lecture 16, gymnosperms Flashcards
what are the major evolutionary traits of gymnosperms?
evolution of woody tissue AND heterospory (microspores–> pollen and megaspores–> ovule)
what makes up woody tissue?
-vascular cambium (xylem inner, phloem outer)
-xylem is primarily made up of tracheids (no vessel elements)
-phloem is made up of sieve cells (no sieve tube elements)
-secondary xylem = wood
what is a pollen grain?
-a microgametophyte
-no antheridia
-develops pollen tube to deliver non-motile sperm
what is an ovule?
an organ that forms the seeds of flowering plants
what is the structure of an ovule
- integument
- nucellus
- yields a female mega-gametophyte
-archegonium reduced to a few cells
-contains egg cells
what is a gymnosperm also known as?
a naked seed (although it has a seed coat)
what are cones in pines?
structures that bear the sporangia (spore-producers)
- microsporangia- male: pollen-producing
-megasporangia - female: ovule producing
the microsporangia are usually on lower branches
what are the two kinds of cones?
- microsporophyll with two microsporangia - contains microspore mother cells (microsporophytes)
- ovuliferous scale with two ovules - contains megaspore mother cells (microsporocyte)
what happens when microsporangia and megasporangia undergo meiosis?
microsporangia form a tetrad of microspores (n) and megasporangia form 4 megaspores
what do each microspore develop into?
develops into 4-celled pollen grain- this is the adult male gametophyte
what cells do the male gametophyte contain?
- 2x prothalial cell
- generative cell
- tube cell
what does the megaspore divide into?
female gametophytes / archegonia
inside the archegonia is the egg (female gamete)
only one egg is fertilized
what forms after fertilization?
four-tiered proembryos a.k.a megagametophyte
uppermost tier become four embryos. the tier below become suspensor cells
what does the integument of the ovule develop into?
a seed coat, protecting the embryo inside
the diploid sporophyte contains…
seed coat and the embryo which is fertilized
what is the role of the haploid gametophyte?
serves as food
what does the resulting seed contain?
both shoot/root meristems and several (eight usually) cotyledons
what is the resulting adult plant?
a 2n sporophyte bearing the heterosporous cones
what is the gametophytic phase in male spores?
tetrad of microspores –> pollen grain (4 cells) –> 1 sperm cell
what is the gametophytic phase in female spores?
megaspores (4 cells, 1 survives) –> 2 female megagametophyte archegonia+eggs
what plants emerged when lycopod forests were replaced by gymnosperms?
modern conifers, cycads, gingko, and gnetidae
what are the 4 phylas of gymnosperms?
- phylum coniferophyta
Conifers - Phylum Cycadophyta
Cycads - Phylum Gingkophyta
Gingkos - Phylum Gnetophyta
Gnetidae
Characteristics of Coniferophyta:
-largest group
-woody secondary growth
-dominant tree species in very northern locations
-needle-shaped growth
-evergreen persistent foliage in many species
what are the traditional conifer species (Coniferophyta Pinaceae)
- pines
- spruces
- larches
- hemlocks
- firs
- cedars
What are the traits of Coniferophyta Taxaceae?
- evergreen
- small trees or shrubs
- female cones very specialized
- single seed and a single scale which develops into a fleshly aril resembling fruit
- attracts birds
- produces taxol - a chemotherapy drug
what are the characteristics of Cycadophyta Cycads?
- woody secondary growth
- short height
- very hard and stiff evergreen leaves
- very slow growth
- all dioecious
what are characteristics of Gnetophyta Gnetidae?
- approx. 70 species
- all very weird
- contain vessel elements and tracheids
- evolved independently of the vessel elements in angiosperms
what are the characteristics of Gingkophyta Gingkos?
- smallest group
- only a single species (Gingko biloba)
- was once a much more diverse taxonomy
-characterized by:
-fan-shaped leaves - dioecious
- fruit-like structure for female gametophytes- aril
- no cones!