Download PHOTOSYNTHESIS, RESPIRATION, AND TRANSLOCATION

PHOTOSYNTHESIS,
RESPIRATION, AND
TRANSLOCATION

http://www.emc.maricopa.edu/faculty/far
abee/BIOBK/BioBookPS.html
PHOTOSYNTHESIS

Green plants convert radiant energy
into chemical energy
- utilizes chlorophyll of the chloroplasts
Molecular model of chlorophyll
PHOTOSYNTHESIS

Principal Photosynthetic Process:
Hydrogen + Carbon Dioxide → CH2O
in presence of:
Photosynthetically Active Radiation - PAR
Compensation Points

Light:
as PAR increases. . .
photosynthetic CO2 fixed
equals
respiration CO2 released
no net CO2 movement until more PAR
up to the Light Saturation Level
Compensation Points

CO2:
CO2 fixed by photosynthesis
equals
CO2 released by respiration
no net CO2 movement

Note: PAR level required for
light saturation rises with increasing CO2

Also: as PAR level increases, higher
concentrations of CO2 are required
important differences in C3 and C4 plants
Chemical equation for
photosynthesis (greatly simplified):
6 CO2 + 6 H2O + radiant energy
w/ chlorophyll
Yields:
6O2 + C6H12O6
(Glucose)
GLUCOSE ENERGY
1 mole Glucose (a 6-carbon sugar (C6)),
has energy equal to ~ 686 kcals
Written as: 686 kcal/mol
Light and Dark Reactions

Two reactions in photosynthesis:
Light Reactions - occur only in presence of
light
Dark Reactions - don’t require light; occur
in light or complete darkness
Light reactions involve:




photons
electrons of the chlorophyll molecule
water molecule
NADP (nicotinamide adenine
dinucleotide phosphate)
Visible Light
Light Reaction Process:
1) photons (light packets) energize electrons in
chlorophyll molecule (z scheme)
2) energized chlorophyll splits water molecule
3) NADP captures H+ ion; holds it as NADP-H
4) ATP (adenosine triphosphate) formed by:
a. light energy changed to chemical energy
(NADPH)
b. electron from H2O; energy released forms
ATP
Note: free O2 is released in process
Structure of ATP
Dark Reactions (Calvin Cycle)

Utilize:
• NADPH
• ATP
• CO2
CO2 combines w/ C5 sugar
Ribulose Diphosphate (RuDP)
(catalyzed by RuDP-carboxylase, an enzyme)
Dark Reactions (Calvin Cycle)
u n s t a b l e - immediately splits into two
PGA molecules (Phosphoglyceric acid)
Plants forming these PGA molecules are:
C3 Plants
Dark Reactions (Calvin Cycle)
-
-
-
H from NADPH transferred to PGA via
ATP/NADPH energy
Phosphoglyceraldehyde (PGAL) is
formed (a simple sugar)
PGAL combines into Glucose; however
most PGAL is used to regenerate RuDP
Special enzymes (RuDP-carboxylase)
catalyze RuDP to combine with CO2
Dark Reactions (Calvin Cycle)
Takes:
18 molecules ATP
+ 12NADPH
+ 6CO2
= C6H12O6
also yields 6H2O, 18ADP, and 18P
Modified photosynthetic
equation:
6CO2 + 12H2O + radiant energy
w/ chlorophyll
→ 6O2 + 6H2O + C6H12O6
shows that O2 liberated in light reactions
comes from H2O not CO2 and that there
are newly formed H2O molecules
C3 and C4 Plants



Photosynthetic pathways are
complicated
Simply stated: C3 plants are less
efficient at photosynthesis
Reduced efficiency due to an “energy
robber”:
Photorespiration
Photorespiration



Occurs when C3 plants oxygenase
instead of carboxylase in the dark
reaction; thus refer to enzyme as
Rubisco for short
Less efficient - can’t metabolize glycolate
(C2) produced; only passes one PGA to
be reduced to PGAL
Two carbon atoms are “lost” from cycle
C4 Plants
C4 plants designed to:



reduce O2 concentrations
increase CO2 concentrations
favor carboxylase reaction
C4 Plants
C4 advantages:




photosynthesize at lower CO2
concentrations
higher temperature optimums
higher light saturation points
rapid photosynthate movement
Rate of Photosynthesis
C4 Plants
Examples of C4 plants:
 Corn*
 Sugarcane
 Sorghum
 Bermudagrass
 Sudangrass
Note: C4 weeds also - crabgrass, johnsongrass,
shattercane, pigweed
C3 Plants
Examples of C3 plants:
 Wheat
 Rice
 Soybeans
 Alfalfa
 Fescue
 Barley
CAM Plants
CAM Plants - separate light and dark
reactions according to:
Time of Day
CAM (Crassulacean Acid Metabolism)
Plants include:
Pineapple, Cacti, other succulents
CAM Plants
Light reactions occur during daytime but

Initial fixation of CO2 occurs at night

Allows stomata to remain closed
during the day - conserve H2O
CAM Plants
Also:
 4-carbon Malic Acid “pool” accumulates
overnight (lowers pH)
 During day stomata are closed
 Malic Acid releases CO2 providing
carbon source for dark reaction
CAM Plants
Environmental Factors Affecting
Photosynthesis
Light:
intensity, quality, duration
intensity – (see table 7-1; fig 7-7 p. 127)
- etiolated vs. high light intensity
- compensation point
- saturation point
quality - reds and blues; greens are reflected (fig. 7-6)
duration - longer days = more photosynthesis
Light Spectrum
Light Quality - Chlorophyll
Light Quality - Photosynthesis
Environmental Factors Affecting
Photosynthesis
CO2:
 photosynthetic rate limited by small
amounts of CO2
 increase by air movement; also CO2
generators (greenhouse)
 Normal CO2 content: 300 - 350 ppm
(0.030 - 0.035 %)
Environmental Factors Affecting
Photosynthesis
CO2 (cont)
(see fig. 7-8)
Recall CO2 compensation point:
CO2 evolved in respiration =
CO2 consumed in photosynthesis
Environmental Factors Affecting
Photosynthesis
Temperature (Heat)
2x Photosynthetic Activity for each 10°C
(18°F) increase in temperature
Excess temp can lower photosynthesis
and increase respiration
Environmental Factors Affecting
Photosynthesis
H2O content:




wilted leaves - rate near zero
due to reduced CO2 by closed stomata
water does not directly limit
photosynthesis
(only ~ 0.01 % of water absorbed by
plants is used as H source)
Environmental Factors Affecting
Photosynthesis
but indirectly:




low turgor - stomatal closing
reduced leaf exposure
enzymes affected
excess soil moisture – anaerobic
• Lack of O2 reduces respiration, uptake, etc.
RESPIRATION
Release of energy stored in foods
 Controlled burning or “oxidation” at
low temps by enzymes
Respiration equation:
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy
(glucose) (oxygen) (carbon dioxide) (water)
RESPIRATION
Modified Respiration Equation:


Shows that H2O is an input as well as a
product
Specifies total net energy derived from
one glucose molecule
Modified Respiration Equation:
C6H12O6 + 6O2 + 6H2O→6CO2 + 12H2O + 38ATP + heat
RESPIRATION
Heat energy is of little value to plant (may be detrimental)
ATP energy used for:
 Chemical reactions (energy req.)
 Assimilation (protoplasm)
 Maintenance (protoplasm)
 Synthesis (misc.)
 Accumulation (solutes)
 Conduction (foods)
 Motion (protoplasm, chromosomes)
Gas Exchange in Respiration
Gas exchange is the opposite of
photosynthesis
Respiration takes in O2 and releases CO2
 liberates more O2 than needed for
respiration
 requires more CO2 than released by
respiration
Gas Exchange in Respiration
@ Compensation point (low light intensity):

O2 released in photosynthesis = CO2
released in respiration
COMPARISON OF PHOTOSYNTHESIS
AND RESPIRATION
Under ideal photosynthetic conditions:
Photosynthetic Rate ~ 10x Respiration Rate
COMPARISON OF PHOTOSYNTHESIS
AND RESPIRATION








Photosynthesis
Cells w/chlorophyll
In light
Uses H20 and CO2
Releases O2
Radiant energy to
chemical energy
Dry weight increases
Food and energy produced
Energy stored








Respiration
All living cells
Light and dark
Uses O2
Forms CO2 and H20
Chemical energy to
useful energy
Dry weight decreases
Food broken down
Energy released
Factors Affecting Respiration







Temperature - respiration increases as temperature
increases
Moisture - respiration increases as moisture decreases
(stress)
Injuries - respiration increases with injury
Age of tissue - respiration greater in young tissue
Kind of tissue - respiration greater in meristematic
CO2/O2 - respiration increases with high O2 / low CO2
Stored carbohydrates - respiration increases with
increased stored energy
Respiration Problems/Hazards





deterioration (fungi and bacteria)
rot and decay
loss of dry wt.
loss of palatability
high temperatures / high CO2
(diseases; FIRE hazard)
ENERGY TRANSFER
Glycolysis - sugar splitting
Net production of:
 2 ATP molecules
 2 NADH molecules
Forms:
 pyruvic acid
Aerobic Energy Transfer
If O2 and mitochondria are present:
Krebs cycle - an energy converter
 converts glucose energy into usable
energy via enzymes
 occurs in stroma of mitochondria
“powerhouse”
Mitochondria Cristae
Electron Transport
*must have O2 present
 convert high energy from Krebs (NADH,
FADH) into usable ATP
 occurs along cristae
 fingerlike projections in mitochondria
where:
 cytochromes in enzymes transport electrons
 lowers and releases energy
 last cytochrome passes electrons to O2
 associates with 2 H+ protons forming H2O
ALTERNATE
ENERGY TRANSFER
If no O2 and mitochondria present to
respire alternative is:
fermentation - e.g. fig. 7-14, p. 135
 yeast (fungi) in beer, bread
 silage