Ch 13 Flashcards
Macro essential elements
needed in large quantities; calcium, nitrogen, potassium, phosphorus, magnesium and sulfer
Micro essential elements
needed in low quantities; trace; iron, boron, chlorine, copper, manganese, molybdenum and zinc
Criteria for essentiality
1- element must be necessary for complete, normal plant development through a full life cycle; element must be required for plant growth, differentiation, reproduction or survival
2- element must be necessary and have no substitute that is effective or works in the same way
3- element must be acting within the plant not outside it
Chlorosis
common symptom due to mineral deficiency; yellowing of leaves due to lack of chlorophyll
Necrosis
death of patches of tissues because of lack of certain elements or by bacterial, viral and fungal infections
Mobile elements
chlorine, magnesium, nitrogen, phosphorus, potassium and sulfur; can be translocated to younger tissue
Immobile elements
boron, calcium and iron; after they have incorporated into plant tissue they remain in place
Physical weathering
breakdown of rock by physical forces such as wind, water movement and temperature changes; ice is an important agent; produces a variety of sizes of soil particles
Chemical weathering
involves chemical reactions and the most important agents are acids produced by decaying bodies, especially those of plants and fungi; many organisms secrete acids and carbon dioxide combined with water forms carbonic acid; acid dissolves in water dissociates to proton and anion
Course sand
largest soil particles; 2.0 to 0.2 mm
Fine sand
0.2 to 0.02 mm
Silt
0.02 to 0.002 mm
Clay
finest particles; smaller than 0.002 mm technically known as micelles
Field capacity
water that remains in the soil is held by capillary adhesion/ cohesion; much of this water is available to roots
Cation exchange
in soil, the release of an essential element cation from a soil particle and its replacement by a proton
Soil acidity
soil pH, the concentration of free protons in the soil solution is important for cation exchange and the retention of cations in the soil during heavy rain; soil pH affects the chemical form of certain elements causing them to change solubility
Endodermis and selective absorption
elements enter roots by crossing the plasma membrane and selecting elements by the presence or absence of molecular pumps control entry of ions and molecules; or elements enter by diffusing along the cell walls and intercellular spaces
Mycorrhizae
the roots of most plants form a symbiotic association with soil fungi; the symbiosis permits plants to absorb phosphorus efficiently
Nitrogen fixation
the conversion of N2 gas into nitrate, nitrite or ammonium; all forms of nitrogen that are substrates for a variety of enzymes
Nitrogenase
an enzyme that uses N2 as a substrate; it forces electrons and protons onto nitrigen reducing it from 0 to -3 oxidation state; ammonium is the product
Nitrogen reduction
the process of reducing nitrogen in the nitrate ion NO3- from an oxidation state of +5 to the -3 oxidation state of ammonium which is also the oxidation state of nitrogen in amino acids, nucleic acids and many other biological compounds
Nitrogen assimilation
the actual incorporation of ammonium into organic molecules in the plant body; process is similar to that of an electron transport chain: reduced nitrogen passes through a series of carriers that function repeatedly but in the long run are not changed
Nitrifying bacteria
they oxidize ammonium to nitrite and others oxidize nitrite to nitrate
Nitrification
the conversion of ammonia to to nitrate by microbes
