Chapter 28
What are the three steps to understand diversification?
1. Compare morphological traits 2. Analyze the fossil record 3. Estimate phylogenetic trees.
What were the three main adaptations that early green land plants had?
1. The plants could prevent water loss, which kept cells from drying out and dying. 2. The early plants adapted to provide protection from harmful ultraviolet (UV) radiation. 3. The early plants adapted to move water from tissues with direct access to water to tissues without direct access.
What sequence of events does the alternation of generations always have?
1. The sporophyte produces haploid spores by meiosis 2. the spores germinate and divide by mitosis and develop into multicellular, haploid gametophytes. 3. gametophytes produce unicellular haploid gametes by mitosis 4. two gametes unite during fertilization to form a diploid zygote 5. The zygote divides by mitosis and develops into a multicellular, diploid sporophyte
What three innovations were needed for efficient plant reproduction in a dry environment?
1. spores that resist drying because they are encased in a tough coat of sporopollenin 2. Gametes that were produced in complex, multicellular structures 3. embryos that were retained on and nourished by the parent plant
What were the three key adaptations involved with the diversification of angiosperms?
1. water-conducting vessels 2. flowers 3. fruits these adaptations allowed angiosperms to transport water, pollen, and seeds efficiently.
What does a cuticle do regarding carbon dioxide?
A cuticle can keep CO2 out of a plant. Most plants solve this problem with a stoma. A stoma, or stomata, is a mouth. A stoma consists of an opening surrounded by specialized guard cells. The stoma's pore opens and closes as guard cells change shape, so gas exchange can be accomplished through the pore.
How would you describe a cuticle?
A cuticle is a watertight sealant that covers aboveground parts of a plant and gives ability to survive in dry environments
What has a loss of plant-rich praries contributed to?
A loss of plant-rich praries has contributed to increased concentrations of carbon dioxide in the atmosphere. A loss of praries is partly responsible for rising temperatures associated with global climate change.
What is a seed?
A seed is a structure that includes an embryo and stores nutrients provided by the mother. A seed is surrounded by a tough, protective coat.
How are plants used for medicine?
About 25% of prescriptions written in the United States each year include at least one molecule derived from plants. Most of these compounds are synthesized by plants to repel herbivores.
How did agricultural research begin?
Agricultural research began with the initial domestication of crop plants. Artificial selection for plants with certain properties has led to dramatic changes in plant characteristics.
What is the alternation of generations?
All land plants undergo the alternation of generations, in which individuals have multicellular haploid phase called the gametophyte and the multicellular diploid phase known as the sporophyte. The two phases of the life cycle are connected by the distinct types of reproductive cells- gametes and spores.
What does an ecosystem consist of?
All organisms in a particular area count as an ecosystem. Nonliving physical components of the environment such as the atmosphere, precipitation,surface water, sunlight, soil, and nutrients are part of the ecosystem as well.
In what organisms does alternation of generations not occur?
Alternation of generations does not occur in algal groups most closely related to land plants. In coleochaetes, stoneworts, andconjugating algae, the multicellular form is haploid and only the zygote is diploid.
Describe a seed?
An embryo is surrounded by nutritive tissue which is surrounded by the seed coat.
How does double fertilization occur?
Angiosperm fertilization involves two sperm cells. One fuses with the egg to form a diploid zygote and the other fuses with two nuclei in the female gametophyte, forming triploid 3n nutritive tissue
What is the difference between angiosperms and gymnosperms?
Angiosperms are flowering plants, which have encased seeds. Gymnosperms have naked seeds and are not flowering plants.
What do angiosperms produce?
Angiosperms produce fruits derived from ovaries that contain seeds. Many fruits are dispersed by animals.
What are the three green algae groups most similar to land plants?
Based on DNA sequence analysis, the green algal groups that are most similar to land plants are conjugating algae, coleochaetes, and stoneworts. These green algal groups are largely multicellular and live in freshwater. Land plants likely evolved from green algae that lived in freshwater habitats.
What is the origin of vascular tissue?
Biologists hypothesized that vascular tissue cells were part of water-conducting tissue because some fossilized cells had simple cellulose containing cell walls like water conducting cells found in today's mosses. They also had cell walls with thickened rings containing lignin
How can plants cause problems for humans?
Biologists study weeds that decrease crop productivity and newly introduced species that invade and then degrade natural areas.
How did convergent evolution occur in plants?
Convergent evolution also occurred, as vessels evolved independently in angiosperms, gnetophytes, and several species of seedless vascular plants.
Describe cotyledons?
Cotyledons are first leaves. Cotyledons store nutrients and provide them to the embryo. Monocots have one cotyledons and petals in multiples of 3, while dicots have two cotyledons and petals in multiples of 4 or 5.
What is cuticle, one of the first fossils of early plants found?
Cuticle is a watertight barrier that coats the aboveground parts of today's land plants and helps them resist drying.
What does data suggest about the alternation of generations in land plants?
Data suggests that the alternation of generations in land plants evolved independently of its evolution in other eukaryotes and originated early in land plant history.
What does devegetation lead to?
Devegetation leads to soil erosion.
How are flowers advantageous?
Flowers are adaptations to increase the probability an animal will perform pollination.
How do flowers attract pollinators?
Flowers attract pollinators by providing them with food, either protein-rich pollen or nectar, a sugar-rich fluid. The relationship is mutually beneficial, as the pollinator gets food and the plant gets fertilized. The direct pollination hypothesis has strong experimental support.
Why are different flowers pollinated by different creatures?
Flowers with different scents, shapes, and colors attract different pollinators.
What are freshwater green algae hypothesized to be closely related to?
Freshwater green algae are hypothesized to be closely related to land plants.
What are fruit?
Fruit are a structure derived from the ovary that enclose one or more seeds. The tissues derived from the ovary are often nutritious and brightly colored. While the evolution of flowers made efficient pollination possible, evolution of fruit made efficient seed dispersal possible.
What are gametangia?
Gametangia are fossilized structures of early plants. Stoneworts also develop gametangia. Gametangia protected gametes from drying out and from physical damage. Gametangia are present in all land plants today except angiosperms, where the structures inside the flower perform the same functions.
What process produces gametes in land plants?
Gamete formation results from mitosis, not meiosis.
Which evolved first, gametophyte dominant life cycles or sporophyte dominant life cycles?
Gametophyte dominant life cycles evolved first, and sporophyte dominant life cycles evolved later.
What do green algae and land plants bring to an ecosystem?
Green algae and land plants produce oxygen via oxygenic photosynthesis, build and hold soil by providing food for decomposers, (they hold soil and prevent nutrients from being lost to wind or water erosion. they also hold water in the soil.)
How do green algae and land plants moderate the local climate?
Green algae and land plants provide shade and reduce the impact of wind on landscapes.
What are green algae?
Green algae have traditionally been consideredprotists but we study them along with land plants because they are the closest living relatives to land plants and the transition from aquatic to terrestrial life occurred when land plants evolved from green algae.
How do you analyze morphological traits in green algae and land plants?
Green algae include species that are unicellular or multicellular, colonial, and live in marine, freshwater, or moist terrestrial habitats. The majority of green algae are aquatic and the majority of land plant are terrestrial.
Describe green algae?
Green algae is a paraphyletic group that totals about 8000 species. Green algae are important primary producers in all types of freshwater habitat and in unusual environments such as snowfields and ice floes.
What are traits of green algae?
Green algae live in close association with an array of other organisms. Unicellular green algae are common endosymbionts in planktonic protists that live in lakes and ponds.
What is heterospory?
Heterospory is the production of two distinct types of spores by different structures. All nonvascular plants and most seedless vascular plants are homosporous, meaning they produce one type of spore.
How are plants used for fuel?
Historically, humans relied on wood burning for energy. In industrialized countries, fossil fuels including coal and petroleum or natural gas have replaced wood. Fossil fuels are derived from plants, either living or long-deceased.
What happens to the megaspore?
In a pine tree, the megaspore undergoes mitosis to form the female gametophyte, which will produce egg cells through further rounds of mitosis.
Why is a sporophyte dominated life cycle advantageous?
In a sporophyte dominant life cycle, diploid cells can respond to varying environmental conditions more efficiently than haploid cells can. This is especially true if an individual is heterozygous at many genes. This is called reduction of the gametophyte
Why is upright growth helpful in a terrestrial environment?
In a terrestrial environment, individuals that can grow upright have much better access to sunlight than individuals that cannot.
How does heterospory occur in angiosperms?
In angiosperms, flowers contain microspores and megaspores.
What key traits are similar in both land plants and green algae?
In both land plants and green algae, chloroplast structure is the same, thylakoid arrangements are similar, the cell walls, sperm, and peroxisomes are similar in structure and composition. Chloroplasts synthesize starch as a storage product.
What was the downside to the evolution of embryo retention?
In ferns and horsetails, sporophytes have to live in the same place as their parent gametophyte if the plant has embryo retention. Seed plants overcome this limitation because the embryos of seed plants are portable and can disperse to new locations.
Describe the sporophyte in vascular plants?
In ferns and other vascular plants, the sporophyte is much larger and longer lived than the gametophyte, meaning in vascular plants there tends to be sporophyte dominant life cycle.
In green algae that are closely related to plants, what part in ziploid?
In green algae that are closely related to plants, only the zygote phase is diploid.
What are the two types of spore-producing structures in heterosporous species?
In heterosporous species, there are microsporangia and megasporangia.
Describe the sporophyte in nonvascular plants?
In nonvascular plants, the sporophyte is small and short lived. The sporophyte is largely dependent on the gametophyte for nutrition in a nonvascular plant, so the plant is gametophyte dominant in its life cycle.
What two problems must be overcome in order for plants to grow upright?
In order for plants to grow upright, land plans must transport water from tissues in contact with wet soil to tissue in contact with dry air, and land plants must be rigid enough to avoid falling over in response to gravity and wind.
Why is pollen grain helpful?
In pollen grain, a tiny male gametophyte is surrounded by a tough coat of sporopollenin. The pollen can be exposed to air for long periods of time without drying out. The pollen is carried to the female gametophyte by wind or animals.
What forms wood?
In the stems and branches of some vascular plants, tracheids or a combination of tracheids and vessels form wood.
How are plants dominant primary producers?
Land plants are dominant primary producers in terrestrial ecosystems. They convert energy in sunlight into chemical energy. The sugars produced by land plants support virtually all other organisms in terrestrial habitats.
What are land plants?
Land plants are the first organisms that could thrive with their tissues completely exposed to the air. Before land plants evolved, terrestrial life was limited to bacteria, archaea, and single celled protists. Plants transformed the nature of life on Earth.
How else are land plants important?
Land plants are the key to the carbon cycle, as they take carbon dioxide from the atmosphere and reduce it to make sugars, and land plants fix much more carbon dioxide than they release
Instead of shedding their eggs into water or soil, as did their ancestors, what do land plants do?
Land plants retain their eggs, which form inside archegonia. In contrast to most green algae, zygotes of land plants begin development on the parent plants and form multicellular embryos that remain attached to the plant and can be nourished by the parent
Describe lichens?
Lichens are stable associations between green algae or cyanobacteria and fungi. Lichens are often found in terrestrial environments that lack soil.
What is lignin?
Lignin is an extraordinarily strong polymer.
Where are megasporangia found?
Megasporangia are found inside protective structures called ovules. Each megasporangium contains a megaspore mother cell that divides by meiosis and forms the megaspore.
What is a megasporangia?
Megasporangia produce megaspores, which develop into female gametophytes which produce large gametes called eggs. megasporangia -> megaspores -> female gametophyte -> eggs
What process produces spores in land plants?
Meiosis produces spores in land plants, inside structures called sporangia.
Where do microsporangia and megasporangia develop in the sporophyte?
Microsporangia and megasporangia develop where the cones are in the sporophyte.
What do microsporangia contain?
Microsporangia contain microspore mother cells that divide by meiosis to form microspores and then divide by mitosis to form pollen grains.
What are microsporangia?
Microsporangia produce microspores, which develop into male gametophytes and produce small gametes called sperm. microsporangia -> microspores -> male gametophyte -> sperm
Describe the two groups of cotyledons, monocotyledons and dicotyledons?
Monocots as a group are monophyletic, while dicots are paraphyletic. Many plants once considered dicots are now considered eudicots.
Where do most green algae live?
Most green algae are aquatic.
What were the characteristics of most of the earliest plant fossils?
Most of the earliest plant fossils are microscopic. Some are of thin sheets of waxy material (like cuticle).
What did natural selection favor in early land plants>
Natural selection favored early land plants with three main adaptations meant to solve the drying problem.
Which plants are likely to be homosporous?
Nonvascular plants and most seedless vascular plants are homosporous. sporangium -> spores -> bisexual gametophyte -> sperm and eggs
Describe nonvascular plants?
Nonvascular plants are the first lineages to branch off phylogeny of land plants. The gametophyte is the dominant and longer lived phase of the cycle. The individuals are anchored to soil, rocks, or tree bark by rhizoids. Nonvascular plants lack vascular tissue with lignin-reinforced cell walls. They have flagellated sperm that swim to eggs and spores dispersed by wind.
What are nonvascular plants?
Nonvascular plants lack vascular tissue. Vascular tissue are specialized groups of cells that conduct water or dissolved nutrients throughout the plant body. Nonvascular plants include mosses.
What do nonvascular plants use for reproduction?
Nonvascular plants use spores, not seeds, for reproduction and dispersal.
What happened once green plants made the transition to survive out of water?
Once green plants made the transition to survive out of water, resources such as light and carbon dioxide were more plentiful.
How did stamens and carpels evolve?
Once stamens and carpels evolved, they became enclosed by modified leaves called sepals and petals. Four structures (stamens, carpels, sepals, and petals) then diversified to produce a fantastic array of sizes, shapes, and colors. Specialized cells inside flowers also began producing a wide range of scents
Why is the sun damaging to land plants?
Plants out of water are exposed to harmful uv rays of the sun. The uv light damages DNA by causing thymine dimers. Water absorbs UV light, so algae did not face this problem to the same extent.
How are plants used for fiber and building materials?
Plants provide us with important sources of raw materials. This includes clothing, rope, and household articles such as towels and linens. Woody plants provide lumber for houses and furniture, and fibers to make paper.
What is pollination?
Pollination is the transfer of pollen from one individual's stamen to another individual's carpel. Animals are rewarded for carrying pollen from one flower to anothr.
Describe seed plants?
Seed plants are a monophyletic group that includes gymnosperms and angiosperms. Seed plants are defined by two key synapomorphies: the production of seeds and the production of pollen grains. Angiosperms produce seeds in ovaries, while gymnosperms do not.
What do seed plants consist of?
Seed plants consist of angiosperms and gymnosperms (flowering plants and naked seed plants, respectively).
Describe seed plants?
Seed plants have vascular tissue and make seeds. The seeds consist of an embryo and nutritive tissue, surrounded by a tough protective layer.
Describe seedless vascular plants?
Seedless vascular plants have well-developed vascular tissue. Seedless vascular plants do not make seeds and use spores for reproduction. This group of seedless vascular plants includes ferns.
Describe simple water-conducting tissues?
Simple water conducting tissues evolved by natural selection into more complex, efficient, supportive, and water-conducting tissues. Long, thin, tapering, water-conducting cells called tracheids evolved 380 mya
What was another one of the first plant fossils apart from cuticle?
Some of the first plant fossils include fossilized spores surrounded by material almost identical in structure to sporopollenin.
What do spores lack that seeds do not lack?
Spores are an effective dispersal stage for nonvascular plants and seedless vascular plants, but they lack the stored nutrients found in seeds.
How are spores and gametes produced?
Spores are produced by meiosis inside sporophytes or sporangia and then divide by mitosis to form gametophytes. Gametes are produced by mitosis inside gametangia such as archegonium and antheridium
How are spores dispersed so easily?
Spores can be dispersed hundreds of miles by wind currents. Spores are resistant and lightweight which increases their chances of being dispersed to a suitable environment for growth.
What do spores develop into?
Spores develop into the bisexual gametophyte that produces both the egg and the sperm. Gametophytes can self fertilize and produce offspring.
How are spores dessication resistant?
Spores resist drying as they are encased in a tough coat of sporopollenin, and their tough outer coating helps them survive for fairly long periods of time.
What is sporopollenin?
Sporopollenin is a waxy substance that encases spores and pollen of modern land plants and helps them resist drying. Fossilized spores found in association with spore-producing structures (sporangia/sporangium), similar to sporangia found in some modern, nonvascular plants
In what organisms does the alternation of generations occur?
The alternation of generations occurs only in land plants. It does not occur in humans or other animals.
What are the most fundamental plant adaptations to life in land?
The cuticle and the stomata are the most fundamental plant adaptations to life on land.
which key adaptations allowed early plants to colonize land?
The cuticle, stomata, and vascular tissue were key adaptations that allowed early plants to colonize land. Fundamental adaptations to dry conditions such as the cuticle, pore, stomata, vascular tissue, and tracheids evolved just once.
Why are angiosperms so diverse?
The diversity of angiosperms resulted from coevolution with animal pollinators. Evolutionary changes in angiosperms and corresponding changes in pollinators were highly dependent on each other.
What was needed for land plants to evolve?
The evolution of land plants required adaptations that allowed photosynthetic organisms to move from aquatic to terrestrial environments. In other words, plants had to adapt to living and reproducing in a dry environment.
What is the female gametangia?
The female gametangia is the archegonium (egg-producing).
What happens to the female gametophyte in a pine tree?
The female gametophyte stays attached to the sporophyte as pollen grains arrive and produce sperm to fertilize eggs.
Why was upright growth important?
The first land plants were small or had low, sprawling growth habit. The first plants had to grow in a way that kept many or most of their tissues in direct contact with the moist soil. Otherwise, competition for space and light would have become intense soon after the first plants began growing on land.
What did the first plants have?
The first plants had cuticles to keep them from drying out and UV-ray absorbing compounds that acted as sunscreen.
What is the important of the retention of the embryo in land plant evolution?
The formal name of the land plant group is embryophyta (the embryo plants). and the retention of the fertilized egg in embryophytes is analogous to pregnancy in mammals.
what is the size of the gametophytes of gymnosperms and angiosperms?
The gametophytes of gymnosperms and angiosperms are microscopic.
What function do the life cycles of sexually reproducing eukaroytes serve?
The life cycles of sexually reproducing eukaryotes allow them to increase genetic variability due to meiosis and fertilization, increase the number of individual, and disperse individuals to new habitats.
What is the male gametangia?
The male gametangia is the antheridium )sperm-producing).
Describe the plant fossil record?
The plant fossil record is massive. It has five time intervals. The oldest interval begins 475 mya.
What is the purpose of the secondary cell wall of a tracheid?
The secondary cell wall of a tracheid offers increased structural support, yet water can still move easily through cells because of their pits. Today, all vascular plants contain tracheids.
What happens to the seed in a pine tree?
The seeds mature as the embryo develops. Inside the seed, cells derived from the female gametophyte become packed with nutrients provided by the sporophyte.
What is pollen for?
The sperm of nonvascular and seedless vascular plants have to swim to the egg to fertilize it. This means water must be available for fertilization to occur. Pollen grain in land plants allowed plants living in dry habitats to reproduce efficiently.
Why are angiosperms so successful?
The success of angiosperms revolves around their reproductive organ, the flower. The stamen contains the anther, where microsporangia develop; the carpel contains the ovary where ovules are found. Ovules contain the megasporangia.
How many major events have their been in the diversification of land plants?
There have been five major events in the diversification of land plants. They include: 1. the origin of land plants 2. the silurian-devonian explosion 3. the carboniferous period 4. the diversification of gymnosperms 5. the diversification of angiosperms
what is an angiosperm?
These distinguishing characteristics taken together have made the angiosperms the most diverse and numerous land plants and the most commercially important group to humans. a plant that has flowers and produces seeds enclosed within a carpel. The angiosperms are a large group and include herbaceous plants, shrubs, grasses, and most trees.
What are some traits of tracheids?
Tracheids have thickened, lignin-containing secondary cell walls in addition to cellulose-based primary cell walls. In tracheids, their are pits in the sides and ends of the cell which allow water to flow efficiently between tracheids.
Describe seedless vascular plants?
Vascular plants are a paraphyletic group. The vascular tissue is comprised of lignin reinforced cells. Seedless vascular plants have a sporophyte dominant, longer lived phase of the life cycle. The gametophyte are physically independent of the sporophyte. Eggs are retained on the gametophyte, and the sperm swim to the egg using their flagella. The sporophytes develop on the gametophyte and are nourished by the gametophyte when small.
What did the development of vascular tissue do?
Vascular tissue allowed land plants to transport water from tissues in contact with dry air and also allowed land plants to be rigid enough to avoid falling over in response to gravity and wind
In addition to tracheids, there are vessels, the most specialized type of water-conducting cell. What are the traits of vessels?
Vessels appeared 250 to 270 mya. Vessels are shorter and wider than tracheids, and vessels have gaps on both ends where both cell walls are missing
What are viridiplantae?
Viridiplantae are green plants. This group consists of green algae and land plants. Green algae are important photosynthetic organisms in freshwater habitats, and land plants are key photosynthesizers in terrestrial environments.
Why do biologists study green algae and land plants?
We could not live without green algae and land plants because people rely on them for food, fuel, fibers used to make clothing, building materials, and pharmaceuticals. Agriculture, forestry, and horticulture are among the most important industries based on plants.
Compare and contrast zygotes, spores, and gametes?
Zygotes and spores are single cells that divide by mitosis to form multicellular individuals. Zygotes develop into sporophytes and spores develop into gametophytes. Zygotes are diploid, while spores and gametes are haploid. Zygotes result from the fusion of two haploid cells such as a sperm and an egg, while spores are produced by meiosis inside structures called sporangia. Gametes are produced by mitosis inside gametangia.
what is a gymnosperm?
a plant that has seeds unprotected by an ovary or fruit. Gymnosperms include the conifers, cycads, and ginkgo.
What is adaptive radiation?
adaptive radiation occurs when a single lineage produces a large number of descendant species that are adapted to a wide variety of habitats -angiosperms represent one of the great adaptive radiations in the history of life
What are the two major groups of angiosperms?
angiosperms include two major groups: monocotyledons (monocots) and dicotyledons (dicots) -groups are divided based on differences in their cotyledons or first leaves
Describe the gametophytes of seed plants?
the gametophytes of seed plants are either male or female, but never both. Meanwhile, all nonvascular plants and most seedless vascular plants produce gametophytes that can self fertilize and produce offspring because they are bisexual
