Plant Evolution & Plant Evolution & Diversity – Ch. 22-25Diversity – Ch. 22-25

Kingdom Protista: Algae & Protozoa

• Organisms in this Kingdom don’t fit clearly into what we call plant, animal, or fungi.

• Most diverse eukaryotic Kingdom (>60,000 species). • We are interested in this Kingdom because of the

Chlorophytes & Charophyceans - green algae.

The line between Kingdom Protista and Kingdom Plantae is still being discussed……

Fig 29.4

Origin of Plants

Characteristics of Green Algae - Chlorophytes

• There are unicellular and multicellular forms• Can live symbiotically with fungi as lichens

Fig 28.30

Volvox - freshwater

Caulerpa - intertidal

Ulva – sea lettuce

Characteristics of Green Algae - Charophyceans• fresh water ponds• They are considered to be the closest ancestors of true

plants. Evidence:1. .

2. .

3. .

4. Both form a cell plate during cell division5. Genetic evidence – charophyceans share a greater %

of similar DNA with true plants than any other algae

Plants

• So how are they different from Charophyceans??

What challenges did plants face when they “moved” onto land?

Adaptation to life on Land:

1. .

2. .

3. .

4. Multicellular gametangia5. Multicellular, dependent embryos

1. Apical Meristems –

2. Alternation of Generations

• 2 multicellular life stages:1. Sporophyte:

• Diploid• Divides by meiosis to form spores• Spores – haploid cells that can grow into a

new, multicellular, haploid organism (the gametophyte) without fusing to another cell.

2. Gametophyte: • Haploid• Divides by mitosis to form the gametes (egg

and sperm)• Egg & sperm fuse to form the diploid zygote,

which divides by mitosis to form the sporophyte

3. Walled spores produced in sporangia

• Sporopollenin protects the spore from harsh environmental conditions

• Sporangia =

• Sporocytes = the diploid cells within the sporangia that divide by meiosis to form the haploid spores

sporocytes

4. Multicellular gametangia• Gametangia =

• 2 types of gametangia:1. Archegonia – 2. Antheridia –

• Sperm travel to the egg, fertilizing it within the archegonia.

5. Multicelluar, dependent embryos

• Zygote divides by mitosis to become the sporophyte.

Other examples of adaptations to life on land: (not all plants have the following):

1. Cuticle –

2. Secondary compounds –

3. Roots –

4. Shoots - stems and leaves to make food. 5. Stomata – openings in the leaf surface to allow gas exchange for

photosynthesis and to regulate water loss.

More Adaptations

4. .

5. A vascular system that transports food & water from roots to shoots and vice versa.

Fig 29.7

Nonvascular Land Plants: Bryophytes

• Earliest land plants• 3 Phyla:

1. Hepatophyta – 2. Anthocerophyta – 3. Bryophyta -

• .

• Peat moss (sphagnum): doesn’t decay rapidly, stores 400 bil tons of carbon

• Gametophyte is the dominant generation:

Fig 29.8

Moss life cycle

Phylum Hepatophyta – liverworts

Phylum Anthocerophyta – hornworts

Phylum bryophyta - mosses

Peat bogs – sphagnum

moss

Fig 29.10

Vascular Plants

• Vascular tissue:– Xylem = water & mineral transport– Phloem = food (carbohydrates) transport

• .

• Sporophytes branched, independent of gametophyte parent

Seedless Vascular Land Plants

-Egg & sperm need moist environment to fertilize (similar to bryophytes)

Two phyla of seedless vascular plants:

1. Phylum Lycophyta (Club Mosses)

- flammable spore clouds- were tree-like in the Carboniferous period

Phylum Lycophyta: clubmosses, spikemosses, quillwarts

2. Phylum Pterophyta

a) Whisk ferns –

b) Horsetails –

c) Ferns – produce clusters (sori) of sporangia on underside of leaves (fronds)

Phylum Pterophyta: ferns, horsetails, whisk ferns

Fig 29.12 Life cycle of a fern

Forests of the Carboniferous period (290-360 mil years ago):

• Heat + pressure + time ----> coal• Pulled lots of CO2 out of atmosphere, cooling the earth &

forming glaciers• Larger species died out when climate became drier

Terrestrial Adaptations of Seed Plants1. Seeds replace spores as main means of dispersal.

• Why?

2. Gametophytes became reduced and retained within reproductive tissue of the sporophyte

3. Heterospory –

4. Zygote develops into an embryo packaged with a food supply within a protective seed coat.

5. Pollen & Pollination - freed plants from the requirement of water for fertilization.

1. Seeds replace spores as main means of dispersal.• old way (ferns & mosses) =

• new way: the sporophyte RETAINS its spores within the sporangia & the tiny gametophyte develops within the spore.

• ovule =

• after fertilization, the ovule becomes the seed• seed = sporophyte embryo + food supply (mature ovule

tissues)

2. Reduction of the gametophyte:

Similar to Fig 30.2

3. Heterospory – separate male & female gametophytes

• Old way: sporangia spores bisexual gametophyte (antheridia sperm, archegonia -> eggs)

• New way:

• Microsporangia microspores male gametophyte sperm

4. Ovules and seed production

• Megasporangia protected by layers of tissue called integuments.

• Ovule =

• After fertilization, embryo develops, ovule becomes a seed

Fig 30.3

5. Pollen & Pollination

• Microsporangia microspores male gametophyte sperm

• Pollen =• Pollination =

• Pollen tube brings sperm to egg within the ovule

Two types of seed plants:

1. Gymnosperms •Evolved first•“naked seed” –

• 2. Angiosperms

•Evolved from gymnosperms: Sporophylls rolled together to form ovaries.

Gymnosperms

• Four phyla:1. Ginkophyta – 2. Cycadophyta – 3. Gnetophyta – 4. Coniferophyta –

Dominate forests of the N. hemisphere Most are evergreen Needle-shaped leaves to reduce water loss

during drought

Phylum Cycadophyta

Phylum Ginkophyta

Phylum Gnetophyta

Phylum Coniferophyta

Fig 30.6

Angiosperms

• One phylum: Anthophyta

• Formerly only 2 classes: monocots & dicots. Now 4 clades (evolutionary lines):

1. Basal angiosperms2. Magnoliads3. Monocots4. Eudicots

Evolutionary success of Angiosperms due to:

1. .

2. Flowers – attract pollinators3. Fruits – many forms for variety of dispersal

mechanisms

Fig 30.3

Notice the triploid stage!•Each pollen grain (male gametophyte) produces two sperm•Sperm travel down the pollen tube & into the ovule.•Double fertilization –

•Ovule matures into the seed – contains sporophyte embryo & endosperm (food).•Ovary (female sporangium tissues) matures into the fruit.

Kingdom Fungi (A tiny bit of Ch. 21)

But Fungi:

• their bodies are filamentous

• the organization of large structures such as mushrooms and morels is completely different from plants, • they are heterotrophs (aquire nutrients by absorption)• Hence the boot!!

Ecological Roles of Fungi:

1. Decomposers –

Ecological Roles of Fungi:

2. Parasites – absorb nutrients from living hosts.

Ecological Roles of Fungi:

3. Mutualists with plants –

. ex. mycorrhizae

•Lichens: symbiotic association of cyanobacteria or green algae and fungi.

–Lichens are very sensitive to air pollution; used as indicators of air quality.

Lifestyles of Fungi, continued

• Mycorrhizae: mutualistic association of plant roots and fungi.

– Fungus receives food from the root exudates.