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Chapter 40

Chapter 40 Detailed Notes

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Tristan Long

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Chapter 40: Plant and Animal Nutrition  By weight, tissues of most plants are >90% water  Most of plant’s nutrition comes from photosynthesis  Smaller amounts of other nutrients come from soil or water  Essential elements (17 in plants)  Necessary for growth/reproduction  Cannot be substituted  One or more roles in metabolism 40.1a Hydroponics Is ANew Way to Study Plant Nutrition • Hydroponics o Experimental method for identifying minerals absorbed into plant tissues that were essential for growth o Julius Von Sachs measured amounts of compounds containing specific minerals and mixed them in different combinations with pure water. He then grew plants and studied their growth after eliminating one element at a time  Sachs developed a list of 6 essential plant nutrients (descending order of amount): nitrogen, potassium, calcium, magnesium, phosphorus, sulfur o In a hydroponic apparatus, many plants are grown in a single solution containing pure water and a defined mix of mineral nutrients o In absence of sufficient oxygen for respiration, plant’s roots do not absorb nutrients efficiently (same thing for poorly aerated soil) 20.1c Essential Macro- and Micronutrients for Plants • Hydroponics revealed plants need 17 essential elements • Essential element: one that is necessary for normal growth and reproduction and cannot be replaced by another element • 9 of elements are macronutrients because plants incorporate large amounts of them in tissues o Carbon, hydrogen, oxygen make up 96%  Not considered minerals  Obtained from air and water whereas others are from soil  With addition of nitrogen, they are basic building blocks of proteins and amino acids and stomata control o Others are calcium, sulfur, and magnesium • Micronutrients are mineral elements required in trace amounts, but they are vital to survival o Hard to exlude chlorine o May be enough seeds for multiple generations (Ni) o Some are specific to plant types • Vital in plant metabolism, starch synthesis, protein synthesis, photosynthesis, aerobic respiration Root Systems Extensive root systems are adaptations to limited mineral nutrients  Make up 20-50% of total plant mass  Roots grow as long as plant lives Roots have mechanisms to increase uptake  Root hairs (large SA:V ratio)  Membrane transporters  Mycorrhizae: Symbiotic Associations between fungus and roots of plant (phosphorous) Soil  Soil-mineral particles, compounds, ions, decomposing organics, water, air, organisms  Sand, silt, and clay particles  Humus: Decomposing organics (-ive charge)  Relative amount of soil particles determine soil properties  As soils develop, tend to take on characteristic vertical profile, with series of layers or horizons with distinct texture and composition Soil Horizons 0 horizon: surface material Ahorizon  Topsoil has most biological activity and usually most fertile, most roots B horizon  Subsoil accumulates nutrients, woody roots C horizon  Parent material, no organic material, partially weathered fragments and grains of rock Soil in Deciduous and Rainforests Soil in Coniferous Forests Soil in Grasslands Desert Soils Soil Solution Nitrogen Limitations Nitrogen (N)  Abundant element in air, most limiting to plant  Triple bond requires specific enzyme  Nitrogen cycle provides soil nitrogen Nitrogen fixation incorporates atmospheric N into plant-available compounds 2  Nitrogen-fixing bacteria Nitrogen Cycling  Bacterial ammonification breaks organic N compounds into NH (ammonium) 4+ + -  Plants take up NH , 4ut “prefer” NO 3  Bacterial nitrification oxidizes NH to 4O (nitrat3)  High rates of nitrification, except in acidic soils  Plants convert NO to 3H to ass4milate N into organic compounds Nitrogen Fixation  Most N is fixed by plant symbioses with bacteria  Plant+provides organic molecules for respiration energy, bacteria provide NH 4  Legumes form root nodules with Rhizobium or Bradyrhizobium  Bacterial nod genes expressed with flavenoid signal from plant  Infection thread allows bacterial invasion  Bacteroids enclosed in nodule (leghemoglobin and nitrogenase) Root Nodule Formation 40.1d Consequences of Nutrient Deficiencies for Plants • Lettuce and other leafy plants need more N and Mg • Stunted growth, abnormal leaf colour, dead spots on leaves, abnormally formed stems, fewer chloroplasts • Different plants have different needs for (or toxicity to) elements o Soil determines where and how well plants grow • Nutrient deficiencies have symptoms with clues to metabolic function o Stunted growth, leaf color, dead spots, abnormal stems, chlorosis 40.1e Essential Elements for Animals • Fuel o Carbs and fats are primary • Building blocks o Organic molecules serve as building blocks for carbs, lipids, proteins, nucleic acids o Protein synthesis cannot happen without 20 amino acids present • Vitamins and coenzymes o Vitamins: organic molecules required in small quantities o Coenzymes, non protein that assist in enzymatic catalysis 40.1f Essential Elements for Humans • Humans need 8 essential amino acids: lysine, tryptophan, phenylalanine, threonine, valine, methionine, leucine, isoleucine o Infants and young also need histidine • Vitamins fall into 2 classes: o Water-soluble  Any excess vitamins leave in urine o Fat-soluble  Body stores these as fat 40.2a Soil Components and Particle Sizes Determine Properties of Soil • Relative proportions of different sizes of mineral particles help determine the number and volume of pores – air spaces – soil contains • Soil that is sticky when wet is mostly clay • Mineral particles are intermixed with various organic components including humus (decomposing parts of plants and animals, animal droppings, and other organic matter) o Hummus can absorb a great deal of
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