Reproduction in Plant and Animals

Reproduction is the biological process by which new individual organisms – "offspring" – are produced from their "parents". Reproduction is a fundamental feature of all known life; each individual organism exists as the result of reproduction. There are two forms of reproduction: asexual and sexual.

Plants

Asexual Reproduction

Asexual reproduction involves a single parent and results in offspring that are genetically identical to the parent. This method is common in plants, particularly in stable environments.

• Binary Fission: A method of asexual reproduction that involves the splitting of a parent cell into two daughter cells.
  • Example: Bacteria
• Budding: A type of asexual reproduction in which a new individual develops from some generative anatomical point of the parent organism.
  • Example: Yeast, Potatoes
• Fragmentation: A form of asexual reproduction where an organism is split into fragments. Each of these fragments develops into mature, fully grown individuals that are clones of the original organism.
  • Example: Spirogyra, Mosses, Liverworts
• Spore Formation: A method of asexual reproduction in which an organism produces spores, which are small, single-celled reproductive bodies that are capable of growing into a new organism.
  • Example: Fungi, Ferns
• Vegetative Propagation: A type of asexual reproduction in which new plants grow from the vegetative parts of a parent plant, such as the roots, stems, or leaves.
  • Example: Potato, Strawberry
• Artificial Propagation by Tissue Culture: A method of asexual reproduction in which a small piece of plant tissue is grown in a laboratory to produce a new plant.
  • Example: Orchids
• Apomixis: Some plants can produce seeds without fertilization.
  • Example: Dandelions

Sexual Reproduction

Sexual reproduction involves the fusion of male and female gametes (sperm and egg) to form a zygote, resulting in offspring with a unique genetic makeup. This genetic diversity is advantageous in changing environments. In most plants, sexual reproduction occurs in the flower.

• Parts of a Typical Flower:
  • Calyx: The outermost whorl of a flower, consisting of sepals. They protect the flower in the bud stage.
  • Corolla: The whorl of a flower inside the calyx, consisting of petals. They are often brightly colored to attract pollinators.
  • Androecium: The male reproductive organ of a flower, consisting of stamens. The stamen produces pollen grains, which contain male gametes.
  • Gynoecium: The female reproductive organ of a flower, consisting of carpels or a pistil. The pistil contains the ovules, where the female gamete (egg) is formed.
• Pollination: The transfer of pollen from the anther (part of the stamen) to the stigma (part of the pistil).
  • Self-Pollination: The transfer of pollen from the anther to the stigma of the same flower or another flower on the same plant.
  • Cross-Pollination: The transfer of pollen from the anther of a flower on one plant to the stigma of a flower on another plant of the same species.
• Agents of Pollination:
  • Insects: Flowers pollinated by insects are usually large, brightly colored, and have a sweet scent.
  • Water: Flowers pollinated by water are usually small and inconspicuous.
  • Wind: Flowers pollinated by wind are usually small, inconspicuous, and do not have a scent.
• Fertilization:
  • Pollen grain lands on stigma.
  • Pollen tube grows down to ovule.
  • Male gamete travels down the pollen tube to the ovule and fuses with the female gamete to form a zygote.
  • The zygote develops into an embryo, which is contained within a seed. The ovary of the flower develops into a fruit that protects the seed.
• Artificial Pollination: The process of transferring pollen from the anther of a flower to the stigma of another flower by hand.

Animals

Asexual Reproduction

Asexual reproduction is more common in invertebrates but also occurs in some vertebrates.

• Fission: The parent organism splits into two or more individuals.
  • Example: Sea anemones, some starfish
• Budding: A new individual grows out from the parent's body.
  • Example: Hydras, corals
• Fragmentation: The parent's body breaks into several pieces, and each piece can grow into a new adult.
  • Example: Planarians, sea stars
• Parthenogenesis: An egg develops into an individual without being fertilized.
  • Example: Some insects, reptiles, amphibians, and even sharks.

Sexual Reproduction in Humans

Most animals reproduce sexually. Sexual reproduction involves the fusion of male and female gametes (sperm and egg) to form a zygote, resulting in offspring with a unique genetic makeup.

• Male Reproductive System:
  • Testes: Produce sperm and testosterone.
  • Scrotum: A sac of skin that holds the testes.
  • Epididymis: A long, coiled tube that stores sperm.
  • Vas Deferens: A tube that carries sperm from the epididymis to the urethra.
  • Urethra: A tube that carries both urine and sperm out of the body.
  • Penis: The male organ of copulation.
• Female Reproductive System:
  • Ovaries: Produce eggs and estrogen.
  • Fallopian Tubes: Tubes that carry eggs from the ovaries to the uterus.
  • Uterus: A muscular organ where a fertilized egg implants and develops.
  • Cervix: The lower part of the uterus.
  • Vagina: A muscular tube that connects the cervix to the outside of the body.
• Fertilization: The fusion of sperm and egg can occur either externally or internally.
  • External Fertilization: The male and female release their gametes into the surrounding environment, where fertilization occurs. This is common in aquatic animals like fish and starfish.
  • Internal Fertilization: The male deposits sperm directly into the female's reproductive tract. This is common in terrestrial animals, including humans, cows, and dogs.
• Development: After fertilization, the zygote develops into an embryo. Depending on the species, the embryo can develop inside an egg laid outside the female's body (oviparity), or it can develop inside the female's body, receiving nourishment from her (viviparity).