Plant Diversity II: The Evolution of Seed Plants

CampbeCampbell, 5ll, 5thth Edition, Chapter 30 Edition, Chapter 30

Nancy G. MorrisNancy G. Morris

VolunteerVolunteer State Community CollegeState Community College

Evolution of Seed Plants

Gametophytes of seed plants continue pattern of reduction

Sporophytes continue pattern of dominance

(Figure 30.1)

Reproductive Adaptations of Seed Plants

Gametophyte develops within the spore retained in the tissues of the parent sporophyte.

(Figure 30.1)

Trend in Dominance of Sporophyte

Reproductive Adaptations of Seed Plants

The seed replaced the spore as the main means of dispersing offspring. (Figure 30.2)

The seed, which is the fertilized ovule, consists of a sporophyte embryo packaged along with a food supply within a seed coat.

Figure 30.2 From Ovule to Seed

Reproductive Adaptations of Seed Plants

Pollen became the vehicles for sperm cells in seed plants.

The pollen grain, which is the immature

male gametophyte, can be dispersed through the air by wind or transported by animals.

GGymospermsymosperms

Bear their seeds “naked” on the surfaces of sporophylls.

Pine Life Cycle -- key reproductive adaptation of seed plants (Figure 30.4)

– 1) Dominance of the sporophyte – 2) Development of seed from

fertilized ovules– 3) Flagellated sperm replaced by

pollen

4 Divisions of Gymnosperms

Division Cycadophyta – sago palms

Division Ginkgophyta – ginkgo

Division Gnetophyta – Welwitshia

Division Coniferophyta – pines, firs, redwoods, spruce, hemlock, bald cypress

(Figure 30.3)

Figure 30.4Gymnosperm Life Cycle

Angiosperms

Terrestrial adaptation continued with the refinement of vascular tissue– both xylem vessel elements &

fibers evolved from tracheids, a type of xylem. (Figure 30.5)

Figure 30.5 Tracheids

Angiosperms

The flower is the defining reproductive adaptation (Figure 30.6)– Sepals, petals, stamens (which

produce pollen), carpels (which produce ovules), are whorls of modified leaves that make up flowers.

Figure 30.6

Flower Anatomy

Angiosperms

Fruits help disperse the seeds of angiosperms (Figure 30.7)– Ovaries ripen into fruits,

which when opened disperse seeds to new locations.

Life Cycle of the Angiosperm

Alternation of Generations Life Cycle Figure 30.8

Double fertilization occurs when a pollen tube discharges two sperm into the embryo sac (the female gametophyte within an ovule). One sperm fertilizes the egg, the other combines with two nuclei to produce the food-storing endosperm.

Figure 30.8 Life Cycle of Angiosperm

Consider this…

Angiosperms & animals have shaped one another’s evolution. – Pollination of flowers by animals &

transport of seeds by animals are two important relationships in terrestrial ecosystems.

Agriculture is based almost entirely on angiosperms.– Human cultures depend on the

cultivation & harvest of angiosperms, especially the fruits of grains.

Consider this…

Plants transform the atmosphere and the climate.– By lowering the concentration of CO2, plants

probably contribute to the cooling of the Earth. Plants are a renewable resource. Plant diversity is a nonrenewable

resource.– Destruction of the tropical rainforests is an

especially urgent problem because they contain the greatest diversity of plants on Earth.

Embryological Development of a Plant