Overview
This lecture covers the structure, reproduction, and life cycle of angiosperms (flowering plants), focusing on their reproductive adaptations, flower parts, fruit types, seed dispersal, and double fertilization.
Angiosperms: Basic Facts
- Angiosperms are flowering plants with over 250,000 species, divided into Monocots and Eudicots.
- They use pollinators (insects, animals) rather than wind for precise pollination.
- Defining reproductive adaptations are flowers (for pollinator attraction) and fruits (for seed dispersal).
Flower Structure and Function
- Main flower parts: stamen (male) and pistil/carpel (female).
- Stamen consists of anther (produces pollen) and filament.
- Pistil/carpel includes stigma (sticky, receives pollen), style, and ovary (contains ovules).
- Sepals protect the bud; petals attract pollinators.
- Ovules develop into seeds after fertilization; ovary becomes the fruit.
Types of Fruit & Seed Dispersal
- Fruit is a ripened ovary for seed dispersal.
- Aggregate fruit: from several ovaries of one flower (e.g., raspberry).
- Multiple fruit: from ovaries of multiple flowers (e.g., pineapple).
- Seeds are dispersed by wind, animals, or attaching to fur.
- Some seeds require scarification (nicking the seed coat) to germinate, imitating passage through animal digestive tracts.
Angiosperm Life Cycle and Double Fertilization
- Angiosperms have alternation of generations; the dominant sporophyte generation is diploid.
- Heterosporous: produce microspores (male, pollen) and megaspores (female, embryo sac).
- Male gametophyte (pollen grain) develops in anthers and contains two haploid nuclei.
- Female gametophyte (embryo sac) has eight haploid nuclei in seven cells, including the egg and central cell.
- Pollination leads to pollen tube growth; two sperm nuclei travel down the tube.
- One sperm fuses with the egg: forms diploid embryo.
- Other sperm fuses with two nuclei in central cell: forms triploid endosperm (nutritive tissue).
- Double fertilization is unique to angiosperms, producing both embryo and endosperm in the seed.
Key Terms & Definitions
- Angiosperm — flowering plant with seeds enclosed in fruit.
- Stamen — male reproductive part: anther + filament.
- Carpel/Pistil — female reproductive part: stigma, style, ovary.
- Ovule — structure in ovary, develops into seed after fertilization.
- Fruit — mature ovary containing seeds.
- Aggregate fruit — fruit from multiple ovaries of one flower.
- Multiple fruit — fruit from ovaries of several flowers.
- Scarification — process of nicking seed coat to aid germination.
- Double fertilization — two sperm nuclei fertilize egg (embryo) and central cell (endosperm).
- Endosperm — triploid tissue that nourishes seed embryo.
Action Items / Next Steps
- Review and memorize parts of a flower and their functions.
- Understand and be able to explain double fertilization.
- Be able to identify examples of fruit types (aggregate, multiple).
- Study alternation of generations in angiosperms.