BIO Plants 4 - Seed Plants & Gymnosperms

3 innovations of seed plants

wood, seeds, pollen

era has tallest trees

now (holocene) but they are carniferous that evolved cretaceous era

tree simple vs strict definition

plant with single stem, branching canopy, can reach large heights thanks to specialized cells

has wood and increases in girth (trunk thickens)

Gilboa Tree

• first tree like plant

• mid devonian → late … 8m → 20m

• dont have true wood - just xylem stands that with spoungy tissue around

• paleobotanical discovery

First Carboniferous Era Forest

• ancient fern, clubhorse, and giant horsetail forests (50m tall) that dominated wetlands that covered pangea

• shallow roots and plants would fall over and get compressed peat→ coal

**coal not renewable resource

Wood

Vascular Cambium: ring of cells beneath bark that produces xylem and phloem

dead xylem cells accumulate

woods is made up of lignified xylem

**all allow for growth wide and height

Emerald Ash Borer

invasive beatle whos larvae eat phloem and outer xylem…trees dont store nutrience and starve to death 1-2 years later

Archaeopteris

fossils found - extinct genus of fern like trees - show the evolutionary transition from ancient trees to modern gymnosperms

• similar conifer wood

• trunks 30m with reinforced branch joints

• fern like leaves

• reproduce via heterspory (2 types of spores)

Distinct Life Cycle Charecteristics from Fern Life Cycle **might delete

• no longer dependent on water for mating

• pollination

• diploid life stage doing dispersal

• gametophytes not free living - germinate on female tissue

• reduced gametophyte stage 

Heterospory description

key innovation of gymnosperms

2 sizes of spores with different sexes

• megaspores (F) → become seeds

• microspores (M) → become pollin

lead to evolution of seeds and pollin

Evolution megagamyetophyte to seeds

changes happening simultaneously…

• becomes 1 megaspore per sporeangium (instead of MANY)

• megaspore retained in sporangium while it germinates

• integument - megaspore becomes surrounded by protective outer layer

• ovule - megasporagium enclosed in integument - not exposed to air and can colonize drier evironment

integument

protective tissue that surround sporangium - protection from environmental conditions…will eventually develop into seed coat

ovule

megasporaguim that is completely closed expect for micopile in integument

consequences of need of male gametophyte to burrow to access female gametophyte (megaspore)

plants can recognize own pollen and then prevent inbreeding (egg fertilizing own pollen)

seed

a fertilized ovule

heterospory as an important evolutionary step

lead to evolution of seeds pollen, Protection of the Female Gametophyte, nourishment of embryo from parent plant - enhancing survial rates

evolution of microgametytophyte to pollen

• microspores evolve into pollen grains or male gametophyte

• these are 2-3 cells covered in coat of sporopellenin (makes pollen desication resistant) and can travel through environment without water

• germinates when lands on right spot of female tissue and becomes pollen tube and then pollen swims through

allowed for efficient reproduction in dry habitats

**male gametes no longer has to travel through environment … pollen is only released when pollen tube formed

modern gymnosperm ‘naked seed’ charecteristics

• seed plants without flowers or ovaries

• their seeds are solitary (rare) or develop in/on scales/leaves

• ovules are open to the air to be directly pollinated (by pollen that does travel through air)

age of gymnosperms

mesozoic

cycads specifically dominated and many herbivore dinos ate them

extant gymnosperms

cycads, ginkos, conifers

Cycads

• mostly tropical

• 100 species

• slow growing and live long

• large cone at apex of trunk

• have seperate female and male plants

• motile sperm with 40000 tails 

ginkgos

• first appeared 270 mya, didn’t diversify a lot

• 1 extant species, most closely related to cycads

• visibly related to prehistoric fossils

• seperate female and male plants

• motlie sperm

• males are resistant to pollution

conifers ‘cone bearers’

• most diverse extant gymnosperms - 630 species

• woody, cone bearing

• dominate boreal forest (largest boreal environment

• tallest and oldest non-conal living organism

pine dryness specialization

hot and cold

thin waxy densly packed needles reduce wind

pine cold specialization

thick bark, cone shelter seedsp

pine snow adaptation

cone shaped, down facing, flexible branches

urban heat island effect

dark material that absorb heat

canyons created by tall buildings that trap heat

**montreal is 10C hotter that surrounding land

cooling effect

trees have largest cooling effect

bc of shade, evaporative cooling (like sweat)

2ND: temp difference under canopy creates breeze that cools significantly