Exam # 1 Study Guide Lectures: 1 - 5Lecture 1 (January 14)Introduction to Soil and Plant NutritionWhere do plants get their nutrients? What is their mass made up of?Aristotle suggested that plants are soil eaters. However, after the Van Helmot experiment of measuring the amount of soil change over a plants’ life, it was concluded that plants get their nutrients elsewhere. Plants obtain inorganic materials from the air and soil and synthesize organic matter from these inorganic precursors.Most of a plant’s mass is water. Excluding the water, 96% of a plant’s dry mass is derived from CO2, which is assimilated into carbohydrates during photosynthesis. The other 4% of dry mass is comprised of inorganic substances in the soil (ions).Lecture 2 (January 16) Overview of Essential Elements, Nutritional Deficiencies, and Soil PropertiesWhat are the essential elements? What are macronutrients and micronutrients? What are the symptoms of a nutritional deficiency? What are the ideal properties of soil?An essential Element is a chemical element that is required for a plant to complete its life cycle and produce another generation. To determine if an element is essential for plant growth, scientists grow a plant using hydroponics with and without the element.Macronutrients are nutrients that plants need in large quantities. Nitrogen, phosphorous, and potassium are the three elements that farmers and gardeners supplement to soil because plantsneed them in large quantities to grow efficiently. Nitrogen is a building block of amino acids, proteins, nucleic acids, hormones, and coenzymes. Potassium is a major solute of water valves, which is important in the stomata of a plant. The other essential elements that are not considered macronutrients and are only needed in small amounts for a plant to survive are the micronutrients. One of the most important micronutrients is iron because of the different heme components that play a role in the electrontransport system of photosynthesis. Micronutrients are rarely limiting to plant growth and function as cofactors in biological reactions.Symptoms of a nutritional deficiency depend of mobility of nutrients. Immobile nutrients refers to nutrients that do not move easily through plants and are more likely to stick around in older tissues where they are being used. Symptoms of an immobile nutrient deficiency will appear in newer tissues that are being produced because they continue to remain in the older tissues. Mobile nutrients are more likely to move from their original source to where they are needed. Symptoms will appear in older tissues because they are needed by the younger, growing tissues.For example, magnesium is a mobile nutrient that is a component of chlorophyll. In a nutrient deficiency situation, the older leaves will appear to be suffering from chlorosis. BIOL 240W 1st EditionSoil properties are very important because a plant, which is stuck in the ground, relies on soil forits nutritional needs. Roots are in the A horizon, or topsoil. It is important that soil not only has available nutrients, but also an ideal texture. A mixture of sand, silt, and clay is called a loam. It contains all three sizes of particles of soil. It is important because there must be enough fine particles that provide surface area for cation exchange, but enough coarse particles in order to allow for water drainage and oxygen spaces.Lecture 3 (January 21) Overview of the Cation Exchange, The Nitrogen Exchange, and Symbiotic Relationships.How does the cation exchange work? Why are anions a problem? Why is the nitrogen cycle important? What are the properties of the symbiotic relationships in plants?Cation exchange is the process of displacing cations/minerals attracted to negative soil particles,allowing them to be taken up by the plant. Plants undergo cellular respiration in their roots: H2O + CO2  H2CO3  HCO3- + H+. During this process, hydrogen ions become available to displace nutrients and exchange places during respiration. The displaced cations enter root hairsby diffusion.Soil pH affects cation exchange and the chemical form of minerals. Plants thrive in acidic soil because more acidic soil allows an abundance of H+ to displace more minerals. However, acid rain makes soil less fertile. In addition, at pH <~5, Aluminum becomes soluble and mobile. The plant can then take up Aluminum, but if these concentrations become too high in the plant, they become toxic.Anions, such as NO3-, SO42-, PO4-, do not have anything to attach onto in the soil. Rain takes theseanions with them. Phosphate is problematic in this case. It is the most limiting rock-derived nutrient and forms highly insoluble aggregates with many substances. The roots cannot take in these insoluble aggregates. Only a limited fraction of phosphate is soluble, and this can be easilylost during rainfall.Nitrogen is also hard to obtain because it is not derived from fragmentation of rocks. Although the atmosphere is mostly N2, it is a very stable as a gas and hard to obtain for plants. Nitrogen is an important component of DNA, RNA, amino acids/proteins, hormones, and coenzymes. During one process of nitrogen fixation, microbes break down organic matter, and ammonifying bacteria take amino acids and create NH4+. This provides a small amount of nitrogen by plant.Nitrogen-fixing bacteria provide most nitrogen. However, two species of bacteria are chemosynthetic autotrophs. They use the NH4+ created during nitrogen fixation and create nitrite, then convert it to nitrate. Unfortunately, nitrate is an anion, and can be leeched from thesoil during rainfall.Another problem with nitrogen fixation is that nitrogen-fixing bacteria use the enzyme nitrogenase, which is very sensitive to oxygen. Oxygen is needed for respiration in order to create the energy to undergo nitrogen fixation, but this inhibits the nitrogenase. To overcomethis, plants formed relationships with Rhizobium. Rhizobium penetrate the root of a plant in order to deal with the oxygen problem. The step-by-step- process is not important to memorize.Overall, it is important to know that nodules are created to overcome the oxygen problem. In addition, leghemoglobin is present to take up oxygen molecules before they inhibit nitrogenase.These nodules create a permeability barrier that regulates oxygen transit. In this relationship, the plant receives NH4+, and Rhizobium receives sugars. Another symbiotic relationship formed with plants is