I. Plants and the Colonization of the Land A. An Introduction to the Plant Kingdom

1. Characteristics of Plants Autotrophic: Contain chlorophyll a & b, carotenes Multicellular, cell walls contain cellulose Eukaryotic, Nucleus, membrane bound organelles, starch stored in plastids

2. A generalized View of a Plant Lifecyle Alternating generations between a sporophyte which is a diploid spore producing generation and a gametophyte which is a haploid gamete producing plant All modern plants are heteromorphic- their sporophyte and gametophyte generations differ in morphology One main trend in evolution of plants is toward a reduction of the haploid generation and the dominance of the diploid generation

Plant Life Cycle: Zygote Spores Lower plants have a dominant gametophyte generation while higher plants have a dominant sporophyte generation Sperm Gametophyte Generation Haploid Zygote In Water Egg Spores Sporophyte Generation Diploid

B. Major Events in Plant Evolution

Evolution of Land Plants 1. Non-vascular plants evolved from green algae. Therefore, non-vascular plants must have adaptations that allow water-dwelling algae to overcome the problems of living on land and to best utilize the resources available there.

What is going on?

What problems do these plants face on land?

Which group has an advantage over the other group? Why? Plant Group 2 Plant Group 1

Does plant group #3 have an advantage over groups 1 & 2 Does plant group #3 have an advantage over groups 1 & 2? If so, what is it? Plant Group 3 Group 2 Group 1

What advantages does plant group #4 have over the other plants?

All lower plants (groups 1-4) have a significant gametophyte generation. That’s right, they reproduce like animals using sperm and egg! How do sperm travel to the egg? Water of course! Therefore, these plants must be located near water or inhabit areas with abundant rainfall. Group 3 Plant Group 4 Group 2 Group 1

Pollen How do higher plants assure that their gametes reach their significant other even when they live in dry areas?

2. Moving onto land caused plant cells to dehydrate and the following structures evolved to reduce water loss Cuticle- waxy layer that prevents evaporation from plant tissues above ground Stomata- openings through the waxy layer that allows gas exchange Gametangia- protective jacket of cells that prevent the gamete from dehydrating Rhizoids- epidermal cells with elongated regions to anchor the plant and provide surface area for water absorption Lignin- material embedded in cellulose to strengthen it

Major Events in Plant Evolution 3. Development of vascular tissues- tissues that conduct water and minerals allowed plants to grow tall a) Xylem- dead cells that conduct water b) Phloem- living cells that conduct sugars, amino acids and other nutrients 4. Reduced gametophyte generation allows the sporophyte to protect the gametophyte from drought, UV radiation and provide it with nutrients

Major Events in Plant Evolution 5. Production of pollen allows the male gametophyte to be protected by a tough coat of cells and can transport the sperm though the air. Pollen replaced swimming sperm 6. Origin of the seed- plant embryo packaged with nutrients. 7. The emergence of Angiosperms- flowing plants that have protective coats on their seeds and reproductive organs that aid pollination

Multicellular, Eukaryotic and Autotrophic Classification of the Plant Kingdom Multicellular, Eukaryotic and Autotrophic Bryophytes Tracheophytes Algae Land dwelling mosses, liverworts, hornworts Have Vascular tissue Water Dwelling Lack vascular tissue Seedless Seed Producing

Seedless Tracheophytes Psilophyta: Lack roots (have rhizoids), and have no leaves. Ex. Whisk ferns Sphenophyta: Lack roots and have small leaf-like structures called microphyls. Ex. Horse tails Lycophyta: Lack roots and have small leaf-like structures called microphyls Ex. Clubmosses Pterophyta: have fronds (macrophyls) and rhizomes (under-ground stem modified for water absorption) Ex. Fern

Seed Producing Vascular Plants Gymnosperms: Have true roots, stems, leaves, pollen and seeds without a seed coat. Ex. Conifers and Evergreens Angiosperms: True roots, stems, leaves, flowers, fruits and seeds with seed coats. Ex. Flowering Plants