Overview
This lecture covers plant reproductive strategies, focusing on both asexual and sexual reproduction, alternation of generations, flower anatomy, pollination mechanisms, fertilization events, and fruit/seed function.
Asexual Reproduction in Plants
- Plants reproduce asexually through rhizomes (underground stems), corms (modified bulbs), plantlets (leaf margins), and apomixis (mitotic seed formation).
- Asexual reproduction produces genetically identical clones.
Alternation of Generations
- Plants alternate between diploid (sporophyte) and haploid (gametophyte) multicellular stages.
- Sporophytes produce haploid spores by meiosis; spores form gametophytes by mitosis.
- Gametophytes produce gametes, which fuse to create the diploid zygote that develops into the sporophyte.
Flower Structure and Function
- Carpel (female): stigma (pollen receptor), style (conducts pollen tube), ovary (contains ovules/eggs).
- Stamen (male): anther (pollen production), filament (stalk).
- Petals attract pollinators; sepals protect the bud.
Sexual Reproduction Process
- In angiosperms, the male gametophyte (pollen grain) and female gametophyte (embryo sac) are formed after meiosis and mitosis.
- Double fertilization: One sperm fertilizes the egg (zygote), the other fuses with polar nuclei (endosperm).
Pollination and Fertilization
- Pollination is the transfer of pollen to the stigma; fertilization is union of egg and sperm.
- Self-fertilization (selfing) and outcrossing are two reproductive options; mechanisms like temporal/spatial avoidance and molecular matching prevent selfing.
Pollination Syndromes
- Animal-pollinated flowers have features to attract specific pollinators (e.g., color for birds, scent for bats).
- Wind-pollinated flowers have reduced petals and lack nectar.
Seeds and Fruits
- Seeds have a seed coat (protection), endosperm (nutrients), cotyledon(s), and embryonic plant.
- Fruits protect seeds and aid dispersal via animals.
- Simple, aggregate, and multiple fruits develop from different floral origins.
Key Terms & Definitions
- Rhizome — underground horizontal stem for asexual reproduction.
- Corm — storage stem resembling a bulb.
- Plantlet — small plant growing on leaf margin.
- Apomixis — seed formation without fertilization.
- Sporophyte — diploid, spore-producing plant stage.
- Gametophyte — haploid, gamete-producing plant stage.
- Stamen — male flower part (anther + filament).
- Carpel — female flower part (stigma, style, ovary).
- Double Fertilization — two sperm fertilize egg and polar nuclei.
- Endosperm — nutritive tissue in seeds.
- Self-incompatibility — inability to self-fertilize due to molecular recognition.
Action Items / Next Steps
- Review diagrams of alternation of generations, flower anatomy, and fertilization.
- Study differences between asexual and sexual reproduction mechanisms.
- Memorize key flower parts and their functions.
- Prepare for discussion on plant development in the next lecture.