Evolution of the Seed Evolution of the Seed PlantPlant

3 Important Adaptations3 Important Adaptations

Reduction of Reduction of gametophytegametophyte

Advent of the seedAdvent of the seed Evolution of pollenEvolution of pollen

In seed plants, the miniature female In seed plants, the miniature female gametophytes develop from spores gametophytes develop from spores

that are retained with the sporangia that are retained with the sporangia of the parental sporophyteof the parental sporophyte

Advantage- female gametophytes do Advantage- female gametophytes do not have to cope with many not have to cope with many

environmental stresses. These as environmental stresses. These as well as the young embryos are well as the young embryos are

sheltered from drought and harmful sheltered from drought and harmful UV radiation by being enclosed in UV radiation by being enclosed in moist reproductive tissues of the moist reproductive tissues of the parental sporophyte generation.parental sporophyte generation.

Seeds become an important means of Seeds become an important means of dispersing offspringdispersing offspring

A seed is complex multicellular A seed is complex multicellular reproductive structure reproductive structure

(spore-a single cell)(spore-a single cell)

A seed:A seed:

Sporophyte embryoSporophyte embryo Food supplyFood supply Protective coatProtective coat

All seeds plants are All seeds plants are heterosporousheterosporous

MALEMALE FEMALEFEMALE

In seed plants layers of sporophyte In seed plants layers of sporophyte tissues called INTEGUMENTS tissues called INTEGUMENTS

envelop the mega sporangium. The envelop the mega sporangium. The whole structure, integument, is whole structure, integument, is

called an ovule.called an ovule.

A female gametophyte develops A female gametophyte develops within a megaspore and produces within a megaspore and produces one or more eggs. If an egg cell is one or more eggs. If an egg cell is fertilized by a sperm, the zygote fertilized by a sperm, the zygote

develops into a sporophyte develops into a sporophyte embryo. The entire ovule embryo. The entire ovule

develops into a seed.develops into a seed.

Seeds may remain Seeds may remain dormant for years.dormant for years.

Pollen eliminates the need Pollen eliminates the need for water in fertilizationfor water in fertilization

Microspores Microspores develop into develop into pollen grains-pollen grains-which mature to which mature to male male gametophytes of gametophytes of seed plants. seed plants. Pollen is protected Pollen is protected by sporopollen.by sporopollen.

Pollen Cone

Pollination is the transfer of pollen to ovules

When pollen lands in the vicinity of an When pollen lands in the vicinity of an ovule, it will elongate a tube that ovule, it will elongate a tube that

discharges on or more sperm into the discharges on or more sperm into the female gametophyte.female gametophyte.