- Reproduction is the process by which living organisms produce new individuals similar to themselves. It ensures continuity of life on earth.
- Nucleus of the cell contains DNA (Deoxyribose Nucleic Acid) which is the heredity material.
- DNA replicates and forms new cells causing variation. So, these new cells will be similar but may not be identical to original cell.
- Variations are useful for the survival of the individual and species over time as well as basis for evolution.
Types of Reproduction
- A single individual give rise to new individual.
- Gametes are not formed.
- New individual is identical to parent.
- It is extremely useful as a means of rapid multiplication.
- Adopted by lower organisms.
- Two individuals i.e., one male and one female are needed to give rise to new individual.
- Gametes are formed.
- New individual is genetically similar but not identical to parents.
- It is useful to generate more variations in species.
- Adopted by higher organisms.
Modes of Asexual Reproduction
- The parent cell divides into daughter cells.
- Binary fission: 2 cells are formed. Example: amoeba.
- Multiple fission: Many cells are formed.
- The organism breaks-up into smaller pieces upon maturation, each piece develops into new individual. Example: Spirogyra.
- If organism is somehow cut or broken into many pieces, each piece grows into a complete organism. Example: Planaria, Hydra.
- A bud is formed which develops into tiny individual. It detaches from parent body upon maturation and develops into new individual. Example: Hydra
In many plants, new plants develops from vegetative parts such as:
- By roots: Example: dahlias, sweet potato.
- By stem: Example: potato, ginger.
- By leaves: Example: bryophyllum (leaf notches bear buds which develop into plants).
Artificial methods in Vegetative Propagation
(i) Grafting: Example: Mango
(ii) Cutting: Example: Rose
(iii) Layering: Example: Jasmine
(iv) Tissue culture: New plants are grown by using growing tip of a plant.
These growing cells are kept in a culture medium leads to the formation of callus. Callus is then transferred to hormone medium which causes growth and differentiation.
Example: ornamental plants, orchid.
Benefits of tissue culture
- We can grow plants like banana, rose, jasmine etc. that have lost the capacity to produce seeds.
- New plants are genetically similar to parents.
- Helps in growing seedless fruits.
(v) Spore Formation: Spores are small bulb like structures which are covered by thick walls. Under favourable conditions, they germinate and produce new organism.
- When reproduction takes place as a result of the fusion of male and female gametes is called sexual reproduction.
- Fusion of gametes is called fertilization which results in variation.
Sexual Reproduction in Plants
- Flowers are the reproductive organs of plants.
- A typical flower consists of four main whorls namely sepals, petals, stamen and pistil.
Types of Flowers
- Bisexual flower: Both male and female reproductive parts are present.
Example: Hibiscus, mustard.
- Unisexual flower: Either male or female reproductive part is present.
Example: Papaya, watermelon.
Structure of Flower
Process of Seed Formation
- Pollen grains, produced in the anther, are transferred to the stigma of same flower (self pollination) or stigma of another flower (cross pollination) through agents like air, water or animals.
- Pollen grains germinate and form pollen tubes which pass through style to reach upto the ovules present in ovary.
- The fusion of male and female gametes is called fertilization. Zygote is produced inside the ovary.
- Zygote divides to form embryo. Ovule develops thick coat and changes into seed gradually.
- Ovary changes into fruit and other parts of flower fall off.
- The seed germinates to form a plant under suitable conditions such as air, moisture etc.
Reproduction in Human Beings
- Humans use sexual mode of reproduction.
- Sexual maturation: The period of life when production of germ cells i.e. ova (female) and sperm (male) start in the body. This period of sexual maturation is called puberty.
Changes at Puberty
- Common in male and female
- Thick hair growth in armpits and genital area.
- Skin becomes oily, may result in pimples.
- In girls
- Breast size begin to increase.
- Girls begin to menstruate.
- In boys
- Thick hair growth on face.
- Voice begin to crack.
These changes signals that sexual maturity is taking place.
Male Reproductive System
- A pair of testes are located inside scrotum which is present outside the abdominal cavity.
- Scrotum has a relatively lower temperature needed for the production of sperms.
- Male germ cell i.e. sperms are formed here.
- Testes release male sex hormone (testosterone).
Function of testes:
- Regulate production of sperms.
- Bring changes at puberty.
(ii) Vas deferens
- It passes sperms from testes upto urethera.
- It is a common passage for both sperms and urine. Its outer covering is called penis.
(iv) Associated glands
- Seminal vesicles and prostate gland add their secretion to the sperms. This fluid provide nourishment to sperms and make their transport easy.
- Sperm along with secretion of glands form semen.
Female Reproductive System
- A pair of ovary is located in both sides of abdomen.
- Female germ cells i.e. eggs are produced here.
- At the time of birth of a girl, thousands of immature eggs are present in the ovary.
- At the onset of puberty, some of these eggs start maturing.
- One egg is produced every month by one of the ovaries.
(ii) Oviduct or Fallopian tube
- Receives the egg produced by the ovary and transfer it to the uterus.
- Fertilisation i.e. fusion of gametes takes place here.
- It is a bag-like structure where development of the baby takes place.
- Uterus opens into vagina through cervix.
Fertilisation of egg
- When egg is fertilised
- The fertilized egg called zygote is planted in uterus and develops into an embryo.
- The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. It provides a large surface area for the exchange of glucose, oxygen and waste material.
- The time period from fertilization upto the birth of the baby is called gestation period. It is about 9 months.
- When egg is not fertilised
- The uterus prepares itself every month to receive fertilized egg.
- The lining of the uterus becomes thick and spongy, required to support the embryo.
- When fertilisation had not taken place, this lining is not needed any longer.
- This lining breaks and comes out through vagina as blood and mucus.
- This cycle takes around 28 days every month and called menstruation.
- Reproductive health means a total well-being in all aspects of reproduction i.e. physical, emotional, social and behavioural.
Sexually Transmitted Diseases (STDs)
- Many diseases can be sexually transmitted such as:
(i) Bacterial: Gonorrhoea and syphilis
(ii) Viral: Warts and HIV-AIDS
- Use of condom prevents these infections to some extent.
- Contraception: It is the avoidance of pregnancy, can be achieved by preventing the fertilisation of ova.
Methods of contraception
(i) Physical barrier
- To prevent union of egg and sperm.
- Use of condoms, cervical caps and diaphragm.
(ii) Chemical methods
- Use of oral pills
- These change hormonal balance of body so that eggs are not released.
- May have side effects.
(iii) Intrauterine contraceptive device (IUCD)
- Copper-T or loop is placed in uterus to prevent pregnancy.
(iv) Surgical methods
- In males the vas deferens is blocked to prevent sperm transfer called vasectomy.
- In females, the fallopian tube is blocked to prevent egg transfer called tubectomy.
- The practice of killing a female child inside the womb is called female foeticide.
- For a healthy society, a balanced sex ratio is needed that can be achieved by educating people to avoid malpractices like female foeticide and prenatal sex determination.
- Prenatal sex determination is a legal offence in our country so as to maintain a balanced sex ratio.