(Tune: "Auld Lang Syne")



When sunlight bathes the chloroplast, and photons are absorbed

The energy’s transduced so fast that food is quickly stored,

Photosynthetic greenery traps light the spectrum through

Then dark pathway machinery fixes the CO2

Two chlorophyll;s (a,b to you) are cleverly deployed

In photosystems I and II, within the thylakoid

System I takes energy, at 700 (red)

While system II (with pigment b ) takes 680 instead.

At manganese on center II, see oxygen displace

As water’s split, and protons too, leave membrane inner face

Electrons that we thus produce, cross, ‘photo-fortified’

Plastoquinone then to reduce, upon the other side.

Meanwhile at I, chlorophyll a is photo-oxidized

(At ‘positive holes’, formed that way, electrons are much prized),

Electrons that we thus eject reduce NADP

With ferredoxin we suspect, as intermediary.

The hole in I we now negate, plastoquinol moves in

With b and f to mediate, and plastocyanin,

That redox loop, potential large, runs exergonically

With membrane-separated charge, and thence to ATP

That Z track by electron pair, reduced NADP,

Plucked oxygen from water’s care, and made some ATP.

Now we’ve got power to reduce, and ATP to spare,

Food in the dark we can produce, from CO2 in air.

Ribulose bisphosphate takes, a mole of CO2

Gives two 3-phosphoglycerates, (if Calvin’s story’s true)

NADPH now provides, reducing power to make

Two phosphoglyceraldehydes (as ATP we break)


There now occurs a jolly jig (the details we’ll ignore)

With carbon chains both small and big, to ribulose once more,

Each time round, as CO2, is fixed we’ve chains to spare

And we can make hexoses new, from triose phosphate pair.

Other routes involve C4, or pyruvate to fat,

NADPH as before, is vital still for that,

ATP still provides the drive, the moral still is this &emdash;

The one thing that keeps life alive is photosynthesis.