Exam 2 Notes: Set 3
Exam 2 Notes: Set 3 Bio 1144
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This 6 page Class Notes was uploaded by Murry on Thursday February 11, 2016. The Class Notes belongs to Bio 1144 at Mississippi State University taught by Thomas Holder in Spring 2015. Since its upload, it has received 22 views. For similar materials see Biology II in Biology at Mississippi State University.
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Date Created: 02/11/16
Exam 2 Notes: Set 3 Regulation of Plant Growth o 5 Hormone Types: 1. Auxins • 1 group of hormones that scientists isolated • Produced in shoot tips, leaves, fruits, and seeds (never isolated in roots) • Growth promoting hormones • Requires ATP to move through phloem • Effects: o Promotes cell elongation o Promotes stem elongation o Promotes stem expansion o Promotes development of fruit o Inhibits bud development (auxins promote growth for only 1 season) o Inhibits the abscission (falling off) of leaves, flowers, and fruits 2. Cytokininsst • 1 isolated in coconut milk • Growth promoters • Produced in seeds, fruits, and roots • Effects: o Promotes mitosis and cytokinesis o Promotes development of buds o Inhibits leave senescence (loss & break down of chlorophyll) 3. Gibberellins • Gibberellic Acids • Growth promoting • Found throughout plant, but produced primarily in seeds • Effects: o Promotes stem elongation by cell elongation o Promotes cell division o To promote breakdown of food reserves in germinating seeds § Seed coat on outside § Inside of seed mainly stored food (starch) § Embryotic plant lives down in the corner § Aleurone layer – outermost portion of food material o Food Breakdown Steps: § Intake of water and causing swelling and cracking of seed coats § Embryotic plant secretes Gibberellins § Gibberellins transported to Aleurone layer § Aleurone layer secretes enzyme (alpha-amylase) that breaks down bonds of starch molecules § Starch à glucose à yields ATP through cellular respiration à ATP used for plant growth o Embryo directs process; takes its cues from water intake; makes seed plants have survival advantage 4. Abscisic Acid • Growth inhibitor • Found in mature leaves, dormant buds, and seeds • Effects: o Inhibits cell elongation (This is a good thing because cells can grow too fast and make the cell wall weak.) o Inhibits alpha-amylase secretion by the Aleurone layer o Promotes production of storage compounds in seeds to prevent early germination o Promotes leaf senescence (changing color) 5. Ethylene • Growth inhibitor • Probably not a real hormone, but a plant growth regulator; it is not transported through the plant • It is a gas that is released from the plant • Effects: o Interacts with 3 growth promoting hormones to regulate cell size and shape o Promotes abscission of (the dropping off of) leaves, fruits, and flowers o Promotes fruits ripening • Growth from seed requires breaking of dormancy o This requires a combo of internal and external factors o Internal § Hormones § Stored food § Absorption of water § Embryo swelling o External § Sunlight § Temperature § Longer day length § Soil moisture o Seed contains: seed coat(s), embryo, stored food o As seed coats crack: § Radicle (1 root) – grows down § Shoot (stem and leaves) – grows up § Cotyledons – “embryonic leaves” emerge • Monocots have 1 • Dicots of 2 • Seedling Plant o Result of mitosis and cytokinesis (cell reproduction) o Increase in cell size o Internal Development: § Plant cells à plant tissue à plant organs à § Tissue – an aggregation of functionally similar cells § Organ – 3 organs in a plant: root, stem, leaf § Organism – 3 organs make up the plant Plant Nutrition • Essential Elements (nutrients) required: (16 total) o C, H, and O (obtained from carbon dioxide and water) o 13 soil nutrients § Absorbed as dissolved particles in water taken up by the roots § Transported through the roots; follows xylem pathway along with water § How much of these nutrients required depends on type of plant § Macronutrients (6) • Require over 1 gram per kg of dry weight of plant • These are all essential • Nitrogen (N) – component of proteins, nucleic acids, code enzymes, and compose chlorophyll • Potassium (K) – an enzyme activator; also involved in opening and closing of leaf’s stomata; ionic balance of cells • Phosphorous (P) – component of nucleic acids, biological energy molecules, coenzymes, and phospholipids • Calcium (Ca) – component of cell walls; regulator of membrane and enzyme activities; involved with membrane permeability • Sulfur (S) – component of some proteins and some coenzymes • Magnesium (Mg) – enzyme activator; component of chlorophyll § Micronutrients (7) • Called “trace” elements/minerals; must be there but not in big quantities à less than 1 gram per kg of dry weight of plant • Molybdenum (Mo) – necessary for nitrogen fixation and absorption • Copper (Cu) – activator or component of many enzymes, esp. those associated with metabolism (photosynthesis) • Zinc (Zn) – activator or component of many enzymes • Manganese (Mn) – activator of enzymes; part of chloroplast membrane; involved with oxygen release from the chloroplast • Chlorine (Cl) – involved with ion balance and oxygen production during photosynthesis • Boron (B) – associated with membrane structure and necessary for nucleic acid synthesis • Iron (Fe) – necessary for chlorophyll production Plant Transport – Movement of Water and Solutes in Plants • Xylem – moves water and nutrients from soil • Phloem – moves food, carbohydrates, and hormones • Importance of Water o Needed for photosynthesis o Provides support for plant organs o Needed for conduction (movement/flowing) o Needed for cell elongation o Nearly all chemical reaction involve water o Average plant cell is 90% water o A solvent for most substances § Solution – a mixture of 2 or more compounds § Solvent – the compound in a solution usually in greatest quantity and usually a liquid § Solute – the compound in a solution of lesser quantity and usually dissolved • Physical Properties of Water o Composed of 2 hydrogen atoms and 1 oxygen atoms o A polar molecule with a neutral charge o Hydrogen bonding – each end bonded to 4 other molecules; provides a tight net o Cohesiveness – molecules stick together tightly o Adhesiveness – sticks to other polar compounds (Ex: cellulose – the major component of the cell wall) o Used as a temperature stabilizer (can cool things and heat things) o A good transport medium (remember: water FLOWS); moves from high concentration to low concentrations o Best biological solvent o Found in all 3 physical forms within the Earth’s temperature range (solid, liquid, gas) • Principles of Water and Molecule Movement o Physical processes: no energy required! o Bulk Flow – the movement of molecules in response to pressure or gravity from high to low o Diffusion – the movement of molecules along a concentration gradient from high to low concentration o Osmosis – diffusion of water across a selectively permeable membrane from high to low concentration o With osmosis, water passed through freely through membrane, but solutes do NOT. o Water Movement (and Soil/Minerals) through Plant: § Transpiration – the loss of water exiting through stomata of the leaves in vapor form; the “cost” that land plants pay (Ex: each corn plant requires about 55 gallons of water; of that water 2% is normal maintenance like photosynthesis, elongation, growth, etc. The other 98% is lost or transpired like sweating.) § Transpiration required for water to move through plant § Leaf: organ that conducts photosynthesis and transpiration § Openings in lower epidermis of leaf are stomata. Stomata regulated by pair of guard cells. Important because carbon dioxide is needed for photosynthesis and fuses into through stoma. Oxygen and water vapor filters through then exits through stoma. § Guard Cells are special types of epidermal cells. They are always in pairs. § Guard cells function to control water loss. Close when water levels are low. Open when the cells are full of water (called Turgid). § Water vapor and oxygen easily diffuse out, and carbon dioxide easily diffuses in. § If guard cells are closed, nothing can get or out. So it’s better for guard cells to be open. § Daytime/Sunlight – carbon dioxide levels low in leaf § Guard cells pump in potassium, which decreases the water concentration. § Water from nearby xylem moves by osmosis into guard cells – turgid § Guard cells swell and stoma will open § Pump out potassium, water moves out, and the guard cells shrink and close. o Causes of Water Loss: § Ultimately, sunlight heating up the leaf causes water to evaporate § This causes lower water concentrations in the mesophyll cells. § Emptying mesophyll cells cause a pull, and the water in the stem xylem is pulled into the mesophyll. The emptying stem xylem then pulls more water from the root xylem. Roots pull water (and nutrients dissolved in water) from the soil. § This process is called the Transpiration Stream – the pathway of transpiration (described above); stream only runs one way, up through the plant o C.A.T. Mechanism: § Once stomata open, the process is purely physical (no ATP): • Pulling of water molecules one molecule at a time o Cohesion – water molecules together o Adhesion – water sticks to cellulose in the plant cell wall; water doesn’t slide back down o Tension – pull due to water loss by evaporation from mesophyll § No energy is expended because there is a change in water concentration all the way down § Energy (in the form of sunlight) is needed to cause evaporation o Translocation – movement of solutes (food and hormones) § Similarities between Translocation and Transpiration: • Physical properties that require water § Differences: • Translocation o Bidirectional (can move up or down) o Phloem o Moves solutes o Must use ATP energy from the plant • Transpiration o Unidirectional: Only moves in one direction o Xylem o Moves water/minerals o Only uses sunlight energy; none from the plant § Food is dissolved in water and moved in the form of sucrose (unrefined sugar) § Food (carbohydrate) will always move from source to sink • Source – sight of excess carbohydrate • Sink – the storage sight or sight where sugar is quickly needed • Ex: plant is producing flowers, and sugar from the root moves to the flowers. Source and initial sink = root storage. Sink = flowers. § Pressure Flow Hypothesis: • Phloem Tissue consists of sieve tube members and companion cells which load and unload the STMs (requires ATP) § At Source: companion cells pump sucrose into STMs (requires ATP) § As sucrose concentration increases, water concentration decreases as well as pressure § Adjacent xylem has higher water concentration, so water moves in through osmosis to increase pressure § Bulk flow of sucrose moves from higher pressure to lower pressure § At Sink: companion cells unload sucrose (requires ATP) § Sucrose converted to starch for storage in the root cortex § Without sucrose, water potential changes, higher water potential in STM § Water moves from STM to adjacent xylem by osmosis § ATP spent only by cells at source and sink § Bulk flow and osmosis requires no energy Transpiration Stream Transpiration
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