Alaska. How Doeas Photosynthesis Work In 24Hr Daylight.

[Colmc54]

In the recent BBC Natural History series on Alaska I was impressed by the massive pumpkin that came within 6lbs of beating the record. Such growth was attributed, not withstanding the dedicated work of the grower, to the effect of 24 hour daylight during the Alaskan Summer.

Photosynthesis consists of two phases one is the light dependent phase and the other the light independent phase. I was curious to know if the two phases can run concurrently in 24 hour daylight, as suggested by the programme, without reaching a point where the efficiency of the overall process begins to wane.

Plants are not my area of scientific expertise so I hope someone can shed some light on this for me (no pun intended).

[Svejk]

I thought photo/s worked in sunlight and a different process(respiration?) occurred in the dark.

[Hypognosis]

@Svejk

In fact, respiration occurs *all the time* in a plant. The difference is that, under ideal conditions, the photosynthesis is supplying all the plant's internal needs with enough excess to pump the leftovers out into the atmosphere.

I have to emphasise "ideal conditions" because cellular processes run faster at higher temperatures. In summer, or in the tropics, the cell processes using up oxygen all-but outpace the photosynthesis.

Tropical hardwoods notoriously take longer than a human lifetime to get from planting to felling. Meanwhile, paper manufacturers use softwood trees which are grown closer to the arctic circle. Lower temperature, lower respiration rates and more rapid laying down of wood mass.

Whenever I hear "the rain forest is the lungs of the planet", I think of the above and hold my tongue. (It's too much explanation for casual conversation).

[Hypognosis]

@Colmc54

I didn't see the programme but I'd have to say that the pumpkin example was proof that 24-hour light is good for plant growth.

Re-examining the words, "light independant" does _not_ mean the same as "compulsory for light to be absent". It just means "light isn't needed for this bit".

By analogy, a ball doesn't get to the top of the stairs unless you throw it there (you input energy: you're representing sunlight) but it can roll back and bounce downstairs again by itself, releasing that energy as sound, with each bounce.