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What is the evolutionary significance of megaphylls? |
They increase the surface area for photosynthesis. |
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The evolutionary significance of megaphylls is that they increase the surface area for photosynthesis. Megaphylls are leaves. They provide a large surface area to maximize photosynthesis. Leaves increase the surface area of the plant body and serve as the primary photosynthetic organ of vascular plants. In terms of size and complexity, leaves can be classified as either microphylls or megaphylls. Almost all vascular plants have megaphylls, leaves with a highly branched vascular system; a few species have reduced leaves that appear to have evolved from megaphylls. So named because they are typically larger than microphylls, megaphylls support greater photosynthetic productivity than microphylls as a result of the greater surface area served by their network of veins. |
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Evidence suggests that land plants arose from within which protist lineage? |
Charophytes |
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Evidence suggests that land plants arose from within the charophyte lineage. The charophytes are one of two main groups within the green algae. Studies of nuclear and chloroplast genes from a wide range of plants and algae indicate that certain groups of charophytes—including Chara and Coleochaete—are the closest living relatives of land plants. Although this evidence suggests that land plants arose from within the charophyte lineage, it does not mean that plants are descended from these living algae. The chlorophytes are the other main group comprising the green algae. Ciliates are a large and diverse group of protists and are not closely related to the green algae. The cercozoans are a large group of amoeboid and flagellated protists that feed using threadlike pseudopodia. The choanoflagellates are the protist group thought to be most closely related to animals. |
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What characteristic of Sphagnum peatlands is responsible for their ability to inhibit decomposition? Low pH All of the listed characteristics inhibit decomposition. Low temperature Phenolic compounds produced by Sphagnum |
All of the listed characteristics inhibit decomposition. |
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The Sphagnum moss accumulated in peatlands does not decay readily, in part because of phenolic compounds embedded in its cell walls. The low temperature, pH, and oxygen level of peatlands also inhibit decay of moss and other organisms in these boggy wetlands. As a result, some peatlands have preserved corpses for thousands of years. Globally, an estimated 450 billion tons of organic carbon is stored in peatlands. |
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Which of the following is a trait unique to land plants? Chloroplasts Walled spores produced in sporangia All the listed traits are unique to land plants. Cellulose |
Walled spores produced in sporangia |
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Walled spores produced in sporangia is a trait unique to land plants. Multicellular organs called sporangia (singular, sporangium) produce the spores, haploid reproductive cells that can grow into multicellular plants by mitosis. The polymer sporopollenin makes the walls of plant spores tough and resistant to harsh environments. This chemical adaptation enables spores to be dispersed through dry air without harm. Green algae, brown algae, and dinoflagellate protists all have cell walls made of cellulose. Chloroplasts with chlorophylls a and b are present in green algae, euglenids, and a few dinoflagellates, as well as in plants. Some photosynthetic algae are multicellular. Brown algae are the largest and most complex multicellular algae, and their photosynthetic blades can be attached to supporting stipes that rise more than 60 meters from the seafloor. |
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In sporophyte ferns, the leaves are __________. |
megaphylls |
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In sporophyte ferns, the leaves are megaphylls. Many ferns have leaves that are megaphylls, commonly called fronds, which are subdivided into leaflets. The sporophytes typically have horizontal stems that give rise to the fronds. A frond grows as its coiled tip, the fiddlehead, unfurls. The leaves of sporophyte ferns are megaphylls. The photosynthetic portion of a fern gametophyte is a thallus. Sporangia produce spores. Kelps have photosynthetic organs known as blades. |
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The gametophyte stage of the plant life cycle is most conspicuous in __________. |
mosses |
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The gametophyte stage of the plant life cycle is most conspicuous in mosses. Mosses have a dominant gametophyte. Unlike vascular plants, in all three bryophyte phyla the haploid gametophytes are the dominant stage of the life cycle: That is, they are usually larger and longer-living than the sporophytes, as shown in the moss life cycle. Sporophytes are typically present only part of the time. When bryophyte spores are dispersed to a favorable habitat, such as moist soil or tree bark, they may germinate and grow into gametophytes. The sporophyte is the conspicuous stage of the ferns. The sporophyte is the dominant stage in horse tails, club mosses, and seed plants. |
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What structures allow plants to readily take up carbon dioxide from the atmosphere? |
Stomata |
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Stomata allow plants to readily take up carbon dioxide from the atmosphere. Because plants are covered with a waxy cuticle, diffusion of carbon dioxide into the leaf interior must be facilitated through stomata, tiny pores that allow for gas exchange. Moss sporophytes have specialized pores called stomata (singular, stoma), which are also found in all vascular plants. These pores support photosynthesis by allowing the exchange of CO2 and O2 between the outside air and the sporophyte interior. Stomata are also the main avenues by which water evaporates from the sporophyte. In hot, dry conditions, the stomata close, minimizing water loss. Cuticles are a waterproof layer. Gametangia produce gametes. Mitochondria produce carbon dioxide as a waste product of cellular respiration. Capsule is another term for sporangia, where spores are produced by meiosis. |
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During what period did seedless vascular plants form extensive forests of tall trees? |
Carboniferous |
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During the Carboniferous period, seedless vascular plants formed extensive forests of tall trees. By the Carboniferous period (359-299 million years ago), the lycophyte evolutionary lineage included small herbaceous plants and giant trees with diameters of more than 2 meters and heights of more than 40 meters. The giant lycophyte trees thrived for millions of years in moist swamps, but they became extinct when Earth’s climate became drier at the end of the Carboniferous period. The monilophytes called horsetails were also very diverse during the Carboniferous period, some growing as tall as 15 meters. Colonization of land by plants first occurred in the Ordovician period. In the subsequent Silurian period, early vascular plants diversified. Major extinctions of terrestrial life occurred at the end of the Permian period. In the subsequent Triassic period, the cone-bearing plants came into dominance. |
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Sori can be found in which of the following? |
Pterophytes |
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Sori can be found in pterophytes. Sori are the small structures on the underside of the fronds from which spores are released. Phylum Pterophyta includes the ferns, which possess structures on their fronds called sori. Mosses are members of phylum Bryophyta and do not possess sori. Liverworts are members of phylum Hepatophyta and do not possess sori. Hornworts are members of phylum Anthocerophyta and do not possess sori. Charophytes are a type of algae. |
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How are gametes produced by bryophytes? |
By mitosis of gametophyte cells |
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Bryophytes produce gametes by mitosis of gametophyte cells. The haploid gametophyte produces gametes by mitosis. The leafy gametophyte is the prevalent generation in the bryophyte life cycle. Unlike vascular plants, in all three bryophyte phyla the haploid gametophytes are the dominant stage of the life cycle: That is, they are usually larger and longer-living than the sporophytes, as shown in the moss life cycle. |
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To examine meiosis in ferns, you would study __________. |
the sporangia |
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To examine meiosis in ferns, you would study the sporangia. The mature diploid sporophyte produces haploid spores by meiosis. These spores are encased in sporangia. On the underside of the sporophyte’s reproductive leaves are spots called sori. Each sorus is a cluster of sporangia. Meiosis occurs inside the sporangia, producing haploid spores which develop into the gametophyte. Antheridia produce sperm. Archegonia produce eggs. The mature diploid sporophyte produces haploid spores by meiosis. These spores are encased in sporangia. |
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Water is brought into mosses primarily by __________. |
diffusion through all cells |
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Water is brought into mosses primarily by diffusion through all cells. The gametophytes of mosses and other bryophytes generally form ground-hugging carpets in moist environments, partly because their body parts are too thin to support a tall plant but also because they lack vascular tissue, which would enable long-distance transport of water and nutrients. Some mosses have conducting tissues, but phylogenetic analyses suggest that these tissues are not homologous with the xylem of vascular plants. Mosses lack the leaves of vascular plants. Mosses also lack the roots of vascular plants. Bryophyte gametophytes are anchored by delicate rhizoids, which are long, tubular single cells (in liverworts and hornworts) or filaments of cells (in mosses). Unlike roots, rhizoids lack specialized conducting cells and do not play a primary role in water and mineral absorption. |
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In what way do megasporangia differ from microsporangia? |
Megasporangia produce spores that develop into female gametophytes, whereas microsporangia produce spores that develop into male gametophytes. |
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Megasporangia differ from microsporangia in that megasporangia produce spores that develop into female gametophytes, whereas microsporangia produce spores that develop into male gametophytes. Most seedless vascular plant species are homosporous: They have one type of sporangium that produces one type of spore, which typically develops into a bisexual gametophyte, as in most ferns. In contrast, a heterosporous species has two types of sporangia and produces two kinds of spores: megasporangia and microsporangia. Megasporangia and microsporangia are separate structures, and one does not develop into the other. The megaspores produced by megasporangia are comparatively bigger, not more numerous, than the microspores produced by microsporangia. All plant spores are protected by sporopollenin. |
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Typically, the upper part of a bryophyte capsule that contains the spores features a ring of interlocking, tooth-like structures known as the __________. |
peristome |
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Typically, the upper part of a bryophyte capsule that contains the spores features a ring of interlocking, tooth-like structures known as the peristome. These "teeth" open under dry conditions and close again when it is moist. This allows moss spores to be discharged gradually via periodic gusts of wind that can carry them long distances. By these means a single moss capsule can distribute up to 50 million spores. Germinating moss spores characteristically produce a mass of green, branched, one-cell-thick filaments known as a protonema (plural, protonemata). Strobili are cone-like structures of lycophytes and most gymnosperms comprised of modified leaves that bear sporangia. A microphyll is a small, often spine-shaped leaf of a lycophyte supported by a single strand of connective tissue. |
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The antheridia of mosses produce __________. |
sperm |
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The antheridia of mosses produce sperm. A feature distinguishing early land plants from their algal ancestors was the production of gametes within multicellular organs called gametangia. Antheridia (singular, antheridium) are the male gametangia. In many groups of present-day plants, the sperm have flagella and swim to the eggs through water droplets or a film of water after being released from the antheridia. Eggs are produced by the female gametangia called archegonia. Haploid spores are the reproductive cells produced by the moss sporangium that can develop into a new haploid organism without fusing with another cell. Germinating moss spores characteristically produce a mass of green, branched, one-cell-thick filaments known as a protonema (plural, protonemata), and in favorable conditions, they produce one or more "buds." Mosses do not possess leaves, which are an adaptation of vascular plants. |
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Alternation of generations in all land plants is between __________. |
a multicellular haploid organism and a multicellular diploid organism |
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Alternation of generations in all land plants is between a multicellular haploid organism and a multicellular diploid organism, the gametophyte and sporophyte, respectively. Each generation gives rise to the other. This type of reproductive cycle evolved in various groups of algae but does not occur in the algae most closely related to land plants. Take care not to confuse the alternation of generations in plants with the haploid and diploid stages in the life cycles of other sexually reproducing organisms. |
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In moving to land, plants had to overcome which of the following challenges? |
Desiccation |
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In moving to land, plants had to overcome desiccation. Because their ancestors were aquatic, successful adaptation to a terrestrial environment required plants to develop a way to prevent desiccation. Many species of charophyte algae inhabit shallow waters around the edges of ponds and lakes, where they are subject to occasional drying. In such environments, natural selection favors individual algae that can survive periods when they are not submerged in water. In charophytes, a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out. The accumulation of such traits by at least one population of charophyte ancestors probably enabled their descendants—the first land plants—to live permanently above the waterline. These evolutionary novelties opened a new frontier: a terrestrial habitat that offered enormous benefits. More available CO2 is found in the atmosphere than in the oceans. Plants were the first photosynthesizers to colonize land, so competition was not an issue. When plants first began to inhabit terrestrial environments, there were very few herbivores of any kind. Among the choices provided, only desiccation was an important challenge to be overcome as plants moved into terrestrial environments. |
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Where would you find a fern gametophyte? |
On moist soil |
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Fern gametophytes live on moist soil. Fern sperm use flagella to swim through moisture to fertilize the egg. The small heart-shaped gametophyte grows on or just below the soil level in moist areas. Among living vascular plants, however, the sporophyte (diploid) generation is the larger and more complex plant in the alternation of generations. In ferns, for example, the familiar leafy plants are the sporophytes. You would have to get down on your hands and knees and search the ground carefully to find fern gametophytes, which are tiny structures that often grow on or just below the soil surface. The underside of the leaf (frond) is where you would find sori. Rhizoids are found in bryophytes. The small heart-shaped gametophytes grow on or just below the soil level in moist areas. Ferns are seedless plants. The small heart-shaped gametophyte grows on or just below the soil level in moist areas. |
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Which of the following is a genus in the phylum Monilophyta? |
Equisetum |
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The genus Equisetum is in the phylum Monilophyta. Monilophyta includes the ferns horsetails and whisk ferns and other seedless vascular plants. The monilophytes called horsetails were very diverse during the Carboniferous period, some growing as tall as 15 meters. Today, only 15 species survive as the single, widely distributed genus Equisetum found in marshy places and along streams. Selaginella is a genus of spike moss in the phylum Lycophyta. Isoetes is a genus of quillwort in the phylum Lycophyta. Marchantia is a genus of liverwort in the phylum Hepatophyta. Sphagnum is a genus of moss in the phylum Bryophyta. |
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The "dots" on the underside of a fern frond are spore cases; therefore, what is true of the plant to which the frond belongs? |
It is a sporophyte. |
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The "dots" on the underside of a fern frond are spore cases; therefore it is a sporophyte. The spots on the underside of reproductive leaves are sori, which release spores, indicating the parent plant is a sporophyte, or spore-producing organism. One milestone in the evolution of plants was the emergence of sporophylls, modified leaves that bear sporangia. Sporophylls vary greatly in structure. For example, fern sporophylls produce clusters of sporangia known as sori (singular, sorus), usually on the undersides of the sporophylls. Plants produce spores. Plants produce gametes. Gametophytes produce gametes. A spermatophyte does not produce spores. |
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The tissue called phloem has what function in vascular plants? |
Distribution of sugars, amino acids, and other organic products |
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The tissue called phloem functions in the distribution of sugars, amino acids, and other organic products. Vascular plants have two types of vascular tissue: xylem and phloem. Vascular tissue helped enable vascular plants to grow tall. Their stems became strong enough to provide support against gravity, and they could transport water and mineral nutrients high above the ground, outcompeting short plants for access to the sunlight needed for photosynthesis. In addition, the spores of tall plants could disperse farther than those of short plants, enabling tall species to colonize new environments rapidly. Overall, the ability to grow tall gave vascular plants a competitive edge over nonvascular plants, which rarely grow above 20 centimeters in height. Conduction of water and minerals is carried out by xylem. Absorption of water and minerals from the soil is handled by the roots of vascular plants. In vascular plants, sporophylls are modified leaves that bear sporangia. Spores are dispersed from the sporangia. |
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Fern gametophytes are __________. |
free-living, multicellular organisms |
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Fern gametophytes are free-living, multicellular organisms. Ferns produce small heart-shaped gametophytes that sustain themselves by photosynthesis and produce haploid gametes. Most fern species produce a single type of spore that develops into a bisexual photosynthetic gametophyte. Each gametophyte develops sperm-producing organs called antheridia and egg-producing organs called archegonia. Gametophytes are haploid. Gametophytes produce gametes. Gametophytes are involved in sexual reproduction. The underside of the leaf (frond) is where sori are found. |
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The development of the __________ prevents plants from drying out and protects them from microbes. |
cuticle |
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The development of the cuticle prevents plants from drying out and protects them from microbes. The waxy cuticle, which is not found in algae, gives the aerial portion of the plant protection from desiccation. Many derived traits that relate to terrestrial life have evolved in many plant species. For example, the epidermis in many species has a covering, the cuticle, which consists of wax and other polymers. Permanently exposed to the air, land plants run a far greater risk of desiccation (drying out) than their algal ancestors. The cuticle acts as waterproofing, helping prevent excessive water loss from the aboveground plant organs, while also providing some protection from microbial attack. The apical meristem is a type of plant tissue in the tips of roots and buds of shoots that generates new cells for lengthwise growth. Gametangia are gamete-producing structures. Though the stomata can close to prevent excessive desiccation, its primary function is to facilitate gas exchange. Stomata also cannot protect the plant from airborne microbes. Flavonoids absorb ultraviolet radiation and act as signals in symbiotic relationships. |
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Which of the following is true of the life cycle of bryophytes? |
A moist environment is required for sexual reproduction. |
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A moist environment is required for sexual reproduction in bryophytes. Bryophyte sperm typically require a film of water to reach the eggs. Given this requirement, it is not surprising that many bryophyte species are found in moist habitats. The fact that sperm swim through water to reach the eggs also means that in species with separate male and female gametophytes (most species of mosses), sexual reproduction is likely to be more successful when individuals are located close to one another. Unlike in flowering vascular plants, bryophytes lack mutualisms with animals to facilitate the transfer of gametes. Both sexual reproduction (production and fusion of sperm and eggs) and asexual reproduction (production of spores) occur in the bryophyte life cycle. The cells of bryophyte sporophytes contain plastids that are usually green and photosynthetic when the sporophytes are young. Even so, bryophyte sporophytes cannot live independently. A bryophyte sporophyte remains attached to its parental gametophyte throughout the sporophyte’s lifetime, dependent on the gametophyte for supplies of sugars, amino acids, minerals, and water. |
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The embryophytes are __________. |
the land plants |
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The embryophytes are the land plants. As part of a life cycle with alternation of generations, multicellular plant embryos develop from zygotes that are retained within the tissues of the female. The parental tissues protect the developing embryo from harsh environmental conditions and provide nutrients such as sugars and amino acids. The embryo has specialized placental transfer cells that enhance the transfer of nutrients to the embryo through elaborate ingrowths of the wall surface (plasma membrane and cell wall). That the multicellular, dependent embryo is such a significant derived trait is why the land plants are also known as embryophytes. The haploid stage in plant alternation of generation is the gametophyte. The green algae are a protist group that possesses some of the reproductive traits of plants. Archegonia are the structures of a moss that produce and house eggs. Protonema are the masses of one-cell-thick filaments through which moss spores absorb water and minerals. |
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A major division in plant systematics is based on whether a particular species has __________. |
vascular tissue |
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A major division in plant systematics is based on whether a particular species has vascular tissue. The major branch point in plant systematics occurs between plants having vascular tissue and nonvascular plants. One way to distinguish groups of plants is whether or not they have an extensive system of vascular tissue, cells joined into tubes that transport water and nutrients throughout the plant body. Most present-day plants have a complex vascular tissue system and are therefore called vascular plants. Plants that do not have an extensive transport system—liverworts, mosses, and hornworts—are described as "nonvascular" plants, even though some mosses do have simple vascular tissue. Sporophytes are found in all plants. Apical meristems are common in all plants. Gametophytes are found in all plants. All plants exhibit alternation of generations. |
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Which of the following statements about algae and plants is true? |
Plants have a waxy, waterproof cuticle, and algae do not. |
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The statement, plants have a waxy, waterproof cuticle, and algae do not, about algae and plants is true. Algae do not need a waterproof cuticle because they live in the water. Many key traits of land plants also appear in some protists, primarily algae. For example, plants are multicellular, eukaryotic, photosynthetic autotrophs, as are brown, red, and certain green algae. Plants have cell walls made of cellulose, and so do green algae, dinoflagellates, and brown algae. And chloroplasts with chlorophylls a and b are present in green algae, euglenids, and a few dinoflagellates, as well as in plants. Derived traits that relate to terrestrial life have evolved in many plant species. For example, the epidermis in many species has a covering, the cuticle, which consists of wax and other polymers. Permanently exposed to the air, land plants run a far greater risk of desiccation (drying out) than their algal ancestors. The cuticle acts as waterproofing, helping prevent excessive water loss from the aboveground plant organs, while also providing some protection from microbial attack. Both plants and algae have cell walls made of cellulose. Algae do not produce embryos. Both plant and algal chloroplasts contain chlorophylls a and b. Many algae are multicellular. |
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Which is a key difference between alternation of generations in plants and sexual reproduction in nonplant organisms? |
In plants, the haploid and diploid stages are both multicellular. |
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A key difference between alternation of generations in plants and sexual reproduction in nonplant organisms is that, in plants, the haploid and diploid stages are both multicellular. The life cycle of humans, for example, includes a single-celled haploid stage and a multicellular diploid stage. The life cycles of all plants include a gametophyte (or haploid generation) that alternates with a sporophyte (or diploid) generation. The life cycles of all land plants alternate between two generations of multicellular organisms: gametophytes and sporophytes. Each generation gives rise to the other, a process that is called alternation of generations. In plants, both stages are multicellular. In bryophytes, the diploid generation is dependent on the haploid generation. The life cycle of humans, for example, includes a single-celled haploid stage and a multicellular diploid stage. The fusion of gametes forms a zygote before an embryo also occurs in plants. |
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What is advantage is conferred to algae and plants that possess sporopollenin? |
Reproductive cells are more resistant to desiccation. |
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An advantage conferred to algae and plants that possess sporopollenin is that their reproductive cells are more resistant to desiccation. Sporopollenin is a durable polymer that prevents the exposed zygotes of algae from drying out. A similar chemical adaptation is found in the tough sporopollenin walls that encase plant spores. Sporopollenin does not function as a toxin. Asexual reproduction is widespread among protists that lack sporopollenin. Haploid and diploid stages alternate in all sexual life cycles. Pollen is an adaptation of seed plants and is not produced by algae. |
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Which of the following are traits shared by land plants and their closest relatives among the algae? Formation of a phragmoplast All of the listed traits of land plants are present in their closest relatives among the algae. Rings of cellulose-synthesizing proteins in the plasma membrane Structure of flagellated sperm |
All of the listed traits of land plants are present in their closest relatives among the algae. |
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All of the listed traits of land plants are present in their closest relatives among the algae, suggesting that land plants evolved from algae. The cells of both land plants and their algal relatives have distinctive circular rings of proteins in the plasma membrane. These protein rings synthesize the cellulose microfibrils of the cell wall. In contrast, more distantly related algae have linear sets of proteins that synthesize cellulose. Similar structural correspondence exists in a comparison of the groups’ sperm. Finally, particular details of cell division are shared only between land plants and their closest relatives among the algae. For example, a group of microtubules known as the phragmoplast forms between the daughter nuclei of a dividing cell. A cell plate then develops in the middle of the phragmoplast, across the midline of the dividing cell. The cell plate, in turn, gives rise to a new cross-wall that separates the daughter cells. |
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