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35 Cards in this Set
- Front
- Back
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Angiosperm lifecycle |
●In angiosperms, the sporophyte is the plant that we see; they are larger, more conspicuous and longer-lived than gametophytes
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Flower structure and function |
●Flowers are the reproductive shoots of the angiosperm sporophyte; they attach to a part of the stem called the receptacle
●Flowers consist of four floral organs: carpels, stamens, petals, and sepals ●Stamens and carpels are reproductive organs; sepals and petals are sterile ●A carpel has a long style with a stigma on which pollen may land ●At the base of the style is an ovary containing one or more ovules ●A single carpel or group of fused carpels is called a pistil ●A stamen consists of a filament topped by an anther with pollen sacs that produce pollen |
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Four general trends can be seen in the evolution of flowers
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●Bilateral symmetry
●Reduction in the number of floral parts ●Fusion of floral parts ●Location of ovaries inside receptacles |
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Gametophyte development |
●Angiosperm gametophytes are microscopic and their development is obscured by protective tissues
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Development of female gamteophytes |
●The embryo sac, or female gametophyte, develops within the ovule
●Within an ovule, two integuments surround a megasporangium ●One cell in the megasporangium undergoes meiosis, producing four megaspores, only one of which survives ●The megaspore divides without cytokinesis, producing one large cell with eight nuclei ●This cell is partitioned into a multicellular female gametophyte, the embryo sac |
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Development of male gametophytes |
●Pollen develops from microspores within the microsporangia, or pollen sacs, of anthers
●Each microspore undergoes mitosis to produce two cells: the generative cell and the tube cell ●A pollen grain consists of the two-celled male gametophyte and the spore wall |
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Pollination |
●In angiosperms, pollination is the transfer of pollen from an anther to a stigma
●After landing on a receptive stigma, a pollen grain produces a pollen tube that grows down into the ovary and discharges two sperm cells near the embryo sac |
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Double fertilization |
●Fertilization, the fusion of gametes, occurs after the two sperm reach the female gametophyte
●One sperm fertilizes the egg, and the other combines with the two polar nuclei, giving rise to the triploid food-storing endosperm (3n) ●This double fertilization ensures that endosperm only develops in ovules containing fertilized eggs |
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Seed development |
●After double fertilization, each ovule develops into a seed
●The ovary develops into a fruit enclosing the seed ●When a seed germinates, the embryo develops into a new sporophyte |
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Methods of pollination |
●The transfer of pollen from anthers to stigma can be accomplished by wind, water, or animals
●Wind-pollinated species (e.g., grasses and many trees) release large amounts of pollen |
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Coevolution |
●Coevolution is the joint evolution of interacting species in response to selection imposed by each other
●Many flowering plants have coevolved with specific pollinators ●The shapes and sizes of flowers often correspond to the pollen transporting parts of their animal pollinators ●For example, Darwin correctly predicted a moth with a 28-cm-long tongue based on the morphology of a particular flower |
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The development of a seed into a flowering plant |
●Endosperm development ●Embryo development ●Seed dormancy ●Seed germination ●Seedling development ●Flowering |
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Endosperm development |
●Endosperm development usually precedes embryo development
●In most monocots and many eudicots, endosperm stores nutrients that can be used by the seedling ●In other eudicots, the food reserves of the endosperm are exported to the cotyledons |
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Embryo development |
●The first mitotic division of the zygote splits the fertilized egg into a basal cell and a terminal cell
●The basal cell produces a multicellular suspensor, which anchors the embryo to the parent plant ●The terminal cell gives rise to most of the embryo ●The cotyledons form and the embryo elongates |
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Structure of mature seed |
●The embryo and its food supply are enclosed by a hard, protective seed coat
●The seed enters a state of dormancy ●A mature seed is only about 5–15% water |
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Eudicot embryo |
●In some eudicots, such as the common garden bean, the embryo consists of the embryonic axis attached to two fleshy cotyledons (seed leaves)
●Below the cotyledons the embryonic axis is called the hypocotyl and terminates in the radicle (embryonic root); above the cotyledons it is called the epicotyl ●The plumule comprises the epicotyl, young leaves, and shoot apical meristem |
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Monocot embryo |
●A monocot embryo has one cotyledon
●Grasses, such as maize and wheat, have a special cotyledon called a scutellum ●Two sheathes enclose the embryo of a grass seed: a coleoptile covering the young shoot and a coleorhiza covering the young root |
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Seed germination and development |
●Germination depends on imbibition, the uptake of water due to low water potential of the dry seed
●The radicle (embryonic root) emerges first; the developing root system anchors the plant ●Next, the shoot tip breaks through the soil surface ●In many eudicots, a hook forms in the hypocotyl, and growth pushes the hook above ground ●Light causes the hook to straighten and pull the cotyledons and shoot tip up ●In maize and other grasses, which are monocots, the coleoptile pushes up through the soil creating a tunnel for the shoot tip to grow through |
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Flowering |
●The flowers of a given plant species are synchronized to appear at a specific time of the year to promote outbreeding
●Flowering is triggered by a combination of environmental cues and internal signals |
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Fruit structure and function |
●A fruit is the mature ovary of a flower ●It protects the enclosed seeds and aids in seed dispersal by wind or animals ●In some fruits, such as soybean pods, the ovary wall dries out at maturity, whereas in other fruits, such as grapes, it remains fleshy |
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Fruits are categorized based on their developmental origins |
●Simple fruits develop from a single or several fused carpels
●Aggregate fruits result from a single flower with multiple separate carpels ●Multiple fruits develop from a group of flowers called an inflorescence ●An accessory fruit contains other floral parts in addition to ovaries |
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Fragmentation |
●Fragmentation, separation of a parent plant into parts that develop into whole plants, is a very common type of asexual reproduction
●In some species, a parent plant’s root system gives rise to adventitious shoots that become separate shoot systems ●Apomixis is the asexual production of seeds from a diploid cell |
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Pros and cons of asexual |
Advantages and Disadvantages of Asexual and Sexual Reproduction●Asexual reproduction is also called vegetative reproduction because progeny arise from mature vegetative fragments●All genetic material is passed to the progeny●Asexual reproduction can be beneficial to a successful plant in a stable environment●However, a clone of plants is vulnerable to local extinction if there is an environmental change
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Pros and cons of sexual |
●Sexual reproduction generates genetic variation that makes evolutionary adaptation possible
●However, only a fraction of seedlings survive ●Some flowers can self-fertilize to ensure that every ovule will develop into a seed ●However, many species have evolved mechanisms to prevent selfing |
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Mechanisms that prevent self-fertilization |
●Dioecious species have staminate and carpellate flowers on separate plants
●Others have stamens and carpels that mature at different times or are arranged to prevent selfing ●The most common is self-incompatibility, a plant’s ability to reject its own pollen ●Researchers are unraveling the molecular mechanisms involved in self-incompatibility ●Some plants reject pollen that has an S-gene matching an allele in the stigma cells ●Recognition of self pollen triggers a signal transduction pathway leading to a block in growth of a pollen tube |
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Totipotency |
●Totipotent cells, those that can divide and asexually generate a clone of the original organism, are common in plants
●Humans have devised methods for asexual propagation of angiosperms ●Most methods are based on the ability of plants to form adventitious roots or shoots |
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Vegetative propagation |
●Vegetative reproduction that is facilitated or induced by humans is called vegetative propagation
●Many kinds of plants are asexually reproduced from plant fragments called cuttings ●A callus is a mass of dividing, undifferentiated totipotent cells that forms where a stem is cut and produces adventitious roots ●A twig or bud can be grafted onto a plant of a closely related species or variety ●The scion is grafted onto the stock |
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Plant breeding |
●Mutations can arise spontaneously or can be induced by breeders
●Plants with beneficial mutations are used in breeding experiments ●Desirable traits can be introduced from different species or genera |
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Plant biotechnology |
●In a general sense, it refers to innovations in the use of plants to make useful products
●In a specific sense, it refers to use of GM organisms in agriculture and industry |
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Transgenic |
●organisms that have been engineered to express a gene from another species
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Reducing world hunger and malnutrition |
●Genetically modified plants may increase the quality and quantity of food worldwide
●Some transgenic crops have been developed to produce the Bt toxin, which is toxic to insect pests ●Other crops are able to tolerate herbicides or resist specific diseases |
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Nutritional quality of plants is being improved
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●For example, “Golden Rice” is a transgenic variety being developed to address vitamin A deficiencies among the world’s poor
●For example, transgenic cassava have increased levels of iron and beta-carotene and reduced cyanide-producing chemicals |
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Biofuels |
●Biofuels are fuels derived from living biomass, the total mass of organic matter in a group of organisms
●Biofuels can be produced by rapidly growing crops such as switchgrass and poplar ●Biofuels would reduce the net emission of CO2, a greenhouse gas |
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GMO's and human health |
●One concern is that genetic engineering may transfer allergens from a gene source to a plant used for food
●Some GMOs have health benefits ●For example, maize that produces the Bt toxin has 90% less of a cancer-causing toxin than non-Bt corn ●Bt maize has less insect damage and lower infection by Fusarium fungus that produces the cancer-causing toxin ●Widespread adoption of Bt cotton in India has led to a 41% decrease in insecticide use and an 80% reduction in acute poisoning cases |
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Transgender escape |
●Perhaps the most serious concern is the possibility of introduced genes escaping into related weeds through crop-to-weed hybridization
●This could result in “superweeds” that would be resistant to many herbicides ●Efforts are underway to prevent this by introducing ●Male sterility ●Apomixis ●Transgenes into chloroplast DNA (not transferred by pollen) ●Strict self-pollination |
