animal. This processis called development and it occurs by cell division.
  • One of the most important characteristics of a living being is its ability to reproduce. Cells divide by three different methods. ‘They are Amitosis, Mitosis and Meiosis.

Amitosis (Direct division)

  • It is also called direct cell division. This type of cell division is common inprokaryotes. e.g. bacteria, Amoeba.

Mitosis (or) Indirect cell division

  • Mitosis takes place in somatic cells(body cells). It is a continuous processand takes place in four phase. These are Prophase, Metaphase, Anaphaseand Telophase.


  • Before a cell undergoesmitotic division, it prepares itself for the division.This phase is called interphase.
  • The chromatin material duplicates due to duplication of nucleic acids.


  • Chromatin network begins to coil and appears as long thread-likestructures called chromosomes.
  • Each chromosome consists of two chromatids that lie side by side and arejoined along a point called centromere.
  • Spindle fibres are developed from the poles towards the centre. Nuclear membrane and nucleolus start disappearing


  • The nuclear membrane totally disappears.
  • Chromosomes become shorter and thicker.
  • The chromatids move to the centre of the cell with their centromeres.
  • Centromeres are attached to the spindle fibres.


  • The centromere of each chromosome divides into two
  • When each chromatid gets a centromere,it becomes a chromosome.
  • One of these chromosomes moves to one pole and the other towards theopposite pole by the contraction of spindle fibres


  • The daughter chromosomes reach the poles.
  • The nucleolus d nuclear membrane reappear and thus two daughter nuclei are formed at the two poles of the cell.
  • The spindle fibres disappear
  • This division of nucleus is called karyokinesis.


  • In plant cells, the cytoplasmic division occurs by the formation of a cellplate at the centre of the cell between the two daughter nuclei.
  • Thus at the end of mitosis, two identical daughter cells are formed.

Cell Division

  • Body cells of all animals and plants undergo a cell division called
  • The germinal epithelial cells of animals undergo Meiosis cell division,


  • Meiosis takes place in the specialized diploid cells of gonads and produces four haploid gametes each having half the number of chromosomes as compared to the parent cell
  • Meiosis is completed in two successive divisions- Meiosis – I and Meiosis -II
  • Meiosis-II is similar to Mitosis

Meiosis – I

  • The various events of Meiosis-I are studied under four substages namely Prophase-I , Metaphase -I-, Anaphase – I and Telophase – I.


  • The chromatin reticulum unwabs and individual chromosomes areliberated from one another.
  • This stage is studied under five sub-divisions as Leptotene, Zygotene,Pachytene, Diplotene and Diakinesis


  • Each chromosome splits up longitudinally, except at the centromere.


  • The homologous chromosomes come closer and start pairing.
  • This pairing is called Synapsis, the paired chromosomes are calledBivalents.


  • Each bivalent appears to have four strands as, tetrads orquadrivalents.
  • This exchange of segments of chromatids between homologouschromosomes, is called crossing over


  • The homologous chromosomes separate this separation is called terminalization.


  • The spindle apparatus is formed in the cytoplasm.

Metaphase -I

  • The chromosomes get condensed
  • Bivalents now appear on the equator of the spindle with theirchromatids, pointing towards the equatorial plate.


  • Thespindlefibres contract pulling the chromosomes, towards theopposite poles.
  • This involves, a reduction in the number of chromosomes.

Telophase – I

  • Thus two daughter nuclei each with half the number of chromosomes,are formed at the poles. The spindle fibres disappear.

Meiosis – II

  • Meiosis – II is similar to Mitosis and so it is called Meiotic Mitosis.

Phrophase – II

The bivalent chromosomes gets shortened.

Metaphase -II

The centromeres are attached with the spindle fibres

Anaphase – II

The centromere divides into two and the two chromatids separate and now they are called as daughter chromosomes or new chromosomes

Telophase – II

Thus two  daughter nuclei are formed


  • The cytoplasmic division takes place at right angles to the position ofthe nuclei resulting in the formation of four gametes.

Significance of Meiosis

  • Haploid sex cells are produced, in order to maintain the constancy inthe number of chromosomes of a species.
  • Crossing over results in variation of genetic traits in the offspring.
  • Variations form the raw material for evolution.


  • Inheritance of characters from the parents to the progeny, (i.e heredity)ensures the passing of the parental characters to the progeny.

The inheritance of characteristics through generations is called heredity

Types of Metamorphosis

Incomplete Metamorphosis

Lifecycle of Grasshopper


(e.g Grasshopper,Mayfly)

Complete Metamorphosis

Lifecycle of Butterfly

Egg à Larva Pupa à Adult

(e g Butterfly, silk moth)

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