Life103, Week 7 Notes
Life103, Week 7 Notes Life 103
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This 8 page Class Notes was uploaded by Addy Carroll on Friday March 4, 2016. The Class Notes belongs to Life 103 at Colorado State University taught by Dr. Dale Lockwood and Dr. Tanya Dewey in Winter 2016. Since its upload, it has received 23 views. For similar materials see Biology of organisms-animals and plants in Biology at Colorado State University.
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Date Created: 03/04/16
Life 103 Notes *Adapted from the lecture slides of Dr. Dale Lockwood* Water and Sugar ctn. (see week 6 notes) • Diffusion of water ctn. -Turgid-cell membrane pushed against the cell wall (see textbook figure 36.7b) ~When plants are plasmolyzed instead of turgid, that means they aren’t getting enough water and, as the cell membrane pulls away from the cell wall, the cell starts to wither and shrink -Aka plant is dying because of lack of water ~Permanent wilting point-when a plant is so wilted that no amount of water can bring it back to life -Aquaporins are transport proteins in the cell membrane that allow the passage of water ~Restricts the flow of solutes, only allows water ~The rate of water movement is likely regulated by phosphorylation of aquaporin proteins ~Aquaporins exist in plants and animals • Transport Control -Transport is also regulated by the compartmental structure of plant cells -The plasma membrane directly controls the traffic of molecules into and out of the protoplast ~In other words, the plasma membrane blocks certain things but allows other things to diffuse -The plasma membrane is a barrier between two major compartments, the cell wall and cytosol -The third major compartment in most mature plants cells is the vacuole, a large organelle that occupies as much as 90% or more of the protoplast’s volume -The vacuolar membrane regulates transport between the cytosol and the vacuole • Cellular structures necessary for transportation -In most plant tissues, the cell wall and cytosol are continuous from cell to cell -The cytoplasmic continuum is called the symplast -The cytoplasm of neighboring cells is connected by channels called plasmodesmata ~Holes that go through the cell wall to connect cells to allow desirable substances to pass through from cell to cell -The apoplast is the continuum of cell walls and extracellular spaces • Water and minerals can travel through a plant by three routes -Symplastic route: via the continuum of cytosol -Apoplastic route: via the cell walls and extracellular spaces -Transmembrane route: out of one cell, across a cell wall, and into another cell • Bulk Flow in Long-Distance Transport -Efficient long distance transport of fluid requires bulk flow, the movement of a fluid driven by pressure -Water and solutes move together through tracheids and vessel elements of xylem, and sieve-tube elements of phloem -Efficient movement is possible because mature tracheids and vessel elements have no cytoplasm, and sieve-tube elements have few organelles in their cytoplasm • Absorption of Water and Minerals by Root Cells (see textbook figure 36.8) -Most water and mineral absorption occurs near root tips, where the epidermis is permeable to water and root hairs are located -Root hairs account for much of the surface area of roots -After soil solution enters the rots, the extensive surface area of cortical cell membranes enhances uptake of water and selected minerals • Transport of Water and Minerals into the Xylem (see textbook figure 36.10) -Water can cross the cortex via the symplast of apoplast -Endodermis ~The innermost layer of cells in the root cortex ~It surrounds the vascular cylinder and is the last checkpoint for selective passage of minerals from the cortex into the vascular tissue -The waxy Casparian strip of the endodermal wall blocks apoplastic transfer of minerals from the cortex to the vascular cylinder • Bulk Flow Driven by Negative Pressure in the Xylem (see textbook figure 36.11) -Transpiration ~The evaporation of water from a plant’s surface -Xylem sap ~Bulk flow of water and minerals replacing water lost ~From the steles of roots to the stems and leaves -At night, when transpiration is very low, root cells continue pumping mineral ions into the xylem of the vascular cylinder, lowering the water potential -This causes water flow in from the root cortex, generating root pressure -The root pressure is greater in the roots than the leaves -Root pressure sometimes results in guttation, the exudation of water droplets on tips or edges of leaves (see textbook figure 36.9) -Positive root pressure is relatively weak and is a minor mechanism of xylem bulk flow ~Therefore, there’s some push up from the roots, but mostly pull up by the leaves • Transpiration-Cohesion Theory -Transpiration produces negative pressure (tension) in the leaf, which exerts a pulling force on water in the xylem, pulling water into the leaf -Transpirational pull is facilitated by cohesion of water molecules to each other and adhesion of water molecules to cell walls • Stomata (see textbook figures 36.12 and 36.13) -Account for 95% of water loss -Three cues signal stomatal opening ~Light simulates the uptake of K in guard cells ~Depletion of CO 2ithin the leaf ~Internal clock -Circcadian rhythm -Plants kept in the dark continue to open stomata on a 24 cycle -Water stress is the major cue for closing during the day • Desert Adaptations (see textbook figure 36.14) -Xerophytes-plants adapted to low water conditions ~Reduced leaves ~Crassulacean Acid Metabolism (CAM) • CAM -Stomata open at night -CO 2tored as malate -Released during the day to the Calvin cycle allowing the stomata to be closed during the day -Ferns, gymnosperms, and monocots all have species that use CAM -Most of the CAM species are angiosperms • Movement of Sugar Sources to Sugar Sinks -Phloem sap is an aqueous solution that is high in sucrose -It travels from a sugar source to a sugar sink -A sugar source is an organ that is a net producer of sugar, such as mature leaves -A sugar sink is an organ that is a net consumer or storer of sugar, such as a tuber or bulb -A storage organ can be both a sugar sink in summer and a sugar source in winter -Sugar must be loaded into sieve-tube elements before being exposed to sinks -Depending on the species, sugar may move by symplastic or both symplastic and apoplastic pathways -Transfer cells are modified companion cells that enhance solute movement between the apoplast and symplast • Phloem (see textbook figure 36.15) -Some plants have a form of electrical signaling through the phloem -Moves macromolecules and some types of RNA via plasmodesmata ~Movement of proteins and RNA unique to plants Soil and Plant Nutrition • Dirt is the inorganic, nonliving part of underground, while soil is much more complex, as it involves everything, living and nonliving, belowground • Soil Ecosystems -Fragile Ecosystem ~There are many distinctly different layers of soil as you dig straight down ~Upper layers provide nutrients and water to plants ~Many organisms live in and create the structure of soil -Examples: Plants, bacteria, insects, fungi, nematodes • Soil Composition -Soil Stratification ~Layers known as horizons ~Upper layer is topsoil -Soil particles differentiated by size, smallest to largest: ~Clay-smallest particles; too close together and holds too much water ~Silt-more gaps in particles than clay; better for holding the right amount of water ~Sand-big spaces between particles; not good for retaining water -Topsoil consists of mineral particles, living organisms, and decaying organic material, humus • Soil Horizons (see textbook figure 37.2) -Loams are soils that support highly productive plant growth, composed of roughly equal parts sand, silt, and clay ~A horizon-Topsoil: broken rock of differing sizes and textures, living organisms and decaying organic matter ~B horizon-Less weathered rock and less organic material ~C horizon-Partially broken rock, parent material for upper layers • Inorganic Components + 2+ 2+ -Cations (positive ions, for example, K , Ca , Mg ) adhere to negatively charged soil particles; this prevents them from leaching out of the soil as water flows through ~Leaching occurs when a substance is removed from soil due to liquid passing through ~Negatives don’t attract negatives, so the harmful anions are leached out of the soil so the plants can live ~Example: Acid rain is positively charged, and, when it enters the soil, it depletes it of all the necessary cations, which is why the plants die -During cation exchange, cations are displaced from soil particles by other cations (see textbook figure 37.3) -Displaced cations enter the soil solution and can be taken up by plant roots -Negatively charged ions do not bind with soil particles and can be lost from the soil by leaching from percolating groundwater • Soil Conservation -Agriculture impacts soil ~Depletes nutrients-when a plant is growing, it takes up nutrients from the soil that are then completely removed during harvest ~Increases erosion-the soil is disturbed during planting and harvesting, which causes erosion ~Taxes water resources ~Soil compaction- during planting, the soil is purposefully compacted somewhat, and the result of this is more water runoff because the compacted soil can’t hold as much water, and the runoff causes erosion • Agriculture and Water -Irrigation is a huge drain on water resources when used for farming in arid regions -Usable fresh water is either from surface water (lakes and streams) or ground water (aquifers) -The depleting of aquifers can result in subsidence, the settling or sinking of land -Irrigation can lead to salinization, the concentration of salts in soil as water evaporates ~The water evaporates, leaving the salt particles behind, as they don’t also evaporate ~When this happens, the soil is no longer useful ~This process is irreversible -Drip irrigation requires less water and reduces salinization ~Requires less water input, which consequently reduces salinization • Fertilization -Soils can become depleted of nutrients as plants and the nutrients they contain are harvested -Fertilization replaces mineral nutrients that have been lost from the soil -Commercial fertilizers are enriched in nitrogen, phosphorus, and potassium -Organic fertilizers are composed of manure, fishmeal, or compost -Crop rotations with legumes or other plants that have close associate with nitrogen fixers ~Legumes put necessary nutrients back in the soil because they produce more than they actually need, so crops planted in following years don’t require as much fertilizer -Letting fields go fallow for a season ~Not intentionally planting anything, but letting weeds and cover crops grow, and letting natural biological processes replenish the soil • Modern Agriculture and Soil -Large monoculture farms with high fertilizers have bacteria dominated soil food webs -Natural systems and organic farms have fungal based soil food webs • Controlling Erosion -Topsoil from thousands of acres of farmland is lost to water and wind erosion each year in the United States -Erosion of soil causes loss of nutrients -Erosion can be reduced by: ~Planting trees as windbreaks; it’s harder for the wind to disturb the soil ~Terracing hillside crops ~Cultivating in a contour pattern (see textbook figure 37.6) ~Practicing no-till agriculture; this is where you don’t disturb the soil as much by turning it over before planting, thereby decreasing erosion • Nutrients (see textbook table 37.1) -A chemical element is considered an essential element if it is required for a plant to complete its life cycle ~This is where the organism doesn’t make the nutrient itself, but have to ingest from an outside source ~Example in humans: vitamin C is essential because we can only get it through food, while vitamin D is nonessential because we make it ourselves when given access to sunlight -Nine of the essential elements are called macronutrients because plants require them in relatively large amounts ~The macronutrients are carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, potassium, calcium, and magnesium -The remaining eight are called micronutrients because plants need them in very small amounts ~The micronutrients are chlorine, iron, manganese, boron, zinc, copper, nickel, and molybdenum • Soil Bacteria and Plant Nutrition -Rhizosphere ~The layer of soil bound to the plant’s roots ~The rhizosphere has high microbial activity because of sugars, amino acids, and organic acids secreted by roots -Rhizobacteria ~Free living -Not attached to or dependent on another organism ~Function in the rhizosphere ~Can enter roots • Rhizobacteria -Rhizobacteria can play several roles ~Produce hormones that stimulate plant growth ~Produce antibiotics that protect roots from disease ~Absorb toxic metals ~Make nutrients more available to roots -Inoculation of seeds with rhizobacteria can increase crop yields ~Because much of agricultural soil is composed of bacteria, adding yet more to seeds would consequently benefit growth • Bacteria in the Nitrogen Cycle (see textbook figure 37.10) -Nitrogen can be an important limiting nutrient for plant growth -The nitrogen cycle transforms nitrogen and nitrogen-containing compounds ~Without this transformation, nitrogen would be inert and not useful/not accessible to plants -Most soil nitrogen comes from actions of soil bacteria -Plants absorb nitrogen as either NO (ni3rate) or NH 4+ (ammonium) -Bacteria break down organic compounds or use N to produce NH + 2 3 (ammonia), which is converted to NH 4 - -Nitrification is carried out by bacteria that convert NH i3to NO 3 • Nitrogen-Fixing Bacteria -N is abundant in the atmosphere, but unavailable to plants 2 -Nitrogen fixation is the conversion of nitrogen from N to 2H 3 -Symbiotic relationships with nitrogen-fixing bacteria provide some plant species with a built-in source of fixed nitrogen -Key symbioses occur between nitrogen-fixing bacteria and plants, including those in the legume family (peas, beans, and other similar plants) -Along a legume’s roots are swellings called nodules, composed of plant cells “infected” by nitrogen-fixing Rhizobium bacteria (see textbook figure 37.11 and 37.12) -Inside the root nodule, Rhizobium bacteria assume a form called bacteroids, which are contained within vesicles formed by the root cell -The bacteria of a root nodule obtain sugar from the plant and supply the plant with fixed nitrogen ~Mutualistic relationship Plant Reproduction and Biotechnology (see textbook figures 38.2, 38.4, 38.7) • Pollination (see textbook figures 38.5, 38.12) -In angiosperms, pollination is the transfer of pollen from an anther to a stigma -Pollination can be by wind, water, bee, moth, butterfly, cricket, beetle, wasp, ant, fly, bird, or bat • Plant sexuality -Many angiosperm species reproduce both asexually and sexually -Sexual reproduction results in offspring that are genetically different from their parents -Asexual reproduction can result in a clone of genetically identical organisms • Mechanisms of Asexual Reproduction -Fragmentation, separation of a parent plant into parts that develop into whole plants, is a very common type of asexual reproduction ~If you remove part of a parent plant and then just replant it, then it will grow into a whole new plant -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 or haploid cell -Multiple forms of apomixis ~Nonrecurrent apomixis occurs when the haploid gametophyte gives rise to a haploid individual ~Recurrent apomixis occurs when meiosis is not completed ~Adventive embryony occurs when the embryo arises from the integument or other sporophyte cells ~Vegetative apomixis occurs when the flow is replaced by a bulbil ~Pollen apomixis is when the male pollen grains give rise to seeds without any female interaction • Advantages and Disadvantages of Asexual Versus Sexual Reproduction -Asexual reproduction is also called vegetative reproduction -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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