Overview
This lecture covers the structure, reproduction, and significance of flowering plants (angiosperms), with emphasis on flower anatomy, pollination, fruit, seed dispersal, and the unique process of double fertilization.
Introduction to Angiosperms
- Angiosperms are flowering plants, meaning "container seeds," with about 300,000 species.
- Two major groups: Monocots and Eudicots.
- Flowers attract pollinators for precise pollination, making angiosperms highly advanced.
Flower Structure and Function
- The flower is the key reproductive adaptation of angiosperms.
- Flower parts: stamen (male: anther, filament), pistil/carpel (female: stigma, style, ovary), sepals (protect bud), and petals (attract pollinators).
- Stigma is sticky to catch pollen; ovary protects ovules, which develop into seeds after fertilization.
Fruits and Seed Dispersal
- Fruit is a ripened ovary and plays a role in seed dispersal.
- Aggregate fruits form from multiple ovaries of one flower (e.g., raspberry).
- Multiple fruits form from ovaries of several flowers (e.g., pineapple).
- Seed dispersal methods include wind, animal attachment, and consumption of edible fruit.
- Scarification (nicking) is required for hard seeds to germinate, mimicking passage through an animal digestive system.
Angiosperm Life Cycle & Double Fertilization
- Angiosperms have alternation of generations; dominant phase is the sporophyte generation.
- Heterosporous: produce microspores (male, in anthers) and megaspores (female, in ovules).
- Male gametophyte is the pollen grain; matures with pollen tube growth.
- Female gametophyte (embryo sac) has eight haploid nuclei in seven cells.
- Double fertilization: one sperm fertilizes the egg (forms embryo, 2n); another fuses with two nuclei in central cell (forms endosperm, 3n).
- Endosperm provides nutrients for developing embryo.
- Ovule matures into a seed after fertilization, resuming the sporophyte generation.
Key Terms & Definitions
- Angiosperm — flowering plant with seeds enclosed in an ovary (fruit).
- Monocot/Eudicot — two main groups of angiosperms, differing in seed leaves and other traits.
- Stamen — male flower part; includes anther (makes pollen) and filament (supports anther).
- Pistil/Carpel — female flower part; includes stigma (catches pollen), style, and ovary.
- Gametophyte — plant life stage producing gametes; in angiosperms, pollen (male) and embryo sac (female).
- Double fertilization — process where one sperm forms embryo, another forms triploid endosperm.
- Endosperm — triploid nutritive tissue inside seeds, provides food to embryo.
- Scarification — process of nicking seed coats to promote germination.
Action Items / Next Steps
- Review the parts of a flower and their functions.
- Understand and be able to explain double fertilization in angiosperms.
- Practice identifying examples of fruit types (aggregate, multiple).
- Prepare for questions on angiosperm life cycle, especially gametophyte development and fertilization.