Plant Diversity I Flashcards
how did land plants evolve?
from ancestral green algae
streptophytes
- charophytes and land plants
- monophyletic
- modern charophytes - sister taxon to land plants (embryophytes)
where do streptophytes live and is it always wet or dry?
- many live at edges of ponds
- sometimes dries out -> selection favors survival on dry land
what are the derived traits of streptophytes?
- sporopollenin: layer of polymer, surrounds zygote, prevents desiccation
- similar adaptations in plant spores
what DTs do streptophytes, modern charophytes and land plants have in common?
- rings of cellulose, synthesizing proteins
- structure of flagellated sperm
- cell plate
list the derived traits of land plants
- alternation of generations
- Multicellular Dependent Embryo
- Walled Spores Produced in Sporangia
- Multicellular Gametangia
- Apical Meristems
- Cuticle
- Stomata
Aaliyah Must Win Most Apples Cause She’s *starving
Alternation of Generations
- Haploid gametophyte produces gametes by mitosis
- DIploid sporophyte produces spores by meiosis
2 multicellular stages, 2 unicellular stages
gametophyte (n) -> mitosis -> gametes (n) -> fertilization -> zygote (2n) -> mitosis -> sporophyte (2n) -> meiosis -> spores (n) -> mitosis -> gametophyte (n)
Multicellular, Dependent Embryo
2n embryo (-> sporophyte) retained within tissue of female gametophyte (n)
- nutrients transferred to embryo through transfer cells
- (why land plants sometimes called “embryophytes”)
Walled Spores Produced in Sporangia (Sporangia, Sporocytes and Spores)
- sporangia: multicellular organs on sporophyte where spores are produced
- sporocytes: diploid cells in sporangia, undergo meiosis -> haploid spores
- spores: haploid reproductive cells (spore wall contains sporopollenin) [resistant to hard conditions]
Multicellular Gametangia
- organs on gameteophyte where gametes are produced
- 2 types of gametangia: Archegonia and Antheridia
what are the two types of gametangia?
- archegonia: produce eggs, site of fertilization
- antheridia: produce and release sperm
Apical Meristems
localized regions of cell division at tips of roots and shoots
-cells differentiate from apical meristems
Cuticle
- waxy covering over all above-ground parts
- benefits: prevents desiccation, provides some protection from microbes
- costs: does not allow for gas exchange
Stomata
(singular = stoma)
- tiny openings on surface
- can open and close
- allow gas exchange
- allow water evaporation
how are extant plants grouped?
based on vascular tissue
vascular tissue
transports water and nutrients
nonvascular plants
- bryophytes (bryophyta): mosses and relatives
- basal Land plants
- lack specialized vascular systems/transport tissue (rely on diffusion, osmosis -> typically small, require moist environment for: getting water to all cells and reproduction [sperm swim to egg])
- paraphyletic
vascular plants
- seedless and seed plants
- seedless vascular plants: Ferns and related plants
seed plants
majority of extant plant species
seed
embryo with supply of nutrients with protective coat
gymnosperms
- “naked seed”
- seeds not enclosed in a chamber
- ex: conifers
angiosperms
- “container” seeds
- flowering plants
- seeds enclosed in fruit (peach)
- most dominant type of plant
gametophyte (n)
gamete-forming plant
sporophyte (2n)
spore-forming plant
sporangium
spore-producing structure
what is the moss life cycle
alternation of generations - haploid dominant
moss life cycle (haploid)
male
spore ->mitosis-> male gametophyte->mitosis in antheridium->sperm->swim-> egg in archegonium
female
spore->mitosis->female gametophyte->mitosis in archegonium->egg in archegonium
moss life cycle (diploid)
egg in archegonium (n)->fertilization->zygote->mitosis->sporophyte->meiosis in sporangium->spore
what is the importance of mosses?
- extremely common
- can colonize bare, sandy soil
- sometimes harbor N-fixing bacteria (help retain N in soil)
- Peat
Peat
partially decayed organic matter
- peat moss is important component
- important fuel source
- important C reservoir (3% of Earth’s surface by ~30% of C in soil)
vascular plants
- earliest fossil ~425 mya
- dominant today
list the derived traits of vascular plants
- sporophyte dominant
- transport in vascular tissue
- roots
- leaves
- sporophylls
- spore variations (homo- and heterosporous)
lignin
polymer in cell walls of water-conducting cells of xylem
xylem
tube that conducts water and minerals - contain lignin
phloem
tube that conducts sugars, AAs, and organic products
sporophyte dominant
larger, independent of gametophyte
transport in vascular tissue
don’t have to be flat anymore (enables tall growth [outcompete shorter plants for light, better spore dispersal])
-lignin, xylem and phloem
roots
organs that absorb water and nutrients from soil, anchor plants -> allow for taller growth
leaves
main photosynthetic organs, more SA
sporophylls
modified leaves with sporangia
- very diverse
- ferns: leaves with sori
- gymnosperms-cones
spore variations
2 forms of spore production
homosporous: 1 type of sporangium produces one type of spore
- most seedless vascular plants
- sporangium->meiosis->spore->mitosis->bisexual gametophyte (produces both egg and sperm)
heterosporous: 2 types of sporangia producing 2 spore types
- megasporangium->meiosis->megaspores->mitosis->female gametophyte->mitosis->egg
- microsporangium->meiosis->microspores->mitosis->male gametophyte->mitosis->sperm
seedless vascular plants
- paraphyletic
- 2 clades- Ferns (monilophytes) and related plants
- many are epiphytes, use other plants as substrate, not parasitic (grow on surface of trees)
fern life cycle
- homosporous spore production
- spores grow into free-living bisexual photosynthetic gametophyte
- gametophyte develops antheridia and archegonia
- sperm and egg produced at different times - prevents self-fertilization
- flagellated sperm swim to egg -> fertilization (requires water)
- zygote grows in sporophyte, grows out of archengonium
- spores produced via meiosis in sori: clusters of sporangia under leaves
