Photosynthesis Questions

[Cammmeron!]

Hey guys, just need some help with a few biology questions and was hoping you guys could help me out .

1. Explain how photo-phosphorylation differs from the oxidation phosphorylation occurring in cellular respiration.

2.Both cyclic and non-cyclic pathways operate to varying degrees during photosynthesis. Since the non-cyclic pathway produces both ATP and NADPH, explain the purpose of the cyclic pathway of electron flow.

3. Explain how ATP is produced as a result of light striking chlorophyll molecules during the light dependent phase of photosynthesis.

[Stick]

I think these questions are well beyond the scope of what is covered in VCE Biology. I'm interested to see the answers, however.

[psyxwar]

Okay I'll quickly answer to the best of my ability, but yeah this is outside the scope of VCE biology.

1. Photophosphorylation involves light energy, which drives the electron transport chain and ultimately the addition of a phosphate group to ADP (phosphorylation), whereas in oxidative phosphorylation the energy comes from the organic molecule itself (remember how in glycolysis and the Kreb's the glucose is broken down to ATP and the electron carriers (NADP and FADH2)?). It's called oxidative phosphorylation because the final electron acceptor is molecular oxygen, which as you know becomes reduced to water.

2. Okay, cyclic photophosphorylation generates ATP but no NADPH right? Because the electron is recycled to generate more ATPs, rather than accepted by NADP+ to become NADPH (that goes to the Calvin Cycle). Why? Well, if you look at the actual inputs of the Calvin Cycle, more ATP is necessary than NADPH. Cyclic photophosphorylation enables a plant to produce ATPs necessary to drive to Calvin Cycle without having to produce unnecessary NADPHs.

3. You should know this, but basically the electrons in the chlorophyll molecule become excited, then enter the electron transport chain which is facilitated by your multi-protein complexes (Photosystems). The electron loses energy as it goes through the chain, which pumps hydrogens into the thylakoid discs. This causes a difference in concentration of H+ ions between the interior of the thylakoids and the stroma outside, causing the ions to want to go out. The only way out is something called ATP Synthase, which as you probably guess is responsible for ATP synthesis. So ultimately, the energy produced from the electron transport chain drives ATP synthesis via the enzyme ATP Synthase.

[Cammmeron!]

Thanks so much Psyxwar. I couldn't find the answers anywhere. I got these questions from the Biozone work book, but since they are out of the scope of VCE Biology, no need for me to stress out about them .

[violanoob8]

A great resource would be Campbell Biology which provides great diagrams and commentary on the above processes.

[Yacoubb]

(c) Explain how ATP is produced as a result of light striking chlorophyll molecules during the light dependent phase of photosynthesis.

A photosystem is a cluster of chlorophyll molecules that are involved in the conversion of captured light energy to chemical energy, ultimately, stored in sugars.

When light strikes Photosystem II in the chloroplasts, the electrons become energised. The excess energy found in the electrons causes them to leave the chlorophyll molecules. Because electrons are lost from the chlorophyll molecules, they want to basically get them back, theoretically speaking, replace the ones that escape the chlorophyll molecules. In order to replace them, the chlorophyll molecules steal electrons from H2O, causing that covalent bond to split and for the water to split in H⁺ ions and O₂ molecules, a waste product of photosynthesis.

After this happens, light strikes Photosystem I (another cluster of chlorophyll), and electrons become energised. The electrons then enters the electron transport chain, causing them to lose energy as the electrons move along the electron transport chain. The energy that is lost is used to make ATP (Adenosine Tri-phosphate) from Adenosine Di-phosphate + an inorganic phosphate molecule, and for NADPH to be formed from the charged NADP+ carrier and the H+ ion.

Hope this somewhat helped it is not imperative to know this for VCE Biology, but it is really interesting + could also be of some help. I also KIND OF summarised the light-dependent stage of photosynthesis

[violanoob8]

Just a few adjustments. 

A photosystem is a cluster of chlorophyll molecules that are involved in the conversion of captured light energy to chemical energy, ultimately, stored in sugars.

A photosystem is not only a cluster of chlorophyll molecules, rather they are proteins, with chlorophyll as well as other pigments embedded in it.

After this happens, light strikes Photosystem I (another cluster of chlorophyll), and electrons become energised. The electrons then enters the electron transport chain, causing them to lose energy as the electrons move along the electron transport chain. The energy that is lost is used to make ATP (Adenosine Tri-phosphate) from Adenosine Di-phosphate + an inorganic phosphate molecule, and for NADPH to be formed from the charged NADP+ carrier and the H+ ion.

The electrons in photosystem I do not actually go through an electron transport chain, only the electrons from photosystem II.

Also it is not the potential energy lost from the electron in the electron transport chain that is used to create the ATP, one of the main reasons for the electron transport chain is to create a concentration difference for the H+, which is then used in the process chemiosmosis.

Well, it is good to see you find this quite interesting+ happy studies 

[Yacoubb]

Just a few adjustments. 

A photosystem is not only a cluster of chlorophyll molecules, rather they are proteins, with chlorophyll as well as other pigments embedded in it.

The electrons in photosystem I do not actually go through an electron transport chain, only the electrons from photosystem II.

Also it is not the potential energy lost from the electron in the electron transport chain that is used to create the ATP, one of the main reasons for the electron transport chain is to create a concentration difference for the H+, which is then used in the process chemiosmosis.

Well, it is good to see you find this quite interesting+ happy studies 

Yeah I've consulted my notes + built a much stronger understanding now that I've read multiple sources and really understood the process. I appreciate that though

The energy that is released from the energised electrons after they go through the electron transport chain pumps the hydrogen ions into the thylakoids via the thylakoid membrane, only to be met by ATP synthase that is exiting out of the thylakoid membrane. ATP is then formed from ADP + Pi.

Photosystems are multi-protein complexes that contain different pigment molecules, such as chlorophyll a, as well as other accessory pigments such as chlorophyll b + carotenoids.

Thank you very much!