Topic #10: Gymnosperms
REQUIREMENTS: Powerpoint Presentations
1. Define gymnosperm. What does the name angiosperm imply?
2. Do gymnosperms have flagellated sperm? Some? All? If sperm are flagellated, do they swim externally?
3. Draw the life cycle of pine. How is the male gametophyte delivered to the female cone? What is pollination? Is gymnosperm pollination specifically by certain vectors (e.g., insects; ignore minor exceptions)? Does the female gametophyte form an archegonium? (What is an archegonium?) Does double-fertilization occur? If not, how do the events surrounding fertilization resemble that process?
4. Discuss several advances that are seen in gymnosperms.
5. Do seedless plants typically have a bifacial vascular cambium (i.e., that which gives rise to secondary growth)? Gymnosperms? Typically? Angiosperms? All?
6. Draw a gymnosperm seed. Name three ways it differs from an angiosperm seed. (Hint: endosperm, number of cotyledons, size of female gametophyte.)
7. Describe the general appearance of a cycad. The ginkgo tree. Welwitschia (a member of the Gnetophyta).
POWERPOINT SLIDES: Phylogenetic orientation with a focus on evolution of traits that distinguish the groups and make the advanced forms more adapted to a terrestrial lifestyle. (This series should be used to complement the phylogenetic orientation given at the beginning of the previous topic.)
Our approach to the gymnosperms (about 700 living species) is going to be similar to that taken with the ferns and fern allies, viz., we will focus on one group, the conifers, and just “survey” three others. The other three taxa are essentially “miscellaneous"1 and will be used only sparingly as examples of evolutionary advances. Therefore, no master table follows this topic.
(A) Cycadophyta (cycads).
(B) Ginkgophyta (ginkgo; plural, ginkgoes; variant spelling, also correct,2 gingko).
(C) Gnetophyta3 (vessel-containing gymnosperms).
(D) Coniferophyta (conifers).
Evolutionary Advances of Gymnosperms
Gymnosperm is a "catch-all" term for seed plants that do not produce flowers. The first three groups (above) will be covered rather superficially. Then, the course will be concluded with the life cycle of pine.
The following advances are seen in gymnosperms:
(A) Loss of sperm mobility. In the conifers and Gnetales, the sperm are not flagellated; in cycads and ginkgo, sperm are multiflagellated, but
(B) development of pollen grains (partially developed male gametophytes) has freed even these from the need for liquid water for fertilization. Typically the pollen is wind dispersed, and the sperm arrive at the ovule (after the pollen grain arrives at the structure containing it) not by swimming but through an outgrowth of the male gametophyte, the pollen tube.4 Thus, even in ginkgo and cycads (both of which have flagellated sperm), the presence of external liquid water is not required. In algae generally and in bryophytes, liquid water is required for gamete transfer. In the ferns and their allies, the sperm are flagellated, but archegonia and antheridia are at or below ground level and generally very close together. Some gymnosperms retain sperm motility, but swimming is internal. Angiosperms do not have flagellated male gametes.
(C) Usually, ferns and other extant non-seed-bearing plants lack well-developed vascular cambia (which give rise to secondary growth). Therefore, in general, secondary xylem and phloem are found in greater quantities in gymnosperms than in ferns and their allies. Except for cycads (which superficially resemble palms), secondary growth is pronounced in gymnosperms. Even in cycads, secondary growth is present, albeit sluggish.
(D) The gametophyte generation is further reduced. As implied above, gymnosperms are heterosporous. In general, the male gametophyte (pollen grain) is transferred to the vicinity of the ovule. There, the male gametophyte absorbs nutrition. The female gametophyte (developing from a megaspore and containing perhaps 2000 nuclei) is retained on the parent sporophyte. As a result of the reduction of the haploid generation, antheridia, and in some cases archegonia, are absent.
(E) Seed development, as stressed before, was an important evolutionary advance. As mentioned, seeds can be disseminated widely and by various mechanisms (e.g., in water, like coconuts; by animals, like cocklebur; by wind, like maple). Nonseed plants can also be disseminated by spore movement or migration of fragments. Spores are easily and widely distributed, and nonseed plants tend to be “everywhere,” whereas seed plants may evolve distinct populations or species in localized areas. Of course, the seed also carries a large nutrition packet, is protected well by the seed coat, and has evolved means to time germination with conditions favorable for growth.
As a matter of redundancy, evolution of the seed is traceable: homospory heterospory; diminution of gametophytic stage of life cycle; isogamy oogamy; retention of megaspore within sporophyte (the megasporangium is the nucellus and participates in seed formation); complete development of female gametophyte within sporophyte, germination and growth of the female gametophyte within the megaspore wall.
POWERPOINT SLIDES: A review of traits required for seed evolution.
POWERPOINT SLIDE: Angiosperm seed types (Figs. 61 and 62 of Porter).
By way of review, the angiosperm seed—at least at some time—contains endosperm. This feature is diagnostic. The embryo has one or two cotyledons. Typically (but not on this diagram), the monocot seed reserve is stored in endosperm, whereas the dicot seed reserve is in the cotyledon.
POWERPOINT SLIDE: Pine seed and seedling (Fig. 15.21 of Ritchie and Carola).
In contrast, the remains of the female gametophyte supply nutrition to the germinating gymnosperm embryo. The cotyledons are numerous. (The presence of more than two cotyledons in the conifers is to be contrasted with the presence of two cotyledons in other gymnosperms.)
POWERPOINT SLIDE: Cycad (Kirstenbosch National Botanical Garden, Republic of South Africa).
POWERPOINT SLIDE: Zamia, a native Florida cycad (Florida Governor’s mansion).
Numerous imported cycads grow on campus; they are diminutive palm like trees with dark green foliage.
Cycads are tropical and subtropical; they comprise about 10 genera and 100 species. They are usually large (compared to our native Zamia, but still reach only small tree-like proportions, 15–20 feet tall). Secondary growth is present but sluggish (and cycads are therefore smaller than familiar gymnosperms such as pine). The seed-bearing megasporophylls are arranged in a cone. All species are “dioecious” (that is, microspores and megaspores are produced on different plants5). The sperm are motile.
Only one species survives, and it may no longer be found in the wild.
POWERPOINT SLIDE: Herbarium sample of Ginkgo (National Herbarium, Beijing).
POWERPOINT SLIDE: Dr. Chen points to the single repository of Gingko before its horticultural dissemination (National Herbarium, Beijing).
Ginkgo is a dioecious tree. Female trees produce fleshy seeds that superficially resemble pale cherries (they are not, of course, true fruits, which are produced only by angiosperms). It is widely used as an ornamental, but only male trees are propagated (the seeds are messy and abundant and contain butyric acid, a rancid-smelling substance).
POWERPOINT SLIDE: Ginkgo "fruit."
Secondary growth is present and abundant. Sperm are large (about 180 m) and multiflagellated (>20,000 flagella!).
The Gnetophyta consist of three genera, quite different from each other. The sperm are not motile. The Gnetophyta have vessels (as mentioned, an exception to the generality that gymnosperms lack vessels).
POWERPOINT SLIDE: Welwitschia (Fig. 21-13c of Curtis and Barnes).
POWERPOINT SLIDE: Ephedra (Missouri Botanical Garden).
As was discussed early in this course, double fertilization and the associated formation of the usually triploid endosperm are considered unique and defining features of flowering plants. Ephedra is a nonflowering plant that resembles in some ways flowering plants. Multiple fertilization events are not rare in gymnosperms, and indeed, you will observe the formation of up to several embryos, each in a separate archegonium of a single pine female gametophyte. (Usually, only one embryo survives, however.) Formation of an endosperm is thought to have evolved from a "normal" fertilization. Consider the putative ancestor in which two fertilization events occur. In this ancestor, two fertilizations would lead to the formation of two embryos, but some event triggered the failure of the second "embryo" to develop normally. In this hypothesis, the second, abnormal embryo evolved into the genetic dead-end, the endosperm, on which the other embryo is "parasitic."
Conifers are the most numerous and widespread of the gymnosperms living today. Extensive forest areas are populated virtually solely by conifers.7 Among the most common are pine, cypress, cedar, spruce, and fir. This group includes the largest plants8 and the longest-lived (bristle cone pine, Pinus aristata, lives about 5000 years) and includes about 600 species in 50 genera. All are woody, most evergreen. Secondary growth is present. The leaves are often needlelike or scalelike.
POWERPOINT SLIDE: Metasequoia (dawn redwood) leaf; until the 20th century, this plant was only known from fossils (gift of S. Q. Zhang).
POWERPOINT SLIDE: Podocarpus (with Pretty Girl, north Leon County).
POWERPOINT SLIDE: Sequoia (Yosemite National Park). Note, for perspective, the “portly, rubicund man of middle age.” (Thanks to Winston Churchill from whom I lifted the quote.)
POWERPOINT SLIDE: Early logging of redwood trees (National Geographic Magazine, ca. 1907).9
POWERPOINT SLIDE: Cypress (Biology Unit I).
POWERPOINT SLIDE: Swollen base of cypress (Alapaha River, Georgia).
POWERPOINT SLIDE: Cypress knees (Suwannee River, Florida).
POWERPOINT SLIDE: Cypress stump, from logging, with subsequent growth. (Lamont, FL)
POWERPOINT SLIDE: Cypress Tree, original source on slide. I lifted the photograph from Balfour, III 2002 In Search of the Aucilla. Colson Printing Company, Valdosta, Georgia.
POWERPOINT SLIDE: Araucaria angustifolia (Rio Grande do Sul, Brazil).
POWERPOINT SLIDE: Longleaf pine forest.
POWERPOINT SLIDE: Rayonier Pulp Mill (Jesup, GA).10 When it was revamped in 1992, this became the largest pulp processing plant in the world.
POWERPOINT SLIDES: (from White, R. (1998) Rise Again? The demise of the longleaf yellow pine. Two slides of the local area from Wooden Boat May/June 1998 (no. 142) 34-41 and a third from my collection.
POWERPOINT SLIDE: Collecting gum in Florida (in what is now Eglin Air Force Base). (from Butler C. B. (1998) Treasures of the longleaf pines--naval stores. Tarkel Publishing Co., Shalimar, FL).
POWERPOINT SLIDE: Catface (left, from Lanier County, Georgia) + tin gum cups (originally from Mount Pleasant, Florida (Gadsden County), and now in North Leon County) + clay gum cups (retrieved from a swamp on my farm in Berrien County, Georgia; Hertie cups patent by UF prof. In 1903) + tar barrel .( (originally from near Havana, Florida (Gadsden County), and now in North Leon County). The photograph of the historical sequence of tar receptacles was taken at General Coffee State Park (Nicholls, Georgia).
POWERPOINT SLIDE: Portrait of Mr. Sylvester Copeland taken in the late 1930s or early 1940s, who worked Outlaw trees for Mr. Perry Hendley. This is the only surviving photograph of Mr. Copeland; photographic restoration was by John Crawford.
POWERPOINT SLIDE: Turpentine still (Thomas County, Georgia)11 These local stills used distillation to recover the turpentine from the other components (resin or, as it is also called, rosin). Turpentine had and continues to have many uses.12
POWERPOINT SLIDE: Overview of Turpentine Still at the Agrirama (Tifton, Georgia).
POWERPOINT SLIDE: Loading ramp at McCranie Turpentine Still (Willachoochee, Georgia).
POWERPOINT SLIDES: A series of slides on establishment of longleaf pine in a conservation project (Nashville, GA).
Pine Life Cycle
General overview of pine life cycle:
The following points will be emphasized in the detailed presentation later.
(A) The familiar tree is the sporophyte.
(B) Gametophytes are small and cannot lead an independent existence.
(C) In haploid stages, the sexes are separate.
POWERPOINT SLIDE: Male pine cones (north Leon County, Florida).
POWERPOINT SLIDE: Female pine cones (north Leon County, Florida).
POWERPOINT SLIDE: Pine life cycle (custom).
(A) The mature sporophyte produces microspores and megaspores, borne in separate, morphologically distinct cones. (As is true of all gymnosperms, conifers are heterosporous.)
(B) Microsporangia (male cones) are usually borne on the same tree but tend to be on lower limbs than megasporangia.
(C) Each scale bears two microsporangia, each of which becomes a pollen sac. Each microsporangium contains numerous microspore mother cells, which in spring undergo meiosis.
(D) Each haploid microspore develops into a four-celled pollen grain.
(E) The female cones bear two ovules on each scale. (For technical reasons, we will not refer to this sporangium-bearing structure as a "sporophyll"; each scale is interpreted to be a branch; however, the scales on the male cones are sporophylls.)
(F) Each ovule contains a multicellular nucellus (= megasporangium), which is surrounded by an integument with an opening, the micropyle.
(G) Each ovule contains a single megaspore mother cell. Three of the haploid cells that are formed from meiosis disintegrate.
(H) Pollination occurs in spring.13 Pollen sticks to a drop of sticky fluid. As the fluid evaporates, the pollen grain is pulled down through the micropyle.
(I) Shortly after pollination, the scales close up and thus offer a high degree of protection to the developing ovule. The pollen grain germinates, forming a pollen tube.
(J) About a month after pollination, the megaspore mother cell undergoes meiosis; three of the four megaspores disintegrate. Over the next 12 months, the megaspore produces a female gametophyte of about 2000 cells, which are at first free nuclei.
(K) In the next two months (i.e., 15 months after pollination) two or three archegonia differentiate.
(L) In the meantime, the pollen tube has continued growing. The pollen tube grows into the egg cell and discharges cytoplasm and two sperm nuclei—one unites with the egg nucleus; the other disintegrates. (In a similar way, the eggs in all archegonia may be fertilized, but only one embryo/ovule usually develops fully.)
(M) Over the next few months, embryology is completed, and in autumn of the second year, seeds are shed.
After you have read your textbook, studied your own class notes, studied these class notes, written answers to objective questions as if to turn in, and compared those answers to those of a classmate,
do a self evaluation by taking this model exam.
The key and an explanation follow.
Then, if necessary, (a) consult with one of the TAs, or (b) consult with the instructor, or (c) bring unresolved questions to help session.
Introductory Plant Biology Model Exam V
Grade: Bonus________ Exam Proper______ Total_______
Check here if you wish to withdraw permission to have your grade posted by PIN.
Check here if you have written a detailed explanation by a question. This is your only opportunity to challenge a question if you believe it to have two correct responses with neither substantially better than the other or if you believe that no answer is correct. Start your explanation with “I chose answer ‘D’ instead of answer ‘B’ because . . . .” Only challenges started thus will be considered, and in some cases, credit will be given even if you mark an answer that does not correspond to the key. Identify the question that you challenge: ________________.
I understand that it is a violation of the Honor Code to refer to any information not specifically condoned by the instructor or to receive any information from a source that is not specifically authorized during an exam. I also understand that I should report to the instructor any violation of the Honor Code unless the person who violates the code reports himself or herself. In this course, an additional example of a violation of the Honor Code is to divulge information about exam content to anyone who has not taken the exam or to receive unauthorized information about the contents of an exam before taking the exam.
Bonus Section (Optional Reading)
1. (2 pts) Give the approximate value of leather leaf fern production in Florida (within 3 fold for full credit, within 10 fold for half credit).
2. (2 pts) Give the approximate value of a single large redwood tree on the stump (within 5 fold for full credit, within 10 fold for half credit).
3. (2 pts) Name four major products produced from gymnosperms. Exclude paper products and building and structural materials (one half point for each unique application).
a. ________________ b. _________________ c. _________________ d. _________________
1. Select the best statement.
a. All seed plants must be heterosporous.
b. Gymnosperms are homosporous, but angiosperms are heterosporous.
c. All seed plants are heterosporous, and all nonseed plants are homosporous.
d. There is no relationship between heterospory and seed formation.
2. Select the answer that only includes advanced floral characteristics.
a. fusion of parts, presence of both anthers and carpels, irregularity
b. free central placentation, heterospory, reduction in number of parts
c. double fertilization, basal placentation, free central placentation
d. fusion of parts, irregularity, reduction in number of parts
3. Select the answer that lists attributes in which the primary growth of roots differs from the primary growth of shoots in angiosperms.
a. presence of root cap, presence of secondary growth, presence of lateral appendages
b. arrangement of vascular anatomy, presence of collenchyma, origin of lateral appendages
c. presence of plastids, arrangement of vascular anatomy, presence of parenchyma
d. presence of plastids, presence of secondary growth, origin of lateral appendages
4. Select the best statement true of Archeae but not generally true of Eubacteria and Eukarya.
a. Glucose is not oxidized as a source of energy.
b. Glucose is oxidized as a source of energy.
c. ATP dependent phosphofructokinase (ATP PFK) is not an essential enzyme.
d. One of the first steps in the metabolism of glucose is its conversion to a hexose-P.
5. Select the statement that is true of cyanobacteria and red algae but not true of plants.
a. Photosynthetic light harvesting pigments are complexed with proteins in structures called phycobilisomes that sit on the membrane.
b. Chlorophyll a plays an essential role in photosynthesis.
c. The first step in CO2 fixation involves the production of a 4 carbon compound.
d. The chloroplasts have a bluish cast because of the presence of similar light harvesting pigments.
6. Select the best statement true of chloroplasts of green algae and of plants, but not true of at least some other chloroplasts.
a. They were derived by way of a secondary endosymbiotic process.
b. They contain chlorophyll a, they are enclosed by a double membrane, and starch is generally the carbohydrate storage product.
c. They contain chlorophyll b, they have membranes organized into stacks, and starch is generally the carbohydrate storage product.
d. None of the above is true; green algae do not have chloroplasts.
7. Select the best statement.
a. The first organisms appear in the fossil record at about the same time as astronomical and geological processes permitted Earth to be hospitable to life.
b. The first organisms must have had mechanisms that permitted their survival in the presence of very high levels of atmospheric O2.
c. The three domains of life appeared in the fossil record simultaneously and seem to have evolved independently, although some genes have been shared through lateral gene transfer.
d. A primitive form of sex evolved first in plants, but within 6 billion years this trait spread to most other eukaryotes.
8. Select the statement true of fungi.
a. They have a larger genome than other eukaryotes.
b. Their nuclear membrane may not degrade during mitosis.
c. They are filamentous, lack cellular connections, and have a level of cellular differentiation (“division of labor”) similar to that of prokaryotes.
d. They are strictly haploid, except for the zygote, and monokaryotic.
9. Select the statement that is generally true of Basidiomycetes but generally not true of Ascomycetes.
a. Sexual spores are formed by meiosis.
b. Sexual spores are formed by mitosis.
c. Sexual spores are diploid.
d. Formation of spores is not part of sexual reproduction.
10. Select the statement that best describes how fungi acquire nutrients.
a. An extremely large family of membrane bound ATPases has hundreds of individual members, each specialized for the uptake of a specific nutrient.
b. Ions are acquired primarily through endocytosis (engulfing).
c. A membrane sodium ATPase pumps sodium into the cell, and the sodium attracts other nutrients into the cell.
d. Mechanistically, the fungal process is similar to the way that plants acquire nutrients.
11. Select the trait characteristic of all plants but not characteristic of many green algae.
b. biflagellate sperm
c. oxygenic photosynthesis
d. double fertilization
12. Select the trait characteristic of some vascular seedless plants but not characteristic of bryophytes..
a. heteromorphic alternation of generations
b. abundance of stomata on the gametophyte
c. external fertilization
d. vascular tissue arranged into a protostele
13. Select the best definition of protonema.
a. a multicellular structure that is exclusively involved in asexual reproduction in some groups of bryophytes.
b. a haploid green alga like filament that is the direct result of spore germination
c. a capsule that becomes inflated; its “explosion” results in spore dispersal
d. the first true root formed on the moss sporophyte
14. Select the trait characteristic of bryophytes but not characteristic of other plants.
a. one egg per gametophyte
b. one sporangium per sporophyte
c. release of egg before fertilization
d. zygotic meiosis
15. Select the most nearly true statement.
a. The sporophytes of all homosporous plants are homozygous because of the fusion of genetically identical gametes.
b. The evolutionary ancestor of plants, a green alga (or green alga like organism) had a thick cuticle to protect it from ozone damage.
c. The sporophyte of Psilotum consists essentially of a stem.
d. The gametophyte of ferns and fern allies develops entirely within the walls of the megaspore.
16. Select the best description of the evolution of the megaphyll.
a. fusion of several microphylls
b. adventitious growths on the sporophyll
c. enlargement of a microphyll
d. fusion of dermal and ground tissues of a planar branching system
17. Select the trait characteristic of ferns but not characteristic of mosses.
a. absence of external swimming by male gamete
b. presence of stomata on gametophyte
c. presence of megaphylls
18. Select the most nearly true statement.
a. A few extant and many fossil seedless vascular plants have a vascular cambium and, hence, secondary growth.
b. Fern leaves are either fertile nonphotosynthetic spore bearing organs or sterile photosynthetic organs.
c. Fern pollen is always dispersed by wind.
d. Ferns have microphylls, and seed plants have megaphylls.
19. Select the best statement concerning ferns, as studied in this course.
a. Vessel elements are generally not lignified.
b. Symbiotic relationships with fungi are not found.
c. Roots, when present, are usually adventitious.
d. Xylem is present, but phloem is not.
20. Select the best statement true of the prototypical fern life cycle.
a. Mature eggs and sperm are released into a droplet of liquid water on the underside of the gametophyte.
b. Precise development programs the eggs and sperm of a gametophyte to mature simultaneously.
c. The gametophytes are strictly unisexual.
d. Free flagellated sperm swim to the egg.
21. Select the statement that best describes the flagellation pattern in gymnosperms.
a. The sperm of all taxa have flagella.
b. Flagellated sperm only swim internally.
c. Pollen grains in some rare taxa are flagellated.
d. Both gametes of many gymnosperms are flagellated, but the flagella of the female gamete are only sufficent to propel the gamete from the archegonium.
22. Select the response that includes attributes all of which are required for seed formation and none of which are found in seedless plants.
a. retention of the megaspore on the sporophyte, heterospory, formation of endosperm
b. oogamy, motile male gametophyte, formation of only a single egg on each female gametophyte
c. retention of the female gametophyte on the sporophyte, complete development of female gametophyte within the megaspore wall, motile male gametophyte
d. nonflagellated male gametes, delayed karyogamy, internal fertilization
23. Select the statement true of multiple fertilization but not true of double fertilization.
a. Female gametes are genetically identical to each other, and male gametes are genetically identical to each other.
b. Female and male gametes are all genetically identical.
c. Female gametes are genetically identical to each other, but male gametes are not genetically identical to each other.
d. None of the gametes involved are genetically identical to each other.
24. Select the best description of the ginkgo.
a. small, annual herb with very limited secondary growth
b. fan-shaped deciduous leaves on a moderate sized tree
c. difficult to distinguish from a palm tree
d. high ornamental value a result of persistent decorative fruits
25. Select the statement most nearly true of the pine tree.
a. The seed coat, present in angiosperms, is lacking.
b. Similar to the situation in angiosperms, three of the four megaspores resulting from meiosis abort.
c. The gametophytes are bisexual.
d. The separate events of double fertilization are separated by months.