Reproduction: Reproduction is the process by which living organisms produce new individuals of the same species. Reproduction is necessary for the survival and increase in the population of a species. If organisms do not reproduce, their population decreases and species will become extinct.
Significance of Reproduction:
1. It allows continuity of of a species generation after generation.
2.It plays an important role in evolution by transmitting favorable variations from one generation to another generation.
Body design of organisms:
•Organisms look similar because their body design are similar.
•Reproduction at its most basic level involves making copy of the blue print of body design.
•DNA in the cell nucleus is the information source for making protein and different proteins lead to different body design.
•A basic level of reproduction is the creation of a DNA copy.
•DNA copy is accompanied by a cell division giving rise to two cells.
•DNA copying always involves some variation, hence DNA copies generated are similar but not identical. This tendency of variation during reproduction leads to evolution.
The importance of variation:
DNA copying during reproduction is important for maintaining the body designs of different organisms to survive in the existing environment. But the environment is constantly changing due to changes in temperature, climate, water levels etc. If organisms cannot adjust themselves to the changes in the environment then their species will become extinct.
If there are variations in some individuals of a species they may be able to survive the changes in the environment.
So variations in species is necessary for the survival of different species and for the evolution of new species.
NCERT INTEXT QUESTION
Q1. What is the importance of DNA copying in reproduction?
Ans: The importance of DNA copying during reproduction is that:
(i) It is responsible for the transmission of parental characteristic to its offsprings.
(ii) It also leads to certain genetic variation.
Q2. Why is variation beneficial to the species but not necessarily for the individual?
Ans: Variations allow organisms to exist in diverse habitats or niches. In the absence of variations, a species may be restricted to particular area. If this area gets drastically altered, due to various natural or man-made causes, the species may be wiped out. However, if some variations were present in a few individuals, these colonize other habitats and could survive. But if variations are present in a single organism there would be very little for it to survive.
Types of reproduction:
There are two main types of reproduction in living organisms.
- Asexual Reproduction and
- Sexual Reproduction.
Asexual reproduction: The types of reproduction in which new individuals are produced from a single parent is known as asexual reproduction.
Sexual reproduction: The type of reproduction in which two individuals are involved to produce a new individual is known as sexual reproduction.
Modes of Asexual reproduction:
• There are 7 different modes of asexual reproduction. Different living organisms adopte different modes of reproduction on the basis of their body design. The 7 different modes of asexual reproduction are as follows:
- Fission
- Fragmentation
- Regeneration
- Budding
- Vegetative Propagation
- Tissue Culture
- Spore Formation
1.Fission: Fission is an asexual modes of reproduction by which a unicellular organism divides and forms two or more new individuals.
- Binary Fission and
- Multiple Fission
2.Fragmentation: In this method the body of a simple multicellular organism breaks up into smaller pieces on maturation and each fragment develops into new individuals.
Eg: Spirogyra, Flatworm.
3.Regeneration: It is the ability of a fully differentiated organisms to give rise to new individual organisms from its body part. The body part which contain a specialised cell grow or regenerate into separate individuals.
Eg: Hydra, Planaria, Star fish etc.
4.Budding: In this method, a bud like projection is formed on the body of the organism. The bud then develops into a new individual. It then separates from the parent and forms an independent individual.
Eg:- Hydra, Yeast etc.
5.Vegetative propagation: In this method new plants are produced from the vegetative parts of the plant like root, stem or leaves without the help of any reproductive organs.It may be natural or artificial method.
•Natural vegetative propagation can be done by roots, by stems, and by leaves.
••By Roots: Dahalia, Sweet potato.
••By stems: Ginger(Rhizome), Potato(Tuber),Onion(Bulb)
••By leaves: Bryophyllum
•Artificial Vegetative Propagation can be done by cutting, layering and grafting etc
••Cutting - Rose, Chrysanthemum, Grapes etc.
••Layering - Lemon, Guava, Hibiscus, Bougainvillea, Jasmine, Raspberry, Strawberry etc.
••Grafting – This method is applied to improve variety of fruits like mango, apples, peas.
i. Plants takes less time to grow.
ii. It also helps in the propagation of plants which do not produce seeds like rose, jasmine banana or produce seed with prolonged period of dormancy.
i. There is no genetic variation, so there is less adaptability to the environment.
ii. The disease of the parent plants get transferred to the offspring.
iii. New characters can neither be introduced nor undesirable characters be eliminated.
6.Tissue Culture: In this method new plants are grown by removing tissues or cells from the growing tip of a plant. In this technique, cells are induced to divide artificially by chemicals(Cytokinin) to form a group of cells called ''callus''. Now the callus is transferred to another medium containing hormones for growth and differentiation. The plantlets are now placed in soil, so that it can grow into mature plants.
Note: This technique is commonly used for ornamental plants.
7.Spore formation: In this method structures called sporangia produce tiny cells called spores. When the spores come in contact with a moist surface, it develops into new individuals.
Eg :- Rhizopus(Bread mould) , Mucor, Penicillium etc.
The characteristics of Asexual Reproduction are as follows:
1. Only one individual of an organism is involved.
2. The new individual produced are genetically identical to their parents.
3. It presents a rapid mode of multiplication.
Advantages of Asexual Reproduction
1. Plants takes less time to grow.
2. It also helps in the propagation of plants which do not produce seeds like rose, jasmine banana or produce seed with prolonged period of dormancy.
3. It helps to preserve parental characters.
Disadvantages of Asexual Reproduction:
1. There is no genetic variation, so there is less adaptability to the environment.
2. The disease of the parent plants get transferred to the offspring.
3. New characters can neither be introduced nor undesirable characters be eliminated.
NCERT INTEXT QUESTIONS
Q1. How does binary fission differ from multiple fission?Ans:Q2. How will an organism be benefited if it reproduces through spores?
Ans: Spores are tiny, spherical, asexual reproductive bodies which under favourable conditions, like damp and warm conditions, germinate to produce new plants. They are covered by the hard protective wall, which enables the plant to survive unfavourable conditions.
Q3. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Ans: Multicellular organisms cannot reproduce by cell because they are not simple random collection of cells. In them, specialised cells are organized as tissues and tissues are organised into organs, which then have to be kept at different positions in the body. Cell-by-cell division would be impractical. Multicellular organisms, therefore, require to use more complex ways of reproduction.Moreover, simple multicellular organisms possess special type of tissues which have the potential to grow into a new organism but complex multicellular organisms have no such specialised cells.
Q4. Why is vegetative propagation practised for growing some types of plants?
Ans: Vegetative propagation method is used for growing certain plants which do not produce viable seeds. It is also used for growing of plants bearing superior traits, because they produce genetically identical plants. It is also used for growing plants which require longer time to grow and become mature. Plant which require lot of care during early stages of development are also grown by this method.
Q5. Why is DNA copying an essential part of the process of reproduction?
Ans: Chromosome in the nucleus of a cell contain information for inheritance of features from parent to next generation in the form of DNA. The DNA in the cell nucleus is the information source of making proteins. Therefore, a basic event in reproduction is creation of DNA copy for the next generation.
SEXUAL REPRODUCTION
•Sexual Reproduction: The process of producing new organisms from two parents by making use of their sex cells or gametes is known as sexual reproduction.
Eg: human, fish, dogs, cats and most of the flowering plants.
•Thus the two major process i.e. formation of gametes and fusion of gametes constitutes sexual reproduction.
•Two sexes namely Male( producing male gamete called Sperm) and Female (producing female gamete called Ova) are involved.
Significance of sexual reproduction:
1. It promotes variation and thus promotes diversity of characters in the offspring's.
2. It plays a prominent role in the origin of new species.
Sexual Reproduction in Flowering Plants:
a) Reproductive parts of a flower: The stamen and pistil are the reproductive parts of the flower. Stamen is the male reproductive part. It produces pollen grains in the anther which contains the male germ cell (male gamete). Pistil is the female reproductive part. It produces ovules in the ovary which contain the female germ cell (female gamete).
b) Pollination: The transfer of pollen grains from the anther to the stigma of a flower is called pollination. It takes place by wind(Anemophily), water (Hydrophily), insects(Entomophily) , Animals (Zoophily), Birds (Ornithophily) or Bat (Chiropterophily).
Types of POLLINATION
POLLINATION is of two types:
- Self Pollination
- Cross Pollination
Self pollination: If the pollen grains are transferred from the anther to the stigma of the same flower it is called self pollination. E.g.- Pea, Wheat, Rice, China-rose etc. It can further be of two types:
i) Autogamy: If the transfer of pollen grains from anther of a flower to the stigma of the same flower is called autogamy.
ii) Geitonogamy:- when pollen from one flower transferred over the stigma of another flower borne on the same plant is called Geitonogamy.
Advantages of self pollination:
1. Ensure continuity of a race.
2. It helps to preserve parental characters as the gametes from the same flower is involved.
3. It is not necessary for flower to produce nectar or sent or be colourful.
Disadvantages of self pollination:
1. New verities cannot be obtained.
2. The genetic defects of the breed cannot b removed.
3. Repeated self pollination leads to loss of vigour & vitality of the species.
CROSS POLLINATION: The transfer of pollen grains from the anther of one flower to the stigma of another flower born on other plant of the same species is known as cross pollination.
Advantages of cross pollination:
1. It result in healthier offspring.
2. Seeds produced have much better germinating capacity.
3. More abundent and viable seeds are produced.
4. Variations are introduced by cross pollination.
Disadvantages of cross pollination:
1. Plants have to depend on external agencies for pollination.
2. The pollen grain have to be produced in large quantity to ensure pollination.
c) Fertilisation: After the pollen grain is transferred to the stigma it produces a pollen tube which passes through the style and enters the ovary and ovule. In the ovule the male germ cell (male gamete) fuses with the female germ cell (female gamete) to form a zygote. This process is called fertilisation.After fertilisation the zygote divides several times and forms the embryo which then develops into the seed and the ovary develops into the fruit.
d) Germination: It is the initial stage in the growth of a seed to develop into a seedling under appropriate conditions.
Sexual Reproduction in Human Being:
•Reproduction in human Being is the sexual reproduction involving male reproductive organ and female reproductive organ.
•The reproductive organs of human being i.e. Testis in male and ovary in female become functional only after attaining sexual maturity. In male, sexual maturity is attended at the age of 13-14 years while in female at the age of 10-12 years. This is known as the age of puberty.
SEXUAL MATURITY IN HUMAN BEING:
Various changes takes place in human body at the time of sexual maturity.
Changes common in both boys and girls:-
1) Thick hair growth in armpits & genital area between the thigh (also called Pubic region).
2) Thinner hair on legs, arms and faces.
3) Oily skin and appearance of pimples.
Changes different in boys and girls:
In Girls:
1) Breast size begin to increase.
2) Darkening of the nipple skin.
3) Start of menstruation.
In Boys:
1) Thick facial hair growth.
2) Voice begin to crack.
3) Penis occasionally begin to erect and enlarged followed by night flow.
PUBERTY: It is the age at which the sex hormone or gametes begin to be produced and the boy and girls becomes sexually mature.
Human Reproductive System and it's organ
Male reproductive system:
Male reproductive system consists of two portions-one that produces germ cell and the other that deliver the germ cell to the site of fertilisation. The human male reproductive systems consists of the following organs:
1) Testes(Single- Testis): Testes are one pair lies in a small sac-like structure outside the abdominal cavity called scrotum.
•Function: The function of testes is to produce Sperm and male sex hormone called Testosterone.
•The scrotum decreases the inside temperature by 2 degree centigrade. Thus it provides the optimal temperature for formation of sperms.
2) Epididymis: Epididymis is coiled tube-like structure firmly attached to the testis.
•Function: The function of epididymis is to serves as storehouse of the sperms. Inside the epididymis the sperm become mature and develop motility.
3) Vas-deferens: The sperms are carried by a long tube called vas-deferens or sperm duct into organs called seminal vesicles, where the sperm got nourished and stored.
4) Urethra: Urethra is a common duct for the passage of both urine and spermatic fluid. Urethra carries the sperm to an organ called penis which opens outside through a male genital pore.
5) Penis: The penis forms the external male genital organ. It is copulatory organ with thick muscular wall.
ACCESSORY GLAND:
1) Seminal vesicles: are a pair of thin walled muscular elongated sac which secrete fluid for nourishment of sperms.
2) Prostate gland: also produce fluid which is released in the urethra along with secretion of seminal vesicles.
3) Bulbo-urethral gland/Couper‟s gland: are one pair secrete watery alkaline fluid which neutralise acidic urethra and lubricate the urethra for passage of semen.
SEMEN: the fluid ejaculated through penis during sexual intercourse (3-4ml / ejaculation).
Semen = Seminal fluid + Sperm
Seminal fluid: is secretion of seminal vesicles, prostate and couper's gland.
Function:
1) Provide nutrition and activation of sperm.
2) Neutralise the acidic urethra .
3) Lubrication of urethra and female genitalia to facilitate sexual intercourse.
SPERM: 20-200 million /ml or 300-600 million/ejaculation
• Increased number of sperm cells in the semen increases sperm
competitiveness and should not be considered as biological wastage.
• Life span: 24-48 hours in female genitalia
Female reproductive system:
The human female reproductive system consists of the following organs:
1) ovaries: are one pair located in the abdominal cavity near the kidney. Ovaries are the female primary reproductive organ which perform dual function, the production of female gamete or ovum and the secretion of female sex hormone - Oestrogen & Progesterone.
2) Fallopian tube: are one pair long convoluted tubes that carry ova/egg from the ovary to the uterus. These tubes open into an elastic bag-like structure, the uterus.
3) Uterus/Womb: it is a hollow organ within which embryo develops. Its upper portion is broader, while its lower portion is narrower, called cervix.
4) Vegina: is long (about 8cm) & tubular muscular structure receiving the cervix of the uterus. It is also called “birth canal”. It receives sperms from the male and also serve as the passage through which fully developed foetus is born.
Bio-Mechanism of sexual Reproduction in Human Being.
•The sperm is introduced inside the female vagina through the penis by the process of copulation or mating. Fertilisation occurs in the fallopian tube.
•Sperms are highly active & mobile which move up through cervix into the uterus and then pass into the fallopian tubes.
•In the fallopian tube only one sperm fertilises the ovum to form zygote. This is called fertilisation.(Fertilisation occurs only if copulation takes place during the ovulatory period). The embryo development of the zygote starts immediately in the fallopian tube and pregnancy starts while menstruation stops.
•From fallopian tub, the embryo moves down to reach the uterus. The embryo get embedded in the thick inner lining of the uterus (process is called Implantation). Then a special tissues develops between the uterine Wall and the embryo (foetus) called Placenta, through which the exchange of nutrients ( like glucose), oxygen and waste products take place between the foetus and the mother.
•The time period from the development of foetus inside the uterus till birth is called Gestation period. It is approximately 9 months in human.
•At the end of gestation period the female give birth of the fully developed foetus (The act of giving birth is termed as Parturition).
What happens when ovum is not fertilized:
•Menstrual Cycle( Reproductive cycle/ Sexual Cycle): Menstrual Cycle represent cyclic changes in the reproductive system of female. It begins with menstruation.
Menstruation: The breakdown and removal of the inner thick and soft lining of the uterus along with blood vessels in the form of vaginal bleeding is called menstruation / menstrual flow.
•MENARCHE: The first menstruation which occurs at the age of 11-12 years is called MENARCHE.
•MENOPAUSE: The last menstruation which occurs at the age of 45 years marks the end of the reproductive period is called MENOPAUSE.
REPRODUCTIVE HEALTH
Reproductive Health: A total we'll being in all aspects of reproduction i.e. physical, emotional, social and behavioral is known as reproductive health.
STDs(Sexually Transmitted Disease): Sexually transmitted diseases are the disease which are spread by sexual contact from an infected person to a healthy person. They are caused by various microorganisms that live in worm and moist environments of the vagina, urethra, anus and mouth. Some of the common STDs are:
1. Gonorrhoea: It is caused by bacterium – Neisseria gonorrhoea.
It is characterised by inflammation of urinogenital tract and the patient feels burning sensation during urination. This bacteria infects the Ureters in men and Cervix in Women.
2. Syphilis: It is caused by bacterium - Treponema Palladium. It is characterized by lesions in the mucous membrane of urinogenital tract.
3. Trichomoniasis: It is caused by Protozoan - Trichomonas vaginalis.
It is characterized by some vaginal discharge at the urino genital tract of the female.
4. AIDS(Acquired Immune Deficiency Syndrome): It is caused by virus called HIV (Human Immune Virus) which suppresses the body's immune system and thereby making it susceptible to any disease.
Modes of transmission of AIDS:
- By having Sexual contact with an infected person.
- By the transfusion of blood from an infected person.
- Through infected needles used for injection.
- Through the placenta from the mother to child during pregnancy.
Contraception
Contraception: The avoidance of pregnancy which is achieved by preventing the fertilisation of ova us known as contraception.
METHODS TO AVOID PREGNANCY(Contraception)
Mechanical Barrier method: In this method physical devices such as condoms, diaphragm & cervical caps are used. These devices prevent the entry of sperm in the female genital tract during copulation. Thus acting as mechanical barrier between them.
Chemical methods: In these methods, specific drugs are used by females which are of two types-
- oral pills
- Vaginal pills.
Oral pills(oral contraceptive Ocs): It contains Progesteron hormone mainly which stops the ovary from releasing ovum into the fallopian tube by changing the hormonal balance of the body.
IUCD.(Intrauterine Contraceptive Devices): Copper-T (Placed safely inside the uterus by a doctor) It prevents implantation of embryo in the uterus.
SURGICAL METHOD: In this method, a small portion of vas deferens in male and the fallopian tube in female is surgically removed or tied. It is called VASECTOMY in males and TUBECTOMY in females.
