REPRODUCTION (10TH CBSE & STATE)

******************REPRODUCTION********************

Reproduction is the process by which all organisms multiply in number and increase their population.

Asexual Reproduction

Asexual reproduction is a method of reproduction that involves only one organism. A single organism reproduces two or multiple organisms on its own. This is seen in all unicellular organisms, some multicellular organisms and a few plants.

Sexual Reproduction

The mode of reproduction involves two individuals; one male and one female. They produce sex cells or gametes, which fuse to form a new organism.

Asexual Reproduction

Fission

• Fission is an asexual reproduction that is common in most unicellular organisms.
• When the fission results in two daughter cells, it is binary fission (e.g. paramecium).
• When fission results in many daughter cells, it is called multiple fission (e.g. Plasmodium).
• Planes of fission may be different for different organisms.

Budding

• Budding is a type of asexual reproduction in which a small cyst-like structure is formed on the parent’s body, which gives rise to a new individual.
• Bud may remain attached to the parent (yeast) or may separate and become a new individual (hydra

Regeneration and Fragmentation

• Regeneration is the process of growing back the lost organ or body part by the organism (e.g. lizard).
• Fragmentation is the process by which an organism gets fragmented into smaller pieces, and each piece grows into a whole new organism.
• E.g. Planaria, Hydra

• Fragmentation and Regeneration in Hydra

Spore Formation

Organisms such as fungi make spores that can grow into completely new individuals when dispersed from their fruiting bodies. Spores are produced inside sporangia. They are covered by a thick outer layer that protects them in adverse conditions. When spores get suitable environmental conditions, they germinate and begin to grow.

Vegetative Propagation

• This is a type of asexual reproduction seen in plants.
• The vegetative parts of the plant, like leaves, stems, and roots, give rise to a new plant.
• Vegetative propagation can be artificial or natural.
• Natural vegetative propagation happens through leaves (e.g. bryophyllum), stem (e.g. turmeric, ginger), runners/stolon (e.g. grass runners, strawberry), bulbs ( e.g. onion, lily), etc.
• Artificial methods include cutting, grafting, layering and plant tissue culture.

Sexual Reproduction

Types of Cell Division

Two types of cell division are seen in eukaryotic organisms:

Mitosis

• Takes place in somatic cells
• Maintains the chromosome number
• Produces two, diploid daughter cells
• Required for asexual reproduction, development and growth, cell replacement and  regeneration

Meiosis

• Takes place in sex cells
• Reduces the number of chromosomes by half
• Produces four haploid daughter cells
• Required for sexual reproduction, i.e gamete formation

To know more about Cell division, visit here.

The Reproductive System

In humans, there is a remarkable difference in the male and female reproductive systems. Testes are the main reproductive structure in males where sperms (male gametes) are produced, and ovum (female gamete) is produced inside the ovary. Let us now learn in detail about male and female reproductive systems in humans.

To know more about Human Reproductive System, visit here.

Male Reproductive System

• The main reproductive organ in males is a pair of testes.
• They produce the male sex cells called sperms and also produce the male sex hormone testosterone.

Male Primary Reproductive Organ

• The main reproductive organ in males is a pair of testes.
• They are present in scrotal sacs outside the body and contain seminiferous tubules as the structural and functional unit.
• Male sex cells, sperms, are produced by seminiferous tubules and mature in the epididymis.
• Leydig cells or interstitial cells present in between the seminiferous tubules secrete the hormone testosterone.

Male Accessory Reproductive Organs

• Several accessory reproductive organs aid in the reproductive process.
• The prostate gland and the seminal vesicles are glands of the reproductive system which make semen and nourish the sperm.
• Penis, having the urethra passing through it, is called a copulatory organ.

Male Ducts

• In males, the vas deferens and the urethra are the main ducts.
• A single vas deferens carries sperm from the respective testis up to the urethra.
• The urethra acts as a common passage for semen and urine.

Female Reproductive System

The human female reproductive system consists of a pair of ovaries, a pair of fallopian tubes/oviducts and the accessory organs such as the uterus and the vagina.

Female Primary Reproductive Organ

• The main reproductive organ in a female is a pair of ovaries.
• They produce the female sex cells called eggs or ova and also produce female sex hormones called estrogen and progesterone.

Female Accessory Reproductive Organ

• The uterus, oviducts, and vagina are the accessory reproductive organs in human females.
• The uterus is the site of fetal development, and the vagina receives sperm from the male. Ovum is carried from the ovaries to the uterus through a pair of oviducts.

Menstrual Cycle

Menstruation

• Menstruation is the cyclic event of the release of the ovum from the ovary and its removal from the body when fertilization does not happen.
• During menstruation, the blood-rich endometrium of the uterus also breaks down while the ovum is removed from the body.
• Two pituitary hormones, LH and FSH, and two ovarian hormones, estrogen and progesterone, all have their roles in menstruation.
• In humans, the cycle repeats every 28 days.

Fertilization

Human Reproduction

Humans reproduce sexually. The male produces sperms and the female produces eggs. When the sperm fuses with the egg, it forms a zygote that gives rise to a new progeny.

                        Contraceptive Methods

Reproductive Health

Reproductive health deals with the prevention of STDs and unwanted pregnancy. Understanding the reproductive system is also a part of reproductive health awareness.

Contraceptives

• Contraceptives are devices that prevent unwanted pregnancy and help avoid STDs.
• Contraceptives can be of various types such as mechanical barriers, hormonal/chemical methods, surgical methods, etc.

Coitus Interruptus

• It is a very unreliable contraceptive method where the coitus is stopped before the male ejaculates inside the female reproductive tracts.

Rhythm Method

• Another unreliable method of contraception is where coitus is avoided when the female is fertile and the chances of fertilization are very high.

Condoms

• One of the most effective methods of contraception.
• A mechanical barrier that stops the semen from entering the female tract preventing pregnancy.
• It also avoids the possibility of contracting STDs.

Diaphragms

• Diaphragms are barriers that can be added inside the female reproductive tracts.
• They stop the entry of semen inside the female tract and thus prevent pregnancy.

Contraceptive Pills

• Contraceptive pills are chemical methods of contraception.
• They change the level of hormones in the body that prevents the release of the ovum from the ovaries.

Emergency Pill

• Emergency pills are those pills which can be taken after coitus to avoid pregnancy.
• They quickly change the level of hormones in the body and prevent a successful implantation even if the egg gets fertilized.

IUD

• IUD stands for Intrauterine Device.
• They can be used for a couple of years.
• It is a device that is inserted into the uterus, changing its shape and preventing successful implantation of the zygote.

Sterilization

• Sterilization is a surgical method of going permanently sterile.
• This can be done in both males and females.
• In males, it is called vasectomy and in females, it is called tubal ligation.

Reproduction in Plants

Plants reproduce by both asexual and sexual methods. Vegetative propagation is a type of asexual reproduction in plants. Let’s learn now about sexual reproduction in plants.

Sexual Reproduction in Flowering Plants

• Sexual reproduction in plants happens through flowers.
• Essential whorls of the flowers such as androecium and gynoecium help in the sexual reproduction of plants.

Non-Essential Parts of Flowers

• The typical structure of flowers contains essential whorls and non-essential whorls.
• Sepals and Petals are called non-essential whorls as they do not directly take part in reproduction.
• Sepals protect the inner delicate whorl during bud condition and also perform photosynthesis if they are green in colour.
• Petals, when they are coloured, attract insects for pollination.

Pollination

The process of transfer of pollen grains from anthers to the stigma of a flower is known as pollination.

• It is required for fertilization.
• Pollination has two types, self-pollination (autogamy) and cross-pollination (allogamy).
• In self-pollination, the transfer of pollen grains takes place from anthers to the stigma of the same flower or another flower of the same plant.
• In cross-pollination, pollens are transferred from anthers to the stigma of another flower.
• Many pollinating agents play their roles in cross-pollination. Examples: water, wind, insects, birds, bats, etc.

Fertilization

Fusion of male and female gametes is known as fertilization.

• In flowering plants, after pollination, the pollens germinate on the stigma surface of the pistil and generate two male nuclei.
• Ovule has an egg cell and two polar nuclei.
• One male nucleus fuses with two polar nuclei and forms a triploid endosperm.
• Another male nucleus fuses with the egg cell and forms the zygote that gives rise to the embryo and future plant.
• After fertilization, the ovary becomes the fruit, and the ovules turn into seeds. All other parts wither away.

Frequently Asked Questions on CBSE Class 10 Science Notes Chapter 8 How do Organisms Reproduce

Q1

What is the difference between fission and fusion?

Fission is the process where an atom splits into two or more smaller parts; whereas fusion involves the fusing of two or smaller atoms into a larger particular.

Q2

What is fragmentation?

Fragmentation is a form of asexual reproduction where the parent organism breaks into fragments. Each of these fragments is capable of growing independently into a new organism.

Q3

What is a gamete cell?

Gamete cells are the reproductive cells of an organism. Female gametes are referred to as ova or egg cells, and male gametes are known as sperms.

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HERIDITY AND EVOLUTION (10th class cbse & state) @KDM BIOLOGY

                                                  HERIDITY AND EVOLUTION      @KDM BIOLOGY

Introduction:

  Heredity refers to the passing of characteristics from one generation to the next. 

Evolution is defined as the gradual process by which a simple life form leads to the development of complex organisms over a period of time, spanning several generations. 

. Heredity The transfer of traits from one generation to the next is termed heredity.

 Genes are the functional units of heredity, that transfer characteristics from parents to offspring. 

Genes are short stretches of DNA that code for a specific protein or RNA. 

Genetics is the branch of biology that deals with the study of genes, heredity and variations.

 Sexual reproduction 

 • The mode of reproduction involves two individuals; one male and one female.

 • They produce sex cells or gametes which fuse to form a new organism.

 Genes 

 • Gene is the functional unit of heredity.

 • Every gene controls one or several particular characteristic features in living organisms. Read more: Genes Heredity The process by which the features of an organism are passed on from one generation to another is called heredity.

 • The process is done by genes, which define the characters in the organism. To know more about Heredity, visit here. Mendel's work 

                                                                        MENDEL

 • Gregor Johann Mendel, known as 'Father of Genetics', was an Austrian Monk who worked on pea plants to understand the concept of heredity.

 • His work laid the foundation of modern genetics. 

 • He made three basic laws of inheritance -

  The Law of Dominance,:

The Law of Segregation and The Law of Independent Assortment. Dominant traits .

The traits that express themselves in an organism in every possible combination and can be seen are called Dominant traits. 

 In Mendel’s experiment, we see that the tall trait in pea plants tends to express more than the short trait. • Therefore, the tall trait of the plant is said to be dominant over the short trait.

 Recessive traits A trait which is not expressed in the presence of a dominant allele is known as recessive. 

                                                    MONOHYBRID CROSS

 • So, recessive character/trait is present in an organism but cannot be seen if a dominant allele exists. To know the difference between Dominant traits and Recessive traits, visit here. Monohybrid cross 

 • When only one character is considered while crossing two organisms, then such a cross is known as a monohybrid cross.

 • The ratio of characters, arising out of this cross, at F2 generation is called the monohybrid ratio. • E.g., If a tall plant (TT) is crossed with a dwarf plant (tt), we get 3 tall:1 short plant at the end of the F2 generation. 

 • So, 3:1 is a monohybrid ratio. 

                                                    DIHYBRID CROSS

 • Here, the height of the plant is considered at a time. Below is the example of a monohybrid cross between a true-breeding pea plant with green pods (GG) and yellow pods (gg). Here, the green colour of the pod is the dominant trait. Hence, in the F1 generation, all plants contain green pea pods. To know more about Monohybrid cross, visit here. Dihybrid cross

 • When two characters are considered while crossing two organisms, then such a cross is known as a dihybrid cross.

 • The ratio of characters, arising out of this cross, at F2 generation is called the dihybrid ratio. • E.g., If a plant with round and green pea is crossed with a plant with wrinkled and yellow pea, • The first generation plants would all have round and green peas. 

 • On crossing the same for an F2 generation, we would observe four combinations of characters in the ratio of 9:3:3:1.

 • Thus, 9:3:3:1 is the dihybrid ratio. 

 To know more about Dihybrid cross, 

 Inheritance In Biology, inheritance pertains to the transfer of traits from one generation to another. To know more about Mendel's laws of inheritance, 

 Laws of Mendel :

Law of Dominance says that a gene has two contrasting alleles and one always expresses itself in the organism. It is called the dominant gene and it expresses in any possible combination.

 Law of Segregation says that traits get segregated completely during the formation of gametes without any mixing of alleles.

 Law of Independent Assortment says that the traits can segregate independently of different characters during gamete formation. 

                                                    Sex determination 

 • The process of determining the sex of an individual, based on the composition of the genetic material is called sex determination. 

 • In different animals, sex of an embryo is determined by different factors. 

 • In humans, sex determination happens on the basis of the presence or absence of Y chromosome. • XX is female and XY is male • An ovum always contains X chromosome. 

 • An ovum, upon fusion with Y containing sperm, gives rise to a male child and upon fusion with X containing sperm gives rise to a girl child. To know more about Sex determination, visit here. Traits Traits are characteristic features of an organism, manifested in a physical form that is visible or in a physiological aspect of the organism. Acquired characters

 • The traits that are acquired by an organism over the period of its lifetime are termed acquired characteristics. 

 • These characters that are not passed on to the DNA of germ cells do not get transferred to the next generation. E.g. loss of muscles and less weight due to starvation, loss of limb or tails due to injury, etc. Inherited characters

 • The traits that are inherited from the parents are called inherited characters. 

 • These traits always get transferred to the next generation but depending on the dominance or recessiveness they may or may not be expressed. 

 • Examples are height, skin colour and eye colour. 

                                                           Natural selection 

• It is the phenomenon by which a favourable trait in a population of a species is selected. • Changing natural conditions exert equal pressure on all the existing species. 

 • The species/organisms which are better adapted to the changing conditions survive and reproduce i.e. selected by nature and species/organisms which cannot adapt perish i.e. rejected by nature. 

 Speciation Genetic drift Natural selection can play an important role in deciding the traits that survive in a population. However, random fluctuations in gene variants are seen on many occasions. 

This phenomenon is known as genetic drift. Thus, genetic drift is a change in the frequency of an existing allele in a small population.

Charles Darwin:

  • Charles Darwin also called the "Father of Evolution" was an English Naturalist and Biologist

. • Five years of the expedition in a ship called HMS Beagle to Galapagos Island helped him write his theory of evolution. 

 • In 1859 he published a book called Origin of Species, in which he put his theory of evolution in detail. To know more about Charles Darwin's Contribution to the Theory of Evolution, 

 Evolution Origin of species 

 • After a successful expedition on HMS Beagle, Charles Darwin wrote a book on what he observed on the Galapagos Islands.

 • In the book named 'The Origin of Species, he wrote a detailed theory of evolution which was mostly based on Natural Selection. Origin of life - Haldane's theory 

 • JBS Haldane was a British Scientist who theorized that life originated from organic and lifeless matter. • His theory was proved to be correct by Urey and Miller’s experiment. 

 • It was called the theory of abiogenesis. Evolutionary evidence - fossils 

 • There are plenty of pieces of evidence to support the theory of evolution.

 • Fossils happen to be the biggest of them. 

 • Fossils are the preserved remains of ancient animals or plants that died millions of years ago. 

 • The fossils help us understand the anatomy and even physiology of these organisms and understand how evolution worked and led to the formation of organisms that we see today. Formation of Fossils Fossils are important pieces of evolutionary evidence and are formed by the following steps: • Organisms die and they get buried in mud and silt. 

 • The soft tissues of the body get quickly leaving behind the hard bones or shells • Over time sediments build over it and harden into rock

 • As the bones decay, mineral seep in to replace the contents cell by cell, process called as petrification • If bones decay completely, it leaves behind the cast of the animal. 

   Evolutionary relationships:

  Evolutionary relationships of animals can be deduced by studying the homologous organs and analogous organs.

 Homologous organs are those which have a similar structure but different function.

 • Wings of birds and forelimbs of mammals: they have similar structure but are modified to suit different functions

 • A tendril of pea plant and spine of barberry plant: both are modified leaves, but perform different functions. 

 Analogous organs are those which have a similar function but a different structure and origin too.

 • Wings of bats, birds and wings of insects: both are used for flying, but structurally are very different 

 • Leaves of opuntia and peepal: both perform photosynthesis, but leaves of Opuntia are modified stem whereas peepal leaves are normal leaves. 

 • There are several stages in the evolution of almost every animal that we see today.

Human Evolution :\\

• Humans are known to belong to the primate family. 

 • Humans today have a very close genetic connection to chimps and other primates. 

 • While the complete evolutionary process of Humans from Primates is still a mystery, a larger picture of human evolution has been formed.

 • Some of the ancestors of Humans include Dryopithecus, Ramapithecus, Australopithecus, Homo erectus, Homo sapiens neanderthalensis, Cro-magnon man, and finally us, the Homo sapiens.

 • Human evolution traces back to Africa. Then they migrated all over the world.

NOTES PREPARED BY: KOMMOJU DURGA MOHAN

                                                                  (Dept.of.biology)

                                             e.mail:mohankommoju2003@gmail.com

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