Plants 2

• Essential plant nutrients

  • Nitrogen
  • Potassium
  • Calcium
  • Magnesium
  • Phosphorus
  • Sulfur
• Essential element


  Necessary for normal growth and reproduction, cannot be functionally replaced by a different element, and has one or more roles in plant metabolism
• Macronutrients

  • Carbon
  • Hydrogen
  • Oxygen
  • Nitrogen
  • Phosphorus
  • Potassium
  • Calcium
  • Sulfur
  • Magnesium
• Micronutrients

  • Copper
  • Chlorine
  • Nickel
  • Iron
  • Boron
  • Manganese
  • Zinc
  • Molybdenum
• Nutrient deficiency


  Plants develop characteristic symptoms such as stunted growth, abnormal leaf color, dead spots, or abnormal stems
• Iron deficiency


  Causes chlorosis, a yellowing that results from a lack of chlorophyll
• Magnesium deficiency


  Causes pale color and stunted growth
• Nitrogen deficiency


  Causes chlorosis in older leaves first
• Soils are more likely to be deficient in nitrogen, phosphorus, potassium, or some other essential mineral than have too much of them
• Farmers and gardener have added nutrients in the form of fertilizers to suit the types of plants they wish to cultivate
• Fertilizer numerical shorthand


  Indicates the percentages of nitrogen, phosphorus, and potassium they contain
• Soil anchors plant roots and is the main source of inorganic nutrients
• Soil

  • Develops due to the weathering of rock and inorganic particles in Earth's crust
  • Is the source of water for most plants, and of oxygen for respiration in root cells
• Inorganic soil components

  • Mineral particles
  • Chemical compounds
  • Ions
  • Decomposing organic matter
  • Air
  • Water
  • Assorted living organisms
• Soil texture


  Determined by the relative proportions of sand, silt, and clay
• Clay soils


  Have few pores
• Sandy soils


  Have more pores
• Organic soil components


  Include humus, which is decomposing parts of plants and animals, animal droppings, and other organic matter. It has a loose texture and retains water well, and is a reservoir of nutrients like nitrogen, phosphorus, and sulfur.
• Soil contains bacteria, fungi, nematodes, and other worms and insects that decompose dead plant parts and other organic matter, and earthworms aerate the soil
• Soil horizons

  • O horizon: top layer of surface litter
  • A horizon: Topsoil - humus mixed with mineral particles where roots of most herbaceous plants are located
  • B horizon: Subsoil - larger particles, little organic matter, accumulates mineral ions, contains roots of mature trees
  • C horizon: layer of mineral particles and rock fragments that extends down to bedrock
• Soil solution

  Water and dissolved substances that coat soil particles and fill pore spaces
• Water availability in soil

  Depends on soil composition - sandy soil drains rapidly, humus-rich soil holds water, clay holds water tightly
• Water potential

  Differences in water potential govern the osmotic movement of water through root hairs into plant roots
• Mineral availability in soil

  Cations are reversibly bound by net negative charges on the surfaces of soil particles, while anions move freely into root hairs
• Soil pH

  Affects the availability of some mineral ions - heavy rainfall makes soil acidic, arid regions make soil alkaline
• Minerals, carbon, and other nutrients are returned to the soil by the decomposition of organisms and their wastes
• Nitrogen and phosphorus also enter soil in agricultural chemicals (fertilizers)
• Root adaptations for obtaining and absorbing nutrients

  • Root hairs and ion-specific transport proteins
  • Root secretions that improve access to particular nutrients
• Mycorrhizae


  Symbiotic associations between a fungus and the roots of a plant that promote the uptake of water and ions (especially phosphate)
• Ectomycorrhizae


  Mycorrhizae in which hyphae pass through the walls of cells in the root cortex, commonly forming treelike arbuscules
• Lack of nitrogen is the single most common limit to plant growth

  
• Nitrogen fixation


  The incorporation of atmospheric nitrogen into compounds that plants can take up, carried out by nitrogen-fixing bacteria

  
• Nitrogen cycle


  1. Ammonification

  2. Nitrification

  3. Nitrogen assimilation

  4. Denitrification

  
• Plant-bacteria associations


  Host plants supply bacteria with organic molecules for cellular respiration, and the bacteria supplies the plant with ammonium used to produce proteins and other nitrogen molecules
• Rhizobium and Bradyrhizobium


  Nitrogen-fixing bacteria that reside in root nodules of legumes, reducing nitrogen to ammonium using ATP from their own cellular respiration

  
• Flowering plant reproduction


  • Early development makes an embryo sporophyte enclosed within a seed
  • Some vegetative shoots change and become reproductive floral shoots
  • Floral shoots give rise to flowers that contain cells that divide by meiosis to produce haploid spores
  • Each spore divides by mitosis and grows into a multicellular haploid gametophyte
  • Male and female gametophytes make haploid sperm and eggs (haploid gametes) by mitosis
  • Division of life cycle into diploid, spore-producing generation and haploid, gamete-producing generation is called alternation of generations

  
• Formation of flowers and gametes

  1. Floral shoot (receptacle) develops into a flower with 4 concentric tissue regions (whorls)

  2. 2 outer, vegetative whorls (calyx and corolla)

  3. 2 inner, gamete-producing whorls (stamens and carpel)

  4. Flowers with all 4 whorls are complete flowers

  5. Flowers that lack 1 or more whorls are incomplete flowers
• Trends in changes of flowers over evolution

  • Reduction in the number of floral parts
  • Fusion of floral parts
  • Embedding the ovary deep in the receptacle
  • Shift from radial to bilateral flower symmetry
• Pollen production


  1. Spores that give rise to male gametophytes are produced in a flower bud's anthers

  2. Pollen sacs in anthers hold diploid microsporocytes (sperm microspore mother cells), which undergo meiosis

  3. Each microspore divides by mitosis to form an immature, haploid male gametophyte (pollen grains) with 2 nuclei

  4. One of the 2 nuclei divide again, producing 2 sperm cells and a 3rd that controls development of a pollen tube

  5. When pollen lands on a stigma, the pollen tube grows through carpel tissue and carries the sperm cells to the ovary

  6. A mature male gametophyte is made of the pollen tube and sperm cells (male gametes)

  7. The walls of pollen grains (hardened by sporopollenin) are distinctive of the family to which a plant belongs

  
• Egg production


  1. 1 or more ovules form on the inner wall of the ovary

  2. A diploid megasporocyte (egg megaspore mother cell) divides by meiosis, forming 3 haploid megaspores

  3. 3 megaspores disintegrate and 1 enlarges and develops into the female gametophyte in a sequence of steps

  4. 3 rounds of mitosis occur without cytoplasmic division, resulting in a single cell with 8 nuclei (2 groups of 4)

  5. A polar nucleus from each group migrates to the center of the cell

  6. The cytoplasm divides and cell walls form, producing 1 large, central endosperm mother cell, 3 antipodal cells, and 3 cells (the "egg apparatus")