Geoscience Reference
In-Depth Information
hν
Antenna Complex
chl, Bchl, carotenoids,
phycobilins
Reaction Center
chl, Bchl, proteins,
accessory pigments
Figure 3.1. light harvesting in a photosynthetic organism. Figure shows the relationship
between the antenna complex and the reaction center(s), each containing light-collecting
pigments. Figure redrawn from Canfield et al. (2005).
As a biological innovation, where did oxygen production come from?
To unravel this problem, we must begin by looking at how oxygen pro-
duction by photosynthesis works. Everything starts with light, and in
igure 3.1
, I have reproduced the salient features of how light (
hv
) is
captured during the photosynthetic process. This general picture per-
tains to all types of photosynthesis, including photosynthesis by cyano-
bacteria, the first oxygen producers (as we explore in
chapter 4)
. It also
pertains to plants, or even the anoxygenic phototrophs we met in the
last chapter. To collect light, all phototrophs use an “antenna complex.”
This is made up of a variety of pigments that capture the light (
ig. 3.1
).
Once captured, the light's energy is transferred to the reaction centers.
These constitute the business end of the process where, in the case of
oxygenic phototrophs, oxygen is made. Nature has made things com-
plicated, and in oxygen producers, there are actually two coupled re-
action centers: one is known as photosystem I (PSI) and the other as
photosystem II (PSII). They are coupled together in what is commonly
called the Z-scheme, and as I hope becomes obvious below, this ar-
rangement makes a lot of sense.
