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 xylem
 Molecule to molecule (cohesion)
 From soil to leaf, fruits, flowers
Water

Water does not move alone, carries nutrients for
plant
 Nitrates
 Used for protein
 Phosphates
 Used to make ATP
 Magnesium
 Part of chlorophyll molecule
Water


Water absorbed in large quantities by plants
 Several hundred gallons/plant in some species
 Must absorb water to obtain minerals
Water lost from (or exits) plant through
Transpiration
 Exits through stomates
Dicot leaf structure
Location and structure of
stoma
Transpiration
Upward 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 soils
 Soil 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 between
two 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 proteins
Heat – as temperature increase chemical reactions go faster
until 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:
Glycolysis
TCA Cycle
Electron transport system
C6H12O6 + 6H2O + O2 6CO2 + 12H2O + energy
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)
2)
3)
Glycolysis – each molecule of glucose yields 2 molecules of pyruvic acid
& 4 molecules of ATP
TCA Cycle – pyruvic acid from glycolysis is degraded in a stepwise
manner. Yield is CO2 and H2O electron acceptors to enter electron
transport system
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 Fermentation
Beer/Wine Making
Glycolysis
Citric Acid
TO
Aerobic
Respiration
Anaerobic
Respiration
Lactic Acid Fermentation
Pickle 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