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