3rd and 4th Major Transitions of Plants Flashcards
3rd major evolutionary transition
Development of Seeds
Development of Seeds
All plants beyond this point in evolutionary time use SEEDS FOR REPRODUCTION, Gymnosperms, Earliest seed bearing plants
All species possess female and male cones, which hold the gametophytes that produce eggs and sperm(thus all fertilization and seep development occurs on the cones); DO NOT HAVE MOBILE SWIMMING SPERM!
Gymnosperms
means naked seeds, as eggs are completely open(naked to) fertilization, not enclosed by diploid tissue
***Different from fruits and flowers, which are only found in Angiosperms(a different group)
Groups of Gymnosperms
Cycads(Cycadophyta), Gnetophytes(Gnetophyta), Ginkgo trees(Ginkophyta), Conifers(Pinophyta)
Cycads(Cycadophyta)
Evergreen(meaning they don’t lose leaves seasonally), tropical gymnosperms; Largest sperm in world(0.5-1mm in length); Ancient lineage date back approx. 135 mya
observe image of cones on pg. 29
Gnetophytes(Gnetophyta)
Found in dry, arid desert habitats(Indicates low dependence on water for reproduction); Ancient lineage, date back to approx. 135mya(Pseudofederin from this, come from this group)
Example Welwitschia mirabilis: only in Namib Desert in southern Africa(Indvidiaul plants are often greater than 1,000 years old)
Ginkgo trees(Ginkophyta)
All extinct except Ginkgo biloba; only an ornamental now(extinct in wild);
Ancient, greater than 270 mya, very diverse fossils(trees, shrubs, vines); Based on fossils was found in broad range of habitats(very wet to very dry); range indicates well developed vascular system and reduced reliance on water for reproduction
Conifers(Pinophyta)
Wilderness type environments; Pines, firs, spruces, junipers, cedars, cypress(trees and srhubs) with needle-like leaves
Habitat range from wet to dry habitats(Cypresses to conifers/junipers)
(**remember, if able to live in dry habitats means they do not have swimming sperm)
Known for cultural importance(ornamentals in gardens, important aspect of Christmas)
Known for extremes
Extremes of Conifers(Pinophyta) Examples
Bristlecone Pines: dry cold moutnaintops in western US, some of oldest organisms on Earth
Methuselah is approx.. 4,845 years old
Coastal redwoods are tallest organism on Earth
Sequoias: largest organism relative to biomass(weight)
Extreme Wet and Dry Habitats for Conifers(Pinophyta)
Dry arid(pine), No water needed for reproduction since no mobile swimming sperm
(**challenging due to lack of water; possible since well-developed xylem and phloem for moving water, minerals, nutrients around plant AND storing it)
Wet: Cypresses, the ones covered in water in streams(knees allowing for maintenance of oxygen in roots to prevent rotting); Adapted to very wet habitats, have adaptations for gas exchange while living in water
Needles in Conifers(Pinophyta)
adapted to dry/arid conditions; Thin, narrow; Greatly reduced surface area means losing less water during transpiration; Fewer stomata on needles; Can still take in Co2 in photosynthesis, but lose less water in evaporation; Have thick, waxy cuticle to reduce water loss
Reproduction in Gymnosperms
Water not required, because no mobile sperm; Male and female cones hold the gametophyte;
Pollination/fertilization is where wind moves pollen(male gametophyte containing sperms) from male cone to female cone(contains female gametophyte egg/ovule); if pollen comes into contact with egg/ovule on female cone, fertilization can occur, leading to development of SEED
once mature, winged seeds moved around by wind allow for seed dispersal to new locations and possibly germination and growth
Seed Dispersal across Gymnosperms and Angiosperms
Critical for all gymnosperms and angiosperms (flowering plants); If seeds not dispersed, they would end up at bottom of parent plant where germination is unlikely (low light, less water and nutrients)
To solve issue, approaches to seed dispersal are quite variable; Some plants drop seeds, which are then moved by other forces(wind, water, animals, etc.) while other have adaptations that aid in dispersal
Wind Dispersed Seeds and examples
Notice fluff, wings, “umbrellas”, etc.; That keeps seeds up in air to move long distances; Seeds tend to be small, light, and plants produce many seeds
- Example: milkweed Asclepias
- Example: dandelion Taraxacum
- Example: maple acer
Water dispersed seeds
Larger seeds made of woody plant tissue, typically very buoyant; Float until hey encounter land, then germinate; Do not break down easily in water(time frame not guaranteed of when reaching land)
Fire dispersed seeds and Example
Example: serotinous cones, stay closed until seeds release is triggered; Cones open up after fire, liberating seeds for dispersal
Animal Dispersed Seeds: Passive Movement
“hitchhikers”; Seeds with hooks(like Velcro), spikes that attach to fur, feathers, clothes, etc.
Animal Dispersed Seeds: 2 ways of Active Movement
Seeds gathered by animals species that hid and hoard seeds for later eating; many seeds lost/forgotten, which can then germinate
Fruits with seeds are eaten by animals; seeds them pass through digestive system and feces(end up on ground with potential to germinate); Some plants even require seed passage through and organism in order for germination to occur
Animal Seed dispersal: Active Movement Examples(Name 1 Hidden Example and 2 Digestion Examples)
Ants, red squirrels burying walnuts, woodpeckers store food for future by drilling holes in dead trees or in put in spaces in bark
southern cassowary; Fruitivores, Do not like other organisms, In Australia; Plants not reproducing successfully because they have disappeared; seeds from these plants require passage through digestive tract of them as feces to germinate
mistletoe, parasitic plant: Dispersed by certain bird species, Preferred food of certain species; Birds eat fruit, then spit out mistletoe seed(since cannot pass through digestive system); If lucky enough, seeds are spit out and land on tree branches, germinating and growing roots into branch of tree to live there; Taking advantage of water and nutrients from plant(REQUIRES passage through stomach or digestive system of bird to grow)
4 General Benefits of Seeds
dispersal, energy reserves, protection, and dormancy
Why is dispersal a benefit of seeds?
increases possibilities for dispersal (as we just covered); Can move or be moved into habitats good for germination/growth
Why is Energy Reserves a benefit of seeds? Provide Example?
Seeds contain endosperm(carbohydrates) that provide energy for use during early plant growth
Example: corn(when popped into popcorn, white outer cover is endosperm; kidney beans
Seeds also have cotyledons(seed leaves), allow photosynthesis to occur IMMEDIATELY following germination
Example: squash seeds
Why is protection a benefit of seeds?
hard outer covering reduces physical damage, seed predation
Why is dormancy a benefit of seeds?
Produce Plants that bridge seasons, avoid germination in winter/dry seasons; Allows them to wait for good growing conditions (based upon moisture, temperature, photoperiod)
4th Major Evolutionary Transition
Development of Fruits and Flowers
Development of Fruits and Flowers
Angiosperms, Arose approx. 150 mya; Flowering plants, most speciose; Greater than 275,000 species; range from flowers on ground, paired with fruits, on trees, etc.
Angiosperms
Means “vessel seeds”, eggs(ovules) are encased in diploid tissue(fruits and/or flowers), which does not prevent fertilization by sperm
Why flower and fruit?
At core, all about POLLINATION!!! Increases likelihood of pollination; Angiosperms are NOT DEPENDENT upon wind for successful pollination(Unlike gymnosperms)
- Rely on insects like bees and butterflies, mammals like bats, and birds and lizards(hummingbird, geckos)
- Presence of flower draws them in
How is pollination driven?
Primarily Animal-Driven
Strong selective pressures exist for enhancing successful pollination and pollinator attraction, such as Reward, Odor, and Appearance
Reward of Animal-driven pollination
pollen, nectar; For every flower they visit, they have the potential to drop pollen at the next flowers they visit from the previous
Odor of Animal-driven pollination
Any scent they have(good or bad, sweet or death-like scent) to draw in pollinators are beneficial to the plant
Appearance of Animal-driven pollination
color(natural, UV light), shape(structures, overall shape, conformation)
Attracted to lots of yellows and oranges; More organisms attracted to UV light; centers really pop in UV light
Small orchids(and/or others) can mimic insects in shape and pheromones/perfume to be seen as a pollinator of that species; create Sex-crazed males lol
Pollination Structures
anthers, stamen, and stigma
Anthers
produce pollen(male gametophyte), making it available to pollinators
Stamen
male reproductive structure, paired with anther at tip; Pollen(male gametophyte) can be inadvertently deposited on the stigma
** if animal gathered pollen or gets it stuck to them, move it to other flowers
Stigma
female reproductive structure; Stigma at tip; Pollinator deposits pollen on stigma
Pollen grain has two sperm, which act to fertilize egg/ovule(female gametophyte)
Pollen Grain Process
Pollen grain “germinates” on stigma, producing hollow, root-like structure that grows down the carpel to ovary
Sperm move down structure, sperm one breaks into ovary, allowing sperm two to enter and fertilize the egg/ovule; This leads to successful production of seeds
Can flower reproduce by itself/for itself?
Depends on structures of stigma and anthers, Self-fertilization totally possible; Some plants are hermaphrodites(pollen just drops off anther to stigma); Can be fully functional with this happening, really not any inbreeding effects
