PHOTOSYNTHESIS

1
Chapter 10 PHOTOSYNTHESIS
In photosynthesis light energy is used to
synthesize organic compounds from carbon dioxide
CO2. Oxygen O2 is a byproduct from the oxidation
of water.
H2O
light reactions
Reactions of Photosynthesis
O2
1. Energy transduction reactions ( photochemical
reactions, light reactions) 2. Carbon-fixation
reactions ( dark reactions)
ATP NADPH
carbon reactions
CO2
sugars
2
All life on earth is sustained, directly or
indirectly, by the SUN.
organic food carbohydrates lipids proteins
Photosynthesis
6 CO2 6 H2O ? C6H12O6 6 O2
glucose
Phototroph an organism that derives energy from
light.
Chemotroph an organism that derives energy from
chemical compounds.
Autotroph an organism that is able to
manufacture its own food.
Heterotroph an organism that relies on a food
source/can not manufacture its own food.
C6H12O6 6 O2 ? 6 CO2 6 H2O
glucose
Respiration
3
J. Van Helmont plant substance does not
primarily derive from soil
2.27 kg willow branch in 90.7 kg soil
5 years
65.43 kg
- 0.057 kg
67.7 kg willow branch in 90.7 kg soil
6 CO2 6 H2O ? C6H12O6 6 O2
4
two outer membranes
Thylakoids (stroma thylakoids and grana)
stroma
thylakoid lumen
Fig. 3-12 (a), p. 40
5
Fig. 10-2, p. 151
6
intact chloroplast
stroma
grana
Fig. 10-4, p. 152
7
Reactions of Photosynthesis
1. Energy transduction reactions ( photochemical
reactions, light reactions) 2. Carbon-fixation
reactions ( dark reactions)
from Ravenet al. Biology of Plants
8
oxygen released
sunlight energy
photosystem II
e-
H
electron transport system
Light-dependent reactions
H2O is split
H
lumen (H reservoir)
H
photosystem I
e-
electron transport system
NADP
carbon dioxide used
ADP Pi
H
H
Light-independent reactions
sugar phosphate
water released
Stroma
Fig. 10-3, p. 151
carbohydrate end product (e.g. sucrose, starch,
cellulose)
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Light is a wave and a particle (photon energy
packet/quantum)
Photon energy is inversely proportional to the
wavelength of light characteristic for that
photon.
Electromagnetic energy spectrum
from Ravenet al. Biology of Plants
10
PIGMENTS are capable of trapping/absorbing light
energy.
Pigment a substance that selectively absorbs
part of the visible light and therefore appears
colored.
When light is absorbed by a pigment, only one
photon is absorbed by one pigment molecule at a
time. The energy of the photon is absorbed by an
electron of the pigment molecule, giving this
electron more energy.
11
T. W. Engelmann Colors of light used in
photosynthesis
a crystal prism breaks up a beam of light into a
spectrum of colors
algal filament
oxygen-seeking bacteria
Fig. 10-1, p. 150
12
Photosynthetic pigments Chlorophylls and
Carotenoids

• Absorption maxima of isolated chlorophyll a
• 430 nm blue light
• 680 nm red light

from Ravenet al. Biology of Plants
13
Magnesium is important for chlorophyll synthesis.
porphyrin ring
hydrophobic phytol tail
from Ravenet al. Biology of Plants
14

• Carotenoids
• Carotenes like ß-carotene
• Xanthophylls like zeaxanthin

Beta-carotene is also the precursor of vitamin A,
which can be converted into retinal, a visual
pigment of our eyes.
from Ravenet al. Biology of Plants
15
Chapter 10 PHOTOSYNTHESIS
In photosynthesis light energy is used to
synthesize organic compounds from carbon dioxide
CO2. Oxygen O2 is a byproduct from the oxidation
of water.
H2O
light reactions
Reactions of Photosynthesis
O2
1. Energy transduction reactions ( photochemical
reactions, light reactions) 2. Carbon-fixation
reactions ( dark reactions)
ATP NADPH
carbon reactions
CO2
sugars