Chapter 8 :
Plant Metabolism
Overview
Photosynthesis and respiration are each presented at three different levels: the essence of
the process is examined, the major steps are briefly introduced, and the processes are then
examined in greater detail. One or two levels may be sufficient for some readers; others will
want to explore all three. The chapter discusses the importance of the main features of each
process and summarizes the light reactions, the dark reactions, glycolysis, the Krebs cycle,
and the electron transport system. Throughout, the chapter relates the effect of increased
man-made CO2 emissions to plant growth. It concludes with a tabular comparison between
photosynthesis and respiration, a brief discussion of primary and secondary metabolites, and
assimilation and digestion.
Detailed Lecture Outline
I.
Introduction
A. Photosynthesis
B. Respiration
II. Enzymes and Energy Transfer
A. Enzymes Defined
B. Anabolism and Catabolism
C. Oxidation-Reduction
III. Photosynthesis
A. The Essence of Photosynthesis
1. Photosynthesis defined
a. energy from sunlight is converted into chemical bond energy in the form of
carbohydrates
b. ability of pollutants such as PCBs to stop photosynthesis in many
algae
2. Summary equation for photosynthesis
3. Principle ingredients
a. Carbon dioxide (CO2),0.039% of atmosphere
. recent increase has potential to cause global increase in temperature
b. Water
c. Light
d. Chlorophyll
1) Several types
2) All magnesium containing molecules
3) Light harvesting complex called a photosynthetic unit
• 250-400 pigment molecules
B. Introduction to the Major Steps of Photosynthesis
1. The Light-Dependent Reactions
a. Reactions take place in thylakoid membranes of chloroplast
• light required
b. Water split, producing hydrogen ions and electrons, O2 gas released
c. ATP created
d. NADPH + H+ created
2. The Light-Independent Reactions (Calvin cycle)
a. Reactions take place in stroma of chloroplast
• light not directly required, hence "dark" reactions; but light is required
to activate enzymes involved
b. Calvin cycle
1) Carbon dioxide from air combined with 5-carbon sugar
2) Glucose formed through several reaction steps
C. A Closer Look at Photosynthesis
1. Historical perspective
2. The Light-Dependent Reactions Reexamined
a. Nature of light
1) Wave and particle theory of light
2) Photoelectric effect
3) Photons
• discrete packets of light energy
b. Chlorophyll pigments
• each pigment has typical absorption spectrum
c. Consequences of light absorption by chlorophyll
1) Emit light immediately (fluorescence)
2) Emit light after a delay (phosphorescence)
3) Absorbed energy converted to heat
4) Absorbed energy converted and stored in chemical bond energy
(photosynthesis)
d. Photosystem I contains
1) 200 or more chlorophyll a molecules
2) Small amount of chlorophyll b
3) Carotenoid pigment with protein attached
4) Special reaction-center molecule of chlorophyll a called P700
5) Iron-sulfur proteins (electron acceptors)
e. Photosystem II contains
1) Chlorophyll a molecules
2) ß-carotene pigments attached to protein
3) Small amount of chlorophyll b
4) Special reaction-center molecule of chlorophyll a called P680
5) Primary electron acceptor molecule called pheophytin
f. Photolysis
g. Photophosphorylation
h. Chemiosmosis
3. The Light-Independent Reactions Reexamined
a. The Calvin cycle (3-carbon pathway)
b. Photorespiration
c. The 4-carbon pathway
d. CAM photosynthesis
4. Other Significant Processes that Occur in Chloroplasts
IV. Respiration
A. The Essence of Respiration
1. Respiration defined
• energy releasing process where simple sugars are broken down during a
series of stages controlled by enzymes
2. Summary equation for respiration
3. Anaerobic respiration and fermentation
B. Introduction to the Major Steps of Respiration
1. Glycolysis
2. Aerobic respiration
a. The Citric Acid (Krebs) Cycle
b. The electron transport chain
3. Anaerobic respiration and fermentation
4. Factors affecting the rate of respiration
a. Temperature
b. Water
c. Oxygen
C. A Closer Look at Respiration
1. Glycolysis reexamined
a. Phosphorylation
b. Sugar cleavage
2. Transition Step to the Citric Acid (Krebs) Cycle
a. Pyruvic acid
b. Acetyl CoA
3. The Krebs cycle reexamined
4. Electron transport and oxidative phosphorylation
V. Additional Metabolic Pathways
A. Secondary Metabolism
B. Shikimic Acid Pathway
C. Mevalonic Acid Pathway
VI. Assimilation and Digestion
A. Assimilation Defined
• use of photosynthetic products in the building of protoplasm and cell walls
B. Digestion Defined
• conversion of starch and other insoluble carbohydrates to soluble forms
C. Examples
D. Comparison of Digestion in Plants and Animals