Question

What is photosystem 1 and photosystem 2 and what do they do? What are the steps ?

Answer 1

Photosystem I and photosystem II are located in the thylakoid membranes and are critical for converting light energy into chemical energy in plants. PSII splits water to replace lost electrons, releasing oxygen, while PSI uses light-excited electrons to reduce NADP+ to NADPH. Together they drive the production of ATP and NADPH through non-cyclic photophosphorylation.

Step-by-step explanation:

Photosystem I (PSI) and photosystem II (PSII) are crucial components in the photosynthetic process of plants and cyanobacteria, embedded in the thylakoid membrane. These systems play key roles in the light-dependent reactions of photosynthesis, where solar energy is converted into chemical energy. In these reactions, PSII absorbs light energy which excites electrons, these high-energy electrons are transferred to the electron transport chain (ETC). The lost electrons are replaced by splitting water, releasing oxygen as a byproduct. The electrons then travel from PSII to PSI through the ETC, where PSI also absorbs light and gets its electrons excited. These excited electrons are used to reduce NADP+ to NADPH, which will later be used in the Calvin cycle to produce glucose.

The pathway of electron transfer from photosystem II to photosystem I is essential in this process. It begins with the absorption of light by PSII, energizing electrons that are then passed down the ETC to PSI. PSI finally uses the energized electrons to reduce NADP+, thus creating NADPH. This sequence is known as non-cyclic photophosphorylation and includes the creation of a chemiosmotic gradient due to the movement of protons across the membrane which drives the synthesis of ATP.

Moreover, photosystems contain pigments such as chlorophylls and carotenoids that capture light at various wavelengths, which is then used to excite the electrons necessary for these processes. The interaction of light with the chlorophylls in PSII and PSI is what initiates the conversion of light energy to chemical energy in plants.

Answer 2

P I and PII are proteic compounds present in the thylakoid membrane that contain about 300 chlorophyll molecules each.

Step I

First of all light with a wavelength of 690nm is absorbed by P II. The light excites an electron that leads to the photolysis of water(H2O--->2H+ +2e- + 1/2O2). The two electrons released go into the electron transport chain. The second compound in electron transport chain is plastoquinone that is reduced when it accepts electrons then oxidised when it loses them to P I. The next two compounds are cytocromes that make hydrogen protons go inside the thylakoid when they recieve the electrons.(I will mention what happens to the H+ in the second step). The next compound in the electron transport chain is a compound that contains Fe and S. The electrons finally reach the last step: Reduction of NADP+ to NADPH+H+.

Step II

In the second step is ATP synthesis. Hydrogen protons accumulate inside the thylakoid membrane. An electrochemical gradient is formed. The protons can leave the thylakoid according to this gradient through an enzyme.

When the protons flow through , it turns ADP into ATP.

To sumarize: the role of P II is O2 production through photolysis and ATP synthesis(indirectly) The role of P I is NADPH+H+ synthesis.