Ch 25: Seedless Plants

how long ago did land plants originate?

470 mya, part of archaeplastida

what do plants share a common ancestor with?

charophytes (green algae) in the archaeplastida supergroup of eukaryotes

Chara species

a pond organism

Coleochaete orbicularis

a disk-shaped charophyte that also lives in ponds

green algae and plants: shared characteristics

chlorophytes, charophytes, & plants share:

• multicellularity

• cell walls w/ cellulose

• chloroplasts w/ same pigments (chlorophyll. a &b)

• storage molecule is starch (carb)

• all plants are multicellular, but all green algae are not

Ulva

chlorophyte, multicellular

Chara

charophyte, multicellular

moss

plant, multicellular

from water to land

• most green algae live in water

• desiccation, or drying out, is a constant danger for an organism exposed to air

• both gametes and zygotes must be protected from desiccation

• plants need to develop structural support in a medium that does not give the same lift as water

• the male gametes must reach the female gametes using new strategies, because swimming is no longer

from water to land disadvantages

• risk of desiccation

  • both adult and gametes

• no “support” in air

advantages of land

• CO2 higher

• light intensity higher

• more minerals

• no “herbivores”

• no competition

from water to land

1. life cycle in all land plant exhibits the alternation of generations

2. an apical meristem tissue in roots and shoots

3. evolution of a waxy cuticle to resist

4. cell wall with lignin to support structures off the ground

lignin are only in what kind of plants?

vascular plants

true or false. all plants have alternation of generations: 2n and n multicellular forms

alternation of generations cycle

1. 🌿 The sporophyte is the plant you usually see (like a fern or flower).
   ➤ It makes spores using meiosis (which cuts the DNA in half).

2. 🌬 The spores are tiny and float away or fall to the ground.
   ➤ They grow into the gametophyte.

3. 🌱 The gametophyte is usually smaller and not as noticeable.
   ➤ It makes gametes (sperm and egg) using mitosis.

4. 💧 When sperm and egg join (fertilization), they make a zygote.

5. 🌿 The zygote grows into a new sporophyte — and the cycle begins again!

compare alternation of generations to charophyte life cycle

• only multicellular is haploid

• zygotes does meiosis to produce only 4 diverse offspring

walled haploid spores

• dispersal though air: sporopollenin protects

• made within multicellular sporangium

what is sporopollenin resistant to?

chemically and biological degradation

multicellular gametangia

protecting sperm within antheridium

why do all seedless plants have flagellated sperm?

b/c they need water for reproduction → need to move in the water

where does fertilization occur and where does the zygote form?

the archegonium

where is the egg protected?

the archegonium

Apical Meristems

• continuously dividing cells

• roots and shoots grow towards resources

what do meristems help with the plant with?

grow in length

roots

get water and minerals

shoots

get sunlight and CO2

Waxy cuticle

• waxy coat stops desiccation

• pores needed to allow CO2/O2 exchange

  • controllable stomata in most plants

guard cells

regulates stomata

secondary metabolites

chemicals that deter, repel, or poison competitors, herbivores and parasites

mycorrhizae

• fungus and plant roots

• mutualism with fungi; helps water and mineral absorption

• dates back to first land plants (before true roots)!

what is the mutualism between plants and fungi?

plants provide sugar, fungi provides minerals and water

what phylum that forms endomycorrhizae

glomeromycota

what are arbuscles?

hyphae-like and penetrate the plant cell membrane

what are seedless, nonvascular plants collectively referred to as?

bryophytes

bryophytes

• non-woody, small, ground-covering plants that require water for reproduction

• have rhizoids for attachment (not true roots)

• 3 phyla

3 phyla of bryophytes

1. liverworts

2. hornworts

3. mosses

bryophyte characteristics

• haploid gametophyte is dominant form

• diploid sporophyte depends on gametophyte for food and water

bryophyte: haploid gametophyte is dominant form

• dominant = longest lasting or largest

• makes eggs & flagellated sperm

• most are small, low growing, moist areas

  • needs water for reproduction

• some don’t have a cuticle

diploid sporophyte depends on gametophyte for food and water

• grows within archegonium of gametophyte

• sporangium makes many haploid spores

the diploid sporophyte is completely dependent on what?

the female gametophyte

where is the site of fertilization?

archegonium

liverworts

• most have elevated gametophytes that resemble miniature trees (Marchantia)

• reduced or very small sporophytes; Some “thalloid” and others “leafy”

“thalloid” liverwort ex.

Marchantia polymorpha

parts of the sporophyte

1. foot: absorbs nutrients

2. seta: conducts nutrients to sporangium

3. capsule (sporangium): produces spores by miosis

“leafy” liverwort

Plagiochila deltoidea

Hornwarts

• common name refers to horn-like long tapered shape of sporophyte (not dominant)

• good colonizers of moist soils

• symbiotic relationship w/ nitrogen fixing cyanobacteria

  • need for nutrients, can’t use N2 in the air b/c nonvascular

Mosses

• the most numerous of the non-vascular plants > 10,000 species

• inhabit extreme environments as mountain tops, tundra, and deserts

• sporophyte grows up from female gametophyte to gain elevation for spore dispersal

Mosses ecological importance

• “pioneer” species in nutrient-poor soils (generate livable conditions)

• moss are major primary producers in cold or high-altitude regions

  • cell walls are phenolic compounds → absorb damaging levels of UV radiation

  • Sphagnum “peat moss” bogs: important wetlands, also harvest for fuel (have low pH, low temp, low O2)

  • some peatlands have preserve corpses for thousands of years

peat

formed by gradual decomposition of plant matter

what is the pioneer species in nutrient poor soils?

mosses

Sphagnum “peat moss” bogs

important wetlands, also harvest for fuel

true or false. moss are major primary producers in cold or high altitude regions

true

seedless vascular plants

• have lignin in cell walls → lignified vascular tissue enables vascular plants to grow tall

• until vascular tissue evolved, all land plants were short, ground cover plants

• oldest seedless vascular plant fossils about 425 MYA

  • ferns and club moss

seedless vascular plants characteristics

1. branched sporophytes that are independent of gametophyte for nutrition

2. diploid sporophyte dominants life cycle

3. transport in xylem and phloem (vascular system)

4. evolution of true roots

5. evolution of true leaves

xylem

cells specialized to move water and minerals

phloem

cells specialized to move sugars, amino acids, and other organic products

only lycophytes have microphylls

small, spine-shaped leaves supported by a single strand of vascular tissue, unbranched vascular tissue

almost all other vascular plants have megaphylls

leaves w/ a highly branched vascular system

greater photosynthetic productivity than microphylls

lycophytes w/ microphylls ex.

Krauss’ spike moss

other vascular plants w/ megaphylls ex.

Tunbridge filmy fern

sporophylls 1

leaves modified to bear sporangia

• fern sporophylls look like normal leaves but have sori that generate spores on underside

• lycophyte sporophylls modified into a cone-like structure called a strobilus

sporophylls ex.

Lycopodium obscurum

sporophylls 2

1. Homosporous spore production (most seedless vascular plants)

• sporangium on sporophyll → single type of spore → typically a bisexual gametophyte → eggs and/or sperm

2. Heterosporous spore production (all seed plants and few seedless vascular plants)

• megasporangium on megasporophyll → megaspore → female gametophyte → eggs

• microsporangium on microsporophyll → microspore → male gametophyte → sperm

Homosporous spore production (most seedless vascular plants)

sporangium on sporophyll → single type of spore → typically a bisexual gametophyte → eggs and/or sperm

Heterosporous spore production (all seed plants and few seedless vascular plants)

megasporangium on megasporophyll → megaspore → female gametophyte → eggs

microsporangium on microsporophyll → microspore → male gametophyte → sperm

Lycophytes (club mosses and relatives)

• current species all small (1,200 spp) tropical and temperate

• spike moss: Selaginella apoda

• a quillwork: Isoetes gunnii

true or false. spike mosses and quillworts are heterosporous.

true

true or false. club mosses are heterosporous.

false. club mosses are homosporous

Lycophytes: spike moss ex.

Selaginella apoda

Lycophytes: quillwort ex.

Isoetes gunnii

is peat moss a Lycophyte or Bryophyte?

Bryophyte: non vascular

Pterophytes (Ferns and relatives)

horsetails, whisk ferns, and ferns belong to the phylum Monilophyta

Pterophytes: whisk ferns (Psilotum)

• dichotomous branching

• no true leaves or roots

• homosporous (1 type of spores)

• photosynthesis occurs in stem

Pterophytes: horsetails (Equisetum)

• jointed stems w/ tiny leaves

• strobili

• homosporous

• photosynthesis occurs in stems

Pterophytes: ferns

• most widespread and diverse Monilophytes (20,000 species)

• homosporous

• large megaphylls

• sori on underside of sporophylls

• mostly in understory or as epiphytes

epiphytes

grows on the surface of a plant

fern life cycle

• Sporophyte (Diploid - 2n):

  • This is the main fern plant you see.

  • It has sporangia (spore cases) under the leaves in little brown dots called sori.

  • Inside the sporangia, it makes spores using meiosis (cuts DNA in half).

• Spores (Haploid - n):

  • Tiny and light — carried by wind.

  • Each spore grows into a new gametophyte.

• Gametophyte (Haploid - n):

  • A small, flat, heart-shaped green plant called a prothallus.

  • It has male and female organs:

    • Antheridia = make sperm

    • Archegonia = hold the egg

• Fertilization:

  • Sperm swim (through water!) to the egg.

  • Sperm + egg = zygote (baby fern!)

• Zygote → New Sporophyte (Diploid - 2n):

  • The zygote grows into a new fern plant — the sporophyte.

  • And the cycle starts again!

importance of seedless plants

disappearance of mosses → biological indicator of environmental pollution

ferns → promote weathering of rocks → accelerates topsoil formation

• used as food

peat moss (Sphagnum) → used as fuel (renewable resource)

• also used as soil conditioner

extinct SVPs → coal → energy sources

what is used as a soil conditioner?

peat moss (Sphagnum)

what is a biological indicator of environmental pollution?

disappearance of mosses

what is used as renewable fuel?

peat moss