Chapter 10 Photosynthesis
AP Biology
Mr. Orndorff
April 2004
Site of photosynthesis in a plant (Fig. 10.2)
Overview of photosynthesis(Fig. 10.4)
Electromagnetic spectrum (Fig. 10.5)
Interaction of light
with matter in a
chloroplast(Fig. 10.6)
Absorption and action spectra
for photosynthesis
(Fig. 10.7)
Absorbance Spectrum of Plant Leaf Pigments
Data from AP Biology Class
April 03-04
-0.200
0.000
0.200
0.400
0.600
0.800
1.000
1.200
1.400
1.600
380
400
420
440
460
480
500
520
540
560
580
600
620
640
660
680
700
720
Wavelegnths in nm
Abso
rban
ce
Chlorophyll b
Chlorophyll a
Xantophyll
Carotenes
Fitness of light
High energy photons
Visible light Low energy photons
Drive electrons out of atoms--break bonds
Excite electrons to higher energy levels
Increase molecule vibrations
Screened out by ozone and O2 in atmosphere
Able to penetrate earth’s atmosphere
Screened out by H2O vapor and CO2 in atmosphere
Structure of chlorophyll (Fig. 10.8)
Harvesting light with a
photosystem (Fig. 10.10)
Photoexcitation of isolated chlorophyll (Fig. 10.9)
Noncyclic electron flow (Fig. 10.11)
Mechanical analogy for
the light reaction
(Fig. 10.12)
Dye-reduction technique for measuring rate of photosynthesis
Blank
(1)
Unboiled Chloroplasts
Dark (2)
Unboiled Chloroplasts
Light (3)
Boiled Chloroplasts
Light (4)
No Chloroplasts
(5)
Phosphate Buffer 1 mL 1 mL 1 mL 1 mL 1 mL
Distilled Water 4 mL 3 mL 3 mL 3 mL3 mL +
3 drops
DPIP dye
(replaces NADP+)___ 1 mL 1 mL 1 mL 1 mL
Unboiled Chloroplasts
3 drops 3 drops 3 drops ___ ___
Boiled Chloroplasts
___ ___ ___ 3 drops ___
% Transmission
Chemiosmosis in
mitochondria and
chloroplasts (Fig. 10.14)
Tentative model for thylakoid membrane
(Fig. 10.15)
Cyclic electron flow (Fig. 10-13)
Calvin cycle (Fig. 10.16)
Photorespiration
• In stroma of chloroplasts:
RuBP + O2 glycolic acid + G3P
• In mitochondria and peroxisomes (in presence of light):
glycolic acid + O2 CO2 + H2O
• Drains away up to 50% of carbon fixed by the Calvin cycle in C3 plants.
PEP carboxylase: the enzyme for hot, dry, and bright conditions• PEP carboxylase
binds CO2 at low concentrations.
• Plants keep stomata closed most of the time to save water.
• PEP carboxylase does not bind O2 leading to photorespiration.
• RuBP carboxylase does not bind CO2 at low concentrations.
• Plants must keep stomata open to get enough CO2.
• RuBP carboxylase does bind O2 leading to photorespiration.
C4 anatomy and pathway (Fig. 10.17)
C4 Photosynthesis
In mesophyll cells:• PEP carboxylase adds
CO2 to PEP (3C) to make oxaloacetate and malate (both 4C acids).
• 4C acids transported to bundle-sheath cells via plasmodesmata.
In bundle-sheath cells:• 4C acids + ATP make
CO2 + PEP (3C).
• PEP transported back to mesophyll cells.
• RuBP carboxylase adds CO2 to RuBP to begin Calvin cycle.
C4 vs. CAM Photosynthesis
C4 Photosynthesis
1. CO2 incorported into 4C organic acids in mesophyll cells using PEP carboxylase.
2. 4C organic acids release CO2 to Calvin cycle in bundle-sheath cells.
CAM Photosynthesis
1. CO2 incorported into 4C organic acids at night when stomata are open.
2. 4C organic acids release CO2 to Calvin cycle during the day when stomata closed.
Review of photosynthesis (Fig. 10.19)