lecture 16, gymnosperms

Question 1

what are the major evolutionary traits of gymnosperms?

Answer 1

evolution of woody tissue AND heterospory (microspores–> pollen and megaspores–> ovule)

Question 2

what makes up woody tissue?

Answer 2

-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

Question 3

what is a pollen grain?

Answer 3

-a microgametophyte
-no antheridia
-develops pollen tube to deliver non-motile sperm

Question 4

what is an ovule?

Answer 4

an organ that forms the seeds of flowering plants

Question 5

what is the structure of an ovule

Answer 5

1. integument
2. nucellus
   - yields a female mega-gametophyte
   -archegonium reduced to a few cells
   -contains egg cells

Question 6

what is a gymnosperm also known as?

Answer 6

a naked seed (although it has a seed coat)

Question 7

what are cones in pines?

Answer 7

structures that bear the sporangia (spore-producers)
- microsporangia- male: pollen-producing
-megasporangia - female: ovule producing

the microsporangia are usually on lower branches

Question 8

what are the two kinds of cones?

Answer 8

1. microsporophyll with two microsporangia - contains microspore mother cells (microsporophytes)
2. ovuliferous scale with two ovules - contains megaspore mother cells (microsporocyte)

Question 9

what happens when microsporangia and megasporangia undergo meiosis?

Answer 9

microsporangia form a tetrad of microspores (n) and megasporangia form 4 megaspores

Question 10

what do each microspore develop into?

Answer 10

develops into 4-celled pollen grain- this is the adult male gametophyte

Question 11

what cells do the male gametophyte contain?

Answer 11

1. 2x prothalial cell
2. generative cell
3. tube cell

Question 12

what does the megaspore divide into?

Answer 12

female gametophytes / archegonia

inside the archegonia is the egg (female gamete)

only one egg is fertilized

Question 13

what forms after fertilization?

Answer 13

four-tiered proembryos a.k.a megagametophyte

uppermost tier become four embryos. the tier below become suspensor cells

Question 14

what does the integument of the ovule develop into?

Answer 14

a seed coat, protecting the embryo inside

Question 15

the diploid sporophyte contains…

Answer 15

seed coat and the embryo which is fertilized

Question 16

what is the role of the haploid gametophyte?

Answer 16

serves as food

Question 17

what does the resulting seed contain?

Answer 17

both shoot/root meristems and several (eight usually) cotyledons

Question 18

what is the resulting adult plant?

Answer 18

a 2n sporophyte bearing the heterosporous cones

Question 19

what is the gametophytic phase in male spores?

Answer 19

tetrad of microspores –> pollen grain (4 cells) –> 1 sperm cell

Question 20

what is the gametophytic phase in female spores?

Answer 20

megaspores (4 cells, 1 survives) –> 2 female megagametophyte archegonia+eggs

Question 21

what plants emerged when lycopod forests were replaced by gymnosperms?

Answer 21

modern conifers, cycads, gingko, and gnetidae

Question 22

what are the 4 phylas of gymnosperms?

Answer 22

1. phylum coniferophyta
   Conifers
2. Phylum Cycadophyta
   Cycads
3. Phylum Gingkophyta
   Gingkos
4. Phylum Gnetophyta
   Gnetidae

Question 23

Characteristics of Coniferophyta:

Answer 23

-largest group
-woody secondary growth
-dominant tree species in very northern locations
-needle-shaped growth
-evergreen persistent foliage in many species

Question 24

what are the traditional conifer species (Coniferophyta Pinaceae)

Answer 24

1. pines
2. spruces
3. larches
4. hemlocks
5. firs
6. cedars

Question 25

What are the traits of Coniferophyta Taxaceae?

Answer 25

1. evergreen 2. small trees or shrubs 3. female cones very specialized 4. single seed and a single scale which develops into a fleshly aril resembling fruit 5. attracts birds 6. produces taxol - a chemotherapy drug

Question 26

what are the characteristics of Cycadophyta Cycads?

Answer 26

- woody secondary growth - short height - very hard and stiff evergreen leaves - very slow growth - all dioecious

Question 27

what are characteristics of Gnetophyta Gnetidae?

Answer 27

- approx. 70 species - all very weird - contain vessel elements and tracheids - evolved independently of the vessel elements in angiosperms

Question 28

what are the characteristics of Gingkophyta Gingkos?

Answer 28

- 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!