CBSE Class 10 Science Chapter 8 How Do Organisms Reproduce Notes: Download PDF
Reproduction is the process by which all organisms multiply in number and increase their population.
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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.
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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.
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- Fission is an asexual reproduction that is common in most of the 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.
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- 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).
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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
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Organisms such as fungi make spores that can grow into complete new individuals when dispersed from their fruiting body.
- This is a type of asexual reproduction seen in plants.
- The 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.
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Types of Cell division
Two types of cell division seen in eukaryotic organisms:
- 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
- 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
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The Reproductive System
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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 hormone testosterone.
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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 mature 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.
- 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.
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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 fetal development and vagina receives sperms from the male.
- 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.
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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.
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Reproductive health deals with the prevention of STDs and unwanted pregnancy. Understanding the reproductive system is also a part of reproductive health awareness.
- 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.
- It is a very unreliable contraceptive method where the coitus is stopped before the male ejaculates inside the female reproductive tracts.
- Another unreliable method of contraception where coitus is avoided when the female is fertile and the chances of fertilization are very high.
- 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 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 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 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 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 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.
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Reproduction in Plants
Sexual reproduction in flowering plants
- Sexual reproduction in plants happens through 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 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 and gynoecium are called as essential/reproductive whorls of a flower.
- 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 a stamen and consists of anther and filament.
- Anther produces haploid pollen grains.
- Each individual member of gynoecium is called pistil and consists of stigma, style and ovary.
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.
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 fuses 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.
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