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116 Cards in this Set
- Front
- Back
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Prokaryotes
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1) 4.3bya Molten due to catastrophic impact that gouged out the moon
2) By 3.8bya, oldest evidence of life (oxidized iron in rocks, oxidation requires atmospheric oxygen which only is produced by photosythesis) |
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Theories for the appearance of the first organic molecules
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1) Oparin and Haldane, 1920: early earth may have had a reducing atmosphere (unlike today’s oxidizing atm)
2) These conditions may have been planet -wide or just near volcanoes or other volcanic vents 3)Urey & Milleri, 1953: lightening in early reducing atm can potentially create aa’s and other organic molecules a reducing atm is a key ingredient in the initiation of life |
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Self assembly
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once an ample supply of simple organic molecules is established they can combine on their own to make macromolecules.
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Clay molecules in self assembly
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a) clay particles can act as catalysts to speed up this process.
b) clay particles can also act to speed up the formation of vesicles. |
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Coacervate Vesicles
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a) after the appearance of macromolecules, there needs to be a boundary between the molecules and the outside world
b) lipids found in an aqueous environment can form lipid vesicles (clay speeds up this process) c) chemical reactions can begin in these vesicles aided by clay catalysts |
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Coacervate Vesicle Properties
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These vesicles exhibit some of the properties of life
(1) vesicle membranes can be selectively permeable (2) vesicles can divide (3) vesicles can grow in size |
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Protocell characteristics:
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a) selectively permeable membrane
b) boundary membrane that divides and grows c) RNA-like molecules act as genetic material d) RNA’s as well as aa globs that can act like enzymes e) all processes within protocells can evolve with time and become more and more sophisticated. |
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Protocell behavior
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Protocells eventually behave as simple cells
a) “time is on your side” b) first life probably evolved several times and died out. c) all life is seems to be monophyletic but it isnt known if the first life was an Archeaen or a Bacterium d) first life was probably an extremophile with a simple anaerobic metabolism |
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1st cell characteristics
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4) 1st cell characteristics
a) simple anaerobic metabolism: fermentation? hypothetical simple metabolism b) no organelles d) proliferated like crazy as they (1) divide by binary fission (2) have no predators (3) have an enormous supply of organics to live on |
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Where did 1st life start?
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Since all life requires water, it very like started in water: some possible sites
a) oceans or ponds with silty shores (which provide clay catalysts) are well documented possibilities b) deep sea thermal vents provide raw materials chemical energy and surfaces to reactions to occur (recently proposed possibility) c) Volcanic vents found on land d) Life could have initiated on another planet and was delivered to earth via asteroids |
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Where did the oxygen atm come form?
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a) the first great extinction came where the simple organic molecules that the first proks. lived on were used up
b) some sort of way of providing organic carbon must have evolved (i.e. an autotrophic metabolism) and eventually led to photosynthesis c) once photosynthetic proks existed, in time an oxidizing atm followed due to the oxygen waste produced by PS (oxygen atm between 2.7 to 3.8bya) |
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The dominant domain is...?
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Domain Bacteria
Dominant in terms of #'s of individuals by far (e.g. # of bact in your mouth is way more than the # of people that have ever lived) |
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Why are bacteria the dominant domain?
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- they are extememly successful and diverse.
- live in all environments except maybe the throat of a volcano. ----- hot springs ----- salt ponds ----- deep underground - These extremophiles may be very similar to the 1st bacteria |
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How come bacteria are essential?
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They are diverse in metabolism and habitat and are essential to all ecosystems.
a) PS originated in prokaryotes and cyanobacteria provide O2 and can fix CO2 (e.g. Anabaena spp.) b) some degrade wastes (including dead bodies of plts and animals, e.g. Bacillus spp.) c) involved in many symbiotic relationships ( e.g. bacteria degrade intestinal contents and are necessary for correct development of the GI tract, mycorrhizal relationships abound) d) essential in many other ways |
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Bacteria in biotechnology
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6) some bacteria are easily engineered through biotechnology (e.g. E. coli, others)
a) very useful for making a variety of protein products used in medicine, agriculture, chemistry and research. |
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Examples of bacteria diseases
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a) skin infections
(Staphylococcus aureus) b) intestinal distress (e.g. Salmonella dysenteriae, c) anthrax (Bacillus anthracis) d) Lyme disease (Borellia bergdorferi) |
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What are some characteristics of bacteria?
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1) small size: ~ 1-5 μm
2) no organelles 3) small haploid genome, therefore evolves quickly 4) cell wall of peptidoglycan (a net of glucose amines) that is rigid 5) a normal Phospholipid cm (some have a double cm) 6) can replicate very quickly by binary fission and therefore will evolve very quickly compared to slower growing diploid orgs. |
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How did eukaryotes come to rise?
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It is very likely that prok. gave rise to the Euk’s, but no clear-cut progenitor Prokaryotes have been found that clearly evolved into a Euk.
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Why would finding a progenitor of Prokaryotes be difficult?
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any theory that proposes that a Prok. evolved into a Euk. must account for the Prok. origins of:
•nucleus√ •ER √ •diploid genome √ •mito/plastids √ •mitosis •9+2 flagella seen in Euk. •sexual repro (Lynn Margulis of BC, continues to work on this) |
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Origins of basic Eukaryotic structures
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a) mito/plastids: endosymbiosis
b) nucleus/ER: invagination of cm c) 2n diploid genome can be easily envisioned from (1) fusion of 2 prok genomes OR (2) prok genome replication but non- disjunction occurs |
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Origin of complex Eukaryotic structures
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(1) 9+2 flagella
(a) one guess is a symbiosis between an •a primitive Euk.-like an Archeazoan: e.g. Giardia intestinalis •has 2 nuclei •no mito (but were secondarily lost) •primitive cytoskeleton •primitive rRNA sequences •+And whole spirochete bacteria •provides flagellar filaments •symbioses like this are known |
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if the microtubules found in Euk. flagella were acquired in this manner (symbiosis), does this explain the origins of Euk. cytoskeleton and flagella?
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Maybe
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Does the symbiosis explain the origins of a major part of the spindle apparatus: the spindle fibers?
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Maybe
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Is Kingdom Protista poly or mono phyletic?
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It is polyphyletic and that is one of the main reasons that the idea of K. Protista is outdated.
Candidate Kingdom Archeazoa is also polyphyletic and probably will be divided too. |
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Example of multicellularity
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(i.e. it is a polyphyletic characteristic)
a) algae, fungi and poriferans are good examples: colonial euk. specialization of cells simple multicelled euk. |
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What are some characteristics of fungi?
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1) nearly all are saprophytes: degrade dead matter for C, energy
(a) secrete digestive enzymes and absorb chems (b) along with bacteria are very important degraders in environ. 2) Not photosynthetic (a) not related to plants 3) all mushrooms and filamentous fungi have hyphae (a) can have crosswalls (hyphal filaments are chains of cells) OR (b) are without crosswalls (hyphal filaments are one big cell with many nuclei) 4) cell walls is made of chitin (nearly unique to fungi as a cell wall material, but is found in insect exoskeletons) 5) Some primitive fungi (chytrids) seem to be related to one of the protists that has hyphae, chitin cw, metabolism and genomic characteristics related to the fungi (so are fungi polyphyletic too or is this protist actually a fungus?) 6) repro is asexual (budding, fragmentation, spores) or sexual ( note: Some prehistoric fungi were over 25ft tall.) |
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define saprophytes:
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degrade dead matter for carbon energy.
--- secrete digestive enzymes and absorb chemicals --- along with bacteria are very important degraders in environment. |
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Mycorrhizal relationships
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7) Mycorrhizal relationships abound in the plt kingdom
a) most, if not all plants have fungal infections of their roots b) Mycorrhizae are actually symbioses c) plants require them for effective absorption of water and mineral from soil d) many plants with mycorrhizal relationships can not live w/o the fungus e) may have evolved before roots |
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What are some characteristics of algae?
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1) PS
2) various cw materials (i.e. polyphyletic) 3) single celled or colonial 4) Ox. Respiration 5) marine or freshwater mostly 6) beyond these char, are pretty variable |
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Importance of algae in general?
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1) Phytoplankton are at the base of the food chain and therefore are a major source of food for all animals
2) a major CO2 fixer, they also form the base of the C cycle 3) gave rise to the oxygen atm and the ozone layer 4) good source of cheap protein in some parts of the world 5) Algal extracts are used in many products like ice cream, beer, paint, cosmetics and agar. |
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Origins of Algae
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first seen as fossil prokaryotic algal mats (stromatolites) about 3.5 bya
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What are the 3 divisions of algae?
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1. Red Algae (D. Rhodophyta)
2. Brown Algae (D. Phaeophyta) 3. Green Algae (Division Chlorophyta) |
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What are the basic characteristics of red algae (D. Rhodophyta)?
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- mostly marine
- have red photopigments and chlorphyll a - can have calcium carbonate (CaCO3) in extracellular matrix and can be hard. |
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What are the basic characteristics of brown algae (D. Phaeophyta)?
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a) mostly marine
b) have brown photopigments and chla c) examples (1) kelp (Macrocystis giganticus) (2) diatoms are common plankton organisms e.g. Red tide (3) related organisms: water molds (not PS) e.g. ick of fish e.g. downy mildew of grapes (almost wiped out French wine industry in 1880’s) |
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What are basic characteristics of green algae (chlorophyta)?
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a) origin was probably endosymbiosis of
cyanobacterium (provides PS apparatus) and flagellated heterotrophic euk b) fresh water & marine, other diverse habitats c) have Chla and Chlb (like plants) d) store C as starch in plastids (like plants) e) make phytochromes by the same metabolic pathway as plants f) most have a cellulose cw g) ultrastructural similarities to plants in cell div. h) Class Charophyceae is thought to be the progenitor to plants (based on shared ultrastructure) i) the Chlorophytes are the only algae that are in K. Plantae |
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Which algae is the only one classified in the kingdom plantae?
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chlorophyta. (the green algae)
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Chlamydomonas sp. characteristics
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a) PS with Chla and Chlb
b) cellulose cw c) a typical plt life cycle d) a much studied organism: much plt genetics is done with this Chlamydomonas sp. e) class Chlorophyceae, not in class Charophyceae (An Ancestor of Charophyceae are likely the ancestors to green plts) |
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Chlamydomonas life cycle exhibits...?
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exhibits Alternation of Generations, the reproductive method that is shared by all plts
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What is Alternation of Generations?
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(1) The plant has 2 distinct plant bodies: a Sporophyte generation and a gametophyte generation
(2) sporophyte: makes spores, diploid (3) gametophyte: makes gametes, haploid |
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Describe Chlamydomonas life cycle
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(( https://imageshack.us/a/img845/128/screenshot20130415at822.png ))
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drawbacks to Chlamydomonas life cycle
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a) the Isogamous +/- gametes swim around and find each other: chance meeting
(1) unspecialized gametes: no specific and direct delivery system of one gamete to another gamete (2) isogamy is the ancestral state/oogamy is most derived state (3) swimming gametes must have water for fertilization b) no plant structures that protect gametes or zygote c) they are homosporous: + / - spores are identical, with no derived structures which protect or aid survival |
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comparison of Chlamydomonas to land plts
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(1) All land plts have visibly different versions of male and female repro structures (i.e. oogamy)
(2) all plts have a life cycle derived (evolved) from the isogamous life cycle |
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Important classes of Green algae
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Class Chlorophyceae
Class Charophyceae |
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f. Note on Green Algae
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In 2001, genetic evidence shows the oldest extant plant to be a stonewort, a green alga with CaCO3 deposits for support, that lives in fresh water shallows; class Charophyceae.
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Bryophytes are also known as...
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Non Vascular plants
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Bryophyte intro
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1) Liverworts (P. Marchantiophyta )
2) Mosses (P. Bryophyta) 3) Hornworts 4) remember: unicellular algae (like Chlamydomonas) (a) must live in water and its repro is tied to water (b) no specialized cells for repro |
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For Bryophytes to live on land, what must happen?
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a) develop a means to avoid dehydration
b) develop a means to support the plant body c) develop a means to collect sunlight out of water d) abs water and nutrients from soil e) develop a means to reproduce out of water f) develop a means to avoid UV induced mutation and death |
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Bryophytes: Means to support plant body
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) 1st land plts had little supportive tissue, therefore bryophytes lay close to the ground (some have “pre- vascular” tissue)
b) Bryophytes grow from basal meristems not apical meristems. c) Note: The few extant water plts entered the water secondarily (e.g. Turtle grass) The 1st "real" plts evolved on land~ 0.5 bya. (In other words plts did not evolve in water and then move to land). |
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Bryophytes: develop a means to collect sunlight above ground
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a) evolved organs with light collecting surfaces
(1) tiny leaf-like appendages: scales (2) Note: scales in Bryophytes are not homologous to leaves but are analogous to leaves (based on anatomy) |
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Bryophytes: organs to collect water and nutrients from the soil
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a) developed rhizoids, tiny single cell "rootlet" like appendages
b) note: rhizoids are not homologous to roots but are analogous to roots based on anatomy |
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Bryophytes: reproductive structures: develop a means to reproduce out of water
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a) The male gametangium is called the antheridium (s.) /antheridia (pl.)
b) The female gametangium is called the archegonium (s.)/ archegonia (pl.) |
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Antheridium
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(1) found on gametophyte
(2) antheridia make haploid sperm (i.e. male gametes) (3) antheridia encase and protect sperm until released (4) flagellated sperm require water to swim |
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archegonium
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(1) found on the gametophyte
(2) make haploid eggs (female gametes) (3) encase and protect egg (4) encase and protect zygote |
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Why do Bryophytes have great advantage over unicellular algae in terms of reproductive efficiency?
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(1) no longer rely on plus and minus gametes, bryophyte gametes are oogamous
(2) gametes do not meet by chance, they have gametangia that aid in that process (3) gametes and zygote are protected in gametangia (4) Bryophytes can be either homosporous (i.e. single bisexual gametophyte, ancestral), or heterosporous (separate gametophytes, more derived) |
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Bryophytes; develop a means to avoid UV induced mutation and death
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a) Protection due to ozone layer and not the plt itself
b) ozone absorbs UV c) But it is likely that plts that have dominant diploid (sporophyte) generation are making contingency plans to protect themselves from UV by having at least 2 copies of every gene |
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Bryophytes: dehydration problem
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a) Some Bryophytes have a cuticle: decreases direct evaporation
b) Some Bryophytes evolved the 1st stomata with guard cells c) ancestral state is to have holes directly to interior (e.g. liverworts) |
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Primitive states of Bryophytes (review)
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1) no real vascular tissue
(a) no strength to stand up (b) mostly rely on diffusion to disseminate nutrients 2) no real roots 3) Gametophyte generation (haploid) dominant; sporophyte is small and retained within the gametophyte 4) some have interior of plant directly open to outside through unregulated holes (e.g. liverworts) 5. reproduction still tied to water |
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Bryophyte life cycles
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1) Phylum Marchantiophyta: Liverworts
2) Phylum Bryophyta: Moss |
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Liverwort
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a) can reproduce asexually via gemmae (pl.)
b) sexually by alternation of generation (gametophyte dominant) (gametophyte = thallus + gametangia) |
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Liverwort lifecycle
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(( https://imageshack.us/scaled/large/191/screenshot20130416at122.png ))
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Moss
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a) Life cycle also exhibits alternation of generations (gametophyte dominant) )
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Moss lifecycle
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(( https://imageshack.us/scaled/large/341/screenshot20130416at122.png ))
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Pteridophytes
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Seedless Vascular Plants
1) main groups (a) Phylum Monilophyta: ferns & horsetails (b) Phylum Lycopodiophyta: club mosses |
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Origin of Pteridophytes
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Pteridophytes are derived from the Bryophytes, beyond that its is unclear.
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Advances of seedless vascular plts over the bryophytes
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1) 1st grp to develop true vasc. tissue and lignin
2) leaf evolution: With the evolution of the stele, leaf evolution accelerates. 3) The sporophyte dominant in seedless vasc. plts 4) Much less dependant on water for reproduction due to male spores. 5) have apical meristems and therefore derived pattern of 1° growth 6) Fern life cycle demonstrates many of the evolutionary advances of the seedless vasc. plts |
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Vascular tissue in pteridophytes
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(a) able to stand upright due strength of vasc. tissue and lignin
(b) ability to transport fluid efficiently due to vasc. tissue (1) vasc. tissue limited to tracheids, the more ancestral conductive cell type (c) Protostele (earliest stele) found in lycophytes (club mosses) and whisk ferns. (d) Further evolutionary modifications lead to more advanced steles in ferns and the line which leads to gymnosperms & angiosperms. |
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Leaf evolution in pteridophytes
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a) Microphylls
b) Megaphylls |
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Microphylls
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(1) 1st leaves are microphylls: outgrowths of parenchyma tissues that are then vascularized. Most of these leaves are small.
(2) microphylls are commonly seen in the club mosses and whisk ferns |
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Megaphylls
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(1) protosteles spawn the more advanced steles seen in ferns and seed plts
(2) advanced steles lead to vascularized branching stem systems (3) branching stems fuse to form megaphylls (4) megaphylls have branching vascularization. |
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sporophyte dominant in seedless vasc. plts
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(a) The gametophyte generation is dominant in bryophytes.
(b) Seedless vascular plts are sporophyte dominant (larger, more robust, greater branching, mutations less hazardous due to diploidy). c) gametophyte is small and fragile (although some can withstand drying out) |
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Lower dependance on water of pteridophytes
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a) desiccation resistant
(b) able to be distributed by wind (c) but do not have much of a food reserve to sustain the embryo. |
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Fern Lifecycle
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(( https://imageshack.us/scaled/large/15/screenshot20130416at552.png ))
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retained primitive states of seedless vascular plts
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1) still do not have roots
(a) larger than the rhizoids of bryophytes and multicelled: rhizomes 2) not all have megaphylls, some still have microphylous scales 3) repro better adapted to land, but still primitive as it requires H2O for swimming sperm 4) gametophytes are free-living, unprotected 5) While oogamous, still mostly homosporous except for some of the more advanced seedless vasc. plts. |
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Homosporous spore production
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means
having 1 type of spore that makes a bisexual gametophyte Sporangium in sporophyll -> Single type of spore ->Typically a bisexual gametophyte -> Eggs and sperm |
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Heterosporous spore production
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means having 2 types of spores that make either male or female gametophytes
Megasporangium in megasporophyll - > megaspore -> Female gametophyte -> Egg Microsporangion in microsporophyll -> Microspore-> Male gametophyte -> Sperm For example Water ferns and the lycopod Isoetes |
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the 1st cones are seen in ...?
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horsetails and club mosses, which become important in the gymnosperms.
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the earliest land plant known is?
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is Cooksonia, slightly later vascular plts
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What is Psilotum ?
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It is an example of a P. Monilophyta fern that has lost many of its more derived features.
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What are Gymnosperms?
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They are plts that produce seeds, but do not grow a fruit around them, i.e. the seed is naked.
Most make cones instead. |
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What are the 4 phyla of gymnosperms?
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a) conifers (pines): (P. Coniferophyta), cone with fascicle-borne leaves
b) cycads: (P. Cycadophyta), palm-like cone bearers, mostly tropical c) P. Ginkgophyta, (only Ginkgo biloba is extant: pretty fan-like leaves (on campus next to 200 building) d) Gnetophytes (P. Gnetophyta): no common characteristic but are probably monophyletic. Only one in SD area is Mormon tea of the Anza- Borrego desert (Ephedra sp.) e) several extinct Phyla: Seed ferns and the Bennettitales |
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Comparison of gymnosperms with Bryophytes and seedless vascular plants
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gymnosperms have all of the advances of Bryophytes, and the Seedless vascular plts
a) such as real leaves, cuticle, sporophyte dom., vascular tissue b) plus many more advances which make it a very successful group, even today |
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Gymnosperms are heterosporous or homosporous?
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All Gymnosperms are heterosporous
a) Therefore Gymnosperms make microspores (develop into the microgametophyte) and megaspores (develop into the megagametophytes, the ovule, which then in turn develops into the seed) |
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Roots of gymnosperms
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1) 1st real modern roots
a) have stronger more advanced conductive cells (i.e. tracheids and vessel elements) in Gnetophytes, help hold plt upright b) more advanced stele, better constructed for conduction |
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What does the gymnosperm seed consist of?
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b) The seed consists of seed coat, megagametophyte (food), and embryo
1) the embryo develops from the zygote, which is the product of fertilization. In other words, the zygote comes from the fusion of the microgamatophyte (pollen grain) and megagametophyte (egg) 2) the megagametophyte, a source of stored food, is derived from the megasporangium (the thick cover layer of the female gametophyte) 3) seed coat, which covers the stored food and embryo, is derived from the integuments |
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advantages of the seed
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(1) seeds can provide a period of dormancy
(2) embryo protected from dehydration (3) female gametophyte can provide nourishing oils or protein to embryo (none found in spores) (4) often better dispersal than spores: seeds or seed coats can have wings, hooks or are sticky (5) seed coat offers physical protection for embryo |
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New tricks of gymnosperms
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- No water is required for reproduction
a) no swimming eggs or sperm b) Stoboli (pl.), strobolus (s.) obviate the need for swimming gametes: use wind to disperse pollen and seeds c) Gymnosperms are the 1st plts to break the need for water for reproduction completely |
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The life cycle of gymnosperms includes the use of ...
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Strobuli (cones)
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advantages of the Strobulus
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(1) Cones are more efficient in bringing together sperm and egg
(2) Cones protect the developing embryo by retaining the developing female gametophyte and the next generation sporophyte within the parent plant (3) Cones have seeds which disperse the embryo more widely and gives it a better chance of survival. |
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The conifer tree (which is the 2n sporophyte parent) bears ...
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both pollen cones and ovulate cones.
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pollen cones
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(a) have microsporangia that hold the microspores (like antheridia of Bryophytes)
(b) make microspores by meiosis (c) microspores (the immature male gametophytes, n) develop into pollen (the mature male gametophytes, n) (d) pollen grains have a tough cover and so are durable & desiccation resistant. Notes: |
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ovulate cones
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(a) Each scale of the ovulate cone has 2 ovules
(b) Each ovule has a megasporangium (c) Megasporangium holds a developing megaspore mother cell (2n) (d) The megaspore mother cell (2n) goes through meiosis to form megaspores (n) |
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How long does the pine cycle need?
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2 years
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Size and location of male cones
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male cones are 2-3cm long and are usually on the lower branches to promote out-crossing
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The pollen cone has scales with...
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The pollen cone has scales (microsporophylls) with microsporangia on the lower side of the scale (a pollen cone is a simple system, where microsporangia are directly on the microsporophyll) therefore scales are homologous to leaves, the axis is therefore probably are homologous to a branch.
- the microsporangia contain many microspore mother cells - Each microspore mother cell produces 4 haploid microspores, which develop into 4 winged pollen grains. - the pollen grains represent the microgametophytes |
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Size and location of female cone
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The female cones are much larger and are usually on the upper branches to promote out-crossing
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The ovulate cone consists of...
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the ovulate cone is composed of ovuliferous scales that hold the ovules contained in the megasporangia, plus a sterile bract.
- The megasporangia are found on the upper side of the ovuliferous scale. - sterile bracts subtend branches only, therefore the ovul. scale is a branch system and the axis of the cone is analogous to the trunk of a tree (therefore ovulate cones are compound structures) |
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What is the nucellus?
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The nucellus (2n) is the cell layer directly outside of the megaspore (before the megaspore expands after fertilization). Each megasporangium contains a single megaspore mother cell.
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Each megaspore mother cells produces ....
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Each megaspore mother cells produces
4 haploid immature megaspores, of which only 1 survives to become the mature megaspore. |
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in gymnosperms, the ovule consists of...
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the egg (the mature megaspore) + megasporangium (2n) + integuments.
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in gymnosperms, the Megagametophyte consists of...
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egg + 1n “food” (AKA megagametophyte) (absorbed from megasporangium which is the old 2n nucellus)
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In gymnosperms what is the parental sporophyte ?
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The parental sporophyte is the ovuliferous scale & integuments. Once fertilization has occurred the zygote is formed and it is the next generation sporophyte.
In the seed, the seed coat and any left over nucellus are parental sporophyte |
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When does pollination occur?
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(1)pollination occurs in the spring while the ovulate cone has its scales separated.
(2) once the pollen grain has contacted the micropyle, it undergoes further development eventually making a pollen tube cell and 2 sperm cells. (3) the ovulate cone scales grow together to protect the developing seed. |
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The pollen tube
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The pollen tube grows though the megagametophyte towards the developing archegonia. This will take slightly more than a year.
-the pollen tube grows to the archegonium, and introduces the 2 sperm nuclei into the egg cytoplasm. - 1 sperm nucleus fertilizes the egg nucleus and the other sperm nucleus degenerates. - Usually several eggs in a single ovule are fertilized, usually only one develops into an embryo. |
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The megagametophyte develops how many archegonia?
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The megagametophyte develops 2-3 archegonia, each with an egg cell.
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The conifer seed is composed of how many generations?
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(1) The conifer seed is composed of 3 different generations
(a) the embryo (2n) is the new sporophyte generation (b) the seed coat (from the integument) and any left over nucellus is the old parental sporophyte generation seed coat removed (c) the old female gametophyte generation forms a nutritive envelope around the embryo (“food”) |
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Complete pine lifecycle
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https://imageshack.us/scaled/large/836/screenshot20130416at648.png
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Sporophyte vs Gametophyte
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https://imageshack.us/scaled/large/819/screenshot20130416at650.png
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The Evolution of the Gymnosperms is...
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Unclear.
a) Best guess is that the Gymnosperms evolved from a Seed Fern or Progymnosperm, but the details are unclear. (1) The fossil record shows abundant seed ferns and progymnosperms (both now extinct) with some ancestral and some derived characteristics. |
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evolution of the cone
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(1) the ovulate cone has ovuliferous scales with a megasporophyll, a sterile bract and ovules. Ovule consists of integuments, megasporangium and egg. The megasporangia are found on the upper side of the ovuliferous scale.
(2) sterile bracts subtend branches only, therefore the ovul. scale is a branch system and the axis of the cone is analogous to the trunk of a tree (3) On the other hand, the pollen cone scales are microsporangia, therefore analogous to leaves, the axis is therefore analogous to branches. (4) The message from (1), (2) and (3) is that the male and female cones evolved from different structures. (5) the ancestral structures are believed to be •pollen cone: spirally held leaves on a branch enclose microsporangia •ovuliferous cone: the scales are branches and the axis is a branch bearing structure (what is came from is unknown) |
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evolution of the ovule and seed
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1) necessary adaptations to form an ovule/seed
(a) megaspores retained in megasporangium (b) single megaspore per megasporagium (c) megaspore (when fertilized becomes the developing young sporophyte) retained in megasporangium (d) integument that encloses the megagametophyte (when fertilized is the young sporophyte) develops into seed coat 2) fossil record has early Paleozoic Era plts (570-290 mya) that offer some clues to evolution of enclosing integuments |
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evolution of the unique leaf of Pine
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Pine needle
(1) each needle is a leaf (2) needles are borne in fascicles (3) base of the fascicle is wrapped in scales, i.e. leaves, therefore the fascicle is a short shoot or branch (4) # of needles varies between species (between 1 and 8 per bundle) (5) pine needles have many adaptation to restrict water loss: reduced size, heavy cuticle, low # of stomata, etc. |
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extant groups of Gymnosperms
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(a) Phylum Coniferophyta
(b) Phylum Cycadophyta (c) Phylum Ginkgophyta (d) Phylum Gnetophyta |
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Phylum Cycadophyta
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Cycas sp.
Zamia sp. Characteristics •palm-like fronds •seeds but no flowers •tropical to sub-tropical •house plts to trees |
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Phylum Coniferophyta
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Juniper
Norfolk Pine Dawn Redwood Bald Cypress Yew characteristics: •wide spread •economically important •fascicle-borne leaves |
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Phylum Ginkgophyta
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Maidenhair tree (Ginkgo biloba)
Characteristics •only one specie in the phylum •fan-shaped leaves on short shoots •extinct in wild •extract does not increase memory •dioecious, female seed coat very stinky |
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Phylum Gnetophyta
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Ephedra sp.
Gnetum sp. Welwitschia sp. Welwitschia pollen cones Characteristics •contains 3 very different Genera, but Phylum is monophyletic •several features typically found in Angiosperms are found is some of the Gnetophyta but maybe secondarily acquired (i.e. convergent evolution); molecular evidence may indicate that some extinct Gnetophyte is possibly the ancestor to the Angiosperms •Ephedra spp. are highly branched, “bundles of sticks”, have minute cones, are local in Anza-Borrego Desert •Gnetum spp. are mostly tropical, have naked sporangia and large leaves •Welwitschia spp. are the oddest, with only 2 large strap-like leaves that split as they grow older dioecious: male/female cones, found in the coastal deserts of Namibia |
