Unit 7.2

• Soil & Nutrition


  • Water and carbon dioxide are critical components of plant nutrition
  • Other essential nutrients must be taken up by the plants roots
  • Minerals: Inorganic substance with 2 or more elements

  
• Essential nutrients


  Have 1) an identifiable role in the plant, 2) cannot be replaced by another nutrient, and 3) a deficiency causes death

  
• Essential nutrients


  • Macronutrients
  • Micronutrients
  • Required for growth, enhance growth of plant
• Beneficial nutrients


  Required for growth, or enhance growth of a particular plant

  
• Hydroponics


  • Main method of determining essential nutrients
  • Grow in presence and absence of each mineral
  • Most effective for Macronutrients

  
• Soil


  Mixture of mineral particles, decaying organic matter, living organisms, air, and water

  
• Soil particles


  • Sand - Largest, most open space and drainage
  • Silt - Intermediate size and drainage
  • Clay - Smallest particles, hold water with little room for air
• Humus


  • Decaying organic matter that mixes with top layer of soil, increases benefits
  • Plants do well in soil containing minimum 10—20% humus
• Living organisms in soil


  • Large plants break soil and make room for small plants
  • Animals (toads, snakes, moles, worms, ants, etc.) mix soil as they dig and loosen layers
  • Microorganisms (bacteria, fungi, protozoans) responsible for final decomposition
• Water and mineral uptake


  • Water enters root hairs when the osmotic pressure in the root is lower than found in the soil (osmosis)
  • Minerals can be taken in at much higher concentration than found in soil by use of pumps to move ions

  
• Rhizobium bacteria


  Can live in root nodules on plants, and break down nitrogen. Receive carbohydrates from plant in return
• Mycorrhizae


  • Mutualistic between plant roots and fungus
  • Increase surface area of root system for plants, and break down organic matter in soil, freeing up nutrients for plant
  • Root provides sugars and amino acids for fungus
• Xylem


  Transports water and minerals
• Phloem


  Transports organic materials
• Pressure potential


  • The effect that pressure has on water potential
  • Water moves across a membrane from the area of higher pressure to the area of lower pressure
  • The higher the water pressure, the higher the water potential
  • Pressure potential that increases due to osmosis is called turgor pressure

  
• Osmotic potential


  • Takes into account the presence of solutes
  • Water tends to move from the area of lower solute concentration to the area of higher solute concentration
  • The lower the concentration of solutes (osmotic potential), the higher the water potential

  
• Water transport


  1. Xylem vessels form an open pipeline

  2. Water entering roots creates a positive pressure (root pressure)

  3. Water forced out vein endings along edges of leaves
• Cohesion-tension model of xylem transport


  • Cohesion is the tendency of water molecules to cling together
  • Adhesion is the ability of the polar water molecules to interact with molecules of vessel walls
  • A continuous water column moves passively upward due to transpiration
• Transpiration


  1. Causes water loss through stomata

  2. Water molecules that evaporate are replaced by water molecules from leaf veins

  3. Due to cohesion, transpiration exerts a pulling force (tension) drawing water through the xylem to the leaf cells

  4. Waxy cuticle prevents water loss when stomata are closed
• Opening and closing of stomata


  1. Increased turgor pressure in guard cells opens stoma

  2. Active transport of K+ into guard cells causes water to enter by osmosis and stomata to open

  3. H+ ions accumulate outside guard cells as K+ moves in

  4. Opening and closing of stomata is regulated by light

  5. ABA (abscisic acid) can also cause stomata to close
• Phloem


  • Transports sugar
  • Phloem sap doesn't only move upward or downward as xylem does
  • Travels from source (sugar's origin) to sink (sugars are unloaded)
• Pressure-Flow Model of Phloem Transport

  1. Sieve tubes form a continuous pathway for organic nutrient transport

  2. Sucrose is actively transported into phloem at the leaves

  3. Water follows by osmosis, creating positive pressure

  4. The increase in pressure causes flow that moves water and sucrose from the source to the sink (From leaves down to roots for storage)