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133 Cards in this Set
- Front
- Back
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General features of algae
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-Live in a diversity of habitats, but most are aquatic and live in water
-Unicellular and multicellular forms; the most complex algae rival the giant redwoods -Able to photosynthesize and produce oxygen as a byproduct --> photoautotrophic -About 50% to 70% of the earth’s atmospheric oxygen comes from unicellular marine algae -Certain groups of algae store starch for energy storage and contain cellulose in their cell walls -Not plants: do not form embryo; lack distinct organs found in land plants -Green algae certainly existed in the Paleozoic period, ~500 million years ago -Algae are important in many ecosystems -The most significant ecological role of algae is as plankton--> Free floating, mostly microscopic organisms that inhabit oceans, seas, or bodies of fresh water - Algae are the primary producers that support food chains in marine and freshwater habitats |
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Relationship with green algae and plants
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○ About 7,500 species
○ Unicellular and multicellular ○ Most green algae live in freshwater, but different species also occur in marine habitats, soil, clouds, shady moist sides of trees, fences, etc. ○ Green Algae Are the Ancestors of Plants ○ Able to photosynthesize ○ Photosynthetic pigments: chlorophyll a and b ○ Store starch for energy storage and contain cellulose in their cell walls ○ Chara, the filamentous green algae (stoneworts) ○ The branched, leaf-like structure of the filaments are whorled, as in some plants ○ The most complex and plantlike of the green algae; ancestral to plants ○ Unique sexual organs among the algae ○ Antheridia and oogonia are multi-cellular and surrounded by a layer of sterile cells ○ Produce flavonoid pigments ○ Shared characteristics with plants |
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Green algal blooms
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-Occur when too much nitrogen and phosphorus enter a waterway
-Algae block sunlight needed by underwater plants that provide habitat, and algae's decay robs the water of dissolved oxygen needed by aquatic life |
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Green algae biofuels
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-Efficient, rapid growth, can double biomass in a day
-Can be grown on non-arable land in saline water -Can produce high yields of lipids for biodiesel, starch / polysaccharides for ethanol -Requires CO2 for growth therefore fuel is carbon neutral -Based in Alameda, CA, Aurora Biofuels is a renewable energy startup company which develops algae generated oils as a source of biodiesel fuel -~20 million acres of algae would supply ALL US transportation fuel -Small fraction of current land use -US currently uses ~970 million acres for crops & grazing |
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Main features of brown algae
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○ A large group of mostly marine multicellular algae
○ About 1,500 species ○ A wide range of morphological types, from the most complex of all the algae, the kelps, to microscopic, branched filaments ○ The giant kelps: Stipes, blades, and branching holdfasts that anchor them to the ocean floor; The leafy blades have air bladders that keep the kelps afloat ○ Kelps and rockweeds dominate shorelines and nearby offshore habitats in cool climates worldwide ○ Macrocystis, a member of kelps, may reach 60 m in length, and forms prominent underwater forests ○ Marine forests: habitats of teeming populations of many kinds of animals ○ The pigment fucoxanthin (a type of carotenoid): responsible for the distinctive greenish-brown color |
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Examples of the uses of brown algae
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○ Fucoxanthin is being explored for weight loss
○ Promotes loss of abdominal fat in obese mice; lost 5 to 10% of their body weight ○ A popular nutritional supplement ○ Cautions: Seaweed rich in iodine; excessive consumption --> iodine poisoning ○ Algin- A polysaccharide extracted from the cell walls of brown algae--> Absorbs water quickly: used as a gelling agent by the foods industry for thickening drinks, ice cream, milkshake, salad dressing, jelly beans |
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Main features of red algae
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-Mostly marine organisms
-Microscopic filaments or macroscopic leafy branches -About 3,900 species -Have an abundance of phycoerythrin, a red protein containing a red phycobilin chromophore -Phycobilin chromophores: light-capturing molecules; found in cyanobacteria and in the chloroplasts of red algae -Phycoerythrin: capture and then pass the light energy to chlorophylls for photosynthesis -Several species of red algae grow at about 75 m depth (225 ft) on McGrail Bank, Gulf of Mexico -Phycoerythrin absorbs blue light, which penetrates more deeply into water than do other colors of light -Red algae can photosynthesize at greater depths than other algae --> deep ocean dwelling -Coral reefs: formed by interactions of coralline red algae, sponges, and other organisms when the organisms die -Coralline Red Algae -- symbiotic association; the "cement" that holds the coral reef together -Cell walls: calcium carbonate and magnesium carbonate, which make the walls hard and crusty -Red drift algae arrive in huge mats covering the shore; Sanibel, Florida -While not toxic or dangerous, the piles of algae destroy the tourism value of the beaches -Agar: A polysaccharide obtained from the cell walls of some species of red algae, primarily from the genera Gelidium -Used as a gelling agent in laboratories for nutrient culture media -Agarose gel: used in molecular biology research for separation of DNA and RNA |
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Main features of diatoms
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-About 10,000 species
-Unicellular, either bilaterally symmetrical or radially symmetrical -Unique because of their exquisitely ornamented glass shell (cell walls containing silica) -Occur in both freshwater and salt water -Important primary producers in the food chain of many aquatic ecosystems, especially in oceans -Filter feeders depend on diatoms, and on tiny organisms that feed on diatoms, for food -Oils: up to 40% of a diatom’s mass -Potential diesel fuel substitute -The best known and the most widespread fossil algae -Silica of their cell walls does not decompose: instant fossils -Identified in sediments deposited about 120 million years ago |
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Main features of dinoflagellates
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-About 3,000 species
-Most are marine plankton, but they are common in fresh water habitats as well -Microscopic, (usually) unicellular, flagellated -The cell wall: form plates of cellulose with a distinctive geometry/topology -Bioluminescence: Algae that are commonly found in the fossil record include dinoflagellates and diatoms -Dinoflagellates were preserved --> thick, protective cellulose plates around themselves -The oldest fossils: about 430 million years old |
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Coralline Red Algae
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symbiotic association; the "cement" that holds the coral reef together
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Phycoerythrin
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-A red protein containing a red phycobilin chromophore
-Capture and then pass the light energy to chlorophylls for photosynthesis -Absorbs blue light, which penetrates more deeply into water than do other colors of light |
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Phycobilin chromophores
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Light-capturing molecules; found in cyanobacteria and in the chloroplasts of red algae
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Agar
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-A polysaccharide obtained from the cell walls of some species of red algae, primarily from the genera Gelidium
-Used as a gelling agent in laboratories for nutrient culture media |
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Agarose gel
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Used in molecular biology research for separation of DNA and RNA
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Diatomaceous Earth
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- Diatom cell walls sometime settle in large deposits, the largest of which is ~900 meters deep and 2 kilometers long, in Lompoc, CA
-Harvested commercially and used in many ways -Filters for cleaning swimming pools and clarifying beer and wine -Reflective paint on highways, road signs and license plates |
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Red tides
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-Caused by a bloom of some red pigmented dinoflagellates
-Common along the Gulf coast of Florida and the coast of central California -Secrete a nerve toxin: brevetoxin (Karenia brevis) |
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Brevetoxins
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-Neurotoxins that bind to voltage-gated sodium channels in nerve cells
-Kill millions of fish each year -A 2005 outbreak along Florida's southwest coast: caused a 2,000 mile-wide "dead zone" off the city of St. Petersburg -More than 950 tons of dead creatures that washed up on area beaches -Shellfish (oysters, mussels, scallops, and clams): immune to toxins Humans eat contaminated shellfish: suffer poisoning and death --> neurotoxic shellfish poisoning |
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Life cycle of Chlamydomonas
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-A genus of unicellular green algae
-Asexual reproduction: mitosis -Sexual reproduction: fusion of two cells to form a zygote --> meiosis |
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Life cycle of Fucus
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-Rockweed,a multicellular
brown alga -Sexual reproduction: male thallus-> male receptacle -> antheridium -> meiosis -> flagellated sperm cells; female thallus-> female receptacle -> oogonium -> meiosis -> egg cells; Sperm cell + egg cell -> fertilization -> zygote – free living, not protected -> germination -> thallus |
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Flagellum
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A tail-like structure that projects from the cell body of certain prokaryotic and eukaryotic cells, and it functions in locomotion
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Mitosis
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A process of cell division in which a eukaryotic cell separates the chromosomes in its cell nucleus, into two identical sets in two daughter nuclei
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Meiosis
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-A process of cell division in which the number of chromosomes per cell is cut in half
-Essential for sexual reproduction and therefore occurs in all eukaryotes (including single-celled organisms) that reproduce sexually |
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What are the major groups of land plants?
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-Bryophytes
-Ferns -Gymnosperms -Angiosperms |
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When different groups of plants appeared on the planet?
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Origin of earth--> Origin of life--> Green algae--> Land plants (bryophytes) Silurian period--> Vascular plants (Devonian period)--> Ferns & fern relatives--> Gymnosperms--> Angiosperms--> Human ancestor Australopithecu--> Homo sapiens (modern man)--> Origin of agriculture
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Common features of plants
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-Multicellular eukaryotes
-Photosynthesis: Chloroplasts containing chlorophylls a and b -Cellulose-rich cell wall; starch -Flavonoids and carotenoids -Form multicellular embryos produced via sexual reproduction |
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General features of bryophytes
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-Seedless, nonvascular plants
-23,000 species -Three major groups (phyla): Mosses Liverworts hornworts -Small, compact, green plants -Like green algae Chara, they produce chlorophylls a and b, starch, cellulosic cell walls, flavonoids, swimming sperm cells -Lack highly evolved vascular and lignified tissues, a complex water transport system --> nonvascular plants -Grow low to the ground -A fatty cuticle covering the plant surfaces --> prevent water loss -Lack true leaves, stems, and roots -Absorb water and nutrients at the soil’s surface by diffusion over the surface of bryophytes -Rhizoids: hairlike extensions of epidermal cells along the lower surface--> Anchor plants but absorb only small amounts of water and nutrients -Rhizoids: have mycorrhizal associations -Gametangia (gamete producing structures) and sporangia (spore producing structures) are multicellular and surrounded by a sterile sheath of cells -Zygotes develop into multicellular embryos within parental tissues -Grow in many different habitats -Mosses are especially abundant in the arctic and antarctic -Dominate the vegetation in peatlands -Bryophytes, along with lichens, are among the first organisms to colonize bare rocks and volcanic upheavals -Important as pioneer species in ecological succession; paving the way for colonization by other organisms |
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Asexual reproduction
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-Production of cells with chromosomes identical to the cells from which they arise; mitosis
-Mutations provide genetic variability necessary for evolution |
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Sexual reproduction
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-Sex cells called gametes are produced
-Diploid cells have two sets of chromosomes; one from the male parent and the other from the female parent -Gametes only have one set of chromosome -Two gametes called egg and sperm unite to form a single cell called a zygote -Zygote is the first cell of a new individual |
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Alteration of Generations
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-In a complete life cycle involving sexual reproduction, there is an alteration between a diploid (2n) sporophyte
phase and a haploid (n) gametophyte phase -Diploid (2n): any cell with two sets of chromosomes -Haploid (n): any cell with one set of chromosome -Gametes are haploid; a zygote is diploid |
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Sporophyte
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-The diploid body developed from a zygote
-Produce sporocytes --> meiosis --> haploid spores |
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Gametophyte
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The haploid body developed from the spore
Produce gametes by mitosis |
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Sporangium
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Spore producing structures
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Sporocytes
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Spore-producing
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Spores
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The units of dispersal; short-distance travel; short lifetime
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Antheridium
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Sperm-producing
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Archegonium
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Egg-producing
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Gamete
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-Sex cell
-only have one set of chromosome |
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Zygote
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-Two gametes called egg and sperm unite to form a single cell
-The first cell of a new individual |
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Embryo
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Protected and nourished by gametophyte
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Haploid
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(n): any cell with one set of chromosome
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Diploid
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(2n): any cell with two sets of chromosomes
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Alteration of heteromorphic generations
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Distinctly different generations of gametophyte and sporophyte
Gametophyte: gamete producing plant (generation) Sporophyte: spore producing plant (generation) Gametophyte generation starts with germination of haploid spores Germinated spore first forms a protonema, and later develops into a “leafy” gametophyte plant Haploid gametophytes are the dominant (and most visible) structure of bryophytes Gametophyte nutritionally independent of sporophyte Gametophyte grows and produces antheridia and archegonia Antheridia produce flagellated sperm, and archegonia produce eggs Fertilization requires free water because sperm must swim to the egg Sperm attracted to the egg by special chemicals released by archegonia A sperm fertilizes an egg in the archegonium --> diploid zygote Zygote --> embryo (protected and nourished by gametophyte)--> diploid sporophyte generation of life cycle Sporophyte depends on the gametophyte for nutrition and water Sporophytes produce sporangia containing sporocytes (spore-producing) Sporocytes undergo meiosis --> haploid spores, which are dispersed usually by wind The spore germinates and forms the gametophyte, thus completing the sexual life cycle |
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What is the most dominant feature of bryophytes?
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Haploid gametophytes
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What is nutritionally independent of sporophyte?
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Gametophyte
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What is nutritionally dependent on gametophytes?
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Moss sporophytes
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diploid sporophyte
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Sporophyte depends on the gametophyte for nutrition and water
Sporophytes produce sporangia containing sporocytes (spore-producing) |
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Haploid gametophytes
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the dominant (and most visible) structure of bryophytes
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Mosses
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-Moss gametophytes: green and photosynthetic --> dominant in life cycle
-Moss sporophytes: nutritionally dependent on gametophytes -Mature sporophyte: three parts --> a foot, a seta (stalk), and a capsule enclosing spores -One capsule may form as many as 50 million spores |
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Physcomitrella patens
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A moss used as a model organism for studies on plant evolution, development and physiology--> Its genome, about 500MB organized in 27 chromosomes, was completely sequenced in 2006
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Peat
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-Partially carbonized vegetable matter, usually mosses, found in bogs
-Dead peat moss and other organic materials accumulate and form large deposit called peat bogs -Peat bogs cover ~1% of the earth’s surface -Has a caloric value of 3,300 calories per grams (only half that of coal) -Good source of fuel -Ireland: 20% of its energy from peat |
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Sphagnum peat moss
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-Includes various mosses of the genus Sphagnum, usually found growing in very wet places
-Accumulates at rates exceeding 12 tons per hectare annually -Can absorb 20 times its weight in water -An excellent soil conditioner that retains water; potting soil additive; improve soil structure and texture -Produces large amounts of acids (pH 3.0) and antiseptics that kill decomposers |
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Liverworts
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~8,500 species
-Low-growing plants usually found in wetlands -Named during medieval times -A few liverworts are lobed --> resemblance to the human liver, so the word liver was combined with wort (herb) to form the name liverwort -Prominent haploid gametophytes have two shapes -leafy liverworts: abundant in tropical rain forests and fog belts -Thallose liverworts: often lobed and bilaterally symmetrical |
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Hornworts
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~100 species
-The sporophyte is shaped like a tapered horn, hence the common name -Remains photosynthetic: semi-independence -An evolutionary step toward the independent sporophytes that characterize vascular plants |
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The major adaptations vascular plants evolved to cope with the dry land
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-True leaves, stems, and roots
-Highly evolved vascular and lignified tissues, a complex water transport system --> vascular plants -High off ground |
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Epidermis/ Cuticle
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-Thick cuticle: water proof; prevent from gas exchange
-Survive on dry land: prevent from drying out |
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Cutin and wax
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-Long chain fatty acids; hydrophobic molecules
-Shiny surface; water proof |
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Functions of cutin and wax
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Permeability barriers for water and water-soluble materials
-Prevents plant surfaces from becoming wet and helps to prevent plants from drying out -Deflect excess sunlight |
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How are cutin and wax a physical barrier?
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Protect from pathogen invasion
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Stoma
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-A structure composed of two guard cells flanking an opening (stomatal pore) in epidermis
-Allow gas exchange during photosynthesis -Air containing CO2 and O2 enters the plant through these openings where it is used in photosynthesis and respiration -Oxygen produced by photosynthesis exits through these same openings -Water vapor is released into the atmosphere through these pores in a process called transpiration |
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Stomatal pores
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-Water loss
-Stomatal pore opening is regulated by two guard cells -Plants evolved sophisticated mechanisms to regulate gas exchange and water loss |
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Vascular tissues
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-Large and tall
-Transport of water and food throughout the plant body: a serious problem for any large organism growing on land -Composed of xylem and phloem |
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Polymer Lignin
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-Gives vascular plants the ability to synthesize which adds rigidity to the walls
-->pivotal step in the evolution of plants |
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Xylem
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Transport water and minerals from roots to shoots
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Phloem
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Transport sugars from leaves to other parts of plant body
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Xylem conducting cells
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-Tracheary elements
Dead cells; thick walls (cellulose, hemicellulose and lignin) |
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Tracheids
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The first type of tracheary
elements to evolve; ferns and gymnosperms |
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Vessels
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-Evolved later than tracheids; angiosperms
-How water is transported from roots to shoots -Xylem conducting cells form hollow pipes throughout the plant body |
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Transpiration
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Driving force; Water column
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Phloem conducting cells
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-Sieve elements
-Living cells; thin walls -Need to control where sugars are transported |
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Meristems
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-The cells that are perpetually young and able to divide to produce new cells and tissues
-Allow vascular plants to grow tall and thick -Responsible for new growth |
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Apical meristems
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-Located at the tips of stems and roots
-Responsible for the extension of the plant body --> often the vertical growth of a plant |
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Primary growth
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The growth that occurs at the tips of stems and roots initiated by apical meristems
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Primary tissues
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The tissues arising during primary growth
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Primary plant body
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The part of the plant body composed of primary tissues
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Lateral Meristems
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-Responsible for secondary growth, the growth that thickens the stems and roots; secondary plant body
-Composed of vascular cambium and cork cambium |
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Vascular Cambium
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Produces secondary vascular tissues: secondary xylem and secondary phloem
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Cork Cambium
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Produces cork cells, replacing the epidermis as the dermal tissue system (periderm) of woody plants for protection
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Secondary xylem (wood)
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Transport of water and minerals; support
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Secondary phloem
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Transport of sugars
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Cork cells
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Dead and impregnated with a lipid polymer -- suberin; hydrophobic and water-proof
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Lenticel
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The opening in periderm for gas exchange
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Bark
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Cork together with secondary phloem
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What does the support system of vascular plants do?
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-Organisms living in water are supported by the dense liquid they live in
-Xylem: thick walls; mechanical tissues -Provide mechanical support to the plant body -Allow vascular plants to reach great heights to compete for light |
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Highly-Differentiated Plant body
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-Organs of the plant: roots, leaves and stems
-Provide a system well suited to the demands of life on land -Roots: anchorage and absorption of water and minerals -Leaves: photosynthesis -Stems: elevation leaves to receive the maximal amount of light |
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Life cycle of seedless vascular plants
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-Dominate by the sporophyte, which is the “plant” that everyone thinks of
-Sporophytes are nutritionally independent of the gametophyte -Sporophytes are often perennial; new growth sprouts from underground rhizomes year after year --> asexual reproduction -Sporangia are aggregated into either strobilus or sorus, where spores are produced and usually dispersed by wind -Gametophyte generation starts with the germination of spores -Gametophyte is short-lived and small, sometimes microscopic; nutritionally independent of sporophyte -Gametophyte forms two structures--> Antheridium: sperm-producing Archegonium: egg-producing -Flagellated sperm cell swim through water to eggs; require free water for sexual reproduction -Fusion of sperm and egg results in production of zygote --> embryo --> next generation of sporophyte |
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Life Cycle Comparison between bryophytes and seedless vascular plants
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-Sporophyte-->
Bryophytes: Nutritionally dependent on gametophyte Seedless vascular plants: Dominate the life cycle; Nutritionally independent of gametophyte Gametophyte--> Bryophytes: Dominate the life cycle; Nutritionally independent of sporophyte Seedless vascular plants: small and short-lived; Nutritionally independent on sporophyte Fertilization: Require free water for sperm to swim to the egg Zygote and embryo nourished and protected by gametophyte Unit of dispersal: spores |
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Whisk ferns (Phylum Psilotophyta):
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Psilotum, scientific name
The simplest, most primitive (the oldest or earliest to evolve) of all living seedless vascular plants They only have stems but no roots and no leaves: unique among living vascular plants Instead of roots with root hairs, they have rhizomes with absorptive rhizoids Dichotomously forking (evenly forking) aerial stems Small sporangia (spore-producing) are fused in threes; produced at the tips of very short stubby branches Enations: scalelike outgrowth Fossil plants that resemble whisk ferns: found in Silurian geological formations (~430 million yr ago) One group of these fossil plants, Cooksonia, had naked stems and terminal sporangia Widespread in subtropical regions of the southern US and Asia It is a popular and easily cultivated plant that is grown in greenhouses |
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Club Mosses (Phylum Lycophyta):
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Two main Genera:
Club mosses (Lycopodium): ~400 species Spike mosses (Selaginella): ~700 species Get their common names from their club-shaped or spike-shaped strobili Strobilus: Sporangia (spore-producing) are aggregated into cones, called strobili Strobilus occurs primarily in club mosses, spike mosses, and horsetails but not in ferns Sporophytes: differentiated into leaves (microphylls), stems and roots The Resurrection Plant is one species of spike mosses (Selaginella) Named because of its ability to defy drought conditions Occurs in the deserts of southwestern US and Mexico During periods of drought, it forms a tight, dried-up ball When rain comes, it absorbs water, expand and resume photosynthetic activity Biotechnological applications |
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Horsetails (Phylum Equisetophyta):
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Equisetum, scientific name
Called scouring rushes; epidermal tissue contains abrasive particle of silica Were used by native Americans to polish bows and arrows Occurs worldwide in moist habitats along the edge of streams and forests Sporangia aggregated into a stobilus at the tip of stems ~25 species: unbranched; branched Branched species: branches are whorled at regular intervals Tiny scalelike leaves (microphylls) in whorls at the nodes |
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Ferns (Phylum Polypodiophyta):
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~12,000 living species; the largest among the seedless vascular plants
Primarily tropical plants Possible ancestors of ferns found in Devonian formations; ~375 millions yr old Fern leaves are called fronds; the fronds are divided into segments called pinnae Sporangia are aggregated into a cluster, called sorus, on the undersides of the leaves Ideal house plants; grow in low light Air filters-->One average-size Boston fern removes ~1,800 ug of formaldehyde (a common pollutant from carpets) from the air in a typical room (10ft x 10ft) |
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Coal age plants:
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Some seedless vascular plants had evolved into large trees (up to 120 ft tall) ~300 million yr ago
The swamp-dwelling giant club mosses and giant horsetails dominated the carboniferous period These huge plants formed the extensive coal deposits we mine today Giant club mosses disappeared ~ 250 million yr ago Giant horsetails died out ~150 million yr ago Many of the primitive features of these extinct trees are maintained in the smaller, modern members of these groups |
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What is a seed?
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A small embryonic plant with a food supply encased in a protective coat
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Seedcoat
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Offer maximum protection (thick walls; thick cuticle - waterproof)
Maintain seed dormancy (no germination) |
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Embryo
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Young sporophyte
Contains shoot apical meristems and root apical meristems to grow into a mature sporophyte Contains hormones (abscisic acid) to maintain dormancy Inhibit seed germination on plants |
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Stored food
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Located outside the embryo: pine; corn; wheat; rice
Located within the embryo: peanut; beans |
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How is a seed formed?
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Sporophyte (the plant):
Male sporangia (microsporangia) --> microspore --> microgametophyte (pollen grains containing sperm cells) Female sprorangia (megasporangia) --> megaspore --> megagametophyte Gametophytes: retain on sporophyte |
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Evolution of ovule
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Ovule: the structure in which the megagametophyte enclosed by integument
The egg cell: produced in Megagametophyte Microgametophytes (pollen grains): carried by wind or animals to ovule (or stigma of the carpel) |
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Pollen tubes
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Convey sperm to the egg for fertilization
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Is water necessary for fertilization?
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No
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Integument
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seedcoat, young sporophyte
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Adaptations of seedless vascular plants
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Require free water for sperm to swim to egg
Gametophyte (no vascular tissues) not protected by sporophyte Embryo grows into adult sporophyte directly from gametophyte Spores: the units of dispersal; short-distance travel; short lifetime Vulnerable to harsh environments Dominant during the Carboniferous period Much of the earth was flooded; no competitors At the end of carboniferous period (~286 to 248 million yr ago), the climate turned much cooler and drier; coal-age plants died out; seed plants appeared and took over |
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Adaptions of seed plants
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No free water required for sperm to reach to egg
Delicate megagametophyte retained on sporophyte Embryo: packed in the seed for protection Withstand harsh environments |
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Advantages of seeds
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Unit of dispersal; travel far distance
Seedcoat: maximum protection Withstand extremely harsh environments Stored food Animals often help to disperse seeds-->Help young seedlings to grow large enough to compete for light, water, and minerals Can remain dormant in the soil for many years; germinate when conditions are favorable Seeds thus give plants greater flexibility in copying with stressful environmental conditions, allowing plants to colonize seasonally cold or dry habitats in which seedless plants are at a disadvantage |
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Gymnosperms
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Plants with naked seeds
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Angiosperms
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Plants with seeds enclosed within fruits
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Features of gymnosperms
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All seed plants without fruits
Plants whose pollen is carried by wind directly to ovules (unfertilized seeds) and whose seeds are naked Characterized by secondary growth that usually forms woody trees or shrubs Secondary growth: Vascular cambium -- wood (secondary xylem) and secondary phloem Cork cambium -- cork Most gymnosperms: have tracheids and lack vessels in wood (secondary xylem) Tracheids: the first-evolved conducting cells in xylem Also in ferns and fern relatives Exception: plants in the division Gnetophyte have wood with vessel |
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The simplest seed-bearing structures among gymnopserms
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Ginkgo and yew: seeds are borne singly at the ends of stalks; not in cones -- exceptions
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Ginkgo
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Fleshy seedcoat; embryo
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Yew
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Seed; fleshy cup -- an outgrowth from the base of the ovule
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Cones (strobilus)
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Seeds in a complex structure consisting of several scales grouped together at the end of a stem
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Pollen cones (“male” cones)
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In which pollen grains (male gametophytes) are produced
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Seed cones (“female” cones)
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In which ovules are produced
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Junipers
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The smallest seed cones; have fleshy scales fused into berrylike structure
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Cycads
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The largest seed cones; up to a meter long and weigh over 30 pounds
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Male gametophyte (pollen grains):
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Most gymnosperms: produce huge amount of pollen
Each pollen cone of a pine tree: releases 1 to 2 million pollen grains Conifer forests of Sweden: release 75,000 tons of pollen each spring Contribute to some people’s allergy problem How it is formed: Male cone --> microsporangia --> sporocyte --> meiosis --> tetrad spores --> mitosis --> male gametophyte (pollen grains) Pollen grains: a reduced, immature male gametophyte Each pollen grain: four cells One generative cells --> 2 sperm cells One tube cell --> pollen tube Two prothallial cells --> degenerate Two wings Evolved by a continued reduction in size of the male gametophyte |
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Female gametophyte:
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Seed cone --> ovule --> megasporangia --> megasporocyte --> meiosis --> megaspores --> mitosis --> female gametophyte
Each ovule contains a female gametophyte Female gametophyte: thousands of cells; one to several egg cells inside the archegonium Fertilization:Pollen carried by wind directly to the ovule Pollen tubes convey sperm to the egg; no free water required for fertilization After fertilization, the ovule develops into a seed Integument --> seedcoat Zygote --> embryo Female gametophyte --> endosperm (stored food) |
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Ginkgo (Ginkgophyta)
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The maidenhair tree, a common name derives from the resemblance of its leaves to leaflets of the maidenhair fern
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Ginkgo biloba
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Extinct in nature; descendants of plants that were grown in temple gardens of China
The only living species in its division Remained virtually unchanged for 65 million yrs A living fossil |
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Dioecious of Ginkgo
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“Male” trees: pollen cones
“Female” trees: seed bearing Sperm cells: flagellated |
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Seed of Ginkgo
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a massive seedcoat containing a fleshy outer layer, a hard and stony middle layer, and an inner dry and papery layer
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Ginkgo Deciduous
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Leaves turn golden yellow and then drop off during the fall
A popular cultivated tree; resistant to air pollution Male trees are preferred; female trees -- fleshy seedcoat is stinky and messy |
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Ginkgo extract
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A staple of Chinese herbalists; treat asthma and bronchitis
Praised for its ability to improve memory; hope for Alzheimer’s patients Increase blood flow to the brain; more oxygen and nutrients Enhance concentration and short-term memory Reduce absent-mindedness and anxiety |
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Cycads (Cycadophyta)
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~100 species
Distributed primarily in the tropical and subtropical regions of the world Palmlike leaves: no resemblance to the leaves of other living gymnosperms Dioecious: male and female plants Sperm cells: flagellated; 10,000 to 70,000 spirally arranged flagella The largest seed cones |
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Conifers (Pinophyta)
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Cone-bearing trees
548 species; the largest division Members of the genus Pinus: typical conifers The most abundant trees in the Northern Hemisphere Many of the species in conifer forests are pines |
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Monoecious
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Male cones and female cones are on the same tree
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Examples of Conifers
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Bristlecone pine of the western U.S.: the oldest known plants -- over 4,700 yrs old
other conifers: Yews, firs, spruces, coastal redwood, junipers, cypresses Narrow leaves with pointy tips; evergreen The oldest, tallest, and biggest trees belong to conifers Redwoods: the tallest trees; 385 feet high; 2,000 years old Giant sequoias: the largest trees; confined to the western slopes of California’s Sierra Navada range The General Sherman tree in the Sequoia National park 100 ft around; 272 ft tall; weighs 12 millions pounds |
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3 genera of Gnetophytes (Gnetophyta)
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71 woody species
Ephedra: 40 species Gnetum: 30 species Welwitschia: 1 species; the most distinctive (if not bizarre) of all seed plants |
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Gnetophytes (Gnetophyta)
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Shrubs, scalelike leaves
monoecious or dioecious |
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Benefits of Gnetophytes
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Known for its medicinal uses
Ephedrine: an alkaloid extracted from ephedra stems Herbal medicine: relax bronchial muscles; a decongestant for asthma and bronchitis Ephedrine: activate thermogenesis The body burns calories to generate heat Herbal energy boosters -- stimulant Over-the-counter weight-control supplements Ephedrine has a similar chemical structure to amphetamines Severe side effects Banned by FDA in 2003 |
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Dioecious of Gnetophytes
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Climbing vines or trees
All have broad, simple leaves Similar to those of woody dicots |
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Welwitschia mirabitis
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The sole living representative of its genus
Look like something out of science fiction than a real plant Confined to the Namib and Mossamedes deserts of southwestern Africa; average annual rainfall -- 1 inch; no rain in some years; moisture from fog from the ocean Live to be over 100 yrs old Dioecious: male and female cones on different plants A pair of large, strap-shaped leaves with meristems at its base Leaves split lengthwise -- giving the appearance of multiple leaves woody stems Unique among gymnosperms Most closely related to angiosperms Conducting cells in xylem are vessels Double fertilization: one sperm cell fuses with an egg; the other sperm cell with another cell in the same gametophyte A process otherwise known only in angiosperms |
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Our uses of gymnosperm plants
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The greatest economic impact of gymnosperms in the Northern Hemisphere: use of their wood for making paper and lumber
Conifers: Produce ~75% of the world’s timber and much of the pulp used to make paper Pulpwood for newsprint and other paper (food packaging, cardboard, paperback novels, toilet paper) in North America: white spruce, pine Douglas fir: the most desired timber tree The wood is strong; relatively free of knots; a major source of large beams for construction Red spruce: The tracheids in wood have spiral thickening on their inner walls Give its wood a resonance that makes it ideal for use as soundboards in violins and related musical instruments |
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Taxol
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Comes from Pacific yews (Taxus brevifolia) --> A known poisonous plant
A chemical obtained from the bark; inhibit cell division Kills tumors caused by ovarian cancer |
