Exam 3: Chapters 27, 28, 29 Flashcards
Describe life on land 445 million years ago.
About 445 million years ago, life was abundant in the ocean, but not on land. Biologists hypothesize that all land plants evolved from a common ancestor – an ancient green alga. Green algae and plants share many biochemical and metabolic traits.
What are traits that green algae and plants share?
Plants & Green Algae share: a complex multicellular eukaryote, cellulose cell walls, chlorophylls a and b in plastids, starch as a storage product, may have cells with two anterior flagella Plants (land plants): (embryophytes) develope from multicellular embryos enclosed in protective tissue.
Discuss some environmental challenges of living on land and describe how several plant adaptations meet these challenges.
A waxy cuticle prevents plant tissues from drying out and filters out UV radiation. Tiny pores (stomata) allow gas (carbon dioxide) exchange through the cuticle between the atmosphere and the interior of cells. Plant sex organs (gametangia) have a layer of nonreproductive cells that protects the gametes. The female gametangium protects the developing embryo. Xylem conducts water and dissolved minerals. Phloem conducts dissolved organic molecules such as sugar. Adaptations of land plants include a waxy cuticle to prevent water loss; multicellular gametangia; stomata; and for most plants, vascular tissues containing lignin.
Name the green algal group from which plants are hypothesized to have descended and describe supporting evidence.
Red algae, green algae, and land plants are collectively classified as archaeplastids. Molecular comparisons of DNA and RNA sequences suggest that land plants descended from a group of green algae (charophytes or stoneworts).
Describe the basic plant life cycle alternation of generations.
Plant life cycles have a multicellular haploid stage and a multicellular diploid stage (alternation of generations). The haploid stage (gametophyte generation) gives rise to haploid gametes by mitosis. The diploid stage(sporophyte generation) begins when two gametes fuse, and produces haploid spores by meiosis. Gametophyte generation: Haploid gametophytes produce antheridia (sperm producing) or archegonia (egg producing) gametangia. One sperm cell fertilizes the egg to form a diploid zygote. Sporophyte generation: The zygote divides by mitosis, forming a multicellular embryo (young sporophyte plant) within the archegonium. Sporogenous cells in the mature sporophyte divide by meiosis to form haploid spores.
Describe the basic plant life cycle.
Describe the four major plant groups.
- Bryophytes (nonvascular plants): Mosses and other bryophytes are small nonvascular plants that lack a specialized vascular system to transport nutrients, water, and essential minerals. Rely on diffusion and osmosis to obtain needed materials, which restricts their size. Do not form seeds; they reproduce and disperse primarily via haploid spores.
- Vascular plants (seedless vascular plants, gymnosperms, and flowering plants) have two types of vascular tissues:
- Xylem conducts water and dissolved minerals.
- Phloem conducts dissolved organic molecules such as sugar.
- A key step in evolution of vascular plants was the ability to produce lignin, a strengthening polymer in cells that function for support and conduction.
- Seedless vascular plants: (club mosses and ferns) reproduce and disperse primarily via spores.
- Gymnosperms: reproduce by forming unprotected seeds on a stem or in a cone
- Angiosperms (flowering plants): reproduce by forming seeds enclosed within a fruit
Summarize the features that distinguish bryophytes from other plants.
Bryophytes are the only living non-vascular land plants. Because they have no vascular system to transport water, sugar, and essential minerals, bryophytes are typically small. Bryophytes are the only plants with a dominant gametophyte generation – sporophytes remain permanently attached and nutritionally dependent to the gametophyte.
Name and briefly describe the three phyla of bryophytes.
- Three phyla: mosses (phylum Bryophyta), liverworts (phylum Hepatophyta), and hornworts (phylum Anthocerophyta)
- Mosses (phylum Bryophyta) usually live in dense colonies. Mosses have tiny, hairlike absorptive structures (rhizoids) and an upright, stem-like structure with leaf-like blades, normally consisting of a single layer of undifferentiated cells. Mosses play an important role in forming soil; are important commercially (Sphagnum); and form peat bogs used for fuel – and which occasionally preserve human remains. Mosses and other bryophytes lack vascular tissues and do not form true roots, stems, or leaves.
- Liverworts (phylum Hepatophyta) have a dominant gametophyte generation. Gametophytes body form is often flattened, lobed structure called a thallus that is not differentiated into leaves, stems, or roots. On the underside of the thallus is hair-like rhizoids that anchor the plant to the soil. Liverworts lack stomata.
- (a) Flattened, ribbon-like lobes characterize the gametophyte of the common liverwort (Marchantia polymorpha). This male gametophyte thallus has both asexual gemmae cups and sexual antheridiophores, which produce sperm-bearing antheridia.
- (b) Achegoniophores on the female gametophyte thallus of M. polymorpha produce egg-bearing archegonia. Liverwort sporophytes, which are always attached to and dependent on the gametophyte plant, consists of a foot, seta, and capsule. Meiosis occurs in the capsule and produces haploid spores.
- (c) Porella is a leafy liverwort. The leafy plant is the gametophyte. It bears antheridia and archegonia on special branches that look quite similar to the non-reproductive branches. After fertilization, a small sporophyte develops that produces spores following meiosis.
- Hornworts (phylum Anthocerophyta) superficially resemble liverworts, but their cell structure resembles certain algal cells more than plant cells. Hornworts live in disturbed habitats such as fallow fields and roadsides. A single gametophyte often produces multiple sporophytes, meiosis occurs, forming spores within each sporangium. Sporophytes continue to grow from their bases for the remainder of the gametophyte’s life (indeterminate growth).
Describe the life cycle of mosses and compare their gametophyte and sporophyte generations.
The green moss gametophyte bears archegonia and/or antheridia at the top of the plant. During fertilization, a sperm cell fuses with an egg in the archegonium. The zygote grows into an embryo that develops into a moss sporophyte, which is attached to the gametophyte. Meiosis occurs within the capsule of the sporophyte to produce spores. When a spore germinates, it grows into a protonema that forms buds that develop into gametophytes.
Describe bryophytes in experimental studies.
Botanists use bryophytes to study plant genetics, growth and development, ecology, hormones, and photoperiodism. The moss Physcomitrella patens is important for studying plant evolution – its features and genome can be compared to those of algae and flowering plants.
Describe bryophytes evolution.
All land plants probably evolved from a common ancestral green alga (a monophyletic group). Fossils indicate that bryophytes were probably the first group of plants to arise from the common plant ancestor. The oldest plant fossils – about 425 million years old –resemble modern liverworts in many respects.
Discuss the features that distinguish seedless vascular plants from algae and bryophytes.
Specialized vascular tissues (xylem and phloem) allow vascular plants to grow to large sizes because water, minerals, and sugar are transported to all parts of the plant. Seedless vascular plants have true steams with vascular tissues–most also have true roots and leaves. Leaves are the main organs of photosynthesis. Two types of true leaves (microphylls and megaphylls) evolved independently of each other. Seedless vascular plants have several adaptations that algae and bryophytes lack, including vascular tissues and a dominant sporophyte generation. As in bryophytes, reproduction in seedless vascular plants depends on water as a transport medium for motile sperm.
Name and briefly describe the two phyla of seedless vascular plants.
- Club mosses: Small, evergreen plants with true roots; rhizomes and erect aerial stems; and small, scalelike leaves (microphylls). Sporangia on reproductive leaves are clustered in conelike strobili at the tips of stems, or scattered along stems. Ancient, treelike club mosses were major contributors to our present-day coal deposits. Sporophytes of club mosses (phylum Lycopodiophyta) consist of roots, rhizomes, erect branches, and leaves that are microphylls.
- Coal is an organic material formed from remains of ancient vascular plants, particularly those of the Carboniferous period, 320 mya.
- Ferns: including horsetails and whisk ferns, are a monophyletic group – the closest living relatives of seed plants. Mostly terrestrial plants with a dominant sporophyte generation and true roots. Sporophyte has a horizontal underground stem (rhizome), that bears complex, compound leaves (fronds) that emerge from the ground tightly coiled (fiddlehead).
- Whisk ferns: Relatively simple ferns that have vascularized stems, but lack true roots and leaves. Whenever the stem forks, it always divides into two equal halves (dichotomous branching). Tiny, round sporangia are borne on erect, aerial stems. Haploid prothalli grow underground, are nonphotosynthetic, and apparently have a symbiotic relationship with mycorrhizal fungi.
- Horsetails: Ferns with true roots; hollow, jointed stems impregnated with silica; and small leaves (reduced megaphylls) fused in whorls at each node. Each reproductive branch bears a terminal conlike strobilus that contain sporangia. The life cycle is similar to that of ferns. About 300 million years ago, horsetails were among the dominant plants and grew as large as modern trees.
- Ferns (phylum Pteridophyta) are the largest and most diverse group of seedless vascular plants. The fern sporophyte consists of a rhizome that bears fronds and true roots. Sporophytes of whisk ferns have dichotomously branching rhizomes and erect stems; they lack true roots. Horsetail sporophytes have roots, rhizomes, aerial stems that are hollow and jointed, and leaves thats are reduced megaphylls.
Describe the life cycle of ferns and compare their sporophyte and gametophyte generations.
The fern life cycle alternates between the dominant, diploid sporophyte and the haploid gametophyte (prothallus). Spore production in sporangia (cluster called sori) on fronds of the sporophyte. Prothallus is a tiny, green, heart-shaped structure that grows flat against the ground. Flagellate sperm cells swim from an antheridium to the neck of an archegonium through a thin film of water on the ground underneath the prothallus.
Compare the generalized life cycles of homosporous and heterosporous plants.
- Homospory (production of only one type of spore as a result of meiosis) is characteristic of bryophytes, horsetails, whisk ferns, and most ferns and club mosses.
- Certain ferns and club mosses (spike mosses) exhibit heterospory, in which they produce two types of spores: microspores and megaspores. Each strobilus bears two kinds of sporangia.
- Microsporangia produce microsporocytes which undergo meiosis to form microscopic, haploid microspore, which develop into male gametophytes.
- Megasporangia produce megasporocytes which undergo meiosis to form haploid megaspore, which develop into female gametophytes.
Describe seedless vascular plants in experimental studies.
Botanists use seedless vascular plants as models to study plant physiology, growth, and development. Seedless vascular plants are useful in studying how apical meristems (areas at the tip of a root or shoot where growth occurs) give rise to plant tissues. Ferns are interesting subjects for genetic studies because they are polyploids with multiple sets of chromosomes, but express genes like a diploid plant.
