Do Now:• Lengthwise growth of a root tip into the soil

results mainly from…• Cone bearing plants are known as…• Which of the following statements about

bryophyta is correct? (1.) they have true roots and stems(2.) they can be small or grow large (3.) they lack vascular tissue (4.) the archegonium produces flagellated sperm(5.) the zygote grows into a haploid structure

Plant Diversity I: How Plants Colonized Land

More than 280,000 species of plants inhabit the earth today

Although some are aquatic, most are terrestrial: deserts, grasslands, forests

Land plants evolved from certain green algae called charophyceans

There are four main groups of land plants: bryophytes, pteridophytes, gymnosperms, and angiosperms

Bryophytes: mosses; distinguished from algae by advances that allow for life on land

Pteridophytes: ferns; contain vascular tissue (transport water and food); “seedless plants”

Gymnosperms: conifers; “naked seed” (seeds are not enclosed in a special chamber)

Seed: consists of a plant embryo packaged with food and a protective coat

Angiosperms: flowering plants; “container seed”; most modern-day plants

algal ancestors bryophytes vascular plants the origin of seeds the evolution of flowers

Charophyceans are the green algae most closely related to land plants

Plasma membranes contain rosette cellulose-synthesizing complexes- synthesize the cellulose of cell walls

Same enzymes in peroxisomes that help minimize the loss of product due to photorespiration

Several terrestrial adaptations distinguish land plants from charophycean algae

- growth in length is from apical meristems

- multicellular, dependent embryos

- alteration of generations: gametophyte and sporophyte

• Alternation of generation does not occur in the charophyceans. This suggests that alternation of generation arose independently in land plants.

1.) sporophyte -- multicellular diploid plant body producing spores 2.) spores -- haploid structures from sporophyte 3.) gametophyte -- multicellular haploid plant that develops from a spore -- produces the gametes 4.) gamete 5.) zygote -- produced by fusion of gametes 6.) The zygote develops into a mature sporophyte to start this cycle all over again.

There are other adaptations that are common in many land plants

Adaptations for water conservation:

- formation of a cuticle

- stomata contain guard cells

cuticle of a stem

Adaptations for water transport:Except for bryophytes, land plants have true

roots, stems, and leaves with vascular tissue- xylem: carry water and minerals up from root- phloem: distribute sugars and amino acids throughout the plant

Phloem Xylem

Land plants evolved from charophycean algae over 500 mya

- chloroplasts: chlorophyll b and beta-carotene

- homologous cell walls

- peroxisomes

Alteration of generations in plants may have adapted by delayed meiosis

Charophycean zygote undergoes meiosis to produce haploid spores

Plant zygote undergoes mitosis to produce a multicellular sporophyte to produce haploid spores by meiosis

Adaptations to shallow water preadapted plants for living on land

- natural selection would favor those that could withstand occasional drying

Bryophytes are represented by 3 phyla:

Hepatophyta (liverwarts), Anthocerophyta (hornworts), and bryophyta (mosses)

The gametophyte is the dominant generation in the life cycle of bryophytes

- sporophytes are typically smaller and present only part of the time

- up to 50 million spores can be generated in one spore capsule

Mosses are able to exist in very harsh climates

- able to loose most of their body water without dying, then rehydrate later

Bryophytes were the only plants on earth for 100 million years

Modern vascular plants include ferns (pteridophytes), gymnosperms, and flowering plants (angiosperms)

Differ from bryophytes

- contain phloem and xylem

- dominant sporophyte generation

2 phyla of seedless vascular plants: phylum Lycophyta and phylum Pterophyta (ferns)

Pteridophytes provide clues to the evolution of roots and leaves

Most pteridophytes have true roots with lignified vascular tissue

Lycophytes have small leaves with only a single unbranched vein; known as microphylls

- modern leaves are known as megaphylls

Concept 29.4

A sporophyte-dominant life cycle evolved in seedless vascular plants

Homosporous plants: produce one type of spore

Heterosporus plants: produce megaspores (female) and microspores (male)