Chapter 30 - Plant Diversity II - The Evolution of Seed Plants

Chapter 30 Class Notes – Plant Diversity II: The Evolution of Seed Plants – Page 1
Max Sauberman
AP Biology – Mr. Schilp
Chapter 30
Plant Diversity II:
The Evolution of Seed Plants
Feeding the World:
Seeds changed the course of plant evolution, enabling their bearers to become the dominant producers in most
terrestrial ecosystems.
Seeds allow for a greater range of plant distribution.
Seed Plants:
The reduced gametophytes of seed plants are protected in ovules and pollen grains.
In addition to seeds, the following are common to all seed plants…
- Reduced gametophytes
- Heterospory
- Ovules
- Pollen
Advantages of Reduced Gametophytes:
The gametophytes of seed plants develop within the walls of spores retained within tissues of the parent
sporophyte.
The gametophyte generation is dependent upon the sporophyte.
Heterospory – The Rule among Seed Plants:
Seed plants evolved from plants with megasporangia, which produce megaspores that give rise to female
gametophytes.
Seed plants evolved from plants with microsporangia, which produce microspores that give rise to male
gametophytes.
Ovules and Production of Eggs:
An ovule consists of a megasporangium, megaspore, and one or more protective integuments, the skin of the
ovule.
Gymnosperm megaspores have one integument.
Angiosperm megaspores usually have two integuments.

Chapter 30 Class Notes – Plant Diversity II: The Evolution of Seed Plants – Page 2
The micropyle, the only opening through the integument, allows entry of a pollen grain, containing a male
gametophyte, which develops a pollen tube that discharges sperm, thereby fertilizing the egg.
Fertilization initiates the transformation of the ovule into a seed, which consists of a sporophyte embryo, a food
supply, and a protective seed coat derived from the integument.
Pollen and Production of Sperm:
Microspores develop into pollen grains, which contain the male gametophytes.
Pollination is the transfer of pollen to the part of a seed plant containing the ovule.
Pollen can be dispersed by air or animals, eliminating the water requirement for fertilization.