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How Do Organisms Reproduce?
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 organism, some multicellular organism and few plants.
Sexual reproduction
The mode of reproduction that 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 of the unicellular organism.
-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
Spore formation
Organisms such as fungi make spores that can grow into completely new individuals when dispersed from their fruiting body.
Vegetative propagation
- This is a type of asexual reproduction seen in plants.
-Vegetative part of the plant, like leaves, stem, roots, gives 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.
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 male sex
Tesis
Male main reproductive organs:
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 matured in
the epididymis. -Leydig cells or interstitial cells present in between the seminiferous tubules
secrete hormone testosterone.
Male accessory reproductive organs
-Several accessory reproductive organs that aid in the reproductive
process. -The prostate gland and the seminal vesicles are glands of reproductive system which make semen and nourish the sperms.
- Penis, having urethra passing through it, is called copulatory organ. Male Ducts
- In males, the vas deferens and the urethra are the main ducts.
- A single vas deferens carries sperms from respective testis up to urethra.
-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 main 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
-Uterus and vagina are the accessory reproductive organs in human females.
-The uterus is the site of foetal development and vagina receives sperms from the male.
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 being 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 the reproductive health awareness.
Contraceptives
- Contraceptives are the 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.
Coltus 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 where the coitus is avoided when
the female is fertile and the chances of fertilization are very high.
Condoms
One of the most effective 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 track and thus prevents 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 prevents a successful implantation even if the egg gets fertilized.
Uid
-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
Sexual reproduction in flowering plants
- Sexual reproduction in plants happens through the flowers.
- Essential whorls of the flowers such as androecium and the gynoecium help in the sexual reproduction of plants.
Non-essential parts of flowers
-The typical structure of flower contains essential whorls and non-essential whorls.
-Sepals and Petals are called as 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
Essential whorls of flowers
Androecium produces pollen grains containing male gametes and gynoecium produces ovules which are female gametes.
- Bisexual flowers contain both the whorls while unisexual flowers contain either of them.
-Each individual member of androecium is called as stamen and consists of anther and filament.
-Anther produces haploid pallen grains.
- Each individual member of gynoecium is called as pistil and consists of stigma, style and ovary.
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, 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 pistil and generate two male nuclei.
Ovule has egg cell and two polar nuclei.
One male nucleus fuse with two polar nuclei and forms 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, ovary becomes fruit and ovules turn into seeds. All other parts wither away.
the pores grad
The powrune ce prow eve. The gen