The Seed Plants
Final Review of the Kingdom Plantae.
We have now reached the bottom of our key to the plant kingdom:
A Plant is nonvascular Mosses, liverworts, hornworts
A' Plant has vascular tissue B
B Plant uses spores, not seeds Ferns, club mosses
B' Plant uses seeds C
C Plant does not bear flowers Gymnosperms
C' Plant bears flowers Angiosperms
The seed plants continue the same trends the made the vascular seedless plants more successful than the nonvascular plants. First, with massive amounts of vascular tissue, the seed plants can support crowns far above the ground and reach into the soil for deep water reserves.
Second, the sexual reproduction of the seed plants uses pollen rather than swimming sperm, and does not need liquid water. While gymnosperms use only airborne pollen, many flowering plants use animal pollinators for precise transport of sperm over long distances.
Third, seed plants have dispensed with the small, fragile, independent gametophyte of the ferns and their allies. Instead, the gametophyte is protected within the cones or flowers of the sporophyte, and has been reduced to tiny groups of haploid cells.
Lastly, of course, the seed plants have seeds. Rather than dispersing millions of tiny spores, seed plants disperse a much smaller number of well-equipped propagules. Seeds have a hard seed coat, an internal food reserve, and a multicellular embryo ready to germinate. Flowering plants increase the chances of the seed's success even more by surrounding it with a fruit, which helps to disperse and protect the seed.
Ferns and seed plants have many differences, but one of their similarities is that both have a a dispersal unit containing a plant embryo.
b) enclosed, protected gametophytes. c) vascular tissue.
d) airborne pollen.
The ferns, the gymnosperms, and the angiosperms are all vascular plants. However, the ferns dispersed spores that contained no food reserve and no embryo, they had delicate, independent
gametophytes, and they transferred sperm to egg via a film of liquid water. Don't confuse fern spores with pollen—pollen is a package for sperm, not a dispersal unit that can independently give rise to a new plant.
Seed plants consist of two basic groups: the gymnosperms and the angiosperms.
Gymnosperms are the oldest and largest seed plants (redwoods and sequoias are the tallest and most massive plants), and dominate the colder areas of the earth. Although gymnosperms were the most important plants during the age of dinosaurs, today they are much less diverse than the flowering plants (about 840 species vs. over 300,000). The name gymnosperm means "naked seed," a reference to the fact that the gymnosperm seed lies on a cone scale rather than being enclosed in an ovary.
There are four phyla of gymnosperms:
Cycadophyta cycads (140 species) Ginkgophyta ginkgoes (1 species) Gnetophyta gnetophytes (70 species)
Coniferophyta conifers or cone-bearing plants (630 species) Because of our review of the pine life cycle in lecture, the conifers will serve as a familiar starting point.
The Phylum Coniferophyta. Conifers are the largest, most successful and certainly the most familiar group in the gymnosperms. We use their wood for lumber and paper, and so vast areas in the South have been planted with loblolly, slash, shortleaf and Virginia pines. Christmas trees farms account for more conifer culture. In South Carolina, we are most familiar with pines, but firs, spruces, hemlocks, larches, cedars, redwoods, sequoias and cypresses all are conifers. The center of conifer diversity is in southwestern China.
Most conifers are evergreen. This does not mean that they never drop needles (just look at the ground under a pine tree), but rather that the needles persist for two or more years, and then are dropped and replaced individually rather than all at once. A few conifers (like larches and cypress trees) lose their leaves in winter.
Most conifers are trees, and all have upright stems rather than rhizomes. The trunks of the familiar loblolly pines can get 170 feet tall; redwoods (the world's tallest trees) top 350 feet. These tall straight trunks make the large gymnosperms perfect for lumber. Gymnosperms are also among the oldest living organisms; some giant sequoias may be 4,000 years old, and a much smaller bristlecone pine has been dated at 5,000 years old.
We examined the pine life cycle in lecture. The major innovations in the pine life cycle were the reduction of the gametophyte to a small group of cells in the cone, the use of pollen, and presence of two kinds of spores (megaspores and microspores). You may remember that in the non-seed plants, only the club moss Selaginella was heterosporous. In the seed plants, heterospory is the rule.
Recall that the ovule develops on the scale of a female cone, and that the sulfur-yellow pollen from the male cone is carried in by the wind. Pine pollen blankets cars in the Clemson area every year in early April. It may be one year from pollination until the sperm makes contact with the egg. Then it may take several additional months for the seed to develop. The seed is a complete reproductive package, with a tough seed coat and wing to help disperse the seed, a plant embryo, and a haploid food reserve.
A few conifers seem to have fruits instead of cones. One speaks of juniper (red cedar) berries and yew berries, but these "berries" are modified cones. The critical feature is that the ovule is exposed rather than enclosed in an ovary. The bright red, pea-sized yew "berry" combined with the glossy green of its foliage makes yew a favorite of landscapers.
In previous modules, we were used to hearing about plants scattering spores. Do conifers have spores? Do conifers scatter spores?
a) Yes and yes. b) Yes and no. c) No and no.
Yes, they have spores—megaspores and microspores. However, these spores are not scattered. They are the haploid cells that stay in the cones and give rise to female and male gametophytes,
respectively. What is scattered is pollen, an immature male gametophyte, not a spore.
The Phylum Cycadophyta. Cycads look like short palm trees. A short, thick stem (usually no more than 1 m high) is topped by a profusion of feathery leaves. In the center of the leaves are either male cones or female cones. These cones can be quite large; one Australian species has cones almost 1 m long and weighing as much as 80-90 pounds. The life cycle is very similar to the conifer life cycle, with release of pollen through the air. However, when the sperm are released from the pollen, they are
flagellated, just as they were in the nonseed plants. Sometimes beetles carry cycad pollen between plants, but this seems to be accidental rather than a highly coevolved part of the life cycle, as it is with flowering plants.
Some cycads carry out nitrogen fixation with symbiotic bacteria, and the ancestors of these plants may have been the first land plants to fix nitrogen.
The cycads were very widespread and abundant during the Triassic period (beginning 248 million years ago). In fact, this period is called the "Age of Cycads." Today cycads are mainly tropical and most species are found in the southern hemisphere. One large, showy genus, Zamia, is found in Florida.
The Phylum Ginkgophyta. The ginkgoes, like the cycads, were important parts of the earth's flora during the Age of Dinosaurs, but now are restricted to a single species that occurs naturally only in southeastern China. However, the tree is so handsome (and so resistant to pollution) that it has been widely planted elsewhere; for example, there is a nice line of ginkgoes in front of Newman Hall.
At first, it is hard to believe that the ginkgo is a gymnosperm. It has broad, fan-shaped leaves that turn yellow and drop off in the fall, and female trees seem to produce cherry-sized fruits with a foul, rancid odor of decaying butter (one article on street trees recommended, "Don't plant a female ginkgo unless your plan is to drive all the pedestrians to the other side of the street"). In fact, the "fruits" are fleshy seeds, and the ovules were borne naked on stalks. As in the cycads, the ginkgo sperm is flagellated.
For centuries, the ginkgo has been a part of nontraditional medicine. Extracts from its leaves increase blood flow to the brain. Before you go looking for a ginkgo, however, you should be told that it seems to have no effect on the memory.
The Phylum Gnetophyta. The gnetophytes are a tiny group of three very dissimilar genera.
Ephydra or Mormon tea is a widespread, low bush of American deserts (see the plant below,
photographed near Las Vegas). The fleshy stems suggest why Ephydra is sometimes called "joint fir."
Gnetum is a broadleaved, woody vine of tropical rainforests, and Welwitschia has been called "the most bizarre plant that has ever evolved." Welwitschia is confined to the extremely harsh deserts of southwestern Africa. It consists of a short stem and two enormous, strap-like leaves that grow
continuously, splitting as they grow away from the stem.
The Gnetophyta are an evolutionary mystery. They probably arose from the conifers, but their xylem has vessel elements (not just tracheids) and resembles angiosperm xylem. Also, some gnetophytes have broad leaves like angiosperms, and two kinds of gnetophytes have double fertilization (although it involves two eggs, not an egg and an endosperm nucleus). For these reasons, we used to think that the gnetophytes were the ancestors of the angiosperms, but now it appears that gnetophytes are most closely related to the conifers, and that the cycads and ginkgoes are also closely related. Your textbook presents it like this:
Cycads look very much like palm trees, which are flowering plants. However, you would know you had a cycad and not a flowering plant if you saw that the plant in question had
a) ovules sitting naked on scales. b) a protected gametophyte. c) seeds enclosed in an ovary. d) airborne pollen.
Remember that "gymnosperm" means "naked seed" and "angiosperm" means “enclosed seed." Both gymnosperms and angiosperms have a naked gametophyte and airborne pollen, and angiosperms, not gymnosperms, have seeds enclosed in a ripened ovary wall.
The Angiosperms--Phylum Anthophyta
Flowering plants dominate the earth's flora in the same way that arthropods dominate its fauna (and maybe these two dominances occur because of each other). The flowering plants have about 300,000 species, nearly 30 times as many as the next most diverse phylum, the ferns. All of our important food, fiber and medicinal plants, and most of our lumber trees, are angiosperms. Angiosperms not only feed almost every animal on the planet, but they may be responsible for the evolution of many kinds of insects, mammals and birds.
If we ignore reproductive technique, large angiosperms are very similar to gymnosperms. They reach about the same size and their trunks consist mostly of secondary xylem that conducts between the massive crown and the root system. Gymnosperm xylem is mostly tracheids, while angiosperm xylem is mostly cylindrical vessel elements. Of course, angiosperms have sheetlike rather than needlelike leaves, but remember the broad leaves of the ginkgoes and some gnetophytes.
One big difference between gymnosperms and angiosperms is the diversity of growth forms in the angiosperms. Most gymnosperms are trees or shrublike. Angiosperms have an incredible range of growth forms, from massive trees (in the 1800s, some Australian eucalyptus trees were over 400 feet tall!) to small herbs to floating duckweed, which consists mostly of two tiny leaves. These different growth forms open up niches for angiosperms, such as climbing vines, desert succulents, floating plants, and so forth. As your text points out, a cactus is very well adapted to the desert, and a water lily is very well adapted to growing in the middle of a pond. Diversity of growth forms = diversity of possible niches.
The rest of the differences between the gymnosperms and the angiosperms relate to their method of reproduction. With flowers came a number of reproductive advantages
First, like the gymnosperms, the angiosperms transfer pollen without the need for liquid water. This allows sexual reproduction in dry conditions.
Second, most angiosperms (but not all) use pollinators. Use of insects, birds, bats and monkeys to carry pollen allows precise transport of pollen to even distant plants of the same species. It also avoids selfing, or the fertilization of an egg by the sperm of the same plant. Some angiosperms do self, but for most, pollinators promote outcrossing, or mating with unrelated plants.
Extensive research has been done on the coevolution of angiosperms and their specialized pollinators. The plant attracts its pollinators by providing sugary nectar, bright petals, and sweet smells. Numerous structural features allow the pollinator to land or hover to reach the nectar, and ensure that the pollinator is dusted with pollen in the process. Then, at the next flower the pollinator visits, the part of the pollinator's body that has ben dusted with pollen is forced into contact with the stigma.
Flowers are often specialized for certain types of pollinators. Flowers pollinated by wind (like those of grasses and oaks) tend to be small and dull-colored, and produce vast amounts of very light pollen. Bees prefer flowers that are fragrant, white or yellow, not too deep-throated, and have lots of nectar. Hummingbirds like red flowers (bees can't see red) with deep throats and nectar, but fragrance is not important because the birds have a poor sense of smell. On the other hand, "fragrance" is uppermost to flies, which are attracted to large flowers (like skunk cabbage) that emit the stench of rotting meat.
The third reproductive advantage of the angiosperms is the fruit. Fruits are ripened ovary walls that protect and help disperse the seeds. Fruits include tomatoes, strawberries, acorns,
helicopterlike samaras of maples, burs, milkweed down, and coconuts.
Fruits show almost as much coevolution as pollinators. For example, many immature fruits are hard, green and bitter to discourage premature consumption by animals. When they mature, they often turn red (remember, insects can't see red), soft, plump and sugary. This invites eating, dispersal of the intact seeds in the gut of the consuming animal, and defecation in clump of highly fertile manure. Even if no animal consumes the fruit, the decay of the fruit itself will give the plant a better start in life than the dispersal of the naked seeds of the gymnosperms.
We've said that angiosperms enjoy several advantages over gymnosperms. One of these advantages is not the fact that angiosperms, but not gymnosperms,
a) have a wider variety of growth forms. b) use pollinators.
c) have true seeds.
d) use fruits for seed dispersal.
Both angiosperms and gymnosperms are seed plants. However, only angiosperms enclose their seeds in a fruit and use animal pollinators. Also, angiosperms have a much wider variety of growth forms than gymnosperms do.
The angiosperms are divided into two classes: the Eudicotyledones or dicots and the Monocotyledones or monocots.
The Eudicots. About 70% of angiosperms are dicots. Dicots have two cotyledons in their seeds, their flower parts are in multiples of four and five, the vascular bundles in their young stems are arranged in a circle, and their leaves are net-veined. Almost all plants that get woody and large are dicots, but there are also many herbaceous forms that show no secondary growth.
Recent molecular evidence indicates that the dicots are not a monophyletic taxon. What had been considered primitive dicots, the magnolias and laurels, seem to be more closely related to the monocots than to other dicots.
I'm sure you don't want me to start going through the 200,000 species of dicots, but I will mention the composites, the largest family of dicots, and one in which the highly modified flowers require some explanation. "Composites" are mainly herbaceous plants that include sunflowers, chrysanthemums, zinnias, marigolds, dandelions, thistles, goldenrods, sagebrush, and about 20,000 others.
The name "composite" comes from the flower. Most people would think of a sunflower as consisting of a dark center with a number of yellow petals, but what seems to be a single flower is really an aggregation of hundreds of tiny flowers. The center is composed of dark "disk flowers" and at the margins there are "ray flowers" with one relatively enormous yellow petal.
The composite structure is shown even better by a dandelion. Each of the "petals" this time is a ray flower, and each one produces a single fruit consisting of a seed attached to a fluffy parachute. Again, the purpose of fruits is to protect and disperse the seeds.
One other dicot you should hear about is Arabidopsis thaliana, the mouse ear cress. Arabidopsis is a small weed of the mustard family, and is totally unimportant in the world at large, but very important in the laboratory. Because of its small size, ease of culture, rapid life cycle (5 weeks from seed to seed), and small genome size (diploid cells have 200 million nucleotides, about 7% of that of a human), it is an excellent model organism. Thousands of its mutations are known. As with Drosophila and C. elegans, there are active communities of Arabidopsis researchers who study the effect of mutations on plant development.
The Monocots. These plants (consisting of at least 90,000 species) have one cotyledon in their seeds, flower parts in multiples of three, vascular bundles scattered throughout the area of the stem, and leaves that are often elongated and have parallel leaf veins. Only a few monocots show any secondary growth, although some (like the palms) can get impressively tall and massive just using primary growth. The monocots include the grasses, lilies, onions, palms, bananas and orchids. The orchids are the most diverse family of flowering plants, with over 25,000 species
The monocots are probably the plants with the most direct importance to humans because they contain the grass family. While the grass family is not nearly as diverse as the orchids (it has 8,000 species), "grasses" mean far more than the front lawn. Grasses include wheat, rye, oats, rice and corn, and are our most important food plants. Vast areas of every continent except Antarctica that are too dry to support forests are clothed in grasses, and these grasslands supported vast herds of wild herbivores in the past and now support our beef cattle.
Grass is well adapted to both herbivory and lawn mowers. The meristem is at the bottom of the plant, not the top, so when the top is cropped the meristem can keep pushing up new growth. Any regular cropping selects for grasses as opposed to dicots.
Grass flowers are highly modified and hardly recognizable as flowers. A flower consists of two leaflike wings, the lemma and the palea, enclosing the carpels and stamens. Because grasses are wind-pollinated, the stigmas are feathery and well equipped to catch flying pollen.
If you lose control of your car and run it into an angiosperm, which of the following would serve as evidence that you probably hit a dicot?
a) You can see a 5-petaled flower reflected in a piece of broken glass on the dashboard. b) A net-veined leaf is lying on your crumpled hood.
c) The car's front end is wrapped around the plant's stem. d) All of these would serve as evidence.
Yes, dicots have flower parts in multiples of 4 or 5 (vs. 3 for the monocots), they have net-veined leaves (vs. parallel-net-veined leaves for the monocots), and dicots have secondary growth that could damage a car. The vast majority of monocots don't have secondary growth, although some (like bamboo and the palms) can get impressively thick by using "thickening meristems," technically only resulting in primary growth.
Evolution of the Seed Plants
About 400 million years ago, as jawed fishes and amphibians were first appearing, a plant called a progymnosperm appeared in the first forests of vascular plants. The progymnosperms were large and woody, but reproduced by spores. About 360 million years ago, these plants gave rise to two lines of seed plants: the conifers and the seed ferns.
Seed ferns were probably the first seed-bearing plants. Seed ferns resembled tree ferns, but had abundant secondary growth, and bore seeds on their leaves, just as ferns have sori on their leaves. The seed ferns probably gave rise to cycads and ginkgoes, so these gymnosperms and the conifers had a different origin. The seed ferns went extinct during the Jurassic period, as the Age of Dinosaurs was beginning. The conifers later gave rise to the gnetophytes. Therefore, the conifers and gnetophytes are closely related, and the cycads and ginkgoes form another pair of sister taxa.
Gymnosperms, were widespread but a minor part of the flora in the great Coal Age forests, about 350-300 million years ago, just as mammals were minor as the dinosaurs ruled the earth.
However, conditions became warmer and drier during the Permian period, 286-248 million years ago. This ushered in the greatest mass extinction in the history of life. The largest seedless plants required liquid water for fertilization, and died out. The seed plants, with their fertilization by pollen rather than by swimming sperm, had an advantage and became dominant. This was the same time the reptiles "took over" from the amphibians. Therefore, the great Permian extinction transformed the biota of the planet from an amphibian-club moss-horsetail assemblage to a reptile-gymnosperm one.
The gymnosperms reached the peak of their diversity during the Mesozoic Era, 248-65 million years ago. For almost 200 million years, the dinosaurs walked through forests of conifers, cycads and ginkgoes with fern understory growth.
The next shift was to a mammal-angiosperm world. Unlike the gymnosperms, the
angiosperms probably are an authentic monophyletic group with one ancestor. The first angiosperm probably evolved from the conifers.
As early as 180 million years ago, some conifers had angiosperm-like features, perhaps including pollination by beetles. The earliest angiosperm fossil dates from 125 million years ago, in the early Cretaceous, and these plants were clearly angiosperms, not some intermediate between
gymnosperms and angiosperms. By the time the dinosaurs went extinct 65 million years ago, the
angiosperms were already dominant. In 2002, fossil finds in China indicated that the first flowering plant,
Archaefructus, was an aquatic herb about 25 cm high. It had stamens and carpels (with seeds inside), but no petals or sepals.
Before monocots and dicots existed, several clades of “basal angiosperms” split off. Also, the magnoliids are neither monocots or dicots. Probably, the eudicots evolved before the monocots. The monocots are probably monophyletic, but the “dicots” seem to have had several ancestors, and may be broken up into different groups in the future. Your text shows this as follows:
Over time, angiosperms developed new growth forms such as bushes, trees, and vines. Flowers changed greatly. Flowers got petals, but at first they had a great number of similar petals and were radially symmetrical, like a modern magnolia flower. More advanced angiosperms reduced the number of floral parts, fused parts (such as fusing many petals into a single tubular corolla), and became
bilaterally symmetrical instead of radially symmetrical. Finally, flowers with sepals, petals, stamens and carpels are said to be complete. The more highly evolved flowers lost some of these parts and are called incomplete.
After the death of the dinosaurs, the flowering plants continued to diversify. After about 30 million years ago, the climate cooled and got drier. Forests retreated and vast grasslands spread. This selected for herds of giant mammal grazers, and the constant cropping of the grazers ensured that the grasses would remain dominant. By about 25 million years ago, the flowering plants had essentially reached their modern level of diversity.
One of the important lessons of the flowering plant story is the strong interaction between animal and plant evolution. It is thought that insects diversified so spectacularly in part because of the many new niches opened up by the presence of flowering plants. In fact, the adults of the second largest insect order, the Lepidoptera, feed exclusively on nectar. Conversely, the presence of a great diversity of
pollinators allowed the flowering plants to maintain hundreds of thousands of separate species. 70% of flowering plants are pollinated by insects.
Likewise, the evolution of grasses turned vast amounts of non-forest land into productive grazing areas and spurred the diversification of mammals.
The interaction continues today too. After 9000 years of agriculture, humans have reshaped the landscape with their crops (and with the weeds and pests that go with those crops). Now we are at the threshold of an era of spectacular progress in genetic engineering that may make the coming decades the most rapid period of plant evolution ever seen.
But no matter what happens, one thing won't change: Plants are the basis of life on earth. Not only are they fascinating in their own right as a life form almost completely different from us, but they are our life support system for food, fiber, medicines, oxygen, and even maintenance of the climate. We must understand them and use them wisely.
Consider these events in plant evolution:
1. The first angiosperms.
2. Drier climate selects for gymnosperms. 3. Spread of grasslands.
4. The first bilaterally symmetrical flowers. 5. The seed ferns rule.
The order of these events was a) 2 3 4 1 5
b) 5 2 1 4 3 c) 1 5 2 3 4 d) 5 1 2 3 4
The seed ferns were in their heyday about 360 million years ago. Gymnosperms were favored by the climate shift during the Permian period, 286-248 million years ago. The first angiosperms
appeared 130-120 million years ago, and sometime after that began to develop bilateral symmetry. Finally, grasslands spread about 30 million years ago.
Biology 1110 Seed Plant Worksheet 1. Seed plants utterly dominate the earth’s flora--we have to look hard to find a plant that’s not a seed
plant. Give four reasons why seed plants are so successful.
2. What is the “gametophyte problem” that plagued the seedless vascular plants, and how have seed plants handled it?
3. Distinguish between a spore and a seed. Why does the seed usually have a better chance of success? Distinguish between a spore and a pollen grain.
4. Distinguish between a gymnosperm and an angiosperm. What is the critical identifying feature of the gymnosperms? Hint: What does “gymnosperm” mean?
5. Name the phyla of the seed plants, and give the common name of each phylum. Which of these are gymnosperms? Angiosperms?
6. Name some common types of conifers. Why are they such excellent lumber trees?
7. We call conifers “evergreens,” but does that mean that they never drop their needles?
8. Are the gymnosperms homosporous or heterosporous? Why?
10. “In pines, there is a sharp distinction between pollination and fertilization.” Explain.
11. Describe a cycad. While it might be possible to mistake a cycad for a palm tree, what obvious reproductive feature would allow you to tell them apart?
12. “The cycads and ginkgoes share an illustrious past and a humble present.” Explain.
13. Why did the module say that it is hard to believe that a ginkgo is a gymnosperm? What typical angiosperm features does it have?
14. What primitive reproductive feature (reminiscent of the ferns) is shared by cycads and ginkgoes?
15. What gymnosperm group probably gave rise to the angiosperms?
16. Why are the angiosperms the most important plants on earth?
17. In what non-reproductive ways are the angiosperms different from the gymnosperms? In what reproductive ways are they different?
18. What role does a pollinator (say, a bee) play in the life cycle of a flowering plant? How did the gymnosperms perform this function? Why is it an advantage to use pollinators?
19. What is outcrossing, why is it desirable, and why do pollinators promote it?
20. Why do we say that plants and their pollinators are coevolved? Give some examples of this coevolution.
21. What role does fruit play in the life cycle of a flowering plant? Give some examples of fruits and explain how they play this role.
22. How would you distinguish between a monocot and a dicot? Which group has more species?
23. Explain why “composites” is a good name for the largest family of dicots.
24. What kind of plant is Arabadopsis thaliana? Why is it a good model system for studying flowering plants?
25. Name some common types of monocots. What family of monocots has the most species?
26. Why are the grasses so important to humans? Why did the module say that grasses are “well adapted to both herbivory and lawn mowers”?
27. If you didn’t know that grass flowers are wind-pollinated, how could you make a good guess that they are by looking at them?
28. What was the first seed plant? When did it originate, and from what non-seed plant?
29. When did gymnosperms become dominant? Why did this happen?
30. When did the angiosperms originate? When did they become dominant?
31. Describe the first angiosperms. In what ways did evolution modify the growth forms of these plants? The flowers?
32. Your lecture handout had the following diagram of flowering plant evolution:
Everything on this diagram except the gymnosperms monocots used to be classified as a dicot. Would this make the “dicots” a monophyletic, paraphyletic, or polyphyletic group?
33. The last great event in the diversification of angiosperms occurred about 30 million years ago. What was this event and what caused it?
34. “One of the important lessons of the flowering plant story is the strong interaction between animal and plant evolution.” Explain and amplify.
Biology 1110 Seed Plant Practice Quiz 1. The advantages of the seed plants over the non-seed plants included all of the following except
1. ability to conduct water from deep in the soil to a high crown of leaves. 2. superior survivability of the dispersal unit.
3. an independent, photosynthetic gametophyte that supports itself. 4. ability to carry out fertilization without liquid water.
2. The name "gymnosperm" refers to the ... of these plants.
1. unenclosed ovule 2. heterospory
3. vascular tissue 4. preference for cold climates 3. The seed plant phylum that has the most extant species is the
1. Pteridophyta. 2. Coniferophyta. 3. Cycadophyta. 4. Anthophyta. 4. The role of the ovule in the pine life cycle is to
1. be fertilized by the sperm to form a zygote. 2. contain the female gametophyte.
3. initiate vegetative reproduction. 4. disperse pollen.
5. We speak of red cedar and yew berries and ginkgo fruits, but do any gymnosperms have fruit, and why or why not?
1. No, none do, because none of them surround a seed with a ripened ovary wall. 2. No, none do, because none of them have an embryo containing vascular tissue.
3. Yes, ginkgoes do, because the seed is protected by diploid tissue from the sporophyte. 4. Yes, all the non-conifers do, because only the conifers lack gametangia.
6. Which of these gymnosperms is not paired with its proper phylum?
1. Welwitschia ... Gnetophyta. 2. Zamia ... Cycadophyta. 3. Cypress ... Coniferophyta. 4. Mormon tea ... Cycadophyta. 7. The angiosperms probably originated most directly from the
1. seed ferns. 2. gnetophytes. 3. charophytes. 4. conifers.
8. A significant, nonreproductive difference between the gymnosperms and the angiosperms is that the angiosperms, but not the gymnosperms, have
1. photosynthetic parenchyma tissue. 2. vascular bundles throughout their stems. 3. vessel elements in their xylem. 4. stomata that open during the day. 9. Outcrossing is desirable because it
1. ensures that only the freshest, newest gametes are used in reproduction. 2. avoids expressing homozygous recessive mutations.
3. transfers oxygen to the deepest parts of stems. 4. speeds the process of seed germination.
10. Every summer, Dr. Kosinski's wife used to put a hibiscus plant on the Kosinski back deck. This plant has big, beautifully red, deep-throated flowers, but the flowers have no smell. You would suspect that the hibiscus is pollinated by
1. bees. 2. flies. 3. hummingbirds. 4. bats.
11. It's obvious what plants get out of the plant-pollinator interaction, but what do pollinators get? 1. Nectar. 2. Predator protection 3. Removal of parasites
12. Arabidopsis is considered an excellent plant model system for a variety of reasons; which of these is not one of those reasons?
1. It has a haploid sporophyte. 2. It has a relatively small amount of DNA. 3. It has a rapid life cycle. 4. It is easily raised in the lab.
13. One of the diagnostic features of a monocot is 1. no use of animal pollinators.
2. flowers with a single carpel.
3. presence of stomata on stems and roots and well as leaves. 4. long, linear leaves with parallel leaf veins.
14. The seed plants probably originated about ... million years ago.
1. 425 2. 360 3. 125 4. 65
15. The dominant plants during most of the Age of Dinosaurs were 1. grasses, conifers and cycads.
2. cycads and early flowering plants like magnolias. 3. conifers, cycads and ginkgoes.
4. ferns, horsetails and club mosses.
16. The first flowering plants appear in the fossil record about ... million years ago.
1. 425 2. 360 3. 125 4. 65
17. We believe that the angiosperms are
1. monophyletic. 2. paraphyletic. 3. polyphyletic.
18. Until recently, all angiosperms were divided into monocots and dicots. However, recently some plants (such as ...) have been excluded from the new group called the eudicots because it is thought that they
1. peaches ... did not come from a green alga ancestor.
2. Amborella ... diverged from the main line of angiosperm evolution very early. 3. oaks ... are neither clear monocots nor clear eudicots.
4. star anise ... came from hybridization between monocots and eudicots.
19. Which of the following was not an evolutionary trend from the earliest flowering plants to the modern ones?
1. a greater number of flower parts like petals and stamens. 2. use of herbaceous plants without secondary growth 3. fusion of flower parts
Biology 1110 Seed Plants Practice Quiz Answers 1. 3. Correct. A gametophyte that supports itself is a bad idea. The gametophyte, with its
dependence on wet conditions, was a weak link in the fern life cycle. The seed plants enclose the gametophyte in the sporophyte and the overall adaptability of the life cycle improves. 2. 1. Correct. Gymnosperm means "naked seed." Angiosperm ovules would be enclosed in a flower
first and then later in a fruit.
2. No. Gymnosperms are heterosporous, but that's not what the name means.
3. 4. Correct. 300,000 species in the flowering plants, only 840 or so in all the gymnosperm phyla put together.
4. 1. No, the egg is enclosed in the ovule. 2. Correct.
4. No. The ovule receives pollen. 5. 1. Correct.
6. 4. Correct. Mormon tea is a gnetophyte.
7. 1, 2, 3. No, although the angiosperms came from all of these in this order: charophytes (as the ancestors of all plants), seed ferns (as an early seed plant), conifers. The gnetophytes used to be the best candidate for the ancestors of the angiosperms, but now we think of them as another conifer offshoot.
8. 1. No. Mesophyll is parenchyma tissue, so all seed plants have this. 2. No. That's a monocot-dicot difference.
9. 2. Correct. Outcrossing is mating with organism not closely related to you. It avoids production of homozygous recessive offspring who would express deleterious, recessive mutations. 10. 3. Correct. It's red so they can see it, deep-throated so only they can reach the nectar, and it
doesn't need to have a smell because they are relying on visual cues anyway. You should see the hummingbirds gathering around that thing. They're like a swarm of big, buzzing insects. 11. 1. Correct.
12. 1. Correct, that is not a reason Arabadopsis is a model organism. No plant has a haploid sporophyte.
13. 1. No. Grasses do not use animal pollination, but many monocots do. 2. No. "Mono" refers to cotyledons, not carpels.
4. Correct. Think of the leaf of a corn plant.
14. 2. Correct. The first ones were probably seed ferns.
15. 2. No. Conifers and ginkgoes were much more dominant than flowering plants. 3. Correct.
16. 3. Correct. This is the assumed age of the Archaefructus fossil.
17. 1. Correct. Sure, the angiosperms are a good, monophyletic group with one founding ancestor. 18. 2. Correct. Amborella represents the oldest living angiosperm lineage.
3. No. This would be true of the "Magnoliids," but oak trees are clearly eudicots. 4. No. Star anise branched off before monocots and eudicots existed.
19. 1. Correct. The number of flower parts goes down over time. Think of a primitive flower like a magnolia compared to grass flower.