Post on 29-Dec-2015
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Lecture 11
ABSORPTION, TRANSLOCATION,ASSIMILATION
AND RESPIRATION IN PLANTS
Absorption, Translocation and Assimilation in Plants
Absorption and Conduction of Water Absorption and Transport of Mineral
Nutrients Translocation of Sugars
Water
Absorbed by roots and distributed to all parts of plant; Some plants may be 200 ft tall ( requires much
energy) roots may be 100 ft deep (300 feet total)What is the power source for this work?
Must be continuous water connection in xylemMolecule to molecule (cohesion)From soil to leaf, fruits, flowers
Water
Water does not move alone, carries nutrients for plantNitrates
Used for proteinPhosphates
Used to make ATPMagnesium
Part of chlorophyll molecule
Water
Water absorbed in large quantities by plantsSeveral hundred gallons/plant in some speciesMust absorb water to obtain minerals
Water lost from (or exits) plant through TranspirationExits through stomates
Dicot leaf structure
Location and structure of stoma
TranspirationUpward pull of water is started by evaporation of
molecules from outer surface of mesophyll cells: Mesophyll cells become water deficient and must be
refilled from adjacent cells Water passes from “wetter” plant cells to “drier”
cells and forms an unbroken water chain (cohesion) from the outer surface of leaves to the roots in contact with wet soil
Vapor pressure (water content) difference exists between root surface cells and surrounding soil moisture
Mineral Nutrients
Minerals must be absorbed along with water to be used by plant
Initially, plant nutrients come from the seed, until used up.
- subsequent nutrients are obtained by plant roots from surrounding soil.
Mineral Nutrients
Large amount of energy required for root absorption of water and minerals What is the source of this energy?
Starches and sugars broken down by respiration What molecule is necessary for respiration?
Mineral Nutrients
Oxygen This is reason for poor performance of roots in
waterlogged soilsSoil aeration is very important
Root concentration of soil nutrients is very high Additional absorption is very difficult
Translocation of Sugars
The movement of photosynthetic sugars throughout the plant is primarily through phloem
Movement is mostly downward in the plant with some movement laterally
Most translocated sugar is sucrose (disaccharide) Glucose + fructose (monosaccharide)
Be sure and know the difference betweentwo words that sound a lot alike:
Transpiration and,Translocation
Respiration and Carbohydrate Breakdown
Respiration and Carbohydrate Breakdown
Factors Affecting Plant Respiration Respiration Pathways Electron Transport Absorption, Translocation and Assimilation
of Water
Plant Respiration
Stepwise release of energy captured and stored by photosynthesis Carbohydrates produced in photosynthesis are
reconverted to CO2, water and energy Respiration energy is source for all life processes This reaction does not occur all at once, but is a
series of subreactions and cycles Each step in a reaction is catalized by an enzyme
Enzymes – Protein Catalystes
Enzymes – are composed of proteins (organic catlystes) that assist in making a chemical reaction go faster
Enzymes are affected by the same factors that affect proteinsHeat – as temperature increase chemical reactions go fasteruntil a enzyme becomes denatured (60 C; 30 minutes)
Salting out – as salt concentration increases, available water to suspend enzymes decreases. Charges on the enzyme become neutralized and they “fall” out of solution.
Enzymes - con’t
Heavy Metals – certain heavy metals like (e.g. lead, mercury, cyanide, cadmium) can directly denature an enzyme
Inhibitors – certain substances can act as inhibitors of enzymes
Overall Reaction:
C6H12O6 + 6H2O + O2 6CO2 + 12H2O + energy
GlycolysisTCA CycleElectron transport system
Factors Affecting Respiration
Temperature Rate increases 2 – 4 times for each 10° rise
between 32° and 95° F Stored plant materials (seeds, fruit) will respire
and degrade if not cool stored, specific for each crop
Best temp for ideal growth is night temp 5 - 9° F cooler than day temp
Factors Affecting Respiration
Oxygen concentration Respiration declines as oxygen concentration decreases
Soil conditions Waterlogged, compacted soils lack oxygen, reduces root
respiration Can cause reduced uptake of minerals and vice versa
Light Low light intensities = low respiration because of low
photosynthetic rates
Factors Affecting Respiration
Plant growth Leaves function as both source (photosynthesis) and
sink (respiration) and continues to increase as leaf grows, then peaks and both processes begin to decline
Respiration energy used for: Growth and metabolism Protein degradation and resynthesizing maintenance
Respiration Pathways
A sugar molecule is degraded by a series of reactions, starting with:
1) Glycolysis – each molecule of glucose yields 2 molecules of pyruvic acid & 4 molecules of ATP
2) TCA Cycle – pyruvic acid from glycolysis is degraded in a stepwise manner. Yield is CO2 and H2O electron acceptors to enter electron transport system
3) Electron Transport System – series of oxidation-reductions in which electron acceptors from TCA Cycle and ADP combine to produce ATP and NADPH the energy sources of all life
Structure of an ATP molecule
Glycolysis
Alcoholic FermentationBeer/Wine Making
Glycolysis Citric AcidTO
AerobicRespiration
AnaerobicRespiration
Lactic Acid FermentationPickle Making
TCA (tricarboxylic acid cycle)Citric Acid Cycle
Terminal Oxidation Pathway
Balance Sheet
1 glucose molecule = 38 ATP molecules
2 ATP (net) from glycolysis & 36 from T. O.
Sun’s energy carbohydrates (respiration) chemical energy
Take Home Message
Glycolysis is the first step in any respiration (anaerobic or aerobic) leading to the end product PYRUVATE
Aerobic repiration goes through glycolysis, TCA and TO(38 ATP gained), O2 required, CO2 and H2O released.
Anaerobic repiration goes through glycolysis and then to a final product (2 ATP gained), no O2 required, CO2
released