Reproduction - Class 10 Science

Cheatsheet Content

1. Introduction to Reproduction Definition: Reproduction is the fundamental biological process by which new individual organisms – "offspring" – are produced from their "parents". It is a fundamental feature of all known life. Significance: Perpetuation of Species: Ensures the continuity of life on Earth, preventing extinction. Replacement of Old/Dead Individuals: Maintains the population balance within an ecosystem. Introduction of Variations: Sexual reproduction introduces genetic variations, which are raw materials for evolution. Types: Broadly categorized into Asexual and Sexual reproduction, based on the number of parents and involvement of gametes. 2. Asexual Reproduction (NCERT Page 128) Definition: A mode of reproduction in which a new offspring is produced by a single parent without the involvement of gametes (sex cells) or fertilization. Characteristics: Monoparental: Only one parent is involved in producing offspring. No Gamete Formation/Fusion: Gametes are neither formed nor fused. Genetically Identical Offspring: Offspring are exact genetic copies (clones) of the parent due to mitotic cell division. Rapid Multiplication: Allows for quick increase in population numbers. No Variation: Generally doesn't introduce genetic variation, making populations vulnerable to environmental changes. Methods: a. Fission (NCERT Page 128) Binary Fission: The parent organism divides into two approximately equal-sized daughter organisms. Amoeba: Irregular shape, division plane can be any direction. Nucleus divides first (karyokinesis), followed by cytoplasm (cytokinesis). (PYQ: Draw binary fission in Amoeba). Paramecium: Slipper-shaped, divides transversely. Leishmania: Causes Kala-azar. Elongated body with a whip-like flagellum. Divides longitudinally, meaning the division plane is specific and parallel to the flagellum. (PYQ: Differentiate between binary fission in Amoeba and Leishmania). Multiple Fission: The parent organism divides into many daughter organisms simultaneously. Plasmodium (Malarial parasite): During unfavorable conditions, the parent cell forms a protective cyst wall. Inside the cyst, the nucleus divides repeatedly to form many nuclei, each surrounded by a small amount of cytoplasm. When conditions are favorable, the cyst wall breaks, releasing numerous daughter cells. b. Fragmentation (NCERT Page 129) The body of the parent organism breaks into two or more fragments, and each fragment develops into a complete new individual. Example: Spirogyra (a filamentous green alga). Its long filamentous body simply breaks into smaller pieces, and each piece grows into a new filament. Limitation: This is not applicable to all multicellular organisms. Complex multicellular organisms have highly organized tissues, organs, and organ systems. They cannot simply divide into fragments and grow into new individuals because their specialized cells and tissues cannot differentiate and reorganize to form a complete organism. c. Regeneration (NCERT Page 129) The ability of an organism to regrow lost body parts (e.g., lizard's tail) or to develop an entire new organism from a small cut piece of the body. Examples: Hydra, Planaria (flatworm). If Planaria is cut into several pieces, each piece can regenerate into a complete new Planaria. Mechanism: Specialized cells in these organisms proliferate and differentiate to form new tissues and organs. Distinction from Reproduction: While some organisms like Planaria use regeneration as a form of reproduction, it's primarily a repair mechanism. Not all organisms that regenerate parts can reproduce this way. (PYQ: Is regeneration same as reproduction? Explain with an example). d. Budding (NCERT Page 130) A small outgrowth or bud develops on the parent body due to repeated cell division at one site. This bud matures, detaches from the parent body, and develops into a new independent individual. Example: Hydra (a simple invertebrate). A bud forms, develops mouth and tentacles, and then detaches. Example: Yeast (a unicellular fungus). A small bud forms and detaches, or sometimes remains attached forming a chain of cells. e. Spore Formation (NCERT Page 130) Organisms produce numerous microscopic, asexual reproductive units called spores. These spores are typically covered by thick protective walls (cysts) that enable them to survive unfavorable conditions (like drought or high temperature). Example: Rhizopus (bread mould). It produces sporangia (spore-producing structures) which contain numerous spores. When the sporangium bursts, spores are released into the air. If they land on a moist, nutrient-rich surface, they germinate and grow into new fungal hyphae. (PYQ: Explain spore formation in Rhizopus). f. Vegetative Propagation (NCERT Page 131) A type of asexual reproduction in plants where new plants are produced from the vegetative parts (root, stem, leaves) of the parent plant, rather than from seeds. Natural Methods: By Stem: Rhizome: Underground stems (e.g., Ginger, Turmeric). Tuber: Swollen underground stems with 'eyes' (buds) (e.g., Potato). Bulb: Short, modified underground stem with fleshy leaves (e.g., Onion, Garlic). Runner/Stolon: Horizontal stems growing above ground (e.g., Grass, Strawberry). By Root: Adventitious buds on roots can give rise to new plants (e.g., Sweet potato, Dahlia, Guava). By Leaves: Leaves with adventitious buds can produce new plants (e.g., Bryophyllum leaf, Kalanchoe). Artificial Methods: Used in agriculture and horticulture to produce desired varieties quickly. Cutting: A piece of stem, root, or leaf is cut and planted in soil, where it develops roots and shoots (e.g., Rose, Sugarcane, Bougainvillea). Layering: A branch of the parent plant is bent and covered with soil while still attached to the parent. Roots develop from the covered part, and then it is cut and grown as a new plant (e.g., Jasmine, Lemon). Grafting: Two plants are joined together so that they grow as one. The scion (a shoot part of one plant) is attached to the stock (the rooted part of another plant). This combines desirable traits of both plants (e.g., Mango, Apple, Rose). Tissue Culture (Micropropagation) (NCERT Page 131): Growing new plants from a small piece of plant tissue or cells (explants) in a sterile, nutrient-rich culture medium under controlled conditions. Advantages: Produces genetically identical plants (clones). Can produce a large number of plants in a short time. Helps in growing disease-free plants. Useful for propagating plants that produce infertile seeds or have poor viability (e.g., orchids, banana). Helps in the conservation of rare and endangered plant species. Advantages of Vegetative Propagation (NCERT Page 131): Plants can bear flowers and fruits much earlier than those grown from seeds. It allows the propagation of plants that have lost the capacity to produce seeds (e.g., banana, orange, rose, jasmine). All plants produced are genetically identical to the parent plant, preserving desirable traits (e.g., fruit quality, disease resistance). Economically beneficial for commercial cultivation of certain crops. 3. Sexual Reproduction (NCERT Page 132) Definition: A mode of reproduction involving the fusion of male and female gametes (sex cells), which are usually produced by two different parents (or sometimes by the same parent, e.g., bisexual flowers). Characteristics: Biparental (mostly): Typically involves two parents (male and female). Gamete Formation & Fusion: Specialized reproductive cells (gametes) are formed and then fuse during fertilization. Genetically Diverse Offspring: Offspring are genetically distinct from both parents, exhibiting variations due to the recombination of genetic material from two parents. Slower Process: Generally takes more time and energy compared to asexual reproduction. Significance: Genetic Variation: The most important advantage. It leads to new combinations of genes, enhancing the chances of survival of the species in changing environments. Evolution: Variations are the raw material for evolution, allowing species to adapt and evolve over time. 4. Sexual Reproduction in Flowering Plants (NCERT Page 132) Flower Structure (NCERT Page 132-133): The flower is the reproductive organ of angiosperms (flowering plants). Calyx: Outermost whorl, composed of sepals (green, leaf-like structures that protect the flower bud). Corolla: Whorl inside the calyx, composed of petals (often brightly coloured and scented to attract pollinators). Androecium (Male Reproductive Part): Composed of stamens. Stamen: Consists of two parts: Anther: A bilobed structure that produces and contains pollen grains. Pollen grains contain the male gametes. Filament: A slender stalk that supports the anther. Gynoecium/Pistil/Carpel (Female Reproductive Part): Innermost whorl, composed of one or more carpels. Pistil: Consists of three parts: Stigma: The sticky, receptive tip that receives pollen grains. Style: A slender stalk connecting the stigma to the ovary. Ovary: The swollen basal part containing ovules. Each ovule contains an egg cell (female gamete). Types of Flowers: Unisexual flower: Contains either stamens (male flower) or pistil (female flower) (e.g., Papaya, Watermelon, Corn). Bisexual flower (Hermaphrodite): Contains both stamens and pistil in the same flower (e.g., Hibiscus, Mustard, Rose). Pollination (NCERT Page 133): Definition: The transfer of pollen grains from the anther to the stigma of a flower. Types of Pollination: Self-pollination: Autogamy: Transfer of pollen from the anther to the stigma of the same flower. Geitonogamy: Transfer of pollen from the anther of one flower to the stigma of another flower on the same plant. Ensures seed production even in the absence of pollinators. Leads to less genetic variation. Cross-pollination (Xenogamy): Transfer of pollen from the anther of one flower to the stigma of a flower on a different plant of the same species. Requires external pollinating agents (vectors) like wind (anemophily), water (hydrophily), insects (entomophily), birds (ornithophily), or other animals. Leads to greater genetic diversity and stronger offspring. (PYQ: Why is cross-pollination generally preferred over self-pollination?). Fertilization (NCERT Page 133): When a compatible pollen grain lands on the stigma, it absorbs moisture and nutrients and germinates, producing a pollen tube. The pollen tube grows down through the style, carrying the male gametes (sperm nuclei) towards the ovule in the ovary. Upon reaching the ovule, the pollen tube enters it, and the male gametes are released. One male gamete fuses with the egg cell (female gamete) inside the ovule. This fusion is called fertilization , which results in the formation of a zygote . (In flowering plants, a second male gamete fuses with the central cell to form the endosperm, which nourishes the embryo – this is called double fertilization, but usually not detailed in Class 10). Post-Fertilization Changes (NCERT Page 134): The zygote develops into an embryo (a miniature plant). The ovule develops into a seed , which contains the embryo and stored food. The ovary develops and ripens into a fruit , which protects the seeds and helps in their dispersal. Other floral parts (sepals, petals, stamens, style, stigma) typically wither, dry up, and fall off. Seed and Germination (NCERT Page 134): A seed is a fertilized ovule containing an embryo, stored food (in cotyledons or endosperm), and a protective seed coat. Germination: The process by which the dormant embryo within the seed becomes active and grows into a seedling under favorable conditions (adequate water, optimal temperature, and oxygen). 5. Sexual Reproduction in Human Beings (NCERT Page 134) Puberty (NCERT Page 134): The period during adolescence when the body undergoes significant physical and hormonal changes, leading to sexual maturity and the ability to reproduce. Typically occurs between 10-14 years in girls and 12-16 years in boys. Hormonal Control: The onset of puberty is triggered by the secretion of specific hormones. Males: Testosterone (produced by testes) – stimulates sperm production, development of secondary sexual characteristics (facial hair, deeper voice, muscle development). Females: Estrogen and Progesterone (produced by ovaries) – stimulate egg maturation, breast development, broadening of hips, onset of menstruation. Male Reproductive System (NCERT Page 135): Designed for the production and delivery of sperm. Testes: A pair of oval-shaped organs located in the scrotum. Function: Produce male gametes (sperm) and the male sex hormone testosterone. Scrotum: A muscular pouch that holds the testes outside the abdominal cavity. This ensures that the testes are kept at a temperature slightly lower (2-3 $^\circ$C) than the body temperature, which is essential for healthy sperm production. Epididymis: A coiled tube located on the posterior side of each testis, where sperm mature and are stored. Vas deferens (Sperm duct): A long tube that carries mature sperm from the epididymis to the urethra. Urethra: A tube that extends from the bladder through the penis. It serves as a common pathway for both urine and semen (sperm + seminal fluid) to exit the body. Accessory Glands: Seminal Vesicles: Secrete a fluid rich in fructose, calcium, and certain enzymes. This fluid provides nourishment to the sperm and makes them active. Prostate Gland: Secretes an alkaline fluid that neutralizes the acidity of the vaginal tract, protecting the sperm and increasing their motility. Semen: The mixture of sperm and the secretions from the seminal vesicles and prostate gland. Penis: The external reproductive organ, which facilitates the transfer of sperm into the female reproductive tract. Female Reproductive System (NCERT Page 136): Designed for the production of eggs, fertilization, and development of the embryo. Ovaries: A pair of almond-shaped organs located in the lower abdominal cavity. Function: Produce female gametes (ova or egg cells) and female sex hormones (estrogen and progesterone). A female child is born with thousands of immature eggs in her ovaries. At puberty, some of these begin to mature and are released periodically. Oviducts (Fallopian Tubes): A pair of muscular tubes extending from the uterus towards the ovaries. Function: Serve as the pathway for the egg from the ovary to the uterus. This is also the usual site where fertilization occurs. Uterus (Womb): A pear-shaped, hollow, muscular organ located in the pelvic cavity. Function: Site of implantation of the fertilized egg and development of the embryo/fetus. Its muscular walls can expand significantly during pregnancy. Cervix: The narrow, lower part of the uterus that connects to the vagina. Vagina: A muscular tube that connects the cervix to the outside of the body. Function: Receives sperm during sexual intercourse and also serves as the birth canal during childbirth. Fertilization and Embryonic Development (NCERT Page 136-137): During sexual intercourse, millions of sperm are deposited into the vagina. Sperm travel through the cervix and uterus to the fallopian tubes. If an egg has been released from the ovary (ovulation) and is present in the fallopian tube, one sperm fertilizes it. This fusion of sperm and egg forms a zygote . The zygote undergoes rapid cell divisions (cleavage) as it travels down the fallopian tube to the uterus, forming an early embryo (blastocyst). Implantation: The embryo embeds itself into the thick, richly vascularized (blood-supplied) lining of the uterus. Placenta: A special disc-like tissue that develops between the uterine wall and the embryo. Function: Provides a large surface area for glucose, oxygen, and other essential nutrients to pass from the mother's blood to the embryo. It also facilitates the removal of waste products (like urea and carbon dioxide) from the embryo's blood into the mother's blood. The embryo develops into a fetus (a stage where all body parts are identifiable) over time. Gestation Period: The entire period of development of the fetus inside the mother's womb, typically about 9 months (280 days). Childbirth (Parturition): At the end of the gestation period, rhythmic contractions of the uterine muscles cause the baby to be expelled from the mother's body through the vagina. Menstrual Cycle (NCERT Page 137): The cyclical changes that occur in the female reproductive system, preparing the uterus for a possible pregnancy. The cycle typically lasts about 28-30 days and is regulated by hormones. Key events: Ovulation: Release of a mature egg from one of the ovaries (usually around mid-cycle, day 14). The uterine lining (endometrium) thickens and becomes richly supplied with blood vessels, preparing to receive a fertilized egg. If the egg is NOT fertilized: The unfertilized egg degenerates. The thickened uterine lining is no longer needed. The lining slowly breaks down and is shed, along with blood and mucus, through the vagina. This process is called menstruation or "periods". Menstruation usually lasts for 2-8 days. (PYQ: What happens if the egg is not fertilized in a human female?). 6. Reproductive Health (NCERT Page 138) Definition: A state of complete physical, mental, and social well-being in all matters relating to the reproductive system, not merely the absence of disease or infirmity. Sexually Transmitted Diseases (STDs): Infections transmitted from an infected person to an uninfected person through sexual contact. Bacterial STDs: Gonorrhea: Caused by Neisseria gonorrhoeae . Symptoms include burning urination, discharge. Syphilis: Caused by Treponema pallidum . Symptoms include sores (chancres), rash. Treatment: Curable with appropriate antibiotics. Viral STDs: Warts: Caused by Human Papillomavirus (HPV). Causes genital warts. HIV-AIDS: Caused by Human Immunodeficiency Virus (HIV). Leads to Acquired Immunodeficiency Syndrome (AIDS), which weakens the immune system. Treatment: Viral STDs are generally not curable, but their symptoms can be managed (e.g., antiretroviral therapy for HIV). Prevention of STDs: Avoiding sexual contact with unknown or multiple partners. Using barrier methods like condoms during sexual intercourse. Early diagnosis and treatment of infections. Family Planning / Contraception: The practice of regulating the number and spacing of children through the use of various methods. Importance: To prevent unwanted pregnancies and ensure maternal and child health. To control population growth, which has significant environmental and socio-economic implications. Contraceptive Methods: Barrier Methods: Physically prevent sperm from reaching the egg. Condoms: Thin rubber sheaths worn over the penis (male) or inside the vagina (female). Highly effective in preventing both pregnancy and STDs. Diaphragms/Cervical Caps: Rubber barriers inserted into the vagina to cover the cervix before intercourse. Less effective against STDs. Chemical Methods (Oral Contraceptive Pills - OCPs): Contains hormones (estrogen and/or progesterone) that prevent ovulation (release of egg) and/or make the uterine lining unsuitable for implantation. Highly effective in preventing pregnancy but DO NOT protect against STDs. Can have side effects. Intrauterine Contraceptive Devices (IUCDs): Devices (e.g., Copper-T) inserted by a doctor into the uterus. They prevent implantation of the fertilized egg and can also affect sperm motility. Effective for several years but do not protect against STDs. Surgical Methods (Sterilization): Permanent methods. Vasectomy (Male sterilization): The vas deferens are cut and tied, preventing sperm from reaching the urethra. Tubectomy (Female sterilization): The fallopian tubes are cut and tied, preventing the egg from reaching the uterus and sperm from reaching the egg. Highly effective in preventing pregnancy but do not protect against STDs. 7. Important Diagrams to Practice (PYQ Based) Binary fission in Amoeba or Leishmania (with stages) (NCERT Page 128) Budding in Hydra (with stages) (NCERT Page 130) Spore formation in Rhizopus (showing hyphae, sporangium, spores) (NCERT Page 130) Longitudinal section (L.S.) of a flower (showing all parts: sepals, petals, stamen, pistil with stigma, style, ovary, ovule) (NCERT Page 132) Human Male Reproductive System (lateral view, showing testes, epididymis, vas deferens, seminal vesicle, prostate gland, urethra, penis) (NCERT Page 135) Human Female Reproductive System (lateral view, showing ovaries, fallopian tubes, uterus, cervix, vagina) (NCERT Page 136) 8. Key Differences (Summary Table) Feature Asexual Reproduction Sexual Reproduction Parents Involved Only one parent Usually two parents (male and female) Gamete Formation No gametes are formed Male and female gametes are formed Gamete Fusion (Fertilization) Does not occur Occurs (fusion of male and female gametes) Offspring Genetic Identity Genetically identical to the parent (clones) Genetically similar but not identical to parents; shows variation Genetic Variation Absent (unless mutation occurs) Present; crucial for evolution and adaptation Rate of Reproduction Rapid; large number of offspring produced quickly Slower; fewer offspring produced at a time Role in Evolution Limited role; does not promote evolution due to lack of variation Plays a significant role in evolution due to variation Examples Amoeba, Hydra, Yeast, Spirogyra, Rhizopus, vegetative propagation in plants. Humans, most animals, flowering plants.