Seed Plants and Gymnosperms

Seed

Adaptation of some plants, embryo packaged with food and a protective coat

Derived Traits of Seed Plants

1. Reduced Gametophyte

2. Heterospory

3. Presence of Ovules

4. Pollen

5. Seeds

Derived Traits - Reduced Gametophyte

Gametophyte reduced in size (microscopic), more dependent on sporophyte (larger and more dominant)

Derived Traits - Heterospory

All seed plants are ‘heterosporous’

Megasporangia → produce female gametophyte

Microsporangia → produce male gametophyte

Spores remain in sporophyte until dispersal

Derived Traits - Presence of Ovules

Ovule contains megasporangium (2n), a megaspore (1n), and protective integuments (2n)
Gymnosperm ovules have 1 integument, female gametophyte has thousands of cells

Angiosperm ovules have 2 integuments, reduced to embryo sacs with few nuclei and cells

Derived Traits - Pollen

Microspores develop into male gametophyte in pollen grains

Microspores that aren’t dispersed develop into pollen grain to produce tiny male gametophytes

Cell wall coated by sporopollenin

Each pollen grain has a male gametophyte, with a generative cell and tube cell, that develop into nuclei and pollen tube after pollination
Male gametophyte transported to ovule within pollen grain

Derived Traits - Seeds

Seed develops from fertilized ovule

Contains next generation of sporophyte

Size of seed varies (larger seed = more resources and less that can be produced)

Pollination

Process for fertilization, pollen transferred to part of a seed plant containing ovules

In seed plants, entire pollen grain along with male gametophyte is dispersed, pollen tube developed to discharge sperm into female gametophyte

Benefits: Sporopollenin protects male gametophyte, pollen can travel long distance and can be transported by various agents

Seed Dispersal

Seeds, instead of spores, dispersed

Advantages:

-seeds have protective coats to protect the embyro

-Seeds have an energy supply and can germinate in the dark

-Seeds have additional structures that assist in dispersal

Gymnosperm

Vascular plants, seeds exposed on sporophylls

-Sporophyte is dominant, produces both pollen and ovulate cones

-Gymnosperm develop seeds from fertilized ovules

-Pollens containing male gametophyte are transferred to ovule before sperm is released

Diversity of Gymnosperm

Monophyletic Group containing:
1. Cycadophyta

2. Gingkophyta

3. Gnetophyta

4. Coniferophyta

Gingkophyta

Extant species from china, all populations associated with human habitats

Characteristics:
-Dioecious (trees either male or female)

-Deciduous (shed leaves during fall)

-Presence of ‘fan-shaped’ leaves

-Presence of flagellated sperm

Gnetophyta

Small group of gymnosperm, 75 species, often found in tropic/desert environment

Key Characteristic:
-Xylem contains vessel elements