Overview
This lecture explains the purpose and methods of reproduction in living organisms, distinguishing between asexual and sexual reproduction, describing their processes in detail, and touching upon human reproductive health.
Why Do Organisms Reproduce?
- Reproduction ensures the continuation and survival of species by producing new individuals.
- Body designs are passed on through DNA copying during reproduction.
- DNA copying is not perfect, leading to variations among individuals, which are important for evolution.
DNA Copying and Variation
- DNA contains the genetic blueprint of organisms and is copied during reproduction.
- Errors in DNA copying cause variations; most are minor, but some can be significant.
- Variation is essential for the survival of species in changing environments.
Modes of Asexual Reproduction
- Fission: Unicellular organisms like Amoeba divide into two (binary fission) or many (multiple fission) daughter cells.
- Fragmentation: Simple multicellular organisms like Spirogyra break into pieces, each growing into a new individual.
- Regeneration: Organisms like Planaria and Hydra can regrow into new individuals from body parts.
- Budding: Outgrowths (buds) form and detach to become new organisms, e.g., yeast and Hydra.
- Vegetative Propagation: Plants form new from roots, stems, or leaves (e.g., Bryophyllum, potato).
- Spore Formation: Fungi like Rhizopus produce spores in sporangia, which develop into new individuals.
Sexual Reproduction and Its Significance
- Combines DNA from two parents, leading to greater variation.
- Special germ-cells (gametes) are formed with half the DNA content via meiosis.
- Male gametes (sperm/pollen) are usually motile; female gametes (egg/ovule) contain food stores.
Sexual Reproduction in Flowering Plants
- Flowers contain reproductive parts: stamens (male) and pistil (female).
- Pollen transfer to stigma is called pollination (self or cross).
- Fertilisation occurs when male and female gametes fuse, forming a zygote.
- Ovary matures into fruit; ovule becomes seed; seed germinates under suitable conditions.
Reproduction in Human Beings
- Puberty triggers sexual maturation and development of reproductive organs.
- Male reproductive system: Testes produce sperm; vas deferens, glands, and urethra deliver sperm.
- Female reproductive system: Ovaries produce eggs; fallopian tubes, uterus, and vagina involved in fertilisation and birth.
- Fertilisation (fusion of sperm and egg) occurs in the fallopian tube; embryo implants in uterus; placenta provides nutrition.
- Menstruation is the periodic shedding of the uterine lining if fertilisation does not occur.
Reproductive Health
- Safe sexual behaviour and contraception help prevent pregnancy and sexually transmitted diseases.
- Contraceptive methods include barriers (condoms), hormonal pills, devices (copper-T), and surgical options.
- Female foeticide and sex selection are illegal and harm the sex ratio.
Key Terms & Definitions
- DNA — Genetic material responsible for inheritance.
- Variation — Differences in DNA among individuals, essential for evolution.
- Fission — Splitting of a cell or organism to form new individuals.
- Regeneration — Formation of a new organism from body parts.
- Budding — Outgrowth of a part of an organism that detaches to form a new individual.
- Vegetative Propagation — Asexual reproduction using plant parts (root, stem, leaf).
- Spore — A reproductive cell capable of developing into a new organism.
- Pollination — Transfer of pollen from anther to stigma.
- Fertilisation — Fusion of male and female gametes.
- Menstruation — Monthly shedding of uterine lining in females.
Action Items / Next Steps
- Review textbook section on reproductive organs in flowering plants and humans.
- Try drawing and labelling the male and female reproductive systems as well as a flower.
- Answer exercise questions at the end of the chapter for practice.