Reproduction is the process by which living organisms produce new organisms of the same species. It is important because it maintains the continuity of life from one generation to the next.
Table of Contents
There are two main modes of reproduction:
- Asexual reproduction
- Sexual reproduction
Asexual Reproduction
Asexual reproduction is a rapid mode of reproduction in which only one parent is involved.
The new individuals produced are genetically identical to the parent. Such identical individuals are called clones.
Features Of Asexual Reproduction
- Only one parent is involved.
- Gamete formation does not occur.
- Fusion of gametes does not occur.
- Offspring are genetically identical to the parent.
- It is generally faster than sexual reproduction.
- Cells divide by mitosis or sporulation.
Types Of Asexual Reproduction
Asexual reproduction occurs through:
- Fission
- Fragmentation
- Regeneration
- Budding
- Spore formation
- Vegetative propagation
Fission
Fission is a type of asexual reproduction in which a unicellular organism splits to form two or more new individuals.
There are two main types of fission:
- Binary fission
- Multiple fission
Binary Fission
In binary fission, a single parent organism divides into two nearly equal-sized daughter cells.
Examples
- Amoeba
- Leishmania
- Paramecium
Multiple Fission
In multiple fission, the parent organism divides into many small daughter cells.
Example
- Plasmodium, the malarial parasite
Fragmentation
Fragmentation is a type of asexual reproduction in which the body of an organism breaks into fragments.
Each fragment develops into a complete organism.
Examples
- Spirogyra
- Algae
Regeneration
Regeneration is the ability of an organism to regrow lost body parts.
In some organisms, a complete organism may develop from a body fragment.
Examples
- Hydra
- Planaria
Budding
In budding, a small outgrowth called a bud arises from the parent body.
This bud grows and develops into a new individual.
Examples
- Hydra
- Yeast
Spore Formation
In many organisms, spores act as reproductive cells.
A spore can germinate and form a new colony.
Organisms Reproducing By Spores
- Algae
- Ferns
- Mosses
- Fungi such as Rhizopus
Types Of Spores
| Type Of Spore | Nature | Examples |
|---|---|---|
| Zoospores | Motile | Ulothrix, Oedogonium, Pythium, Albugo |
| Sporangiospores | Non-motile | Mucor, Rhizopus |
| Conidia | Non-motile | Penicillium, Aspergillus, Fusarium |
| Cysts | Thick covering | Vaucheria, Botrydium |
Vegetative Propagation
Vegetative propagation is a type of asexual reproduction in plants.
In this process, new plants develop from vegetative parts such as roots, stems or leaves.
Vegetative propagation is of two types:
- Natural vegetative propagation
- Artificial vegetative propagation
Natural Vegetative Propagation
In natural vegetative propagation, roots, stems or leaves act as reproductive structures.
Vegetative Propagation By Roots
In sweet potato, tuberous roots bear adventitious buds.
When these roots are planted in soil, they develop into new plants.
Example
- Sweet potato
Vegetative Propagation By Stems
In plants like grass and mint, new roots and shoots develop at nodes.
Their stems grow horizontally parallel to the ground.
Roots grow downward into the soil and shoots grow upward to form new plants.
Examples
- Grass
- Mint
Vegetative Propagation In Ginger
Ginger is a modified stem.
It has:
- Nodes
- Internodes
- Scaly leaves
- Axillary buds
The axillary buds present on nodes develop into new plants.
Vegetative Propagation By Leaves
In some plants, leaves produce buds along their margins.
When these leaves fall on moist soil, the buds develop into new plants.
Example
- Bryophyllum
Artificial Vegetative Propagation
Artificial vegetative propagation is done by humans for growing new plants.
It includes:
- Cuttings
- Grafting
- Layering
Cuttings
In this method, a part of the plant is cut and planted to grow into a new plant.
Types Of Cuttings
- Stem cuttings – sugarcane, rose, Bougainvillea
- Root cuttings – apple, lemon
- Leaf cuttings – Begonia
Grafting
In grafting, parts of two plants are joined so that they grow as one plant.
Examples
- Mango
- Guava
- Rubber
Layering
In layering, a branch is made to develop roots while still attached to the parent plant.
Example
- Jasmine
Sexual Reproduction
Sexual reproduction is the process of producing new individuals with the involvement of two parents.
It includes formation of gametes by meiosis and fusion of gametes during fertilisation.
Features Of Sexual Reproduction
- Usually involves two parents.
- Gametes are formed.
- Gametes fuse to form a zygote.
- It produces genetic variation.
- It helps organisms survive changing environmental conditions.
R. Camerarius was the first to describe sexual reproduction in plants.
Sexual Reproduction In Flowering Plants
In flowering plants, all events related to sexual reproduction take place in the flower.
The flower is the reproductive organ of plants.
Types Of Flowers
Bisexual Flower
A flower that contains both male and female reproductive organs is called a bisexual flower.
Unisexual Flower
A flower that contains only one type of reproductive organ, either male or female, is called a unisexual flower.
Neuter Flower
A flower in which both male and female reproductive organs are absent is called a neuter flower.
Structure Of A Bisexual Flower
A flower is a specialized shoot in which leaves are modified into floral structures.
The flower may be supported by a stalk called the pedicel.
A flower without a stalk is called sessile.
The enlarged tip of the stalk is called the receptacle or thalamus.
Four Floral Whorls
A typical bisexual flower has four whorls:
- Calyx
- Corolla
- Androecium
- Gynoecium
Calyx
Calyx is the first whorl.
It is made up of green sepals.
Corolla
Corolla is the second whorl.
It is made up of large and brightly coloured petals.
Androecium
Androecium is the third whorl.
It is the male reproductive part of the flower.
It consists of stamens.
Each stamen has:
- Filament
- Anther
The anther produces pollen grains, which contain male gametes.
Gynoecium
Gynoecium is the fourth whorl.
It is the female reproductive part of the flower.
It consists of the pistil.
The pistil may have one or more carpels.
Each carpel has:
- Stigma
- Style
- Ovary
Functions Of Carpel Parts
| Part | Function |
|---|---|
| Stigma | Receives pollen grains |
| Style | Connects stigma to ovary |
| Ovary | Contains ovules |
| Ovule | Develops into seed after fertilisation |
| Placenta | Attaches ovules to ovary wall |
Complete And Incomplete Flowers
A flower that contains all four whorls is called a complete flower.
A flower in which one or more whorls are absent is called an incomplete flower.
Pollination
Pollination is the transfer of pollen grains from the anther to the stigma.
Pollination is of two types:
- Self-pollination
- Cross-pollination
Self-Pollination
Self-pollination is the transfer of pollen grains from the anther to the stigma of the same flower or another flower of the same plant.
It commonly occurs in bisexual flowers and monoecious plants.
Cross-Pollination
Cross-pollination is the transfer of pollen grains from one plant to the stigma of a different plant of the same species.
Cross-pollination produces more variation.
Agents Of Pollination
Pollination may occur through abiotic or biotic agents.
Abiotic Agents
- Wind
- Water
Biotic Agents
- Insects
- Birds
- Bats
- Ants
- Snails
Types Of Pollination Based On Agent
| Type | Agent |
|---|---|
| Anemophily | Wind |
| Entomophily | Insects |
| Chiropterophily | Bats |
| Myrmecophily | Ants |
| Hydrophily | Water |
| Ornithophily | Birds |
| Malacophily | Snails |
Self-Incompatibility And Dichogamy
Plants may prevent self-pollination through special mechanisms.
This is called self-sterility or self-incompatibility.
Dichogamy
Dichogamy is a mechanism in which anthers and carpels mature at different times.
It is of two types:
- Protandry – anthers mature earlier
- Protogyny – carpels mature earlier
Fertilisation
Fertilisation is the fusion of male and female gametes.
Steps Of Fertilisation In Flowering Plants
- After pollination, pollen grains absorb water and swell on the stigma.
- Pollen grains germinate and form a pollen tube.
- Male gametes travel through the pollen tube.
- Male gametes reach the ovary and then the ovule.
- Fusion of gametes takes place.
Double Fertilisation
In flowering plants, fertilisation includes two fusions:
- Syngamy
- Triple fusion
Because two fusions occur, it is called double fertilisation.
Double fertilisation produces:
- Embryo
- Endosperm
The endosperm in angiosperms is triploid, or 3n.
In gymnosperms, endosperm is haploid, or n.
Post-Fertilisation Events
After fertilisation, the flower undergoes important changes.
- Ovary develops into fruit.
- Ovule develops into seed.
- Embryo develops inside the seed.
Polyembryony
Polyembryony is the formation of multiple embryos.
Example
- Citrus
Parthenocarpy
Parthenocarpy is the formation of fruit without fertilisation.
Such fruits are seedless.
Parthenogenesis
Parthenogenesis is the development of an embryo from an egg without fertilisation.
Vernalisation
Vernalisation is the process in which dormant seeds are exposed to low temperature to induce germination.
Vivipary
Vivipary is the germination of a seed inside the fruit while the fruit is still attached to the mother plant.
Human Reproductive System
Human reproduction is sexual reproduction.
It involves male and female reproductive systems, gamete formation, fertilisation, pregnancy and childbirth.
Male Reproductive System
The male reproductive system includes:
- Testes
- Seminiferous tubules
- Vas deferens
- Urethra
- Penis
- Accessory sex glands
Testes
Testes are a pair of glandular, oval-shaped organs present in the scrotum.
The temperature of the scrotum is about 2–3°C lower than body temperature.
This lower temperature is necessary for sperm formation.
Endocrine tissues of testes produce testosterone.
Seminiferous Tubules
Seminiferous tubules are the structural and functional units of the testes.
They contain spermatogenic cells, which produce sperm cells.
Important Cells In Testes
| Cell Type | Function |
|---|---|
| Sertoli cells | Provide nutrition to sperm cells |
| Leydig cells | Secrete testosterone |
Vas Deferens
Vas deferens are ducts extending from the epididymis to the ejaculatory ducts.
They temporarily store sperm and transport them during ejaculation.
Removal of vas deferens is called vasectomy.
Urethra
The urethra is a thick-walled muscular duct.
It acts as a common passage for urine and semen.
It is also called the urinogenital duct.
Penis
The penis is an erectile copulatory organ.
It helps deposit sperm into the female genital tract.
Accessory Sex Glands In Male
Male accessory sex glands include:
- Seminal vesicles
- Prostate gland
- Cowper’s glands
Seminal Vesicles
Seminal vesicles are located behind the urinary bladder.
They produce about 70% of seminal fluid.
The fluid contains:
- Fructose
- Citrate
- Inositol
- Prostaglandins
- Proteins
Fructose acts as an energy source for sperm.
The mixture of sperm and glandular secretions is called semen.
The pH of semen is about 7.4.
Prostate Gland
The prostate gland is located around the first part of the urethra.
It secretes a thin, milky fluid containing calcium, citrate ions, phosphate ions, enzymes and fibrinolysin.
Inflammation of the prostate gland causes prostatitis.
Cowper’s Glands
Cowper’s glands are also called bulbourethral glands.
Their secretion lubricates the penis and neutralises any urine present in the urethra.
Path Of Sperms In Mammals
The path of sperms is:
Seminiferous tubules → Rete testis → Vasa efferentia → Epididymis → Vas deferens → Urethra
Female Reproductive System
The female reproductive system includes:
- Ovaries
- Fallopian tubes
- Uterus
- Vagina
- Accessory sex glands
Ovaries
Ovaries are a pair of female reproductive organs present in the pelvic cavity.
They are the primary female sex organs.
Functions Of Ovaries
- Produce ova or eggs
- Secrete estrogen
- Secrete progesterone
Fallopian Tubes Or Oviducts
Fallopian tubes extend from the ovary to the uterus.
They conduct the egg and provide the usual site of fertilisation.
Removal of the fallopian tube is called tubectomy.
Uterus
The uterus is located above and behind the urinary bladder.
It is attached to the body wall by ligaments.
The wall of the uterus is made of smooth muscle called myometrium.
The inner lining is called endometrium.
The foetus develops inside the uterus and remains attached by the placenta.
Vagina
The vagina opens to the exterior between the urethra and anus.
It receives semen during mating.
It also acts as the birth canal during childbirth.
Accessory Sex Glands In Female
Female accessory sex glands include:
- Bartholin’s glands
- Mammary glands
Bartholin’s Glands
Bartholin’s glands are also called vestibular glands.
They help in vestibular lubrication.
They correspond to Cowper’s glands in males.
Mammary Glands
Mammary glands are modified sweat glands.
Milk production is stimulated by prolactin, secreted by the anterior pituitary gland.
Milk ejection is stimulated by oxytocin, secreted by the posterior pituitary gland.
Gametogenesis
Gametogenesis is the process of formation of gametes in the gonads.
It includes:
- Spermatogenesis
- Oogenesis
Spermatogenesis
Spermatogenesis is the formation of sperms.
Oogenesis
Oogenesis is the formation of ova or eggs.
Gametogenesis is controlled by gonadotropic hormones secreted by the pituitary gland.
Important hormones include:
- FSH
- LH
- ICSH
Menstrual Cycle
The menstrual cycle includes cyclic changes that occur in the uterus.
It repeats approximately every 28 days.
Phases Of Menstrual Cycle
- Menstrual phase
- Follicular phase or proliferative phase
- Ovulatory phase
- Luteal phase or secretory phase
Menstrual Phase
In this phase, the endometrium breaks down, resulting in discharge of blood.
It is regulated by:
- FSH
- LH
- Estrogen
- Progesterone
If fertilisation does not occur, the corpus luteum degenerates and progesterone level drops.
Follicular Phase
FSH stimulates ovarian follicles to secrete estrogen.
This phase lasts about 10–12 days.
During this phase, the endometrium rebuilds in preparation for pregnancy.
Ovulatory Phase
Ovulation is the release of ovum from the Graafian follicle.
It occurs around the 14th day of the menstrual cycle.
It occurs under the influence of LH.
This phase is critical for fertilisation.
Luteal Phase
The corpus luteum forms and secretes progesterone.
Progesterone maintains the endometrium.
This phase lasts about 12–14 days.
If fertilisation does not occur, the corpus luteum degenerates and the next menstrual cycle begins.
The menstrual cycle and menstruation temporarily stop during pregnancy and lactation.
Menopause
Menopause is the stage when ovulation and menstrual cycle stop permanently.
It usually occurs between 45–50 years of age.
At this stage, women lose the ability to reproduce.
Key Takeaways
- Reproduction maintains continuity of species.
- Asexual reproduction is rapid and produces genetically identical offspring.
- Sexual reproduction produces variation and helps organisms adapt to changing environments.
- Vegetative propagation is common in plants and may occur through roots, stems or leaves.
- Pollination is necessary before fertilisation in flowering plants.
- Double fertilisation produces embryo and endosperm in angiosperms.
- In humans, testes produce sperms and testosterone.
- Ovaries produce ova, estrogen and progesterone.
- The fallopian tube is the common site of fertilisation.
- The menstrual cycle prepares the uterus for pregnancy.
FAQs On Reproduction In Organisms
What is reproduction?
Reproduction is the process by which organisms produce new individuals of the same species.
What are the two main types of reproduction?
The two main types are asexual reproduction and sexual reproduction.
What is asexual reproduction?
Asexual reproduction is a type of reproduction in which only one parent is involved and offspring are genetically identical to the parent.
What are clones?
Clones are genetically identical individuals produced through asexual reproduction.
What is binary fission?
Binary fission is a type of asexual reproduction in which one parent cell divides into two daughter cells.
Which organism reproduces by multiple fission?
Plasmodium reproduces by multiple fission.
What is budding?
Budding is a type of asexual reproduction in which a small bud grows from the parent body and develops into a new individual.
What is vegetative propagation?
Vegetative propagation is a type of asexual reproduction in plants where new plants develop from roots, stems or leaves.
Which plant reproduces through leaves?
Bryophyllum reproduces through leaves.
What is pollination?
Pollination is the transfer of pollen grains from the anther to the stigma.
What is cross-pollination?
Cross-pollination is the transfer of pollen grains from one plant to the stigma of another plant of the same species.
What is double fertilisation?
Double fertilisation is a process in flowering plants where two fusions occur: syngamy and triple fusion.
What does the ovary become after fertilisation?
The ovary develops into a fruit.
What does the ovule become after fertilisation?
The ovule develops into a seed.
What is the function of testes?
Testes produce sperm cells and testosterone.
What is the function of ovaries?
Ovaries produce ova and hormones such as estrogen and progesterone.
Where does fertilisation usually occur in humans?
Fertilisation usually occurs in the fallopian tube.
What is the menstrual cycle?
The menstrual cycle is a series of cyclic changes in the uterus that repeats approximately every 28 days.
Which hormone causes ovulation?
LH, or Luteinizing Hormone, causes ovulation.
What is menopause?
Menopause is the permanent stoppage of ovulation and menstrual cycle, usually occurring between 45–50 years of age.
Last Moment Exam Cheat Sheet – Reproduction In Organisms
- Reproduction produces new organisms of the same species.
- Asexual reproduction involves one parent.
- Asexual reproduction produces clones.
- Binary fission occurs in Amoeba, Leishmania and Paramecium.
- Multiple fission occurs in Plasmodium.
- Fragmentation occurs in Spirogyra.
- Budding occurs in Hydra and yeast.
- Spore formation occurs in Rhizopus.
- Bryophyllum reproduces by leaves.
- Ginger reproduces by rhizome.
- Sweet potato reproduces by tuberous roots.
- Pollination is the transfer of pollen grains from anther to stigma.
- Anemophily means pollination by wind.
- Entomophily means pollination by insects.
- Hydrophily means pollination by water.
- Double fertilisation is found in flowering plants.
- Ovary develops into fruit.
- Ovule develops into seed.
- Endosperm in angiosperms is triploid.
- Testes produce testosterone.
- Seminiferous tubules produce sperm cells.
- Vasectomy is removal of vas deferens.
- Tubectomy is removal of fallopian tube.
- Fallopian tube is the usual site of fertilisation.
- Menstrual cycle occurs approximately every 28 days.
- Ovulation occurs around the 14th day under the influence of LH.
- Prolactin stimulates milk production.
- Oxytocin stimulates milk ejection.
- Menopause usually occurs between 45–50 years.