Section 1B

30.1: Seeds and pollen grains are key adaptations for life on land
30.2: Gymnosperms bear "naked seeds", typically on cones
30.3: The reproductive adaptations of angiosperms include flowers and fruits
Location and Date: St. John's, NL, July 2024

Significance of Seeds:
- Seeds transformed the course of plant evolution and allowed their bearers to become the dominant producers in most terrestrial ecosystems.
- Origin of Seed Plants: About 360 million years ago.
- Dispersal: Seeds can disperse over long distances via wind or other means.

Example: Dandelion seeds have an adaptation called a pappus, comprising fine hairs that reduce falling velocity and aid wind dispersal.
Advantages of Dispersal:
- Can locate new resources.
- Reduces the possibility of inbreeding.
- Limits competition.

Common Characteristics of All Seed Plants:
1. Reduced Gametophytes (haploid phase)
2. Heterospory
3. Ovules
4. Pollen
These adaptations provide new ways to cope with terrestrial challenges, such as drought and UV radiation.

Gametophytes of seed plants are mostly microscopic and develop within the walls of spores retained within the tissues of the parent sporophyte.
- Protects from environmental stresses such as UV radiation and drying.
- Provides nutrients to the gametophyte.

Plant Group	Gametophyte Dominance	Sporophyte	Examples
Mosses and other nonvascular plants	Dominant	Reduced, dependent on gametophyte for nutrition	Gametophyte (n)
Ferns and other seedless vascular plants	Reduced, independent (photosynthetic and free-living)	Dominant	Sporophyte (2n)
Seed plants (gymnosperms and angiosperms)	Reduced (usually microscopic), dependent on sporophyte tissue	Dominant	Gymnosperm: Microscopic female gametophytes inside ovulate cone; Angiosperm: Microscopic female gametophytes inside flowers

The ancestors of seed plants were likely homosporous; seed plants are heterosporous (two kinds of spores).
- Megasporangia produce megaspores, which give rise to female gametophytes.
- Each megasporangium has one functional megaspore.
- Microsporangia produce microspores that give rise to male gametophytes.
- Each microsporangium contains numerous microspores, which develop into pollen.

A microspore develops into a pollen grain, which comprises a male gametophyte enclosed within the pollen wall.
- The tough wall, composed of sporopollenin, protects during transit to the ovule.
- Pollination refers to the transfer of pollen to part of a seed plant containing ovules, which eliminates the need for a film of water and enables dispersal over long distances by air or animals.
- Upon germination, a pollen grain produces a pollen tube that discharges sperm into the female gametophyte within the ovule.

A fertilized ovule transitions to a seed consisting of:
- A sporophyte embryo
- A food supply
- A protective seed coat derived from the integument
- The megasporangium dries out and collapses.

A seed develops from the entire ovule and comprises a sporophyte embryo, food supply, and a protective coat.
Advantages Over Spores:
- Seeds can remain dormant for a range of days to years until conditions are conducive for germination.
- Seeds contain a stored food supply.
- Can be transported over considerable distances by wind or animals.

Gymnosperms are classified into four phyla:
1. Cycadophyta: cycads
2. Gingkophyta: one living species, Ginkgo biloba
3. Gnetophyta: consists of three genera: Gnetum, Ephedra, Welwitschia
4. Coniferophyta: includes conifers such as pine, fir, and redwood.

Angiosperms are seed plants characterized by reproductive structures called flowers and fruits.
- They are the most widespread and diverse plant group, making up around 90% of all plant species.

All angiosperms are organized into a single phylum, Anthophyta, derived from the Greek term for flower, anthos.
Key Adaptations:
- Flowers: Specialized for sexual reproduction
- Fruits: Formed from the ovary wall following fertilization.

Specialization: A flower is a specialized shoot with up to four rings of modified leaves (sporophylls) referred to as floral organs.
- Sepals: Usually green and enclose the flower before it opens.
- Petals: Brightly colored to attract pollinators.
- Stamens: Produce pollen; consist of a stalk (filament) and an anther where pollen is produced.
- Carpels: Produce ovules and comprise an ovary at the base and a style leading up to a stigma, where pollen is received.
A flower is termed complete if all four organs are present; it is incomplete if one or more are absent.

Process: After pollen is released from the anther, it is carried to the stigma.
Self-pollination: Some flowers self-pollinate, but most have mechanisms to ensure cross-pollination, which promotes genetic variability.
Mechanisms to avoid self-pollination may involve
- Timing of maturation for stamens and carpels
- Structural arrangements that discourage self-pollination.

Definition: Fruits develop from ovules after fertilization, formed when the ovary wall thickens and matures.
Functions:
- Protect seeds
- Aid in seed dispersal
Varieties: Mature fruits can be fleshy or dry; examples help illustrate various adaptations in fruit structure that enhance seed dispersal.

Fruits have various adaptations that assist in seed dispersal, utilizing vectors such as:
- Wind
- Water
- Animals to transport seeds to new locations.

Reference to Figure 30.13 captures many details on angiosperms and should be assessed in contrast to previous learning about mosses and ferns.
Good Questions for Reflection:
- Contrast life histories of different plant groups.
- Consider the significance of these adaptations and their implications for plant evolution.