NUTRITION AND TRANSPORT Chapter 39 AP

Plant Nutrition  9 Macronutrients  Carbon  Oxygen  Hydrogen  Nitrogen  Potassium  Calcium  Magnesium  Phosphorus  Sulfur  7 Micronutrients  Chlorine  Iron  Manganese  Zinc  Boron  Copper  Molybdenum

Soil  Mixture of sand, rocks, clay, silt, humus  Most roots found in topsoil  mixture of minerals, living organisms, and humus (partly decayed organic material)  About half is water spaces or air spaces  Cultivated crops change the soil composition  Must be supplied with necessary nutrients  Farmers employ different practices to maintain fields

Nutritional Adaptations  Carnivorous plants  Obtain nitrogen directly from other organisms  Venus flytrap, sundews, pitcher plants, bladderworts

 Nitrogen-fixing bacteria  Cannot use N 2, need NH 3  Some bacteria live in close association or within cells in plant roots that convert N 2 to NH 3 Nodules  Mycorrhizae  Fungi and plant roots (about 90% of plants have this type of relationship  Increase surface area of roots (phosphorus)

Water Movement  How does water get up a 300 ft tree?  Pushing from pressure of water coming into roots  Cohesion of water molecules pulling up and out through leaves (transpiration)  Negative pressure generated by transpiration responsible for most movement through xylem

Forces acting on water in plant is called potential Turgor pressure, also pressure potential, is “+” Potential can be caused by uneven distribution of solute divided by membranes (water will move to higher concentration of solutes) osmosis can be stopped if solute potential of solute is reached Smallest amount of pressure needed to stop osmosis Generally negative number Water potential is combination of pressure potential and solute potential Total potential energy within a plant Water moves to cells with more negative water potential

 Water potential in roots may be close to zero  Farther up the tree you go the more negative water potential becomes Negative water potential achieved when water exits leaves through transpiration  Osmotic absorption in roots and negative water potential by transpiration = most upward movement of water in xylem

Water & Mineral Absorption  Many ions move into root hairs using energy (ATP)  Ions move through or around cells until they reach the Casparian strip  Water & ions must pass through cell membranes (selective)  At night, transpiration may not occur, but active transport of ions continues  Increases solute potential causing more water to enter roots = root pressure  Because of this water may ooze out of special cells in leaves = guttation

Movement Through Xylem  Air moving across leaf surface = loss of water  Water is pulled from roots because of cohesion  Strength of cohesion inversely related to diameter of tube Smaller tube = greater strength  Water columns fail if air bubbles get in  Water can be redirected in order to maintain continuity of water flow

Transpiration  More than 90% of water taken in is lost through leaves  Photosynthesis requires CO2 to enter from stomata  But this allows water to be lost in the form of vapor  Plants have developed ability to close stomata, have thick cuticle, or are C4 and CAM plants to conserve water

 Opening & closing stomata  Guard cells are thick on inside and thinner on outside This produces a bulging effect when turgid (full)  When guard cells take in K+ water moves into the cell by osmosis  K+ passively leaves, so does water and stomata close

 Factors that regulate transpiration  CO2 concentration If CO2 is high in leaf, stomata close  Light Some plants close stomata during day and open at night (CAM)  Temperature If temps are high, transpiration effects would outweigh photosynthesis effects, thus stomata close

Responses to Flooding  Plants can drown  Standing water has less oxygen than moving water  Flooding depletes oxygen in soil and reduces mineral uptake  Hormonal levels can change  Physical changes to waterlogged roots can halt water movement through plant Stomata close in order to keep cells turgid

 Adaptations for life in water  Aerenchyma—parenchyma cells with large air spaces Oxygen can be transported from tissues above water to tissues below water  Larger lenticels  Adventitious roots  Life in salt water  Need supply of oxygen and control of salt balance Pneumatophores with large lenticels for oxygen Succulent leaves to dilute salt intake At root level Secrete large amounts of salt Block salt uptake

Phloem Transport  Translocation—distribution of sugars made in leaves to the rest of the plant  Through phloem tissue  Also hormones  Mass-flow hypothesis  Source to sink From photosynthetic tissues to wherever needed Storage areas of plants can become sources

 Phloem loading  Carbs enter sieve tubes through veinlets at source Energy required Provided by companion cells Water flows into sieve tubes by osmosis Turgor pressure increases At sink carbs are removed Water moves out of sieve tubes dropping turgor = mass flow from more positive pressure at source to more negative pressure at sink