Quick Revision Notes & Formula Sheet

Class 10 Science - How do Organisms Reproduce?

Reproduction: The biological process by which living organisms produce new individuals similar to themselves. It is essential for the survival and continuity of a species on Earth.
DNA (Deoxyribonucleic Acid): The genetic material in the cell nucleus that carries information from parents to the next generation.
DNA Copying: The fundamental event in reproduction. It ensures that offspring receive body designs similar to their parents and is accompanied by the creation of additional cellular apparatus.
Variation: Differences in characters among individuals of the same species. Variations are essential for the survival of species during changing environmental conditions.

Organisms reproduce mainly by two methods:

Asexual Reproduction: Involves a single parent without the formation of gametes (sex cells). Offspring are genetically identical to the parent (clones).
Sexual Reproduction: Involves two parents (male and female) with the fusion of gametes to form a zygote. It produces large amounts of genetic variation.

Fission (खंडن):
- Binary Fission: Parent cell divides into two equal halves (e.g., Amoeba, Leishmania).
- Multiple Fission: Parent cell divides into many daughter cells simultaneously (e.g., Plasmodium - malaria parasite).
Fragmentation (खंड-खंड होना): The body breaks up into smaller pieces upon maturation, and each piece grows into a new individual (e.g., Spirogyra).
Regeneration (पुener भवन): The ability of a fully differentiated organism to give rise to new individual organisms from its body parts (e.g., Planaria, Hydra).
Budding (मुकुलन): A new organism develops as an outgrowth (bud) due to repeated cell division at one specific site (e.g., Hydra, Yeast).
Vegetative Propagation (कायिक प्रवर्धन): Methods of plant reproduction using vegetative parts like roots, stems, and leaves (e.g., Bryophyllum leaves, Potato tubers, Layering in jasmine, Grafting in mango).
- Tissue Culture: Growing new plants from a small piece of plant tissue or cells in a nutrient medium under sterile conditions.
Spore Formation (बीusan निर्माण): Tiny, blob-like structures called sporangia produce reproductive structures called spores, which develop into new individuals on the surface of bread, etc. (e.g., Rhizopus / Bread mould).

Parts of a Flower:
- Sepals: Green, leaf-like structures protecting the flower in the bud stage.
- Petals: Colored parts attracting insects for pollination.
- Stamen (Male reproductive organ): Consists of Anther (produces pollen grains) and Filament.
- Pistil / Carpels (Female reproductive organ): Consists of Stigma (sticky surface for pollen), Style (tube connecting stigma to ovary), and Ovary (contains ovules).
Pollination (परागण): Transfer of pollen grains from the anther to the stigma of a flower.
- Self-pollination: Transfer within the same flower or another flower of the same plant.
- Cross-pollination: Transfer from one plant's flower to the flower of another plant of the same species (via wind, water, or animals).
Fertilization Process:
1. Pollen grain lands on the stigma and germinates to form a pollen tube.
2. The pollen tube travels down the style into the ovary.
3. Male gamete fuses with the female gamete (egg cell) inside the ovule—a process called Syngamy or Fertilization.
4. Zygote is formed.
Post-Fertilization Changes:
- Zygote $\rightarrow$ Embryo
- Ovule $\rightarrow$ Seed
- Ovary $\rightarrow$ Fruit (Sepals and petals fall off).

Humans undergo sexual reproduction and exhibit sexual dimorphism. Puberty is the age at which reproductive organs become functional.

Testes (वृषण): Pair of oval organs located in the scrotum outside the abdominal cavity. They produce male gametes (sperm) and the hormone testosterone.
Scrotum: Maintains a lower temperature than body temperature necessary for sperm production.
Vas Deferens (शुक्र वाहिका): Duct that delivers sperm from testes to the urethra.
Urethra: Common passage for both sperms and urine.
Glands (Seminal vesicles & Prostate gland): Add secretions to sperms, providing nutrition and fluid medium for easy transport. This fluid plus sperm is called semen.

Ovaries (अंडाशय): Pair of primary female organs that produce female gametes (ova/eggs) and hormones like estrogen and progesterone. One egg is produced every month alternately by one of the ovaries.
Fallopian Tube (Oviduct): Tube that carries the egg from the ovary to the uterus; site of fertilization.
Uterus (गर्भाशय): Muscular, pear-shaped bag where the embryo develops.
Cervix & Vagina: Passage through which the baby is born.

Fertilization: Fusion of sperm and egg inside the Fallopian tube to form a zygote.
Implantation: The zygote divides to form an embryo, which gets embedded in the lining of the uterus.
Placenta: A special disc-like tissue embedded in the uterine wall that provides nutrition, glucose, and oxygen from the mother's blood to the embryo, and removes wastes.
Gestational Period: The time period from fertilization to birth (approx. 9 months in humans).
Menstruation (ऋतुस्राव / मासिक धर्म): If the egg is not fertilized, the thick and spongy lining of the uterus breaks down and comes out through the vagina as blood and mucus. Lasts for 2-8 days.

Reproductive Health: Total well-being in all aspects of reproduction (physical, emotional, social, and behavioural).
Sexually Transmitted Diseases (STDs): Diseases spread through sexual contact.
- Bacterial STDs: Gonorrhoea, Syphilis.
- Viral STDs: Warts, HIV-AIDS (Acquired Immuno Deficiency Syndrome).
Contraception (Methods of Birth Control): Prevention of pregnancy.
1. Barrier Methods: Condoms, diaphragms, cervical caps (prevent sperm from meeting the egg).
2. Chemical Methods: Oral pills (change hormonal balance), Spermicides.
3. Intra-Uterine Contraceptive Devices (IUCDs): Copper-T, loop placed in the uterus to prevent implantation.
4. Surgical Methods:
  - Vasectomy: Cutting/tying the vas deferens in males.
  - Tubectomy: Cutting/tying the fallopian tubes in females.
Female Foeticide: Illegal practice of aborting female foetuses, leading to a decline in the child sex ratio.