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  • In a phototrophic eukaryote, where does photosynthesis take place?

Oxygenic and anoxygenic photosynthesis

For photosynthesis to continue, the electron lost from the reaction center pigment must be replaced. The source of this electron (H 2 A) differentiates the oxygenic photosynthesis of plants and cyanobacteria from anoxygenic photosynthesis carried out by other types of bacterial phototrophs ( [link] ). In oxygenic photosynthesis, H 2 O is split and supplies the electron to the reaction center. Because oxygen is generated as a byproduct and is released, this type of photosynthesis is referred to as oxygenic photosynthesis. However, when other reduced compounds serve as the electron donor, oxygen is not generated; these types of photosynthesis are called anoxygenic photosynthesis. Hydrogen sulfide (H 2 S) or thiosulfate ( S 2 O 3 2− ) can serve as the electron donor, generating elemental sulfur and sulfate ( SO 4 2− ) ions, respectively, as a result.

Photosystems have been classified into two types: photosystem I (PSI) and photosystem II (PSII) ( [link] ). Cyanobacteria and plant chloroplasts have both photosystems, whereas anoxygenic photosynthetic bacteria use only one of the photosystems. Both photosystems are excited by light energy simultaneously. If the cell requires both ATP and NADPH for biosynthesis, then it will carry out noncyclic photophosphorylation . Upon passing of the PSII reaction center electron to the ETS that connects PSII and PSI, the lost electron from the PSII reaction center is replaced by the splitting of water. The excited PSI reaction center electron is used to reduce NADP + to NADPH and is replaced by the electron exiting the ETS. The flow of electrons in this way is called the Z-scheme .

If a cell’s need for ATP is significantly greater than its need for NADPH, it may bypass the production of reducing power through cyclic photophosphorylation . Only PSI is used during cyclic photophosphorylation; the high-energy electron of the PSI reaction center is passed to an ETS carrier and then ultimately returns to the oxidized PSI reaction center pigment, thereby reducing it.

In oxygenic photosynthesis 6 carbon dioxide 12 water and light energy is converted to glucose, 6 oxygen, and 6 water. In anoxygenic photosynthesis carbon dioxide, 2H2A and light energy is converted to a carbohydrate and water. H2A = water, H2S, H2, or other electron donor.
Eukaryotes and cyanobacteria carry out oxygenic photosynthesis, producing oxygen, whereas other bacteria carry out anoxygenic photosynthesis, which does not produce oxygen.
a) Drawing of a thylakoid membrane with proteins. Light strikes PS II which breaks water into ½ O2, 2 H+ and an electron. The electron moves to PO, PQH2, cytochrome, PO, and then to PSI. This is an electron transport chain and as the electron moves, H+ is pumped from the stroma to the thylakoid space. Light Strikes PSI and the electron is excited again; it is then moved to FD and then NADP+ reductase. This produces NADPH from NADP+ and H+. Protons from the inner thylakoid space move out to the stroma through ATP synthase which produces ATP. B) the same diagram but in a graphical format with amount of energy on the Y axis. PSII has an antenna pigment and P680 which absorbs light at 680 nm. This excites the electron (moves it up in the graph). The electron then decreases in energy as it moves from PO to OQHS, to cytochrome, to PO and then to PS I. Light at 700 nm strikes P700 and the electron is excited again. The electron then decreases in energy as it moves from FD to NADP+ reductase to NADPH. Moving from PSII to NADPH is non-cyclic photosynthesis. Cyclic photosynthesis is when the electron moves from PSI back to PS II.
(a) PSI and PSII are found on the thylakoid membrane. The high-energy electron from PSII is passed to an ETS, which generates a proton motive force for ATP synthesis by chemiosmosis, and ultimately replaces the electron lost by the PSI reaction center. The PSI reaction center electron is used to make NADPH. (b) When both ATP and NADPH are required, noncyclic photophosphorylation (in cyanobacteria and plants) provides both. The electron flow described here is referred to as the Z-scheme (shown in yellow in [a]). When the cell’s ATP needs outweigh those for NADPH, cyanobacteria and plants will use only PSI, and its reaction center electron is passed to the ETS to generate a proton motive force used for ATP synthesis.
  • Why would a photosynthetic bacterium have different pigments?

Questions & Answers

What is the difference between eukaryotes and prokaryotes?
KINGSFORD Reply
What's a multicellular organism?
KINGSFORD
multicellular organisms is an organism composed of many cells which are to varying degree integrated and independent.
Ruth
Boiling of milk to kill germs is called?
Kasigwa
pasteurization
Aiyedun
pasteurization
Katta
kadha
Katta
pasteurization
Gomathi
what is microscopic
monish
Pasteurization
Hosy
what are Flora
Hosy
you mean like the normal flora?
Tenucharity
pasteurization has to do with killing of the harmful microbes present for safe consumption. Eg. pasteurized yoghurt beside the bacteria that are supposed to be present, there may be harmful ones that have been killed
Tenucharity
what is cell?
Anita Reply
the cell is the functional and structural unit of the body
Ruth
yes ur right
Kasigwa
who add me
Wali
hy
Katta
hy
Shivangi
basic structural, functional, and biological unit of all known living organisms. A cell is the smallest unit of life.
Haru
hi
Ruth
hi
Haru
coming Oct 2 I have a exam on microbiology
Haru
okay all the best
Ruth
hi
sachin
hi
Ruth
plz bro send question of microbiology
umesh
structural and functional unit of the life
monish
this is not the correct answer
Alanna Reply
why
Hayat
why not
Zaajid
what is the correct answer?
vannessa
where is question
Zaajid
ask you question
Zaajid
What are mitochondria
Hayat
what is mitochondria
Hayat
who is the father of microbiology
T-
not
Hayat
Antonie Van Luweenhoek
Ravikumar
Mitochondria is the powerhouse of the Cell. And is the cell organelle which helps cell in generation of energy by Cellular Respiration
Ravikumar
what is a vacual
Star Reply
What is microbiology
Nji Reply
it is the study of microscopic organisms and basically their relation to the environment
Tenucharity
what is elements
Erneet Reply
an Element is a substance that can not be further decomposed by ordinary chemical means.
vannessa
can i get notes of biochemistry
Sneha Reply
yep why not
Abdullah
what is microbiology?
Gayanjali Reply
what is malaria
Gayanjali
bios- life/living things micro- small things that cannot be seen with the naked eye In other words the study of living things that cannot be seen with the naked eye but with the help of a microscope
Coltuneac
logos- science
Coltuneac
it is 10 to the power minus 6 biology which studies life forms on those scales including metabolism , physiology, nutrition requirements
barun
what are prokarytes
NDIMUKIKA Reply
A prokaryotic is a unicellular organanism that lacks a membrane bound nucleus ,mitochondria or other any membrane bound organelle. .......
Maryam
in prokaryotic nucleus is not developed and cell organelles are absent
Harshad
how is one who is feeling blockage in the chest with mucus be diagnosed
Essy Reply
be talking sepitol every morning
Ikenna
is that all?
Ven.phumie
What is prions
Sangeeta Reply
is tuberculosis a viral infection?
hildar Reply
No. It is a Bacterial Infection.
Orooj
what are zn staining
Evelyn Reply
full meaning zeil neelson staining
kezia
By using zn stain we diagnose / examine acid fast bacilli .
Deepak
explain hw bacteria grows
Kanyago Reply
Hw does bacteria grow?
Kanyago
Binary fission
Sangeeta
three successive phase comes in bacteria growth i.e lag phase/adaptation phase ,log phase/exponential phase ,death phase when it is in fermentation process .
Deepak
introduction to virology
Dongyile Reply
is the study of virus
FADAYOMI
Virology
Sangeeta
study of virus which can be seen by using electron microscope i.e below 1micron in size . It requires a host cell to multiply own number to proliferate itself .
Deepak
what 's the unicellular
monish
unicellular is an organism with one kind of cell
Tenucharity

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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