Plant Diversity II

The Evolution of Seed Plants

SEEDS!• Seeds are plant embryos packaged with a food supply in a protective coat

Evolution of Plants

Five Reproductive Adaptations

1. Reduction of the gametophyte: shift from haploid to diploid condition female gametophyte and embryo depend

on sporophyte protection against drought Protects the delicate antheridia and

archegonia Increasing reproductive success

2. Heterospory Production of two types of spores

Megaspores – female gametophyte – eggs

Microspores – male gametophyte - sperm

Five Reproductive Adaptations

3. Ovules: production of eggs• Megasporangium, megaspore plus

protective tissue = ovule• Increases protection of the egg and

developing zygote• Increases reproductive fitness

4. Evolution of pollen• Male gametophyte = pollen grain• Contain two sperm nuclei• Waterproof coat for transfer by

wind• Remember before – water was

required for fertilization• THIS IS A KEY ADAPTATION

Five Reproductive Adaptations

5. Seeds• Advantages over spores

• Multicellular• Layers of protective

material• Supply of stored energy

means seed can WAIT for good germination conditions

• Stored energy supplements early growth of the embryo

Gymnosperms (bare naked)

Cone-bearing plants Lack enclosed chambers

(ovaries) for seeds Ovules and seeds develop on

specialized leaves called sporophylls

Ginkgo, cycads, and conifers All are “evergreens” Needle-shaped leaves Vascular tissue refinement:

tracheids~ water conducting and supportive element of xylem

Reproduction in Gymnosperms

Reproductive Cycle

Gymnosperm Life Cycle

• Sporophyte– produce gametophytes

inside of cones– Pollen cone (male)

• produces microspore via meiosis

– Ovulate cone (female)• produces megaspores

via meiosis• Fertilization

– pollen grains discharge sperm into egg

Angiosperms – Flowers and Fruits

Seed plants that produce the reproductive structures called flowers and fruits.

90% of all plant species

“Flowering plants” Anthophyta

The Flowerdefining structure of angiosperms

Reproductive structure: pollen transfer; specialized shoot with modified leaves

Sepals: enclose flower before it opens - protection

Petals: attract pollinatorsStamens: male, produce

microspores in the anther that develops the pollen grain

Carpels: female, produce megaspores - stigma, style, ovary, ovules

FruitsFruits are the

mature ovaries of the plant

The wall of the ovary thickens to become the fruit.

The purpose of fruit is to disperse the seeds

Monocots and Eudicots

Angiosperms are divided into two groups Monocots

~70,000 species One cotyledon in the seed Parallel leaf veins Flowering parts in multiples of

three

Monocots and Eudicots

Angiosperms are divided into two groups Eudicots

~170,000 species Two cotyledon in the

seed Net leaf veins Flowing parts in

multiples of fours or fives

Angiosperm life cycle