Plant Evolution & Diversity

I. Kingdom Protista: Algae & Protozoa

1. Simple Eukaryotes – mostly single-celled

Amoeba, slime molds, euglenoids, algae

2. Organisms in this Kingdom don’t fit

clearly into what we call plant, animal, or

fungi.

3. Most diverse eukaryotic Kingdom

(>60,000 species).

4. We are interested in this Kingdom because

of the Chlorophytes & Charophyceans – green

algae.

A. Characteristics

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

Fig 29.4

II. Plant Origins

B. Suspects and Evidence

a. Mostly freshwater, but some are marine.

b. Have plant-like chloroplasts.

c. There are unicellular and multicellular forms

d. Can live symbiotically with fungi as lichens

1. Characteristics of Green Algae - Chlorophytes

Volvox - freshwater

Caulerpa - intertidal

Ulva – sea lettuce

Fig 28.30

2. Characteristics of Green Algae - Charophyceansa. fresh water pondsb. They are considered to be the closest ancestors oftrue plants. Evidence: i. Both have same type of cellulose-synthesizingcomplexes in cell membrane ii. Both have peroxisomes for enzyme storage iii. Both have same type of flagellated sperm iv. Both form a cell plate during cell division v. Genetic evidence – charophyceans share agreater % of similar DNA with true plants than anyother algae

III. Plants Shared CharacteristicsA. Plants are multicellular eukaryotes that are

photosynthetic autotrophs.

B. Shared pigments

C. Cellulose cell walls

D. Store glucose as starch

E. Etc.

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

A. Issues Faced 1. Acquire, transport, and conserve water 2. Protect from UV radiation 3. Resist pathogens (bacteria) and herbivores (later) 4. Others?

Then why move onto land?B. Advantages 1. 2. 3. 4.

3. Walled spores produced in sporangia

4. Multicellular gametangia

C. Adaptation to life on Land:

1. Apical Meristems

2. Alternation of generations

5. Multicellular, dependent embryos

1. Apical Meristems – localized regions of cell division at tips of roots and shoots

2. Alternation of Generations

a. 2 multicellular life stages:i. Sporophyte:

* Diploid* Divides by meiosis to form spores* Spores – haploid cells that can grow into anew, multicellular, haploid organism (thegametophyte) without fusing to another cell.

ii. Gametophyte: * Haploid* Divides by mitosis to form the gametes (eggand sperm)

b. Egg & sperm fuse to form the diploid zygote, which divides by mitosis to form the sporophyte

3. Walled spores produced in sporangia

a. Sporopollenin protects the spore from harsh environmental conditions

b. Sporangia = an organ within the sporophyte that produces the spores

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

sporocytes

4. Multicellular gametangia

a. Gametangia = multicellular organs within the

gametophyte that produce the gametes by mitosis.

b. 2 types of gametangia:

i. Archegonia – produce eggs

ii. Antheridia – produce sperm

c. Sperm travel to the egg, fertilizing it within the

archegonia.

5. Multicellular, dependent embryos

a. After fertilization, the zygote remains

within the archegonia, gaining nutrients for

growth from the gametophyte.

b. Zygote divides by mitosis to become the

sporophyte.

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

a. Cuticle – waxy covering to prevent desiccation & microbial attackb. Secondary compounds – odors, toxins, tastes, etc. toattract pollinators and defend against herbivoresc. Roots - absorb water and minerals from the soil d. Shoots - stems and leaves to make food. e. Stomata – openings in the leaf surface to allow gas exchange for photosynthesis and to regulate water loss.

f. Lignin in cell walls to provide structural support for

shoots

g. A vascular system that transports food & water from

roots to shoots and vice versa.

V. Plant Phyla

Fig 29.7

A. Nonvascular Land Plants: Bryophyta1. Characteristics a. Earliest land plants b. Phyla: Hepatophyta – liverworts,Anthocerophyta – hornworts, and Bryophyta –mosses c. Inhabit most environments, including extremes d. Peat moss (sphagnum): doesn’t decay rapidly, stores 400 billion tons of carbon e. Gametophyte is the dominant generation:

Fig 29.8

2. Moss life cycle

a. Hepatophyta – liverworts

3. Bryophyta Phyla

b. Anthocerophyta – hornworts

c. Bryophyta - mosses

Peat bogs – d. sphagnum moss (stores carbon, doesn’t decay, fuel source)

Fig 29.10

B. Vascular Plants 1. Characteristics

a. Vascular tissue Xylem = water & mineral transport and Phloem = food (carbohydrates) transport

b. Dominant generation = sporophyte

c. Sporophytes branched, independent of gametophyte parent

2. Groups

Tiny gametophytes living just above or below soil surface

Egg & Sperm need moist environment to fertilize (similar to bryophytes)

a. Seedless Vascular Plantsi. Characteristics

b. Two phyla of seedless vascular plants:

i. Phylum Lycophyta (Club Mosses) They diverged first from bryophytes with an unbranched

vascular system, flammable spore clouds, and were tree-like in the Carboniferous period

ii. Phylum PterophytaWhisk ferns – no true leaves or roots

Horsetails – hollow air-filled stems (adaptation to water-logged,

low O2 environment)

Ferns – produce clusters (sori) of sporangia on underside of

leaves (fronds)

Phylum Lycophyta: club mosses, spike mosses, quill warts

Phylum Pterophyta: ferns, horsetails, whisk ferns

Fig 29.12

c. Fern Life Cycle

d. Factors forest changes of the Carboniferous period (290-360 mya)

i. Lycophytes (tree-like) & Pteridophytes

ii. First forests

iii. Swampy forests – slow decay in low O2, formed

deep layers of organic matter

iv. Heat + pressure + time => coal

v. Pulled lots of CO2 out of atmosphere, cooling the

earth & forming glaciers

vi. Larger species died out when climate became

drier

3. Terrestrial Adaptations of Seed Plants a. Seeds replace spores as main means of dispersal.

i. Why? ii. More resistant to harsh environ b/c multicellulariii. old way (ferns & mosses) = spores released fromsporangia to disperse and develop into gametophytes iv. new way: the sporophyte RETAINS its spores within the sporangia & the tiny gametophytedevelops within the spore.

v. ovule = female sporangium + female spore. Female gametophyte develops within the spore &produces eggs. vi. after fertilization, the ovule becomes the seedvii. seed = sporophyte embryo + food supply (matureovule tissues)

Similar to Fig 30.2

b. Reduction of the gametophyte:

i. Old way: sporangia spores bisexual gametophyte

(antheridia sperm, archegonia eggs)

ii. New way:

Megasporangia megaspores female gametophyte eggs

Microsporangia microspores male gametophyte

sperm

c. Heterospory – separate male & female gametophytes

d. Ovules and seed production i. Megasporangia protected by layers of tissue

called integuments.

ii. Ovule = integuments, megasporangia, &

megaspore

iii. Megaspore female gametophyte egg &

food supply

iv. After fertilization, embryo develops, ovule

becomes a seed

Fig 30.3

e. Pollen & Pollination i. Microsporangia microspores male

gametophyte sperm

ii. Pollen = male gametophyte

iii. Pollination = transfer of pollen to ovule by wind

or animals

iv. Pollen tube brings sperm to egg within the ovule

4. Two types of seed plants: a. Gymnosperms i. Characteristics Evolved first and “Naked seed” – seeds develop on surface of specialized leaves called sporophylls

ii. Four phyla:Ginkophyta – only Ginko bilobaCycadophyta – Cycads (look like palms)Gnetophyta – Gnetophytes (tropical trees)Coniferophyta – Conifers – cone-bearing trees

Dominate forests of the N. hemisphereMost are evergreenNeedle-shaped leaves to reduce water loss during

drought

Phylum Cycadophyta

Phylum Ginkophyta

Phylum Gnetophyta

Phylum Coniferophyta

Fig 30.6

iii. Gymnosperm life cycle

b. Angiosperms i. CharacteristicsFlowering plants, Most diverse, and Evolved from gymnosperms: Sporophylls rolled together to form ovaries.

ii. One phylum: Anthophyta

Seeds are enclosed in the moist reproductive tissue of the

sporophyte generation (Ovary).

More insects and animals for pollination, less dependent

on wind.

Formerly only 2 classes: monocots & dicots. Now 4

clades (evolutionary lines):Basal angiosperms, Magnoliads, Monocots, & Eudicots

iii. Evolutionary success of Angiosperms

Increased water transport efficiency due to

improvement in xylem tissue: tracheid cells, fiber

cells, vessel elements (gymnosperms only have

tracheids)

Flowers – attract pollinators

Fruits – many forms for variety of dispersal

mechanisms

Fig 30.3iv. Angiosperm life cycle

Notice the triploid stage!Each pollen grain (male gametophyte) produces two spermSperm travel down the pollen tube & into the ovule.Double fertilization – one sperm unites with the egg to form the 2n zygote, other sperm unites with the two nuclei of the female gametophyte to form a 3n endosperm – becomes food for the developing embryoOvule matures into the seed – contains sporophyte embryo & endosperm (food).Ovary (female sporangium tissues) matures into the fruit.

Fig 29.8

Moss life cycle

Fig 29.12

Fern life cycle

Fig 30.6

Gymnosperm life cycle

Fig 30.3

Angiosperm life cycle

VI. Kingdom Fungi

Fungi were once included in the plant kingdom because they produce spores, have cell walls, and are not animals.

A. Characteristics

1. Their cell walls do not contain cellulose

(like plants), but do contain chitin

(like insects, arthropods).

2. Their bodies are filamentous.

3. The organization of large structures such as

mushrooms and morels is completely different from plants.

4. They are heterotrophs (acquire nutrients by absorption).

Hence the boot!!

B. Fungal life cycle

C. Ecological Roles of Fungi:1. Decomposers – absorb nutrients from dead

organic matter, thereby decomposing it. Recycle

nutrients to the soil.

2. Parasites – absorb nutrients from living hosts.

ex. pathogens on crops

3. Mutualists with plants – absorb nutrients from host, but

aid host in mineral uptake from soil. ex. mycorrhizae

1. Molds: rapid growing, asexually reproducing fungi2. Yeasts: single-celled fungi inhabiting moist habitats.

Raise bread & ferment alcohol

C. Lifestyles of Fungi

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

a. Fungus provides shape b. Algae provides food, N to the fungus c. Lichens are very sensitive to air pollution; used as indicators of air quality.

4. Mycorrhizae: mutualistic association of plant roots and fungi.

a. Fungus increases the absorptive surface area of roots, increasing water and potassium uptake

b. Fungus receives food from the root exudates.

2 down and 7 to go!!