Photosynthesis Part 2
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Transcript Photosynthesis Part 2
Electromagnetic energy
› Solar energy or radiation which travels in
space a rhythmic waves and can be
measured in photons
Wavelength
› The distance between crests of adjacent
waves such as those of the electromagnetic
spectrum
Visible Light
› The radiation our eyes see as different colors
Fig. 10-6
10–5 nm 10–3 nm
103 nm
1 nm
Gamma
X-rays
rays
UV
106 nm
Infrared
1m
(109 nm) 103 m
Microwaves
Radio
waves
Visible light
380
450
500
Shorter wavelength
Higher energy
550
600
650
700
750 nm
Longer wavelength
Lower energy
Pigments
› Substances that absorb some wavelengths
of light and reflect others
› Different pigments absorb/reflect different
wavelengths
Photon
› A fixed quantity of light energy
› The shorter the wavelength of light the
greater the energy of a photon
Fig. 10-7
Light
Reflected
light
Chloroplast
Absorbed
light
Granum
Transmitted
light
Which wavelengths are absorbed most?
› Primarily blue and red
Why do plants appear green?
› They reflect green light
What is the role of accessory pigments?
› They allow the plant to absorb energy from
more the visible light spectrum – making the
plant more efficient.
Fig. 10-9
RESULTS
Chlorophyll a
Chlorophyll b
Carotenoids
(a) Absorption spectra
400
500
600
700
Wavelength of light (nm)
(b) Action spectrum
Aerobic bacteria
Filament
of alga
(c) Engelmann’s
experiment
400
500
600
700
When a pigment
absorbs light, it goes
from a ground state to
an excited state, which
is unstable
When excited electrons
fall back to the ground
state, photons are given
off, an afterglow called
fluorescence
If illuminated, an isolated
solution of chlorophyll will
fluoresce, giving off light
and heat
Photosystem (1st
part)
› Light harvesting
complexes
pigment molecules
bounded by proteins;
absorb
transfer energy to
chlorophyll a of
reaction center
Photosystem (2nd
part)
› Reaction Center
Chlorophyll a and a
primary electron
acceptor
Chlorophyll a uses
energy from light
harvesting complexes
to pass a pair of
electrons to the
primary electron
acceptor