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Under normal rules, electrons would
travel to their destinations with quick
random hops. But studies of photosynthetic bacteria and plants suggest that
the electrons might act more like correlated waves instead of hopping particles,
At room temperature, the team used
a laser to excite light-catching proteins
purified from photosynthetic algae. A
second laser pulse revealed where the
resulting excited electrons went. Patterns
of long-lasting electron waves — a property called quantum coherence — indicated quantum weirdness was at work.
“This study shows that quantum
coherence is present at room tempera-
ture,” says Graham Fleming, a chemist at
the University of California, Berkeley. “It
is very likely a general feature of photo-
synthetic light-harvesting complexes,”
says Fleming, a pioneer of studies on
quantum effects in photosynthesis.
The researchers expected to see the
coherence last for about 20 femto-
seconds, Scholes says. Instead, it lasted
for about 400 femtoseconds. These long-
lasting quantum effects may
help explain the mystery
of why the initial electron-
moving reactions in photo-
synthesis are so efficient. In
an extreme version of the
algae’s quantum-mechan-
ical trick, electrons could
simultaneously take all the
possible paths to a photosys-
tem and decide after arriving
which route was best. “That vibrating
electron could put some feelers out and
see which path to take,” Scholes says.
The researchers don’t yet know for
sure whether quantum effects make the
reaction chain more efficient. Scholes
believes that they do, but more stud-
ies and modeling experiments will be
required to say exactly how much of a
boost quantum coherence provides.
“This study
shows that
quantum
coherence
is present
at room
temperature.”
GRAHAM FLEMING
Photosynthetic algae go quantum
By Laura Sanders
A dash of sunlight, a sprinkle of light-harvesting proteins and a healthy dollop
of carbon dioxide is about all it takes to
whip up a batch of tasty plant food — but
you might want some quantum physics
to stir the pot. A team has caught photosynthetic marine- and lake-dwelling
algae performing quantum tricks at room
temperature. The results, in the Feb. 4
Nature , suggest that quantum mechanics
may be at the heart of sunlight-to-energy
conversion in living organisms.
“This is quantum mechanics in a biological system,” says study coauthor
Gregory Scholes, a physical chemist at
the University of Toronto.
Photosynthesis relies on proteins that
absorb incoming photons, or particles of
light. In the algae, these photons excite
electrons in the proteins, touching off
a series of electron transfers that ultimately ferry the energy-laden electrons
to centralized collection stations (called
photosystems) where the conversion of
energy to carbohydrates begins.
Leaves’ loopy networks
tree branches have inspired efficient transit networks, but a new
study looks at the connected loops of leaf veins. in some plants
the loops help circumvent damaged areas and channel nutrients
efficiently, report researchers led by Eleni Katifori of rockefeller
University in New York City. the team programmed a computer
to simulate how efficiently different network patterns could do
the job of leaf veins, which move water and nutrients around.
in the simulations, the looped network performed better than
nonlooped ones in several important ways, the team reported
January 29 in Physical Review Letters. Damage from insects,
weather or parasites can interrupt leaves’ normal venation patterns. Connected circular veins allowed the flow of water and
minerals to circumvent injured areas (dark green dot, shown on
lemon leaf). the looped network also allowed easy adjustment
of the flow rate of water through veins, which can help conserve
moisture on a hot day, Katifori says. — Laura Sanders
