What are delocalized electrons?

[leftventricle]

So in the chlorophyll molecule, inside the phorphyrin ring, well as a part of it - there is the ring of hydrocarbons with alternating single/double bonds, and in the text it says they have delocalized electrons in the bonds which start the photosynthetic process by absorbing light.

How do electrons absorb light now?

[leftventricle]

Also the chlorophyll molecule's hydrocarbon tail is used to anchor the molecule in the phospholipid bilayer membrane, but of which cell? Sorry if it sounds like a silly question.

[leftventricle]

And thirdly if all photosynthetic organisms use chlorophyll a as primary light absorbing pigment, then why is there a need for chlorophyll b?

[JackBean]

for first question you should first understand what are delocalised electrons at all. Look for benzene etc.
If you imagine them as "alternating single/double bonds", that's a mistake. The point is the hybridization state of the carbons, i.e. sp2 hybridization (see wiki), which leaves one p-orbital free for e.g. delocalization of electrons. Such electron orbitals has lower energy than normal p-orbitals and thus these electron need smaller energy to be excited (look for molecular orbitals).

They are anchored in the chloroplasts! In the thylakoid membranes

Because they have slightly different absorption spectra, so chl b works as additional pigment. Similarly as carotenoids. Look for structure of light harvesting complex (this one is little better for you).

I'm linking to Wikipedia, because it's (relatively) good starting point, but it's of course better to look into some books, in your case of plant physiology. E.g. Taiz and Zeiger )

[leftventricle]

All that orbital stuff is quite confusing. :S
Thanks for answering my other questions!

I also had a question about transpiration.

Why does the plant want to limit water loss? Is it because it needs the water to make glucose (or other sugar in photosynthesis)?

Also - if only 85% of water lost is through transpiration - how is the other 25% lost?

[leftventricle]

Also I was reading the textbook and it said that guard cells are photosynthetic epidermal cells...does that mean there is chloroplasts/chlorophyll found in them too?