h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

In the article, you state: "Photosynthesis takes place exclusively inside organelles. These are small organ-like structures found inside cells known as chloroplasts." Actually, the cells are not chloroplasts, the plastids are the chloroplasts. The cells that chloroplasts are found in vary, but are usually concentrated in the palisade parenchyma of the leaf. I don't know that I'd call them organ-like either, since by definition organs are on a much higher level than organelles. I'd just call them small highly-specialized structures found inside some plant cells.

You also state that "Most chlorophyll is green, so most plants are green." I think all chlorophyll is green, but there are other non-green photosynthetic pigments, like the xanthophylls and such.

"This is why plants are removed from hospital rooms at night, preventing the plant removing some of the patient's oxygen." Although plants do respire, it's now known that the amount of oxygen they consume is pretty negligible and doesn't really affect the oxygen content of the room.

One last comment: another piece of evidence for mitochondria/plastids evolving from free-living bacteria is their double membrane. These are the only organelles with double membranes.

Other than that, good article! Nice basic overview of photosynthesis.

One additional fiddling detail. You have "Thus, because of diffusion and there positive charge..." The "there" almost certainly needs to be "their".

Ah, the wonders of adenosine tri-phosphate.

My biology teacher always yells at me when I say "Dark Reaction" instead of "Light-Independant Reaction", but hopefully he will let you off the hook!

Yeah, you're right. That bit about the chloroplasts should be a bit clearer. What I meant to say was "Photosynthesis takes place inside organelles known as chloroplasts." And I meant that organelles are to a cell what organs are to an organism - specialised compartments which allow chemical reactions to occur which would be either too dilute to occur in the cytoplasm, or would interfere with other reactions.

Many thanks for all your comments and I've now corrected the entry, where appropriate, as a result! Great work.

Sam.

Just for the sake of completeness:

Photosynthesis does not strictly necessarily have to occur in organelles. Some Archaebacteria do it on their membrane (using the pigment bacteriorhodopsin to pump protons to the outside).

But I assume this entry is on plant-photosynthesis, so my comment is here just in case...

HELL

Point taken - but it has been theorised that chloroplasts were in fact originally bacteria which got captured by another cell. So essentially (if this theory is correct) bacteria are kind of like free-living chloroplasts.

Hi scaryfish

Well that's still just a theory... A good one, but then again you cannot directly compare the photosynthetic systems of some exquisit halobacteria with the highly effective chloroplast's photosystem...
Anyways, it was just my 0.00000002p for the sake of completeness.

Bye see you around,


HELL