
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